Kaplan Dental Flashcards

Question

``` 25. Canaliculi and Haversian systems: A. are found in acellular cementum B. are found in cellular cementum C. are found in both types of cementum D. are not found in cementum ```

Answer 1

The correct answer is D. Cementum is often described as the dental tissue which most resembles bone. It has a similar mineral content, and has an organic matrix primarily composed of collagen 6 fibers. However, the Haversian systems, concentric tissue layers, lacunae, canaliculi, etc., found in bone are not found in cementum. Remember that these features are not always found in bone. Only compact bone (rather than trabecular bone) has these features. Remember also that acellular cementum could not have such features as Haversian systems, because Haversian systems contain osteocytes (cells) within bony lacunae. However, neither acellular nor cellular cementum actually has these features.

Answer 2

The correct answer is D. The maxillary canine, at the cervix, will have a cross section which is oval and flattened mesiodistally. It is generally slightly wider at the labial end than at the lingual. The pulp cavity at this point is lens-shaped, double convex. It is similar in cross-sectional shape to the mandibula canine.

Answer 3

The correct answer is A. Note that the holding (supporting, occluding) cusps of the posterior dentition are the lingual (palatal) cusps of the maxillary teeth and the buccal (facial) cusps of the mandibular teeth. Buccals of maxillary teeth and linguals of mandibular teeth are guiding cusps. Choice A is the lingual of a mandibular first molar, so it is not a holding cusp, and is a guiding cusp. Choice B is a buccal of a mandibular molar and is a holding cusp. Choice C is a lingual cusp of a maxillary molar and is a holding cusp. Choice D is the lingual of a maxillary premolar and is a holding cusp. Choice E is the palatal (lingual) of a maxillary premolar and is a holding cusp.

Answer 4

The correct answer is B. The maxillary lateral and the third molars show more variability than any other teeth. Besides a wide variety of unusual morphologies (peg lateral, etc.), the maxillary lateral incisor is fairly commonly congenitally missing. In these patients, the canines drift mesially toward the centrals. Also commonly congenitally missing are third molars and premolars.

Answer 5

The correct answer is C. Anodontia (choice A) refers to the complete absence of tooth formation. In oligodontia (choice B), most but not all teeth are missing. Both of these conditions are often associated with ectodermal dysplasia. Hypodontia refers to a small number of congenitally missing teeth. This is fairly common, and is not usually associated with a systemic disease or disturbance.

Answer 6

The correct answer is D. Cervical bulges are overhangs of the crown sticking out above the cervical line of the primary teeth. In primary anteriors, the cervical bulge is found on both the buccal and lingual surfaces. In the molars, it is found only on the buccal. The most conspicuous cervical bulge in the primary molars is that of the primary mandibular first molar. It is often described as being potbelly when seen from the proximal view. The other molars are not as exaggerated in this area, but still show a pronounced buccal cervical bulge.

Answer 7

The correct answer is B. Despite the fact that the mandibular first molar has a distinct mesial root concavity on the mesial side of the mesial root, and that this root sometimes furcates partially upwards from the mesial, complete additional whole roots are usually second distal roots. Buccal and/or lingual additional roots are not found.

Answer 8

The correct answer is C. The distolingual cusp of a maxillary molar is a holding cusp. The general rule for maxillary holding cusps is as follows: a maxillary holding cusp contacts the distal marginal ridge of its mandibular counterpart and the mesial marginal ridge of the mandibular tooth distal to its counterpart, EXCEPT FOR THE MESIOLINGUAL CUSPS OF THE MOLARS, WHICH CONTACT THE CENTRAL FOSSAE OF THEIR COUNTERPARTS. This should be the distal marginal ridge of the mandibular first molar and mesial marginal ridge of the second molar.

Answer 9

The correct answer is A. Lingual cusps of mandibular teeth are guiding cusps, not holding cusps. Therefore, they do not occlude on marginal ridges or central fossae. The general rule for mandibular lingual cusps is that they occlude in the lingual embrasures between their maxillary counterparts and the teeth mesial to their counterparts, EXCEPT for the distolingual cusps of the mandibular molars, which occlude in the lingual grooves of their maxillary counterparts. In this question we are not dealing with the exception of the distolingual cusps of mandibular molars, so in this case, the mandibular second molar mesiolingual cusp contacts the lingual embrasure between its counterpart (the maxillary second molar) and the tooth mesial to it (the maxillary first molar).

Answer 10

The correct answer is C. Only the original inner and outer enamel epithelium take part in root formation. There is no stellate reticulum in between them, as would be found in the original enamel 8 organ. The root form is originally outlined by the epithelial root sheath of Hertwig, which then induces formation of odontoblasts, which then produce root dentin. Pieces of the root sheath, which do not disappear, remain as the epithelial rests of Malassez. These small groups of tissue are ectodermal in origin, as the original enamel epithelium is ectodermal.

Answer 11

The correct answer is A. The maxillary lateral incisor exhibits an almost round root cross section shape at the cervical line. It is not flattened mesiodistally or labiolingually. The pulp chamber mimics the root shape by being round at this point as well. It is very similar in both root shape and pulp shape to those of the maxillary central. Note that as the pulp enters the coronal section, it will begin to widen mesiodistally (flatten buccolingually) in keeping with the crown shape.

Answer 12

The correct answer is C. This may not seem like dental anatomy, but it is actually a calcification question. In order to avoid tetracycline staining or any other intrinsic stain of enamel, we must avoid all ages where tooth crown calcification is occurring. The last tooth to calcify (and erupt) is the third molar. Most third molars erupt at 17 to 21 years, but calcification of enamel occurs mostly at about age 8. So pregnant mothers and children age 8 and younger are not given tetracycline.

Answer 13

The correct answer is E. The lateral pterygoid connects from the greater wing of the sphenoid and the lateral surface of the lateral pterygoid plate to the mandibular condyle, articular disc, and capsule. It is the only muscle that attaches to these structures. The stylomandibular ligament, sometimes given a vague protective function, extends from the styloid process to the lingula of the mandible. The medial pterygoid muscle is an elevator with no direct attachment to the TMJ. The mandibular condyle is separated from the glenoid (temporal) fossa by the articular (TMJ) disc. The condyle does not pull the disc. The disc is also called the meniscus; they are the same thing.

Answer 14

The correct answer is B. The three largest cusps (trigon, or primitive cusp triangle) of the maxillary first molar are the MB, ML, and DB cusps. The DL cusp is smallest, and is known as the talon cusp (or talon). This cusp is also the one which is even less conspicuous as you go from first to second to 9 third molar. Note also that the DB cusp decreases in relative size as you go from first to second and third molar. The order of size of the cusps in this tooth, then, is from largest to smallest: ML, MB, DB, DL, Carabelli.

Answer 15

The correct answer is D. Remember that primary molars are succeeded by permanent premolars. The permanent molars erupt distal to all primary teeth and do not replace them. So the maxillary replacements are 4 for A, 5 for B, 6 for C, 7 for D, 8 for E, 9 for F, 10 for G, 11 for H, 12 for I, and 13 for J. 1, 2, 3, 14, 15, and 16 do not replace primary teeth.

Answer 16

The correct answer is C. Most maxillary molars are considered four-cusped teeth. However, in some cases, the Carabelli cusp (trait) can be large enough to be considered a fifth cusp on a maxillary first molar. The maxillary second molar is usually four-cusped. The mandibular first molar is normally fivecusped with an ML, MB, DL, and DB cusp and a fifth distal cusp. The mandibular second lacks the distal cusp and is normally a four-cusp tooth.

Answer 17

The correct answer is A. Only maxillary incisors have roundish pulp chamber cross sections when cut at the cervical line. This is true for both maxillary centrals and laterals. In general, mandibular centrals and both arch canines will have ovalish pulp chambers, flattened mesiodistally. (Imagine squashing a round pulp from both the mesial and distal sides at once, resulting in a squashed oval, pointing to the buccal and lingual). Remember that the shape of a pulp chamber is usually related to the shape of the surrounding root.

Answer 18

The correct answer is D. The best way to answer the question is to imagine contact points and proximal-incisal angles for the anterior teeth. A small incisal embrasure will be located wherever the contact points are high (incisal) and where proximal-incisal line angles are almost perpendicular. The best example of this arrangement is the central incisors. Their mesial incisal line angles are very square, and the contact is in the incisal third of the tooth. As you go further distally, the line angles become more rounded, especially for canines. These rounded line angles at the incisal, as well as the more apical contacts, dropping to the middle third as you reach the distal of the canine, ensure much larger incisal embrasures

Answer 19

The correct answer is A. As the tooth crown nears eruption, the ameloblasts produce their final product, known as the inner enamel cuticle. This material is acellular, and is firmly adherent to the 10 enamel surface as the tooth erupts. Its older name is Nasmyth's membrane. This cuticle has on its outside a second acellular layer formed from the keratinized remnants of the dental sac. This adherent double layer may persist for some time after the tooth erupts but is eventually worn away, leaving the enamel exposed in the oral cavity.

Answer 20

The correct answer is B. The bony origins of the three TMJ ligaments are primarily from three different bones. The stylomandibular ligament originates from a thin, bony extension of the temporal bone, known as the styloid process. The spine of the sphenoid bone is the major origin of the sphenomandibular ligament. The lateral ligament (temporomandibular ligament) has its origin from the zygomatic process. This process is a fusion of the temporal and zygomatic bones.

Answer 21

The correct answer is A. We can eliminate choice B, as the apex is at the opposite end from the crown. The apical fibers are, of course, most apical, and run from the apex of the alveolar bone socket to the root tip. The oblique fibers are slightly more coronal. They run from the cementum near the apical end, obliquely coronally to alveolar bone. The horizontal fibers are more coronal and run horizontally from cementum to alveolar bone around mid-root. The alveolar crestal fibers are most coronal, and run from the most coronal part of the root to the alveolar crest of bone.

Answer 22

The correct answer is C. This may not be as obvious as it seems. Rule out 4, as the molar only has three roots: the palatal, mesiobuccal, and distobuccal. However, how should they look in a distal view? The palatal root will clearly be visible as the only root on the palatal side. It is massive, and often hooked. On the buccal end, a distal view should easily show the full length of the distobuccal root, so we have two roots so far. What about the mesiobuccal? In this case we can see this root mostly because it is larger than the distobuccal, so some, but not all, of the mesiobuccal root is blocked by the distobuccal. We should, however, see some small sections of it outside of the profile of the distobuccal root.

Answer 23

The correct answer is D. As a general rule, the buccal heights of contour of the premolars are located within the cervical thirds. The lingual heights of contour will normally be more occlusal. On the mandibular first premolar, it is especially occlusal, within the occlusal third.

Answer 24

The correct answer is B. The general rule for innervation by CN V (the trigeminal) is that it innervates the muscles of mastication (temporalis, lateral pterygoid, medial pterygoid, masseter), the mylohyoid, the anterior digastric, and the two tensors (tensor tympani and tensor veli palatini). Note that the buccinator is not included. The buccinator is in the group of muscles of facial expression, which are all innervated by CN VII (the facial nerve).

Answer 25

The correct answer is A. Mandibular incisors are widest near the incisal tip, and their contacts (both central and lateral) are always near the incisal edge. The mandibular canine contact with the lateral incisor is thus in the incisal third. In the canine, the contact is also in the incisal third, but not as incisal as in the lateral. The distal contact of the canine is also in the incisal third, but near the junction of the incisal and middle thirds.

Answer 26

The correct answer is B. The maxillary lateral is the most highly variable tooth in the mouth. It can be normal incisor-shaped, peg-shaped, or congenitally missing, or have a wide variety of invaginations, from small pits to deep pits to dens-in-dente, or tooth-within-a-tooth. This is the case when the invagination is so deep that the radiographic appearance appears to show a small tooth inside the maxillary lateral.

Answer 27

The correct answer is A. There are a number of somewhat confusing anomalies at the dentinoenamel junction. Enamel spindles are odontoblastic processes and dentinal tubules which extend a short way into enamel. Enamel lamellae, on the other hand, extend from enamel into dentin. They are pieces of uncalcified organic enamel material. Enamel tufts are hypocalcified enamel rods. They are individual entities; however, they appear as groups (tufts) when a group of them are viewed laterally.

Answer 28

The correct answer is D. In occlusion, cusps are defined as either holding (supporting) cusps or guiding cusps. Holding cusps, in central occlusion, make contact with the opposing arch, establish vertical dimension of occlusion, and support the forces of occlusion. They are the lingual cusps of the maxillary arch and buccal cusps of the mandibular. When the teeth are in centric occlusion, these cusps are in contact. The other cusps (guiding) are not. The other cusps are either lingual to the contact (lingual cusps of the mandibular arch) or buccal to the contact (buccal cusps of the maxillary arch). Holding cusps generally occlude in the marginal ridge and central fossa areas of the opposing arch. Guiding cusps generally lie in embrasures between teeth, or between cusps of the lingual or buccal surfaces of the opposing arch.

Answer 29

The correct answer is A. The question depends on the fact that the maxillary first premolar has an asymmetric positioning of its two cusps. Rather than having the buccal and lingual cusps in a straight line, the buccal cusp is displaced slightly distally, and the lingual cusp is displaced slightly mesially. This gives the occlusal view of the tooth a slightly twisted appearance. Cusp ridges run from the cusp tip to the proximal edge of the tooth at the marginal ridge. Therefore, if you look facially at the maxillary first premolar, you will see the buccal cusp shifted toward the distal. This makes the cusp tip farther from the mesial, and thus there will be a longer mesial cusp ridge on this tooth.

Answer 30

The correct answer is D. The distolingual cusp of a maxillary second molar is a holding cusp. The general rule for maxillary holding cusps is as follows: a maxillary holding cusp contacts the distal marginal ridge of its mandibular counterpart and the mesial marginal ridge of the mandibular tooth distal to its counterpart, EXCEPT FOR THE MESIOLINGUAL CUSPS OF THE MOLARS, WHICH CONTACT THE CENTRAL FOSSAE OF THEIR COUNTERPARTS. This should be the distal marginal ridge of the mandibular second molar and mesial marginal ridge of the third molar.

Answer 31

The correct answer is A. For the most part, rotation of a tooth during extraction works best on teeth with rounded roots, such as the maxillary central incisor and maxillary canine. It can be used in conjunction with buccal-lingual luxation on teeth with single ovalish roots. It can never be used on double-rooted teeth. Of the premolars above, the maxillary first is always double rooted. Of the others, the maxillary second is sometimes double rooted and sometimes single. For the mandibular premolars, the mandibular first is the most likely to have a single ovalish, but close to round, root. It is theMOST likely premolar on which rotation may be part of the extraction.

Answer 32

The correct answer is D. The mesiolingual cusp of a maxillary second premolar is a holding cusp. The general rule for maxillary holding cusps is as follows: a maxillary holding cusp contacts the distal marginal ridge of its mandibular counterpart and the mesial marginal ridge of the mandibular tooth distal to its counterpart, EXCEPT FOR THE MESIOLINGUAL CUSPS OF THE MOLARS, WHICH CONTACT THE CENTRAL FOSSAE OF THEIR COUNTERPARTS. This should be the distal marginal ridge of the mandibular second premolar and mesial marginal ridge of the first molar.

Answer 33

The correct answer is C. While all three maxillary molars commonly have three roots, the roots and their arrangement differ distinctively from one to the other. Most notable in the first molar is the plierslike appearance of the two buccal roots. The mesiobuccal hooks distally and the distobuccal hooks mesially. The second molar does not have this curvature, and the two buccal roots are more parallel, with both roots inclined distally. The third molar often has three fused roots forming a cone-like structure, or sometimes all distally inclined. These factors are important in exodontia of maxillary molars. Maxillary third molars, in particular, can sometimes be elevated out distally in a rotating manner because of the fused cone-like distally facing roots.

Answer 34

The correct answer is D. The distobuccal cusp of a mandibular molar is a holding (supporting) cusp. The general rule of occlusion of mandibular holding cusps is as follows: the holding cusps of the mandibular teeth occlude on the mesial marginal ridge of their maxillary counterpart, and the distal marginal ridge of the maxillary tooth mesial to their counterpart, EXCEPT distobuccal cusps of mandibular molars occlude with central fossae of their counterparts, the distal cusp of the mandibular first molar occludes with the distal triangular fossa of its counterpart, and the first premolar occludes only with the mesial marginal ridge of its counterpart (but not the canine). In this case, the maxillary counterpart is the maxillary second molar, and the mandibular cusp will occlude in its central fossa.

Answer 35

The correct answer is C. All of the vessels listed supply blood to the PDL, as all of them are in the vicinity of the PDL and all anastomose or send branches there. Out of this group, however, the MAJOR source is vessels branching from the periosteum surrounding the alveolar bone. Note that both lymphatics and nerves follow the path of the blood vessels in the PDL.

Answer 36

The correct answer is C. Look for a mandibular anterior tooth to be your answer here. You will often notice clinically that partially edentulous patients often retain mandibular anteriors despite loss of most 14 other teeth. This is due to the following three factors: 1) they have few significant pits or fissures; 2) they are bathed in saliva most of the time, which resists plaque buildup; and 3) they are cleaned by the normal movements of the tongue. Other teeth cannot fit all three of these categories. Note that mandibular canines are often the last teeth left. This is because, although the mandibular incisors are rarely lost to caries, they are often lost to periodontal disease, partially due to their short roots and easy calculus buildup.

Answer 37

The correct answer is C. The normal (Class I) jaw relationship will result in the mandibular first molar being located one cusp (one-half tooth) mesial to the maxillary first molar. If the mandibular molar is located distal to the maxillary, it indicates a small mandible (micrognathy) or another problem causing the maxillary teeth to be too far mesial and the mandibular too far distal. This is distocclusion is Angles Class II. Mesiocclusion is Angles Class III, where the mandibular first molar is more than onehalf tooth mesial to the maxillary first molar.

Answer 38

The correct answer is B. Periodontal fibers must run from the cementum of the tooth into alveolar bone. The main periodontal fiber types are alveolar crestal, horizontal, oblique, and apical, named for either their position or alignment. The transseptal fiber is classified with the gingival group, as it does not enter alveolar bone. Instead, as the name suggests, it travels from one tooth to another tooth, crossing over the alveolar crest. It attaches directly from the cementum of one tooth into the cementum of another, but does not attach to bone.

Answer 39

The correct answer is C. A lingual ridge runs from the incisal edge down the center of the lingual surface of the crown, toward the cervical end of the crown. It splits the lingual surface in half, and usually has a depression on either side (lingual fossae) which separate the lingual ridge from the mesial and distal marginal ridges. Lingual ridges are found on canines, but not on incisors (choices A and B). The lingual ridge is more pronounced on the maxillary canine than on the mandibular (choice D). This is in keeping with a general rule that the lingual anatomy of the maxillary canine is much more pronounced than that of the mandibular.

Answer 40

The correct answer is A. Oblique ridges are characteristic of maxillary molar teeth. They connect the mesiolingual and distobuccal cusps. The oblique ridge is also considered to be the distal end of the trigon, the major cusp area of the maxillary molar, composed of the ML, MB, and DB cusps. The DL 15 cusp is often reduced and is referred to as the talon (as opposed to the trigon). The trigon is evolutionarily the primitive cusp triangle of the molar crown. Oblique ridges are not found on mandibular molars or on any other teeth.

Answer 41

The correct answer is A. Enamel is the most mineralized and hardest tissue in the human body. Most estimates place the mineral content of enamel at about 95 to 98%. Dentin, though highly mineralized, still has more organic content than does enamel. Most estimates place the mineral content of dentin at about 80%. Cementum is least mineralized, and is most similar to bone. There are varying estimates of its mineral content, but most place it at about 60 to 65%.

Answer 42

The correct answer is E. The best way to answer the question is to imagine that the embrasures are spaces surrounding a small point of contact between two incisors. This small contact point will have space above it, below it, in front of it, and in back of it. These spaces in dental anatomy will be, respectively, incisal, cervical (gingival), buccal (facial), and lingual (palatal). Note that there is no space mesial or distal to the contact point. Immediately mesial or distal to the contact would be tooth structure.

Answer 43

The correct answer is B. Lingual cusps of mandibular teeth are guiding cusps, not holding cusps. Therefore, they do not occlude on marginal ridges or central fossae. The general rule for mandibular lingual cusps is that they occlude in the lingual embrasures between their maxillary counterparts and the teeth mesial to their counterparts, EXCEPT for the distolingual cusps of the mandibular molars, which occlude in the lingual grooves of their maxillary counterparts. In this question we are dealing with the exception of the distolingual cusps of mandibular molars, so in this case, the mandibular second molar distolingual cusp contacts the lingual groove of its counterpart (the maxillary second molar).

Answer 44

The correct answer is E. Buccal cusps of maxillary teeth are guiding cusps, not holding cusps. Therefore, they do not occlude on marginal ridges or central fossae. The general rule for maxillary buccal cusps is that they occlude in the facial embrasures between their mandibular counterparts and the teeth distal to their counterparts, EXCEPT for the mesiobuccal cusps of the molars, which occlude in the buccal grooves of their mandibular counterparts, and the distobuccal cusp of the first molar, 16 which opposes the distobuccal groove of the mandibular first molar. In this question, we are NOT dealing with the exception of the mesiobuccal cusps of the maxillary molars or the distobuccal cusp of the maxillary first molar, so this cusp should follow the general rule and occlude with the facial embrasure between its mandibular counterpart (the mandibular second molar) and the mandibular molar distal to it (the mandibular third molar).

Answer 45

The correct answer is A. Attrition is the mechanical wearing of teeth due to physiologic processes, including chewing and bruxism. Abrasion (choice B) is the mechanical wearing away of tooth structure due to some outside object, such as toothbrush abrasion at the cervical lines of teeth due to hard sideways brushing, or from habitually holding bobby pins or nails with the teeth. Erosion (choice C) is the chemical dissolving of tooth structure. It can be caused by a number of factors, including sucking on lemons and other acidic fruit, excessive intake of acidic beverages (cola), or excessive vomiting, as in bulimia. Bulimics often exhibit normal facial surfaces with severely eroded lingual surfaces.

Answer 46

The correct answer is B. The lingual cusp of a maxillary premolar is a holding cusp. The general rule for maxillary holding cusps is as follows: a maxillary holding cusp contacts the distal marginal ridge of its mandibular counterpart and the mesial marginal ridge of the mandibular tooth distal to its counterpart, EXCEPT FOR THE MESIOLINGUAL CUSPS OF THE MOLARS, WHICH CONTACT THE CENTRAL FOSSAE OF THEIR COUNTERPARTS. This should be the distal marginal ridge of the mandibular first premolar and mesial marginal ridge of the second premolar.

Answer 47

The correct answer is A. Note that the three-rooted maxillary first molar does not have a mesiolingual root. The maxillary first molar most often has three roots: mesiobuccal, distobuccal, and palatal. The palatal root is largest, and its canal is largest and widest. In the case of a fourth canal, it is invariably found in the mesiobuccal root. The distobuccal and palatal roots are invariably onecanalled.

Answer 48

The correct answer is C. This is a case of a best answer with a reasonable second-best answer. The best answer is rough endoplasmic reticulum. The rough ER contains numerous ribosomes, and is known for producing proteins for export. Collagen fibers of the dentin matrix would be good examples 17 of protein made for export (outside of the cell). The second-best answer is probably mitochondria, in that the synthesis of collagen would be energy-consuming. Odontoblasts are single nuclei cells (unlike osteoclasts, which are multinucleated). Note that smooth ER lacks ribosomes, and that the digestive enzyme activity of lysosomes would not be needed for this process.

Answer 49

The correct answer is B. One of the distinctions between the mandibular first-molar mesial and distal roots is the deep root concavity seen running the length of the mesial surface of the mesial root. The distal root, by comparison, will have no similar concavity or a very slight depression. Other differences include the greater likelihood of the mesial root having a distal curvature, and the greater likelihood of the mesial root being partly split by a partial furcation running partway up from the apical end.

Answer 50

The correct answer is B. The distobuccal cusp of a mandibular molar is a holding (supporting) cusp. The general rule of occlusion of mandibular holding cusps is as follows: the holding cusps of the mandibular teeth occlude on the mesial marginal ridge of their maxillary counterpart, and the distal marginal ridge of the maxillary tooth mesial to their counterpart, EXCEPT distobuccal cusps of mandibular molars occlude with central fossae of their counterparts, the distal cusp of the mandibular first molar occludes with the distal triangular fossa of its counterpart, and the first premolar occludes only with the mesial marginal ridge of its counterpart (but not the canine). In this case, the maxillary counterpart is the maxillary third molar, and the cusp should occlude in the central fossa of this tooth. Remember that the mandibular third molar is located one-half tooth mesial to the maxillary.

Answer 51

The correct answer is A. As a rule, the mandible will move toward the side of injury when the lateral pterygoid is damaged. In this case, the right condyle will not move because of the muscle damage. The left condyle moves forward, but because there is no movement on the right side, the left condyle moves out and rotates to the right, with the nonmoving right condyle acting as a pivot point. Damage to the lateral pterygoid will not affect elevation (closing), because the lateral pterygoid is not an elevator. The elevators are the temporalis, medial pterygoid, and masseter.

Answer 52

The correct answer is D. The distal cusp of the mandibular first molar is a holding cusp. The general rule of occlusion of mandibular holding cusps is as follows: the holding cusps of the mandibular teeth 18 occlude on the mesial marginal ridge of their maxillary counterpart, and the distal marginal ridge of the maxillary tooth mesial to their counterpart, EXCEPT DISTOBUCCAL CUSPS OF MANDIBULAR MOLARS OCCLUDE WITH CENTRAL FOSSAE OF THEIR COUNTERPARTS, THE DISTAL CUSP OF THE MANDIBULAR FIRST MOLAR OCCLUDES WITH THE DISTAL TRIANGULAR FOSSA OF ITS COUNTERPART, AND THE FIRST PREMOLAR OCCLUDES ONLY WITH THE MESIAL MARGINAL RIDGE OF ITS COUNTERPART (BUT NOT THE CANINE). Note that mesiobuccal cusps of mandibular molars and buccal cusps of premolars contact marginal ridges.

Answer 53

The correct answer is B. There are a number of somewhat confusing anomalies at the dentinoenamel junction. Enamel spindles are odontoblastic processes and dentinal tubules which extend a short way into enamel. Enamel lamellae, on the other hand, extend from enamel into dentin. They are pieces of uncalcified organic enamel material. Enamel tufts are hypocalcified enamel rods. They are individual entities; however, they appear as groups (tufts) when a group of them are viewed laterally.

Answer 54

The correct answer is A. Lingual cusps of mandibular teeth are guiding cusps, not holding cusps. Therefore, they do not occlude on marginal ridges or central fossae. The general rule for mandibular lingual cusps is that they occlude in the lingual embrasures between their maxillary counterparts and the teeth mesial to their counterparts, EXCEPT for the distolingual cusps of the mandibular molars, which occlude in the lingual grooves of their maxillary counterparts. In this question we are not dealing with the exception of the distolingual cusps of mandibular molars, so in this case, the mandibular third molar mesiolingual cusp contacts the lingual embrasure between its counterpart (the maxillary third molar) and the tooth mesial to it (the maxillary second molar).

Answer 55

The correct answer is A. During extraction, rotation can be used on teeth with rounded conical roots. Two primary examples are maxillary centrals (especially) and maxillary laterals. Rotation may also be used somewhat with maxillary canines. If roots are flattened mesiodistally, then buccal-lingual movement is used instead of rotation, as rotation may cause crown fracture. Mandibular centrals, laterals, and canines (choices B, C, and D) are all flattened mesiodistally, and therefore are usually not rotated during extraction. Mandibular canines also may occasionally have two roots (buccal and lingual), which will prohibit rotation.

Answer 56

The correct answer is A. As a general rule, maxillary incisors have round root sections and round pulp chamber cross sections. Mandibular incisors have more oval ones, and are flattened mesiodistally. This is in keeping with the general root shape of each. Maxillary incisor roots are round, and mandibular ones are flattened to a greater degree. Note that in both arches, as the pulp moves coronally it will flatten buccolingually, in keeping with the coronal shape of all incisors.

Answer 57

The correct answer is D. Two types of marrow space are found within bone, red (hematopoietic), which is the source of blood cells; and yellow (fatty), which does not produce blood cells. The alveloar bone is similar to most bone in the body in having a compact outer layer of lamellar bone and an inner layer of spongy bone. This spongy bone contains marrow space, usually of the yellow (fatty) type, although some red marrow exists, especially in the ramus and condyle of the mandible.

Answer 58

The correct answer is B. The Posselt envelope of motion is a tracing of the extreme border movements of the mandible. It shows how far the mandible can protrude, retrude, open, and close, and all motions connecting these points. Protruded contact position is caused by protruding the mandible as far as possible. This will normally push the mandible past edge-to-edge, until the mandible appears to be in a Class III relationship. As the mandible protrudes, anterior tooth contact causes separation of the teeth out of occlusion.

Answer 59

The correct answer is D. The epithelial rests of Malassez are found in the periodontal ligament and are leftovers from the root formation process. The root is originally outlined by the epithelial root sheath of Hertwig, which is composed of the inner and outer enamel epithelium tissues, without a stellate reticulum in between. The root sheath induces formation of odontoblasts, which then produce root dentin. Pieces of the root sheath, which do not disappear, remain as the epithelial rests of Malassez. These small groups of tissue are ectodermal in origin, as the original enamel epithelium is ectodermal.

Answer 60

The correct answer is D. A characteristic curve of the two buccal root tips of the maxillary first molar toward each other is sometimes referred to as a pliers-handled appearance or pincer appearance. In effect, the roots grow apically and then turn toward each other, forming a U shape. This shape helps explain the stability of the tooth, especially when combined with the tripod-like arrangement of the palatal root. Note that the same roots of the second maxillary molar often both point distally, distinguishing one molar from the other. These roots in the second molar are also more parallel than those in the first molar. In buccal view they seem to sway distally, with the palatal root in the midline and slightly mesially tilted.

Answer 61

The correct answer is C. The mandibular first molar is invariably a five-cusped tooth, with MB, ML, DB, DL, and distal cusps. Maxillary first and second molars are normally four-cusped teeth. The distolingual cusp is usually less pronounced on the second molar. It is often absent on the maxillary third molar, but that answer is not listed. The mandibular second premolar is either a two- or threecusped tooth. The two-cusped variety has a single buccal cusp and a single lingual cusp, while the three-cusped version has a buccal cusp and paired mesiolingual and distolingual cusps. However, both varieties are common, so it is common to find this tooth lacking the distolingual cusp.

Answer 62

The correct answer is E. Buccal cusps of maxillary teeth are guiding cusps, not holding cusps. Therefore, they do not occlude on marginal ridges or central fossae. The general rule for maxillary buccal cusps is that they occlude in the facial embrasure between their mandibular counterpart and the tooth distal to their counterpart, EXCEPT for the mesiobuccal cusps of the molars, which occlude in the buccal grooves of their mandibular counterparts, and the distobuccal cusp of the first molar, which opposes the distobuccal groove of the mandibular first molar. In this question, the contact is the embrasure between second mandibular premolar (the counterpart) and the first molar (the tooth distal to the counterpart).

Answer 63

The correct answer is C. In occlusion, cusps are defined as either holding (supporting) cusps or guiding cusps. Holding cusps, in central occlusion, make contact with the opposing arch, establish vertical dimension of occlusion, and support the forces of occlusion. They are the lingual cusps of the maxillary arch and buccal cusps of the mandibular. When the teeth are in centric occlusion, these cusps are in contact. The other cusps (guiding) are not. The other cusps are either lingual to the contact (lingual cusps of the mandibular arch) or buccal to the contact (buccal cusps of the maxillary arch).

Answer 64

The correct answer is C. Protrusive movement is defined as moving the mandible outward, away from the head. If you are in centric occlusion, you will protrude to move toward an edge-to-edge position. The lateral pterygoid moves both condyles forward when it contracts, so the initial protrusive movement is forward. When the condyle contacts the articular eminence in the glenoid fossa, it cannot move directly forward anymore and begins to glide downward along the surface of the fossa.

Answer 65

The correct answer is C. In the permanent mandibular first molar, the mesial root is usually slightly curved distally, and the distal root is straighter but pointing toward the distal. In the second molar, both roots are usually significantly inclined toward the distal and curved distally at the end. They tend to resemble each other more than the two roots of the first molar do. They are also closer together. The roots in the first molar are more widely spread.

Answer 66

The correct answer is C. The attachment fibers are usually divided into two groups, the gingival group and the periodontal group. Gingival fibers attach tissues, not including alveolar bone. For example, circular fibers run only within gingiva, encircling the tooth. Dento-gingival fibers run from cementum to gingiva. Dento-periosteal fibers run from cementum to periosteum. Periodontal fibers run from alveolar bone to cementum, and include alveolar crestal, oblique, horizontal, and apical.

Answer 67

The correct answer is A. Buccal cusps of maxillary teeth are guiding cusps, not holding cusps. Therefore, they do not occlude on marginal ridges or central fossae. The general rule for maxillary buccal cusps is that they occlude in the facial embrasures between their mandibular counterparts and the teeth distal to their counterparts, EXCEPT for the mesiobuccal cusps of the molars, which occlude in the buccal grooves of their mandibular counterparts, and the distobuccal cusp of the first molar, which opposes the distobuccal groove of the mandibular first molar. In this question we are dealing with the exception of the mesiobuccal cusps of maxillary molars, which occlude with the buccal grooves of their mandibular counterparts. In this case, the maxillary second molar mesiobuccal cusp contacts the mandibular second molar buccal groove (its counterpart).

Answer 68

The correct answer is C. Only maxillary incisors have roundish pulp chamber cross sections when cut at the cervical line. Laterals are egg-shaped with the widest portion labial, not round. This is true for both maxillary centrals and laterals, which are egg-shaped with the widest portion of the labial not round. In general, mandibular incisors and both arch canines will have oval-shaped pulp chambers, flattened mesiodistally. (Imagine squashing a round pulp from both the mesial and distal sides at once, resulting in a squashed oval, pointing to the buccal and lingual). Remember that the shape of a pulp chamber is usually related to the shape of the surrounding root.

Answer 69

The correct answer is C. Two roots are a fairly rare occurrence in canines, but are occasionally found in the mandibular canine. They are almost unknown in the maxillary. If they are found in the mandibular canine, they will be buccal and lingual, similar to those found in premolars.

Answer 70

The correct answer is D. The gingival masticatory mucosa is characterized by keratinization, thin or absent submucosa, and a firm, direct binding of the lamina propria to the periosteum. In general, the submucosa is thicker in the lining mucosa. Note that submucosa, when present, is always found beneath lamina propria, and is never between epithelium and lamina propria. If all four tissues are present in a digestive mucosa, the order from the outside will be: epithelium, lamina propria, muscularis mucosae, submucosa.

Answer 71

The correct answer is E. The distolingual cusp of a maxillary third molar is theoretically a holding cusp, however it is often missing on this tooth. The general rule for maxillary holding cusps is as follows: a maxillary holding cusp contacts the distal marginal ridge of its mandibular counterpart and the mesial marginal ridge of the mandibular tooth distal to its counterpart, EXCEPT FOR THE MESIOLINGUAL CUSPS OF THE MOLARS, WHICH CONTACT THE CENTRAL FOSSAE OF THEIR COUNTERPARTS. This should be the distal marginal ridge of the mandibular third molar and no mesial marginal ridge, because there is no tooth distal to the third molar. So the answer is either the cusp does not exist, or it contacts only the distal marginal ridge of the mandibular third molar.

Answer 72

The correct answer is B. The fibers of the periodontal ligament are collagenous and insert into the compact, lamellar outer layer of the tooth socket. This is similar to fibers of a tendon inserting into bone. The appearance of the bone with the collagen fibers causes it to be named bundle bone. The fibers themselves are called Sharpey's fibers. Tomes processes (choice A) are projections of ameloblasts into developing enamel. Von Ebner lines (choice C) are found in dentin and show the incremental laying down of dentin tissue. Lines of Owen (choice D) are found in dentin as well, and are exaggerated Von Ebner lines found in areas of trauma during dentin formation.

Answer 73

The correct answer is B. The dental pulp is a connective tissue characterized by multiple collagen fibers running in all directions, and large numbers of fibroblasts, which produce the fibers. There are also capillaries, neurons, lymphatic channels, and different types of leukocytes, including macrophages, neutrophils, and eosinophils. However, the predominant cell type is the fibroblast. Note that the pulp is lined by the dentin-forming odontoblasts, but there are no ameloblasts, which form enamel.

Answer 74

The correct answer is C. The three sections of the tooth bud are the enamel organ, the dental sac, and the dental papilla. The enamel organ, not surprisingly, produces enamel and contains the inner enamel epithelium, stratum intermedium, stellate reticulum, and outer enamel epithelium. The dental papilla, a mesodermal derivative, produces both dental pulp and dentin. The dental sac, also mesodermal, produces both cementum and the periodontal ligament.

Answer 75

The correct answer is C. The origins and insertions of the TMJ ligaments are as follows: The sphenomandibular ligament arises from a spine on the sphenoid bone and runs forward and downward to insert on the lingula and deep ramus of the mandible. The stylomandibular ligament arises from the spine of the temporal bone known as the styloid process and inserts on the lower ramus and angle of the mandible. The lateral ligament is also known as the temporomandibular ligament. It descends from the lower border and tubercle of the zygoma to the posterior lateral condyle. Its fibers merge with those of the articular capsule.

Answer 76

The correct answer is D. Most often, the maxillary first molar has three canals: a mesiobuccal, a distobuccal, and a palatal. The palatal is usually largest and widest. Occasionally (30%) the first molar may have a fourth canal, located within the mesiobuccal root, slightly lingual to the mesiobuccal canal. When found, it is the smallest and thinnest of all canals in the tooth.

Answer 77

The correct answer is C. Alveolar bone is a combination of cortical (compact) bone and trabecular (spongy) bone. The cortical bone is on the outside surface, both next to the tooth root and also continuous with the cortical bone of the maxilla and mandible. The cortical bone adjacent to the tooth root is sometimes referred to as lamina dura. Nerves and blood vessels travel primarily through the more porous cancellous bone between the two cortical plates. Note that alveolar bone can be lost rapidly either in periodontal disease or following tooth extraction.

Answer 78

The correct answer is D. As you move from centric occlusion to edge-to-edge position, the mandibular teeth separate from the maxillary and a space is created between the two arches. Try this yourself, as you protrude and slide the mandible forward. The anterior teeth act as a guide as you slowly separate from occlusal contact until only incisal edges of incisors contact. At this point, the increased space between the arches adds to vertical dimension. There is no vertical overlap (overbite; choice C) nor is there any horizontal overlap (overjet; choice B) at this point. So protrusion to edge-toedge increases vertical dimension while decreasing both vertical and horizontal overlap.

Answer 79

The correct answer is C. The mandibular central incisor is often described as the most symmetrical tooth when viewed from the labial. The incisal edge is horizontal, the mesial and distal contacts are at the same height, and the mesioincisal and distoincisal line angles are equal. In addition, the tooth is not rotated. The mandibular lateral incisor crown is rotated, and its distal contact point is more apical than the mesial.

Answer 80

The correct answer is D. Remember that the function of Golgi apparatus is to modify and package proteins produced for export by the cell. In this way, an odontoblast would be similar to any other protein-producing secretory cell. Proteins produced by ribosomes on the rough ER will enter the ER and travel to the Golgi apparatus. Here, within the flattened sacs of the Golgi, the collagen and other fibers will be modified and packaged to be sent to the edge of the cell for secretion as dentin matrix. So the large production demands of producing collagen and other proteins for predentin should result in odontoblasts having large, numerous, and active Golgi bodies.

Answer 81

``` The correct answer is B. This is one of the biggest, shortest, roundest, flattest type questions that NBDE Part 1 loves so much. The maxillary canine is the longest tooth in the mouth, measured cusp tip to root tip. It is about 3 mm longer than the maxillary central (choice A), 1 mm longer than the mandibular canine (choice C), and 4 mm longer than the maxillary second premolar (choice D). Note that the mandibular central is the narrowest tooth in the mouth. ```

Answer 82

The correct answer is C. Caries is most commonly found in grooves, pits, and fissures of teeth. Sucrose and other substrates collect and S. mutans secretes lactic acid to dissolve enamel. All posterior occlusal surfaces are susceptible to caries, as they contain pits, fissures, and grooves. Maxillary molars have distinct lingual pits or grooves which may become carious. Likewise, buccal pits are common on mandibular molars. Note that lingual surfaces of mandibular molars are generally smooth, without pits and fissures.

Answer 83

The correct answer is D. Anatomically, roots of the maxillary first molar are closest to the sinus, which dips downward in this area. Periapical x-rays of the area sometimes reveal that the roots of the first molar border right on the sinus margin. Although the first molar is the MOST likely tooth to have a root enter the sinus, roots of the second premolar and second molar can occasionally end up there as well.

Answer 84

The correct answer is C. Premolars do not vary far from a vertical line when viewed from the mesial or distal. Both maxillary and mandibular incisors tip their roots greatly toward the lingual, and canines less so. Mandibular molar roots lean buccally while maxillary molar roots lean palatally.

Answer 85

The correct answer is C. Erosion is the chemical dissolving of tooth structure. It can be caused by a number of factors, including sucking on lemons and other acidic fruit, excessive intake of acidic beverages (cola), or excessive vomiting, as in bulimia. Bulimics often exhibit normal facial surfaces with severely eroded lingual surfaces. This is due to the effect of strong mineral acid from the stomach (hydrochloric acid at pH 2). Attrition (choice A) is the mechanical wearing of teeth due to physiologic processes, including chewing and bruxism. Abrasion (choice B) is the mechanical wearing away of tooth structure due to some outside object, such as toothbrush abrasion at the cervical lines of teeth due to hard sideways brushing, or from habitually holding bobby pins or nails with the teeth. Internal resorption (choice D) is the loss of dentin from pathologic dissolving by processes inside the pulp chamber. It can follow tooth trauma.

Answer 86

The correct answer is A. Gemination is a form of fusion, where a single root attempts to form two crowns, and these crowns share dentin and enamel. A dilaceration is a sharply bent root, especially near the apex. Concrescence is joining of two teeth by cementum union. Taurodonts are teeth, usually molars, with short roots relative to crown size, and large pulpal chambers, giving rise to a bulllike appearance. Dens-in-dente refers to a tooth-within-a-tooth appearance and is due to invagination, usually in a maxillary lateral incisor.

Answer 87

The correct answer is B. The buccal cusp of a mandibular premolar is a holding (supporting) cusp. The general rule of occlusion of mandibular holding cusps is as follows: the holding cusps of the mandibular teeth occlude on the mesial marginal ridge of their maxillary counterpart, and the distal marginal ridge of the maxillary tooth mesial to their counterpart, EXCEPTdistobuccal cusps of mandibular molars occlude with central fossae of their counterparts, the distal cusp of the mandibular first molar occludes with the distal triangular fossa of its counterpart, and the first premolar occludes only with the mesial marginal ridge of its counterpart (but not the canine). In this case, the maxillary counterpart is the maxillary second premolar, and the tooth mesial to it is the first premolar.

Answer 88

The correct answer is C. This may seem counterintuitive, as excess motion of the condyle results in the mandible being locked in a forward and open position. However, anatomically, what is happening is that the condyle has moved forward, down the surface of the articular eminence, past the tip of the eminence, and past the bulk of the articular tubercle. It is now past a large, inferiorly projecting mound of bone (the tubercle). To return the condyle to normal position, a downward (inferior) force is needed to positon the condyle once again below the articular tubercle and eminence. The inferior directed force is also needed to counteract the elevating forces of the medial pterygoid, masseter, and temporalis muscles. On repositioning, the mandible often snaps strongly into normal position, due to these strong elevations.

Answer 89

The correct answer is E. If you view the maxillary first molar from the occlusal, its shape is that of a rhombus, or equal-sided parallelogram. In any parallelogram, one pair of opposite corners will be obtuse, while the other pair of opposite corners will be acute. In the maxillary first molar, the opposite pair of MB and DL are acute, while the pair ML and DB are obtuse.

Answer 90

The correct answer is D. The mandibular central and lateral incisors can be viewed as almost twins. They are similar in dimension both mesiodistally and buccolingually. (The lateral may be slightly, but not significantly, larger). Their roots are similar in length, although the lateral may have a more pronounced distal inclination. The crowns are of similar anatomy. However, the lateral has a twisted or rotated crown, as if you took a central and then slightly rotated the crown around the long axis of the root. The root may appear to face forward, while the incisal edge is curved in keeping with the normal curve of cusp tips of the mandibular arch.

Answer 91

The correct answer is E. Lingual cusps of mandibular teeth are guiding cusps, not holding cusps. Therefore, they do not occlude on marginal ridges or central fossae. The general rule for mandibular lingual cusps is that they occlude in the lingual embrasures between their maxillary counterparts and the teeth mesial to their counterparts, EXCEPT for the distolingual cusps of the mandibular molars, which occlude in the lingual grooves of their maxillary counterparts. In this question we are not dealing with the exception of the distolingual cusps of mandibular molars, so in this case, the mandibular first premolar lingual cusp contacts the lingual embrasure between its counterpart (the maxillary first premolar) and the tooth mesial to it (the maxillary canine).

Answer 92

The correct answer is D. The alveloar bone is similar to most bone in the body in having a compact outer layer of lamellar bone and an inner layer of spongy bone. This spongy bone contains marrow space, usually of the yellow (fatty) type, although some red marrow exists. Collagen fibers of the periodontal ligament insert into the outer cortical compact layer, and are known as Sharpey's fibers. Compact bone with Sharpey's fibers is also known as bundle bone.

Answer 93

The correct answer is C. The TMJ has an upper and lower compartment, separated by the articular disc, which is composed of fibrous connective tissue. Both the upper and lower compartments are synovial; that is, they produce synovial fluid. Synovial fluid aids in lubricating the articular surfaces of the joint, and is found in many movable joints. Note that the synovial membrane lines the inside of the joint but not the actual articulating surfaces. These surfaces are fibrous connective tissue over hyaline cartilage.

Answer 94

The correct answer is B. The odontoblast function is to lay down the protein matrix for the formation of dentin. Protein matrix is an exported protein, and therefore the cell must have highly developed 28 machinery for production and export of protein. This usually involves ribosomes attached to ER (rough ER) and Golgi bodies. The ribosomes translate RNA messages into assembled proteins and send them in the ER to the Golgi apparatus, where they are modified and packaged for export. Odontoblasts do not have flagella, and there is no special reason to have highly developed lysosomes for internal digestion. As metabolically active cells they would have elevated mitochondria levels, but this would not be as notable as the extensive protein producing apparatus.

Answer 95

The correct answer is C. This is a fairly common occurrence. A child of about 6 years will often present to the dental clinic with a parent, and the parent will be concerned about a double row of teeth. In these cases, the permanent mandibular incisors are erupting before the primaries have completely exfoliated. An x-ray usually confirms partial resorption of the primary roots, and the primaries are allowed to exfoliate. No further treatment is usually indicated. In rare cases where the permanents erupt buccally, extraction of the primaries and tooth movement of the permanents is in order, however this is highly unusual.

Answer 96

The correct answer is A. Both types of oral epithelium (masticatory and lining) are stratified, not simple, squamous epithelium. In masticatory epithelium it is highly keratinized and thickened. This type of mucosa covers the hard palate and gingival areas. The submucosa of these tissues is usually poorly developed or absent. Lining mucosa is generally thin and nonkeratinized, and has a glandular lamina propria and a well developed submucosa.

Answer 97

The correct answer is D. While theoretically it may appear that the correct answer is choice A, most authors state that there is no contact with the maxillary canine distal marginal ridge, and the canine remains slightly out of contact but near the area of the buccal cusp of the mandibular first premolar. The general rule of occlusion of mandibular holding cusps is as follows: the holding cusps of the mandibular teeth occlude on the mesial marginal ridge of their maxillary counterpart, and the distal marginal ridge of the maxillary tooth mesial to their counterpart, EXCEPT DISTOBUCCAL CUSPS OF MANDIBULAR MOLARS OCCLUDE WITH CENTRAL FOSSAE OF THEIR COUNTERPARTS, THE DISTAL CUSP OF THE MANDIBULAR FIRST MOLAR OCCLUDES WITH THE DISTAL TRIANGULAR FOSSA OF ITS COUNTERPART, AND THE FIRST PREMOLAR OCCLUDES ONLY WITH THE MESIAL MARGINAL RIDGE OF ITS COUNTERPART (BUT NOT THE CANINE).

Answer 98

The correct answer is D. The buccal cusp of a mandibular canine is not considered to be a holding (supporting) cusp. Therefore, the general rule of occlusion of mandibular holding cusps does not apply. The canine, as an anterior tooth, will normally be slightly out of contact between its maxillary counterpart and the tooth immediately mesial to it. In this case, the maxillary counterpart is the maxillary canine, and the tooth mesial to it is the lateral incisor.

Answer 99

The correct answer is B. The lamina propria is a loose connective tissue located within the mucosal layer, just underneath the epithelium. In the oral cavity, it will be found below the outer layer of stratified squamous epithelium. The lamina propria in the oral cavity often forms wedge-like extensions into concavities in the epithelium, known as connective tissue papillae. The corresponding epithelial extensions into the connective tissue are known as rete pegs.

Answer 100

The correct answer is C. Increased cementum production (hypercementosis) is a common x-ray finding. Its cause is not completely known, but it seems to occur more often in teeth that have lost function and/or are supererupted, rather than in teeth with excessive function (occlusal trauma). Occlusal trauma is recognized clinically by heavy contact (using articulating paper), and high mobility. It is recognized radiographically by a widened PDL space and possibly with accompanying bone resorption. Note that in loss of function, teeth often have a narrowed PDL.

Answer 101

The correct answer is E. The question depends entirely on the definition of succedaneous. A succedaneous tooth succeeds (replaces) another tooth. So only permanent teeth can be succedaneous. Note, however, that permanent molars are never succedaneous, as they erupt distal to all primary teeth (choices C and D). Only permanent incisors, canines, and premolars can be succedaneous (refer to choices A and B). Of all succedaneous teeth, the permanent mandibular central incisor is usually first, appearing at about age 6, close to the eruption of the nonsuccedaneous permanent mandibular first molar

Answer 102

The correct answer is C. Although the time varies, 2 to 3 years is a common average time. Remember that as a crown erupts, the root is still forming, and x-rays of newly erupted teeth show varying levels of root formation. This has important implications in endodontics, when we may try to cause a tooth to complete its root formation in order to better manage it for restoration. A few examples of typical time lags are: maxillary central incisor, eruption 7-8 years, root completion 10 years; maxillary canine, eruption 11-12 years, root completion 14 years; mandibular second molar, eruption 11-13 years, root completion 14-15 years.

Answer 103

The correct answer is A. One of the distinctions between the mandibular first-molar mesial and distal roots is the deep root concavity seen running the length of the mesial surface of the mesial root. The distal root, by comparison, will have no similar concavity or a very slight depression. This concavity will sometimes express itself as a partial split (bifurcation) of some small section of the apical end of the mesial root into two roots. This feature is rare to unknown on the distal root. Other differences include the greater likelihood of the mesial root having a pronounced distal curvature.

Answer 104

The correct answer is C. One way to eliminate answers is to note that the labial view of the maxillary canine is not symmetrical. The mesial cusp ridge is shorter than the distal cusp ridge. This means that the distance from the cusp tip to the mesial contact is shorter than that from the cusp tip to the distal contact. Another way to look at it is that the distal cusp ridge dips lower (more cervical). Therefore, the distal height of contour will be more cervical than the mesial. The mesial height of contour is at about the junction of incisal and middle thirds, while the distal is at the middle of the middle third. Do not consider choice E, even though it follows the pattern discussed above. These contacts (middle, cervical) are too cervical for an anterior tooth.

Answer 105

The correct answer is C. Sharpey's fibers is an older name for the collagenous bundles of the periodontal ligament which connect the tooth to the tooth socket. The two tissues entered by these fibers are cementum on the tooth, and the cortical bone plate of the alveolar bone. When they enter the cortical plate, the resulting bone, when viewed under the microscope, is termed bundle bone. The fibers do not penetrate the bone enough to reach the cancellous inner layers of the alveolar bone.

Answer 106

The correct answer is B. Although some variation exists, the most common arrangement of canals in the mandibular first molar is two canals in the mesial root (MB and ML), and one in the distal. The largest is normally the distal, followed by the MB, then the ML. Approximately 25% of mandibular first molars will have four canals: MB, ML, DB, and DL. 131. The lingual fossa is normally deepest on which

Answer 107

The correct answer is B. The maxillary lateral is noted for its variability, and one area of great variety is the lingual fossa. It is normally more pronounced than that of any other incisor and often contains a pit, from narrow and shallow to deep and extensive. Extremely deep pits may give a dens-in-dente 31 appearance. In operative dentistry the maxillary lateral is the only incisor in which you will occasionally see lingual pit amalgams. The lingual surface is often marked by a lingual marginal groove and tubercles on the cingulum. In general, expect any type of unusual variety to be most commonly found on maxillary laterals.

Answer 108

The correct answer is D. Buccal cusps of maxillary teeth are guiding cusps, not holding cusps. Therefore, they do not occlude on marginal ridges or central fossae. The general rule for maxillary buccal cusps is that they occlude in the facial embrasure between their mandibular counterpart and the tooth distal to their counterpart, EXCEPT for the mesiobuccal cusps of the molars, which occlude in the buccal groove of their mandibular counterpart, and the distobuccal cusp of the first molar, which opposes the distobuccal groove of the mandibular first molar. In this question, the contact is the embrasure between first and second mandibular premolars.

Answer 109

The correct answer is D. To answer this question, place your own teeth in centric occlusion (maximum intercuspation). Notice that the occlusion is held in place by the lingual cusps of maxillary teeth and the buccal cusps of mandibular teeth. Mandibular lingual cusps are not in contact. In protrusion, the anterior teeth act to separate the maxilla and mandible as the mandible moves forward. The anterior teeth act as guides in retrusion as well (try it). So far the mandibular lingual cusps are not involved. If you make a left working movement (slide your mandible left), notice that the mandibular lingual cusps on the left, drag against the lingual side of the maxillary lingual cusps. In the nonworking side (in this case, the right side), the mandibular lingual cusps move AWAY from contact.

Answer 110

The correct answer is B. Masticatory mucosa consists of the gingiva and lining of the hard palate. Most of the other areas of the oral cavity are lined by lining mucosa. Specialized mucosa is found on the dorsum of the tongue and contains taste buds and various papillae. The characteristics of masticatory mucosa are keratinization, thin or absent submucosa, and tight binding of the lamina propria to underlying periosteum. Lining mucosa is generally nonkeratinized, with a thin lamina propria. Near the teeth, the gingiva and lining mucosa (alveolar mucosa) meet at the mucogingival junction.

Answer 111

The correct answer is C. For the most part, despite an overall size difference and some differences in ratio (crown:root, crown height:mesiodistal length), the primary teeth generally resemble the 32 permanents for all teeth EXCEPT the first molars. Primary central and lateral incisors and canines are fairly close to small versions of the permanents. Primary second molars very closely resemble permanent first molars. However, primary first molars are unique. The primary maxillary first is premolar-like in crown form but possesses three roots. The primary mandibular molar is molar-like in form, but with an unusually pronounced mesial section and a much less developed distal section. It does not resemble any permanent tooth.

Answer 112

The correct answer is A. An unusual aspect of the maxillary first premolar is the mesial-distal placement of the cusps. The buccal cusp is off center toward the distal, while the lingual cusp is off center toward the mesial. If you look at the tooth from the lingual, therefore, you will always see two distinct cusp tips, one slightly to the mesial or distal of the other. This placement, when viewed occlusally, is said to give the tooth a twisted appearance. This situation is not found in the second premolar, where the cusps are almost equal in size and straight in alignment.

Answer 113

The correct answer is C. There are a number of somewhat confusing anomalies at the dentinoenamel junction. Enamel spindles are odontoblastic processes and dentinal tubules which extend a short way into enamel. Enamel lamellae, on the other hand, extend from enamel into dentin. They are pieces of uncalcified organic enamel material. Enamel tufts are hypocalcified enamel rods. They are individual entities; however, they appear as groups (tufts) when a group of them are viewed laterally.

Answer 114

The correct answer is B. Two types of marrow space are found within bone: red (hematopoietic), which is the source of blood cells; and yellow (fatty), which does not produce blood cells. The alveloar bone is similar to most bone in the body in having a compact outer layer of lamellar bone and an inner layer of spongy bone. This spongy bone contains marrow space, usually of the yellow (fatty) type, although some red marrow exists. The chief places where red marrow is found in the oral cavity are the condyle, the angle of the mandible, and the maxillary tuberosity.

Answer 115

The correct answer is C. Some teeth almost invariably have a divided pulp canal, such as the maxillary first premolar. This tooth normally has two roots, although the level at which the division occurs can vary. The other three teeth listed are normally single rooted with single undivided pulp canals. However the maxillary central incisor almost never varies from a single rounded root. In contrast, you can sometimes, although rarely, find divided roots, especially near the apex, for the mandibular lateral and canine.

Answer 116

The correct answer is C. As is generally the case, the distal contact of this tooth is more cervical than is the mesial contact. On the mesial side, where it contacts the central incisor, the contact will be near the junction of incisal and middle thirds. However, on the distal side, it is slightly more cervical, usually around the middle of the middle third. This is the contact with the maxillary canine. On the canine, this height of contour is at the junction of the incisal and middle third

Answer 117

The correct answer is E. Buccal cusps of maxillary teeth are guiding cusps, not holding cusps. Therefore, they do not occlude on marginal ridges or central fossae. The general rule for maxillary buccal cusps is that they occlude in the facial embrasures between their mandibular counterparts and the teeth distal to their counterparts, EXCEPT for the mesiobuccal cusps of the molars, which occlude in the buccal grooves of their mandibular counterparts, and the distobuccal cusp of the first molar, which opposes the distobuccal groove of the mandibular first molar. In this question we are dealing with the exception of the distobuccal cusps of the maxillary first molar, which occludes with the distobuccal groove of its mandibular counterpart, the mandibular first molar.

Answer 118

The correct answer is D. Isomorphy refers to a close similarity in morphology and crown shape between two teeth. The most notable examples of isomorphy are the primary second molars with the permanent first molars IN BOTH ARCHES. Thus, by looking at a primary second molar in either arch, you can very accurately predict the morphology of the permanent first molar in that same arch. Isomorphy does not exist between primary first and second molars, as both first molars are very unusual in shape and both second molars closely resemble permanent first molars.

Answer 119

The correct answer is D. The TMJ is a synovial joint, similar to most other movable joints. It is different in having a fibrous articular disc. The surface of the disc is fibrous connective tissue, and the surface of the articulating surfaces of the glenoid fossa are fibrous connective tissue overlying hyaline cartilage. These surfaces are not covered with synovial tissue; however, their smooth functioning is dependent on the production of synovial fluid elsewhere in the joint. This production occurs in all nonarticulating surfaces of the joint, which are lined with synovial tissue.

Answer 120

The correct answer is C. Despite a somewhat premolar-shaped crown, the primary maxillary first molar is consistent in root form with all maxillary molars, primary or permanent, in having three roots. They are the mesiobuccal, distobuccal, and palatal. Premolars will routinely have either one or two roots. Primary molars lack a common root trunk, and have widespread roots which allow space for the developing premolar crown underneath.

Answer 121

The correct answer is D. MOD preparations can be difficult because tooth structure must be removed from three tooth surfaces. The remaining tooth structure can be weak, and pulp horns may be exposed. They are especially hard in small teeth with large pulp horns. The primary mandibular first molar is a good example. It has a very narrow distal end, is small overall, and has very high mesial pulp horns. Additionally, little tooth structure remains after the MOD is cut. Permanent mandibular first premolars are small, but not like the primaries. They should have a slanted occlusal floor, but an MOD is possible. Permanent maxillary second molars are generally large and would be the best of this group for making an MOD preparation. The primary mandibular second molar, while small, is larger than the first molar, and has the same shape as a permanent first molar, making it not as difficult to perform an MOD preparation.

Answer 122

The correct answer is B. Both the inner and outer enamel epithelium are solid lines of cells with no space between the cells in each line. Between these two layers of cells we find the stratum intermedium, close to the inner enamel epithelium; and the stellate reticulum, filling the space between the stratum intermedium and outer enamel epithelium. The stratum intermedium is generally a few layers of squamous epithelium. The stellate reticulum is a reticulum (net-like network) of widely separated cells (think of stars in the sky). These cells are surrounded by a clear liquid matrix and are connected by cell processes.

Answer 123

The correct answer is choice D. Eruption and exfoliation questions are common NBDE Part 1 topics. Answers are approximate, of course, and subject to variation. However, you should know the most common average ages for all teeth. For maxillary primaries, the centrals exfoliate at year 7-8, laterals at 8-9, canines at 11-12, first molars at 10-11, and second molars at 11-12. Remember that these are averages. Always eliminate wildly wrong answers first.

Answer 124

The correct answer is C. Reviewing the surfaces, the lingual surface of the canine contains the bulbous cingulum. The surface of the lingual is thus slanted at roughly 45 degrees from the long axis (as represented by the root). Likewise, the facial surface slants inward as you go from cervical to incisal. The distal surface slants lingually as the tooth narrows coronally. Our answer is mesial. The mesial surface is vertical overall, with no large bulge. Notice that the distal is always more rounded and bulbous than the mesial, which is relatively straight and, if extended, would roughly parallel the root.

Answer 125

The correct answer is A. Lingual cusps of mandibular teeth are guiding cusps, not holding cusps. Therefore, they do not occlude on marginal ridges or central fossae. The general rule for mandibular lingual cusps is that they occlude in the lingual embrasures between their maxillary counterparts and the teeth mesial to their counterparts, EXCEPT for the distolingual cusps of the mandibular molars, which occlude in the lingual grooves of their maxillary counterparts. In this question we are not dealing with the exception of the distolingual cusps of mandibular molars, so in this case, the mandibular first molar mesiolingual cusp contacts the lingual embrasure between its counterpart (the maxillary first molar) and the tooth mesial to it (the maxillary second premolar).

Answer 126

The correct answer is B. The lateral pterygoid muscle has two heads. The superior head arises from the greater wing of the sphenoid bone, and the inferior head from the lateral plate of the lateral pterygoid bone. They extend posteriorly to the mandibular condyle, TMJ capsule, and TMJ disc. Fibers from the upper head enter the capsule and merge with the fibrous connective tissue of both the capsule and disc. This is related to the function of the muscle in protruding the mandible, and pulling the disc with the condyle during protrusion, depressing (opening), and lateral movements. No other muscle enters the TMJ.

Answer 127

The correct answer is C. A characteristic curve of the two buccal root tips of the maxillary first molar toward each other is sometimes referred to as a pliers-handled appearance or pincer appearance. In effect, the roots grow apically and then turn toward each other, forming a U shape. This shape helps explain the stability of the tooth, especially when combined with the tripod-like arrangement of the palatal root. Note that the same roots of the second maxillary molar often both point distally, distinguishing one molar from the other. These roots in the second molar are also more parallel than those in the first molar.

Answer 128

The correct answer is D. Predentin would be found in between odontoblasts and true dentin. The odontoblasts lay down predentin, which is primarily protein matrix composed almost entirely of collagen. As it mineralizes farther away from the odontoblastic layer, it becomes true dentin, with its high mineral content. Ameloblasts form enamel and are not involved in dentin or predentin production.

Answer 129

The correct answer is D. The mandibular second premolar has a variety of occlusal appearances due mostly to its two-cusped or three-cusped nature. There is a slightly larger buccal cusp area, and then either an approximately equal-sized lingual cusp, or a pair of lingual cusps, known as the mesiolingual and distolingual cusps. Together, these two form an area slightly smaller than the buccal cusp. In the event of the three cusps, an occlusal Y groove pattern is common. On the two-cusped variety, either an H (more common) or U (less common) pattern may be found.

Answer 130

The correct answer is B. Both circular and transseptal fibers are classified in the gingival fiber group. As such, they do not enter alveolar bone. Circular fibers run circumferentially around the tooth, contained completely within the gingiva. Transseptal fibers insert in the cementum of one tooth, travel horizontally above the alveolar crest, and insert into the cementum of an adjacent tooth. Oblique, horizontal, and apical fibers are all periodontal fibers, and insert in cementum on one end and alveolar bone on the other.

Answer 131

The correct answer is B. Succedaneous refers to a tooth that succeeds another tooth; that is, a tooth that replaces a previous tooth. Remember that permanent incisors and canines replace primary incisors and canines (choices A, D, and E). Permanent premolars replace primary molars (choice C). Thus, all the permanent teeth mentioned so far are succedaneous. Permanent molars are not succedaneous as they do not replace primary teeth. The permanent first molar develops distal to all primary teeth, and later the second and third molars do likewise. Molars do not replace any primary teeth and are therefore not succedaneous.

Answer 132

The correct answer is C. The alveolar crestal fibers are examples of fibers of the periodontal ligament, rather than gingival group fibers. The distinction is that periodontal fibers attach on one end into cementum, and on the other into alveolar bone. Gingival fibers do not attach to bone. The alveolar crest fibers attach from cementum to alveolar bone at the alveolar crest. Dento-gingival fibers attach from cementum to gingiva, dento-periosteal fibers from cementum to periosteum, and circular fibers run circularly around the tooth within the gingiva.

Answer 133

The correct answer is D. Although none of the teeth listed is commonly double rooted, the mandibular canine is the most likely of this group. Maxillary laterals (choice A) are highly variable and are often the most variable teeth in the mouth. However, their variability does not usually include double-rooted appearance. Mandibular centrals and laterals (choice B) often have proximal root grooves. If these grooves are deep, there may be an appearance of becoming double rooted, but they rarely are. Maxillary canines (choice C) are invariably single rooted. Mandibular canines are occasionally double rooted. The point of separation into two roots may be toward the cervical of the root, or almost at the apex. This double-rooted possibility is significant for both exodontia and endodontics.

Answer 134

The correct answer is B. If we arbitrarily call the long axis of the root vertical, only the apical periodontal fibers are nearly parallel (vertical). The apical fibers run vertically from the apex of the alveolar bone socket to the root apex cementum. More coronally, the next fibers, the oblique, run obliquely (slanted) from near apical cementum to more coronal alveolar bone. Horizontal fibers run horizontally from cementum to bone, which is thus perpendicular to the root axis. The most coronal alveolar fibers run obliquely from coronal cementum, apically slanted toward the alveolar crest of bone.

Answer 135

The correct answer is D. Remember that the mandibular teeth, being smaller, are set one-half tooth mesial to the corresponding maxillary tooth. That is, the maxillary central contacts the mandibular central and half of the mandibular lateral. The maxillary lateral contacts both the mandibular lateral and canine. Note that the maxillary canine cusp tip sits in the embrasure between the mandibular canine and first premolar, although the incisors are the main contacts in protrusive movement.

Answer 136

The correct answer is B. The Carabelli cusp (trait) is a variable cusp or extension of the mesiolingual cusp of the maxillary first molar. Its expression varies from that of a full cusp, at its largest, to a small protuberance at its smallest. Its expression varies among various races and ethnic groups. Some anatomists describe it as a cusp, making the maxillary first molar a five-cusped tooth. Others consider it a variety or trait of a four-cusped tooth. It is sometimes missing, and a groove or pit is found in the normal Carabelli cusp region of the mesiolingual cusp.

Answer 137

The correct answer is B. The vertical dimension of occlusion (VDO) is a vertical measurement on the front of the face when the teeth are in full occlusion (centric occlusion). When the face is at rest, the teeth are slightly apart, and the vertical dimension of the front of the face is slightly longer. This is the vertical dimension of rest (VDR). The distance between the teeth at this point is the freeway space (FS). So when we take the smaller VDO and add the few millimeters of the FS, we get the slightly longer VDR. VDR is generally 2 to 5 mm more than VDO.

Answer 138

The correct answer is A. Only maxillary incisors have roundish pulp chamber cross sections when cut at the cervical line. This is true for both maxillary centrals and laterals. In general, mandibular incisors and both arch canines will have ovalish pulp chambers, flattened mesiodistally. (Imagine squashing a round pulp from both the mesial and distal sides at once, resulting in a squashed oval, pointing to the buccal and lingual). Remember that the shape of a pulp chamber is usually related to the shape of the surrounding root.

Answer 139

The correct answer is C. Of the tissues comprising the tooth structure, only enamel is formed from ectoderm. It is made by ameloblasts, which are ectodermal derivatives. Cementum, produced by cementoblasts, and dentin, produced by odontoblasts, are both mesodermal derivatives (choice B). Note also that pulpal tissue is mesodermal. No tooth structural tissue is endodermal (choice A).

Answer 140

The correct answer is B. Dentin forms the bulk of both the crown and root of the tooth. In the crown, it underlies the outer enamel. In the root, it underlies a thin layer of cementum. The original dentin of the crown and root is primary dentin and is the most regular in structure. The pulp continues to form dentin later in life at the dentin-pulp border. This results in smaller pulp chambers with age. This dentin is secondary dentin, and is less regular in structure than is primary dentin. Reparative dentin is formed as a defense against caries, irritation, deep restorations, etc. It is the least regular in structure, and is alo known as sclerotic dentin. There is no tertiary dentin.

Answer 141

The correct answer is D. The primary first molars, both maxillary and mandibular, are unique in morphology and bear little resemblance to any permanent teeth. Primary incisors and canines resemble their permanent counterparts closely, except in certain proportional ways. Likewise, primary second molars are notable for closely resembling their permanent FIRST molar counterparts. The primary maxillary first molar is a little like a premolar in shape, but generally has one minor and two major cusps. It is both small and squat in appearance. The mandibular primary first molar is fourcusped but has a distinctly larger development of the mesial end. The MB and ML cusps generally comprise two-thirds of the area of the crown.

Answer 142

The correct answer is B. The alveloar bone is similar to most bone in the body in having a compact outer layer of lamellar bone and an inner layer of spongy bone. This spongy bone contains marrow space, usually of the yellow (fatty) type, although some red marrow exists. Haversian systems, with concentric rings of bone with osteocytes and canaliculi, which surround a canal with artery, vein, and nerve, are found only in compact (lamellar) bone. These systems do not exist within the inner spongy layers of bone, whether we are looking at alveolar bone or any other bone in the body.

Answer 143

The correct answer is D. The temporalis is a strong, broad, flat muscle which can both elevate (close) and retrude (pull back) the mandible. This is due to the fact that it contains both vertical and nearly horizontal muscle fibers. The vertical fibers pull the mandible straight upward (elevation), while the horizontal fibers pull straight backward (retrusion). The most anterior fibers of the temporalis are the vertical. As you move posteriorly, they become first diagonal, and then horizontal. NBDE questions in the past have referred to this muscle as being an elevator in the anterior and an elevator/retruder in the posterior

Answer 144

The correct answer is B. As is often the case, the maxillary lateral incisor is the answer for weirdest or most variable tooth. In this case, it is the most common supernumerary (doubled incisor), as it is also the most common missing, oversized, or undersized incisor. Note that the most distal tooth (lateral incisor, second premolar, third molar) in a set is always more likely to be missing or have a supernumerary. Note also that the most common supernumerary is the mesiodens. This tooth is found in the maxillary midline. It is not, however, considered an additional central. It has a morphology unique to itself and different from centrals.

Answer 145

The correct answer is B. Eruption and exfoliation questions are common in this section. The mandibular primary centrals are often the first teeth lost, most commonly at age 6. Often they exfoliate as the permanent first molars are erupting. For mandibular primaries, the centrals exfoliate at year 6- 7, the laterals at year 7-8, the canine at year 9-10, the first molar at year 10-11, and the second molar at age11-12. Remember that all exfoliation questions are approximations of average ages. The wrong answers must be fairly far off the mark.

Answer 146

The correct answer is A. The mesiolingual cusp of a maxillary second molar is a holding cusp. The general rule for maxillary holding cusps is as follows: a maxillary holding cusp contacts the distal marginal ridge of its mandibular counterpart and the mesial marginal ridge of the mandibular tooth distal to its counterpart, EXCEPT for the mesiolingual cusps of the molars, which contact the central fossae of their counterparts. This should be the central fossa of the counterpart, the mandibular second molar.

Answer 147

The correct answer is D. First, eliminate choices A and B, as the disc divides the joint compartment into upper (superior) and lower (inferior) compartments only. In the upper compartment, the upper surface of the disc acts as a cushion as the mandibular condyle slides forward. This cushion slides against the articular eminence in the movement of the condyle in a forward and downward direction. When rotating about an axis during opening, the condyle slides against the lower surface of the disc which conforms to the shape of the condylar head. So we say that translation occurs in the upper compartment and rotation in the lower.

Answer 148

The correct answer is A. Mandibular central incisors contact at the most incisal point found on any tooth. The contact is located just below the incisal edge. On the distal surface, it is still incisal and near the edge, but is slightly more cervical than the contact found on the mesial side of the tooth.

Answer 149

The correct answer is A. Primary teeth are often said to have a short or squat appearance of their crowns compared to those of permanent teeth. This is because these teeth are often relatively wide mesiodistally and short incisocervically. This results in a LARGE ratio of mesiodistal diameter to incisocervical crown height. This ratio is smaller in the permanent teeth, which lack the short, squat appearance of primaries. One example: for maxillary central incisors, the primary tooth ratio is 1.083 (the tooth is just slightly bigger mesioincisally than in crown height), while for the corresponding permanent incisor it is .809 (the mesiodistal diameter is only 80% of the crown height).

Answer 150

The correct answer is A. As a general rule, primary teeth are whiter than their permanent counterparts. This shade difference is often noticed by parents. It is common for parents to notice, for example, that newly erupted permanent mandibular incisors are a few shades darker or more yellowish than the primary maxillary incisors that may remain as the mandibular permanent incisors erupt. In the mixed dentition (normal, unstained, not heavily carious, and no tetracycline effects), you can often pick out the primary versus permanent teeth by color alone.

Answer 151

The correct answer is B. In general, canines are wider mesiodistally than lateral incisors(both arches), so we should eliminate the canine (choice D). In general, maxillary incisors are wider mesiodistally than their mandibular counterparts, so we should eliminate the maxillary lateral (choice A). So it should only be a question of mandibular lateral versus central. On the average, the central is slightly smaller, about 0.5 mm smaller, and this gives it the distinction of narrowest anterior tooth mesiodistally. The Dental Board exam really loves longest, shortest, roundest, fattest, etc., type questions. Note that the maxillary canine is the longest tooth in the mouth

Answer 152

The correct answer is A. In looking at a maxillary central incisor from the facial, you will see that the mesioincisal angle is a sharp, nearly right angle. This is especially noticeable where the two centrals meet and a very small embrasure is present. The distoincisal angle, by contrast, is more rounded (choice C). On the lateral, the mesioincisal (choice B) is again sharper than the distoincisal (choice D), which is very rounded. However the angle on the lateral does not approach the sharpness of that on the central.

Answer 153

The correct answer is C. While the mandibular third molar is often so variable that it is hard to make useful predictions about it, these generalities apply to mandibular first, second, and third molars as you move distal in the arch: 1) they decrease in mesiodistal length, and 2) their roots decrease in length. Third-molar crowns may resemble normal molars or may be missing whole cusps. In rare cases they are roundish or ovoid, but they are always smaller than their second-molar counterparts, which are always smaller than the first molars. Note that buccolingual length is always shortest in the third molar but about equal in the first and second.

Answer 154

The correct answer is C. The mandibular first molar is invariably a five-cusped tooth, with MB, ML, DB, DL, and distal cusps. Maxillary first and second molars are normally four-cusped teeth. The distolingual cusp is usually less pronounced on the second molar. It is often absent on the maxillary third molar. This is an arch trait: the gradual diminishment in size of the distolingual cusp as you go posteriorly in the maxilla. In the lower arch, the mandibular second premolar can also be viewed as possibly lacking a distolingual cusp. This tooth is either two- or three-cusped. The two-cusped variety has a single buccal cusp and a single lingual cusp, while the three-cusped version has a buccal cusp and paired mesiolingual and distolingual cusps. However, both varieties are common, so it is common to find this tooth lacking the distolingual cusp as well, although that answer is not listed here.

Answer 155

The correct answer is C. Chemical analysis of the enamel matrix has not adequately identified the protein involved, but it is clear that it is neither keratin, as was once thought, nor collagen, which is the matrix of both dentin and bone. The protein is extremely high in proline, but makes up less than 1% of the enamel mass.

Answer 156

The correct answer is B. Primary teeth are notable for cervical bulges; that is, extension of the crown at the cervical line. In the primary anteriors, these bulges extend over both the buccal and lingual surfaces, as though the cervical line was a tightened belt and was tightened further to make the crown overhang in both front and back. In the primary molars, by contrast, the cervical bulge is buccal only.

Answer 157

The correct answer is E. It should be noted that the MAJOR function of pulp is the production of dentin, as dentin is the major structural tissue of both crown and root. Any question on the dental boards that asks for the "most important" function will have dentin formation as the answer. However, the pulp is also sensory (clearly). All sensory fibers in the pulp carry pain sensation, regardless of whether the original stimulus is hot, cold, or touch. The nutritive function of pulp consists of providing materials to the dentin through the odontoblastic processes. The defensive function of the pulp consists of a limited ability to produce a defensive inflammatory response, and the formation of reparative dentin when the tooth is damaged.

Answer 158

The correct answer is B. The ligaments, being fibrous connective tissue in composition, play no role in movement of the condyle. Muscular tissue is necessary for this movement, specifically fibers from 43 the upper head of the lateral pterygoid muscle. There is disagreement among anatomy sources as to the function or role of the ligaments. None give the ligaments an extremely important function, but most claim that they help limit motion of the mandible beyond a certain point, or act as barriers to excessive forward or downward motion. Others give the ligaments a general strengthening function which adds stability to the joint. Most importantly, the Dental Boards usually agree with the general notion of adding strength, stability, and limits of movement to the joint.

Answer 159

The correct answer is C. The question may be answered on general principle, in that the third molars are often the most unpredictable teeth in either arch. The specific patterns referred to here are the pit-groove patterns. In third molars, you will often find supplemental grooves at right angles to the main grooves, and additional pits and fissures not normally seen in first and second molars. The crenulated pattern refers to a highly grooved overall occlusal surface with grooves running in all directions, leaving a lacy, nook-and-cranny occlusal surface.

Answer 160

The correct answer is C. Odontoblasts form dentin and surround the dental pulp. The dentin forms the bulk of both the tooth crown and root. However, dentin is not one of the opposing surfaces within the periodontal ligament. Within the ligament, the alveolar bone of the tooth socket lies next to the cementum surface of the tooth root. On the cemental side of the ligament, cementum-forming cementoblasts are found. On the bone side, bone-forming osteoblasts and bone-remodeling osteoclasts are both found. In addition, numerous collagen fiber bundles insert in both the cementum and alveolar bone, forming the connection that keeps the tooth in place in the socket.

Answer 161

The correct answer is A. The Carabelli cusp (trait) is a variable cusp or extension of the mesiolingual cusp of the maxillary first molar. Its expression varies from that of a full cusp, at its largest, to a small protuberance at its smallest. Its expression varies among various races and ethnic groups, including an increased incidence in people of Asian descent. Some anatomists describe it as a cusp, making the maxillary first molar a five-cusped tooth. Others consider it a variety or trait of a four-cusped tooth. It is sometimes missing, and a groove or pit is found in the normal Carabelli cusp region of the mesiolingual cusp.

Answer 162

The correct answer is A. By definition, a working movement occurs when the mandibular teeth on one side move laterally across the surfaces of the maxillary teeth toward their own side. In other 44 words, in a left working movement, left mandibular cusps move laterally left across the cusps of the maxillary left teeth. The other side is known as the nonworking (balancing) side. In this case, the balancing side is the right side. In a left working movement, the balancing side also moves left, as the mandible cannot move both left and right at the same time.

Answer 163

The correct answer is A. For the most part, rotation of a tooth during extraction works best on teeth with rounded roots, such as the maxillary central incisor and maxillary canine. It can be used in conjunction with buccal-lingual luxation on teeth with single ovalish roots. It can never be used on double-rooted teeth. Of the incisors above, the maxillary central is most likely to have a roundish root. The others tend to have roots which are more ovalish rather than round and are luxated primarily, with some rotation. In general, maxillary incisor roots are more rounded than are mandibular roots.

Answer 164

The correct answer is A. Beware of choice D. Although mandibular third molars are notoriously variable in both crown and root form, there are some good generalizations. Almost invariably, the mesial (trigonid) end of the crown is wider, larger, and more distinct than the distal (talonid). The most common pattern is a four-cusp tooth, with MB and ML being the largest cusps and the whole occlusal surface tapering toward the distal.

Answer 165

The correct answer is D. Another way of asking the question is: which tooth does not lean toward the buccal or lingual? The maxillary first premolar is almost straight vertically, estimated to be about 5 degrees from vertical. Premolars, as a class, have the least bucco-lingual angulation. The central tends to lean greatly toward the lingual (28 degrees), the lateral about the same (26 degrees), and the canine slightly less. Do not bother to remember degree measures, which are mentioned only for comparison. Do not confuse this leaning with the mesiodistal leaning (when viewed from the buccal or lingual). These measurements differ significantly for the teeth listed, with the central incisor being most vertical.

Answer 166

The correct answer is D. Both 23 and N are mandibular left incisors. Remember that A through J are maxillary, while K through T are mandibular. The mandibular replacements are 20 for K, 21 for L, 22 for M, 23 for N, 24 for O, 25 for P, 26 for Q, 27 for R, 28 for S, and 29 for T. Remember that permanent molars 17, 18, 19, 30, 31, and 32 do not replace primary teeth

Answer 167

The correct answer is A. The mesiobuccal cusp of a mandibular molar is a holding (supporting) cusp. The general rule of occlusion of mandibular holding cusps is as follows: the holding cusps of the mandibular teeth occlude on the mesial marginal ridge of their maxillary counterpart, and the distal marginal ridge of the maxillary tooth mesial to their counterpart, EXCEPT distobuccal cusps of mandibular molars occlude with central fossae of their counterparts, the distal cusp of the mandibular first molar occludes with the distal triangular fossa of its counterpart, and the first premolar occludes only with the mesial marginal ridge of its counterpart (but not the canine). In this case, the maxillary counterpart is the maxillary third molar, and the tooth immediately mesial to it is the maxillary second molar.

Answer 168

The correct answer is B. The primary mandibular first molar is a highly unusual tooth. Although it technically contains four cusps, in typical molar fashion it has a great variety in the prominence of those cusps. The MB and ML cusp are most prominent, and the mesial section of the crown comprises two-thirds of the crown area. Both the DB and DL cusps are much reduced. The range of cusp size, in decreasing order is: MB, ML, DB, DL. The ML cusp is notable for a pointy, cone-like shape.

Answer 169

The correct answer is D. The central fossa, containing a central pit, is located within the main cusp triangle (trigon) of the maxillary first molar. The three major cusps: MB, ML, and DB, surround the fossa and form the trigon, or primitive cusp triangle. The DL cusp (talon) is not part of the trigon, does not surround the central fossa, and is the smallest cusp of the tooth (excluding the Carabelli cusp or trait).

Answer 170

The correct answer is A. In postural rest position, the mandible stays a comfortable distance from the maxilla, with the teeth slightly separated. The freeway space between the teeth is often 2-5 mm. There is no tooth contact, and the position is determined and maintained by the muscles of occlusion and related tendons and ligaments. Centric occlusion involves full tooth contact. Centric relation is normally a few millimeters distal to centric occlusion and is achieved by moving distal from centric occlusion. This procedure involves tooth contact. Protruded contact involves contacting guidance of the maxillary and mandibular teeth during protrusion.

Answer 171

The correct answer is A. Mandibular first molars are the largest teeth in the mouth, in mesiodistal dimension. While they are also large buccolingually, they are invariably larger mesiodistally by about 0.5 to 1.0 mm. This is in contrast to the maxillary first molar, which is slightly larger buccolingually than mesiodistally, usually by about 1.0 mm. The mandibular second molar is about equal in both directions and is thus more symmetrical than the first molar.

Answer 172

The correct answer is A. In a left working movement, the mandible shifts to the left. From a central position, the left side of the mandible is moving away from center (laterally). The right side of the mandible, although also moving left, is moving toward the center (medially). The left TMJ purely rotates when the right is rotating and translating mechanically. Note that it is impossible for both sides of the mandible to move either laterally or medially at the same time.

Answer 173

The correct answer is A. Maxillary first premolars are almost always double rooted. When single rooted, they always have two separate root canals. The level of division of the two roots varies, from complete division up to the crown, to only a small separation apically. The mandibular first premolar is most often singlerooted, and the mandibular second premolar is almost always single rooted (double roots are rarer than in the mandibular first). The maxillary second premolar is most often single rooted. The extreme likelihood that the maxillary first premolar will have two roots has implications for both endodontics and exodontia of this tooth. It is also reported that some small percentage (5% in one study) are actually triple rooted.

Answer 174

The correct answer is D. The mesiolingual cusp of a maxillary molar is a holding cusp. The general rule for maxillary holding cusps is as follows: a maxillary holding cusp contacts the distal marginal ridge of its mandibular counterpart and the mesial marginal ridge of the mandibular tooth distal to its counterpart, EXCEPT FOR THE MESIOLINGUAL CUSPS OF THE MOLARS, WHICH CONTACT THE CENTRAL FOSSAE OF THEIR COUNTERPARTS. This should be the central fossa of the counterpart, the mandibular first molar.

Answer 175

The correct answer is B. In any set of teeth (incisor, premolar, molar), the distal tooth is more likely to be congenitally missing than the mesial. So lateral incisors are missing more than centrals, second premolars are missing more than first premolars, and third molars are more commonly missing than first or second. Of all of these, the MOST commonly missing is the maxillary lateral incisor. Note that choice A is therefore incorrect.

Answer 176

The correct answer is C. This is known as an arch trait, as it is true for both incisors of each arch. Both incisors of the maxilla are wider mesiodistally. Both incisors of the mandible are wider buccolingually. The maxillary central, in particular, is known for the greatest assymetry in this regard. It is much wider mesiodistally than buccolingually, and that difference, expressed as a ratio, is greatest for that incisor. It is also the largest incisor, in both dimensions, in absolute size.

Answer 177

The correct answer is B. Primary dentin (choice A) surrounds the pulp chamber when the tooth is first formed and erupts. It is the initial dentin that makes up the base of both the crown and root. If the young tooth has a given size pulp chamber, further dentin formation, secondary dentin, later in life, will begin to fill the chamber with dentin, making it smaller. Internal resorption (choice C) is loss of dentin, resulting in a larger pulp chamber. External resorption (choice D) involves the exterior of the root and does not change the pulp chamber size. Pulp fibrosis (choice E) would change the histology of the cells in the chamber, but not the chamber's size.

Answer 178

The correct answer is C. The palatal or lingual root of the maxillary first molar is the most massive by far. It is normally straight but palatally inclined, giving the three roots a tripod-like appearance. The mesiobuccal root (choice A) is second in size, and the distobuccal (choice B) is smallest. The mesiobuccal is often curved distally and the distobuccal curved mesially. This pliers-like appearance is not found in the maxillary second and third molars.

Answer 179

The correct answer is A. If you see enough small children in your practice, you'll often notice that a 6-month-old child will have only two teeth: the two mandibular centrals. These are commonly the first teeth to erupt, and most commonly do so at 6 months. Mandibular laterals are often seen at about 9 months. Maxillary centrals and maxillary laterals average about 8 months. First molars then precede canines in both arches, and second molars are last in both arches. The last primary is usually the maxillary second molar at about 24 months. These times may vary considerably. Know the most common order: central, lateral, first molar, canine, second molar.

Answer 180

The correct answer is B. In a left working movement, the mandible moves toward the left. The left side is then known as the working side and the right side as the nonworking (balancing) side. The lateral pterygoids pull the mandibular condyles forward, so the pull of both together results in protrusion. For only a left-sided movement, the left lateral pterygoid does not contract and the left condyle stays in a relatively unchanging position (it does rotate slightly). The right lateral pterygoid contracts and pulls the right side of the mandible outward, and then it turns left, as the left side of the mandible is stationary. Remember that the right lateral pterygoid moves the mandible left, and the left lateral pterygoid moves the mandible right.

Answer 181

The correct answer is C. The mandibular first premolar is the exception to premolar form in many ways. It is canine-like with a reduced lingual cusp, resembling a cingulum. Its occlusal table tilts downward from buccal to lingual in a slanted fashion. It is also slightly higher on the distal side than the mesial, and its mesial marginal ridge is less prominent than its distal marginal ridge. This means that in a mesial view you can see some of the occlusal table because it slants toward you. From the distal view, this is not true. The higher distal end blocks any occlusal view from that direction.

Answer 182

The correct answer is D. The mandibular and maxillary canines exhibit similar cross sectional shapes at the cervical line. The mandibular canine cross section is oval and flattened mesiodistally. It is generally slightly wider at the labial end than at the lingual. The pulp cavity at this point is lensshaped, double convex.

Answer 183

The correct answer is E. There are two facts or concepts involved in correctly answering this question. The first is that the mandibular first molar is a five-cusped tooth, named corresponding to the cusps listed in the answer choices. The second is that the pulpal anatomy reflects the cuspal anatomy (or vice versa). Tall, large cusps are likely to have tall, large pulp horns. Small cusps generally have small associated pulp horns. In this case, the distal cusp is generally the smallest of the cusps of the mandibular first molar, so its pulp horn is likely to be smallest as well.

Answer 184

The correct answer is D. The premolars are usually considered to be two-cusped teeth (bicuspids). The exception to the rule, to a small extent, is the mandibular second premolar. Often, the lingual cusp area is divided into a mesiolingual cusp and a distolingual cusp. This gives the tooth a threecusped appearance. A two-cusped variety also exists, with a large lingual cusp instead of the two smaller ones. In the three-cusped variety, a lingual groove separates the two lingual cusps. Note that the two-cusped and three-cusped varieties are not grossly different in size, as the single lingual cusp is about the same size as a mesioloingual and distolingual combined. The other premolars exist primarily in double-cusped varieties only.

Answer 185

The correct answer is D. Lingual cusps of mandibular teeth are guiding cusps, not holding cusps. Therefore, they do not occlude on marginal ridges or central fossae. The general rule for mandibular lingual cusps is that they occlude in the lingual embrasures between their maxillary counterparts and the teeth mesial to their counterparts, EXCEPT for the distolingual cusps of the mandibular molars, which occlude in the lingual grooves of their maxillary counterparts. In this question we are dealing with the exception of the distolingual cusps of mandibular molars, so in this case, the mandibular first molar distolingual cusp contacts the lingual groove of its counterpart (the maxillary first molar).

Answer 186

The correct answer is A. The mesial marginal groove, extending from the marginal ridge, along the mesial side of the crown into the proximal area (mesial concavity) and down into the mesial root concavity, is a characteristic of many maxillary first premolars. This has implications for both calculus removal (scaling and root planing) and restoration (placement of well adapted matrix bands). It is not found in the other premolars, although they may sometimes have some less pronounced root concavities. Root concavities are less common and less pronounced in the mandibular premolars.

Answer 187

The correct answer is A. This can vary considerably, but using average eruptions, all permanent first molars usually erupt at around age 6 to 7, so four first molars are likely. Rule out all premolars, which generally erupt between age 9 and 12. Likewise, canines usually erupt between age 9 and 12. For the incisors, usually the mandibular centrals are in at about age 6, so that makes eight so far. Mandibular laterals and maxillary centrals and laterals usually erupt between 7 and 9 years. So the average 6- year-old has all first molars and mandibular centrals as erupted permanent teeth.

Answer 188

The correct answer is B. Contacts ensure that food does not get lodged between teeth and into the sulcus. Food, debris, and plaque in that area will lead to inflammation, tissue destruction, and bone loss. Contacts do not protect the incisal surface, as they are below (cervical to) that area. They do protect the gingiva (see above), but not especially the alveolar mucosa, which is more cervical and basically below the tooth region. The alveolar mucosa begins at the mucogingival junction. Contact is not involved in restoration retention. All restorations must be retained by retention within the individual tooth itself.

Answer 189

The correct answer is D. We often do not think of anterior teeth as having marginal ridges, as they are less distinct than on the posterior teeth; and in the posterior teeth, they are often points of occlusal contact. However, the maxillary canine, as well as other anterior teeth, does have both a mesial and distal marginal ridge. The lingual anatomy of the maxillary canine has a cusp tip, with mesial and distal marginal ridges sloping down from it. Centrally, a lingual ridge splits the lingual surface in two. In between the marginal ridge and the lingual ridge, we find two depressions, the mesiolingual fossa and the distolingual fossa.

Answer 190

The correct answer is A. Early in tooth bud formation, the tissues of the enamel organ-outer enamel epithelium, stellate reticulum, stratum intermedium, and inner enamel epithelium-form adjacent to the dentin-forming tissues of the dental papilla. In fact, at this stage, the ameloblasts and future odontoblasts are in contact along the length of the tooth bud. The dentin production begins first, and predentin is laid down by odontoblasts. This predentin production induces the ameloblasts to begin enamel production by cells of the inner enamel epithelium. Thus, dentin is produced above the odontoblasts while enamel is formed below the inner enamel epithelium. Both dentin and enamel are deposited between these two layers, and the former site of the junction of the two layers becomes the DEJ, or dento-enamel junction. By tooth completion, the enamel organ is at the surface of the gingiva while the odontoblasts are producing dentin for the tooth root. Thus, these cell layers are very far apart at this point.

Answer 191

The correct answer is C. One of the best reasons to know standard and unusual root shapes for the various maxillary and mandibular teeth is to use the correct motion on the forceps when performing extractions. In general, rounded roots are primarily rotated, including the maxillary central incisors and maxillary canines. All double and triple rooted teeth cannot be rotated and must be luxated in the buccal and lingual directions. Mesial-distal motion is normally ruled out because of the existence of adjacent teeth. It is used in rare cases where there is no mesial and distal adjacent tooth. The maxillary central is invariably single rooted with a rounded root, and can almost always be rotated without breaking the crown off of the root.

Answer 192

The correct answer is C. Mammelons are bumps on the incisal edge of incisors. They are most commonly found on central incisors of both arches, and if found on the laterals, they are less prominent than those found on the centrals. There are normally three, but this is variable. The three are termed mesial, central, and distal. They are often worn off on adult teeth through years of occlusion

Answer 193

The correct answer is C. While the mandibular third molar is often so variable that it is hard to make useful predictions about it, these generalities apply to mandibular first, second, and third molars as you move distally in the arch: 1) they decrease in mesiodistal length, and 2) their roots decrease in length. Third-molar roots may resemble normal molars or may be missing roots or have additional roots. Roots are often partially or totally fused. In some cases they form a cone-like, fused mass, making exodontia much simpler in these cases. In all cases, however, their roots are shorter than those of their second-molar counterparts, which are always smaller than those of the first molars.

Answer 194

The correct answer is C. Posterior contact is normal during centric occlusion and maintains the vertical dimension of occlusion. In a normal dentition, however, the incisors are slightly out of contact during centric occlusion. When the mandible moves forward (protrusion), the incisal edges of the mandibular anteriors meet the lingual surfaces of their maxillary counterparts as the teeth separate during opening. (Try it in your mouth!). Note that during retrusion (moving the mandible from centric occlusion to a more distal position), no such contact occurs. During working (lateral) movements, only posterior teeth and canines contact (group function), or canines contact alone (canine/cuspid protected guidance).

Answer 195

The correct answer is D. If you like rules, the rule is that if a lateral pterygoid is injured, the mandible moves toward the injured side. If you wish to understand this rule better, imagine two intact lateral pterygoids protruding the mandible normally. Now cut the left lateral pterygoid, and imagine that the left side stays in place but the right side continues to protrude. In effect, the mandible will rotate around the axis of the left side. The left side stays in place while the right side rotates left. Lateral pterygoids have little effect on closing.

Answer 196

The correct answer is B. Lining mucosa covers most of the oral cavity except for the hard palate and gingival areas. It is usually loose, freely movable, and has a well-developed submucosa. The lamina propria is often highly glandular. The epithelium is thin and nonkeratinized. Epithelial ridges and rete pegs are uncommon and short.

Answer 197

The correct answer is A. The lateral ligament, also known as the temporomandibular ligament, is found extending downward from the lateral surface of the zygoma. The zygoma is formed from the contact of the zygomatic section of the temporal bone and the temporal portion of the zygomatic bone. The ligament is roughly triangular in shape, and on its medial side is found the articular capsule and joint. Fibrous connective tissue composes both the ligament and capsule, and there is a fibrous connection between them.

Answer 198

The correct answer is C. The articular disc of the TMJ is composed of fibrous connective tissue. Some sources state that chondrocytes are found within it, so it is sometimes referred to as fibrous connective tissue with an underlying base of fibrocartilage. Its shape is biconcave, somewhat like that of an erythrocyte, with a raised outer portion and depressed middle. The central portion is avascular, and only the periphery, especially the posterior periphery is vascularized.

Answer 199

The correct answer is A. The stellate reticulum is an ectodermal tissue located between the inner and outer enamel epithelium. The stellate, or star-like, appearance of the tissue is caused by the arrangement of few cells within a network, separated by intracellular fluid. The inner enamel epithelium will differentiate into ameloblasts and form enamel. The outer enamel epithelium eventually merges with the gingiva as the tooth erupts. A small cell layer between the inner enamel epithelium and stellate reticulum is referred to as the stratum intermedium. Its presence is necessary for proper ameloblast function. The dental sac is mesodermal and forms cementum and the periodontal ligament. The dental papilla is mesodermal and forms pulp and dentin. The enamel organ consists of inner and outer enamel epithelium, stellate reticulum and stratum intermedium and forms enamel. It is ectodermal in origin.

Answer 200

The correct answer is B. The origins and insertions of the TMJ ligaments are as follows: The stylomandibular ligament arises from the spine of the temporal bone known as the styloid process and inserts on the lower ramus and angle of the mandible. The sphenomandibular ligament arises from a 53 spine on the sphenoid bone and runs forward and downward to insert on the lingula and deep ramus of the mandible. The lateral ligament is also known as the temporomandibular ligament. It descends from the lower border and tubercle of the zygoma to the posterior lateral condyle. Its fibers merge with those of the articular capsule.

Answer 201

The correct answer is A. You could answer this on general principal, that the mandibular first premolar is the most canine-like premolar tooth in almost every way. However, in detail, the mandibular first premolar has a round root cross section and a roundish pulp chamber at the cervix. The second premolar has a generally more flattened shape in the mesiodistal direction and a correspondingly oval pulp chamber. It may be constricted at the center with a corresponding hourglass shape. The maxillary first premolar root is flatttened mesiodistally, as is the pulp chamber. It is usually constricted at the center, indicating the two roots and two canals found in the tooth. The second maxilllary premolar, with one root, is less likely to be constricted into an hourglass shape.

Answer 202

The correct answer is C. Specialized mucosa is found on the dorsum of the tongue and contains taste buds and various papillae, including circumvallate, foliate, fungiform, and filiform. Masticatory mucosa consists of the gingiva and covering of the hard palate. Most of the other areas of the oral cavity are lined by lining mucosa. The characteristics of masticatory mucosa are keratinization, thin or absent submucosa, and tight binding of the lamina propria to underlying periosteum. Lining mucosa is generally nonkeratinized, with a thin lamina propria. Near the teeth, the gingiva and lining mucosa (alveolar mucosa) meet at the mucogingival junction.

Answer 203

The correct answer is B. Masseteric hypertrophy means gain in muscle substance of the masseter muscle. The masseter is located on the lateral part of the ramus and angle, and its growth in thickness can be seen as a squareness of the lower face on frontal view. People who brux (express tension by clenching their teeth) often develop this larger-than-normal size masseter. It can sometimes be confused with parotid swelling, although the parotids are slightly higher in location. Remember that the medial pterygoid is medial, not lateral, to the ramus. Loss of muscle substance would be atrophy rather than hypertrophy.

Answer 204

The correct answer is A. The mesiobuccal cusp of a mandibular molar is a holding (supporting) cusp. The general rule of occlusion of mandibular holding cusps is as follows: the holding cusps of the mandibular teeth occlude on the mesial marginal ridge of their maxillary counterpart, and the distal marginal ridge of the maxillary tooth mesial to their counterpart, EXCEPT DISTOBUCCAL CUSPS OF MANDIBULAR MOLARS OCCLUDE WITH CENTRAL FOSSAE OF THEIR COUNTERPARTS, THE DISTAL CUSP OF THE MANDIBULAR FIRST MOLAR OCCLUDES WITH THE DISTAL TRIANGULAR FOSSA OF ITS COUNTERPART, AND THE FIRST PREMOLAR OCCLUDES ONLY WITH THE MESIAL MARGINAL RIDGE OF ITS COUNTERPART (BUT NOT THE CANINE). In this case, the maxillary counterpart is the maxillary first molar, and the tooth mesial to it is the second premolar.

Answer 205

The correct answer is A. A mesiodens is a supernumerary located midline in the maxilla. It has a wide variety in morphology and is usually extracted. It is the most common and frequently causes a diastema between the central incisors. The other relatively common supernumeraries are the second maxillary lateral incisor, third mandibular premolar, and fourth maxillary molar.

Answer 206

The correct answer is C. In evolution, three cusps of the maxillary molar are considered to be the primary cusp triangle, and the original three cusps of the evolving molar. They form the trigon, and are the MB, ML, and DB cusps. The fourth cusp, the DL, is the smallest, is considered to be a minor cusp, and is known evolutionarily as the talon, or talon cusp. This cusp is less conspicuous as you go from first to second to third maxillary molar.

Answer 207

The correct answer is C. The answer depends only on the fact that ameloblasts form enamel, not dentin. Clearly, odontoblasts, as dentin formers, influence pulp size because the pulp is surrounded by dentin. Caries may cause deposition of reparative or secondary dentin. The same is true for other factors, such as abrasion, heavy occlusal wear, erosion, etc. Pulp tends to become smaller and more calcified with age, so age is also a factor. Be careful when reading questions on your test! Occasionally you will find a careful-reading question like this one.

Answer 208

The correct answer is B. In any set of teeth (incisor, premolar, molar), the distal tooth is more likely to be congenitally missing than the mesial. So lateral incisors are missing more than centrals, second premolars are missing more than first premolars, and third molars are more commonly missing than first or second. Of all of these, the MOST commonly missing is the maxillary lateral incisor. Note that choice A is therefore incorrect.