Spring - Quiz 1

Question 1

What are the three types of problems that orthodontics treats?

Answer 1

1. Psychosocial
2. Oral Function
3. Trauma, periodontal disease, and tooth decay

Question 2

Severe malocclusion is a social handicap. True or False?

Answer 2

True

Question 3

What is the major reason why people seek ortho treatment?

Answer 3

To minimize psychosocial problems

Question 4

Temperomandibular dysfunction patients are found in what four groups?

Answer 4

1. Masticatory muscle disorders
2. TM joint disorders
3. Chronic mandibular hypomobility
4. Growth disorders

Question 5

Muscle spasms and fatigue should be fixed by orthodontics first. True or False?

Answer 5

False, simpler methods first

Question 6

Orthodontics alone is rarely useful for patients with internal joint pathology. True or False?

Answer 6

True

Question 7

What is disk displacement?

Answer 7

Trauma or aging of the ligaments that oppose the ac)on of the lateral pterygoid muscle are stretched or torn so when the muscle contracts the ligaments cannot return the disk to its proper position and a resulting pop upon opening and/or closure is seen.

Question 8

TMD is no more prevalent in patients with severe malocclusion than in the general population. True or False?

Answer 8

True

Question 9

What can splint therapy help identify?

Answer 9

Used to help identify if the malocclusion is a possible cause of the patients TMD.

Question 10

Bite splints should always be full coverage of all the teeth, either maxillary or mandibular. True or False?

Answer 10

True

Question 11

The disappearance of TMD during ortho treatment is often only temporary. True or False?

Answer 11

True

Question 12

What types of problems can cross bites and traumatic occlusions cause?

Answer 12

Extreme wear, gingival recession, bone loss, influence growth, cause stress on the TMJ.
Early ortho intervention can fix these problems.

Question 13

Long term studies show that ortho treatment increases chance of later periodontal problems. True or False?

Answer 13

False

Question 14

What happens in dental age 6?

Answer 14

Mandibular central incisors
Mandibular first molars
Maxillary first molars

Question 15

What happens in dental age 8?

Answer 15

Maxillary lateral incisors

Question 16

What happens in dental age 11?

Answer 16

Mandibular canines
Mandibular first premolars
Maxillary first premolars

Question 17

What happens in dental age 12?

Answer 17

Maxillary canine
Maxillary and mandibular second premolars
Maxillary and mandibular second molars

Question 18

What happens in dental age 15?

Answer 18

Roots of all permanent teeth except third molars are done

Question 19

When does the eruptive movement of the tooth begin?

Answer 19

The eruptive movement of the tooth begins soon after the root begins to form, and the roots emerge from the dental follicle.
– This supports the idea that metabolic activity within the periodontal ligament is necessary for eruption.
– But elongation of the tooth root is not.

Question 20

What two processes are necessary for pre-emergent eruption?

Answer 20

– First, there must be resorption of the bone and the primary tooth roots, overlying the crown of the erupting tooth.
– Secondly, there must be a propulsive mechanism to move the tooth in the direction where the overlying path has been cleared.

Question 21

What are some conditions that interfere with pre-emergent eruption?

Answer 21

In children with cleidocranial dysplasia the permanent teeth do not erupt because of abnormal resorption of both bone and the primary teeth.
• The eruption of the primary teeth is also delayed due to fibrotic gingiva
• Interestingly, if the mechanical obstruction of eruption is removed in these patients, the teeth may erupt spontaneously and can be brought into the arch with orthodontic force
• This is an example of a defect in the patients ability to remove the overlying structures during tooth eruption, which causes delayed eruption or the impaction of the involved teeth

Question 22

The rate of bone resorption and the rate of tooth eruption, are controlled physiologically by the same mechanism. True or False?

Answer 22

False, they are not
• This means that the tooth’s occlusal eruption movement, does not control the dissolution of the overlying bone and primary teeth.
• If an unerupted permanent tooth is wired (accidentaly) to the adjacent bone when a jaw fracture is repaired, eruption of the tooth is mechanically stopped.
• But in this situation, bone resorption to clear an eruption path through expansion of the dental follicle continues.
• This mechanism can go wrong in a follicular cyst.

Question 23

What activates the signal for resorption of bone over the crown of a tooth?

Answer 23

The completion of the crown, which also removes the inhibition of the genes that are necessary for root formation

Question 24

What is the rate limiting factor in pre-emergent eruption?

Answer 24

Because a tooth will continue to grow and form the tooth’s root regardless of whether the overlying bone and primary teeth are removed, It would seem clear therefore, that resorption of the overlying bone is the rate limiting factor in pre-emergent eruption
• Because resorption of the overlying bone is the controlling factor, a tooth that is still embedded in bone can continue to erupt after root formation is completed, but in this situation surgical orthodontic eruption is often necessary.
• Remember, active formation of the root, is not necessary for continued clearance of an eruption path, or for movement of a tooth along the eruption path.

Question 25

Teeth will not continue to erupt if its apical area has been removed, as in an apicoectomy. True or False? And how is a dilaceration formed usually?

Answer 25

False, it still can. So the proliferation of cells associated with lengthening of the root, is not an essential part of the eruption mechanism.
• Normally, the rate of eruption is such that, the apical area remains at the same place while the crown moves occlusally.
• But if the eruption is mechanically blocked, the proliferating apical area will move in the opposite direction.
– This can cause a distortion of the root in an abnormal direction called a dilaceration.
• Despite many years of study, the precise mechanism through which the propulsive force is generated remains unknown.

Question 26

What is primary failure of eruption?

Answer 26

It is a condition that is characterized by non syndromic eruption failure of permanent teeth in the absence of mechanical obstruction.
• This indicates that there is a defect in the propulsive mechanism of tooth eruption
• Typically in PFE patients the posterior teeth are more frequently affected, with the first and second molars being more frequently affected than the premolars and canines.
• If a tooth in a further anterior position presents with an eruption disturbance, the posterior teeth are usually, but not always, affected as well.
• The affected teeth resorb the alveolar bone above the crown, but erupt only partially or fail to erupt at all.
• Both deciduous and permanent teeth can be affected.
• This condition is usually asymmetrical, and primarily non-ankylosed teeth tend to become ankylosed as soon as orthodontic forces are applied. (Did the orthodontic force cause the ankylosis, or was the ankylosis identified after application of the orthodontic force). Application of a straight wire on these patients can be disastrous.

Question 27

What did the UNC Ortho study conclude about treating PFE teeth orthodontically?

Answer 27

A PTH1R (parathyroid hormone receptor) mutation is strongly associated with failure of orthodontically assisted eruption or tooth movement and should therefore alert clinicians to treat PFE and ankylosed teeth with similar caution-ie, avoid orthodontic treatment with a continuous archwire

Question 28

What is the juvenile post-emergent spurt?

Answer 28

• Once a tooth emerges into the mouth, it erupts rapidly until it approaches the occlusal level and is subjected to the forces of mastication.
• At that point, its eruption slows and then as it reaches the occlusal level of the other teeth, and is in complete function, eruption all but halts.
• The stage of relative rapid eruption from the time a tooth first penetrates the gingiva until it reaches the occlusal level is called the Juvenile post-emergent spurt.
• In the 1990’s the development of new instrumentation made it possible to track the short-term movements of teeth during the post emergent spurt, and this showed that eruption occurs only during a critical period between 8 PM and 1 AM.

Question 29

Why does the post-emergent juvenile spurt happen at a specific time each night?

Answer 29

• This day time and night time eruption difference seems to reflect an underlying rhythm, which is probably related to the very similar cycle of growth hormone release.
• Experiments with the application of pressure
against an erupting premolar suggest that eruption is stopped by force for only one to three minutes.
– (Tongue pressures/Thrusting)

Question 30

What forces oppose eruption of teeth?

Answer 30

– Chewing forces
– Soft tissue forces
• Lips
• Cheeks
• Tongue
• If eruption typically only occurs during the quiet periods between 8pm and -1am, the soft tissue pressures probably are more important in controlling eruption than the heavy pressures that occur during chewing
• Light pressures of long duration are more important in producing orthodontic tooth movement than heavy intermittent pressures like chewing.

Question 31

How does the mandible grow with erupting teeth?

Answer 31

• Teeth that are in function erupt at a rate that parallels the rate of vertical growth of the mandibular ramus.
• As the mandible continues to grow, it moves away from the maxilla creating a space into which the teeth erupt.
• The maxillary and the mandibular teeth normally divide this space equally.
• How the tooth eruption matches the skeletal growth is unknown, and since some of the more difficult orthodontic problems arise when eruption does not coincide with growth, this is an important area of further study.
• The most likely scenario is that after the tooth is in occlusion, the rate of eruption is controlled by the forces opposing eruption, not by those forces promoting eruption.

Question 32

What is the total eruption path distance of a first permanent molar?

Answer 32

2.5 cm
• Of this distance, nearly half is traversed after the tooth reaches the occlusal level and is in function (1.25 cm).
• This makes an ankylosed tooth appear to submerge over a period of time, as the other teeth continue to erupt normally.
• This can also be seen in a patient with a lateral tongue thrust.
– The pressure from the tongue prevents the eruption of the teeth as the maxilla and mandible grow causing a posterior open bite.

Question 33

What are the treatment options for an adult tooth that undergoes ankylosis during post emergent eruption?

Answer 33

– Extraction
• May need bone grafts and connective tissue grafts in area where ankylosised tooth was extracted.
• What if the ankylosised tooth is an anterior tooth?
• If we extract an anterior tooth we will need treatment plan a way to replace the missing tooth until an implant can be placed.
– Implants cannot be placed until all vertical growth is complete.
» Typically 18 or 19 years of age. Can be longer in males.
– Crowns
• What about crown to root ratio?
• What about bone and periodontal health of adjacent teeth?
– Surgery
• Luxation
• Distraction osteogenesis

Question 34

If there is an adult tooth underneath the ankylosised tooth, do you have to extract the ankylosised tooth?

Answer 34

Not always, but the adult tooth will typically have a delayed eruption, which can be problematic.
• Extraction of the ankylosised primary tooth is recommended if the primary tooth drops below the height of contour of the adjacent teeth.
– This is recommended if the patient is missing the permanent tooth or if the permanent tooth is present. (Space maintenance is almost always required).
– Extraction of the ankylosised primary tooth helps prevent periodontal and bone defects to the adjacent teeth and helps stop bone loss in the extraction site, which will need an implant later.
• Other options?
– Build up primary tooth to place it into occlusion
– Leave primary tooth in place as it is.

Question 35

During adult life, teeth continue to erupt at a slow rate. True or False?

Answer 35

True

Question 36

If an adult tooth’s opposing tooth is lost at any age, a tooth can again erupt. True or False?

Answer 36

True.
– This demonstrates that the eruption mechanism remains active and capable of producing significant tooth movement through out an individuals life.
• Wear of the teeth may become significant as the years pass.
– If extreme wear occurs, eruption may not be able to compensate for the loss of tooth structure, and the vertical dimension of the face will decrease.
– But, typically the wear of the teeth is compensated by additional eruption, and the face height remains constant, or even increases slightly in the fourth, fifth and sixth decades of life.

Question 37

What principle is orthodontic treatment based on?

Answer 37

The principle that if prolonged pressure is applied to a tooth, tooth movement will occur as the bone around the tooth remodels by selectively being removed in some areas and added in others.
• Because the bony response is mediated by the periodontal ligament, tooth movement is primarily a periodontal ligament phenomenon.

Question 38

What happens if the periodontal ligament is destroyed?– What can happen if the cementum of the tooth and the alveolar bone come into contact without a healthy PDL?

Answer 38

Ankylosis

Question 39

How wide is a typical PDL? And what does it contain?

Answer 39

Under normal circumstances the PDL occupies a space approximately 0.5mm in width, and contains a network of parallel collagenous fibers, which insert into the cementum of the root and the alveolar bone.
• The PDL space also contains cellular elements including:
– mesenchymal cells
– fibroblasts
– osteoblasts
– vascular and neural elements
– The PDL space also contains tissue fluids

Question 40

What part of the PDL specifically is being constantly remodeled and renewed during normal function?

Answer 40

The collagen of the ligament is constantly being remodeled and renewed during normal function by fibroblasts and fibroclasts.
Remodeling and recontouring of the bony socket and the cementum of the root is also constantly being carried out, though on a smaller scale by osteoclasts and cementoclasts respectively.

Question 41

The PDL contains blood vessels. True or False?

Answer 41

True. Although the PDL is not highly vascular, it does contain blood vessels and cells from the vascular system.

Question 42

The PDL contains nerve endings. True or False?

Answer 42

True.
Nerve endings are also found within the ligament, both the unmylelinated free endings associated with perception of pain and the more complex receptors associated with pressure and positional information (proprioception)
• The PDL space is filled with fluid and this fluid is the same as that found in all other tissues and is derived from the vascular system.
– This fluid filled chamber with porous walls acts like a shock absorber for the tooth during normal function.

Question 43

How does pressure affect fluid squeezed out of the PDL?

Answer 43

• During the first second of pressure on a tooth, very little fluid is squeezed out of the PDL space. (shock absorber)
• If the pressure is maintained, the fluid is rapidly expressed, and the tooth displaces within the PDL space, compressing the PDL against the adjacent bone which causes pain (usually takes between 3-5 seconds of pressure)
• Orthodontic tooth movement is made possible by the application of these prolonged forces.
• Light prolonged forces in the natural environment (lips, cheeks and tongue) resting against the teeth, also have the same potential to move teeth as orthodontic forces created by braces.

Question 44

Resting pressures from the lips or cheeks and tongue are usually balanced. True or False?

Answer 44

False

Question 45

In what area of the mouth is tongue pressure greater than lip pressure?

Answer 45

Mandibular anterior

Question 46

In what area of the mouth is lip pressure greater than tongue pressure?

Answer 46

Maxillary incisor

Question 47

What does active stabilization of the PDL imply?

Answer 47

That there is a threshold for orthodontic force and any force below this threshold would be ineffective in moving a tooth.
• This threshold appears to be between 5 – 10 grams/square cm.
• Active stabilization produced by metabolic effects in the PDL probably explains why teeth are stable in the presence of imbalanced pressures that would otherwise cause tooth movement.

Question 48

What happens on a tooth if the pressure equilibrium is not in balance?

Answer 48

This is the envelope of stability. The teeth occupy a position inside the oral cavity where the pressures placed against them by the surrounding soft tissues and tongue are in equilibrium
• If the pressure equilibrium is not in balance due to any number of factors and the force exceeds 10 gm, the tooth will move to the position of least resistance and occupy and space, which places these forces back into balance.
• This plays an important factor in understanding orthodontic retention and relapse

Question 49

What are the metabolic events that take place in the PDL?

Answer 49

Forces generated within the PDL itself, can produce tooth movement.
Formation of cross-linkages and maturational shortening of collagen fibers.
The phenomenon of tooth eruption, makes it plain that forces generated within the PDL itself, can produce tooth movement.
After a tooth emerges into the mouth further eruption dependson metabolic events within the PDL

Question 50

What are piezoelectric currents?

Answer 50

• During normal function forces on the teeth can be quite high but only last for 1 second or less
• Under a heavy load quick displacement of the tooth within the PDL space is prevented by the incompressible tissue fluid, (shock absorber) which transfers the force to the alveolar bone, which bends in response.
• Bone bending in response to normal function generates piezoelectric currents that appear to be an important stimulus to skeletal regeneration and repair. This is the mechanism by which bony architecture is adapted to functional demands.
• Piezoelectricity is a phenomenon observed in many crystalline materials (Hydroxylapatite in bone) in which a deformation of the crystal structure produces a flow of electric current, as electrons are displaced from one part of the crystal lattice to another.
• Piezoelectric signals have two unusual characteristics
– A quick decay rate, the signal quickly dies away to zero even though the force on the bone is maintained.
– The production of an equivalent signal, opposite in direction when the force is released.
• This is caused by the migration of electrons from one location to another when the crystal structure is deformed and an electric current flow is observed.
• As long as the force is maintained the crystal structure is stable and no further electrical events are observed.
• When the force is released, the crystal returns to its original shape and the reverse flow of electrons is seen.

Question 51

What is a streaming potential in regards to piezoelectric currents?

Answer 51

• Ions in the fluids that bathe living bone interact with the complex electric field generated when bone bends causing electric signals in the form of volts, as well as temperature changes.
• These small voltages observed in the fluid ions, are called a streaming potential, and also like piezoelectric currents have a rapid onset and alteration as changing stresses are placed on the bone.
• Without these stress-generated signals bone mineral is lost and general skeletal atrophy ensues (astronauts)
• Signals generated by the bending of alveolar bone during normal chewing almost surely are important for the maintenance of the bone around teeth.

Question 52

What could be used if stress-generated signals were important in producing the bone remodeling associated with ortho tooth movement?

Answer 52

A vibrating application of pressure would be advantageous.

Question 53

What are the chemical messenger components of tooth movement?

Answer 53

• This classic theory of tooth movement relies on chemical rather than electrical signals as the stimulus for cellular differentiation and ultimately tooth movement
• Chemical messengers are important in the cascade of events that lead to remodeling of alveolar bone and tooth movement, and both mechanical compression of tissues and changes in blood flow can cause their release.
• When a sustained force is placed on a tooth, the tooth shifts positions within the PDL space compressing the ligament in some areas, while stretching it in others.
• The mechanical effects on the PDL cells cause the release of cytokines, prostaglandins, and other chemical messengers.
• Blood flow is also decreased in the compressed PDL area, while blood flow is maintained or increased where the PDL is under tension.
• These alterations in blood flow quickly create changes in oxygen/carbon dioxide levels, which act either directly or indirectly in stimulating the release of other biologically active agents that then stimulate cellular differentiation and activity.

Question 54

What happens to the fluids when force is applied to a tooth?

Answer 54

Fluids are expressed out of the PDL space and the tooth moves in its socket, (takes a few seconds, )Then the blood flow through the partially compressed PDL decreases and within a few hours the resulting change in the chemical environment produces an increase in prostaglandins (especially prostaglandin E) and interleukin-1 beta levels, which increases cyclic adenosine monophosphate (cAMP), which is an important second messenger for cellular differentiation
• Since prostaglandins are released when cells are mechanically deformed, it appears that prostaglandin release is a primary rather than a secondary response to pressure
• Prostaglandins have the interesting property of stimulating both osteoclastic and osteoblastic activity, making prostaglandins particularly suitable as a mediator of tooth movement.
• The cAMP levels typically increase after 4 - 6 hours of sustained pressure
– This amount of time to increase cAMP levels and produce this cellular response correlates well with the philosophy that if a removable appliance is worn less than 6 hours per day, it will not have any orthodontic effects, and appliances worn above this threshold will produce some tooth movement.

Question 55

The lighter the pressure that is placed on a tooth the greater should be the reduction in blood flow. True or False?

Answer 55

False, the greater the pressure is the answer.
• At a certain magnitude of continuous pressure, blood vessels are totally occluded and a sterile necrosis of PDL tissue ensues, which has traditionally been referred to as hyalinized because the area appears to be absent of any cells due to the inevitable loss of all the cells when the blood supply is lost.
• When the PDL is compressed to the point that blood flow is totally cut off, differentiation of osteoclasts within the PDL space is not possible.
• After a delay of several days, osteoclasts within the adjacent marrow spaces attack the underside of the lamina dura in the process called undermining resorption.
• During undermining resorption tooth movement is delayed due to a delay in the stimulation of the differentiation of the cells within the marrow spaces and is also due to the thickness of bone that must be removed from the underside of the area, before any tooth movement can take place

Question 56

What is frontal resorption in orthodontic movement?

Answer 56

When a light continuous force is placed on a tooth, the PDL is compressed but blood flow to the area is not completely occluded.
• Studies in cellular kinetics indicate that osteoclasts are activated from a local population of progenitor cells in the PDL and then a second wave of osteoclasts are brought in form distant areas via blood flow.
• These cells attack the adjacent lamina dura removing bone in a process called frontal resorption and tooth movement begins soon thereafter.
• Soon after frontal resorption occurs osteoblasts recruited locally from progenitor cells in the PDL form bone on the tension side and begin remodeling activity on the pressure side.

Question 57

What are the differences between frontal resorption and undermining resorption?

Answer 57

With frontal resorption, a steady attack on the outer surface of the lamina dura results in smooth continuous tooth movement.
• With undermining resorption, there is a delay until the bone adjacent to the tooth can be removed. At that point, the tooth “jumps” to a new position, and if the heavy force is maintained, there will again be a delay until a second round of undermining resorption can occur
• Not only is tooth movement more efficient when an area of PDL necrosis is avoided, but pain is also lessened.
• However, even with light forces, small avascular areas are likely to develop in the PDL and tooth movement will be delayed until these areas can be removed by undermining resorption.
• The smooth progression of tooth movement with light force that is shown may be an unattainable ideal in clinical orthodontics.
• When continuous force is used in clinical practice tooth movement usually proceeds in a more stepwise fashion because of the inevitable areas of undermining resorption that occur
• In clinical practice an individual tooth’s movement will typically include areas of frontal and undermining resorption with undermining resorption being the rate limiting step in the tooth’s movement

Question 58

What is the definition of force?

Answer 58

A load applied to an object that will tend to move it to a different position in space

Question 59

What is the definition of center of resistance?

Answer 59

A point at which resistance to movement can be concentrated for mathematical analysis. For an object in free space, the center of resistance is the same as the center of mass. If an object is partially restrained as is the case for a tooth root embedded in bone, the center of resistance is located approximately halfway between the root apex and the crest of the alveolar bone.

Question 60

What is the definition of moment, regarding tooth movement?

Answer 60

A measure of the tendency of a force to rotate an object around some point. A moment is generated by a force acting at a distance. Quantitatively, it is the product of the force times the perpendicular distance from the point of force application to the center of resistance.

Question 61

What is the definition of couple, regarding tooth movement?

Answer 61

Two forces equal in magnitude and opposite in direction. A couple will produce pure rotation, spinning the object around its center of resistance, while the combination of a force and a couple can change the way an object rotates while it is being moved.
• Two unequal forces applied to the crown of a tooth to control root position can be resolved into a couple and a net force to move the tooth.
• If a 50 gm force were applied to a point on the labial surface of an incisor tooth 15 mm from the center of resistance, a 750 (1550) gm-mm moment (the moment of the force, or MF) would be produced, tipping the tooth.
• To obtain bodily movement, it is necessary to apply a couple to create a moment (the moment of the couple, or MC) equal in magnitude and opposite in direction to the original movement.
• One way to do this would be to apply a force of 37.5 gm pushing the incisal edge labially at a point 20 mm from the center of resistance. (37.520) = 750
• To achieve a net 50 gm for effective movement, it would be necessary to use 200 gm against the labial surface and 150 gm in the opposite direction against the incisal edge.
• Controlling forces of this magnitude with a removable appliance is very difficult, almost impossible—effective root movement is much more feasible with a fixed appliance.

Question 62

What is the definition of center of rotation, regarding tooth movement?

Answer 62

The point around which rotation actually occurs when an object is being moved, When two forces are applied simultaneously to an object, the center of rotation can be controlled and made to have any desired location. The application of a force and a couple to the crown of a tooth, in fact, is the mechanism by which bodily movement of a tooth, or even greater movement of the root than the crown, can be produced.
The center of resistance (or rotation) (CR) for any tooth is at the approximate midpoint (six-tenths of the distance between the apex of the tooth and the crest of the alveolar bone (slightly apical)) of the embedded portion of the root.
• If a single force is applied to the crown of a tooth, the tooth will rotate around CR (i.e., the center of rotation and center of resistance are identical) because a moment is created by applying a force at a distance from CR.
• The perpendicular distance from the point of force application to the center of resistance is the moment arm. Pressure in the periodontal ligament will be greatest at the alveolar crest and opposite the root apex.

Question 63

How do we generate the moment of a couple necessary to control root position in orthodontics?

Answer 63

A rectangular archwire fitting into a rectangular slot can accomplish this.
• How this is done - The wire is twisted (placed into torsion) as it is put into the bracket slot.
– The two points of contact are at the edge of the wire, where it contacts the bracket.
• The moment arm therefore is quite small, and forces must be large to generate the necessary MC.
• A 50 gm net lingual force would generate a 750 gm-mm moment.
– To balance it by creating an opposite 750 gm-mm moment within a bracket with a 0.5 mm slot depth, a torsional force of 1500 gm is required. (0.5 x 1500 = 750)

Question 64

What ratio determines the type of tooth movement that takes place?

Answer 64

The ratio between the moment produced by the force applied to move a tooth (MF) and the counterbalancing moment produced by the couple used to control root position (MC) determines the type of tooth movement.
• With no MC, (MC/MF = 0), the tooth rotates around the center of resistance (pure tipping).
• As the moment-to-force ratio increases (0 1, the center of rotation is displaced incisally and the root apex will move more than the crown, producing lingual root torque.

Question 65

What happens to the center of resistance for a tooth with loss of alveolar bone height?

Answer 65

It moves the center of resistance closer to the root apex.
• The magnitude of the tipping moment produced by a force is equal to the force times the distance from the point of force application to the center of resistance.
– If the center of resistance moves apically, the tipping moment produced by the force (MF) increases because the moment arm is longer, and a larger countervailing moment produced by a couple applied to the tooth (MC) would be necessary to produce bodily movement.
• This is almost impossible to obtain with traditional removable appliances and very difficult with clear aligners, even when bonded attachments are added.
• For all practical purposes, a fixed appliance is required if root movement is the goal in patients who have experienced loss of alveolar bone height.

Question 66

What are the characteristics of rotational or tipping tooth movement?

Answer 66

• Tipping or rotational movement is produced by application of a single force to the crown of a tooth, which creates rotation around a point approximately halfway down the root (six tenths).
• Heavy pressure is felt at the root apex and at the crest of the alveolar bone, but pressure decreases to zero at the center of resistance. The loading diagram therefore consists of two triangles as shown
• Optimal force to create an rotational movement of a tooth is quite low and is around 35-60 grams (Lower number for incisors higher number for molars)

Question 67

What are the characteristics of translational tooth movement?

Answer 67

• Translation or bodily movement of a tooth requires that the PDL space be loaded uniformly from alveolar crest to apex, creating a rectangular loading diagram.
• Twice as much force applied to the crown of the tooth is required to produce the same pressure within the PDL for bodily movement as compared with tipping
• Optimal force to create an translational movement is around 70-120 grams.

Question 68

What are the characteristics of intrusion and extrusion tooth movements?

Answer 68

• When a tooth is intruded, the force is concentrated over a small area at the apex.
• For this reason, extremely light forces are needed to produce appropriate pressure within the PDL during intrusion.
• Optimal intrusive forces are 10-20 grams
• Optimal extrusive force are the same as that for rotational 35-60 grams

Question 69

What would an ideal spring accomplish for tooth movement?

Answer 69

• An ideal spring would maintain the same amount of force regardless of distance a tooth had moved and would be the most ideal force system for orthodontic tooth movement.
– But with real springs the force decays at least somewhat as tooth movement occurs.
• Forces that are maintained between activations of an orthodontic appliance, even though the force declines, are defined as continuous forces.
• In contrast, interrupted forces drop to zero between activations.
• Intermittent forces fall to zero when a removable appliance is taken out, only to resume when the appliance is reinserted into the mouth. These forces also decay as tooth movement occurs.

Question 70

In regards to a force-deflection curve for an elastic material like an orthodontic arch-wire, what is the stiffness?

Answer 70

The stiffness of the material is given by the slope of the linear portion of the curve.

Question 71

In regards to a force-deflection curve for an elastic material like an orthodontic arch-wire, what is the range?

Answer 71

The range is the distance along the X- axis to the point at which permanent deformation occurs (usually taken as the yield point, at which 0.1% permanent deformation has occurred).

Question 72

In regards to a force-deflection curve for an elastic material like an orthodontic arch-wire, what is the proportional limit?

Answer 72

Proportional limit is point below which the force placed on an object creates a proportional deflection on the object. (There is a linear relation between the two.)

Question 73

In regards to a force-deflection curve for an elastic material like an orthodontic arch-wire, what is the spring-back?

Answer 73

Spring-back is the position the wire will return to after it has been deflected.
• If deflection has exceeded the proportional limit to the yeild point,the spring-back will not return to the wire to its original position.

Question 74

In regards to a force-deflection curve for an elastic material like an orthodontic arch-wire, what is the failure point?

Answer 74

The point at which the wire breaks.

Question 75

Which is the X and which is the Y value for a typical force-deflection curve?

Answer 75

Deflection is on the X axis, and Force is on the Y axis.

Question 76

It appears to be easier for some children to cope with a defect if other peoples responses are consistent, rather than if they are not. True or False?

Answer 76

True.
– It has been shown that a patient that is grossly disfigured he/she can anticipate a consistently negative response by their peers.
– Whereas an individual who has a “less severe” problem is sometimes treated differently because of their abnormality but other times they’re not.
– It appears to be easier for some children to cope with a defect if other peoples responses are consistent, rather than if they are not.
– Unpredictable responses produce anxiety,and if the child is worried someone might make fun of them, this can have strong negative emotional and developmental effects.
– Probably the major reason people seek orthodontic treatment is to minimize psychosocial problems related to their dental and facial appearance. A smaller percentage of patient seek orthodontic treatment for their malocclusion and TMD (Temporal mandibular dysfunction).
– Orthodontic problems are not“just cosmetic.”
• They have a major effect on a persons self- esteem, confidence and quality of life, as well as improvement in dental health.

Question 77

What do you have to worry about with protruding maxillary central incisors or severe class II occlusion?

Answer 77

• Malocclusion, particularly protruding maxillary incisors can increases the likelihood of an injury to the teeth.
• There is about one chance in three that a child with untreated class II malocclusion will experience trauma to the upper incisors.
– Most of the time the result is only minor chips to the enamel, but sometimes the damage can be more severe.
• In a patient with an extreme overbite, where the lower incisors contact the palate, this can cause significant tissue damage and bone loss to the lingual aspect of the maxillary incisors.
– This can lead to early loss of the upper incisors. This malocclusion can also result in extreme wear on the mandibular incisors.

Question 78

Sustained force of the type used to induce orthodontic tooth movement produces prominent cyclic stress generated signals. True or False?

Answer 78

False, it does not. As long as the force is sustained nothing happens. If stress-generated signals were important in producing the bone remodeling associated with orthodontic tooth movement, a vibrating application of pressure would be advantageous.

Question 79

What two things can cause the release of chemical messengers for bone remodeling?

Answer 79

Chemical messengers are important in the cascade of events that lead to remodeling of alveolar bone and tooth movement, and both mechanical compression of tissues and changes in blood flow can cause their release.

Question 80

Are prostaglandins a primary or secondary response to pressure?

Answer 80

Primary. Since prostaglandins are released when cells are mechanically deformed, it appears that prostaglandin release is a primary rather than a secondary response to pressure

Question 81

Prostaglandins stimulate osteoblastic but not osteoclastic activity. True or False?

Answer 81

False. Prostaglandins have the interesting property of stimulating both osteoclastic and osteoblastic activity, making prostaglandins particularly suitable as a mediator of tooth movement.

Question 82

Which three proteins are increased when the PDL is compressed and blood flow is decreased to a tooth socket?

Answer 82

Then the blood flow through the partially compressed PDL decreases and within a few hours the resulting change in the chemical environment produces an increase in prostaglandins (especially prostaglandin E) and interleukin-1 beta levels, which increases cyclic adenosine monophosphate (cAMP), which is an important second messenger for cellular differentiation.

Question 83

cAMP levels typically increase how many hours after sustained pressure in the tooth socket?

Answer 83

4-6 hours. This amount of time to increase cAMP levels and produce this cellular response correlates well with the philosophy that if a removable appliance is worn less than 6 hours per day, it will not have any orthodontic effects, and appliances worn above this threshold will produce some tooth movement.

Question 84

What is not possible anymore if blood vessels are occluded in the PDL and necrosis ensues and is “hyalinized?”

Answer 84

When the PDL is compressed to the point that blood flow is totally cut off, differentiation of osteoclasts within the PDL space is not possible.
• After a delay of several days, osteoclasts within the adjacent marrow spaces attack the underside of the lamina dura in the process called undermining resorption.
• During undermining resorption tooth movement is delayed due to a delay in the stimulation of the differentiation of the cells within the marrow spaces and is also due to the thickness of bone that must be removed from the underside of the area, before any tooth movement can take place

Question 85

When is the center of rotation and center of resistance identical?

Answer 85

If a single force is applied to the crown of a tooth, the tooth will rotate around CR (i.e., the center of rotation and center of resistance are identical) because a moment is created by applying a force at a distance from CR.

Question 86

What is the equation for a moment?

Answer 86

The force (gm) X the moment arm (which is the distance from the point of force to the center of resistance)

Question 87

What is Mc?

Answer 87

Moment of the couple, meaning the forces are equal and in opposite directions balancing each other out, otherwise it is just Mf.

Question 88

When Mc/Mf = 0, what type of tooth movement do you get?

Answer 88

Pure tipping, spinning of the tooth pretty much around its axis, this is when the center of resistance is equal to the center of rotation.

Question 89

When Mc/Mf = somewhere in between 0 and 1, what type of tooth movement do you get?

Answer 89

You get controlled tipping. The center of rotation is displaced further and further apically away from the center of resistance, producing what is called controlled tipping.

Question 90

When Mc/Mf = 1, what type of tooth movement do you get?

Answer 90

You get translation or bodily movement. The center of rotation is displaced to infinity and bodily movement (translation) occurs.

Question 91

When Mc/Mf = something greater than 1, what type of tooth movement do you get?

Answer 91

You get lingual root torque. The center of rotation is displaced incisally and the root apex will move more than the crown, producing lingual root torque.

Question 92

If the center of resistance moves apically, what happens to the tipping moment produced by the force (Mf)?

Answer 92

If the center of resistance moves apically, the tipping moment produced by the force (Mf) increases because the moment arm is longer, and a larger countervailing moment produced by a couple applied to the tooth (Mc) would be necessary to produce bodily movement.
• This is almost impossible to obtain with traditional removable appliances and very difficult with clear aligners, even when bonded attachments are added.
• For all practical purposes, a fixed appliance is required if root movement is the goal in patients who have experienced loss of alveolar bone height.