Lecture 9 Flashcards
the first key to normal occlusion is ___
molar relationship
how many “keys to occlusion” did lawrence andrews develop?
6
how did lawrence andrews determine the 6 keys to occlusion?
they were established as meaningful not solely because all of the keys were present in the cases he studied, but also because the lack of even one of the 6 keys was a defect predictive of an incomplete end result in treated orthodontic models
describe the molar relationship of normal occlusion
-the traditional description of a normal class I molar relationship is the MB cusp of the maxillary 1st molar occludes with the buccal groove of the mandibular 1st molar -however, all of andrews’ cases showed the distal surface of the maxillary 1st permanent molar contacting the mesial surface of the mandibular 2nd molar, and the closer the case is to this molar relationship, the better the opportunity for normal occlusion, so the sufficiency of the traditional description of a normal class I molar relationship is questioned
the second key to normal occlusion is ___
crown angulation (or tip)
what is crown angulation with respect to normal occlusion?
the gingival portion of the long axes of crowns is more distal than the incisal portion
the degree of crown angulation/tip is the angle between ___
the long axis of the crown, as viewed from the labial or buccal surface, and a line bearing 90* from the occlusal plane
what does a “plus” or “minus” crown angulation mean?
-a plus reading is awarded when the gingival portion of the long axis of the crown is distal to the incisal portion -a minus reading is assigned when the gingival portion of the long axis of the crown is mesial to the incisal portion
relative to andrews 2nd key to normal occlusion, normal occlusion is dependent upon proper ___, especially for which teeth?
proper distal crown tip, especially for the maxillary anterior teeth since they have the longest crowns
relative to andrews’ 2nd key to normal occlusion, the degree of tip of the ___ determines the amount of ___, and therefore has a considerable effect on posterior occlusion as well as anterior esthetics
the tip of the incisors determines the amount of M-D space they consume
andrews’ 3rd key to normal occlusion is ___
crown inclination (bucco-lingual inclination or torque)
what does a plus and minus reading for crown inclination mean?
-a plus reading is given if the gingival portion of the crown is lingual to the incisal portion -a minus reading is given when the gingival portion of the corwn is labial to the incisal portion
maxillary and mandibular ___ crown inclincations are intricately complementary and significantly affect ___
-anterior -overbite and posterior occlusion
properly inclined anterior crowns contribute to ___
normal overbite and posterior occlusion
the contact points (the position where maxillary occlusal contact should be occurring) move ___ in relation to the mandibular teeth, in concert with the increase in __positive/negative__ maxillary anterior crown inclination
-distally -positive
in all of the cases andrews studied, a negative crown inclination existed in each crown from maxillary ___ through the maxillary ___, with a slightly more negative crown inclination existing in the maxillary ___ and ___
-canine -second premolar -first and second molars
describe how maxillary posterior crown inclination seems counter intuitive to the curve of wilson
the buccal surface of the maxillary posterior teeth have a lingual inclination but also typically have longer lingual functional cusps to contact the mandibular posterior teeth, facilitating the curve of wilson
in all of the cases andrews studied, there was a progressively greater negative crown inclination from mandibular ___ to ___
canines to the second molars
andrews’ fourth key to normal occlusion is ___
elimination of rotations
for “normal occlusion”, why should teeth be free of undesirable rotations?
a rotated tooth occupies more space than a straight tooth, creating a situation unreceptive to normal occlusion
andrews’ fifth key to normal occlusion is ___
tight interproximal contacts
why should patients with genuine tooth-size discrepancies, like peg laterals, have these size discrepancies corrected?
it will allow for proper tight contact points so that the orthodontist will not have to close spaces at the expense of a proper occlusion
andrews’ sixth key to normal occlusion is ___
flat occlusal plane
why are flat-to-slight curves of spee necessary for a “normal occlusion”?
-there is a natural tendency for the curve of spee to deepen with time, because the lower jaw often grows for a longer period of time than the upper jaw -this causes the lower anterior teeth, which are normally confined by the upper anterior teeth and lips, to be forced back and up, resulting in crowded lower anterior teeth and/or a deeper overbite and deeper curve of spee
which angles classification is the most common and what percent of the US population has it?
angles class I, 70%
in a class I occlusal relationship, the ___ of the maxillary first molar articulates with the ___ of the mandibular first molar
-triangular ridge -buccal groove
in a class I occlusal relationship, the maxillary central incisors overlap the mandibular incisors by ___mm
1-2mm
in a class I occlusal relationship, the maxillary canine lies between the mandibular ___ and ___
canine and first premolar
class I occlusal relationships are associated with a ___ facial profile, where the nose, lips, and chin are harmoniously related
orthognathic (straight)
class II occlusal relationships are less common and occur in about ___% of the US population
25%
in a class II occlusal relationship, the ___ of the maxillary first molar falls approximately between the ___ and ___, or the ___ of the mandibular first molar articulates posteriorly to the ___ of the maxillary first molar
-MB cusp -mandibular first molar and the second premolar -buccal groove -MB cusp
class II occlusal relationships are associated with a ___ facial profile
-retrognathic (convex) -the lower jaw and chin may also appear small and withdrawn
in a class II occlusal relationship, the mandibular incisors occlude ___ to the maxillary incisors and typically are in a ___, and may not be in ___
-posterior -deep bite -occlusion
in a class II occlusal relationship, the maxillary canine is ___ to the mandibular canine
mesial
in a class II occlusal relationship, the mandibular incisors are typically tipped in what direction?
bucally
which angles classification is sometimes referred to as a “sunday bite”, and what is it referring to?
-it describes an individual that functions in a class I relationship, but also has a CR/CO shift that allows the patient to function in a class II relationship -a class II patient can fool a professional by biting in a class I position in CO but really they are a class II if they bite in CR
which angles classification is the least common?
-class II (5% of the US population)
in a class III occlusal relationship, the ___ of the maxillary first molar falls approximately between the ___ and ___, or the ___ of the mandibular first molar articulates anteriorly to the ___ of the maxillary first molar
-MB cusp -mandibular first molar and second molar -buccal groove -MB cusp
a class III occlusal relationship is associated with a ___ facial profile
-prognathic (concave) -the chin may also protrude
in a class III occlusal relationship, the mandibular incisors overlap ___ to the maxillary incisors, resulting in a ___
-anteriorly -negative overjet
in a class III occlusal relationship, the maxillary canine is ___ to the mandibular canine
distal
in a class III occlusal relationship, the mandibular incisors will typically be tipped in a ___ direction
lingual
what is pseudo-class III malocclusion?
-the mandibular incisors are forward of the maxillary incisors when in centric occlusion -the patient has the ability to bring the mandible back to centric relation without strain (CR/CO shift) -this type of malocclusion is milder than a true class III and is easier to correct orthodontically
malocclusions in which there is a distal relationship of the mandible to the maxilla make up which angles classification?
class II
what is a class II division I?
class II molar relationship with protruded maxillary incisors
what is a class II division II?
a class II molar relationship where the maxillary lateral incisors are tipped labially and where the central incisors are typically retrudeddd
which class II division patients typically have better growth patterns and require different treatments?
division II
when are class II divisions divided into subdivisions?
when the class II only occurs on one side of the dental arch
what is a class II division II subdivision left?
-describes an occlusion that is a class I molar on the right side and class II on the left side
a patient can be categorized as being class I, II, or III as a dental condition or a skeletal condition. are they always the same classification?
-not always -for example, a patient could have their dental occlusion in a class II relationship, but skeletally they patients maxilla and mandible are normal and would be classified as a skeletal class I -this patient would then be classified as a dental class II and a skeletal class I
typically when a patient has a straight profile, the mandible is proportionally ___ in size to the maxilla, and a dental class ___ molar relationship is formed
-similar -I
typically when the mandible is proportionally smaller than the maxilla, a dental class ___ relationship is formed and a ___ profile is seen
-II -convex
typically when a mandible is relatively greater in size than the maxilla, a dental class ___ relationship is formed and a ___ profile is seen
-III -concave
when describing primary molar relationships, the ___ aspect of the second primary molars is used, and is termed the ___ plane
-distal -terminal
at what point in time do you shift from a primary molar relationship to a permanent molar relationship?
when the second primary molars are lost and during the adolescent growth spurt
the amount of differential mandibular growth and molar shift in the the ___ space determines the permanent molars relationship
leeway
what is leeway space?
-the size differential between the primary posterior teeth and the permanent canine and premolars -usually the sum of the primary tooth widths is greater than that of their permanent successors, so when these primary teeth fall out, there is usually a slight amount of space
the leeway space for the maxillary arch is about ___mm per side, and for the mandibular arch is about ___mm per side
-1.5mm -2.5mm
which terminal plane is the normal relationship in the primary dentition?
flush terminal plane
what is the flush terminal plane relationship?
the distal surfaces of the second primary molars are in an end to end relationship
flush terminal planes will typically shift to a ___ or ___, but this relationship is usually temporary until the second primary molars are lost and the permanent molars then move into a ___ relationship
-class II molar or end-to-end -class I: this tends to happen at age 10 or 11 and is termed the late mesial shift
both the mesial step and the flush terminal plane relationship usually result in the development of a class ___ permanent molar occlusion, but not always
-I -sometimes the flush terminal plane can end up in an end on relationship if the mesial shift doesn’t occur
a mesial step relationship can result in a class ___ or ___ relationship
I or III
in ___ relationships, the permanent molars erupt into a class II relationship or an end on molar relationship
distal step
the primary dentitions normal canine relationship typically has the ___ of the primary maxillary canine articulating with the ___ of the primary mandibular canine
-mesial inclined plane -distal inclined plane
T or F: spacing is normal throughout the anterior part of the primary dentition
true
where is the maxillary primate space located?
between the primary lateral incisors and primary canines
where is the mandibular primate space located?
between the primary canines and the primary first molar
when are primate spaces normally present?
from the time the teeth erupt
___ spaces between the primary incisors are often present from the beginning, but become somewhat larger as the child grows
developmental
generalized spacing of the primary teeth is a requirement for proper ___, which is most frequently caused by growth of the ___
-proper alignment of the permanent incisors -growth of the dental arches
facial lingual position variations can be possible due to differences in growth of the ___
width of the maxilla or the mandible
___ crossbite in the posterior teeth is characterized by contact of the maxillary facial cusps in the opposing mandibular central fossae and the mandibular lingual cusps in the opposing maxillary central fossae
facial crossbite (buccal crossbite)
facial/buccal crossbite results in reversal of ___
the roles of the cusps on the involved teeth, with the mandibular lingual cusps and the maxillary facial cusps becoming supporting cusps and the maxillary lingual cusps and mandibular facial cusps becoming non-supporting cusps
___ crossbite results in a very poor molar relationship that provides little functional contact and is very difficult to correct orthodontically
lingual crossbite (scissor crossbite)
it is important that any restorative work done maintains the proper shape of the occlusal surfaces of teeth to ensure that ___
the functional occlusal contact relationships are restored in harmony with both dynamic and static conditions
maxillary and mandibular teeth should contact uniformly on closing to allow what 3 things?
-optimal function -minimize trauma to the supporting structures -allow for uniform load distribution throughout the dentition
positional stability of well-aligned teeth is crucial if ___ and ___ are to be maintained over time
arch integrity and proper function
T or F: most dentitions deviate from optimal alignment and occlusion
true
many patients adapt well to less than optimal occlusion, but malocclusion may be associated with undesirable changes to what 4 possible things?
-teeth -musculature -TMJ -periodontium and alveolar bone
over time, many concepts of ideal occlusion have been proposed, but in the literature, the concepts of what is ideal, acceptable, and harmful continue to be developed, but class ___ occlusions are the most widely accepted as ideal
I
complex three dimensional mandibular movement can be divided into which two basic components?
translation and rotation
___ is the movement in which all points within a body have identical motion
translation
during translation, the ___ muscle contracts and moves the condyle-articular disc assembly forward
lateral pterygoid
simultaneous, direct anterior movement of both condyles is termed ___
protrusion
simultaneous, direct posterior movement of both condyles is termed ___
retrusion
___ movement is when the body of the mandible is turning about an axis
rotational
rotational movement can happen in what 3 planes?
-sagittal -horizontal -frontal