aetiology of malocclusion: soft tissue factors Flashcards
what part of the teeth position is determined by
a. skeletal factors
b. soft tissues
a. skeletal factors: dental based
b. soft tissues: crowns
3 oral soft tissues contributing to tooth position
- tongue
- lips
- cheek
why are soft tissue forces difficult to measure 4
- move around
- 3 dimensional (diffucult to see on x rays)
- radiolucent
- forces are light and awkwardly situated
what pressures from the tongue cause tooth movement? explain
resting forces
these are smaller than forces when swallowing but are constant.
5 observations of influence of soft tissues on tooth position
- spontaneous alignment of crowded teeth to the neutral position following extractions
- partial overjet reduction is less stable (more likely to relapse) than complete overjet reduction so upper and lower incisors touch
- everted lips associated with proclined incisors
- size of tongue correlates with proclination of incisors
- appliance to move tongue out the way allows incisors to meet
occlusal class from
a. tight lips
b. loose lips
a. tight lips: class 2 div2
b. loose lips: class 2 div 1
why are soft tissues significant to ortho 3
- contribute to malocclusion
- compensate for skeletal factors (dentoalveolar compensation, see pic)
- influence stability of treatment (expanded arches more likely to relapse)
4 things to look at when examining lips for ortho
- lip competence (upper lip)
- lip line (lower lip)
- length of upper lip (at rest and smiling)
- lip form (if everted or not)
define lip competence
lips meet together at rest without any muscular activity
which muscle masks incompetence
mentalis
boundaries of lip competence and when this is clinically significant
mildly half crown height (clinically significant)
how competence changes with age
low competence 9-11 years because permanent incisors have erupted and child is not fully grown
this gets better as child (and upper lip) grows
define/ normal lip line
lower lip in relation to upper incisors. normally overlaps 3-6 mm of incisor crown at rest
2 consequences of high lip line
- retroclination of upper incisors
- favours stability of overjet reduction
2 consequences of low lip line
- permits proclination of upper incisors
- instable overjet reduction
what to do with increased overjet and unfavourable lips 2
- accept overjet OR
- treat with rigour and guarded prognosis (fully reduce overjet (
influence and tx of upper lip length
influences amount of upper incisor visible (>2mm thought to be unattractive). only tx is surgery to lift maxilla
explain how digit sucking can cause a crossbite
sucking -> contraction of cheeks -> moves upper teeth in (lower teeth held out by flattened tongue) -> crossbite
what else does digit sucking cause
anterior open bite
2 factors affecting influence of tongue on soft tissues
- function eg thrusts
- size
2 types of tongue thrust and explain
- adaptive (most common): in pts with incompetent lips to create anterior seal when swallowing. not that clinically important
- endogenous/ primary (rare): in pts with down syndrome
what are adaptive tongue thrusts often associated with
incomplete overbite (lower incisors overlap the upper in the vertical plane but do not touch the upper teeth or palate (due to tongue in the way)
2 features of endogenous tongue thrust
- anterior open bite
- bimaxillary proclination (ass with anterior open bite)
is tongue thrust associated with lisps?explain
no. no relationship between timing of tongue thrust and lisp
common age for tongue thrust and why
babies (60%). to create anterior seal in absence of teeth
examples of how tongue size influences mandibular arch form 2
- macroglossia (large tongue) -> large arch width
- partial glossectomy -> shrinkage of arch width
