aetiology of malocclusion: soft tissue factors

Question 1

what part of the teeth position is determined by

a. skeletal factors
b. soft tissues

Answer 1

a. skeletal factors: dental based

b. soft tissues: crowns

Question 2

3 oral soft tissues contributing to tooth position

Answer 2

• tongue
• lips
• cheek

Question 3

why are soft tissue forces difficult to measure 4

Answer 3

• move around
• 3 dimensional (diffucult to see on x rays)
• radiolucent
• forces are light and awkwardly situated

Question 4

what pressures from the tongue cause tooth movement? explain

Answer 4

resting forces

these are smaller than forces when swallowing but are constant.

Question 5

5 observations of influence of soft tissues on tooth position

Answer 5

• 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

Question 6

occlusal class from

a. tight lips
b. loose lips

Answer 6

a. tight lips: class 2 div2

b. loose lips: class 2 div 1

Question 7

why are soft tissues significant to ortho 3

Answer 7

• contribute to malocclusion
• compensate for skeletal factors (dentoalveolar compensation, see pic)
• influence stability of treatment (expanded arches more likely to relapse)

Question 8

4 things to look at when examining lips for ortho

Answer 8

• lip competence (upper lip)
• lip line (lower lip)
• length of upper lip (at rest and smiling)
• lip form (if everted or not)

Question 9

define lip competence

Answer 9

lips meet together at rest without any muscular activity

Question 10

which muscle masks incompetence

Answer 10

mentalis

Question 11

boundaries of lip competence and when this is clinically significant

Answer 11

mildly half crown height (clinically significant)

Question 12

how competence changes with age

Answer 12

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

Question 13

define/ normal lip line

Answer 13

lower lip in relation to upper incisors. normally overlaps 3-6 mm of incisor crown at rest

Question 14

2 consequences of high lip line

Answer 14

• retroclination of upper incisors

- favours stability of overjet reduction

Question 15

2 consequences of low lip line

Answer 15

• permits proclination of upper incisors

- instable overjet reduction

Question 16

what to do with increased overjet and unfavourable lips 2

Answer 16

• accept overjet OR

- treat with rigour and guarded prognosis (fully reduce overjet (

Question 17

influence and tx of upper lip length

Answer 17

influences amount of upper incisor visible (>2mm thought to be unattractive). only tx is surgery to lift maxilla

Question 18

explain how digit sucking can cause a crossbite

Answer 18

sucking -> contraction of cheeks -> moves upper teeth in (lower teeth held out by flattened tongue) -> crossbite

Question 19

what else does digit sucking cause

Answer 19

anterior open bite

Question 20

2 factors affecting influence of tongue on soft tissues

Answer 20

• function eg thrusts

- size

Question 21

2 types of tongue thrust and explain

Answer 21

• 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

Question 22

what are adaptive tongue thrusts often associated with

Answer 22

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)

Question 23

2 features of endogenous tongue thrust

Answer 23

• anterior open bite

- bimaxillary proclination (ass with anterior open bite)

Question 24

is tongue thrust associated with lisps?explain

Answer 24

no. no relationship between timing of tongue thrust and lisp

Question 25

common age for tongue thrust and why

Answer 25

babies (60%). to create anterior seal in absence of teeth

Question 26

examples of how tongue size influences mandibular arch form 2

Answer 26

• macroglossia (large tongue) -> large arch width

- partial glossectomy -> shrinkage of arch width