7. Study Models and Occlusion

Question 1

Define ‘occlusion’

Answer 1

• the way the teeth of the upper and lower jaws meet and move over each other in function

Question 2

Define ‘static occlusion’

Answer 2

• a patients occlusion at rest (when not eating)
• patient may be biting together (intercuspal position) or more relaxed with teeth apart (rest position)

Question 3

Define ‘intercuspal position’

Answer 3

• position of maximum intercuspation of teeth
• if you close teeth into where bottom and top normally fit together
• clench back teeth this is ICP
• fundamental position in orthodontics and restorative dentistry as to not interfere with normal occlusion with filling etc

Question 4

Define ‘rest position’

Answer 4

• teeth are slightly separated by a couple of mm
• teeth usually only in contact for short time each day
• completely relax in seated position and let jaw hang

Question 5

Define ‘normal bite’ as in no crossbite or scissorbite

Answer 5

• normally upper arch is wider than lower so palatal cusps of upper posteriors contact central fossa of lowers and buccal cusps of lowers fit into central fossa of uppers

Question 6

Define ‘crossbite’

Answer 6

• lower jaw is slightly wider than upper so buccal cusps of upper molars and premolars contact central fossa of lowers and lingual cusps of lowers contact central fossa of uppers

Question 7

Define ‘scissorbite’

Answer 7

• upper jaw significantly wider than lower jaw so teeth don’t contact

Question 8

Define ‘functional cusp’

Answer 8

• cusp that bites into central fossa of opposing posterior tooth in intercuspal position
• usually palatal cusp of upper teeth and buccal cusp of lowersDefi

Question 9

Define ‘working side’

Answer 9

• when jaw moves side to side to chew food
• the side it moves towards is working
• can depend on where the food is moved in chewingDefi

Question 10

Define ‘non-working side’

Answer 10

• the side which food is not moved to when you chew

Question 11

Define ‘guidance teeth’

Answer 11

• teeth that make contact as patient slides lower jaw to working side and back again
• important for making crowns/bridges because if they’re for guidance teeth they’ll do more work and wear faster

Question 12

Define ‘overjet’

Answer 12

• horizontal overlap of upper and lower incisors
• measured in mm with ruler from most prominent tooth

Question 13

Define ‘overbite’

Answer 13

• vertical overlap of upper and lower incisors
• measured in mm using ruler or by % coverage of lower incisors as ruler is hard in mouth

Question 14

To assess overbite by % coverage of lower incisors, you …

Answer 14

• estimate how much of the height of the lower incisors is covered by uppers
• in ICP

Question 15

Define ‘Class I incisal relationship’

Answer 15

• lower incisal edges occlude with or lie immediately below cingulum plateua of upper central incisors

Question 16

Define ‘Class II div 1 incisal relationship’

Answer 16

• lower incisor edges lie posterior to cingulum plateau of upper central incisors
• for div 1, upper incsiors are proclined and overjet is generally larger

Question 17

Define ‘Class II div 2 incisal relationship’

Answer 17

• lower incisal edges lie posteriorly to the cingulum plateau of upper central incisors
• for div 2, upper incisors are retroclined and overjet is generally minimal/decreased

Question 18

Define ‘Class III incisal relationship’

Answer 18

• lower incisor edges lie anterior to cingulum plateua of upper central incisors
• overjet is reduced/reversed

Question 19

Define ‘class I molar relationship’

Answer 19

• mesiobuccal cusp of upper 6 occludes buccal groove of lower 6
• upper 6 is in half in groove of lower 6, half behind

Question 20

Define ‘class II molar relationship’

Answer 20

• upper 6 is a full tooth in front of Class I
• half upper 6 in groove of lower 6 and half is in front

Question 21

Define ‘class III molar relationship’

Answer 21

• upper 6 is a full tooth distal to lower 6 and Class I
• here if canines were also Class III, they would be behind the lower 4s

Question 22

If a tooth was in between classes, how are they referred?
Use 2 1/4 for example

Answer 22

• use fractions to refer to difference from type 1
• if a tooth was 1/4 of a tooth width away from being class 1 but was moving towards a 2 position, it would be 1/4 unit of Class II