occlusion (OB8)

Question 1

what is occlusion

Answer 1

• contact between teeth - within arches and between arches (usually sit 2-5mm apart at rest):
• > contact points
• > arch form
• > tooth alignment
• > cross bites
• > intercuspal position
• > molar relationships
• > incisor relationships

Question 2

tooth contact (between adjacent teeth)

Answer 2

• contact point/ area: stagnation- caries risk
• contact point is critical for: food displacement during mastication onto grinding surface of tooth and arch alignment/stability (therefore it is important to restore a contact point, this can be done by matrix bonds)
• > approximal contact = contact points are higher up on anterior teeth
• > stagnation point is just below contact point
• > contact areas are larger than contact points (on molars eg.)

Question 3

arch form

Answer 3

• upper arch is longer than lower (has longer mesial-distal surface) and is slightly narrower at 8’s (horse shoe shape)
• lower arch is slightly wider at the back (8’s)
• > therefore when arches sit on top of each other, the upper arch ideally sits outside the lower arch (upper buccal cusps are buccal to lower buccal cusps)

Question 4

intercuspal position with ideal occlusion

Answer 4

-each upper tooth contacts with its lower antagonist and its distal neighbour (eg. upper 5 contacts with lower 5 and lower 6)

Question 5

tooth alignment

Answer 5

• teeth do not sit perfectly vertically
• tooth alignment is determined by:
• > path of eruption
• > forces exerted on the teeth (by: teeth/as adjacent teeth push mesial teeth straight, soft tissues and other factors eg. thumbs or orthodontics = small forces over a long time)
• upper incisor teeth are inclined mesially
• upper premolars inclined bucally/ at an angle of 5degrees to the vertical axis
• upper molar occlusal surfaces face bucally/ at an angle of 20 degrees to the vertical axis
• lower molar occlusal surfaces face lingually

Question 6

tooth alignment neutral zone

Answer 6

• neutral zone = zone of equilibrium between forces exerted on a tooth
• this is clinically important in denture construction

Question 7

curve of wilson

Answer 7

• description of occlusal surface
• coronal/lateral curve
• > upper teeth buccal surfaces pointing outwards
• > lower teeth point inwards
• upper buccal cusps outside lower buccal cusps
• > describes position of buccal cusps of upper and lower jaw in comparison to each other

Question 8

bilateral cross-bite

Answer 8

-lower buccal cusps outside upper buccal cusps

Question 9

unilateral cross-bite

Answer 9

• one side is in cross-bite (lower buccal cusps outside upper buccal cusps)
• other side is normal (upper buccal cusps buccal to lower buccal cusps)

Question 10

curve of spee

Answer 10

-describes intercuspal position

Question 11

angle’s classification

Answer 11

• relationship between upper and lower 6’s (first molar)
• 6’s are are key to the occlusion (as they are first posterior/often first permanent teeth that come through and have no deciduous predecessor)
• relationship between MB cusp of the upper 6 to the MB groove of the lower 6

Question 12

class I angle’s classification

Answer 12

MB cusp of upper 6 sits in MB groove of lower 6

Question 13

class II angle’s classification

Answer 13

• upper arch is relatively forward

- MB cusp of upper 6 sits anterior to MB groove of lower 6, DB cusp of upper 6 sits in MB groove of lower 6

Question 14

class III angle’s classification

Answer 14

-MB cusp of upper 6 sits behind MB groove of lower 6

Question 15

overbite

Answer 15

• between tip of upper tooth and tip of lower tooth (area between upper incisor and lower inisor edge)
• tooth overlap in the VERTICAL plane

Question 16

open bite

Answer 16

• type of overbite (tooth overlap in the vertical plane)
• however there is no overlap atall in an open bite
• > sucking thumb etc can cause open bite

Question 17

incisor relationships

Answer 17

• overbite
• openbite
• overjet
• reverse overjet
• incisor classification

Question 18

overjet

Answer 18

• tooth overlap in the horizontal plane

- >prominent upper incisors (sticking out)

Question 19

reverse overjet

Answer 19

-due to more prominent mandible

Question 20

incisor classification

Answer 20

• relates the lower incisor tip to the cingulum plateau of the upper incisor
• > note that molar and incisor relationships may be different in patients

Question 21

class I incisor classification

Answer 21

lower incisor tip sits in cingulum plateau of upper incisor

Question 22

class II div I incisor classification

Answer 22

• lower incisor tip is behind cingulum plateau of upper incisor but still contacts upper incisor
• > due to increased overjet

Question 23

class II div II incisor classification

Answer 23

• retroclined upper incisors
• lower incisor tip sits behind the cingulum plateau of the upper incisor however there is no contact point between upper and lower incisor

Question 24

class III incisor classification

Answer 24

• lower incisor tip sits infront of cingulum plateau of upper incisor
• > due to reversed overjet on normal occlusion