what is occlusion
- 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
tooth contact (between adjacent teeth)
- 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.)
arch form
- 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)
intercuspal position with ideal occlusion
-each upper tooth contacts with its lower antagonist and its distal neighbour (eg. upper 5 contacts with lower 5 and lower 6)
tooth alignment
- 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
tooth alignment neutral zone
- neutral zone = zone of equilibrium between forces exerted on a tooth
- this is clinically important in denture construction
curve of wilson
- 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
bilateral cross-bite
-lower buccal cusps outside upper buccal cusps
unilateral cross-bite
- 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)
curve of spee
-describes intercuspal position
angle’s classification
- 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
class I angle’s classification
MB cusp of upper 6 sits in MB groove of lower 6
class II angle’s classification
- 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
class III angle’s classification
-MB cusp of upper 6 sits behind MB groove of lower 6
overbite
- between tip of upper tooth and tip of lower tooth (area between upper incisor and lower inisor edge)
- tooth overlap in the VERTICAL plane
open bite
- 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
incisor relationships
- overbite
- openbite
- overjet
- reverse overjet
- incisor classification
overjet
- tooth overlap in the horizontal plane
- >prominent upper incisors (sticking out)
reverse overjet
-due to more prominent mandible
incisor classification
- relates the lower incisor tip to the cingulum plateau of the upper incisor
- > note that molar and incisor relationships may be different in patients
class I incisor classification
lower incisor tip sits in cingulum plateau of upper incisor
class II div I incisor classification
- lower incisor tip is behind cingulum plateau of upper incisor but still contacts upper incisor
- > due to increased overjet
class II div II incisor classification
- 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
class III incisor classification
- lower incisor tip sits infront of cingulum plateau of upper incisor
- > due to reversed overjet on normal occlusion
