1. Essentials of Occlusion
Department of Endodontics, Prosthodontics, and Operative Dentistry
University of Maryland, Baltimore

2. Preview Factors affecting distribution of occlusal forces
Occlusal schemes of the natural dentition
Defining occlusal interferences
How to evaluate an occlusion

3. Degree of Force Direction of Force

4. 1. Forces applied along the long axes of teeth are generally well tolerated
Compare to pounding the top of a fencepost
With proper contact, posterior teeth receive force along the long axis in MI

5. 2. Forces applied at an angle to the long axis have potential to cause harm
Compare to forces used to remove a fence post
May cause mobility, wear, or fracture
Anterior teeth take non-axial forces in all positions
Posterior teeth take non-axial forces in all excursive contacts and with unreciprocated incline contacts in MI

6. 3. During excursions, the farther forward contact occurs, the less force is being applied
Compare to applications of a nutcracker
Williamson and Lundquist study shows elevator muscle contraction decreasing as posterior teeth disocclude
Rationale for anterior protection and progressive disocclusion in group function

9. 4. The greater number of teeth in simultaneous contact, the less force applied to individual teeth
Rationale for group function, but more significant in MI
Becomes more significant as tooth loss occurs

10. 5. In excursions, friction intensifies forces applied to individual teeth
Wear facets produce friction during excursions
As wear facets increase in area, friction and force intensify

11. Occlusal Schemes in the Natural Dentition

12. Anterior Protection Mutual Protection Canine Protection
Anterior Group Function

14. Canine Guidance:
Lateral Movement

16. Anterior Protection All teeth contact in MI
Posterior teeth protect anterior teeth from non-axial forces in MI
Anterior teeth protect posterior teeth from non-axial forces during all excursions
By far the most favorable scheme for restorative dentistry

17. Group Function
Posterior teeth contact on working side during excursions
No contact on non-working side during excursions
No posterior contact during protrusive movements
All teeth contact in MI

19. Progressive Disocclusion

25. Partial Group Function

26. Bilateral Balance

28. Effects of Occlusal Curves

29. Anteroposterior Curve

30. Mediolateral Curve

31. Occlusal Interferences
Prematurities
Deflective occlusal contacts
Interferences to healthy occlusal schemes

32. Interferences to Healthy Occlusal Schemes
Centric interferences
Working side interferences
Non-working side interferences
Protrusive interferences

33. Centric Interferences
Arc of closure interferences
Line of closure interferences

34. Arc of Closure Interference

35. Line of Closure Interference

36. Excursive Interferences

37. Working side interferences
Excursive contacts on other than inner inclines of maxillary buccal cusps
Excursive contacts disallowing progressive disocclusion
Excursive contacts producing broad wear facets

42. Non-Working Side Interferences
Any contact on the non-working side during excursions is an interference
Contact causes elevator muscle contraction as condyle translates
Lateral pterygoid is placed in competition with elevator muscles

46. Protrusive Interferences
Any posterior contact during protrusion
Occurs with steep antero-posterior curve or steep cuspal inclines
May occur after loss of mand. 1st molar
Potentially most damaging because of wear on anterior teeth/ loss of anterior guidance

50. Evaluating an Occlusion

51. Favorable Conditions Strong anterior guidance
Relatively flat occlusal curves
Intact dentition with no third molars
Posterior cuspal inclines less than anterior guidance inclines
All teeth contacting in MI

52. Unfavorable Conditions
Most are conditions used to create a balanced occlusion in complete dentures

53. 1. Little or no anterior guidance
No vertical overlap
No contact in maximum intercuspation

55. Steep occlusal curves
Steep medio-lateral curve makes non-working side interferences likely
Steep antero-posterior curve makes protrusive interferences likely
Missing posterior teeth with tipping or supraeruption may produces changes in occlusal curves

56. 3. Third Molars
Occlusal curves are exaggerated in third molars

57. 4. Wear Facets
Incisors- Wear on incisal edges reveals protrusive bruxing
Canines- Wear on incisal edge indicates lateral bruxing. Look for non-working interferences on the contralateral side
Posteriors- Learn how wear facets on inclines are formed

58. Wear Facet Analysis

60. 5. Excessively steep posterior cuspal inclines
If the inclination of posterior cuspal inclines exceeds the inclination of anterior guidance, posterior inclines cannot clear during excursions

62. 6. Excessively steep orientation of the occlusal plane
If the inclination of the occlusal plane equals or exceeds the inclination of horizontal condylar guidance, the posterior teeth may not be able to disocclude in protrusive excursions

73. The End!