1. Criteria for Optimum Functional Occlusion
Dr. Pauline Hayes Garrett
Dr. Patricia W. Kiln
Department of Endodontics, Prosthodontics and Operative Dentistry
University of Maryland, Baltimore

2. This material is taken from:
Okeson, J.P. (2003). Management of Temporomandibular Disorders and Occlusion
6th Ed. , St. Louis, MO: Mosby, Chapter 5
Wheeler’s Dental Anatomy, Physiology and Occlusion, Ash, Eighth Edition, Saunders, 2003, Chapter15,
pgs

3. Objectives!
Explain and describe the criteria for optimum function of the masticatory system.
Identify and explain optimum occlusal contacts and function in the absence of pathology.

4. The masticatory system consists of an extremely complex and interrelated group of muscles, bones, ligaments, teeth and nerves
Illustration Reprinted from: Okeson, J.P. (2003). Management of Temporomandibular Disorders and Occlusion, 5th Ed. , St. Louis, MO: Mosby, Chapter 3.with permission from Elsevier. Pg.31
The mandible is a bone suspended from the skull by ligaments and a muscular sling. The elevator muscles (masseter, medial pterygoid, and temporalis) raise the mandible. When force is applied, contact is made in three places…the two TMJs and the dentition. These forces are potentially quite heavy so damage could occur at all three sites.

5. Anatomic structures of the TMJ (temporomandibular joint):
Articular disc – dense fibrous connective tissue; no nerves or blood
vessels so it can endure heavy forces without damage or pain.
Illustrations Reprinted from: Okeson, J.P. (2003). Management of Temporomandibular Disorders and Occlusion, 5th Ed. , St. Louis, MO: Mosby, Chapter 3.with permission from Elsevier. Pg.113
The articular disc separates, protects and stabilizes the condyle in the mandibular fossa during functional movements.
Fibers from the upper head of the Lateral Pterygoid pull the disk down and forward.

6. ARTICULAR DISC - SHAPE , ATTACHMENTS AND FUNCTION
Peripherally the disc is attached to the fibrous capsule and the superior head of lateral pterygoid  (anteriorly). Fig. A  
Medially and laterally the disc is tightly attached to the head of the condyle by the medial and lateral collateral (discal) ligaments. (figure B) They are composed of collagenous connective tissue.
These ligaments function to restrict the disc from moving away from the condyle and permit the disc to move anteriorly and posteriorly together with the condyle (as a condyle-disc unit) during translation.  They also function during the rotation of the TMJ.
Illustrations Reprinted from: Okeson, J.P. (2003). Management of Temporomandibular Disorders and Occlusion, 5th Ed. , St. Louis, MO: Mosby, Chapter 3.with permission from Elsevier. (Fig. A ,pg 113),( Fig B, Pg.14)

7. Positional stability of TMJ
Determined by muscles pulling across the joint to prevent dislocation
Major stabilizing muscles
Masseter
Medial pterygoid
Temporalis
Superior head of the lateral pterygoid

8. CENTRIC RELATION: Most musculoskeletally stable position of the TMJ

9. Optimum functional tooth contacts: Maximum Intercuspation
When closing in Centric Relation results in a cusp tip to cusp tip occlusal position.
The neuromuscular system can possibly slide the condylar position (via a Centric Slide) so that a cusp tip to fossa relationship was attained.

10. Optimum functional tooth contacts
To be in harmony, all must be stable
Stable occlusion leads to both effective functioning AND minimal damage to all components

11. Optimum functional tooth contacts
The musculoskeletal system is capable of applying much more force than necessary for effective function …so…
It’s important to establish occlusal conditions to accept heavy forces without damage while still being efficient

12. Optimum functional tooth contacts
Optimum occlusal conditions, then, require even and simultaneous contact of all possible teeth.
This maximizes the stability of the mandible…and
Minimizes the amount of force on each tooth

13. With only two posterior
contacts, all force is
loaded on that side causing
the muscle system to pull
the condyle on the unopposed side further into the mandibular
fossa. This causes an unnatural shift and possible damage to one or both sides of the TMJ.

14. With two posterior contacts on each side, the same load is more equally distributed and the mandible is more stable and balanced.

15. As the number
of occluding teeth increases,
the force to each tooth decreases
since the load is distributed over
a greater area.

16. This new information allows us to redefine the criteria for optimum functional occlusion:

17. This new information allows us to redefine the criteria for optimum functional occlusion:
Centric Relation coincides with maximum intercuspation = optimum functional occlusion = Centric Occlusion.

18. Centric Occlusion may or may not = Maximum intercuspation
The first Tooth Position when the condyles are in centric relation = Centric Occlusion
The occlusion of opposing teeth when the mandible is in centric relation. This may or may not coincide with the maximal intercuspal position.

19. Direction of force placed on teeth
Osseous tissue does not tolerate pressure forces
Pressure forces exerted on bone, cause bone to resorb (go away)
The periodontal ligament helps control these forces and provide stimulation
Pressure = bad
Tension = good
The periodontal ligament converts a destructive force (pressure) into an acceptable force (tension).
Periodontal
Ligament
Bone

20. Periodontal ligament accepts various directions of occlusal force
Cusp tip or fossa contact
Force is directed vertically through the long axis
Force is well accepted due to the alignment of the periodontal ligament fibers

21. Periodontal ligament accepts various directions of occlusal force
Contacts on inclines
A horizontal component causes tipping
Some areas of the periodontal ligament (PL) are compressed while others are elongated
Forces are not effectively dissipated to the bone

22. Criteria for optimum functional occlusion…
The definition must now include the concept that each tooth should contact in such a manner that the forces of closure are directed through the long axis of the tooth
This is also know as Axial Loading

23. Forces applied along the long axes of teeth are generally well tolerated
Axial Loading:
the process of directing
occlusal forces through the long axis of the tooth
Compare to pounding the top of a fencepost
With proper contact, posterior teeth receive force along the vertical or long axis in MI

24. 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

25. Axial loading accomplished in two ways:
Development of tooth contacts on cusp tips or flat surfaces, perpendicular to the long axis of the tooth (marginal ridges, bottom of fossae).
Tripodization – each cusp contacting a fossa in such a way that three contacts points are made
Both of these methods eliminate off-axis forces, allowing the PL to reduce forces to the bone

26. Which teeth can best accept horizontal forces?
Damaging horizontal forces of eccentric movement must be directed to the anterior teeth, positioned furthest from the fulcrum
Examining all anterior teeth, it is apparent that the canines are best suited to accept these forces. [WHY?]

27. Cuspids are best suited to accept horizontal forces of Occlusion
Long, thick roots
Better crown/root ratio
Surrounded by dense bone
Extensive periodontal ligament
Most proprioceptively sensitive tooth in the mouth

28. Canines disocclude the posterior teeth in lateral excursions. When
disocclusion
Guidance Canine
Canines disocclude the posterior teeth in lateral excursions. When
this condition exists, it is called canine guidance.

29. Scheme of Occlusion: Canine Guidance

30. Scheme of Occlusion: Canine Guidance
To restart movie, click on image!

31. IF canines not positioned well (or absent)
When restoring this occlusal scheme the best alternative is group function
Group function is when several posterior teeth on the working side contact during excursions
No contact on non-working side during excursions
No posterior contact during protrusive movements
Most desirable is canine plus premolars and the MB cusp of the first molar
More posterior than the MB cusp of first molar not desirable because of increased force that can be generated closer to the fulcrum (TMJ) and force vectors (muscles).

32. Group function
Laterotrusive (working) contacts must provide adequate guidance to disocclude teeth on the opposite side of the arch immediately… BECAUSE
Mediotrusive (non-working) contacts can be destructive due to the amount and direction of forces applied to the joint and dental structures (horizontal = bad)

34. Group Function: Working Side
Note: Shift of midline laterally and slightly anteriorly

35. Group Function: Balancing Side (No Contacts)

36. Scheme of Occlusion: Group Function
To restart movie, click on image!

37. Anterior Group Function
A form of articulation in which the canines and incisors (usually just the lateral incisors) function together to disocclude the posterior teeth during lateral and lateral protrusive excursions of the mandible. In this scenario the premolar would probably work in conjunction with the lateral incisor to support the lateral and lateral protrusive excursions.

38. Anterior and posterior teeth function differently
Posterior teeth accept forces well during closure of mouth. Because of their position in the arch, forces can be directed along the long axis of the teeth and dissipated
Posterior teeth function effectively in stopping the mandible during closure

39. ANTERIOR GUIDANCE
Posterior
Disocclusion
Anterior guiding contacts

40. Anterior and posterior teeth function differently
Anterior teeth are not positioned to accept heavy forces. Their labial angle makes it impossible to achieve axial loading.
They CAN direct eccentric forces
Illustrations Reprinted and modified from: Okeson, J.P. (2003). Management of Temporomandibular Disorders and Occlusion, 5th Ed. , St. Louis, MO: Mosby., with permission from Elsevier. Pg. 124

41. Malocclusion!
This patient has an anterior open bite and will not have the normal wear pattern of a young adult.
Note: This patient has no anterior guidance!

42. Anterior and posterior teeth function differently
Posterior teeth should contact slightly more heavily than anterior teeth in centric occlusion. This is called mutually protected occlusion.

43. Interferences Three Types:
Interference to the desired Occlusal scheme (Canine Guidance/Group function): excursive interference
eg. Mediotrusive/Non-working side interference
Prematurity (usually a high restoration)
Deflective Occlusal Contact (centric interference-usually natural)

44. Contacts on inclines (eccentric forces)
When forces are NOT effectively dissipated to the bone, a pathologic response may be elicited
Neuromuscular reflex activity
Avoidance
Protection
Figures reprinted from: Evaluation, Diagnosis, and Treatment of Occlusal Problems, 2nd ed., Peter Dawson, Mosby,1989. pg , with permission from Elsevier.

45. Deflective Occlusal Contacts
Arc of closure interferences
Centric Interferences
In these slides, the “red” areas indicate interferences. The indicated treatment is an occlusal adjustment to remove the interference.
Line of closure interferences
Figures reprinted from: Evaluation, Diagnosis, and Treatment of Occlusal Problems, 2nd ed., Peter Dawson, Mosby,1989. pg , with permission from Elsevier.

46. Summary
When the mouth closes, the condyles should be in the most supero-anterior (musculoskeletally stable) position, resting on the posterior slopes of the articular eminences with articular discs properly interposed. In this position, there should be even and simultaneous contact of all posterior teeth. Anterior teeth contact, but more lightly than posterior teeth

47. Summary
All tooth contacts should provide axial loading of occlusal forces when possible.
When the mandible moves into laterotrusive position, there should be adequate tooth-guided contacts on the laterotrusive side (working) to disocclude the mediotrusive (non-working) side immediately. The most desirable guidance is provided by the canines (canine guidance)

48. Summary
When the mandible moves in protrusive position, there should be adequate tooth-guided contacts on the anterior teeth to disocclude all posterior teeth immediately= Christensen’s effect
In the alert feeding position, posterior tooth contacts should be heavier than anterior tooth contacts.