Criteria for Optimum Functional Occlusion

Department of Endodontics, Prosthodontics and Operative Dentistry

University of Maryland, Baltimore

Dr. Pauline Hayes GarrettDr. Patricia W. Kiln

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. 421-433

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.

The masticatory system consists of an extremely complex and interrelated group of muscles, bones, ligaments, teeth and nerves

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.

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

Anatomic structures of the TMJ (temporomandibular joint):

Articular disc – dense fibrous connective tissue; no nerves or bloodvessels so it can endure heavy forces without damage or pain.

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.

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

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 

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)

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.

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

CENTRIC RELATION: Most musculoskeletally stable position of the TMJ

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.

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

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

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

With only two posteriorcontacts, all force isloaded on that side causingthe muscle system to pullthe condyle on the unopposed side further into the mandibularfossa. This causes an unnatural shift and possible damage to one or both sides of the TMJ.

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

As the numberof occluding teeth increases,the force to each tooth decreasessince the load is distributed overa greater area.

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

Centric Relation coincides with maximum intercuspation = optimum functional occlusion = Centric Occlusion.

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

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.

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).

Bone

PeriodontalLigament

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

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

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

Forces applied along the long axes of teeth are generally well tolerated

• Axial Loading:the process of directingocclusal 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

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

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

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?]

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

Canines disocclude the posterior teeth in lateral excursions. Whenthis condition exists, it is called canine guidance.

Posterior Posterior disocclusiondisocclusion

Guidance Canine

Scheme of Occlusion:Canine Guidance

Scheme of Occlusion: Canine Guidance

To restart movie, click on image!

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).

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)

Group Function:Working Side

Note: Shift of midline laterally and slightly anteriorly

Group Function:Balancing Side

(No Contacts)

Scheme of Occlusion: Group Function

To restart movie, click on image!

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.

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

ANTERIOR GUIDANCE

Anterior Anterior guiding guiding contactscontacts

Posterior Posterior DisocclusionDisocclusion

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

• 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!

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.

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)

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.438-439, with permission from Elsevier.

Deflective Occlusal Contacts

In these slides, the “red” areas indicate interferences. The indicated treatment is an occlusal adjustment to remove the interference.

Arc of closure interferences

Line of closure interferencesFigures reprinted from: Evaluation, Diagnosis, and Treatment of Occlusal Problems, 2nd ed., Peter Dawson, Mosby,1989. pg.438-439, with permission from Elsevier.

Centric Interferences

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

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)

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.