Dental Anatomy Lecture 10

What is Maximum Intercuspation (MIP or MIC)?

The complete intercuspation of the opposing teeth independent of condylar position, sometimes referred to as the best bite of the teeth regardless of the condylar position

A tooth-dictated position

What do the maxillary lingual cusps occlude with in MIC?

Mandibular fossa or marginal ridges

What do the mandibular buccaneers cusps occlude with in MIC?

Maxillary fossa or marginal ridges

What three areas is force applied to the skull in occlusion?

The two TMJs and the teeth

What is the average human bite strength?

120-162 PSI

Where is bite force transmitted to?

The TMJs

The joints can be damaged if not controlled

Centric relationship (CR)

The position of the condyle in the fossa when the teeth are not contacting and the elevator muscles contract

A maxillomandibular relationship, independent of tooth contacts, in which the condyle articulate in the anterior-superior position against the posterior slopes of the articular eminences; in this position, the mandible is restricted to a purely rotary movement; from this unstrained, physiologic, maxillomandibular relationship, the patient can make vertical, lateral, or protrusive movements; it is a clinically useful, repeatable reference position

When do we use CR?

When a pt does not have MIC

What is Centric Relation considered the most reliable for?

Reliable, repeatable reference points obtainable in edentulous and dentate patients for accurately recording the relationship between mandible and maxilla and ultimately for controlling the occlusion

When do the muscles of mastication function with less intensity?

When the condyle are in centric relation at the time the teeth are in maximum intercuspation

Electromyography (EMG)

Measures muscle response or electrical activity in response to a nerve’s stimulation of the muscle

How are the condyles in the fossa in CR?

In their most superior-anterior position in the articular fossae

How does the temporalis muscle position the mandible in the TMJ?

Superiorly

How does the medial pterygoid position the mandible in the TMJ?

Superiorly and anteriorly

How does the masseter muscle position the mandible in the TMJ?

Superiorly and anteriorly

The articular disc

Composed of dense fibrous connective tissue devoid of nerves and blood vessels

This allows it to withstand heavy forces without damage or pain

Separates, protects and stabilizes the condyle in the fossa during mandibular movements

What is positional stability determined by?

The muscles that pull across the joint and prevent dislocation of the articular surfaces (elevator muscles)

What do the directional forces of the elevator muscles determine?

The optimal orthopedically stable joint position

This is an orthopedic principle that is true for all joints

Muscles stabilized joints, therefore, every mobile joint has a musculoskeletally stable position

What are the major muscles that stabilize the TMJ‘s?

The elevators

What is the direction of force placed on the condyles by the masseter and medial pterygoids?

Superoanterior

What three muscle groups are primarily responsible for joint position and stability?

Temporal muscles, masseter, and pterygoids

The posterior aspect of the mandibular fossa

Quite thin and not meant to bear stress

Are the condyle retrodiscal tissues load bearing?

No