STATIC AND FUNCTIONAL OCCLUSION - 1

Occlusion

Static relationship between incising/masticating surfaces of maxillary & mandibular teeth or analogues.

Occlusion (functional definition)

Relationship between maxillary & mandibular teeth when in functional contact during mandible activity.

What does occlusion involve beyond teeth?

Teeth, jaws, TMJ, ligaments, muscles of mastication, investing tissues.

Who proposed the first classification of occlusion?

Edward H. Angle, 1898-1899.

Angle's definition of normal occlusion

Class I: MB cusp of maxillary 1st molar aligns with buccal groove of mandibular 1st molar.

Significance of Angle's classification

Basis for orthodontics and treatment planning of malocclusion.

NIH conclusion about malocclusion

Malocclusion ≠ always pathology; many patients adapt without issues.

Bilateral balanced occlusion

Denture setup concept where both working and non-working sides contact simultaneously for stability.

Why did flat plane occlusion fail?

Not physiologic; did not provide stability in natural dentition.

Why was centric relation introduced in dentures?

Provided a repeatable jaw position for record taking.

How many definitions of Centric Relation (CR) exist?

Over 26 since its introduction.

What is Centric Relation (CR)?

Most anterior-superior position of condyle-disc assembly in glenoid fossa, independent of tooth contact, restricted to purely rotary movement about transverse horizontal axis.

Is CR a tooth-to-tooth or jaw-to-jaw relationship?

Jaw-to-jaw.

What is Centric Occlusion (CO)?

First tooth contact when mandible is in CR.

What is Maximum Intercuspation Position (MIP)?

Occlusal position of maximal intercuspation of teeth, independent of condyle position.

Do CR and MIP coincide?

Not always; in most patients they differ.

What are the 4 major philosophies of occlusion?

Centric relation-based, Conformational, Neuromuscular, Joint-based.

What is the focus of CR-based philosophies?

Build occlusion with condyle seated in CR.

What are the 3 main CR schools?

Gnathology, Bioesthetics, Pankey/Dawson.

What is Gnathology?

1930s Dr. Stallard: Equal centric stops, long axis loading, anterior contacts only in protrusion.

What is Bioesthetics?

1960s Dr. Bob Lee: Specific anterior form (long centrals, short rounded laterals, long pointed canines) to create anterior coupling, prevent bruxism and wear.

Pankey/Dawson philosophy

1970s 'Functional Occlusion': CR as reference.

Long Centric

Slide (1.5-2.0 mm freedom CO→MIP without vertical change).

How is Long Centric achieved?

Flatten mandibular incisal edges and broaden maxillary cingulum to allow horizontal slide without opening vertical.

Conformational occlusion

Maintain patient's existing bite if no occlusal problems; common in general dentistry.

Neuromuscular occlusion

1967 Dr. Jankelson: Uses EMG/TENS to relax muscles; trigeminal nerve role emphasized; condylar position guided by physiologic muscle rest.

Joint-based occlusion

Uses MRI/CBCT to assess condyle-disc relationship; does not assume healthy joint; applied in unstable patients.

TMJ surface

Covered by fibrocartilage (not hyaline cartilage).

Parts of the articular disc

Anterior band, intermediate zone (thinnest), posterior band.

Insertion of superior head of the lateral pterygoid

Anterior band of disc.

Bilaminar zone

Posterior attachment: superior strut to mandibular fossa, inferior strut to condyle.

TMJ movement during opening

First 10% rotation (hinge), remainder translation along eminence.

Anterior guidance

Anterior teeth guide posterior disclusion in protrusion/excursions.

Canine guidance

Mandibular canines contact maxillary canines in lateral movement, discluding posteriors.

Mutually protected occlusion

Anteriors protect posteriors in excursions, posteriors protect anteriors in MIP.

Group function

Multiple teeth on working side share occlusal load in lateral excursion, non-working side discluded.

When does group function usually occur?

In worn dentitions, missing or periodontally compromised canines.

Benefits of protected occlusion

1) Better food penetration, 2) Posterior protection in excursions, 3) Posterior forces along long axis, 4) Efficient shearing from ridges.

Agreement among occlusion philosophies

1) Occlusion must be part of every patient assessment, 2) Even contacts, 3) Anterior guidance in excursions, 4) Teeth within muscle forces, 5) Interferences eliminated.

Main controversy in occlusion

Static occlusion (teeth only) vs functional occlusion (teeth, joints, muscles, soft tissues).

Occlusion linked to TMD debates

Different philosophies propose different causes/treatments for TMD.

Percentage of TMD that is myogenous

~90% of TMD originates from muscles of mastication.