OCCLUSION : Concept For Restoring Teeth
It is must for a dentist to provide occlusion that successfully permits efficient masticatory function. To maintain harmony in occlusion posterior teeth must pass close to but not contact the opposing teeth during mandibular movement.
Fundamentals of occlusion
1. Occlusal interferences:
Occlusal interferences are interferences at occlusal contact that produce mandibular deviation from closure to maximum intercuspation. There are 4 types of occlusal interferences:
C. Non working
Centric interference is a premature contact when the mandible patient centric relation. It causes deviation in posterior, anterior and or lateral direction.
Working interference: Working interference occurs in which the direction of mandible has moved that is the working side.
Non-working interference: Non-working interference is on the opposite side in which the mandible has moved that is the non working side in the lateral excursion.
Protrusive interference: Protrusive interference is a premature contact between the mesial aspect of mandibular posterior teeth and the distal aspect of maxillary posterior teeth.
2. Normal versus pathologic occlusion:
The present concept relation is the most anterior superior position of the condyle in the glenoid fossa.
Pathologic occlusion is when there is Disharmony between the teeth and temporomandibular joint resulting in trauma to teeth, musculature and joint.
While restoring, dentist must strive to produce an occlusion that requires minimum adaptation.
Okeson described criteria for such occlusion:
a) During closure, condyles or in the most superior anterior position against the slope of eminence. Anterior teeth are slight contact and the posterior teeth are in the solid contact.
b) Occlusion forces directed in the long axis of the teeth.
c) In protrusive excursion, anterior tooth disocclude the posterior teeth.
3. Organization of occlusion:
There is recognized concept that does describe the teeth contact in various excursive movement of mandible:
A. Bilateral balanced occlusion:
According to GPT, it is bilateral, simultaneous, anterior and posterior occlusal contact of teeth in centric and ecentric position
According to bilateral balanced occlusion, maximum number of teeth should contact in all excursive positions of mandible.
It is difficult achieve bilateral balanced occlusion natural dentition and fixed partial dentures. But Is Particularly useful in complete denture fabrication since contact on non working side prevents the tipping movement and maintains denture stability.
B. Unilateral balanced occlusion:
aka: Group function
According to GPT, multiple contact relations between the maxillary and mandibular teeth in lateral movement on the working side, where by simultaneously contact of several teeth act as group to distribute occlusal forces.
There are contacts on the laterotrusive (working side) and no contact on mediotrusive (non working side) in excursive movement. Thus load is distributed among the periodontal support of all posterior teeth on the working side. There is no posterior tooth contact in protrusive movement.
As the concept of unilateral balanced occlusion evolved, some degree of freedom of movement in anterior posterior direction advantages, this concept is termed as long centric concept.
C. Mutually protected occlusion:
aka: Canine protected occlusion
According to this concept, posterior teeth protect anterior teeth and vice versa. Centric relation coincides with the maximum intercuspation.
4. Effects of an anatomic determinants:
A. Molar disocclusion:
When patient is subjected with repeated mandibular movements there is some deviation in the path of tracing. Measurement of separation of molar disocclusion showed separation of 0.5mm in working, 1mm in non working, and 1.1mm in protrusive movement.
B. Condylar guidance:
Inclination of condylar path may vary from steep to shallow impatient to patient during excursive movement. It forms an average angle of 30.4 degree with horizontal reference plane. The cusp height is kept longer, if protrusive inclination is steep. However, if inclination is shallow, cusp height must be shorter.
C. Anterior guidance:
During protrusion of mandible, the incisal edges of mandibular anterior teeth slide over the lingual concavity of maxillary anterior teeth and posterior teeth disocclude. The track of incisal edges from maximum intercuspation to edge to edge occlusion is termed as protrusive incisal path. The angle varies from 50-70 degrees.
1.Methods of checking occlusion contact:
A. Occlusal tapes:
Patient is medicated with antisialogogues and then teeth are thoroughly wiped. A 15 micro GHM occlusal tape is held with the help of miller’s forcep and mandible is guided to centric relation contact position.
B. Shim stock:
A 12 Micron foil is held between the teeth help of mosquito forceps and checked for resistance on pulling.
C. Sandblasted surfaces:
Used for metal surfaces. Occlusal Surface is sandblasted with 15 micron aluminium oxide. Matte finished restoration is placed in the patient mouth and movements are made. Shiny surface on the particular area depicts interference or high points which are then removed.
It is an electronic device which enables tooth contact on a monitor screen. For exact location T- scan is used conjunction with tapes, shim stock and sandblasted surfaces.
2. Centric relation contact position (CRCP):
It is the initial contact during mandibular closure with the condyles in superior most position.
3. Movement from centric relation contact position to intercuspal position:
Deflective contacts in centric relation lead to a path of closure which avoids single tooth contact. It can be subdivided into two types-
a) Large vertical:horizontal ratio
b) Large horizontal:vertical ratio
Patient with Large vertical tends to have little horizontal movement of condyles, whereas those with large horizontal have larger horizontal movement of condyles.
4. Lateral positions and excursions:
It is divided into-
A. Working side contact:-
It is further divided into-
a) Group function
b) Canine guidance
B. Non working side contacts
5. Straight protrusion:
Patient Is Instructed to close into ICP and then flight straight forward until the incisors meet edge to edge.
6. Lateral protrusion:
Patient is instructed to close in ICP then move forward and to one side. Protrusive contacts on both sides are marked with marking tapes.
Selective grinding is indicated to improve minimal occlusion conditions and can be used in managing certain temporomandibular disorders.
An anterior slide of less than 2mm can be successfully eliminated by selective grinding procedure. When the slide has greater horizontal component, it is more difficult. If it is almost parallel with arc of closure, elimination is usually easier.
1. Treatment goals for selective grinding:
A. Developing an acceptable centric relation contact position:-
The major goal is to develop a stable intercuspal contact position when the condyles are in CR that is to eliminate the CR slide.
CR slide can be classified-
a) Anteriosuperior slide
b) Anteriosuperior and right slide
c) Anteriosuperior and left slide
A. Achieving the centric contact position:-
Centric relation is achieved bimanually. Teeth are brought lightly together and first tooth contact is identified. Mouth is then wide opened and teeth are dried. Articulating paper is placed and patient is asked close till the first contact. Mandible is again guided to CR till the teeth lightly tapped on the paper. Contact areas are located for maxillary and mandibular teeth. A small green stone in high speed one piece is used for reshaping the inclines into cusp tips or flat surfaces, to eliminate the CR slide. When a contact is located on an incline near the central fossa, it is reshaped into a flat surface. Teeth are re-dried, remarked, and revalidated until only the cusp tip contact a flat surface. All contracting incline areas must be eliminated and sound cusp tip to flat surface contacts are established. When a cusp tip does not contact an opposing tooth surface during ecentric movements, the opposing flat surface is reduced. When a cusp tip does contact an opposing tooth surface, the cusp tip is reduced. Ideally there should be 4 CR contacts on each molar and 2 on each premolar. Minimum goal is to achieving at least 1 CR contact for every opposing tooth. Anterior teeth that contact heavily during the development of posterior CR contacts are reduced. When the patient closes and taps in CR, all posterior teeth are felt evenly.
b) Developing an acceptable lateral and protrusive guidance:-
Canines should contact during laterotrusive movements and disocclude all posterior teeth. Acceptable laterotrusive contacts between the buccal cusp and not the lingual cusp. Lingual laterotrusive contacts and mediotrusive contacts are always eliminated since they produce occlusal instability. During a straight protrusive movement the mandibular incisors pass down the lingual surfaces of maxillary incisors, disoccluding the posterior teeth.
Determining the plane of occlusion
A Correct plane of occlusion allows protrusion without posterior interference. If curve of spee is too concave or too high posteriorly, one or more posterior teeth may interfere in protrusive movement.
Incisal plane must be parallel with the interpupillary line.
Flatter the anterior guidance, lesser the capability of disoccluding.
3. Irregular occlusal plane caused by lost but unreplaced posterior teeth:
Teeth have a tendency to lean into space while the unopposed teeth in the opposite arch supraerupt until they meet. The resultant is tilted or elongated teeth. Effect is same as curve of spee that is too high posteriorly. When an upper molar has supra erupted, it should be shortened to permit protrusion of mandible without posterior contact. The same is true for lower posterior teeth that have invaded into the space.
4. Curve of spee too low posteriorly:
There is no major problem if it is kept too low but if it is grossly over done it can create poor aesthetic.
5. Curve of Spee too high or low in front:
If lower premolars are higher than the cuspids, they can interfere with the anterior protrusive guidance. If the lower premolars are lower than anterior, they result in poor aesthetics.
Decision on occlusion scheme prescribed should be made before fabrication of definitive restoration.
1. Gnathological scheme:
Movements of condyles in the fossa determine the occlusal form. This scheme is suitable for large vertical: horizontal ratio cases where CRCP and IP coincide. Teeth are waxed up on a fully adjustable articulator and cusp fossa tripod contacts are provided.
2. Long centric:
Long centric scheme is described in one of my blog post. Click here to read about long centric.
3. Pankey-Mann-Schuyler concept:
Functionally generated path technique is used for wax up of upper posterior and plane is determined on curve of Monson. Absence of non working side contact and group function on working side with an area of freedom not more than 0.5mm.
4. Yuodelis scheme for advanced periodontitis cases:
The aim is for simultaneous contact of posterior teeth in CRCP coinciding with IP. Anterior disocclusion is provided for protrusive excursions and canine disocclusion for lateral excursions. cuspal Anatomy is arranged so that if Canine disocclude, posterior teeth drop into group function.
5. Nyman and Lindhe scheme for extremely advanced periodontitis cases:
No emphasis is placed on contacts but even contacts should be provided in IP and emphasis on supragingival margin placement of restorations. Anterior disocclusion is provided when distal support is present. In long tooth borne cantilevered restorations, simultaneous contacts are provided on cantilever.