Occlusion has been described as the most important subject in all the disciplines of dentistry, and for good reason, because the teeth come together, and function together. Occlusion also been described as one of the most confusing subjects in all disciplines of dentistry. Attempts to understand Occlusion have ranged from mechanical, mathematical, and geometrical analysis of tooth contact and jaw movement, to the biological and functional analysis based on the behavior of natural dentitions under different environmental conditions.
Terminology and definitions
Occlusion: the static relationship between the incising or masticating surfaces of the maxillary or mandibular teeth or tooth analogues.
Occlusion = contacts between teeth
While articulation refers to static and dynamic contact relationship between the maxillary or mandibular teeth as they moves against each other during function.
Centric relation : maxillomandibular relationship in which the condyles articulate with the thinnest avascular portion of their respective discs with the complex in the anterior-superior position against the shapes of the articular eminencies. Or – is the most retruded position of the mandible to the maxilla when the condyles are in the most posterior unstrained position in the glenoid fossa from which , lateral movement can be made , at a given degree of jaw separation (bone –to- bone relation).
Centric Occlusion: is the Occlusion of opposing teeth when mandible in the Centric relation. This may or may not coinside with the maximum intercuspal position in natural dentition . ( tooth – to- tooth relation)
In complete denture centric occlusion, the facial cusps of the mandibular teeth contact the central fossa of maxillary teeth, while the lingual cusps of maxillary teeth fill into the central fossae of the mandibular teeth. This facial overlap prevents cheek biting when the dentures in Maximal intercuspal position (intercuspation). The complete intercuspation of the opposing teeth independent of condylar position.
In the lower compartment of the TMJ Between the superior surface of the condyles and the inferior surface of the articular disk.
Trarsilatory, or gliding, movements of the mandible)
Take place in the upper compartment of the TMJ Between the superior surface of the articular disk as it moves with the condyles and the inferior surface of the glenoid fossa.
The Mandibular movement also can be classified into opening, closing, protrusive and lateral.
In the lateral movement we may have :
Working side(A) is the side that the mandible moves towards in a lateral excursion.
Non-working side(B)-is the side that the mandible moves away from during a lateral excursion. occlusal interferences-defines as any tooth contact that inhibits the remaining occluding surfaces from achieving stable and harmonious contacts.
How does mandibular movement effect on occlusion?
To make teeth work in coincidence with the mandibular movement in different functional situation
To understand various aspects of occlusion
To select and adjust recording devices and articulators
To arrange artificial teeth
occlusion in the Natural dentition are:- the pathways the teeth take are dependent on the cusps and morphology of the occlusal surfaces of the teeth, as well as on the morphology of the joints. In chewing, the lower teeth move across the uppers, passing through the intercuspal position, usually without stopping. The intercuspal position is used during chewing, swallowing, and during deliberate clenching of the teeth
The concepts of natural occlusion are:-
mutually protect occlusion Canine protection occlusion( CPO) The basic premise of CPO is that:
on laterotrusive movements of the mandible, only the canines(possibly first premolars) contact and therefore protect the remaining dentition from adverse occlusal torsion forces on contacts to and from centric occlusion(and/or centric relation).
Furthermore, it is contended that CPO is the optimal(ideal) type of functional occlusion for the natural dentition and is the functional occlusion type toward which restorative and orthodontic treatments should be directed. .
The advocates of CPO argued that humans innately possess the long and dominant canine that is evident in carnivorous animals.
They further argued that the canine is the strongest human tooth type and has the most sensitive proprioceptive fibers.
They therefore concluded that the canines are the best teeth to protect the occlusion from eccentric forces that occur on movement to and from centric occlusion( and /or centric relation).
Group function exists when there are multiple contact relations between the maxillary and mandibular teeth in lateral movements on the working side whereby simultaneous contact of several teeth acts as a group to distribute occlusal forces.
Balanced occlusion This type of occlusion rarely found in natural dentition and considered as an occlusal interference. The balancing contacts, for the most part, were contacts and not interferences. Next, most balancing side contacts were on the distal sides of the posterior molars.
occlusion in complete denture
The absence of direct attachment between the dentures and the patient's musculo- skeletal system requires a different set of guidelines of good occlusal practice, in addition all the teeth are attached to one base so the force on a single tooth may affect all the base.
objectives of occlusion in complete denture:-
Preservation of remaining tissues
Propel masticatory eificiency.
Enhancement of denture retention, support and stability.
Enhancement of phonetics and esthetics
Requirements of complete denture occlusion
stability of occlusion at centric relation and in an area forward and lateral to it
2-Balanced occlusal contacts bilaterally
3-Control of horizontal force by buccolingual cusp reduction according to residual ridge resistance, form and interarch distance
4-Functional lever balance by favorable tooth-to-crest ridge position
5-cutting, penetrating, and shearing efficiency of occlusal surfaces
6-Anterior incisal clearance during all posterior masticatory movement.
Concepts of denture occlusion
3- Monoplane occlusion.
Balanced occlusion: Means bilateral simultaneous anterior and posterior occlusal contact of the upper and lower teeth in centric and eccentric positions(protrusive and lateral) OR is the continuing contacts of as many mandibular and maxillary artificial teeth as possible in all excursive movements away from, and into, the position of maximum intercuspation.
Maximal intercuspal position:
Note the simultaneous Protrusive contact between anterior and posterior teeth.
Non-Working side Working side
Note the simultaneous contact in the teeth on both side in the lateral movement.
Factors of balanced occlusion :
mandibular guidance generated by the condyle and articular disc traversing the contour of the glenoid fossae.
the influence of the contacting surfaces of the mandibular and maxillary anterior teeth on mandibular movements
The plane of occlusion:
is established by the height of the lower cuspid and in the posterior by the height of the retromolar pad. It is also related to the ala- tragus line as in the upper arch.
The compensating curve:
the arc introduced in the construction of complete removable dental prostheses to compensate for the ing influences produced by the condylar and incisal guidance during lateral and pro(K mandibular excursive movements
Cusps on teeth or the inclination of cuspless teeth:
When a balanced occlusion is selected you have to use adjustable articulator, record vertical and centric jaw relations first then a protrusive record should be made.
in order to set the condylar guidance in the articulator:
1. place a v-shaped" notches.
2. The patient should be allowed to protrude a minimum of 5-6 mm, but less than 12 mm.
3. Elastomeric registration material is placed over the entire mandibular rim and the patient closes in an anterior position.
4. when the material sets, the record bases and registration are removed, placed on the articulator.
5. The condylar elements are released from the hinge position, the instrument protruded. and the records approximated The condylar elements are rotated until there is maximum interdigitation of the registration and opposing occlusal rins
The incisal guidance angle is formed by the vertical overlap(overbite) between the teeth ltis only dependent on the amount of horizontal overlap(overiet. In natural teeth, these dimensions of overbite and on cijet are determined by the positions of the teeth in complesedentures, they are determined by other factors, mainly aesthetics, phonetics, and function, This means they can be controlled by the dentist, within the limitations of the other factors that determine owerall tooth position
This diagram shows the difference in the guidance engle degree different ovejet but with same overbite
occlusal Plane cannot be altered substantially since functional requirements dictate position. It usually govern by the ala-tragus line in the upper arch and position in relation to the corner of the mouth and retromolar pad in the lower arch The degree of cuspal Inclination is dependent on multiple factors(residual ridges, neuromuscular contro, esthetics, etc). However in genera it is better to reduce cuspal inclination to help reduce horizontal forces of occlusion.
The compensating curve is very helpful in obtaining balanced occiusion and depending on the posterior tooth forms it can easily be corrected to facilitate posterior tooth contacts in eccentric positions.
The lingual cusp tips should be in contact with the central fossae of the opposing mandibular teeth. The cuspal inclines of the mandibular teeth are relatively flat, resulting in potentially less lateral forces and displacement during function, Theoretically, there should be less lateral displacement of the denture and less lateral forces during function when using lingualized posterior denture teeth. In lingualized occlusion you may use flat lower teeth.
Potential for bilateral balance
Centralizes vertical forces
Minimizes tipping force
Facilitates bolus penetration(mortar and peste effect) Easier to adjust occlusion
Simpler technique, less precise CR records
May be used in Class ll. Class Ill and crossbite
1-for patients with severe alveolar bone resorption resulting in little or no ridge.
2-Patient have a discrepancy between the size of the narrowing and receding upper ridge compared with the widening and receding lower jaw.
3-This setup technique is also indicated for patients with implant-supported overdentures to eliminate lateral forces that can rock abutments loose over time.
4-Additionally, lingualized occlusion is appropriate for intra coronal attachments to avoid breakage.
5-High esthetic demands
6-Displaceable supporting tissues.
7-Weak muscles of mastication
8-Previous successful denture with lingualized occlusion.
This concept of occlusion assumes that the anteriorposterior plane of occlusion should be parallel to the denture foundation area and not dictated by condylar inclination.
The plane of occlusion is completely flat and level.
There is no curve of Wilson or curve of spee (compensating curve) incorporated into the set up.
There is no vertical overlap of the anterior teeth.
When using this concept of occlusion the patient is instructed not to incise the bolus.
Indications of Monoplane occlusion:
Jaw size discrepancies, maloodusions
cross-bite, a II, III
reduces horizontal forces
Uncoordinated java movements
Types of occlusal scheme:-
An anatomic tooth : is one that is designed to simulate the natural tooth form. The standard anatomic tooth has inclines of approximately 33 degree or more.
Advantages of Anatomic occlusion Anatomic
Better penetration of food bolus,
Decrease of vertical stresses.
Harmony with muscles of mastication and TMJ during functional and non- functional movements.
Disadvantages of Anatomic occlusion:
precise technique required.
2. greater lateral forces
3. more time, not long-lasting, require occhusal adjustment
4. difficult to tooth position in class II, IIÏ
when the cusp incline is less steep than the conventional anatomic tooth of 33 degree it can be classified as a modified or semianatomic tooth. It can be considered basicaly anatomic and will articulate in three di
Advantages of Semi-anatomic Cusp Teeth :-
2. Good chewing efficiency
3. Aalanced occlusion de
4. Less lateral forces
5. Functional occlusal balance
Disadvantages of Semi-anatomic Cusp
1. Same as for anatomic teeth.
2. More difficult to achieve cross arch, cross tooth balance.
3. Esthetics reduced somewhat by decreasing the incisal guidance of anterior teeth.
A non-anatomic tooth
is essentially flat and has no cusp heights to interdigitate with an opposing tooth and Non anatomichas suloi to enhance its comminuting effect on food. They articulate in only two dimensions.
Advantages of Non-anatomic occlusion
1. Slightly more esthetic than neutrocentric occlusion.
2. patients with poor neuromuscular coordination, difficult to obtain precise, repeatable jaw relation records.
3. Less time involved in set up and articulation.
4. patients with cross bite or class llI relationships and particularly for patients with class II relationships who move the mandible far forward in functional relationships.
Disadvantages of Non-anatomic occlusion
1- Use of a compensating curve may cause the same damaging effects as cuspal inclines.