Complete Denture Occlusion Rola M. Shadid, BDS, MSc

Occlusion the static relationship between the incising or masticating surfaces of the maxillary and mandibular teeth, or tooth analogs Articulation the contact relationship between the occlusal surfaces of teeth during function

Centric occlusion Eccentric occlusion * Protrusive occlusion Lateral occlusion an occlusion other than centric occlusion

Non working (balancing) side Working side the side toward which the mandible moves in a lateral excursion Non working (balancing) side that side of the mandible that moves toward the median line in a lateral excursion.

Occlusal Schemes For CD Balanced articulation Nonbalanced articulation (linear or monoplane articulation) Lingualized articulation Functionally generated occlusal scheme

Balanced Occlusion/Articulation Bilateral simultaneous contact betw. anterior & posterior teeth during all centric and eccentric positions There should be no interferences during movement from centric position to eccentric positions The movements should be in harmony with TMJ & neuromuscular control

Advantages of Balanced Occlusion To improve stability & retention To decrease soreness & resorption of residual ridge To improve oral comfort of the patient

Mechanics Of Balanced Occlusion Christensen’s phenomenon* *In natural teeth or in unbalanced occlusion, when the mandible moves in protrusive direction, the condyles move down the slope of the glenoid fossae, causing the whole mandible to move downwards and the posterior teeth to separate. This is separation, called Christensen’s phenomenon. When mandible is protruded, only the incisal edges of upper and lower anterior teeth contact. Such an occlusion in complete denture could cause tipping and instability of the denture in posterior section.

How Could You Achieve Balanced Occlusion In CD?

Factors That Affect Occlusal Balance

Factors Affecting Balanced Occlusion (Hanau’s Quint) * 1. Condylar Guidance 2.  Incisal Guidance 3.  Plane of occlusion Cuspal inclination Compensating curve. *Rules for balanced denture articulation including incisal guidance, condylar guidance, cusp length, the plane of occlusion, and the compensating curve described by Rudolph Hanau in 1926. Except for the condylar guidance, all factors can be altered by dentist.

Condylar Guidance* Mandibular guidance generated by the condyle and articular disc traversing the contour of the glenoid fossae The posterior determinent of mandibular movement * When mandible is protruded, the condyles travel downward and forward along the articular eminence. This slope along which the condyles travel forms the condylar guidance because it guides the movement of condyles.

Condylar Guidance Angle The angle formed by an imaginary horizontal line at the superior head of the condyle and the path that the condyle will pass through during function Varies from individual to individual because of anatomical differences

Incisal Guidance * It’s the influence of the contacting surfaces of the mandibular & maxillary anterior teeth on mandibular movement * When the mandible is protruded, the lower incisors glide downwards along the lingual slopes of upper incisors. Thus the lingual slopes of upper anterior teeth, the overbite and overjet guide the forward movement of the mandible.

Incisal Guidance Angle The angle formed by the intersection of the plane of occlusion and a line within the sagittal plane determined by the incisal edges of the maxillary and mandibular central incisors when the teeth are in maximum intercuspation

Incisal Guidance Angle This angle varies directly with the vertical overbite and inversely with the horizontal overjet This angle is set to 10˚ in CD and not exceeding 20˚

Incisal Guidance ↓ Incisal Guidance Angle by ↑ horizontal overlap

Incisal Guidance For CD, the incisal guidance should be as shallow as esthetics and phonetics will permit when arrangement of anterior teeth to reduce protrusive displacing forces

Incisal Guidance ↓ Incisal Guidance Angle by either:* ↑ horizontal overlap ↓ vertical overlap * When very little overjet can be set (usually due to ridge position and jaw relation problems), a balanced occlusion should be set to have less, or in some cases, no overbite. This will prevent incisor contact causing immediate separation of the posterior teeth in excursive movements.

If Increased Incisal Guidance Angle For CD? During protrusion: Upper denture drops at the back Lower denture slides backward

Its inclination can be altered slightly * Plane Of Occlusion Its inclination can be altered slightly * It is not as important as other factors *The inclination of occlusal plane can be altered to achieve occlusal balance. However, altering the occlusal plane can lead to serious problems and so has a less important role.

Cusp Height & Angulation * It is the smooth gliding of the cusp tips along the cusp inclines of the opposing teeth to provide balanced articulation *Cusp angle: It is the angle between palatal incline of mesiobuccal cusp and horizontal plane

Cusp Height & Angulation Anatomic teeth are easier to balance than nonanatomic teeth Cuspal inclines should not be too steep as it can increase lateral forces It is possible to decrease cuspal height by using compensating curves

Compensating Curves Artificial curves introduced into complete denture occlusion to achieve balanced occlusion Are among the most important determinents of occlusal balance

Compensating Curves The anteroposterior curving (in the median plane) and the mediolateral curving (in the frontal plane) within the alignment of the occluding surfaces and incisal edges of artificial teeth that is used to develop balanced occlusion

The Curvatures In Natural Dentition Curve of Spee An arc of a circle 65mm to 70mm radius that touches the tips of all the mandibular teeth when the skull is viewed laterally; when continued it touches the anterior surface of the condyles

The Curvatures In Natural Dentition Curve Of Monson A proposed ideal curve of occlusion in which each cusp and incisal edge touches or conforms to a segment of the surface of a sphere 4 inches (102mm) in radius with its centre in the region of the glabella.

Compensating Curves Anteroposterior curve * Mediolateral curve ¤ * It is incorporated into artificial occlusion raising the distal portions of first and second molars to conform to a curve. This curve compensates for the christensen’s phenomenon. ¤ the curve is obtained by tilting the upper molars such that the buccal cusps are higher then the palatal cusps. Consequently, the lower molars are tilted lingually. It compensates for wedge like opening formed in nonworking side when the mandible is moved laterally.

Compensating Curves The steepness of the curve necessary to achieve balance is the result of guiding influence of angle of condylar guidance and angle of incisal guidance It is functionally and mechanically advantageous to keep compensating curve as modest as possible → This is accomplished by setting as shallow an incisal guidance as phonetics, esthetics permit

Theilmann’s Formula IGxCG = CHxOPxCC

According To The Formula To achieve balanced occlusion: For high condylar guidance we need to have high compensating curve, occlusal plane and cuspal height. To achieve balanced occlusion: For high incisal guidance we need to have high compensating curve, occlusal plane and cuspal height.

According To The Formula To achieve balanced occlusion, the steeper the condylar guidance, the greater the cusp height toward the posterior or the steeper the compensating curves

According To The Formula To achieve balanced occlusion, the steeper the compensating curves, the less the cusp height toward the posterior

Question Q) Suppose that the incisal guidance is set and the condylar guidance is steeper than your chosen 20 degree teeth. To obtain balanced occlusion in your complete denture, what should you do? steepen the compensating curves in both sagittal and frontal planes steepen the compensating curves in only sagittal but not frontal plane decrease the inclination of occlusal plane decrease the steepness of compensating curves in both sagittal and frontal planes steepen the condylar guidance none of the above

Occlusal Schemes For CD

Philosophies of Denture Occlusion Many philosophies of arranging denture occlusion No definitive scientific studies prove one occlusal scheme clearly superior

Occlusal Schemes Balanced articulation Nonbalanced articulation (linear or monoplane articulation) Lingualized articulation Functionally generated occlusal scheme

Lingualized Occlusion Max. lingual cusps contact central fossae/marginal ridge ~ 1mm space between buccal cusps

Lingualized Occlusion Lingualized occlusion is a type of bilaterally balanced occlusal schemes * Anatomic teeth are used in the maxilla opposing a flat-cusped, or shallow cusped mandibular tooth. * Lingualized occlusion differs from traditional fully balanced schemes by having only the lingual cusp of the maxillary tooth contacting the mandibular teeth to maintain this contact

Lingualized Occlusion Forces directed toward lingual side Maxillary lingual cusps articulate with the mandibular central fossae Elimination of contacts on the buccal cusps in both centric and eccentric The aim is to provide greater masticating efficiency and the elimination of lateral interferences

Lingualized Occlusion Maxillary anatomic (33°) Mandibular Teeth Steep Condylar Guidance Shallow cusped (Anatoline) Shallow Condylar Guidance Non-anatomic (Portrait 0°) Lingualized (lingual contact)

Lingualized Occlusion Verify centric No max. buccal cusp contacts in: • Centric • Lateral excursions

Contraindications Of Balanced Occlusion & Lingualized Occlusion Extreme cases of the following: Difficulty in obtaining repeatable centric record (incoordination, jaw malrelations) Severe ridge resorption (lateral forces displace the denture) may more easily be handled with a monoplane scheme

Monoplane Articulation (Neutrocentric Concept) Cuspless teeth (0°) on a flat plane with 1.5-2.0 mm overjet No cusp to fossa relationship No anterior contacts in centric position

Monoplane Articulation Eliminate cusps lateral forces reduced improves stability Simplifies tooth arrangement

Monoplane Articulation No overbite (would cause tilting) Overjet of 2 mm is used to create an illusion of overbite

Monoplane Articulation Excursions - may or may not contact on balancing sides Depends on condylar inclination and other aspects of the tooth arrangement

Monoplane Articulation Anterior teeth make contact in excursions Modifications have been proposed to minimize the tilting potential: Compensating curves

Monoplane Occlusion without condylar influence

Monoplane Occlusion

Monoplane Articulation Advantages Technically easier to achieve Use when: Difficulty obtaining repeatable centric records (muscle incoordination) Skeletal malocclusion (Class II, III) Severe residual ridge resorption Reduces horizontal forces

Monoplane Articulation Disadvantages Poorer appearance Can be unstable if condylar guidance is steep (posterior teeth separate, leaving only the anteriors in contact)

Monoplane Articulation Contraindications: The patient has high expectations for improved appearance Very steep condylar guidance may make a monoplane scheme less stable, unless modifying ramps or compensating curves are used.

When 1.5-2.0mm of overjet can be set, a lingualized occlusion (left) can have overbite set. Monplane occlusion (right) should normally have no overbite set. Because setting of anterior teeth affects the incisal angle, which can also cause separation of the posterior teeth, the clinician should stipulate how anterior teeth are set. In general, for a monoplane occlusion, no overbite is set. For lingualized occlusion, an overbite may be set to improve appearance if the posterior teeth can balance in excursions. If the incisors prevent the posterior teeth from balancing by disocluding them (usually this occurs when very little horizontal overlap or overjet is present), then the incisal angle can be set to zero (i.e. no overbite).