Fundamentals Of Occlusion FahimVohra SDS 333 Fundamentals Of Fixed Prosthodontics Chap 2, Pg11-23.
Outline • Definitions • Mandibular movement • Normal vs Pathological Occlusion • Occlusal Interferences • Schemes of Occlusion • Determinants of Occlusion
Why Is Occlusion Important ? • Assist in diagnosis • Planning in restorative care To minimize failure Ensure predictable outcome by minimising loads on teeth Managing the environment so that we get the minimal amount of surprises (Similar to wearing a car seatbelt), the less the patient has to adapt the better.
Definitions OCCLUSION A relationship between the masticatory surfaces of the maxillary and mandibular teeth The relationship between tooth contacts and mandibular movements
Centric Occlusion Relationship of the mandible to the maxilla when the teeth are in maximum occlusal contact, irrespective of the position or alignment of the condyle-disk assemblies. The relationship between the maxilla and mandible when the teeth are maximally meshed with the mandible in its most cranial position
A relationship of the mandible to the skull where the condyle is in an anteriorly, superiorly braced position along the articular eminence of the glenoid fossa, with the articular disc interposed between the Condyle and eminence. Centric Relation
Mandibular Movements • Mandibular movements occur around three axes a) Horizontal axis b) Vertical axis c) Sagittal axis
Horizontal Axis (Rotation) This movement occurs in the sagittal plane when the mandible in centric relation makes a purely rotational opening and closing border movement around the transverse horizontal axis, which extends through both condyles.
Vertical axis (Rotation) This movement occurs in the horizontal plane when the mandible moves into a lateral excursion. The center for this rotation is a vertical axis extending through the rotating or working-side condyle.
Working side • The side towards which the mandible moves during excursion OR Mandible moving toward the cheek • Working side condyle pivots within the socket and is better supported. Balancing side (Non working side) • The side opposite to the direction in which the mandible moves OR Mandible moving toward the tongue • Balancing side condyle has a downward orbiting path and is more prone to injury or damage.
Balancing Side Condyle has downward path Working Side Condyle pivots Movement direction Mandible and TMJ
Sagittal Axis This movement occurs when mandible moves to working side, the condyle on the opposite side (Non working side) travels forward and downwards simultaneously. When viewed in the frontal plane, this produces a downward arc on the non working side, rotating about an anteroposterior (sagittal) axis passing through the other condyle
Pure Hinge Movement It occurs as the result of the condyles rotating in the lower compartments of the temporomandibular joints within a 10- to 13-degree arc, which creates a 20- to 25-mm separation of the anterior teeth
Translation Movement • Occurs when the mandible moves forward (protrusion) • Teeth, condyles, and rami, all move in the same direction and to the same degree. • Occurs within the superior cavity of the joint
Maximum Opening(Translation & Rotation) Occurs in the upper compartment of the joint as the mandible drops down farther . Then the horizontal axis of rotation shifts to the area of the mandibular foramen, as the condyles translate forward and downward while continuing to rotate.
Protrusive Position When the mandible slides forward so that the maxillary and mandibular anterior teeth are in an end-to-end relationship, it is in a protrusive position.
Bennett Movement It is defined as “the bodily lateral movement/ lateral shift of mandible resulting from movements of condyles along lateral inclines of mandibular fossa during lateral jaw movement” Dr Norman Bennett
Bennett Angle The angle formed between the sagittal plane and the average path of advancing condyle as viewed in the horizontal plane during lateral mandibular movements. Average range is 7.5-12.8 degree BSC WSC Bennett angle Sagittal plane
Posterior Determinant of Occlusion TMJ – Temporomandibular Joint Bony surfaces The dentist has no control on the posterior determinants i.e. TMJ
Anterior Determinant of Occlusion Teeth • Incisors • Canines • Premolars • Molars
Anterior Determinants Of Occlusion Posterior teeth Provide vertical stops Guide mandible to CO Anterior teeth Guide mandible in protrusive, retrusive and lateral excursions The closer the tooth located to a determinant , more it will be influenced by it.
Occlusal Interferences • Interferences are undesirable occlusal contacts that may produce mandibular deviation during closure to maximum intercuspation or may hinder smooth passage to and from the intercuspal position . • These can be of following types • Centric • Working • Non working • Protrusive
Centric Interferences It is a premature contact that occurs when the mandible closes with the condyles in their optimum position in the glenoid fossae (CR) . It will cause deflection of the mandible in a posterior, anterior, and/or lateral direction
Working Side Interference It occurs when there is contact between the maxillary and mandibular posterior teeth on the same side of the arches as the direction in which the mandible has moved. If that contact is heavy enough to dis-occlude anterior teeth, it is an interference .
Non-Working Side Interference • It is an occlusal contact between maxillary and mandibular teeth on the side of the arches opposite the direction in which the mandible has moved in a lateral excursion . • It has the potential for damaging the teeth, PDL, MOM and TMJ due to changes in the mandibular leverage, the placement of forces outside the long axes of teethand disruption of normal muscle function.
Protrusive Interference • It is a premature contact occurring between the mesial aspects of mandibular posterior teeth and the distal aspects of maxillary posterior teeth . • The proximity of the teeth to the muscles and the oblique forces make them potentially destructive. • They also interfere with the patient's ability to incise properly
Ideal Occlusion An ideal occlusion should provide comfort and function in a predictable way. 1) Ideal occlusion at tooth level Cusp tip to fossa or cusp to marginal ridge contact – i.e no incline contacts 2) Ideal occlusion at articulatory system level Posterior stability, Anterior guidance, Lack of posterior interferences. 3) Ideal occlusion at patient level Within the adaptability of the rest of the articulatory system.
Features Of Ideal Occlusion • Anterior Guidance: • In lateral excursions of the mandible, working-side contacts (preferably on the canines) disocclude or separate the nonworking teeth instantly. • In protrusive excursions, anterior tooth contacts will disoccludethe posterior teeth.
Protrusive Guidance Excursive Guidance
Features Of Ideal Occlusion B) Posterior stability: Enough posterior teeth in each arch with solid and stable contacts in appropriate positions to evenly distribute loads and to allow the mandible to close in a reproducible CO. Posterior teeth contact more heavily than anterior teeth It is enhanced by tall cusp – deep fossa Maintains teeth position CO or ICP is easily reproduced Increased masticatory function Signs of lack of PS, drifting, fremitus, fractured rest, mobility & wear
Features Of Ideal Occlusion C) Absence of posterior interferences The non-working side
Features Of Ideal Occlusion D) Centric Occlusion is achieved at centric relation position E) Occlusal loads are axially transmitted through the teeth
Organization Of Occlusion • There are three recognized concepts that describe how teeth should contact in various mandibular positions • Bilateral balanced occlusion • Unilateral Balanced occlusion (Group function) 3. Mutually protected occlusion (Canine protected)
Bilateral Balanced Occlusion • It dictates that a maximum number of teeth should contact in all excursive positions of the mandible. • Use for complete denture occlusal scheme as contacts on non-working side prevent tipping of the denture • Not used for fixed prosthodontics, as very difficult to achieve
Unilateral Balanced Occlusion • Also called group function • It requires teeth on the working side to be in contact in lateral excursion and teeth on the non-working side are free of any contact. • Avoids destructive , oblique forces on the non-working side. • Prevents wear of maxillary palatal and mandibular buccal cusps
Mutually Protected Occlusion • Also called canine protected occlusion • Anterior teeth overlap prevents the posterior teeth from making any contact on either the working or the nonworking sides during mandibular excursions. • Anterior teeth bear all the load and the posterior teeth are dis-occluded during excursions. Protecting the posterior teeth • In CO, posterior teeth direct forces through their long axis and anterior teeth are slightly in or out of contact. Protecting the anterior teeth.
Guidance Describes the influenced path the mandible takes as a result of the contacting surfaces of the teeth. Depending on the contact and shape of the teeth they should be in harmony
Protrusive Guidance Influenced path the mandible takes as a result of a forward thrust
Canine Describes the way in which lateral excursions are affected by tooth to tooth contacts involving the canine teeth only resulting in disclusion of the posterior teeth Lateral Guidance
Group function When lateral excursions are guided by more than one tooth other than the canines Lateral Guidance
Hanau’s Quint By modifying the following five factors, a scheme of occlusion can be developed that will suit a particular patient best. 1. Condylar guidance 2. Incisal guidance 3. Occlusal plane orientation 4. Compensating curves 5. Height of the Cusp Except for the condylar guidance, all other factors can be modified during the fabrication of a prosthesis and the anterior guidance plays a predominant role.
Anterior Guidance • Guidance produced by the teeth themselves and not the temporomandibularjoint (can be on any tooth) • The influence of contacting surfaces of anterior teeth on mandibular movements. • The influence of contacting surfaces of the guide pin and anterior guide table on articulator movements. • The fabrication of a relationship of the anterior teeth preventing the posterior tooth contact in all eccentric mandibular movements.
Protrusive Incisal Path The track of the incisal edges of the mandibular teeth from maximum intercuspation to edge-to-edge occlusion.
Protrusive Incisal Path Angle The angle formed by the protrusive incisal path and the horizontal reference plane is the protrusive incisal path inclination. It ranges from 50 – 70 degrees and is often 5-10ºsteeper than the sagittal condylar guidance.
Incisal Guide Angle The angle formed with the horizontal plane of occlusion and a line in the sagittal plane between the incisal edges of maxillary & mandibular central incisors when the teeth are in maximum intercuspation. The angle formed in the sagittal plane between the horizontal plane and the slope of the incisal guide table.