Occlusion- contact of opposing surface of teeth of two jaws. Centric relation- untranslated hinge position of mandible to maxilla Centric occlusion - occlusion of teeth as the mandible closes in centric relation. This is the reference position from which all the horizontal position are eccentric.
Disclusion- contacting of designated groups of teeth in order to disallow any contacting of other groups of teeth. Anterior disclusion describe contacting of anterior teeth to prevent occlusion of posterior teeth during eccentric closures of mandible. During lateral movement, orbiting(non-working) condyle revolves in orbit around rotational center of opposite rotating(working) condyle Eg.during right lateral movement right condyle is working or rotating condyle and left condyle is orbiting or non-working condyle. Vice versa in left lateral movement.
Maximum intercuspation - most closed complete interdigitation of mandibular and maxillary teeth irrespective of condyle centricity. Protrusion- forward movement of mandible. Retrusion- backward movement of mandible. Transtrusion- total lateral translation or side shift of mandible. Mediotrusion- lateral movement towards midline of head of orbiting or non working condyle. Laterotrusion- lateral movement away from midline of working condyle.
Sur trusion- upward movement of working condyle from its centric position. Detrusion- downward movement of either condyle from its centric position. Hinge axis- imaginary line connecting rotational center of one condyle and around which mandible makes opening and closing rotational movement.
The TMJ is a synovial joint further classified as ginglymus joint. (sliding hinge) The articulation consists of a single bone, the mandible articulating by bicondylar synovial joints with temporal bones of the cranium ALSO CALLED AS GINGLYMODIARTHROIDAL TYPE OF JOINT, MEANING IT HAS A RELATIVELY SLIDING TYPE OF MOVEMENT BETWEEN BONY SURFACES IN ADDITION TO HINGE MOVEMENT.
Components of the joint: Articular surface of the temporal bone The Condyle Cartilage and Synovium The Interarticular disc/ Meniscus Ligaments
It is in the Sqamous temporal portion oftemporal bone.Consists of 3 parts:Mandibular or glenoid fossa.Articular eminencePreglenoid plane.
It is the concave portion of the temporal bone.Boundaries: Posteriorly: Squamotympanic or Petrotympanic fissure Medially: Spine of sphenoid Laterally: Root of zygomatic process of temporal bone Anteriorly : Articular eminence The glenoid fossa is covered by a dense, avascular fibrocartilage consisting largely of bundles of collagen fibres with occasional elastic fibres.
It is a small prominence on the zygomatic arch.It is thick and serves as functional component of TMJOn its lateral aspect, articular tubercle is present whichserves as the point of attachment for the collateralligaments.It is a cylindrical bony projection and covered with athin layer of fibro cartilage.
The mandible is a U shapedbone that articulates with thetemporal bone by means ofthe articular surface of itscondyle.The head is covered withfibrocartilage and articulateswith temporal bone to formTMJ.
The constriction below the head is the neck.The lateral surface of the neck providesattachment to the lateral ligament of the TMJ.Its anterior surface presents a depressioncalled Pterygoid fovea for the attachment oflateral pterygoid.Two condyles of the same patient may beasymmetrical.
The TMJ is a diarthroidal paired joint, means that thereare two joint movements, which occur in separatecompartments of this synovial joint and that one jointcannot operate without the other.The disc divides the articular space into twocomponents.The lower or inferior compartment- condylodiscalcompartment between condyle and disc.The upper or superior compartment- temporodiscalbetween the disc or temporal bone or glenoid fossa.
The articular disc seperates the mandibularcondyle from direct articulation with mandibularfossa of temporal bone.It is composed of dense fibrous connective tissue,for the most part devoid of any blood vessels andnerve fibres.
In sagittal plane it is divided into 3 planes.1. Anterior band2. Intermediate band3. Posterior band
In the normal joint, the articularsurface of the condyle is locatedon the intermediate zone of the disc.The shape of the disc isdetermined by the morphologyof the condyle and mandibular fossa.The disc is somewhat flexible and can adapt to the functionaldemands of the articular surface.
Ligaments associated with the TMJ arecomposed of collagen, which do not stretch andact predominantly as restraints to motion of thecondyle and the disc.They play an important role in protecting thestructures of the joint.The TMJ has support of 3 functional ligamentsand 2 accessory ligaments.
• Functional ligaments- Serve as major anatomical component for the joint. a] Collateral/Discal ligament b] Capsular ligament c] Temporomandibular ligament• Accessory ligaments-Serve as passive restraints to mandibular motion. a] Sphenomandibular ligament. b] Stylomandibular ligament.
COLLATERAL/DISCAL ATTACHMENTSThese ligaments attach the articular disc to themedial and lateral poles of the condyle.These are called the discal ligaments.These are composed of collagenous connectivetissue fibers and they do not stretch.They function to restrict the movement of the discaway from the condyle and permit the disc to rotateanteriorly and posteriorly on the condyle.
• The capsule of TMJ is described as fibrous non elastic membrane surrounding the joint.• The capsule seals the joint and provides passive stability.• The active stability is achieved by proprioceptive nerve endings in the capsule.• To resist medial, lateral and inferior forces thereby holding the joint together.• It offers resistance to movement of joint only in the extreme range of motion.• Secondary function of the capsular ligament is to contain the synovial fluid within the superior and inferior joint spaces.
• It is located on the lateral aspect of each TMJ.• This ligament runs downwards and backwards from the lateral aspect of the articular eminence to the posterior aspect of the neck.
Its function is to limitthe posteriormovement of thecondyle during pivotingmovements such as,when the mandiblemoves laterally inchewing position. Italso protects the innerlateral pterygoidmuscle from overlengthening orextension.
• The sphenomandibular ligament arises from the spine of the sphenoid and extends downwards to a small bony prominence on the medial aspect of the mandible called the lingula.• It does not have any limiting function on TMJ.• It is a remnant of Meckels cartilage.• It assists the lateral pterygoid in translatory and rotatory movement.
• It arises from the styloid process and extends downwards and forwards to the angle and posterior border of the ramus of the mandible.• It limits the protrusive movement of the mandible.• It is taut in protrusion of the mandible and relaxed when the mandible is wide opened.
The muscles of mastication are directly concerned with mandibular movements in mastication and speech.4 pairs of muscles make up a group called the muscles of mastication.1. Masseter2. Temporalis Accessory muscles3. Medial pterygoid 1. Buccinator4. Lateral pterygoid 2. Digastricus.
These four pairs of muscles attached to mandible,primarily responsible for Elevating Depressing Protruding Retruding Lateral movement
It is a quadrilateral muscle.The fibers are arranged in3 layersSuperficial layer:Origin : anterior 2/3 of inferior surface of zygomatic arch. & maxillary process of zygomatic arch.Insertion: angle of mandible , posterior half of the lateral surface of mandibular ramus.
Middle layer:Origin: medial aspect of 2/3 ofzygomatic arch.Insertion: middle part of ramus.Deep layer:Origin: deep surface ofzygomatic arch.Insertion : upper part of ramus& coronoid process.Most powerful closing muscleof jaw
Action :Elevates the mandibleto close the mouth.Retraction of mandible& clenching of teeth.Superficial fibers helpin protrusion ofmandible.
This is a fan shaped muscle and fills the temporalfossa. The temporal fascia covers the muscle.
Origin:Temporal fossa &deep surface oftemporal fasciaInsertion:Fibers converge toinsert on tip & medialsurface of coronoidprocess of mandibleand anterior borderof ramus of mandible
Action: Anterior and middlefibers elevate mandible. Posterior fibersretract the mandible.
It is a quadrilateral muscle with 2 heads.A small superficial head & a large deep head.
Origin:Superficial head: frommaxillary tuberosity andadjoining pyramidalprocess of palatine bone.Deep head: larger, arisesfrom medial surface oflateral pterygoid.Insertion:The fibres rundownwards, backwards &laterally to insert intomedial surface of theangle and adjoining partof ramus of mandible.
Actions:When both side musclecontracts together itelevates the mandibleWhen one side musclecontracts jaw is pulled toopposite side.It also helps in protrusionof the mandible and helpsin lateral movements of thejaw.
It is a shortand thickmuscle with2 distinctheads.
Origin:Upper head- small, arises frominfra temporal surface ofgreater wing of sphenoid.Lower head – large, arises fromlateral surface of lateralpterygoid plate.Insertion:Fibres run backwards, laterally,converge to insert intopterygoid fovea in the anteriorsurface of neck of mandible,adjoining articular disc andcapsule of TMJ.
Actions:Depresses the mandible.Lateral and medialpterygoid muscles ofboth sides act togetherto protrude themandible.Helps in side to sidemovements of the jaw.
Temporalis, masseter, medial pterygoid muscle elevates the jaw and have great power in keeping the teeth clenched. The mouth opens by relaxation of these muscle and by weight of mandible cooardinated with contraction of suprahyoid and infrahyoid group of muscle, platysma and lateral pterygoid muscle. Infrahyoid and suprahyoid muscle also helps in function of degluttination, phonation and mastication.
Muscle contract iso tonically and iso metrically Iso-tonic M.C.- occurs in absence of resistance with shortening of muscle fibres without increase in muscle tone making the associated skeletal parts are moved by this contraction. Iso-metric M.C.- occurs in presence of resistance without shortening of muscle fibres with increase in muscle tone and it resists the associated skeletal parts movement.
It is compound diarthrodial joint or Ginglymoarthrodial articulation Mandible has two action – Ginglymoid action by rotation. Diarthrodial action by translation.
These movements occur in 3 cranial planes Transverse Saggital Frontal
It occurs in lower compartment of TMJ. It occurs around 3 axis Horizontal- mandible rotates around horizontal or hinge axis to produce opening and closing movement. Frontal- mandiblar rotates around vertical axis of one condyle. It results in lateral excursion. The condyle around which rotation occurs called as rotating or working condyle and opposite condyle is called orbiting or non- working condyle. Saggital- lateral excursions are made and orbitting condyle travels downward and forward during rotation around saggital axis.
It occurs in upper compartment of TMJ. It occurs simultaneosly in all 3 cranial planes. In this muscular contraction makes change in relationship of condyle and articular disc with articular fossa.
Stuart describes condylar factors as determinants ofocclusal morpholgy and effect on acceptable cuspheight and fossa depth and allowable ridge andgroove direction of teeth, called as posteriordeterminants of occlusion .These are-Side shiftPath of rotating condyleIntercondylar distancePath of orbiting condyle
This is the detrusion of orbiting(non working) condyle in relation to horizontal cranial reference plane. Greater angle of the path, greater cusp height and deeper the fossa.
Transtrusion or lateral shifting of mandible as lateral movement is made. This is produced by combination of rotation and translation in both horizontal and frontal planes. Greater the immediate shift, shorter is allowable cusp height. Presence if immediate shift also requires mesial positioning of oblique grooves and ridges of mandibular teeth and more distal positioning of oblique ridges and grooves of maxillary teeth. During right lateral movement, greater mediotrusion of left condyle that is produced by side shift, greater must lingual concavity of maxillary canine in order to allow smooth cyclic chewing movement without conflict.
Distance between the rotational center of one condyle to the rotational center of the other side of condyle is called as intercondylar distance. Larger the distance, more distal positioning of oblique ridges and grooves on mandibular teeth and mesial positioning of ridges and grooves of maxillary teeth. Smaller the distance vice-versa.
Laterotrusion- lateralmovement of rotatingcondyle.Horizontal plane: thesemovements give antero-posterior componet whicheffects the ridge and groovedirections of occlusalsurface.Lateroprotrusion- outwardand forward movement.Distal positioning ofgrooves and ridge is done inmandibular teeth.
Lateroretrusion-outward and backwardmovementMesial positioning ofgrooves and ridges isdone on mandibularteeth.For maxillar y teethvice-versa
Frontal plane- it gives the vertical component affects the depth of grooves, height of cuspsand angle of ridges. Laterosurtrusion- outward and upward movement. It demands shallower grooves and less cusp height.
Laterodetrusion- outward and downward movement. Demands deeper grooves and greater cusp height.
Path of rotatingcondyle affects thepath of mandibularcanine on working sideand influence theamount of allowablelingual contour ofopposing maxillarycanine.
The factors within dentition which influences the mandidular movement are called as anterior determinants of occlusion. These are – Occlusal plane Curve of spee Facial position of teeth Vertical and horizontal overlap of anterior teeth
Position of teeth in relation to rotational centers of condyle and to horizontal cranial reference plane is transferred to articulator by means of facebow. Interocclusal records made in centric relation are used to place mandibular cast in proper relation to rotational centers and cranial reference planes.
Effect of curve of spee is determined by comparing plane of each tooth in curve with path of orbiting condyle with same rule as in occlusal plane.
The more plane of occlusion diverges from path of non working condyle, greater is allowable cuspal height. The more nearly parallel occlusal plane to path of non working condyle the shorter is allowable cuspal height.
Greater the vertical height, greater will be cusp height. Greater the horizontal overlap, lesser will be cusp height.
The upper extent of posselt”s envelope of motion is product of tooth contact. The movements of mandible along all other borders of envelope and movements within envelope are without tooth contacts and are controlled by craniomandibular articulation and the quantity of muscular activity. If Occlusal contacts are not created properly with growth and development will interfere with condylar controls so that condylar centricity is lost.
Faulty occlusal contours of dental restorations may also produce deflective occlusal contacts causing mandible to move away from centric relation closure in order to allow maximal intercuspation of teeth. This maximum intercuspal position is an eccentric closure. Premature contacts occuring on the inclines of cusps produce lateral forces on teeth that create undesirable lateral pressure and tension on periodontal tissue. While occlusal forces donot cause periodontal disease, it produces increased tooth mobiltybecause of compensatory widening of periodontal ligament space.
The craniomandibular articulation allows changes in relation of its parts in order to accommodate guiding influence of tooth inclines during mandible”s attempt to reach the position of maximal intercusping. The accomodation produces an eccentric maximal intercusping of teeth. The repeated demands resulting from this intercusping can produce hypertonicty in associated muscle beyond their capacity to adapt and myofacial pain devlops.
Disharmony between condylar centricity and maximal intercusping may also produce excessive wear of the teeth that are responsible for the deflective interferences.
All functions of mandibular movements such as chewing, speaking and swallowing begin with opening movement of jaw. For chewing a cycle of lateral depressing and elevating movement is generated. The chewing take place within the envelope of motion and unique for each individual. Tooth position and tooth morphology may contribute to development of this cycle, however extremes in either factor may prevent a smooth cycle function.
Dental occlusion should be designed so as not to interfere with these muscle produced and condylar controlled cyclic actions. This requirement and the purpose of occluding teeth to provide a stable closure of mandible in centric relation are major considerations in an occlusal scheme that promotes health of supporting tissues, has a reasonable degree of permanence and provides efficient comfortable group uses of teeth.
The protective proprioreceptors responses minimizes the occurrence of occlusal conflict of premature contacts by controlling muscle tension and by developing an adaptive arc of closure into an eccentric maximal closing. However if damage resulting from these interferences warrants change it can be done by following- Occlusal adjustments if teeth Restoration of form and function by recusping Surgical or orthodontic movement of teeth Removal of teeth in some cases.
Lingual cusp of maxillary teeth and facial cusp of mandibular teeth are stamp or centric holding cusp. The facial cusp of maxillary teeth and lingual cusp of mandibular teeth are shearing cusp.
Development of occlusion can result in fitting one stamp cusp into fossa and fitting another stamp cusp into embrasure area of two opposing teeth. It is also called as tooth to two teeth occlusion or cusp embrassure occlusal pattern.
It produces an interdigitative relation of cusps and fossa of one tooth with cusps and fossa of only one opposing tooth. This arrangement is also called as tooth to one tooth occlusion.
Given by stallard and stuart In protrusive movement two or more mandibular anterior teeth occlude with maxillary incisors. All mandibular teeth occlude simultaneously with maxillary teeth in centric relation. Maxillary lingual cusp occlude in fossa of each mandibular opponent. Mandibular facial cusp occlude in fossa of each maxillary opponent. The mandibular anterior teeth relate to lingual surface of maxillary anterior teeth as stamp cusps into fossa. In lateral closure only canines on the working side occlude. In lateroprotrusive closure, the lateral incisor may share closure contacts with canines. The stamp cusps of premolars and molars occlude with opposing fossa with 3 point contact in centric relation.
Adjustment of occlusion can be done by- Selective reshaping of ridges of cusps. Changes can be made at angles of marginal ridge. Reduction of cusp height can be done. Reduction of sulcus by reducing angles of triangular and oblique ridges. While reduction do not create flat areas, always maintain rounded contours polished sur face of cusps and ridges. All eccentric inter ferences should be removed first then only centric relation inter ferences should be removed.
It is three point contact of each stamp cusp into its respective fossa by grinding of tooth surface. It is unrealistic to give 3 point contact but grinding tooth surface of stamp cusp can be done in such a manner to give 2 point contact for stabilty.
If contact occur between premolars or molars while moving teeth in end to end incisal relationship, then grind it from distal inclines of maxillar y facial cusps and mesial inclines of mandibular lingual cusps.
If contacts occurs between opposing premolars or molars on non-working side while moving mandible in end to end relation of canine on working side, then make oblique grooves directed mesially on maxillar y teeth to ser ve pathway for mandibular facial cusps and on distal inclination of mandibular teeth for maxillar y lingual teeth.
Teeth are moved into extreme lateral position to extent of end to end relation of canine on working side. If there are interferences or simultaneous contact between premolars or molars on the working side, remove tooth structure from mesial inclines of facial cusp of maxillar y teeth and distal inclines of lingual cusp of mandibular teeth.
Centric relation occlusal contacts are corrected only after all eccentric interferences are removed. The mandible is closed in centric relationuntil initial tooth contact is made.if increasing the closing force deflects mandible to more closed position , corrections must be made. Reductions are made on mesial slopes of maxillar y teeth and distal slopes of mandibular teeth.