There may be an occlusal disharmony(shaded bar) which is not ideal, but which is tolerated by the patient because it is below his threshold of perception and discomfort (A). If the threshold is lowered, the disharmony which has been previously tolerated may produce symptoms in the patient. (B). Treatment is then rendered by first raising the patient’s threshold, and then decreasing or eliminating the disharmony (C).
Iv.tooth prep v. occlusion
IV. TOOTH PREPARATION A. Definition of Tooth Prep -Tooth Preparation is the mechanical treatment of dental disease or injury to hard tissues that restores a tooth to its original form or contour
IV. TOOTH PREPARATIONB. Objectives of Tooth Prep1. Reduction of the tooth in miniature to provideretainer support2. Preservation of healthy tooth structure to secureresistance form3. Provision for acceptable finish lines4. Performing pragmatic axial tooth reduction toencourage favorable tissue response from artificialcrown contours
IV. TOOTH PREPARATIONC. Principles in Tooth Prep1. Preservation of tooth structure2. Retention and resistance form3. Structural durability of the restoration4. Marginal integrity5. Preservation of the periodontium
IV. TOOTH PREPARATIOND. Basic Steps of Tooth Prep1. Incisal/ Occlusal Reduction2. Facial Reduction3. Lingual/ Palatal Reduction4. Proximal Reduction5. Gingival Margins/ Finishing Lines6. Rounding up of Sharp Corners and Line Angles7. Finishing
BIOLOGICConservation of tooth structure MECHANICALAvoidance of overcontouring Maximum surface areaSupragingival margins Apical extensionHarmonious occlusion Adequate thickness of metalProtection against tooth fracture Bulk at margins ESTHETIC Minimum display of metal Maximum thickness of porcelain Porcelain occlusal surfaces Subgingival margins
Depth Guides /Orientation GroovesHelp dentists in the preparation of teethPrevent overreduction as well as underreduction
1. Incisal/ Occlusal Reduction Anterior teeth – 1.5 – 2mm or 2/3 of the incisal 3rd Posterior teeth – -metal occlusal 1.5-2mm -metal and porcelain/ fiber reinforced FC-1.5-2mm GC-1-1.5mm
Different Levels of Finishing LinesSupragingivalEquigingivalSubgingival
5. Gingival Margins/ Finishing LinesIs it bad to place marginssubgingivally?
BIOLOGIC WIDTHWhat is Biologic Width? It is a band of soft tissue attachmentWhat is its composition? It is composed of approximately 1mmof junctional epithelium and 1mm ofconnective tissue fibers.
The dentogingival junction includes the gingival sulcus (A-B) approximately 0.8 mm .The junctional epithelium (B-C) 0.7 to 1.3mm (average 1mm)The connective tissue attachment (C-D) 1.07mm.The biologic width (B-D) averages 2mm in occlusogingival height.DCB A
“When you bury the collar, You attend the funeral of the periodontium”
BIOLOGIC WIDTHWhat is its significant clinical implication? Crown margins can be placed subgingivally but should not encroach the Biologic Width.
IF VIOLATED … Inflammation and Osteoclastic ActivityBone Resorption andPocket Formation
A joint is a joining together of two bones. The temporomandibular joint (TMJ) isthe articulation between the temporal bone and the mandible. It is bilateral, andmovement of the right and left sides are interrelated and function as a singleunit.. The condyle of the mandible articulates with the mandibular(GLENOID) fossae of the temporal bone. The specific location is the posteriorslope of the articular tubercle and the anterior portion of the mandibular(glenoid) fossae. The condyle does not fit into the center of the mandibularfossae but rests closer to the articular tubercle. The condyle and articulareminence do not actually touch, the articular disc (meniscus) rests betweenthem. This disc is a pad of dense fibrous connective tissue that is thickest at theposterior ends, thinnest in the middle and thicker again at the anterior ends. Thearticular disc, in effect, separates the temporomandibular joint into upper andlower joint spaces. Laterally and medially, the disc is attached to the condyleitself, so that whenever the condyle glides forward and backward, the discmoves with it. The condyle and articular eminence are covered by densecollagenousconnective tissue, which contains no blood vessel or nerves.Synovial fluids bathes this structures, providing nourishment and lubricationthat enables the bones to glide over each other without friction. A thick fibrous capsule surrounds and encloses the entire joint. The
disc and capsule are fused anteriorly, and some fibers of the lateral pterygoid muscle insert into the disc. Posteriorly, the disc and capsule are not directly attached but are connected by means of a retrodiscal pad, a pad of loose connective tissue that allows for anterior movement of the joint. Nerve and blood supply- Innervation is supplied by two nerves, the auriculotemporal and ,masseteric nerves, which are branches of the mandibular nerve (V3), blood supply is provided by branches of the superficial temporal and maxillary arteries. Movement- TMJ movement within the temporomandibular joint is essentially of two types: Hinge (swinging) motion and gliding movement.The condyle of the mandible articulates with themandibular (glenoid) fossae of the temporal bone. Thespecific location is the posterior slope of the articulartubercle and the anterior portion of the mandibular(glenoid) fossae. The condyle does not fit into the center ofthe mandibular fossae but rests closer to the articulartubercle . The condyle and articular eminence do notactually touch, the articular disc (meniscus) rests betweenthem. This disc is a pad of dense fibrous connective tissuethat is thickest at the posterior ends, thinnest in themiddle, and thicker again at the anterior ends. Thearticular disc in effect, separates the teemporomandibularjoint into upper and lower joint spaces. Laterally andmedially, the disc is attached to the condyle itsel, so thatwhenever the condyle glides forward and backward, thedisc moves with it.The condyle and articular eminence are covered by dense collagenous connective tissue, which contain s no blood vessel ornerves. Synovial fluid bathes these structures, providing nourishment and lubrication that enables the bones to glide over eachother without friction. A thick fibrous capsule surrounds and encloses the entire joiunt. The disc and capsule are fusedanteriorly....(contiued above)
Mandibular movementMandibular movement can be broken down into a series of motions thatoccur around three axes:2.Horizontal This movement, in the saggital plane occurs when the retrudedmandible produces a purely rotational opening and closing movementaround the hinge axis, which extends through both condyles.
2. Vertical The movement occurs in the horizontal plane when themandible moves into a lateral axcursion. The center for thisrotation is a vertical axis extending through the working sidecondyle.
Sagittal When the mandible moves to one side, the condyle on the sideopposite from the direction of movement travels forward. As it does, itencounters the eminentia of the glenoid fossa and moves downwardsimultaneously. When viewed in the frontal plane, this produces adownward arc on the side opposite the direction of movement, rotatingabout an anteroposterior (sagittal) axis passing through the othercondyle.
Various mandibular movements are comprised of motions occuring about one ormore of the axes. The up and down motion of the mandible is a combination oftwo movements... ...There is a purely rotational componentproduced by the condyle rotating in the lowercompartment of the temporomandibularjoints. ...There is also some gliding movement in the upper compartment of the jaw.
When the mandible slides forward so that the maxillary andmandibular teeth are in an end to end relationship, it is in a protrusiveposition. Ideally, the anterior segment of the mandible will travel a pathguided by contacts between the anterior teeth.
Mandibular movement to one side will place it in a working, or laterotrusive relationship on that side and a nonworking or mediotrusive relationship on the opposite side;e.g., if it moves to the left, the left side is the working side, and the right side is the nonworking side. In this type of movement, the condyle on the nonworking sidewill arc forward and medially (A). Meanwhile, the condyle on the working side will shift laterally and usually slightly posteriorly (B). This bodily shift of the mandible in the direction of the working side was first described by Bennet.The presence of an immediateor early side shift has beenreported in 86% of thecondyle studied. In addition todemonstrating thepredominant presence of earlyside shift, Lundeen and Wirthhave shown its mediandimension to be approximately1.0, with a maximum of3.0mm. Following theimmediate side shift, there isgradual shifting of themandible.
The determinants of mandibular movement The two condyles and the contacting teeth are analogous to the three legs of an inverted tripod suspended in the cranium. The determinants of the movements of that tripod are: -posteriorly, the right and left temporomandibular joints; -anteriorly, the teeth of the maxillary and mandibular arches; - And overall, the neuromuscular system.The dentist has no control over the posterior determinants, the temporomandibularjoints.they are unchangeable.However, they influence the movements of the mandible, and of the teeth, by the pathswhich the condyles must travel when the mandible is moved by the muscles ofmastication. The measurement and reproduction of those condylar movements is thebasis for the use of the articulator.The anterior determinant, the teeth, provides guidance to the mandible in several ways.The posterior teeth provide the vertical stops for mandibular closure. They also guidethe mandible into the position of maximum intercuspation, which may or may notcorrespond with the optimum position of the condyles in the glenoid fossae. Theanterior teeth (canine to canine) help to guide the mandible in right and left lateralexcursive movements and in straight protrusive movements.Dentists have direct control over the tooth determinant by orthodontic movement ofteeth; restoration of the occlusal surfaces ;and equilibration, or selective grinding, ofany teeth which are not in harmonious relationship. Intercuspal position and anteriorguidance can be altered, for better or for worse, by any of these means.
The Determinants of Occlusion The closer to a determinant that a tooth is located, the more it will be influenced by the determinant. A tooth placed near the anterior region will be influenced greatly by anterior guidance, and only slightly by the temporomandibular joint. A tooth in the posterior region will be influenced partially by the anterior guidance.The neuromuscular system,through proprioceptive nerveendings in the periodontium,muscles, and joints, monitors theposition of the mandible and itspaths of movement. Throughreflex action, it will program themost nearly physiologic paths ofmovement possible under the setof circumstances present. Dentisthave indirect control over thisdeterminant. Procedures done tothe teeth may be reflected in theresponse of the neuromuscularsystem.
The Determinants of OcclusionCondylar GuidanceAnterior/Incisal GuidanceOcclusal PlaneOcclusal CurveCusp Height
The Types of OcclusalInterferencesCentric InterferenceWorking InterferenceNon-Working InterferenceProtrusive Interference
One of the objectives of restorative dentistry is to place the teeth in harmonywith the temporomandibular joints. This will result in minimum stress on theteeth, and only a minimum effort need be expended by the neuromuscularsystem to produce mandibular movements.When the teeth are not in harmony with the joints and with the movements of themandible, an interference is said to exist.Occlusal interferencesInterferences are undesirable occlusal contacts which may produce deviationduring closure to maximum intercuspation, or which may hinder smoothpassage to and from the intercuspal position. There are four types of occlusalinterferences:5.Centric7.Working9.Nonworking4. Protrusive
The centric interference is a premature contact which occurs when the mandiblecloses wit the condyles in a retruded, superior position in the glenoid fossa. It will cause deflection of the mandible in a forward and/ or lateral direction.
A working interference may occur when there is contact between the maxillaryand mandibular posterior teeth on the same side of the arches as the directionin which the mandible has moved. If that contact is heavy enough to discludeanterior teeth, or interfere with the smooth progress of the nonworking sidecondyle, it is an interference.
A nonworking interference is an occlusal contact between maxillary andmandibular teeth on the side of the arches opposite the direction in which themandible has moved in a lateral excursion. The nonworking interference is of aparticularly destructive nature. The potential for damaging the masticatoryapparatus has been attributed to changes in the mandibular leverage, theplacement of forces outside the long axes of the teeth, and disruption of normalmuscle function.
The protrusive interference is a premature contact occurring between themesial aspects of the mandibular posterior teeth and the distal aspects ofmaxillary posterior teeth. The proximity of the teeth to the muscles and theoblique vector of the forces make contacts between opposing posterior teethduring protrusion potentially destructive.
The protrusive interference is a premature contact occurring between the mesialaspects of mandibular posterior teeth and the distal aspects of maxillaryposterior teeth. The proximity of the teeth to the muscles and the oblique vectorof the forces make contacts between opposing posterior teeth during protrusionpotentially destructive.
There may be anis lowered, the If the threshold occlusal disharmony which versus pathologic occlusion disharmony Normal had been (shaded bar) which ismay ideal, previously tolerated not produce but which only slightlyby the normal of the population is symptomsis tolerated more than 10% In in the patient. (a patient there complete a pathologic occlusion can become harmony between the teeth and the because it is below his threshold ofSimple muscle joints. Only in that small group occlusion). perception and temporomandibular discomfort. teeth give waymaximum intercuspation when hypertonicity may achieve to muscle do the spasm, the mandible headaches and position with the with chronic is in a retruded localized tenderness. optimal superior retruded position in condyles in the the fossae.Treatment is thenthen rendered by 90% of the population,And position of In the other nearly the then decreasing or eliminating thefirst raisingintercuspation is 1.25+mm forward of the retruded maximum the disharmonypatient’s position.threshold,
ARTICULATORS -is a mechanical device which of the simulates the movements of the mandibleThe principle employed inthe use of articulators is themechanical replication of thepaths of movement of theposterior determinants, thetwmporomandibular joints.The instrument is then usedin the fabrication of fixedand removable dentalrestorations which are inharmony with thosemovements.
As the mandible closes around the hinge axis ( m h a ), thecusp tip of each mandibular tooth moves along an arc
The large dissimilarity between the hinge axis of the smallarticulator ( a h a ) and the hinge axis of the mandible ( m h a ) willproduce a large discrepancy between the arcs of closure of thearticulator (broken line) and of the mandible (solid line).
A majordiscrepancyexists between thenonworking cusppath on the smallarticulator (a) andthat in the mouth
The dissimilarity between the hinge axis of the full sizesemi-adjustable articulator ( a h a ) and the mandibular hinge axis( m h a ) will cause a slight discrepancy between the arcs ofclosure of thearticulator(broken line)and of themandible(solid line)
There is only a slightdifference between cusp pathson a full size articulator(c)and those in the mouth(m), even though the castmounting exhibits aslight discrepancy
The condyle travels a curved path in mandibular movements ( A )This is reproduced in semi-adjustable articulators as a straightpath ( B ).
..However, the angle changes between an open (C) and a closed (D) nonarcon instrument <a3 not equal to <a4. For the amount of opening illustrated, there would be a difference of 8 degrees between the condylar inclination at an open position ( where theThearticulator settings are adjusted ) and a closed position (at which angle between the condylar inclination and the .Occlusal plane of is used ). the articulator the maxillary teeth remainsconstant between an open (A) and a closed (B)articulator <a1=<a2.
Transfer of the tooth hinge-axis relationship Two caliper-style face-bows are in use at the present time: the Quick mount Face-bow When a precision face-bow transfer is made, both side arms are adjusted so that the stylus at the end of each arm is located over the hinge axis (arrow). A third reference point, such as the plane indicator shown here, is used.An air activated pantograph forrecording mandibular movements the Slidematic Face-bow