Removable Prosthodontics Dental Materials.docx

Removable Prosthodontics Dental Materials (part III) Denture Prosthetic teeth Resin denture teeth provide good esthetics wear resistance bond chemically to resin bases Composite resin denture teeth cause less wear to opposing enamel and gold surfaces than porcelain teeth They are the material of cho...

Removable Prosthodontics Dental Materials (part III) Denture Prosthetic teeth Resin denture teeth provide good esthetics wear resistance bond chemically to resin bases Composite resin denture teeth cause less wear to opposing enamel and gold surfaces than porcelain teeth They are the material of choice for single dentures opposing natural dentitions Porcelain denture teeth are mechanically attached to the resin bases by pins or diatoric holes (Disadvantage: mechanical attachment limits the use of the teeth in complete denture fabrication) Requirements of Prosthetic Denture Teeth Durable bond with the denture base material Resistance to oral fluids/solvents High heat-distortion temperatures No permanent deformation under forces of mastication High impact strength to withstand forces during mastication High abrasion resistance with little or no wear to maintain the predetermined vertical dimension of occlusion and withstand parafunctional movements Esthetically pleasing, inconspicuous, with adequate translucency, color stability, good surface texture, and ease of characterization to produce a natural appearance Easily adjusted and refined by grinding and easily polished Advantages and Disadvantages of Porcelain Teeth Porcelain teeth cause significant wear of opposing enamel and metallic occlusal surfaces; This prohibits their use in single complete dentures opposing natural teeth or those with gold occlusal surfaces The teeth are quite brittle and easily crack or chip on impact The teeth are difficult to grind for occlusal adjustments because they lose their surface glaze, and polishing is quite difficult; They are not indicated in limited interarch spaces because of the very limited ability to reshape their cervical areas Porcelain teeth produce noisy clicking sounds upon contact with each other Their higher density increases their weight Mismatches in the coefficient of thermal expansion of porcelain and resins produce stresses in the resin base, which may lead to distortion of the bases They exhibit high heat distortion temperatures They allow the dentures to be rebased without a need to replace the teeth They are insoluble in oral fluids and in most organic solvents They are dimensionally stable and hard in comparison with the softer resins Porcelain teeth have a high wear resistance that is equal to or greater than natural teeth, and 10 to 20 times that of resin teeth They exhibit no permanent deformation under occlusal loading Summary of Prosthetic Teeth In the selection of denture teeth for complete dentures and considering the above properties of the various materials: AVOID combining posterior resin teeth with anterior porcelain teeth There is a significant difference in abrasion resistance in both materials, with Resin wears more rapidly than porcelain, this creates destructive occlusal forces in the anterior, leading to ridge resorption and instability of the prostheses A comparison of properties (Methyacrylate Resin and Procelain Teeth) Insert table*** Comparison of Properties: Methacrylate Resin, Porcelain Teeth Methacrylate Resin Porcelain Bond w resin Base Chemical bond Mechanical via pins, diatoric holes Mechanical Properties Less Brittle, high resistance and toughness Very brittle/chipping on impact Solubility in Oral fluids, dimensional changes Insoluble w some dimensional change Insoluble, inert in oral fluids No dimensional change Maintenance of Vertical Dimension (VDO) Low abrasion resistance Significant wear Wear can reduce VDO Excellent abrasion resistance Hard, insignificant wear VDO maintained Resistance to Thermal Shocks Good resistance Less than resins Effect on Opposing Occlusion Can oppose natural teeth or metallic occlusal surfaces Abrades opposing tooth enamel/metallic surfaces Tooth contouring/occlusal adjustment/repolishing Relatively easy Difficult, may result in loss of surface glaze Grinding of ridge/lap areas Easy to grind w/o compromising tooth-resin bond Difficult to position or retain in limited interarch space Esthetic Properties Excellent, characterized as required Excellent, can be characterized Clicking Sounds None on contact w opposing teeth (natural feel) Noisy/clicking occurs w opposing porcelain teeth FACEBOW TRANSFER, MOUNT EDENTULOUS MODELS, SET DENTURE TEETH Articulator (WM 2240 by whipmix) Mechanical instrument that represents the TMJ and jaws to which maxillary and mandibular casts attached to simulate some or all mandibular movements Facebow To record the anteroposterior(AP) and medial lateral (ML) spatial position of the maxillary occlusal surface relative to the hinge axis from the patient to the articulator. Helps hold the maxillary cast in place during mounting Arbitrary facebows: Sufficient for most dental procedure Approximate horizontal hinge axis and rely on anatomic average values. Three point reference >>>>> The use of an anterior reference point enables the clinician to duplicate the recorded position on the articulator at future appointments. Serves as a reference to average anatomic values Allows subsequent casts to be mounted without a repeat recording Kinematic facebows: Precisely locate and reproduce the horizontal hinge axis. Can change patient’s vertical dimension of occlusion on the articulator without error. Pantograph: Used with a fully adjustable articulator Uses a kinematic hinge axis facebow The hinge axis of the mandible can be determined to be within 1 mm by observing the movement of the kinematic facebow styli positioned immediately lateral to the TMJ close to the skin. The locator is adjusted so the pointer remains stationary during hinge movement >> Clinical steps to facebow Heat a sheet of baseplate wax in hot tap water until it becomes soft and flexible. Adapt the wax to the bitefork so that it is uniformly covered. Place the wax-covered bitefork against the maxillary teeth. Center the shaft of the fork with the patient's midline. Support the bitefork and have the patient close lightly into the wax to obtain shallow impressions of only the cusp tips. Cool the wax and remove the bitefork from the mouth. Trim away excess wax. This record can be achieved using PVS bite registration paste on this bite fork Patient guides earpieces as the dentist inserts bitefork shaft into toggle under facebow >> The three thumbscrews on the top of facebow are tightened. Firm pressure is placed on the end of the nasion relator, and the thumbscrew is tightened The two toggles are tightened with a hex driver or a T-screw The 2200 series instrument has a permanent non-adjustable intercondylar width of 110 mm. This corresponds to the "M" width shown on the facebow. Some articulators will require that you record this setting Loosen the thumbscrew Remove the plastic nasion relator. Loosen the three thumbscrews on top surface of the facebow by one-quarter turn Patient slowly opens then you carefully remove the entire assembly from the head. Recheck and securely tighten the toggles. It is sometimes difficult to adequately tighten these toggles while the facebow is on the patient's head. Articulator features Arcon Type Semi Adjustable Adjustment for condylar inclination Adjustment for progressive and/or immediate side shift (Bennett angle/side shift) Centric lock: centric latch is snapped closed to hold condyles in a retruded position Condylar inclination: The angle of inclination of the condylar guidance to an accepted horizontal plane Bennett angle: The angle formed by the sagittal plane and the path of the advancing condyle during lateral mandibular movement, as viewed in the horizontal plane. Adjustment for progressive and/or immediate side shift Anterior guidance: How the anterior teeth protect the posterior teeth when the mandible is brought forward. Anterior teeth guidance is recorded in acrylic resin on the anterior guide table.