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The purpose of this investigation was to evaluate the dissipation of a force applied to an assembled stack of implant components. The stack consisted of a 10-mm threaded implant, a screw-retained abutment and a screw-retained gold crown. The dissipation of force was analyzed in relation to varying the implant diameter with and without a concomitant change in abutment diameter. Two experimental groups were evaluated. The first group consisted of 25 titanium screw-form implants (Implant Innovations, Inc.). These implants measured 10 mm in length and 3.25 mm, 3.75 mm, 4.0 mm, 5.0 mm, and 6.0 mm in diameter. The second group included 15 titanium screw-form implants (Nobel Biocare, Inc.) measuring 10 mm in length and 3.75 mm, 4.0 mm, and 5.0 mm in diameter. All implants were embedded in standardized photoelastic resin blocks. Points of interest were marked on each block using standardized templates to ensure consistency. Implants were restored using system-specific conical abutments and standardized single-unit restorations. A strain gauge was affixed to each abutment, and an eccentric load of 176 N was applied to the restoration. Periimplant stresses were measured using photoelastic analysis. Abutment strain was determined using an electronic strain indicator. Data were collated and compared using ANOVA and the Duncan multiple range statistical tests. When stress was analyzed at points on the resin-implant interface or a fixed distance from the interface, stress tended to decrease from the 5-mm-wide implant to the 6-mm-wide implant. Stress in relation to the 3.25-mm, 3.75-mm, and 4.0-mm implant was not as well defined, indicating the possibility that some deformation of implants was occurring. Increased abutment width resulted in decreased abutment strain. Therefore, using a wider abutment may be helpful in preventing preload reduction in clinical applications. This may reduce the incidence of loosening and fracture of abutment and restoration screws.

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A rationale for the use of Twin-Flex clasps is presented. Twin-Flex clasps may provide improved esthetics, an increased number of clasping sites, and enhanced patient comfort when compared with conventional clasping systems. Two fabrication methods are described, and departures from conventional clasping techniques are explained.

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STATEMENT OF PROBLEM: Metal ceramic restorations have been implicated in the discoloration of associated gingival tissues. Attempts to remedy this by altering the design of the metal frameworks for such restorations may lead to unacceptable decreases in fracture resistance. PURPOSE: This study evaluated a new metal framework design for metal-ceramic restorations. MATERIAL AND METHODS: Twenty artificial crowns were fabricated with various degrees of facial metal reduction; 0, 1, 2, and 3 mm. The study was conducted in two parts. The first part evaluated changes in light transmission into adjacent root tissue. A light box was fabricated so sample crowns could be illuminated on a mounted natural tooth. The root of the tooth remained outside the light box, and the light transmitted through the crowns into root tissue was measured with a light meter. The second part of the study evaluated changes in fracture strength. The sample crowns were subjected to a vertical load until fracture with use of an Instron machine at a crosshead speed of 1 mm per minute. The load at fracture was recorded. RESULTS: Results indicated a statistically significant increase in light transmission with 1 mm framework reduction or greater, and fracture strengths did not decrease with up to 1 mm of framework reduction. A 1 mm facial axial reduction of the metal framework may be indicated for anterior metal-ceramic restorations.

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Proper extension and adjustment of denture borders is a critical component in successful removable prosthodontic treatment. Unfortunately, commonly marketed disclosing media may not provide appropriate viscosities for the accurate assessment of denture border extensions. This article provides a technique for the mixing, unit-dose packaging, and utilization of a disclosing medium that is extremely well-suited for denture border applications. The technique employs commonly available materials and compiles with current "unit-dose" guidelines.

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A technique for the fabrication of light-activated maxillary record bases is described. The use of a segmental polymerization process provides improved palatal adaptation by minimizing the effects of polymerization shrinkage. Utilization of this technique results in record bases that are well adapted to the corresponding master casts.

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Recently, an injection system for use with microwaveable denture base resins was introduced. Preliminary evaluation of this system was performed a university-based dental laboratory. This article provides a description of the complete denture fabrication technique, as well as observations regarding its design and practicality.

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Metal bases sometimes are used to enhance the physical properties of complete dentures. Unfortunately, improper positioning of metal-resin finish lines may adversely affect phonetics. In the past, placement of these finish lines has been somewhat arbitrary. This article describes a precise method for the placement and contour of metal-resin finish lines. The resultant prostheses should exhibit surfaces that reestablish proper anatomic, physiologic, and phonetic contours.

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A checklist is presented for use in evaluating and planning the treatment of patients for complete-denture therapy. A thorough explanation of each item and classification included in the checklist list also is presented. Classifications from the classic prosthodontic literature are used wherever possible and their sources are referenced appropriately.

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A variety of materials have been used in the fabrication of denture bases. The advantages and disadvantages of these materials are discussed. Special emphasis is placed on polymeric material. particularly poly (methyl methacrylate) (PMMA). The chemical basis for formation of PMMA is provided to facilitate understanding.

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Successful porcelain repair requires conditioning of porcelain surfaces. Conditioning is intended to facilitate wetting by repair materials and improve interfacial bonding. The objective of this investigation was to determine the effects of selected surface treatments upon the wettability of a representative feldspathic porcelain. Dynamic contact angle analysis and scanning electron microscopy were used to characterize the effects of such treatments. Standardized porcelain specimens were subjected to the following five treatment regimens: (1) control (no treatment); (2) airborne particle abrasion using 50 microns aluminum oxide; (3) etching with ammonium bifluoride gel; (4) etching with acidulated phosphate fluoride gel; and (5) etching with hydrofluoric acid gel. Following treatment, specimens were cleansed and dried. Advancing contact angles were quantified using dynamic contact angle analysis. Mean values and 95% confidence intervals were (in degrees): control, 63.8 +/- 2.7; ammonium bifluoride, 39.4 +/- 2.0; airborne particle abrading, 29.1 +/- 2.9; acidulated phosphate fluoride, 24.9 +/- 1.7; and hydrofluoric acid, 16.5 +/- 1.2. Significant differences were found between all treatment groups (P = .05). Subsequent scanning electron microscopy examination of treated surfaces indicated lesser contact angles were associated with surfaces displaying deeper and wider grooves. Apparently, the resultant increase in surface area produces increased wettability. It is inferred that an increase in surface area may correspond to enhanced resin-porcelain bonding.

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Proper trimming of stone dies is an essential step in fixed prosthodontics. Die trimming requires meticulous technique and a thorough understanding of required elements in die design. By dividing the die into three zones, die contour requirements can be better understood, discussed, and demonstrated. A two-step technique provides optimal results, incorporating a logical plan with the use of proper magnification and illumination.

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For many years, gold and base metal alloys have been used in the construction of cast removable partial dentures. Each alloy has desirable properties, yet neither is ideally suited for all portions of a framework. A method has been developed to fabricate prostheses by casting gold alloy against a base metal alloy. This procedure allows the practitioner to combine the favorable characteristics of both alloys within a single framework. Consequently, the practitioner may create frameworks that more effectively meet the biomechanical demands of the oral environment.

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