The International Journal of Prosthodontics, 02/1994

Articulators have long been used for analyzing occlusal relationships during mandibular movements. However, a comprehensive evaluation of occlusal relationships can be hindered by the instrument as well as the casts. Recent developments in computer technology avoid these limitations by providing the ability to visualize and analyze occlusion. The process is accomplished by recording occlusal form and mandibular movements optically and then digitizing them for computer use. The computer can generate a visual simulation of the patient's occlusion at any position during mandibular movement, which enables analysis of the articulation from any perspective.

In 1989, 47 titanium copings veneered with a low-fusing ceramic were fabricated for 24 patients. Forty-four crowns could be examined after a period varying between 26 and 30 months. It was found that the bulk ceramic of two crowns had fractured. California Dental Association ratings for Surface and Color had changed markedly from the Excellent to the Acceptable level, and for Anatomic Form there was a small shift from the Excellent to the Acceptable level. The factor of Margin Integrity was recorded as satisfactory for all crowns and a large majority were rated Excellent.

The physical and viscoelastic properties of two resilient denture liners, the polyphosphazine-based Novus and silicone-based Molloplast b, have been characterized. The two materials were found to have comparable tensile strengths and frictional properties but differed in their tear strengths, water sorptions, and solubilities. Novus had a greater tear strength and lower solubility, but greater water sorption, than Molloplast b. Compressibility studies indicated that significantly less force was required to compress 2- and 3-mm thicknesses of Novus by 0.2 and 0.4 mm than for Molloplast b. Dynamic mechanical analysis indicated that Novus should have a greater propensity for energy/impact absorption.

The purpose of this investigation was to compare the tensile bond strength of one poly(vinyl siloxane) impression material/adhesive system to three different custom tray materials 10 minutes, 48 hours, and 7 days after adhesive application. One autopolymerizing (Fastray) and two light-polymerizing (Triad and Extoral) custom tray resins were examined. The Triad tray resin exhibited the significantly highest mean adhesive tensile bond strengths, and the Fastray resin exhibited the lowest. It was also observed that the 48-hour adhesive drying time group exhibited the highest mean adhesive tensile bond strengths for all the materials tested, and the 10-minute group exhibited the lowest.

The CELAY system for producing ceramic inlays and onlays using a resin pattern and copy milling is described. The mechanism uses no electronic assistance or imaging. Two different resin patterns are used, and direct and indirect techniques are described. All internal and external surfaces are reproduced by the technique.

There has been an increasing interest in the use of implants for partially edentulous patients. This introduces other biomechanical situations than those experienced in completely edentulous patients. In a prospective multicenter study, 521 implants in 154 patients were loaded with 197 free-standing prostheses. The patients have been followed for 3 years. The cumulative success rate for the prostheses was 94.8% and for the implants it was 93.9%. Most of the lost prostheses were only supported by two implants. A frequent technical complication was fracture and loosening of gold screws, which was more frequent in prostheses supported by only two implants.

This study evaluated the fracture resistance of three types of all-ceramic crowns and compared these to the fracture values of metal ceramics. Uniform metal ceramic specimens; veneered, cast glass-ceramic; and porcelain fused to two different dispersion-strengthened ceramic cores (Hi-Ceram and In-Ceram) were investigated. The metal ceramic specimens demonstrated a significantly higher resistance to fracture than did the Hi-Ceram or veneered glass-ceramic units but did not significantly differ from the In-Ceram specimens. The metal ceramic crowns showed cracks only in the ceramic layer, whereas the all-ceramic specimens underwent global fracture.

Shear-thinning, the decrease in the apparent viscosity of an impression material under a shear load, is a characteristic of many elastomeric impression materials and improves handling properties. However, it is unknown whether the subsequent viscosity of such material continues to be lower. This study compared the apparent viscosities of five elastomeric impression materials under two conditions. One group of the materials was manually spatulated and injected through an impression syringe before being tested; the other group of materials was manually spatulated only. It was found that the viscosities of these materials were not affected by the shear load applied during syringing.

This study investigated the relative significance of irradiation duration (20, 40, 60, or 80 seconds) and intensity; filler type (Silux Plus, a microfill or P-50, a hybrid); and shade (Universal or Gray) on the polymerization of resin composite within the depth of a simulated photopolymerized restoration. From the data, a mathematical model that predicts the extent of resin polymerization based upon the above stated variables was generated. The monomer conversion of specimens was determined by infrared spectroscopy. The results are of great clinical use and indicate that the most significant factor influencing resin composite polymerization is thickness of overlying resin composite. Both duration of exposure and light intensity demonstrate high and equal impact. Color and filler type have only minimal influence. The predictive model for resin composite polymerization provided a very good fit (r2 = .949).

The occlusal surfaces of inlays and onlays milled by the CEREC system are essentially flat, and surface morphology must be produced with rotary instruments. Six methods of finishing a machinable glass-ceramic material (Dicor MGC) were investigated using laser specular reflectance to assess the relative surface smoothness. The results indicated that all the methods produced a similarly smooth surface.

This article describes the methods and materials used to easily and quickly capture excursive mandibular border movements. The novel method can be used for edentulous and dentulous patients and provides bilateral, three-dimensional record stability. It allows an uncomplicated method of setting a semiadjustable articulator.

The purpose of this study was to determine the fracture load for three different core materials supported by three different post systems. The study was divided into nine separate groups, and each group comprised 10 samples. Specimens were placed in a special jig on a 45-degree angle, and the fracture load values were obtained using a universal testing machine. A 3 x 3 factorial two-way analysis of variance (P .0408) was used to test the effects of core material and post type on the fractural resistance. Fracture load values (as measured in pounds) were: Flexi-Post/Ti-Core, 204.9; Vlock/Ti-Core, 218.8; Parapost/Ti-Core, 164.8; Flexi-Post/Tytin, 156.0; Vlock/Tytin, 100.6; Parapost/Tytin, 134.6; Flexi-Post/Ketac-Silver, 69.4; Vlock/Ketac-Silver, 50.4; and Parapost/Ketac-Silver, 37.7. The titanium composite, Ti-Core, had the greatest fracture load values in all instances; the silver-filled glass-ionomer specimen, Ketac-Silver, had the least. The Flexi-Post and the microthread, Vlock, had the greatest fracture load values, and the Parapost had the least. Both the Flexi-Post and Vlock post have large bulky heads with many vertical and horizontal grooves, apparently facilitating the locking of the core material into the post.