The International Journal of Prosthodontics, 06/1992

The reproduction of natural tooth color using porcelain restorations is quite cumbersome, for it is difficult to select, communicate, reproduce, and evaluate color objectively. The present process of color reproduction lacks precision and is primarily dependent on the individual efforts and abilities of the dentist and ceramist. The computer color-matching system, aided by a spectrophotometer and computer, can be an excellent method for reproducing specific colors of various objects. This paper reports application of the system to reproduce various opaque colors used for metal ceramic restorations.

Textured opaque porcelains have been introduced to improve the appearance of metal ceramic restorations by increasing light refraction. This investigation compared the shear bond strength of a textured opaque porcelain with that of a conventional opaque porcelain. Opaque and body porcelains were fired onto six different alloys and the specimens were loaded to failure by applying shear force at the alloy-porcelain interface. No significant differences in bond strength were found between the textured and conventional opaque porcelains for any of the alloys tested.

The inaccuracy of premixed porcelain shades may cause errors when color matching porcelain crowns. Most brands of porcelain are labeled to match shades of the Vita shade guide, but produce slightly different colors from this guide upon firing. The purpose of this study was to quantify in CIE delta E* units the color differences between the Vita shade guide colors and four commercial porcelains for metal ceramic crowns. Two operators prepared shade-guide teeth from six shades of four brands of porcelain. Opaque, body, and incisal layers were fired in the form of shade-guide teeth on Vita ceramic carriers used for making custom shade-guide teeth. The colors of these teeth were measured with a Beckman spectrophotometer with an integrating sphere. The average delta E* values for the differences between the colors of the Vita shade guide and the fired porcelains for each of the brands were 3.1, 2.9, 4.1, and 2.0, respectively, for the first operator and 4.1, 2.6, 2.8, and 1.6, respectively, for the second operator. The color difference between the custom shade-guide teeth and the Vita master shade guide were significantly affected by both brands and shades. The overall average error resulting from the differences in colors between the Vita shade guide and fired porcelains was 3.0 for the first operator and 2.8 for the second operator. The mean delta E* between the teeth prepared by the two operators was 3.6. The color difference between the teeth made by the two operators was not significantly affected by brands or shades.

This study compared the tactile sensitivity of splinted abutment and denture teeth of 16 fixed partial dentures (FPD) supported by blade implants and 16 removable partial dentures (RPD) in patients with Kennedy Class I and Class II edentulous conditions. No significant differences were noted between the tactile thresholds of the natural abutment teeth and artificial teeth in the FPD and RPD groups. The splinted abutment teeth required 45.4 g, or 5.4 to 5.8 times higher occlusal loads than did those needed for the comparable nonsplinted teeth, to detect the stimulus. A further increase of 54% in thresholds with the FPD and over 100% with the placement of the RPD indicated the superiority of the RPD in terms of load distribution as a result of the cross-arch splinting and mucosal support. Moderate positive correlations (r = 0.37 to 0.46; P .05) between tactile thresholds and masticatory performance were found, signifying that reduced tactile perception was not responsible for the incomplete restoration of the masticatory function with RPDs or FPDs but might be contributing to increased masticatory performance within both treatment groups.

Partial-coverage porcelain laminate restorations may successfully be used to create undercuts for removable partial denture abutment teeth. If recontouring of such restorations becomes necessary after placement, surface polishing would be necessary prior to removable partial denture fabrication. In this study the wear of luted porcelain laminates, which received a polished surface treatment and contacting I-bar clasps, was quantified over a simulated 2-year period when subjected to removable partial denture placement and removal. Scanning electron photomicrographs and computer imaging were used for wear measurement. These data were compared to previously recorded data on wear of I-bar tips against human enamel and glazed, luted, porcelain-laminate restorations under the same experimental conditions. No measurable wear was observed on any of the laminate specimens. I-bar clasps tested against the glazed laminate restorations exhibited the greatest mean wear, and those tested against the polished laminates exhibited the least mean wear.

This paper follows a previous report of an investigation regarding treatment of patients having atrophic mandibles. These patients either had surgery and received new dentures or received new dentures only. This paper reports the opinions of the patients concerning their treatment after an average of 6.5 years. The results showed that the patients in the group with atrophic mandibular ridges that were surgically treated were more generally satisfied with their dentures in comparison with the group of patients with atrophic ridges that were not surgically treated. The attitudes of the latter did not differ from the control group of patients having normal ridges.

Resin-bonded prostheses were clinically evaluated following a mean period of 41 months. The abutment teeth were minimally prepared, and one groove was placed on the surface approximating the edentulous space. Retainers were treated using the Silicoater technique. Thirty-four prostheses were made for 32 patients. Four patients were lost from the study and 30 units were re-examined. Two prostheses had debonded. The results suggest that resin-bonded prostheses can be successful if meticulous attention is given to the procedures outlined.

An in vitro study was conducted to determine the accuracy of fit of the acrylic resin pattern for the implant-supported prosthesis to the implant abutments. A master model containing five Nobelpharma titanium implants was fabricated using Ivocap acrylic resin. Using this model, five standardized acrylic resin patterns were fabricated from the three test dental acrylic resins. The fabricated patterns remained on the master model for 24 hours before removal and subsequent measurement. To compute the accuracy of each pattern, three special measuring points were firmly attached to each gold cylinder prior to pattern fabrication and the x, y, and z coordinates of these measuring points were determined. Measurements were made prior to pattern fabrication, with the cylinders on their respective abutments and after pattern fabrication, when the pattern had been removed from the master model. The results of this study showed that there was a significant difference in accuracy between the test acrylic resins and that none of these materials was completely accurate.

This in vitro study measured the changes in the fracture resistance of posterior crowns as a function of crown length. The crowns, 10 for each group, were made of a feldspathic porcelain (Ceramco), a glass-ceramic material (Dicor), and an alumina-reinforced glass (In-Ceram). Three different crown lengths were tested on acrylic resin dies. The restorations were fractured in a testing machine using a steel ball, 12.7 mm in diameter, that contacted the occlusal surface at three distinct points. Statistical analysis was performed using the Weibull distribution. The fracture resistance increased significantly with increasing crown length for all crown materials.

Previous studies have shown that light-polymerized denture base resins have a cytotoxic effect on oral epithelial cells. The purpose of this in vitro study was to examine the effects of two denture base resin sealants when used on three light-polymerized denture base resins. Sample disks were examined for their effect on protein synthesis. Results indicate that one sealant protected the cells against toxic effects of the materials (P .05), while one sealant enhanced toxicity up to 88% above that attributed to the resin alone.

This paper demonstrates the potential for cross contamination with bacteria and viruses from impression materials and evaluates the efficacy of four disinfection systems on irreversible hydrocolloid impressions contaminated with Streptococcus sanguis or poliovirus. An irreversible hydrocolloid impression was made of a contaminated acrylic resin template. The impression was disinfected and residual microorganisms were harvested by sonication, cultured, and counted. The results showed that the impression material could act as a vehicle for the transfer of both bacteria and viruses. Further, the virus was shown to be present in the body of the impression and under certain conditions may evade decontamination.