Effective taper criterion for the full veneer crown preparation in preclinical prosthodontics.

PURPOSE: Effective taper criteria must define a realistic, measurable goal that the student can visualize and achieve. Six degrees is widely accepted as the taper criterion for the full veneer crown preparation. However, studies show the actual taper of most preparations to be greater than 12 degrees. The purpose of this study was to determine whether 12 degrees is an effective taper criterion for the full veneer crown preparation in preclinical prosthodontics instruction. MATERIALS AND METHODS: A group of 191 full veneer crown preparations with 6 degrees as the taper criterion, and a group of 130 full veneer crown preparations with 12 degrees as the taper criterion were evaluated. All preparations were accomplished by preclinical dental students working on typodonts under examination conditions. RESULTS: The overall mean taper for each group exceeded the targeted criterion. The overall mean taper for the 6 degrees group was 14,490. When 12 degrees was the criterion, the overall mean taper was 15,580. The t test results indicate significant differences (p < .0001) between the targeted criterion and the actual preparation mean taper in all samples except one: the faciolingual measurements in the 12 degrees group. The faciolingual measurement of 12,920 was not statistically significantly different (.0542) from the targeted criterion of 12 degrees. CONCLUSION: The use of a 12 degrees taper criterion did not result in preclinical students achieving the goal of a 12 degrees taper. However, a 12 degrees criterion is more realistic than a 6 degrees criterion for full veneer crown preparations.

Microleakage of light-cured glass-ionomer restorative materials.

The microleakage of three glass-ionomer restorative materials, one chemically cured and two light cured, was evaluated. Ten restorations of each material were placed, according to manufacturer's instructions, in Class V cavities in bovine incisors. All cavities were prepared with 90-degree cavosurface margins and were located at the cementoenamel junction. Sectioning of the teeth after thermocycling and immersion in methylene blue dye revealed only occasional slight leakage and no statistically significant difference among the three materials.

The relationship between the width of the mouth, interalar width, bizygomatic width, and interpupillary distance in edentulous patients.

The width of the mouth, interalar width, bizygomatic width, and interpupillary distance were measured in edentulous patients. The widths varied widely, even when the population was separated into groups by sex and/or race. When mean values were studied, black men differed significantly from black women, white women, and white men in interalar and bizygomatic widths; white women differed from the other groups in all widths. No correlation was found between the widths for the population as a whole, nor when the population was further divided into race, sex, or group. When artificial teeth were chosen for eight randomly selected patients using a method recommended for each of the widths, the same mold was dictated by two methods for seven patients, and by three methods for five patients.

Three-dimensional stability of new denture base resin systems.

Ten maxillary dentures were constructed on standard-sized casts in each of four acrylic resins. Uniform placement of the artificial teeth and thickness of the base were maintained by use of a silicone rubber mold. Metal shot was luted in preselected positions to the dentures and the land of the cast. Frontal, lateral, and occlusal radiographs were made of the dentures at time intervals of (1) before processing, (2) after processing, (3) immediately after removal from the cast, and (4) 30 days later. Study of the radiographs revealed significant variations in position of the metal shot from the before-processing baseline within each group of dentures and significant differences between groups of dentures.