Evaluation of the dimensional changes and surface roughness of gold crowns cast with rapidly prepared phosphate-bonded investment: a pilot study.

STATEMENT OF PROBLEM: Accelerated bench-set and burnout schedules are used with little knowledge of the effect acceleration has on clinical factors determining casting success. PURPOSE: This pilot study investigated the effect of 2 rapid mold preparation schedules on full crown castings by comparing size, margin sharpness, and surface roughness. MATERIAL AND METHODS: Three groups of 10 crowns were cast with a type III gold alloy. All crowns were nominally identical, only their mold preparation schedules differed. Two groups used accelerated schedules; the third group was cast using a conventional schedule. Group comparisons were based on direct microscopic measurements of crown diameters (x50 magnification), and surface roughness was measured. Margin sharpness was judged by amount of marginal length lost in the axial direction as a result of the casting process. RESULTS: Measured crown diameters, indexing size for the 3 groups, were not significantly different. Crowns made with the conventional schedule had greater surface roughness, and better margin sharpness or length. CONCLUSION: Crowns were successfully cast using accelerated mold preparation techniques and considerable time was saved, but a small loss of margin length or fineness was observed.

Prosthodontic management of ectodermal dysplasia: a review of the literature.

Ectodermal dysplasia is commonly a difficult condition to manage with prosthodontics because of the typical oral deficiencies and because the afflicted individuals are quite young when they are evaluated for treatment. It is important that these individuals receive dental treatment at an early age for physiologic and psychosocial reasons. This article reviews the literature that pertains to the prosthodontic treatment of the disorder and the review includes considerations in behavior management and timing of treatment.

Effect of acid etching on the flexural strength of a feldspathic porcelain and a castable glass ceramic.

This project studied the effect of altering surface topography by chemical etching on the strength of a feldspathic porcelain and castable glass ceramic. Fifty specimens of each ceramic material were subjected to five different etch times (in groups of 10). A silane coupling agent and composite resin cement were applied. Specimens were then subjected to a three-point flexural strength test. Representative specimens were examined under scanning electron microscope to elucidate more information on the effect and the depth of etch. There was no significant difference in the mean flexural strengths between the etched and nonetched groups and no significant difference between the different etching times for either material. Photomicrographs revealed dissimilar etch depths and selective dissolution of the phases. It appears that chemical etching can improve the retention of ceramic laminate veneers without significant loss of strength.

Marginal accuracy of metal ceramic restorations with porcelain facial margins.

This study compared porcelain facial margins made with the direct-lift technique using high-fusing shoulder porcelains and the platinum foil technique with conventional body porcelain. Marginal accuracy was measured directly and the marginal sharpness computed by the software program MacDraft. Both Vita high-fusing shoulder porcelain and Vita SM 90 porcelain produced restorations that had significantly smaller mean facial marginal openings than crowns created with platinum foil. However, the SM 90 porcelain recorded significantly greater cross sectional or internal marginal discrepancies than the other two techniques (p < 0.05). Externally, the shoulder porcelains followed the facial rounding of the stone die; thus porcelain marginal roundings can be manifested as either negative roundings or underextensions and positive roundings or overextensions. The lack of marginal sharpness of porcelain facial margins may be influenced more by the die material rather than by the marginal porcelain or the technique.

Vectorial analysis of the static equilibrium of forces generated in the mandible in centric occlusion, group function, and balanced occlusion relationships.

Mechanical analyses supporting various and prevailing stomatognathic concepts of occlusal function are sparse. This study, using a mechanical model, simulates a system in function and provides a vectorial analysis based on a static equilibrium of forces generated in a mandible at 10 different positions. The positions analyzed were one in centric occlusion and nine in eccentric positions. Four eccentric positions were in a balanced occlusal relationship and five were in group function. Among other conclusions that were drawn, the most relevant seems to be the finding that cusp inclines and condylar path inclination have a profound influence on the forces acting within the joints and dentition.

Ceramic shade prescriptions for work authorizations.

The basic application provides essential data for ceramic veneer fabrication. Three-dimensional information divides the space for body and enamel components. The second body shade selection improves shade matching in the middle one-third of the tooth and enhances the appearance of the enamel component. Dentists are encouraged to recognize the influence each component has upon the total shade composition. A format is established for recording clinical information. The use of available ceramic systems is seemingly unlimited. The method presented provides flexibility for recording the most detailed shade information in simple graphic and verbal terms. Technical simplification is a by-product of complete, precise work information. Clinical judgements based on color and ceramic knowledge, as well as experience, can be conveniently converted into concise component descriptions. Using the suggested guidelines with reasonable care, a comfortable experience base for prescribing difficult shades can quickly develop.