Effects of rapid burnout type gypsum-bonded investment on performance of castings. Part 1. Surface aspects and fit of crowns

Accuracy of ringless casting and accelerated wax-elimination technique: a comparative in vitro study

PURPOSE

The purpose of this study was to determine whether the ringless casting and accelerated wax-elimination techniques can be combined to offer a cost-effective, clinically acceptable, and time-saving alternative for fabricating single unit castings in fixed prosthodontics.

MATERIALS AND METHODS

Sixty standardized wax copings were fabricated on a type IV stone replica of a stainless steel die. The wax patterns were divided into four groups. The first group was cast using the ringless investment technique and conventional wax-elimination method; the second group was cast using the ringless investment technique and accelerated wax-elimination method; the third group was cast using the conventional metal ring investment technique and conventional wax-elimination method; the fourth group was cast using the metal ring investment technique and accelerated wax-elimination method. The vertical marginal gap was measured at four sites per specimen, using a digital optical microscope at 100× magnification. The results were analyzed using two-way ANOVA to determine statistical significance.

RESULTS

The vertical marginal gaps of castings fabricated using the ringless technique (76.98 ± 7.59 μm) were significantly less (p < 0.05) than those castings fabricated using the conventional metal ring technique (138.44 ± 28.59 μm); however, the vertical marginal gaps of the conventional (102.63 ± 36.12 μm) and accelerated wax-elimination (112.79 ± 38.34 μm) castings were not statistically significant (p > 0.05).

CONCLUSIONS

The ringless investment technique can produce castings with higher accuracy and can be favorably combined with the accelerated wax-elimination method as a vital alternative to the time-consuming conventional technique of casting restorations in fixed prosthodontics.

Marginal gap of crowns made with a phosphate-bonded investment and accelerated casting method

STATEMENT OF PROBLEM

Numerous materials and methods have been used for complete crown fabrication. Conventional investing and casting procedures for phosphate-bonded investments require a 2- to 4-hour process before completion. Accelerated laboratory techniques have been used, but may not result in castings with equal marginal accuracy.

PURPOSE

This study measured the marginal gap and determined the clinical acceptability of single castings invested in a phosphate-bonded investment with the use of conventional and accelerated methods.

MATERIAL AND METHODS

Forty-four individual stone casts were poured from impressions made from a master die. Conventional and accelerated methods of investing and casting were followed in the fabrication of 44 single-unit castings. Twenty-two casts were used in each of the 2 groups. Each casting and its respective stone die were examined with a microscope at 4 predetermined sites. Perpendicular and 25-degree tilted measurements of marginal gap were documented for each. Evidence of marginal gap was then evaluated by t test.

RESULTS

Measurements recorded on the perpendicular and on a 25-degree tilt showed no statistically significant difference between conventional and accelerated groups. All gap measurements except one were within the range of clinical acceptability. The measurements revealed that conventional and accelerated perpendicular gap means were 13.2 and 13.6 microm, respectively, and the average tilted gap means were 31.6 and 32.2 microm, respectively.

CONCLUSIONS

A phosphate-bonded investment (Ceramigold) selected for an accelerated casting technique produced single castings within 30 minutes with marginal gaps comparable to those found that used conventional methods.

Marginal fit and surface roughness of crowns made with an accelerated casting technique

STATEMENT OF PROBLEM

Conventional investing and casting techniques following the manufactures' recommendations are time-consuming. Accelerated casting techniques have been reported, but their accuracy has not been adequately studied for complete crown castings.

PURPOSE

This study evaluated the marginal fit and surface roughness of complete crowns made with a conventional and an accelerated casting technique.

MATERIALS AND METHODS

Part I of the study determined the mean time interval required for each investment to reach its maximum exothermic setting reaction temperature. Part II determined the marginal discrepancy of standardized complete crowns cast in a high noble metal ceramic alloy, with the use of four phosphate-bonded investments. A conventional technique (as recommended by the manufacturer) was compared with an accelerated technique that used 13- to 17-minute bench set time (as determined in part 1 for each investment)_ and 15-minute wax elimination cycle in a 815 degrees C (1500 degrees F) preheated furnace. Part III evaluated the surface roughness of castings made with the same techniques as in part II.

RESULTS

For the marginal discrepancy and surface roughness, crowns fabricated with the accelerated casting technique were not significantly (P > 0.05) different from those fabricated with the conventional technique.

CONCLUSION

The accelerated casting technique described in this study could be a vital alternative to the time-consuming conventional techniques.

Dental materials: 1995 literature review

This critical review of the published literature on dental materials for the year 1995 has been compiled by the Dental Materials Panel of the United Kingdom. It continues the series of annual reviews started in 1973 and published in the Journal of Dentistry. Emphasis has been placed upon publications which report upon the materials science or clinical performance of the materials. The review has been divided by accepted materials classifications (fissure sealants, glass polyalkenoate cements, resin composites, dentine bonding, dental amalgam, endodontic materials, casting alloys, investment materials, resin-bonded bridges and ceramo-metallic restorations, all ceramic restorations, denture base and soft lining materials, impression materials, dental implants, orthodontic materials and biomechanics). Three hundred and thirty articles published in 68 titles have been reviewed.