PubMed · 2944324
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G Schlegl. 1986. [The new generation in titanium casting technology].. https://pubmed.ncbi.nlm.nih.gov/2944324/
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It is the desire of every dentist and dental technician to produce a restoration that will fit the patient with a minimum of adjustments and certainly one that does not require remaking. Yet many abuse the materials with which they work, either through improper manipulation, lack of familiarity with their properties, or by attempting to reduce laboratory time by taking short cuts. Wax is one of the materials that requires more knowledge and skill to manipulate accurately because it has a considerably higher coefficient of thermal expansion (and contraction) than any other dental material. It often contributes considerably to the inaccuracies of cast dental restorations. This article provides a review of dental waxes used to make prosthodontic castings and points out some of the properties of waxes that must be controlled to make accurate restorations.
Recently, several new products of investments for "quick heating" have been put on the Japanese market. The total casting procedure time for this quick heating method involves only one hour; 30-minutes waiting after the start of mixing before placing the mold directly into the 700 degrees C furnace and 30-minutes heating in the furnace. The purpose of this study was to evaluate two variables effecting casting accuracy using these new investments. The effect of thickness of the casting liner inside the casting ring and the effect of waiting time before placing the mold into the 700 degrees C furnace were evaluated. A stainless-steel die with a convergence angle of 8 degrees was employed. Marginal discrepancies of the crown between the wax patterns and castings were measured. The size of the cast crown became larger when the thickness of the ring liner was thick and when the waiting time before placing the mold into the furnace was long. These results suggest that these new investments have the advantage of providing sound castings using short-time casting procedures. However, it is necessary to pay careful attention to the casting conditions for obtaining reproducible castings.
The authors examine the detail reproduction capacity and surface roughness of 11 commercially available materials [6 plasters (stones?), 2 epoxy resins and 3 polyurethane resins] indicated for the construction of working models with individually extractable dies. The study was performed in vitro according to the method outlined by the ADA in specification no. 19 relating to materials for elastomeric imprints. This specification describes the use of a steel test-block with which it is possible to prepare a master imprint in polyvinylsiloxane. This imprint allows the grooves of the test-block to be reproduced in the form of angular crest which represent the details to be reproduced. Both the master imprint and the samples to be tested were prepared according to the manufactures instructions. The study was performed in three stages: macroscopic analysis, microscopic analysis, profilometric analysis. The macroscopic analysis did not show any differences between the different materials tested. The microscopic analysis showed that when enlarged 40 times the resins revealed a smoother surface than the plasters. The surface quality of plasters was improved by using a hardening solution recommended by the manufacturer as an alternative to water, or by using spacer paint. The plaster materials gave excellent angular definition contrary to the epoxy and polyurethane resins. The use, where advised, of the hardening solution as an alternative to water did not alter this parameter. The electronic profilometer used for the profilometric analysis comprised a diamond sensor which, when run along the surface, recorded all roughness, translating it into chart form.(ABSTRACT TRUNCATED AT 250 WORDS)