Continued Linear Setting Expansion in Two Proprietary Type IV Dental Stones

Abstract

Objective: To report linear setting expansion of two commercially available type lV dental stones at various time periods.

Methodology: An Analytical study design conducted from December to June 2006 involving 60 stone casts poured in impressions of a machined brass model. After an elapse of a post-mixing and pouring period of 2 hours, the initial linear setting expansion as observed between chosen reference points on each cast was made using traveling microscope. On each cast, further observations and recordings of the linear expansion between reference points were also made at test periods of 24, 4g,72, 96, 12O and 158 hours.

Results: Generally, linear setting expansion continued over the test periods with the highest expansion values at 168 hours on some casts. Expansion reached at peak value for casts poured in Silky Rock at the 95 hours test period as compared to 120 hours in those made in GC Fuji Rock stone. ln case of GC Fuji Rock, 44.8% of the overall expansion occurred by the test period of 2-hours as compared to 76.7% in case of Silky Rock. Furthermore, the observed values for the setting expansion at the 2-hours test period were different from those provided by the manufacturers and for one product were significantly different.

Conclusion: Considering the observed varying setting behavior of the test stones and its deviation from the manufacturer's provided data and the many available ones for dental application, the importance of continued research in the area is highlighted.