Surface detail, compressive strength, and dimensional accuracy of gypsum casts after repeated immersion in hypochlorite solution

Abstract

One method used to disinfect a dental cast is immersion in a disinfecting solution. Repeated immersion of a cast in disinfectant may affect surface detail as well as other physical properties. The purpose of this study was to evaluate the changes in surface detail quality, dimensional accuracy, and wet compressive strength of dental casts as a result of repeated disinfection in slurry containing 0.525% sodium hypochlorite solution. Two different test specimen configurations were used, one for evaluating surface detail quality and dimensional accuracy and the other for compressive strength. Sixty specimens each were made of type III and type IV dental stone (Excalibur). Thirty specimens were immersed in slurry, a supernatant solution of calcium sulfate in distilled water (control casts), and 30 in slurry with sodium hypochlorite (test casts) solutions for 30 minutes and air dried for 24 hours. This process was repeated 7 times before testing. Linear dimensional change, surface detail quality, and wet compressive strength were determined according to American National Standards Institute/American Dental Association (ANSI/ADA) standards. The data were analyzed using 2-way analysis of variance and 2-sample independent t tests (alpha=.05). For specimens prepared with type III and type IV stone, treatment by immersion in slurry (control casts) and in slurry with sodium hypochlorite (test casts) resulted in an increase (P<.0001) in linear dimensional change. The type IV casts treated with slurry with sodium hypochlorite showed significantly less (P<.0001) mean linear dimensional change (0.025%) compared with type III stone casts (0.063%), and the values remained within the ANSI/ADA specified standards. Both test solutions caused some degree of erosion or damage to the surface quality of casts made from type III and type IV stones. However, the difference between the control and test casts was not significant. Slurry with 0.525% sodium hypochlorite solution decreased the compressive strength of both types of stones significantly (P<.001) compared with distilled water slurry. However, the values remained close to ANSI/ADA standards. The results demonstrated that repeated immersion of type III and type IV stone specimens in slurry with distilled water and slurry with 0.525% sodium hypochlorite, along with drying in air, caused a significant increase in linear dimension and a significant decrease in wet compressive strength. Although both the solutions caused some degree of damage to surface details for type III and type IV stones, the difference was not significant.