Effect of handling technique and water/gypsum relation on dental stone compression strength

Abstract

The plaster is widely used in dentistry with different purposes. Despite of several authors defend the accurate control of the water/powder ratio for plaster products, in clinical practice, professionals usually neglect the manufacturers’ instructions and make empiric manipulation of dental plaster. The objective of this study is to assess the influence of the agglutination method of the water in powder or powder in water mixture, as well as the relation of random water/powder on the dry compression strength of two types of plaster, and also, to propose the replacement of a beaker by an experimental rubber bowl. In this study, type III and type IV plaster were tested (n = 8). For each one, five groups were defined with different manipulation methods: Gc-group control, GI-BGP (balance, graduate rubber bowl and powder on the liquid), GII-BPA (balance, test tube and water on the powder) GIII-AGP (random mixture, graduate rubber bowl and powder on the water), GIV-BAA (balance, random mixture and water on the powder). In total, 80 specimens were tested. After 7 days at 37 degrees Celsius, specimens (2 cm in diameter and 4 cm in height) were compressed in a universal testing machine. According to the results (kgf), obtained by the compression for the type III plaster, there was no difference for the agglutination method (p = 0.25), but for the type IV plaster, there was difference among the treatments (p = 0.03), since the use of an experimental rubber bowl made the strength values, similar to the other groups, possible. Key words: Plaster. Compression strength.