Efeito da manipulação e da classificação nas propriedades físicas e mecânicas do gesso

Abstract

Dental plasters are made from gypsum (calcium sulfate dihydrate). When gypsum is subjected to the calcination process, it results in water molecules and a fine hemihydrate powder, which is called gypsum powder. The types of plasters used in dentistry are distinguished by the crystal shape and compaction, and due to their differences, each is intended for specific work within prosthesis laboratories. The objective of this work was to evaluate the effect of manual and mechanical vacuum manipulation on thermography and surface roughness in different types of plaster: commom or type II, type III stone and type IV stone. For this, we have used the three types of plaster mentioned above and the two types of manipulation (manual and mechanical vacuum). The samples were divided into six groups: n=3 for temperature analysis (GT groups) and n=10 for surface roughness evaluation (GR groups): GT2M, GT3M, GT4M, GR2M, GR3M, GR4M with plaster type II, type III stone and type IV stone, respectively, which were manually manipulated (M) and GT2V, GT3V, GT4V, GR2V, GR3V, GR4V with common plaster, type III stone and type IV stone, respectively, which were mechanically handled under vacuum (V). Temperature results were qualitatively analysed, and surface roughness results were submitted to statistical analysis. Temperature x time graphs showed that vaccum handling reached the temperature peak in less time than manual handling, regardless of the type of plaster used. Regarding each type of manipulation, the type IV plaster reached a higher temperature in less time. The roughness data showed that there was a statistically significant difference between the types of manipulation and between the types of plaster. Manual manipulation had higher surface roughness than vacuum manipulation, and type II and III plaster had greater roughness than type IV. In conclusion, the vacuum manipulated IV plaster presents lower surface roughness and reaches the temperature peak in a shorter time in the prey reaction in comparison with the other types of plaster analysed.