Influence of re-using reversible hydrocolloids on the linear alteration of coating models.

Reusing reversible hydrocolloids too many times may cause alterations of the coating model and produce unsatisfactory RPPs. The aim of this study was to analyze the linear alterations of coating models reproduced from molds obtained with two commercial brands of reversible hydrocolloid (RH) with 15 reuse cycles of the material. A metal model was used with 4 marks (A, B, C and D) on which the distances AB, BC, CD, DA, BD and AC could be measured lineally. Ten models were divided into two groups according commercial brand of RH: group VIPI-Duplicator VIPI and group K27--Duplicator K27l. The RH was heated in a microwave oven and poured into a flask containing the model. The mold was filled with the ethyl silicate coating, and after crystallization, refractory models were obtained. This was repeated in the 15 re-use cycles of each RH. The refractory models obtained from the 1st, 5th, 10th and 15th times of re-use of RHs were measured under a measuring microscope. The means were submitted to the Analysis of Variance, Tukey and Dunnet tests, to a 5% level of significance. Group VIPI showed linear alterations in relation to the plaster models, for distances AB (1 use = -1.25% and 5th re-use = -1.20%); AD (1st use = 0.76%, 10th re-use = 0.65% and 15th re-use = 0.52%); BD (1st use = 0.58%). Both commercial brands analyzed produced coating models with acceptable linear alterations in up to 15 reuse cycles, no statistical difference being observed between them.