The influence of tray space and repeat pours on the accuracy of monophasic polyvinylsiloxane impression.

AIM: While literature demonstrates that the optimum accuracy is obtained with the custom trays, the use of stock trays for elastomeric impressions appears to be popular in general practice. The aim of the study was to evaluate the effect of thickness of impression material on the dimensional accuracy of impressions made from monophasic polyvinylsiloxane impression material. This study also studies the dimensional stability of the impressions poured at different time intervals.

MATERIALS AND METHODS: A metal model simulating two abutment teeth was fabricated along with reference lines inscribed on them. Custom impression trays were fabricated with spacer thickness of 2, 4 and 6 mm. impressions were made using monophasic polyvinyl siloxane impression material. The impressions were poured and stone models were obtained. The dimensional accuracy of the impressions were determined indirectly by measuring the dimensional changes of the recovered stone models. The dimensional stability was also evaluated by pouring the impressions at time intervals of 1 hour, 24 hours and 7 days. The obtained data was statistically analyzed.

RESULTS: The results of the study indicated that the impressions made from 2 and 4 mm tray space produced more accurate stone models when compared to 6 mm tray space. There was no significant deviation in the mesiodistal and buccolingual dimensions when impressions were made using impression trays with 2, 4 and 6 mm tray spacers. There was a significant decrease in interabutment distance (p = 0.001) and height of the abutment (p = 0.024) when impressions were made using impression trays with a tray space of 6 mm. There were no significant differences found among the stone models obtained from 1 hour, 24 hours and 1 week pour times.

CONCLUSION: The mesiodistal and buccolingual dimensions of the abutments were not affected by the variations in thickness of impression material. There was a decrease in the height of the abutment which was clinically not significant. As the thickness of the impression material increased, the interabutment space decreased, which is a factor of concern when impressions are made for fixed partial dentures.

CLINICAL SIGNIFICANCE: When monophasic polyvinylsiloxane is used as the impression material, stock trays can be used for making impressions for individual castings.