A Comparison of Dimensional Accuracy of Addition Silicone of Different Consistencies with Two Different Spacer Designs - In-vitro Study.
INTRODUCTION
Dimensional accuracy of impression materials is crucial for the production of working casts in Fixed Prosthodontics. The accurate replication of tooth preparations and their arch position requires impression materials that exhibit limited distortion.


METHODS
This study was conducted to comparatively evaluate the dimensional accuracy of additional silicones by comparing two different techniques and spacer designs, by measuring the linear changes in interpreparation distance. The impressions were made from a stainless steel master die simulating a three unit bridge. A total 80 die stone (type IV, Ultrarock) models were obtained from the impressions made using two different parameters. The two different parameters are Multimix and Monophasic technique and different spacer designs.


RESULT
The interpreparation distance of the abutments in the casts was measured using a travelling microscope. Each sample was measured thrice and the mean value was calculated. The results obtained were statistically analysed and the values fall within the clinically acceptable range.


CONCLUSION
The most accurate combination is multimix technique with spacer design which uses less bulk of impression material.
Technique for adapting a spacer for a custom impression tray.
A method of adapting a spacer for the custom trays used to make a definite impression for complete dentures is presented. The technique can be used under a variety of conditions and offers several advantages.
The dimensional changes of elastomeric impression materials under various conditions of humidity.
Abstract The dimensional changes of four modern elastomeric impression materials have been investigated under three different relative humidity conditions. It was found that the dimensional changes of these materials could be markedly affected by their storage conditions. Although no material was found to be completely stable, under particular conditions some materials were superior to others. It was also found that the curing system used for polysulphide materials profoundly affects their behaviour, whilst the presence of a thinner in a polyether material also has a strong influence on its behaviour. Recommendations are given on the optimum conditions for the different materials.