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Abstract
This study investigated the dimensional accuracy and stability of both polyether and polyvinyl siloxane.
The study included the effect of mixing methods where hand mix versus auto- mixing technique the effect of disinfectant on the accuracy of impression and pouring the impressions at different times of storage (1 hour,4 hours and 24 hours).
Impressions were made for a master model cast of mandibular arch with two prepared abutments; right second premolar and right second molar with a shoulder finish line made as to give a definite margin that was easily defined where there was an occlusal shoulder and a gingival shoulder used for occluso-gingival (O-G) measurements. , there was an occlusal holes made on occlusal surface of both teeth as to be used as reference points for inter-abutment distance record of the prepared abutment. All dimensions were measured on casts retrieved from impressions made on master model.
The impressions were then poured with improved stone into stone casts, according to times under investigations.
Data were presented as means and standard deviation values. One sample t-test was used to compare between means inter-abutment distance and occluso-gingival height measurements of the tested groups and measurements of the master cast. Student’s t-test was used to compare between mean differences (deviations) from the master cast of the two mixing techniques, two impression materials and specimens with and without disinfectant. One-way Analysis of Variance (ANOVA) was used to compare between mean differences (deviations) from the master cast after 1, 4 and 24 hours. Duncan’s pair-wise comparison test was used to determine significant differences between the means when ANOVA test is significant.
The results of this study revealed that the elastomeric impression materials used in this study exhibited comparable clinical accuracy when properly handled.
In general it was seen that:
The vinyl polysiloxane was more accurate and dimensionally stable than polyether. The auto-mix technique showed higher mean dimension than hand mix, auto mixing in general exhibits lesser voids contents so seemed to be the least predictable fluctuating of the techniques tested but also the effect of other variables may affect its accuracy.
The disinfection and the storage time have no or minimal effect on the accuracy of the impression material used.