Dimensional measurement accuracy of recent polyether and addition silicone monophase impression materials after immersion in various disinfectants : An in vitro study

Introduction: The aim of this study was to evaluate and compare the long-term dimensional measurement accuracy of recent polyether and addition silicone monophase impression materials after their immersion in three disinfectants (dual phenol, 2% glutaraldehyde and 0.5% sodium hypochlorite) for 10 minutes and 1 hour. Methodology: Two standardized stainless steel dies were prepared (ADA specification No.19) for making impressions with monophase addition silicone (Aquasil Ultra Monophase) and polyether (Impregum Soft) impression materials. A total of 140 impressions (70 with addition silicone and 70 with polyether) were made. Ten impressions of each material were allotted to each of the seven treatment groups: (1) No disinfectant immersion (2) Immersion in dual phenol for 10-minutes (3) Immersion in 2% glutaraldehyde for 10-minutes (4) Immersion in 0.5% sodium hypochlorite (NaOCl) for 10-minutes (5) Immersion in dual phenol for 1-hour (6) Immersion in 2% glutaraldehyde for 1-hour and (7) Immersion in NaOCl for 1-hour. Dimensional stability was evaluated after 24-hours, 1-week, 2-weeks and 4-weeks storage. Statistical analyses were performed using Separate 2-factor repeated measure ANOVAs and Bonferonni post hoc tests (α = 0.05). Results: The expansion produced by disinfection in monophase addition silicone was found to be statistically insignificant (P>0.05) as compared to non-disinfected specimens. However, all disinfection protocols resulted in statistically significant (P≤0.05) expansion of polyether in comparison to non-disinfected impressions. There was significant shrinkage of both impression materials over time at room temperature. The dimensional changes at 4 weeks storage were found to be more than 0.5%, which is unacceptable in accordance with ADA guidelines. However, mean percent dimensional changes were found to be satisfactory after 2 weeks storage period. Conclusion: The dimensional measurement accuracy of both disinfected and non-disinfected monophase addition silicone and polyether is affected by storage. However, all measurements met the ADA criteria even at 2 weeks storage. Irrespective of disinfection, the pouring of impressions after 4 weeks of storage is not advisable.