Evaluation and comparison of dimensional accuracy of newly introduced elastomeric impression material using 3D laser scanners: an in vitro study.

AIM: Aim of the present study was to comparatively evaluate dimensional accuracy of newely introduced elastomeric impression material after repeated pours at different time intervals. MATERIALS AND METHODS: In the present study a total of 20 (10 + 10) impressions of master model were made from vinyl polyether silicone and vinyl polysiloxane impression material. Each impression was repeatedly poured at 1, 24 hours and 14 days. Therefore, a total of 60 casts were obtained. Casts obtained were scanned with three-dimensional (3D) laser scanner and measurements were done. RESULTS: Vinyl polyether silicone produced overall undersized dies, with greatest change being 0.14% only after 14 days. Vinyl polysiloxane produced smaller dies after 1 and 24 hours and larger dies after 14 days, differing from master model by only 0.07% for the smallest die and to 0.02% for the largest die. CONCLUSION: All the deviations measured from the master model with both the impression materials were within a clinically acceptable range. CLINICAL SIGNIFICANCE: In a typical fixed prosthodontic treatment accuracy of prosthesis is critical as it determines the success, failure and the prognosis of treatment including abutments. This is mainly dependent upon fit of prosthesis which in turn is dependent on dimensional accuracy of dies, poured from elastomeric impressions.

A comparative evaluation of flexural strength of commercially available acrylic and modified polymethylmethacrylate: an in vitro study.

AIM: The purpose of this study was to evaluate and compare the flexural strength of commercially available acrylic (trevalone) and modified polymethylmethacrylate (PMMA). MATERIALS AND METHODS: Four groups were tested; Group 1- control group regular MMA, group 2-2% methacrylic acid, 88% MMA, group 3-16% methacrylic acid, 84% MMA group 4- 20% methacrylic acid, 80% MMA 15 resin specimens of each group were polymerized. After processing, the specimens were subjected for flexural strength testing using three point bending test in a Universal Testing Machine. All data was statistically analyzed with one-way ANOVA, differences within the groups were analyzed by Scheffe's analysis. RESULTS: As the ratio of incorporated methacrylic acid to PMMA increased, the flexural strength decreased. Analysis of data revealed a significant decrease in flexural strength of specimens (p < 0.000) after incorporation of 12%, 16%, 20% methacrylic acid to heat polymerized acrylic resin, when compared with the control group. Lowest flexural strength was observed with specimens containing 20% methacrylic acid and highest flexural strength was observed with specimens containing conventional monomer without methacrylic acid. CONCLUSION: It was observed that as the concentration of methacrylic acid in heat polymerized acrylic resin increases, the flexural strength decreases. Lowest flexural strength was observed with specimens containing 20% methacrylic acid and highest flexural strength was observed with specimens containing conventional monomer without methacrylic acid. CLINICAL SIGNIFICANCE: The major advantages of addition of methacrylic acid to polymethylmethacrylate could be for the elderly people with restricted manual dexterity or cognitive disturbances, especially for patients who do not follow an adequate denture cleansing protocol and diabetic patients who are more susceptible for denture stomatitis.