Effect of Cartridge Storage Time and Ambient Laboratory Conditions on the Stability of Mechanical Properties of Bis-Acryl Interim Resin Materials.

PURPOSE: To investigate the stability of mechanical properties during the entire shelf life of chemically-activated bis-acryl interim resin materials stored at ambient laboratory conditions. MATERIALS AND METHODS: Four bis-acryl interim resin materials with no explicit recommendation for refrigerator storage were selected (Luxatemp Plus, Visalys Temp, Structur 3, Structur Premium). Following cartridge storage at ambient laboratory conditions in 6-month intervals, 30 specimens (2.0 × 2.0 × 25.0 mm3 ) were prepared in each case and stored in distilled water (37.0 ± 1.0 °C) with 3 different water storage times (2 hours, 24 hours, 7 days). Flexural strength, modulus of elasticity, modulus of toughness, and elastic recovery were determined (3-point bend test). Data were subjected to a three-way multivariate analysis of variance (MANOVA) to determine overall significance, followed by a series of separate one-way ANOVAs after data were split, using Tukey and Games-Howell post hoc tests to identify significant differences between groups (α = 0.05). RESULTS: While Luxatemp Plus showed no significant decrease for all mechanical properties during the investigated shelf life of 21 months (p > 0.05), Visalys Temp exhibited a continuous decline of the corresponding values (p < 0.05), irrespective of the water storage time. Structur 3 and Structur Premium properties remained almost unchanged during the first 6 months of the examination period. Subsequently, a progressive decrease was observed for flexural strength and modulus of elasticity, while most modulus of toughness and elastic recovery results revealed little alteration. CONCLUSION: Depending on the bis-acryl interim resin material, mechanical properties appeared to be susceptible to continuous degradation processes during cartridge storage at ambient conditions, especially towards the end of the material shelf life. For some materials, the chemical stabilization and recommended storage conditions should be revised by the manufacturers to prevent premature aging during shelf life.

Correlation between polymerization shrinkage and marginal fit of temporary crowns.

OBJECTIVES: During polymerization, temporary c&b materials (t-c&b) undergo shrinkage which may lead to marginal inaccuracies of the temporary restoration. The degree of correlation between these two factors is still unknown. Hence, the objective of this study was to determine the polymerization shrinkage of t-c&bs and to evaluate, to which degree the shrinkage is correlated to the width of the marginal gap. METHODS: Six different t-c&bs (2 monomethacrylates and 4 dimethacrylates) were used to fabricate temporary crowns (n = 12) on two prepared teeth (stainless steel) of different diameters (5 and 7 mm). The crown diameters and marginal discrepancy were measured at various storage times after mixing (10, 30, 60 min) using a travelling microscope. In addition, the shrinkage (bonded-disk method) and content of inorganic filler (ashing method) were recorded. The statistical analysis was carried out using parametric tests, the F-test and Pearson's correlation (p = 0.05). RESULTS: The marginal discrepancies increased as a function of increasing storage time (10 min: 0.162-0.218 mm; 60 min: 0.271-0.521 mm). Lower values were recorded for monomethacrylates than for the dimethacrylates (greatest changes recorded during the first 30 min). The shrinkage values recorded 10 min after mixing varied between 3.25 and 4.10%. There was no significant relationship between the width of the marginal gap and shrinkage (p > 0.05). SIGNIFICANCE: Shrinkage values are not suitable to predict the marginal accuracy of a temporary restoration. At least 30 min should elapse between fabricating and trimming temporary crowns to avoid further inaccuracies.