Stress Development of Restorative Materials Stored in Water or Phosphate-Buffer-Solution

Objective: To determine the development of polymerization shrinkage- and/or expansion stress of the „bioactive ceramic materials” Doxadent and Doxa T in comparison to Ketac Molar, Dyract AP, and Tetric Ceram, when stored in water and phosphate buffer solution (phbs) by means of a photoelastic investigation. Methods: All the materials (n = 20) were filled in cylindrical cavities (Ø 5mm) in Araldit B epoxide resin platelets (40x40x3mm). For Tetric Ceram and Dyract AP (Exposure time: 60s, Optilux 501, 800mW/cm2), a pre-treatment was conducted (Rocatec) to ensure an adhesive binding to the platelets. Another set of Tetric Ceram and Dyract AP specimens were applied without pre-treatment. The samples were stored dark (n=10) and wet (n=10) in water (37°C) and phbs (37°C), respectively. Stress data (MPa) were calculated based on the diameter of the isochromatic curves of first order, obtained from the Araldit-platelets. Results: The isochromatic curves of Doxa T and Doxadent had to be interpreted as expansion stress due to the lack of bonding to the plates. For Dyract AP and Tetric Ceram which were bonded to the platelets, these isochromatic curves, showing up initially, were interpreted as shrinkage stress. Results: After 16 weeks, Ketac Molar and Dyract AP did not show any isochromatic curves at all, while Tetric Ceram, bound adhesively to the platelets, showed a reduction in polymerization shrinkage stress of 50% (water) and 48.3% (phbs). After 24h and 16 weeks, Doxa T showed a lower (7.2% resp. 8.3%) expansion stress force than Doxadent both in water and phbs. Descriptive statistical analysis was carried out. Conclusion: In contrast to Ketac Molar, measurable isochromatic curves were present for Doxa T and Doxadent after 16 weeks, which might be interpreted as a higher expansion due to water sorption. This study was supported by Doxa AB, Uppsala, Sweden.