The Development of Novel Low Shrinkage POSS Based Nanocomposites

Traditional dental composites exhibit 2-4 % volumetric shrinkage during the polymerization process. This post-gel shrinkage results in significant stresses in the surrounding tooth structure and composite tooth bond leading to premature restoration failure. Objective: This study aimed to design and develop novel low shrinkage nanocomposites based on POSS (Polyhedral Oligomeric Silsesquioxane) for dental applications. Methods: Four POSS based nanocomposites with various types of methacrylate and/or epoxide functionalities were designed and synthesized in this research. The post-gel polymerization shrinkage of the synthesized materials were then investigated and compared with unfilled 1:1 (control) Bis-GMA / TEGDMA materials. All samples investigated were polymerized using a dental light-curing unit (BISCO VIP) at 500 mW/cm² for 40 seconds. A strain-monitoring device and test configuration was used to measure the linear polymerization shrinkage of all polymers during and post light polymerization up to 60 minutes. Three specimens were made for each material. Results obtained were analyzed using ANOVA/Scheffe's post-hoc test at significance level 0.05. Results: Post-gel linear shrinkage for the unfilled Bis-GMA/ TEGDMA polymeric resins and newly synthesized nanocomposites were found to range from (0.42 ± 0.08) to (0.69 ± 0.09) % and (0.01 ± 0.01) to (0.13 ± 0.02) % respectively. Shrinkage associated with unfilled Bis-GMA/ TEGDMA resins was found to be significantly higher than all synthesized POSS based materials immediately after light polymerization and at 1, 10, 30 and 60 minutes post light polymerization. Conclusions: Hence, POSS based nanocomposites show potential for use as dental restorations and presents a promising approach to achieve novel low shrinking nanocomposites based dental materials.