Abstract
This in vitro study evaluated the Knoop hardness of the composite resins Charisma (C) and Durafill VS (D) polymerized in 3 different conditions: at room temperature (A) (23 +/- 1 degrees C); refrigerated at 4 +/- 1 degrees C and immediately photo-activated after removal from the refrigerator (0); and, refrigerated at 4 +/- 1 degrees C and photo-activated after a bench time of 15 min at room temperature (15). One hundred and twenty specimens (4 mm diameter and 2 mm depth) were made using a stainless steel mold and following manufacturer's instructions. All specimens were tested immediately after polymerization (I) and after 7 days of water storage in the dark at room temperature (7d). The data were subjected to ANOVA and post-hoc Tukey's test (alpha=0.05). On the top surface, C(AI) was statistically similar to C(15I) and D(AI) to D(15I) (p>0.05). On the bottom surface, C(AI) presented higher hardness values when compared to COI and C(15I) (p<0.05). The D groups showed no significant differences (p>0.05) on the bottom surfaces for any tested polymerization condition. After 7 days of storage, the Knoop hardness decreased significantly (p<0.05) for groups C(7d) and D(7d) except for C(07d), which was not different from C(OI) at either surface (p>0.05). D(07d) showed higher Knoop hardness (p<0.05) values on the top surface when compared to the other groups.
Highlights
The curing of methacrylate-based composite resins for dental applications is a major issue due to its importance regarding biocompatibility [1], bacterial growth associated with the release of unreacted monomers [2] and improvement of the material’s physical properties [3].The balance of the components in the organic formulation has been proven essential during the polymerization process [4]
The results suggest influence of refrigeration on Knoop hardness values for the hybrid (C) and microfilled (D) composite resins tested in this study
Both resins presented changes in the hardness values verified right after the polymerization (I) between the specimens prepared at room temperature (A) and just after removal of the resin from refrigeration at 4oC (0)
Summary
The curing of methacrylate-based composite resins for dental applications is a major issue due to its importance regarding biocompatibility [1], bacterial growth associated with the release of unreacted monomers [2] and improvement of the material’s physical properties [3].The balance of the components in the organic formulation has been proven essential during the polymerization process [4]. Some studies have investigated the possibility that resin monomer flexibility and the temperature during polymerization may affect the conversion rate and the material properties [4]. Relatively recent research has shown favorable results regarding the increase of the conversion rate with pre-heated composites [9], few studies have addressed the cooling of methacrylate resin materials [9,10]. This is an important issue to be investigated because the refrigerated storage of composite resins is a common practice to increase their shelf-life and is suggested by some manufacturers
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