Effect of Repeated Preheating Cycles on Flexural Strength of Resin Composites

Abstract

The aim of this study was to assess the flexural strengths of three resin composites prepared at room temperature or cured after 20 or 40 cycles of preheating to a temperature of 45°C. Three resin composites were evaluated: Enamel Plus HFO (Micerium) (HFO), Enamel Plus HRi (Micerium) (HRi), Opallis + (FGM) (OPA). One group of specimens for each composite was fabricated under ambient laboratory conditions, whereas in the other groups, the composites were cured after 20 or 40 preheating cycles to a temperature of 45°C in a preheating device. Ten specimens were prepared for each group. A three-point bending test was performed using a universal testing machine at a crosshead speed of 0.5 mm/min. Data were analyzed with a two-way analysis of variance (ANOVA) test and a Games-Howell test (α = 0.05). The two-way ANOVA showed that both the material and the number of heating cycles were significant factors, able to influence the flexural strength values (p<0.05). However, there was not a statistically significant interaction (p>0.05). For all three composites flexural strengths were not affected after 20 preheating cycles in comparison with the control groups (0 preheating cycles) but were, however, significantly decreased when 40 prewarming cycles were conducted. The HRi and OPA groups had the highest flexural strengths, with no statistically significant differences among them. HFO presented significantly lower flexural strengths in comparison with HRi.

The effect of repeated preheating of dimethacrylate and silorane-based composite resins on marginal gap of class V restorations

“…13 Based on the aforementioned studies and the results of other studies, repeated preheating cycles 7,35 and prolonged duration of preheating 7 haveneither a significant effect on composite resin mechanical properties, nor a detrimental effect on the monomer component of composite resin. 7 Therefore it is possible to explain why adaptation increases and marginal gaps decreases when both these composite resins are preheated.…”

“…As mentioned earlier, preheating is to warm composite resin before placing it in the cavity and photo-polymerizing it. 13 Since composite resin is a viscoelastic material, increasing its temperature decreases its viscosity and increases its liquidity, 15 which is attributed to thermal vibration and the subsequent separation and further sliding of monomers. 6 In these conditions, the resin film thickness decreases and it easily adapts to the cavity walls; 31 therefore, less gap formation can be expected after preheating.…”

“…13 Increasing the temperature decreases viscosity, possibly affecting the polymerization kinetics and increasing the conversion rate. 14 The mobility of molecules and free radicals is influenced directly by temperature and indirectly by decreased viscosity.…”

“…Although many studies have shown that preheating has no detrimental effect on the mechanical properties of composite resins, 22,23 in these studies the mechanical properties have been evaluated after only one thermal cycle; however, under clinical conditions, a syringe containing composite resin is repeatedly used for restoration of several cavities and if preheating is applied, this syringe will undergo several thermal cycles. 13 Considering the importance of the interfacial bond between composite resin and the cavity walls, differences in the chemical structure and polymerization processes between silorane-based and dimethacrylate-based composite resins and their possible effect on the behavior of composite resin after several heat treatment procedures, the aim of the present study was to determine the effect of preheating cycles of silorane- and dimethacrylate-based composite resins on gap formation at the gingival margins of Class V cavities.…”

Protocol for a new concept of no‐prep ultrathin ceramic veneers

“…The adhesive agent is brushed on the adhesive surface of veneers and teeth and, to avoid inaccuracies of fit, it is not light‐polymerized before restoration placement. A microhybrid composite (Enamel Plus HRi; Micerium, Avegno, Genova, Italy) is warmed up with the preheating device preset to 55°C, put on the cementation surface of veneers, and used as luting agent. Preheated composites are handled with preheated metal tools, so as to maintain the temperatures reached by the composites as long as possible.…”