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Hardness and postgel shrinkage of preheated composites
Daranee Tantbirojn1, Supaporn Chongvisal, David G Augustson
1Department of Restorative Sciences, University of Minnesota, Minneapolis, MN, USA. dverslui@uthsc.edu
Objective:
To evaluate the effect of composite preheating and light-curing duration on hardness and postgel shrinkage.
Method And Materials:
A hybrid composite (Filtek Z250, 3M ESPE) and a nanofilled composite (Filtek Supreme Plus, 3M ESPE) were preheated in a Calset (AdDent) heating device at its highest setting (68°C) before being light cured for 5, 10, 20, or 40 seconds. Vickers hardness of the top (0 mm) and bottom (2 mm) surface of the samples was measured 5 minutes after polymerization. The development of postgel shrinkage during polymerization was measured with a strain gauge. The results were compared to those of samples cured at room temperature. The sample size was five for each composite/temperature/light-curing duration combination. The results were statistically analyzed with two-way ANOVA and least squares means.
Results:
Preheating composites before light curing did not affect the bottom hardness or postgel shrinkage (P>.05) but significantly increased the top hardness of the Supreme Plus composite at all light-curing durations (P<.05). Shorter light-curing durations than recommended by the manufacturer significantly reduced top and bottom hardness of both composites, regardless of preheating (P<.05).
Conclusion:
Under the experimental conditions in this study, preheating of the composites only slightly increased hardness values and did not negatively affect postgel shrinkage. Reducing the light-curing durations, however, significantly reduced the hardness at both the top (0 mm) and bottom (2 mm) surfaces. Clinicians should ensure sufficient light-curing duration to obtain good mechanical properties rather than depending on composite preheating.
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