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Quintessence Publishing: Journals: QI
Quintessence International

Edited by Eli Eliav

ISSN 0033-6572 (print) • ISSN 1936-7163 (online)

March 2011
Volume 42 , Issue 3

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Hardness and postgel shrinkage of preheated composites

Daranee Tantbirojn, DDS, MS, PhD/Supaporn Chongvisal, DDS, MS/David G. Augustson, BA/Antheunis Versluis, PhD

PMID: 21465004

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 (68C) 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. (Quintessence Int 2011;42:e51e59)

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