Preclinical assessment reveals reduced post-gel shrinkage strain for bis-GMA-based composites, highlighting significant marginal integrity improvements.
Background This study investigated the influence of repeated preheating of bulk‐fill resin composites on post‐gel shrinkage strain (PGSS) and marginal gap formation. Methods Eighty Samples (A) were prepared and assigned to two groups ( n = 40) based on material type: thermoviscous composite containing Bis‐GMA (A1) and matrix‐modifying bulk‐fill composite free of Bis‐GMA (A2). Each group was further divided into four subgroups according to the number of preheating cycles at 54°C: C1 (no preheating, room temperature control), C2 (preheated once), C3 (preheated five times), and C4 (preheated 10 times) for the PGSS test. Additionally, 80 human premolars with standardized Class II (MOD) cavities were restored using the same group allocations to assess marginal gap surface area. PGSS and gap formation were measured and analyzed using independent t ‐tests and two‐way ANOVA ( p < 0.001). Results PGSS increased with repeated preheating cycles. All preheated groups showed lower PGSS values in the Viscalor Bulk (Bis‐GMA–based) composite. The marginal gap surface area significantly decreased in all preheated groups versus controls. BisGMA‐containing composites exhibited greater gap formation compared to BisGMA‐free materials. Conclusions Repeated preheating increases PGSS but enhances marginal adaptation. BisGMA‐free composites show superior performance in minimizing marginal gaps.
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Amir et al. (2025) studied this question.
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