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Published on: July 21, 2014
Post-Gel Polymerization Shrinkage Strain and Marginal Integrity of Repeatedly Preheated Thermo-Viscous and
Ahmed Amir1, Rasha Zaghlool2, Mona Riad3
1Conservative Dentistry Department, Faculty of Dentistry, Badr University, Assiut, Egypt.
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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