Polymerization shrinkage strain, modulus, and shrinkage stress related to tooth-restoration interfacial debonding in bulk-fill composites

Abstract

Objectives. The aim of the present study was to measure the polymerization shrinkage, modulus, and shrinkage stress of bulk-fill and conventional composites during polymerization and to investigate the relationship between tooth-composite interfacial debonding and polymerization shrinkage stress of the composites.

Methods. Polymerization shrinkage, dynamic modulus, and shrinkage stress of two non-flowable bulk-fill: SonicFill (SF) and Tetric N-Ceram Bulk-Fill (TNB)

two flowable bulk-fill: Filtek Bulk-Fill (FB) and SureFil SDR Flow (SDR)

one non-flowable conventional: Filtek Z250 (Z250)

and one flowable conventional: Filtek Z350 XT Flowable (Z350F) composites were measured using custom-made instruments. Acoustic emission (AE) analysis was performed to evaluate the tooth-composite interfacial debonding during polymerization of the composites in Class 1 cavities on extracted third molars.

Results. Polymerization shrinkage (%) of Z350F (3.53) at 10 min was the highest, followed by FB (3.05), SDR (2.99), TNB (2.22), Z250 (2.09), and SF (2.05). Complex shear modulus (MPa) after 20 s of light-curing was highest in SF (996.2), followed by Z250 (831.8), TNB (723.6), Z350F (553.2), SDR (421.3), and FB (334.8). Polymerization shrinkage stress values (MPa) were: Z350F (3.51), TNB (2.42), Z250 (2.38), SF (2.36), FB (2.24), and SDR (1.68). The numbers of AE events were: Z350F (12.6), TNB (7.0), Z250 (7.0), FB (6.8), SF (6.6), and SDR (6.0). Z350F showed the highest polymerization shrinkage stress and AE event number (p < 0.05). SDR exhibited the lowest polymerization shrinkage stress (p < 0.05). The polymerization shrinkage stress for TNB, Z250, SF, and FB as well as the number of AE events for TNB, Z250, FB, SF, and SDR were not significantly different (p > 0.05).

Conclusions. Composites that exhibited greater polymerization shrinkage stress generated more tooth-composite interfacial debonding. In contrast to similar outcomes among the non-flowable composites (conventional: Z250, bulk-fill: TNB and SF), the flowable bulk-fill composites (FB and SDR) demonstrated lower polymerization shrinkage stress and tooth-composite interfacial debonding than did the flowable conventional composite (Z350F).