A standardized method to determine the effect of polymerization shrinkage on the cusp deflection and shrinkage induced built-in stress of class II tooth models

• Published in: Journal of the mechanical behavior of biomedical materials 2020-11, Vol.111, p.103987-103987, Article 103987
• Main Authors: Pottier, Jean Gabriel, Gregg, Andrew, Aregawi, Wondwosen, Nasiri, Ehsan, Fok, Alex, Liu, Yi, Kreplak, Laurent, Price, Richard B., Labrie, Daniel
• Format: Article
• Language: English
• Subjects: Built-in stress; Bulk filling; Composite Resins; Cuspal deflection; Dental Restoration, Permanent; Elastic Modulus; Finite element analysis; Incremental filling; Interfacial stress; Materials Testing; Polymerization; Resin-based composite; Restoration; Tooth model
• ISSN: 1751-6161; 1878-0180
• DOI: 10.1016/j.jmbbm.2020.103987

Using standardized aluminum tooth models, this study: 1) measured the deflection along the cusp wall of models with a Class II cavity restored using either bulk filling or horizontal incremental filling techniques, and 2) calculated the cusp deflection and built-in stress within the restored tooth models for both filling techniques using a finite element (FE) model. Standardized tooth models with Class II cavities 4 mm deep, 4 mm high and 6 mm wide were machined out of aluminum. The models were restored using Filtek Posterior Restorative A2 shade resin-based composite (RBC). Both bulk filling and horizontal incremental filling techniques were used to restore the tooth models. After photocuring for 20 s from a single peak wavelength light-curing unit (LCU) with a radiant exitance of 1.25 W/cm2, the deflection of the cusp wall surface was measured using a profilometer. A FE model was used to predict the cuspal deflection and built-in stress of the restored tooth models. The elastic modulus within the FE model was parameterized using cusp deflection data obtained on a bulk filled tooth model. An agreement was found between the measured and predicted cusp deflection only when considering partial stress relaxation within the first incremental layer for the two-layer incremental filling technique. The calculated built-in stress was significantly reduced within the RBC and along the cavity walls when the cavity was filled incrementally in a horizontal direction compared to when it was bulk filled, resulting in a significantly smaller cusp deflection. The FE model was first calibrated and then validated using measured cusp deflection data. Partial stress relaxation may play a significant role in the horizontal incremental filling technique. The model can be used to predict where the built-in stress within the tooth model occurs. This study explains why for a given RBC, a horizontal incremental filling and curing technique results in lower built-in stress within the restored tooth and lower cusp deflection compared to the bulk curing technique. [Display omitted] •Agreement between measured and predicted cuspal deflection along the model wall.•Bulk fill restoration led to greater cuspal deflection than for incremental filling.•Bulk fill restoration led to greatest built-in stress within the restored model.•Partial stress relaxation occurred within the first layer for incremental filling.