Objective: This paper studied in vitro the effect of the C-factor on interfacial debonding during curing of composite restorations using the acoustic emission (AE) technique. Finite element (FE) analyzes were also carried out to evaluate the interfacial stresses caused by shrinkage of the composite resin in restorations with different C-factors. Materials and methods: Twenty extracted third molars were divided into 4 groups of 5. They were cut to form Class-I (Groups 1 and 2) and Class-II (Groups 3 and 4) cavities with different C-factors. The average C-factors of the four groups were 3.37, 2.88, 2.00, and 1.79, respectively. The cavities were then applied with an adhesive and restored with a composite, which was cured by a halogen light for 40 s. A 2-channel AE system was used to monitor the interfacial debonding, caused by shrinkage stress, between the tooth and restoration through an AE sensor attached to the surface of the specimen. Recording of the AE started at the same time as curing of the composite and lasted 10 min. Simplified FE models were used to evaluate the interfacial stresses in restorations with different C-factors, with a thermal load (temperature decrease) being applied to the composite resin to simulate its shrinkage. Results: The mean and standard deviation of the total number of AE events for the four groups were 29.6 ± 15.7, 10.0 ± 5.8, 2.6 ± 1.5, and 2.2 ± 1.3, i.e. the number of AE events increased with an increase in the C-factor. The FE results also showed that, the higher the C-factor of the restoration, the higher the interfacial tensile stress between the tooth and restoration. Significance: From the results of the AE tests and FE simulations, it can be concluded that, the higher the C-factor, the higher the shrinkage stress and the more likely is interfacial debonding.
Bibliographical noteFunding Information:
The authors would like to acknowledge 3M ESPE for providing the restorative materials, the Minnesota Dental Research Center for Biomaterials and Biomechanics (MDRCBB) for providing the test devices, and the Minnesota Supercomputing Institute (MSI) for their computing services in support of this study. Xiaozhou Liu would like to thank the China Scholarship Council and the MDRCBB for financially supporting her study visit to the MDRCBB.
- Acoustic emission
- Composite restoration
- Finite element method
- Interfacial debonding
- Shrinkage stress