Acoustic emission analysis of tooth-composite interfacial debonding during photo-cured composite restoration

Abstract

Objectives: The aim of this study was to detect tooth-composite interfacial debonding during composite restoration by means of acoustic emission (AE) analysis, and to investigate the effect of composite properties, adhesives systems, and light curing methods on AE characteristics. Methods: The polymerization shrinkage, peak shrinkage rate, flexural modulus, and shrinkage stress of a methacrylate-based universal hybrid, a flowable, and a silorane-based composite were measured. Class I cavities on 49 extracted premolars were restored with one of three composites and one of the following adhesives: two etch-and-rinse adhesives, two self-etch adhesives, and an adhesive for the silorane-based composite. An AE sensor was applied with grease to the glass slide holding the tooth to detect debonding sound at the tooth-composite interface. The signals from the AE sensor were amplified and stored on a computer. AE analysis was done for 2,000 sec during light-curing. SEM images of the tooth-composite interface were obtained with the epoxy replicas of sliced specimens. Results: The silorane-based composite exhibited the lowest shrinkage (rate), the longest time to peak shrinkage rate, the lowest shrinkage stress, and the fewest AE events. AE events were detected immediately after the beginning of light-curing in most composite-adhesive combinations, but not until 40 sec after light-curing began for the silorane-based composite. AE events were concentrated at the initial stage of curing in self-etch adhesives compared with etch-and-rinse adhesives. In the SEM image, flowable resin showed wider gaps at the dentin-composite interface compared with the other groups, while silorane-based composite showed narrower gaps. Significance: Reducing the shrinkage (rate) of composites resulted in reduced shrinkage stress and less debonding as evidenced by fewer AE events. AE is an effective technique for monitoring, in real time, the debonding kinetics at the tooth-composite interface.