Evaluation of polymerization shrinkage of dental composites by an optical method

• The polymerization shrinkage in human and bovine teeth was evaluated by a video extensometer (AVE).
• Human and bovine teeth accommodated the same volume of composite resin.
• Two different light power units were used to polymerize both kinds of teeth.
• The teeth wall stiffness plays a major role in shrinkage process.
• The use of bovine teeth to predict the human teeth behavior must be used very carefully.

This study proposes an alternative methodology for evaluating polymerization shrinkage of dental composites using an advanced video extensometer (AVE) system. This equipment measures the displacement between two points drawn on a tooth's wall without requiring physical contact with the tooth. By doing so, the polymerization process was monitored by the cusp deflection. This technique was used in human and bovine teeth, where the cavities were prepared under controlled conditions so that the volume of the composite used was the same in both types of teeth. After the cavity preparation, the specimens were acid etched, washed and dried, and then the adhesive was applied and polymerized. The composite was then inserted into the cavity. Polymerization was performed with two different light polymerizing units (LD Max and Optilight Max — Gnatus do Brasil), and the displacement curve of the tooth cusp was recorded for a period of 400 s. After a statistical analysis, it was concluded that the technique was capable of evaluating shrinkage by the deflection from the cusps and that the human and bovine teeth do not react in a similar manner towards the polymerization shrinkage of composites.