Evaluation of microleakage of composite resin restorations by an electrochemical technique: the impedance methodology

Objectives. The aim of our in vitro study was to quantitatively evaluate dentin microleakage by means of the impedance technique. Methods. Forty-five 2 mm thick dentin disks were embedded in a hollow polyurethane resin cylinder. The system used was a ‘like’ permeation cell. Standard cylindrical cavities (1.5 mm deep, 3.5 mm diameter) were prepared on the occlusal side of the disk. The current passing through the dentin was measured to calculate impedance and to establish resistance of the sample. The doses were then randomly divided into nine groups (n=5). Each group was bounded with a different adhesive system and filled with microhybrid composite resin (Filtek P60). The initial measurement with the empty cavity and the record measurement (t=0) were performed to evaluate initial resistance after filling. Samples were then thermocycled. Results. At t=0, the highest value was obtained with EP (550%), the lowest with PLP (115%). The values of other adhesives ranged in a group (350–450%) without statistical difference. After thermocycling, all groups exhibited no significant difference (350–230%) except PLP (50%). The lower joint degradation rate (5%) was obtained with OS with a significant difference for all systems, the higher with PLP (35%). The results for other adhesives ranged from 20 to 27% without significant difference. Significance. Dentin microleakage may be quantified with the impedance technique and this has shown that, except for PLP, the differences between the two families of adhesives are slight. This methodology is able to prove the influence of thermocycling in terms of joint degradation.