Thermocycling and dwell times in microleakage evaluation for bonded restorations

To answer criticisms of an insufficient number of cycles in thermocycling in an earlier paper (Wendt et al., 1992), this study was initiated to evaluate the effect of different dwell times during long-term thermocycling in microleakage analysis of bonded restoratives.

A total of 90 resin-bonded restorations, Tytin/Liner F, (Kerr/Bisco), APH/Universal Bond 3, (LD Caulk) and Heliomolar/Syntac, (Vivadent), were inserted in Class V preparations in human third molars. Group A restorations were stored in 0.5% basic fuchsin dye for 166 h. Group B restorations were thermocycled for 5000 cycles in 0.5% basic fuchsin dye baths at 5 +/- 1 degrees C and 55 +/- 1 degrees C with a dwell time of 10 s in each bath. Group C was thermocycled as in Group B but with a dwell time of 60 s. Readings by defined criteria were taken from each of two 1 mm sections along the cemental margin.

There were no significant differences (p < 0.05) in the extent of dye penetration at the tooth restoration interface for the thermocycled composite restorations when compared to composite restorations with no thermocycling. There was a significant difference (p < 0.05) in the extent of dye penetration at the tooth restoration interface for the thermocycled amalgam restorations when compared to dye-exposed amalgam specimens with no thermocycling.

During microleakage analysis, the need for thermocycling is dependent upon the extent the restorative is thermally conductive in relation to its mass. The dwell time should be clinically relevant, i.e., 10 s, and is important only if the restorative is thermally conductive.