THERMOCYCLING AND DWELL TIMES IN MICROLEAKAGE EVALUATION FOR BONDED RESTORATIONS

Objectives. To answer criticisms of an insufficient number of cycles i n thermocycling in an earlier paper (Wendt et al., 1992), this study w as initiated to evaluate the effect of different dwell times during lo ng-term thermocycling in microleakage analysis of bonded restoratives. Methods. A total of 90 resin-bonded restorations, Tytin/Liner F, (Ker r/Bisco), APH/Universal Bond 3, (LD Caulk) and Heliomolar/Syntac, (Viv adent), were inserted in Class V preparations in human third molars. G roup A restorations were stored in 0.5% basic fuchsin dye for 166 h. G roup B restorations were thermocycled for 5000 cycles in 0.5% basic fu chsin dye baths at 5 +/- 1 degrees C and 55 +/- 1 degrees C with a dwe ll time of 10 s in each bath. Group C was thermocycled as in Group B b ut with a dwell time of 60 s. Readings by defined criteria were taken from each of two 1 mm sections along the cemental margin. Results. The re were no significant differences (p < 0.05) in the extent of dye pen etration at the tooth restoration interface for the thermocycled compo site restorations when compared to composite restorations with no ther mocycling. There was a significant difference (p < 0.05) in the extent of dye penetration at the tooth restoration interface for the thermoc ycled amalgam restorations when compared to dye-exposed amalgam specim ens with no thermocycling. Significance. During microleakage analysis, the need for thermocycling is dependent upon the extent the restorati ve is thermally conductive in relation to its mass. The dwell time sho uld be clinically relevant, i.e., 10 s, and is important only if the r estorative is thermally conductive.