Clinical evaluation of the Soft-Start (pulse-delay) polymerization technique in class I and II composite restorations

The polymerization shrinkage of resin composites may affect restoration quality. A double blind, randomized clinical trial was carried out to compare two curing techniques-Soft-Start (SS) and the plasma arc curing light (PAC). The hypothesis that, delaying the gel point (with SS) improves marginal seal, was tested at alpha=0.05. Also, this report includes two-week, three-month, one-year and two-year results for post-op sensitivity. Twenty informed participants, each needing two Class H and/or complex Class I restorations, gave written consent. All the teeth were trans-illuminated to rule out pre-op crack lines before restoration placement. Fifty Z100-Single Bond restorations (25/SS and 25/PAC) were placed under rubber dam. Protocols: PAC (Control)-incremental curing <2.0 mm, 2000 mW/cm(2) for 10 seconds for all layers, SS (Treatment)-incremental. curing <2.0 mm, 600 mW/cm(2) for 20 seconds, except the final layer or enamel replacement increment, which was cured as follows-(mW/cm(2)/time) 200/3 seconds, wait 3 minutes; 200/3 seconds, wait 5 minutes; 600/20 seconds from multiple angles.