Retentive strength of an amalgam bonding agent: chemical vs light vs dual curing

Dentin bonding agents have been shown to enhance retention of amalgam resto rations by mechanical means. Little research is available on which mode of curing may optimize amalgam bonding. This in vitro study compared the bond strengths exhibited by three variations of a bonding agent, each using a di fferent curing mode, with two earlier versions of amalgam resin liners and cavity varnish. The six test groups of lining agents for amalgam restoratio ns included [C] chemical-cured, [L] light-cured and [D] dual-cured versions of one filled adhesive resin (Clearfil Liner Bond 2V), [LF] Light-cured, F illed resin (Clearfil Liner Bond 2, Kuraray Co.); [LCF] Light- and Chemical -cured, Filled resin Clearfil Liner Bond + Protect Liner, Kuraray Co) and [ V] Varnish (Copalite, Cooley & Cooley, Ltd). For each group, 20 Class V cav ity preparations were cut in human molars. The preparations were 2.5 mm dee p and 3 mm wide at the pulpal floor, with a slightly divergent taper. After treating the preparation with the bonding agent, a 3/4 inch, 18 gauge flat -headed wire nail was seated in the cavity with its head at the pulpal floo r of the preparation, and Tytin amalgam (Kerr Corp, Romulus, MI) was conden sed into the preparation around the nail. All restorations were stored for 24 hours in distilled water at 37 degreesC, then subjected to 2500 thermal cycles (8 degreesC to 58 degreesC). After one week the samples were tested to failure in tension using an Instron Universal Testing Machine (crosshead speed = 2 mm/min) and peak load (kg) was recorded. Significant differences in retention were found using ANOVA and the Games & Howell post hoc test ( p=0.05). The mean loads at failure (+/- SD) were C 13.1 (+/-2.4), L 218 (+/ -6.1), D 26.8 (+/-7.4), LCF 23.8 (+/-7.4), LF 21.4 (+/-3.3) and V 2.0 (+/-1 .8). All dentin-bonding agents exhibited significantly greater retention th an the varnish. While the bond strengths of the dual cured (D) and the ligh t-cured (L) liners were not significantly different from one another, both were significantly higher than the chemically-cured (C) resin liner in term s of retention.