Valiant PhD-XT Amalgam Delayed-Addition Self-Adhesion Shear-Bond Strength Study

OBJECTIVES:  To determine the effects of a reliably consistent condensation force and dwell time of each condensation stroke on fusing new to old amalgam.

METHODS:  A stabilization jig was implemented holding 15 friction-fit 1” diameter cylindrical resin specimen blocks face up, each with 15/64” wide x 4mm deep wells drilled to contain the condensed substrate Valiant PhD-XT amalgam.  At time intervals of 0-min (Control), 15-min, 60-min, 24-hr, 1 week and 70 days, fresh amalgam was condensed against their razor-blade-shaved substrate amalgam surfaces through a 3.5mm diameter central hole in a split-ring delrin disk which served to mold the amalgam test additions.  These 15 delrin mold disks were machined for a friction fit within the 15 holes of the stabilization jig tray. A consistent, measured force of 4-lb was delivered with a spring-loaded amalgam carrier adapted with a precision-machined 1 mm-diameter stainless steel condenser tip.  Amalgam button additions were built up in 3 increments with a pattern of eight 4-lb 1-1/2-second condenser thrusts per layer. MTS shear-bond testing (112-pound load cell and 1-mm/minute crosshead speed) occurred 24-hr post-condensation.  One-way ANOVA statistical analysis was conducted to analyze the results.   

RESULTS: The mean shear-bond forces were not statistically different from the intact Control group except at 1-hr. 

(N = 15 per sample)	Control	15 min	1 hr	1 day	1 week	70 days
Mean Shear-Bond Strengths (lbf)	60.8	66.8	24.2	55.0	54.6	54.4

CONCLUSION:  Under the condensation-pressure conditions of this study, addition of new Valiant PhD-XT amalgam to smooth, previously-set similar- amalgam surfaces, up to at least 70 days, results in shear-bond strengths not statistically different from the originally-condensed Controls.  Direct reparability of this type of amalgam under adequate condensation forces appears indicated. Further studies may elucidate the diminished amalgam-addition receptivity at 1-hr post-trituration.