The fracture strength of amalgam overlying base materials.

Conclusions reached within the constraints of this study showed the following: 1. Fracture strength of Class II amalgam restorations decreased as the thickness of the bases increased. 2. Fracture strengths of amalgam restorations based with different thicknesses of zinc phosphate cement underline with 0.5 mm Dycal were not different from each other. 3. The strength of the restorations varied with the type of base. Zinc phosphate cement is equal to no base and superior to zinc phosphate cement plus Dycal, which is equal to Dycal. Dycal is superior to Cavitec, which is the same as Cavitec plus Dycal. 4. The base materials did not fracture. The amalgam restorations were stronger over a base with a higher modulus of elasticity, indicating that modulus of elasticity of a base is more important than compressive strength in supporting an amalgam restoration. 5. There is no advantage (no improvement in resistance to fracture of the amalgam restoration) to be gained from placing zinc phosphate cement over Dycal. 6. When a calcium hydroxide liner is not needed, the cements with a higher modulus of elasticity, such as zinc phosphate cement and reinforced ZOE, will provide for stronger amalgam restorations than Cavitec and unreinforced ZOE.