THE EFFECT OF VARIOUS BASES ON THE FRACTURE-RESISTANCE OF AMALGAM

This study compared the compressive force required to fracture amalgam over nine base materials: a calcium hydroxide product (Dycal); two autocured glass ionomers (GlasIonomer Base Cement and Ketac-Bond); three light-cured glass ionomers (Photac-Bond, Variglass VLC, and Vitrebond); two light-cured resins (Timeline and VLC Dycal); and a zinc phosphate cement (Fleck's Zinc Cement). For the control group, 10 aluminum dies (25 mm x 12 mm x 10 mm) were milled with 3.0 mm x 3.0 mm slots, which were filled with hand-condensed Tytin amalgam with no underlying base. For experimental groups, 10 aluminum dies of equal dimension were milled with 3.5 mm x 3.0 mm slots. Following manufacturer's instructions, the nine base materials were successively placed in these 10 dies using a depth-limiting device made of light-transmitting clear acrylic to ensure a 0.5 mm thickness, and Tytin amalgam was again condensed over each base such that the depth of the amalgam equalled that in the control. All test specimens were stored in 100% humidity for 48 hours then fractured in compression on an Instron machine. Mean force, in Newtons (S D in parentheses), required to fracture the specimens was: Control: 1934(210), Zinc Cement: 1874(147), GlasIonomer Base Cement: 1839(174), Ketac-Bond: 1723(225), Vitrebond: 1485(155), Photac-Bond: 1422(294), Advanced Formula II Dycal: 1296(237), VLC Dycal: 1035(116), Variglass: 909(294) and Timeline: 906(275). ANOVA and Student-Newman-Keuls statistical analysis (alpha = 0.05) indicated that the autocuring glass ionomers, GlasIonomer Base Cement and Ketac-Bond, and a zinc phosphate cement, Zinc Cement, provided significantly more fracture resistance for amalgam than the other bases tested and were not statistically different from a no-base control.