Fracture strength of class 2 amalgams with various cavity-lining materials

This in vitro study compared the fracture resistance of class 2 amalgam res torations placed over seven materials: three resin-modified glass-ionomer c ements (Fuji II LC, Vitrebond, and Vitremer), one polyacid-modified composi te resin (VariGlass VLC), two conventional glass-ionomer cements (Ketac-Bon d and GlasIonomer Cement), and one calcium-hydroxide material (Dycal). Eigh ty maxillary molars with flattened occlusal surfaces were divided into 14 e xperimental groups and two control (no liner) groups. One standardized clas s 2 amalgam cavity preparation was completed per tooth. Lining materials st andardized at a thickness of 0.5 mm were placed in the approximal box porti on of 10 test specimens per experimental group. Spherical amalgam was hand condensed into each cavity preparation. At 1 hour and again at 7 days, five samples from each group were fractured in compression using an Instron Uni versal Testing Machine. The force was directed at 10 degrees to the long ax is of the tooth, 2.0 mm inside the approximal portion of the restoration. R esults were analyzed using a two-way ANOVA for time and material. No statis tically significant differences were found among the materials and controls at either time interval tested (P > 0.05). A statistically significant dif ference was found (P < 0.05) when comparing 1-hour and 7-day strengths. The 7-day specimens were more resistant to fracture than the 1-hour specimens. Conclusion: the fracture resistance of amalgam restorations was not affect ed by the presence of a material 0.5 mm thick placed in the approximal box when 3 mm of bulk of amalgam remained over it.