Repair of an old amalgam restoration preserves the tooth as it is difficult to remove a restoration without removing an integral part of the tooth itself. Defective amalgam restorations are usually treated conservatively with new amalgam or other restorative materials using a light or dual cure adhesive system. Objective: The aim of this in vitro study was to evaluate fracture strength of Black II amalgam restorations repaired with composite resin or amalgam in conjunction with light or dual cure adhesive resin. Methods: 40 sound and free from cracks extracted molars were randomly assigned to 4 groups of ten teeth. Standard Black II cavities were prepared without proximal steps and flat floor. The teeth were restored with amalgam and stored at tap water for 20 days at room temperature. Group 1 was kept as control. From Group 2 to 4, 2 mm deep amalgam was removed from mesials of the restorations. Group 2 restored with a light-cure adhesive resin (SE Bond, Kuraray, Japan) and composite (Clearfil AP-X, Kuraray, Japan), Group 3 restored with a light-cure adhesive resin (SE Bond, Kuraray, Japan) and amalgam, Group 4 restored with a dual-cure adhesive resin (Liner Bond 2V, Kuraray, Japan) and amalgam. After finishing and polishing, the specimens were submitted to fracture resistance test in a universal testing machine at a crosshead speed of 2mm/min. Results: The mean load necessary to fracture the samples in each group were (in N): G1:769.85±207.19a, G2:1096.94±167.61b, G3:738.03±179.76a, G4:683.69±134.20a. Data were submitted to ANOVA and Tukey Post-Hoc test that demonstrated differences among some groups showed above with different letters. Conclusions: The restorations repaired with composite resin showed the highest fracture strength. The type of adhesive system (dual or light-cure) had no effect on fracture strength of restorations repaired with amalgam.

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