Background and Aim : Tooth fracture is a common complication following MOD restorations. This study sought to assess the effect of different cusp coverage patterns on fracture resistance of maxillary premolar teeth in MOD composite restorations .

  Materials and Methods : In this in vitro experimental study, 40 human maxillary sound premolar teeth were chosen and stored in Chloramine solution. Using bleaching shield, an over impression was made from each tooth and then wide MOD cavities were prepared. The teeth were randomly divided into 4 groups of 10 each: Group A, without cusp coverage Group B, with 1.5 mm palatal cusp coverage Group C, with 1.5 mm buccul cusp coverage and group D, with 1.5 mm both buccal and palatal cusp coverage. The cavities were restored using Z100 composite resin and the prepared over impressions (in order to restore the normal anatomy of teeth). The teeth were then stored in water at 37°C for 24h and their fracture resistance was assessed using Universal Testing Machine. The load at fracture was recorded in N. Data were analyzed using one-way ANOVA and Tukey’s test with 95% CI .

  Results : The mean fracture strength was 873.11±243.5 N in group A, 750.53±270.7 N in group B, 824.22±330.2 N in group C and 1499.25±305 N in group D. The results showed that the fracture resistance of MOD restorations with the coverage of both cusps was significantly more than that of other groups ( P<0.05 ).

  Conclusion : MOD restorations with cusp coverage in maxillary premolar teeth increased the fracture strength of teeth against compressive forces. However, covering only one cusp had no significant effect on fracture strength.