This study compared the cuspal fracture resistance of posterior teeth restored with four different adhesive restorations. Fifty sound, maxillary human premolars were randomly divided into a control group and four experimental groups with 10 teeth in each. Specimens in the first group were intact teeth that were tested as unprepared. The remaining four groups received mesio-oclusodistal cavity preparations and were restored with a hybrid composite (Filtek Z250), a packable composite (Filtek P60), an ormocer (Definite) and an amalgam (SDI Permite) with an amalgam bonding agent (Amalgam Bond Plus). All groups were stored in water at 37degreesC for 15 days and thermocycled 1000 times between 5degrees-55degreesC. The specimens were preloaded five times in compression to 10 kg using two metal rods that contacted only the teeth on the cuspal inclines. The teeth were then loaded occlusally in an Instron Universal Testing Machine until fracture occurred. The means of force required to fracture the teeth in each of the five groups was analyzed using one-way ANOVA and Tukey Test.