Objective: Endodontic access cavities may sometimes be prepared through permanent composite resin restorations because many teeth requiring endodontic therapy may have large permanent coronal composite restoration of acceptable quality. Between the appointments, temporary cements are used to seal access cavities but they may have negative effect on bonding of repaired composite restoration. The purpose of this study was to compare shear bond strength of composite to composite which had been in contact with various temporary restorative materials. Methods: Standard cavities were prepared on one hundred forty acrylic resin blocks and obturated with composite (Clearfil AP-X, Kuraray, Japan) and randomly divided into seven groups, including twenty each. Group 1 received any treatment. From group 2 to 7, composite surfaces were covered with the following cements temporarily: Zinc-oxide/calcium sulphate (Cavit-G, 3M ESPE, Germany), two different Zinc-oxide Eugenol (ZnOE, Cavex, Holland and IRM, Dentsply, USA), Zinc-phosphate (Adhesor, Spofa Dental, Germany), Zinc-polycarboxylate (Adhesor Carbofine, Spofa Dental, Germany) or Glass ionomer cement (Argion Molar, Voco, Germany). The cements were removed mechanically over the composite surfaces after one week storage in distilled water at 37^oC and the composite surfaces were treated with adhesive system (Clearfil SE Bond, Kuraray, Japan). Composite resin build ups were created on composite surfaces. Shear bond strength was measured after 24h using a universal testing machine at a crosshead speed of 1 mm/min. The data was calculated in MPa and the results were statistically analyzed using one-way ANOVA and Tukey tests. Results: Shear bond strength values were as follows: Group1:39.32±3.30^a, Group2:38.92±3.27^a, Group3:33.36±2.49^b, Group4:34.19±3.22^b, Group5:38.61±3.65^a, Group6:38.72±2.43^a, Group7:37.68±3.25^a. Eugenol-containing cements significantly reduced shear bond strengths of composite to composite (p<0.05), while the other temporary materials had no adverse effect on shear bond strength (p>0.05). Conclusions: These findings suggested that eugenol-containing temporary filling materials have negative effect of composite to composite shear bond strengths.

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