Introduction & Objective: Preparation of access cavity to root canal is a critical phase in endo-dontic treatment. The purpose of this study was to evaluate the effect of access cavity loca-tion (labial or palatal) on fracture resistance of endodontically treated maxillary central teeth. Materials & Methods: In this experimental laboratorial study, 84 intact human maxillary central incisors with similar dimensions were selected. The teeth were divided into 4 test groups as follows: Group 1 : teeth without access cavity (control group) Group 2: teeth with labial ac-cess Group 3: teeth with palatal access and Group 4: teeth with labial & palatal accesses. Root canals were cleaned and lateral condensation technique was used to obdurate the canals and root canal therapy was completed. The access cavities were restored with a light cured microhybrid resin composite. Continuous compressive force at a crosshead speed of 2 mm/min was applied by a testing machine. Load at fracture was recorded in MPa. Modes of fracture were assessed using stereomicroscope at X20 magnification. Data was analyzed us-ing One - Way analysis of Variance and Tukey HSD tests.

Results: Means and standard deviations of fracture resistance for the 4 tested groups were: G1: 1172.2±224.05N, G2:990.4±199.324 N, G3: 861.95±237.089N and G4:784.27± 221.586 N. There was significant difference in fracture resistance values between G1 (control) and each tested group (P < 0.05). Mean fracture resistance for the test group with labial access was higher than the test group with palatal access but no significant difference was observed. Group 2 showed statistical difference compared with group 4 (P=0.017) but there is no sig-nificance between group 3 and group 4(P=0.666). Fracture modes in all groups were an oblique pattern and maximum and minimum of unfavorable fractures were seen in the control group with 48% and group 3 with 5%.

Conclusion: Preparation of access cavity reduces tooth fracture resistance. Palatal and labial& palatal accesses decrease considerably tooth fracture of resistance.