This study evaluated the effect of the material and the extension of the relocated margin on the marginal adaptation of the extra coronal restoration and microleakage at the tooth/resin interface after thermo-mechanical cyclic loading. Materials and methods: 196 teeth were divided into six groups according to type of cavity design and build-up restoration. All the groups received a standardized MO cavity preparation. The gingival seat was located 2 mm above the CEJ. Group I was without any modification and restored with direct composite. For Group II, III and IV the gingival seat extended 2mm below the CEJ and restored with direct, flowable, indirect composite respectively. Group V had MOD cavity where the proximal boxes had the same criteria of the mesial preparation of Groups II-IV. Samples of Group VI received the same preparation as Groups II, III and IV but was extended another 4mm in the buccal direction. Groups V and VI were restored with direct composite. Margin gap and microleakage scores were evaluated after cyclic loading Results: Group VI and IV showed the highest mean margin value compared to different cavity designs and materials used for CMR respectively, however within clinically acceptable range. Group III showed the highest microleakage scores. Conclusions: The use of CMR with single or multiple narrow cavities is more favorable than with wide cavities. CMR is a logical option in teeth with deep proximal cavities that needs to be crowned.