Introduction: The original technique of endocrowns described the use of porcelain, in vitro thermo-mechanical aging showed that endocrowns made of more flexible composite resin or newer resin nanoceramic materials may also have a successful outcome. The aim of the present study was to evaluate the marginal integrity of endodontically treated teeth restored with CAD/CAM Ceramill® comp and Cerasmart endocrown bonded with two adherence protocols (total etch and self-etch) before and after Thermo-mechanical aging.Materials and methods: A total of 28 freshly extracted human mandibular posterior teeth were collected. Teeth were sectioned perpendicular to the long axis 2mm coronal to the proximal cementoenamel junction. The molar teeth were randomly divided into two main groups according to the type of the endocrowns material used and two subgroups according to the bonding protocol. Group 1: Restored with Cerasmart endocrowns (14 samples). Subgroup (a): Total etch bonded Cerasmart endocrowns (7 samples). Subgroup (b): Self-etch bonded Cerasmart endocrowns (7 samples). Group 2: Restored with Ceramill® Comp endocrowns (14 samples). Subgroup (a): Total etch bonded Ceramill endocrowns (7 samples). Subgroup (b): Self-etch bonded Ceramill endocrowns (7 samples). All sampleswere subjected to thermo-mechanical aging to simulate one year. Vertical marginal gap distance was evaluated before and after aging. Using stereomicroscope with a fixed magnification of 90X. Then the data obtained were collected, tabulated and then subjected to statistical analysis.Results: It was found that Cerasmart material group recorded higher gap mean values (47.089±4.3µm) than Ceramill material (44.918±4.6µm). However, the difference was insignificant. The self-etch subgroup recorded statistically non-significant higher gap mean values (46.995±3.4µm) than total etch subgroup (45.013±3.04 µm) either before or after aging. And Irrespective of material or bonding approach it was found that thermo-mechanical aging affected marginal gap significantly (p=0.0002 < 0.05) where (before aging mean (47.421±2.65µm) > after aging mean value (44.587±3.09µm)). Conclusion: It was concluded that Both materials are promising to be used for endocrowns in terms vertical marginal gap in the posterior lower region. And both bonding protocols can be used successfully when bonding hybrid ceramic endocrowns with adhesive resin cement.