Clinical evaluation of all restorations will be performed according to:~- Modified United States Public Health Service (USPHS) Ryge Criteria, at base line (1 week), 3, 6 and 12 months after cementation.
This study will be performed to evaluate the clinical performance (Plaque accumulation, fracture of (restoration or tooth), postoperative sensitivity, secondary caries, marginal fit and discoloration) of two CAD/CAM fabricated ceramic restorations (zirconia-reinforced lithium silicate glass ceramic and hybrid ceramic) with different preparation designs (modified occlusal veneer and endocrown) for rehabilitation of permanent first molars affected with different severity level of molar incisor hypomineralisation (MIH), evaluated at different time periods