Statement of the problem Despite improvements in dental ceramics, failure of bilayered restorations mainly by chipping and delamination of veneer with different degrees remains a disadvantage of this type of restorations. Accordingly the need for ceramic restoration repair became a widspread alternative to replacement of defective restorations especially in complex cases . However it is not always easy for the clinician to select the best repair protocol when dealing with different ceramic types and different chipping patterns.
Purpose: The purpose of this study was to evaluate the shear bond strength between a commercially available repair system (Ceramic Repair kit) with a lithium disilicate glass ceramic (e.max CAD) and zirconia based ceramic (InCoris ZI) subjected to different degrees of veneering ceramic chipping..
Materials and Methods: A total of sixty ceramic samples were designed and fabricated in this study using the CAD/CAM technology . The samples were divided into two groups; Group 1: Thirty samples constructed from lithium disilicate glass ceramic (e.max CAD). Group 2: Thirty samples constructed from zirconia ceramic (InCoris ZI). Each of the previous groups was further subdivided into three equal subgroups depending on the amount of bonded repair material to the ceramic core and to the veneering ceramic: Subgroup 1 (control): Ten samples with ceramic repair material bonded directly onto the ceramic core (100% core). Subgroup 2: Ten samples with 25% of the ceramic repair material surface bonded to veneering ceramic surfaces, and the other 75% to ceramic core and Subgroup 3: Ten samples with 50% of the ceramic repair material surface bonded to veneering ceramic, and the other 50% to ceramic core. Shear bond strength test was done by loading the samples parallel to its the long axis at the composite ceramic interface at a crosshead speed of 0.5 mm/min until fracture . The maximum load at failure was recorded in Newtons (N) unit and was divided over the bonded area(mm2) to convert to MPa unit. Data was then collected, tabulated and statistically analyzed.