Experimental Study to Evaluate the Internal Fit between Computer Aided Designing/Computer Aided Manufactured (CAD-CAM) Zirconia Coping and Pressable Ceramic Coping

Marginal fit of the dental restoration is important to prevent microleakage and periodontal problems so as to avoid secondary caries around the abutment teeth. The purpose of the study was to compare and evaluate the internal fit of copings manufactured using a CAD/CAM-system and laboratory-made heat-pressed ceramics. For this research, typodont mandibular left first molar was prepared about 1.5mm occlusal reduction and 6˚ taper both mesiodistally and buccolingually with shoulder finish line of 1.0mm width to receive all ceramic crown which was duplicated in silicone impressions and the respective working casts were formed using Type IV die stone and the restorations were made by CAD-CAM system for zirconia coping and wax pattern for heat-pressable lithium disilicate ceramics. Total of 20 dies were made and divided into Group I- zirconia copings and Group II - heat pressable lithium disilicate ceramics, in which 10 crowns were made in each group. The crowns were cemented to the respective dies with cyanoacrylate cement using finger pressure. The samples were then sectioned facio-lingually and the three zones measured were 2mm above the marginal finish line in both lingual and buccal side and one in the center of the occlusal surface. The mean horizontal and the vertical internal adaptation discrepancies statistically analyzed using Mann-Whitney test. It was concluded that CAD-CAM milled zirconia copings showed closer adaptation in the axial walls than heat pressed ceramic copings. But in the mid occlusal level where the adaptation was closer in heat pressed ceramic copings than the CAD-CAM milled zirconia copings.