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Aim: The aim of this study was to evaluate the internal and marginal fit accuracy using cone beam computerized tomography as an innovative nondestructive method and to assess the fracture resistance of the recently introduced zirconia reinforced lithium silicate glass ceramic in comparison to lithium disilicate and monolithic zirconia. Materials and Methods: Three types of CAD/ CAM ceramic blocks were used; zirconia reinforced lithium silicate glass ceramics (Vita Suprinity), lithium disilicate glass ceramic (IPS e.max CAD) and partially sintered translucent zirconia (In-Coris TZI). A ceramic master die was fabricated and scanned using the Cerec Omnicam to produce a total number of 30 crowns, which were divided into 3 groups (n = 10) according to the ceramic material used . Group I: Vita Suprinity. Group II: IPS e.max CAD and Group III: InCoris TZI. A highly computerized cone beam tomography (CBCT) was used to evaluate the fit accuracy of the crowns on the master die. For fracture resistance test, epoxy resin dies were optically scanned using Omnicam scanner and 30 crowns were fabricated using the CAD/ CAM ceramic materials (n = 10) for each tested material. The crowns were cemented using self-adhesive resin cement. A compressive load was applied at a cross head speed of 1mm/min and the fracture load in Newtons was recorded for each specimen. Fractured crowns were examined to determine the mode of fracture. Results: Marginal and internal fit evaluation showed that group I (Vita Suprinity) recorded the least mean in respect to all measuring points (103.6±10.4μm), while group III (In Coris TZI) showed the highest mean in respect to all points (146.7±9.23μm). For fracture resistance, In Coris TZI zirconia showed the highest fracture load (4548.9±200.9 N), while the lowest mean value was recorded in Vita Suprinity (3484.8±22.17 N). There was no significant difference between Vita Suprinity and IPS e.max CAD. Conclusion: Vita Suprinity crowns showed the best marginal and internal fit when compared to the other two materials. InCoris TZI exhibited the highest fracture strength of all three groups. All values were within a clinically acceptable range for the three ceramic materials tested. (1572) Maha Adly Abd El Moaty and Amir Shoukry Azer E.D.J. Vol. 64, No. 2 INTRODUCTION In recent years, various CAD/CAM – machinable ceramic materials have been developed in order to enable the esthetic demands of prosthetic restorations to be accomplished.(1) The clinical selection of ceramic systems is based on the mechanical and optical properties of the materials. (2) Clinical evaluations have indicated an excellent clinical survival rate (over 95%) of zirconia-based FPDs and crown restorations. In terms of fracture resistance zirconia have the potential to withstand physiological occlusal forces in the posterior region and provides alterations to metal ceramic restorations.(3) However, chipping/ delamination of the veneering ceramic has been repeated as the most frequent complication of bilayered zirconia restorations.(4-6) In recent years monolithic glass-ceramics have been developed in order to provide exceptional esthetics, without requiring a veneering ceramic. It has been reported that greater structural integrity can be accomplished by elimination of the veneered ceramic and its bond interface.(7) Lithium disilicate ceramic restoration is one of the monolithic systems that have gained popularity for anterior and posterior single crowns and partial coverage restorations because of its superior physical properties. Due to enhanced translucency and different shades of lithium disilicate, anatomically continued monolithic restorations are feasible.(8,9) CAD/CAM lithium disilicate blocks are manufactured with an optimized pressure casting process to minimize microstructural defects. As the blocks are formed in an immediate phase due to partial crystallization, they are easier to machine and can obtain high strength.(1) Combined with esthetic concerns, they could be used for single crown restorations in the anterior and posterior regions.(2) Recently, a zirconia reinforced lithium silicate glass ceramic (Vita Suprinity)(10) for dental CAD/CAM applications has been introduced to the dental market. It is used for the fabrication of inlays, onlays, partial crowns, veneers, anterior and posterior single tooth restorations on implant abutments. The manufacturer has claimed that this newly developed generation of glass ceramic materials combine the positive characteristics of zirconia and glass ceramics. The zirconia particles are incorporated in order to reinforce the ceramic structure by crack interruption. It has been supposed that after crystallization, the ceramic material exhibited enhanced mechanical properties and highest esthetic requirements. It is anatomically contoured as monolithic ceramic restoration due to enhanced translucency and different shades. (10) Accuracy of fit is considered a very important factor in crown fabrication. Inadequate fit creates a potential space between the restoration and the prepared tooth. As space increases, more luting material is exposed to the oral environment. Bacterial plaque can easily accumulate in this defective areas, which causes gingival inflammation, caries and pulpal affection. In addition, variation in fit creates stress concentration which may reduce the strength of the restoration and consequently cause its fracture.(11) Computerized tomography (CBCT) allows accurate three dimensional imaging of hard tissue structures and is capable of providing submillimeter resolution images of high diagnostic quality with short scanning time and relatively low radiation exposure dose. In addition, CBCT is a non-destruction method that does not require sectioning which may distract the assembly of crown & die and allow three dimensional analysis of the fit accuracy at greater number of measuring points using the on screen software tools without affecting the original dimensions of the specimens.(12) However not much is known about the marginal fit and fracture resistance of these new materials. The aim of this study was to evaluate the internal and marginal fit accuracy (adaptation) using cone beam computerized tomography as an innovative non-destructive method, and to assess the fracture resistance of the recently introduced zirconia reinforced lithium silicate glass ceramic EVALUATION OF FRACTURE RESISTANCE AND FIT ACCURACY OF THREE TYPES (1573) in comparison to lithium disilicate and monolithic zirconia. The proposed hypothesis was that there is no difference between the three CAD/ CAM monolithic ceramic materials. MATERIALS AND METHODS Three types of CAD/CAM ceramic blocks were used in this study; zirconia reinforced lithium silicate glass ceramic (Vita Suprinity), lithium disilicate glass ceramic (IPS e.max CAD) and partially sintered translucent zirconia (In-Coris TZI). The materials used, their composition and manufacturers are presented in table (I). Fabrication of the ceramic master die An ivory upper first molar was seated in a typodont model and prepared to receive a full ceramic crown with the following criteria in the preparation: occlusal reduction 1.52 mm, axial reduction 1-1.2 mm, axial taper 10-12 degrees, and 1mm supragingival circumferential chamfer finish line. All transitions from the axial to the occlusal surface were rounded, smooth, and free from sharp angles or undercuts.(13) Before preparation of tooth, a silicone mold was made with normal-setting polyvinyl siloxane impression material for the coronal portion of the tooth. These pre-preparation silicone mold was used as reference guide to assist in checking for enough clearance during preparation. The prepared ivory tooth was scanned using a laboratory optical scanner (ZirkonZahn S600 ARTI, Italy) and a wax pattern of the die was milled from a block of white wax (CopraPlex, WhitePeaks, Germany). The wax pattern was invested, TABLE (I) Materials used and their composition. Materials Commercial name Composition Manufacturer Zirconia reinforced Lithium silicate Vita Suprinity SiO2 56-64 Li2O 15-21 K2O 1-4 P2O5 3-8 AL2O3 1-4 ZrO2 8-12 Ce O2 0-4 Pigments 0-6 Vita, Zahnfabrik Germany Lithium disilicate IPS EMAX CAD wt% SiO2 57°80.0 LiO 11.0-19.0 K2O 0.0-13.0 P2O5 0.0-11.0 ZrO2 0.0-8.0 ZnO 0.08.0 Colouring oxide 0.0-12.0 Ivoclar Vivadent Liechtenstein Trnaslucent Zirconia In Coris TZI ZrO2 + HFO2 + Y2O3 99.0% Y2O3 5.6% AL2O3 ≤ 0.35% Other Oxides except Er2 03 ≤ 0.2% Sirona Bensheim Germany (1574) Maha Adly Abd El Moaty and Amir Shoukry Azer E.D.J. Vol. 64, No. 2 burnt out and a ceramic ingot was heat-pressed into the mold space to produce the ceramic master die from lithium disilicate ceramic (IPS e-max press, Ivoclar Vivadent, USA), figure (1). Marginal and internal fit evaluation The ceramic die in the typodont model was scanned without application of powder using white LED light of CEREC AC Omnicam (Sirona Dental Systems, Bensheim, Germany). The acquired optical data was transferred into an accurate three dimensional digital dies resembling the original preparation with fine details of all surfaces and margins. Five scans were performed to obtain five full-colored 3D models for the die and neighbouring teeth for milling crowns. In case of zirconia crowns, the software was designed to enlarge the milled crown by 30% as it will be milled in a partially sintered state. A total of 30 crowns (specimens) were fabricated for this test. Group I (Vita Suprinity): Ten crowns were designed using (CEREC 3D software, Version 4.2, Sirona Dental Systems, Bensheim, Germany) by making a copy of the anatomy of the contralateral tooth or ‘Bioreference’ mode with 80 μm die spacer. A Cerec inLab MC XL milling unit was used for CAM process of the designed crowns using zirconia reinforced lithium silicate blanks followed by crystallization firing at 850°C for 22 minutes in the Programat CS furnace. No internal adjustments, glazing, or poli

EVALUATION OF FRACTURE RESISTANCE AND FIT ACCURACY OF THREE TYPES OF CAD/CAM FABRICATED CROWNS USING CONE BEAM COMPUTERIZED TOMOGRAPHY