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Objective: To evaluate the vertical marginal gap and internal fit of two types of monolithic zirconia crowns fabricated using two different CAD/CAM machines. Materials and methods: A sound human maxillary first premolar was selected to receive all ceramic crown preparation. The prepared premolar was then duplicated to produce twenty epoxy dies divided into two groups. Twenty Standardized monolithic translucent zirconia (10 Prettau, & 10 Incoris TZI crowns) were CAD/CAM fabricated onto the epoxy dies. The vertical marginal gap before cementation was measured using a metallurgic microscope. Then the crowns were cemented onto their corresponding epoxy dies using Panavia F 2.0. Half of the specimens were sectioned bucco-lingualy and the remaining specimens were sectioned mesio-distally. Measurements of the internal fit on the Buccal, lingual, mesial, distal and occlusal were taken using a metallurgic microscope. Results were tabulated and statistically analyzed using Wilcoxon signed rank test. Results: The Prettau crowns showed statistically significantly higher vertical marginal gap (Prettau 96.91 ± 2.78 & Incoris TZI 59.17 ± 6.4 μm) and inferior internal fit than that of Incoris TZI crowns (Prettau 117 ± 3.67 & Incoris TZI 103.2 ± 3.61 μm). Conclusions: The Incoris TZI crowns had better marginal integrity and internal fit than that of Prettau crowns. (476) Tarek Abdel Hamid, et al. E.D.J. Vol. 64, No. 1 and biocompatibility but also on the marginal integrity and internal fit. Large marginal gaps lead to dissolution of the cement with subsequent dental plaque accumulation facilitating marginal leakage and secondary decay.7,8 It is well agreed in the literature that marginal fit is one of the major factors responsible for causing secondary decay and periodontal disease.9,10,11 It has been proven by McLean12 in 1971 that clinically allowable marginal fit is within 120-μm range when fabricating a dental restoration. Over the last years, most studies on monolithic zirconia focused mainly on the mechanical properties (fracture resistance13, flexural strength & chipping resistance14, and hardness15), the effect of surface treatment on the mechanical properties, the wear of the zirconia on the antagonists,16 and effect of the low temperature degradation. 17 Little information is available about the marginal gap and internal fit of these restorations. Seok J.H. and Jin HC18 reported that the marginal discrepancy and internal fit was smaller in Ceramill system than ZirkonZahn. However both were within clinically acceptable range of marginal discrepancy. Freire et al 19studied the marginal fit of monolithic restorations (monolithic zirconia Lava plus, monolithic lithium disilicate IPS Emax CAD, and conventional metal ceramic crowns. They found that the monithic lithium disilicate produced the lowest discrepancy and they concluded that the accuracy of fit of the three groups was within the range of clinical acceptance range. So the aim of this study was to evaluate the vertical marginal gap and internal fit of two monolithitc zirconium crowns (Prettau and Incoris TZI) constructed by two different CAD/CAM systems(Zirkon Zahn,Italy and Cerec, Sirona ). The null hypothesis tested in this study that there is no difference in the vertical marginal gap and internal fits between the two systems. MATERIALS AND METHODS Tooth preparation and die fabrications A freshly extracted non-carious, non-restored sound permanent Upper human premolar was selected for this study. The tooth was mounted in an acrylic base to allow accurate positioning of the tooth in a milling machine (which was used for tooth preparation). The tooth was prepared using a milling machine (AF 30, Nouvag AG ST. Switzerland) (figure 1a) modified by custom made adaptor to accommodate high speed contra-angle (NSK, Tokyo, Japan). Tooth preparation was done using tapered diamond stone with flat end (TF 12, Mani Inc. Japan) and head diameter 1mm so that the preparation had 1mm shoulder finish line and 6 degree convergence angle (figure 1b) which was achieved by the taper of the diamond bur. Occlusal reduction was done after removing the tooth from the milling machine. Using a cylindrical diamond bur (SF 14, Mani Inc. Japan) with diameter of 1.5mm. Depth cut grooves of 1.5mm were cut in the occlusal surface at 45 ̊ angle with the long axis of the tooth. The prepared tooth had 6.5mm height, 4mm mesiodistal diameter and 7mm bucco-palatal diameter at the cervical part. The preparation was finished by fine diamond stone at low speed. The prepared tooth was duplicated using silicon duplicating material [Dupliflex,Vilamalla (Girona) Spain ] and poured into 20 epoxy resin dies (Kemapoxy, CMB, Egypt) (figure 1c). The epoxy dies were then duplicated into twenty working stone dies for crown constructions using a scanable stone (Optic Scanning stone, ETI Empire Direct, Anaheim, CA, USA).

Vertical Marginal gap and internal fit of two types of fully anatomic zirconia crowns constructed by different CAD/CAM system