We will evaluate the accuracy of fit of zirconia crowns by comparing printed and milling first molar crown. model with a mandibular first molar prepared (6 degree taper, 1.5 mm chamfer finish line) will be digitized using our laboratory scanner (D2000, 3Shape; Blue LED Multi-line; 5 – 8 µm accuracy). The digitized file of the preparation will be used to design a full coverage restoration (crown) using the Dental Designer Software (3Shape). The master file of the designed restoration (.stl file) will be used to fabricate the printed zirconia crown(n=20). Once the restorations are fabricated we will use the same laboratory scanner described above to digitize (scan) each crown. We will use Geomagic software (Geomagic Control X, 3D systems) to superimpose the digitized file representing each fabricated crown over the master design file. We will use software- defined best-fit algorithms to analyze the three-dimensional accuracy of fabricated crowns relative to the master design. This analyses results in positive and negative deviations between the superimposed data sets. We will calculate the absolute values of the deviations, resulting in two values per each fabricated crown. The accuracy of the fabricated crowns will be expressed in terms of trueness (the comparison between a reference data set and a test data set). In addition, the same master design file will be used to fabricate milled zirconia (n=20) crowns using substractive dental technology (“milling”, DS1300, DentaSwiss). We will use the same methods described above to assess the accuracy of milled zirconia crowns and compare the results to results obtained from printed zirconia crowns. Two-way analysis of variance will be used to compare between the groups. Main effects evaluated will include crown-type and fabrication method and the interaction between these two main effects. Dunnett’s multiple comparison test will be used for post-hoc analysis. A p<0.5 will be considered significan

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