Effect of Digital Blocking of Reversed Tapered Preparations in Comparison to Conventional Wax Blocking on Fracture Resistance of Monolithic Zirconia Crowns .

Document Type : Original research articles

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Building 135 West Arabella, New Cairo, Egypt.

Abstract

Background: Intra-oral digital scanning can correctly capture single abutment tooth preparations, and the CAD software's algorithms can manage to design restoration for reversed tapered abutment. Aim: The purpose of this in vitro study was to assess the fracture resistance of CAD/CAM zirconia crowns made on reverse-tapered preparations with two different blocking techniques. Materials and methods: Thirty dies were 3D printed using SolidWorks software. Blocking reverse taper preparation, was done with two different blocking techniques, conventional wax blocking and digital blocking . Group II (B) (-4 TOC) n=5 and group III (D) (-8 TOC) n=5 underwent conventional wax blocking, Group II (C) (-4 TOC) n=5 and group III (E) (-8 TOC) n=5 used the software's algorithms (EXO-CAD) to block undercuts digitally and Group I (A) (12 TOC) served as the control (n=10). Thirty dies were individually scanned, and a separate design was made for each die (Generic type), scanning was done with Cerec Omnicam intraoral scanner. Thirty CAD/CAM monolithic translucent zirconia crowns were milled with 120μm of cement space. Cementation was done using self-adhesive resin cement (Thera-Cem). Fracture test was done using universal testing machine. SEM analysis was used to identify crack origins and propagation directions, and intra and intergroup analyses were performed of fractured parts. Results: Only tapering angle had a significant effect on fracture resistance (p=0.012). Conclusion: There was no significant difference between digital or conventional blocking nor their effect on fracture resistance test, 12⸰ TOC control group showed the highest fracture resistance and -8⸰ TOC showed the least.

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