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Strength and fracture pattern of monolithic CAD/CAM-generated posterior crowns
Andreas Bindl1, Heinz Lüthy, Werner H Mörmann
1Division of Aesthetic and Computer Restorations, Department of Preventive Dentistry, Periodontology and Cariology, Center for Dental and Oral Medicine, University of Zurich, Zurich, Switzerland. andreas.bindl@zzmk.unizh.ch
Summary
Adhesive cementation significantly improved the fracture strength of ceramic crowns compared to zinc-phosphate cementation. Lithium disilicate crowns showed better performance with zinc-phosphate cement than other ceramics, but adhesive cementation is recommended for weaker ceramic types.
Area of Science:
- Dental Materials Science
- Biomaterials Engineering
- Prosthodontics
Background:
- Monolithic posterior CAD/CAM crowns are widely used in restorative dentistry.
- The choice of cementation technique significantly impacts the mechanical performance of ceramic restorations.
- Lithium disilicate, leucite glass, and feldspathic ceramics are common materials for these crowns.
Purpose of the Study:
- To evaluate and compare the fracture strength and patterns of monolithic posterior CAD/CAM crowns fabricated from different ceramics.
- To test the hypothesis that zinc-phosphate cemented lithium disilicate crowns would exhibit similar fracture strength to adhesively cemented crowns.
- To determine the optimal cementation strategy for various ceramic materials used in posterior restorations.
Main Methods:
- Fabrication of monolithic posterior crowns (1.5mm thickness) from lithium disilicate, leucite glass, and feldspathic ceramic using CEREC 3 CAD/CAM.
- Two cementation groups: (A) zinc-phosphate cement and (B) adhesive cementation on resin-based composite dies.
- Load-to-fracture testing on 15 crowns per ceramic type and cementation group, with crack pattern analysis on additional samples.
Main Results:
- Adhesive cementation (B) resulted in significantly higher fracture loads across all ceramic types compared to zinc-phosphate cementation (A) (P < 0.001).
- Lithium disilicate crowns cemented with zinc-phosphate (A-1) demonstrated significantly higher fracture loads than leucite glass (A-2) and feldspathic ceramic (A-3) crowns (P < 0.001).
- While lower, the fracture load of zinc-phosphate cemented lithium disilicate crowns (A-1) approached that of adhesively cemented lithium disilicate crowns (B-1).
Conclusions:
- Adhesive cementation effectively enhances the fracture strength of weaker ceramic materials like leucite glass and feldspathic ceramics.
- Zinc-phosphate cementation is a feasible option for lithium disilicate crowns, though adhesive cementation provides superior strength.
- The study rejects the initial hypothesis, highlighting the significant benefit of adhesive cementation for overall ceramic crown strength.