Fracture-resistant monolithic dental crowns

• Capacity of crown restorations to sustain high bite force has been measured on manufactured, anatomically-correct specimens for three classes of monolithic materials.
• Extended finite element modeling has been used to follow the progression of embedded cracks in the crown/dentin structure, revealing a complex evolution to failure that cannot be inferred from more traditional FEM.
• Zirconia is confirmed to be the most durable of available monolithic ceramics, with lithium disilicate intermediate and dental composite weakest. All perform favorably relative to natural tooth enamel.

ObjectiveTo quantify the splitting resistance of monolithic zirconia, lithium disilicate and nanoparticle-composite dental crowns.MethodsFracture experiments were conducted on anatomically-correct monolithic crown structures cemented to standard dental composite dies, by axial loading of a hard sphere placed between the cusps. The structures were observed in situ during fracture testing, and critical loads to split the structures were measured. Extended finite element modeling (XFEM), with provision for step-by-step extension of embedded cracks, was employed to simulate full failure evolution.ResultsExperimental measurements and XFEM predictions were self-consistent within data scatter. In conjunction with a fracture mechanics equation for critical splitting load, the data were used to predict load-sustaining capacity for crowns on actual dentin substrates and for loading with a sphere of different size. Stages of crack propagation within the crown and support substrate were quantified. Zirconia crowns showed the highest fracture loads, lithium disilicate intermediate, and dental nanocomposite lowest. Dental nanocomposite crowns have comparable fracture resistance to natural enamel.SignificanceThe results confirm that monolithic crowns are able to sustain high bite forces. The analysis indicates what material and geometrical properties are important in optimizing crown performance and longevity.