Graded structures for all-ceramic restorations

One failure mode of all-ceramic restorations is radial cracking at the cementation surface, from occlusally induced flexure of the stiffer ceramic layer(s) on the softer dentin underlayer. We hypothesize that such failure may be substantially mitigated by an appropriate grading of elastic modulus through the ceramic thickness. In this study, we fabricated graded structures by infiltrating glass into zirconia plates, with resulting diminished modulus in the outer surfaces. The plates were then bonded to a polymeric base and subjected to flexure by contact loading until fracture. Comparison of infiltrated specimens with non-infiltrated controls showed a significant increase in the fracture loads, by a factor of nearly 2. Finite element analysis revealed the cause of increase in the load-bearing capacity to be diminished tensile stresses within the lower-modulus graded zone, corresponding to an increase in material strength. The results confirmed that suitably graded structures can be highly beneficial in the design of next-generation all-ceramic restorations.