Effect of core design on fracture resistance of zirconia-lithium disilicate anterior bilayered crowns

PURPOSE. The effect of core design on the fracture resistance of zirconia-lithium disilicate (LS2) bilayered crowns for anterior teeth is evaluated by comparing with that of metal-ceramic crowns. MATERIALS AND METHODS. Forty customized titanium abutments for maxillary central incisor were prepared. Each group of 10 units was constructed using the same veneer form of designs A and B, which covered labial surface to approximately one third of the incisal and cervical palatal surface, respectively. 1.52 pressed-on-zirconia (POZ) and porcelain-fused-to-metal (PFM) crowns were divided into "POZ_A," "POZ_B," "PFM_A," and "PFM_B" groups, and 6000 thermal cycles (5/55 degrees C) were performed after 24 h storage in distilled water at 37 degrees C. All specimens were prepared using a single type of self-adhesive resin cement. The fracture resistance was measured using a universal testing machine. Failure mode and elemental analyses of the bonding interface were performed. The data were analyzed using Welch's t-test and the Games-Howell exact test. RESULTS. The PFM_B (1376.8 +/- 93.3 N) group demonstrated significantly higher fracture strength than the PFM_A (915.8 +/- 206.3 N) and POZ_B (963.8 +/- 316.2 N) groups (P<.05). There was no statistically significant difference in fracture resistance between the POZ_A (1184.4 +/- .319.6 N) and POZ_B groups (P>.05). Regardless of the design differences of the zirconia cores, fractures involving cores occurred in all specimens of the POZ groups. CONCLUSION. The bilayered anterior POZ crowns showed different fracture resistance arid fracture pattern according to the core design compared to PFM.