Groove Effect of Abutment on Fracture Resistance of Monolithic Zirconia

Objectives: Monolithic zirconia restorations might make thin due to high bending strength. When central pit and central fissure on occlusal surface of restoration could be made thin, the height of abutment teeth have been kept. However, the minimum thickness and abutment tooth form of the zirconia restorations on the fracture resistance remains to be clarified. The present study aimed to examine fracture resistance of monolithic zirconia crowns on abutment tooth with groove.
Methods: Zirconia crowns with simple design were fabricated and amount of space between antagonists was ensured to be constant in this study. Abutment tooth dies having two kinds design were made, flat model and model with occlusal groove along to the central fissure. The dies were fabricated that the crown of minimum thickness at the central occlusal pit was 0.3, 0.5, and 0.7 mm. Crowns were bonded with an adhesive resin cement (PanaviaV5, Kuraray Noritake Dental) and cemented with a glass ionomer cement (AdsieldGI, Kuraray Noritake Dental). All specimens were tested with a universal testing machine (AG-I 20kN, Shimadzu). The statistical analysis were performed using two-way ANOVA and Tukey multiple comparison.

Results: Zirconia crown with 0.3 mm wall thickness was lowest fracture load among tested specimens regardless of groove on abutment die (p<0.01). The groove on abutment die showed smaller fracture load than without groove, and the fracture load of zirconia crowns using adhesive resin cement was larger than that using glass ionomer (p<0.01). The fracture location of the zirconia crowns was fractured to a central pit of zirconia crown, and the location for zirconia crown with large groove moved to outside from central pit.
Conclusions: Monolithic zirconia indicated the use of adhesive resin cement was useful when abutment was prepared the occlusal groove.