Effect of the Diameter and Preparation Method of the Occlusal Screw Access Channel on Fracture Resistance of Cement-retained Implant-supported Posterior Monolithic Zirconia Crowns

The favorable fracture resistance of implant-supported crowns is important. Zirconia crowns can be an acceptable treatment in relation to metal‒ceramic crowns for achieving the best clinical success.

The present study evaluated the effect of the diameter and preparation method of the occlusal screw access channel on the fracture resistance of cement-retained implant-supported posterior monolithic zirconia crowns for their retrievability.

Fifty-six implant-supported posterior multi-layer monolithic zirconia crowns were designed. Twenty pieces with an initial occlusal channel were designed with 2.3 and 3.5 mm diameters (n =10 each). In addition, 30 pieces with an intact occlusal surface as the control group or the crowns in which the occlusal channel was prepared with a bur were designed in 10 and 20 samples, respectively. Six additional crowns were also designed for SEM evaluations after their preparation with a bur.

The maximum fracture resistance value was recorded in the control group, followed by the initial access channel group with a 2.3 mm diameter. The minimum fracture resistance value was recorded in crowns with a 3.5-mm diameter hole prepared with a bur. The mean fracture strength in the groups with a 2.3 mm diameter was higher than in groups with a 3.5 mm diameter (P<0.05). Cracks in samples prepared with a bur were seen under SEM.

This study showed that using an initial access hole with a diameter of 2.3 mm is the best choice in hybrid implant-supported crowns. However, when it is necessary to prepare an access hole with a bur, it should be done with the smallest possible diameter.