Abstract
Background
The presence of screw access hole on the occlusal surface might affect the strength of an implant-supported crown. This study aimed to compare the fracture resistance among 5 mol% yttria-stabilized tetragonal zirconia polycrystal (5Y-TZP), lithium disilicate, and composite resin implant-supported premolar crowns with either a cement-retained or a combined cement- and screw-retained design after cyclic loading.
Methods
Forty-eight maxillary first premolar crowns and their abutments were attached on dental implants (ø4.0 x 10 mm) embedded in epoxy resin blocks and equally divided into 6 groups (n = 8) based on crown material (5Y-TZP (Z), lithium disilicate (L), and composite resin (C)) and restoration design (a cement-retained design and a combined cement- and screw-retained design). After 500,000 cycles of cyclic loading, the fracture resistance of each specimen was measured using a universal testing machine and analyzed using the Kruskal Wallis H test to compare between crown materials within each restoration design. The Mann-Whitney U test or independent t test was used to compare the restoration designs within each crown material (α = 0.05).
Results
The fracture loads in the Z groups with a cement-retained and a combined cement-and screw-retained designs (1514±442 N and 1171±204 N) were significantly higher than those in the L group (1077±247 N and 849±116 N) and C group (1066±213 N and 648±190 N). There was no significant difference in fracture loads between the L and C groups in both restoration designs. Within the same crown material, the fracture loads of both restoration designs in the Z group were comparable. In contrast, in the L and C groups, the fracture loads in the cement-retained groups were significantly higher than those in the combined cement- and screw-retained groups.
Conclusions
Fracture resistance of an implant-supported crown is dependent on the crown material. Z demonstrated the highest fracture resistance, followed by L and C. The presence of a screw access hole did not impact the fracture resistance in Z. In contrast, for both L and C, the fracture resistance decreased with the presence of a screw access hole.