Effect of the Coronal Wall Thickness of Dental Implants on the Screw Joint Stability in the Internal Implant-Abutment Connection

Purpose: To evaluate the effect of implant coronal wall thickness on load-bearing capacity and screw joint stability. Materials and Methods: Experimental implants were customized after investigation of the thinnest coronal wall thickness of commercially available implant systems with a regular platform diameter. Implants with four coronal wall thicknesses (0.2, 0.3, 0.4, and 0.5 mm) were fabricated. Three sets of tests were performed. The first set was a failure test to evaluate load-bearing capacity and elastic limit. The second and third sets were cyclic and static loading tests. After abutment screw tightening of each implant, vertical cyclic loading of 250 N or static loading from 250 to 800 N was applied. Coronal diameter expansion, axial displacement, and removal torque values of the implants were compared. Repeated measures analysis of variance (ANOVA) was used for statistical analysis (α = .05). Results: Implants with 0.2-mm coronal wall thickness demonstrated significantly low load-bearing capacity and elastic limit (both P .05). These implants also showed significantly large coronal diameter expansion and axial displacement after screw tightening (both P .05). Greater vertical load and thinner coronal wall thickness significantly increased coronal diameter expansion of the implant, axial displacement of the abutment, and removal torque loss of the abutment screw (all P .05). Conclusion: Implant coronal wall thickness of 0.2 mm produces significantly inferior load-bearing capacity and screw joint stability. Keywords: axial displacement, coronal wall thickness, internal conical connection, load-bearing capacity, wedge effect