Effect of Casting Procedures on Screw Loosening in UCLA‐Type Abutments

Abstract

Machined abutments retained a significantly greater percentage of torque compared with cast abutments. Casting procedures decrease the percentage of applied torque, which may influence final screw joint stability.

Screw loosening of different UCLA-type abutments after mechanical cycling

“…Any irregularities in the mating surfaces will likely result in preload reduction 28 . The casting procedures may have contributed to these results since the 21 . Therefore, it is important to point out that any irregularity in the mating surfaces should be detected, as changes occur between contacting parts when the screw is tightened because all the metallic contacting surfaces flatten slightly and the microscopic distance between contacting surfaces decreases 21 …”

“…Several factors may cause reduction or loss of preload in single tooth restorations such as casting procedures, superstructure inaccuracy, occlusal morphology and insertion torque, occlusal overload and physical properties of the screw materials 28-29 . Kano et al 21 studied the casting effect on torque maintenance by detorque measurements of UCLA-type abutments and observed a detorque mean of 92.3% for the machined titanium abutments, 81.6% for the pre-machined palladium abutments cast with palladium, 86.4% for plastic abutments cast with nickel-chromium, and 84.0% for plastic abutments cast with cobalt-chromium alloy.…”

“…Eccentric and compressive forces are generated during chewing movements and influence the screw retention 3,8,[17][18][19][20] . The optimal preload values for the implant/abutment screw joint have not been fully identified and in single tooth implants this value is critical for screw joint stability 21 . The purpose of this study was to evaluate the loss of applied torque (detorque) values in cast and pre-machined (UCLA) type abutments for external hex abutment/implant interface of single implant-supported prostheses subjected to mechanical cycling.…”

“…Other studies also compared plastic, pre-machined and machined abutments and concluded that lower preload has developed for all components subjected to casting 15,21,30 . This study confirms such results and shows that casting procedures can decrease detorque values even in pre-machined cast abutments, like those used.…”

Effect of Coated Surfaces influencing Screw Loosening in Implants: A Systematic Review and Meta-analysis

“…[1][2][3][4][5] Various factors are attributed to its loosening such as screw design, elasticity of the bone, elasticity of the screw joint, initial preload, friction coefficient, applied torque, and rate of tightening.…”