The Relationship Between Implant Preload and Screw Loosening on Implant-supported Prostheses

Abstract

The purpose of this study was to determine whether varying the preload on the implant-abutment complex would affect screw loosening under simulated loading conditions. Abutment screws in sample models were tightened to 25, 30, 35, and 40 N-cm. One group of samples was allowed to stand for 3 hours after being torqued and then loosened. Another group of samples was retorqued after 10 minutes with the same initial torque value and then allowed to stand for 3 hours before loosening. For the load group of samples, the abutments were torqued into place, retorqued after 10 minutes, and a load applied for 3 hours before loosening. Cyclic loading was carried out using a servo-hydraulic testing machine with the values cycled between 1 and 26 pounds and the load applied directly to the abutments. Analysis of variance, analysis of covariance, and linear regression analysis was performed. Within the parameters of this in vitro investigation, the following recommendations can be made: (1) retightening abutment screws 10 minutes after the initial torque applications should be routinely performed and (2) increasing the torque value for abutment screws above 30 N-cm can be beneficial for abutment-implant stability and to decrease screw loosening.

Abutment screw loosening in single-implant restorations: A systematic review

“…More than 97% of SIR studied maintained a stable implant-abutment connection after 3 years of service. This is in agreement with results from in vitro studies, [18][19][20][21] which have demonstrated stable abutment screw joints for internal-connection implants as well as for external-connection implants with improved screw materials and preload. This study did not look into other types of mechanical complications, such as screw fracture, where implantabutment connection geometry might play a role.…”

“…[14][15][16][17] The stability of the external implant-abutment connection was subsequently improved by altering the screw alloys and their surfaces and applying proper torque values to establish higher initial preloads. 3,[18][19][20][21] …”

“…[14][15][16][17] The stability of the external implant-abutment connection was subsequently improved by altering the screw alloys and their surfaces and applying proper torque values to establish higher initial preloads. 3,[18][19][20][21] Industry surveys 22,23 have shown that externalhex implants still dominate the European and US markets, although there is a continuous rise in internal-connection implants. The literature is lacking studies that compare the incidence of abutment screw loosening in implant systems of different connection geometries following the improvements in screw materials and preload.…”

Long-term stability of an injection-molded zirconia bone-level implant: A testing protocol considering aging kinetics and dynamic fatigue

“…The abutment consisted of a concave-shaped transgingival part (gingival height [GH] of 3.0 mm) and a tapered part to be exposed to the oral cavity (5 mm in height). The abutment screws were tightened at 25 Ncm and, additionally, retightened 10 min after the initial torque application to counteract a possible reduction in preload [15].…”

Microbiological Seal of Two Types of Tapered Implant Connections

“…Increasing the torque beyond 30 N may be beneficial for the stability of the implant-abutment and reduce the risk of loose screws (16,17). Furthermore, increased screwing torque in Morse taper connections improves their sealing capacity, since no contamination was observed for abutments tightened with a 40 N torque (18).…”