Loosening of the fixing screw in single implant crowns: predisposing factors, prevention and treatment options.

The problem of technical complications in implants and implant-supported restorations has existed for decades. The most frequent complication is the loosening of the fixing screw, which although is not catastrophic, if it occurs repeatedly, it may affect the success of the implant therapy and the patient satisfaction. Factors that affect the frequency of prosthetic complications include: the implant-abutment connection, para-functional habits, cantilevers, and the type of restoration. Regarding the implant-abutment connection, the first systems were those with an external hexagon. Because of their small height and the disadvantages that this entails, other connection types were developed, such as those of hexagonal and conical connection, which decreased the complication rates, including the loosening of the fixing screw. On the dilemma "cement- or screw-retained restoration", the choice depends on biological, technical, and aesthetic factors. Cement-retained restorations are simpler in construction with lower cost and clinicians are more familiar with the clinical procedure. On the other side, if the fixing screw of the abutment is loosened in a cement-retained restoration, it may be a difficult and demanding clinical task to fix this prosthetic complication. Screw-retained restorations are more prone to loosening of the fixing screw, but allow easy retrievability and repair. Their use however, is often restricted because of diverting or unfavorable inclination of the alveolar ridge and the implant. The aim of this article was to present clinical solutions for the complication of screw-loosening through clinical examples and discuss the factors that may predispose to its occurrence. CLINICAL SIGNIFICANCE: The problem of technical complications in implants and implant-supported restorations has existed for decades. The most frequent complication is the loosening of the fixing screw which, although is not catastrophic, if it occurs repeatedly, it may affect the success of the implant therapy and the patient satisfaction. Factors that affect the frequency of prosthetic complications include: the implant-abutment connection, para-functional habits, cantilevers and the type of restoration. The treatment options for the clinician are limited but certain preventing measures during construction of the restoration may be helpful to overcome this clinical problem.