Although osseointegrated dental implants have become a predictable and effective modality for the treatment of single or multiple missing teeth, their use is associated with clinical complications. Such complications can be biologic, technical, mechanical, or esthetic and may compromise implant outcomes to various degrees. This article presents prosthetic complications accompanied with implant-supported single and partial fixed dental prostheses.
Although osseointegrated dental implants have become a predictable and effective modality for the treatment of single or multiple missing teeth, their use is associated with clinical complications.
Such complications can be biologic, technical, mechanical, or esthetic and may compromise implant outcomes to various degrees.
Our review showed that six categories of technical or mechanical complications were associated with single implant restorations and partial fixed implant-supported prostheses: loosening of screws, fracture of screw, fracture of framework, fracture of abutment, chipping or fracture of veneering material, and decementation.
Biomechanics of Implant-Supported Restorations in Partially Edentulous Patients
The diagnosis and treatment planning of single restorations and partial fixed prostheses supported by dental implants require comprehensive scientific knowledge and a clear plan for definitive restorations before treatment begins. One of the most important factors in minimizing the incidence of biomechanical complications of single-implant restorations (SIRs) and partial fixed implant-supported prostheses (PFISPs) is to decrease the resistance to adverse leverage forces during function. To minimize adverse leverage forces on anterior SIRs and PFISPs, implants should be placed as vertical as possible to the forces applied during function, and the fabrication of incisal guidance should be shallow. For posterior SIRs and PFISPs, implants should be centered mesiodistally and as perpendicular as possible to the occlusal surface so that leverage can be minimized during function. Other factors that may affect biomechanical forces on SIRs and PFISPs are cuspal inclination, implant inclination, horizontal offset of the implant, and apical offset of the implant. Weinberg and Kruger reported that every 10-degree increase in cusp inclination leads to a 30% increase in the torque applied to the restoration during function ( Fig. 1 ). Also, every 10-degree increase in implant inclination may lead to a 5% increase in the torque applied to the restoration during function ( Fig. 2 ). Moreover, a 1-mm increase in the horizontal offset of an implant restoration introduces a 15% increase in torque during function, and a 1-mm increase in the vertical offset introduces a 5% increase ( Figs. 3 and 4 ). Biomechanically, the functional load applied to an implant restoration is directed to the coronal portion of the crestal bone around the body of the implant. Therefore, extra care should be taken when multiple factors are present, such as heavy occlusal forces, a laterally positioned implant, and steep cuspal inclination, because the stress is concentrated at the abutment-implant connection, the point at which complications may occur. This concentration of functional load at the crestal bone and at the connection between the crown or abutment and the implant increases when the vertical interarch space increases. Finite element analysis of implant-supported restorations has shown that the largest amount of stress is concentrated at the coronal part of the alveolar bone at the implant-bone interface. This stress level increases with the vertical interarch space.