Practical Guidelines Based on Biomechanical Principles
In any structure subjected to functional loads, there may be situations leading to overload and subsequent complications. Implant treatment defines a structure based on both biological tissue (bone) and mechanical components (implant and superstructure). Overload in this biomechanical edition where chewing forces exert a repeated bending of a part of this structure leading to marginal bone loss and/or component failure. An important consequence of this detrimental nature of excessive bending is that the partially edentulous situation is more susceptible to overload than the full-arch restoration, due to the more linear implant configuration in the partially edentulous case.
The most comprehensive prospective clinical long-term study on implant treatment of partially edentulous patients is a 5-year multicenter study presented by Lekholm et al (1994). From this material and from the 3-year report of the study, it can be concluded that a sufficient number of fixtures is essential for minimizing potential complications. The authors showed a significantly lower rate of failures for protheses supported by three implants than for those supported by two implants. In a retrospective clinical study, Quirynen et al (1992) claimed that overload may lead to marginal bone resorption. This suggestion is in agreement with results reported. In an analysis of clinically fractured fixtures, Ranger et al (1995) demonstrated the importance of sufficient number of implants for predictable long term results. In addition, the authors illustrated the influence of implant position, geometry of the prosthetic reconstruction, and the patient's chewing habits.