The main difference between an osseointegrated implant and a tooth is the absence of a periodontal ligament at the implant site. This results in significantly decreased sensitive feedback and reduced mobility. Therefore, implants can be exposed to increased occlusal load when adopting the same occlusal concept applied to teeth. This potential overload can lead to prosthetic and implantological complications that may reduce the lifespan of the implant and the restoration. Although there is currently little evidence on occlusion concepts for implant-supported restorations, this article seeks to provide a guideline for appropriate implant occlusion. An occlusal clearance on implant-supported restorations might be advantageous, as it conceivably allows for adequate loading of teeth and implants to compensate for the physiological mobility of the teeth. In addition, the shape of the restoration needs to be designed in such a way that no excessive forces are transferred onto the implant. Eccentric forces on implant-supported restorations should be avoided. Routine monitoring of the occlusion and potential adjustments might prevent complications of implants and restorations due to overload.
Failures in implant dentistry include crown fractures, chipping of the veneering ceramic and implant fractures (Sailer et al. 2022). Due to the lack of a periodontal ligament, implants might be subjected to a higher risk of occlusal overload (Lee et al. 2019; Trulsson 2005). Occlusal overload has been defined by the glossary of prosthodontic terms as “the application of functional or para-functional occlusal loading in excess of what the prosthesis, implant components, or osseointegrated interface are capable of withstanding without structural or biologic damage” (Langer et al. 1993). According to this definition, occlusal overload relates to structural or biological damage by the application of forces through physiological forces or parafunctional habits (Sheridan et al. 2016). According to the Frost's mechanostat model, the occlusal overload refers to the level of microstrain, which corresponds to a catabolic bone reaction (Melsen & Lang 2001). This can be attributed to strains in excess of 3,000 micro strain while mild overload is defined by strain between 1,500 and 3,000 micro strain (Klinge et al. 2012). Mechanical complications such as fractures or loosening of implants and prosthetic components indicate excessive occlusal forces/overloading (Figs 1 - 2) (Ding et al. 2022; Fu et al. 2012; Wassell et al. 2015).
Although scientific data is scarce, overload of osseointegrated implants may lead to hard and soft tissue defects (Hämmerle & Tarnow 2018). According to the current state of science, there is no scientifically accepted occlusion concept that describes the occlusion on implants in comparison to teeth (Carlsson 2009; Kim et al. 2004; Koyano & Esaki 2015). This article discusses the biophysical background of tooth-supported and implant-supported prostheses, which can lead to possible complications. It also introduces, despite sparse scientific data, an occlusion concept that may well prevent potential complications in implant dentistry. The proposed clinical procedures and rules may help to provide implant-supported reconstructions that may fit into dentitions and may be accepted by patients.