The impact of occlusion on dental implant outcomes presents significant challenges. We see it, we appreciate it, but we don’t fully understand it. A concept that occlusal forces would influence the outcome of dental implant therapy might challenge assumptions based on our understanding of robust ankylosed teeth stability. Additionally, the effect of occlusal forces on the periodontium gives little guidance to the osseointegrated implant since the tooth attachment to alveolar bone is indirect and mediated through a fibrous connective tissue interface. Animal studies conducted by the Polsen and Lindhe groups indicated that in the absence of plaque and inflammation, occlusal forces did not result in loss of attachment (reviewed in Harrel 2023). Despite these experiences and experiments, there has been and still exists confusion as to how best to view implant occlusion and more specifically occlusal overloading as either primary, secondary or irrelevant in the case of dental implant failure and bone loss. The aim of this report is to review present considerations of occlusion in dental implant therapeutic outcomes and to consider what clinical factors influence occlusal loading effects on the implant bone interface, the implant component interfaces and the implant supported/retained prosthesis.

Today we understand the maintenance of bone at the implant surface to be controlled by at least two sets of factors. One is biomechanical forces acting through the implant on the enveloping bone. The other is the inflammatory environment that influences osteoclastogenesis (and impairs osteogenesis) at the implant/tissue interface. The inflammatory environment is a critical determinant of cellular function in bone modeling/remodeling but is beyond the scope of this current report. Early in the development of endosseous screw-shaped dental implants, Brunski underscored the significance of biomechanics in implant design where he concluded that three key factors were relevant: 1) the nature of the biting force, 2) the transfer of biting forces to interfacial tissues, and 3) the interfacial tissue reaction to stress transfer (Brunski 1988; Brunski 1992). The nature and transfer of biting forces to interfacial tissues can promote or deter bone formation, modeling and remodeling at the implant/tissue interface.

Bone responses to imposed occlusal loading include both bone formation and bone resorption and this has been conceptualized in terms of Wolff’s law. This law states that bone models and remodels in response to the mechanical stresses imposed upon it, resulting in a structure that is adapted to the applied stresses. In terms of endosseous implants, then, bone should be accrued at the implant surface under ‘physiologic’ conditions and bone should be lost under ‘pathologic’ conditions (Fig. 1).

In an ideal clinical scenario, occlusal loads are presented through a prosthesis to bone as strains within the ideal magnitude range that engenders healthy bone modeling and remodeling. An important clinical feature of a successful dental implant is that the bone surrounding a dental implant continuously undergoes healthy remodeling. Force-related overloading can impair this process, and, in the presence of inflammation, this can lead to bone loss at the implant. Extreme overloading itself can cause microcracks in the bone that induce bone loss and implant failure. The clinical picture is more complex and involves multiple factors (Table 1). Implant therapy must involve planning, surgical and restorative procedures that address the risk of mechanical overloading.

The mechanical damage of bone surrounding the implant is related to the nature of the occlusal forces transmitted through the prosthesis and the implant to the surrounding bone. Measured occlusal forces range from about 100 N to 400 N and increase from the anterior to posterior tooth positions and can be exceeded under specific conditions. Physiologic forces are typically well tolerated as demonstrated by experimental modeling, while excessive forces increase stresses in the abutment-implant and the implant-bone interfaces (e.g., Borges Radaelli et al. 2018). Lateral loading of implants in the finite element analysis environment results in greater stresses at the implant bone interfaces (Lin et al. 2010). It is interesting that a finite element analysis revealed that the strain induced in bone at 100 N loaded implants is far greater than for similarly loaded teeth (Robinson et al. 2019). The transmission of these forces through the dental implant/abutment complex is affected by the aforementioned factors (Table 1) and is highly relevant to the creation of an ‘ideal’ biomechanical environment for dental implant success.

With this background, we would expect that many clinical situations would pre-dispose dental implants to overload-related failure. Yet, many studies have failed to demonstrate that this occurs with great frequency and there is little data to support a causal relationship between occlusal loading and clinical implant failure (Isidor 2006; Chang et al. 2013; Naert 2012). Pre-clinical studies demonstrated that loading actually favors the accrual of bone at the dental implant surface (e.g., Heitz-Mayfield et al. 2004; Lima et al. 2019). Conversely, excessive lateral loading was shown to induce bone resorption at integrated implants (Piccinini et al. 2016; Ferrari et al. 2015) and implicates non-axial overloading as a particular risk factor to osseointegration. And when a co-destructive environment (plaque accumulation and overloading) was modeled in a primate model, bone loss and implant failure did occur (Isidor 1997). The experimental non-axial loading and biofilm-related inflammation that leads to implant loss reflects common clinical scenarios that serve as warnings to clinicians seeking reproducible dental implant success.

There is also clinical evidence that indicates the ability of osseointegration to be sustained in the face of high occlusal loading. For example, the use of ultra-short dental implants is one example of the robust nature of osseointegration, provided it occurs in the context of health. The use of splinted 4-mm-long dental implants was successful in restoring single and multiple teeth in the posterior mandible over 3 years (Leighton et al. 2022). Systematic reviews have supported the use of short implants in posterior restorations (implying higher occlusal forces) (Carosi 2021). Yet, clinical experience using short dental implants can provide evidence of occlusal overload occurring over time and, perhaps, in biologic environments that challenge effective bone remodeling (e.g., diabetes-related inflammation, osteoporosis, etc.).

The high success reported for the original osseointegrated prostheses ad modum Branemark invoked significant distal cantilevers and was associated with high implant and prosthesis survival (Adell et al. 1981). However, examples observed in clinical practice include the overload-implicated loss of distal-most implants supporting fixed dentures with cantilevers (Fig. 2).

Misch concluded that the majority of late implant failures were attributable to excessive loading (Misch 2022). It is proposed here that occlusal risks affecting osseointegration can be managed by careful assessment and planning of implant therapy.