From the Desk of Dr Rob Ormerod

As a Specialist Prosthodontist, I have traditionally avoided cantilevers in full arch implant bridges, opting to over-engineer and place at least six implants in these cases to limit or avoid cantilevers entirely. However, cantilevers on implant bridges may have been given an undeservedly bad reputation.

Complete arch fixed prostheses present high success rates with excellent clinical performance, regardless of whether they are supported by four or six implants. One of the criteria for evaluating this success is the assessment of bone loss around implants. With a multifactorial aetiology, bone loss is considered normal when values do not exceed 1.5 mm in the first year and 0.2 mm annually. In vitro studies attribute these losses to factors such as tension, bone density, the number, length, distribution, and inclination of implants and abutments, arch curvature, the rigidity of the prosthetic framework, and the extension of the cantilever.

One of the possible causes of bone loss is the presence of cantilever extensions in the posterior of these prostheses, which are more subject to the influence of loading forces. These forces can affect the marginal tissues of the distal implants and potentially harm their survival. The average length of cantilevers is 15 mm. I have always tried to limit mine to 10 mm. Cantilevers support the forces applied to these extensions, transferring them to the abutments and subsequently to the adjacent bone. This transfer is often related to bone loss and biological complications.

A recent 2024 study by Pereira et al. concluded that the number of implants in complete arch implant-supported fixed prostheses, whether three or four implants as opposed to more extensive prostheses, did not influence peri-implant bone loss. Larger horizontal cantilevers were not correlated with greater bone loss, while a larger vertical cantilever favoured more bone loss during a one-year follow-up.

In my experience, cantilevers, both vertical and horizontal, do result in significantly higher mechanical complications compared to non-extension cases. These complications affect the prosthodontics rather than the biological aspects.