If your patient had a long edentulous ridge, would you place multiple adjacent implants or only one with a cantilever? What considerations would you have to take into account? Here at ARIA, we’ll go through some factors to consider, including the mesiodistal length, occlusion, aesthetics and cost.
Mesiodistal Length
A large factor in determining how many implants can be placed into an edentulous ridge is its span. Our periodontist and prosthodontist lecturers recommend a minimum of 1.5mm between the tooth and an implant. This helps to reduce inter-crestal bone resorption and maintain peri-implant stability. Therefore, given that the minimum size of an implant is around 3mm, we would need a minimum length of around 5-6mm to place one implant between two teeth. For two adjacent implants, a minimum of 3mm is recommended between the two. This therefore requires around 12mm of edentulous space to place two adjacent implants between teeth.
But not every patient requiring replacement of multiple adjacent teeth may have this mesiodistal width available. In such cases we may consider alternative options. One option is the use of a dental implant supporting a multi-unit cantilever. This can help prevent implants placed too close to each other or adjacent teeth. This is especially useful to maintain bone volume and soft tissue contours, especially the papilla height. Therefore, cantilevers may be a means to preserve the natural ridge and soft tissue contour, enhancing aesthetics.
An implant supporting a 2-unit cantilever
Courtesy of Dr Praveen Nathaniel
Occlusion
The prosthetic crown 12 cantilevered off the implant placed at 11 is at most in light occlusion.
Courtesy of Dr Praveen Nathaniel
There are some concerns, however, about the long-term survival of a dental implant supporting a cantilever. Unequally distributed masticatory forces may place too much load and strain on the implant itself or surrounding bone. This may cause an increase in failure due to implant fracture, peri-implant bone fracture or resorption, prosthetic crown fracture, or screw loosening. This may especially be an issue in the posterior region where there is a greater exposure to heavy loading.
Studies, however, have not proven that implants supporting a multi-unit cantilever necessarily compromise the peri-implant bone (Wennstrom et al., 2004). Cantilever crowns should be placed in an area with no or only light occlusion, and not exposed to excursive movements. The number of cantilever units should also be reduced to help minimise rotational occlusal forces that can cause implant component failure. Studies have shown that cantilevers with few units do not cause peri-implant bone loss that is of significance (Zurdo, Romão, & Wennström, 2009). Our Master Implant Programs held in Adelaide and Melbourne cover tips and tricks to avoid excessive loading and ways to identify this.
Cost
It is also worth noting that implant supporting a multi-unit cantilever is a viable option for patients who cannot afford multiple implants. Careful case selection, however, is essential. If there is an increased chance of failure due to a long edentulous span, high occlusal load or parafunctional movements, this may not be advised. Mentoring from out dental specialists can help you with your case selection and treatment planning to better ensure implant success.
References
Wennstrom, J., Zurdo, J., Karlsson, S., Ekestubbe, A., Grondahl, K., & Lindhe, J. (2004). Bone level change at implant-supported fixed partial dentures with and without cantilever extension after 5 years in function. Journal of Clinical Periodontology, 31(12), 1077-1083. doi:10.1111/j.1600-051x.2004.00603.x
Zurdo, J., Romão, C., & Wennström, J. L. (2009). Survival and complication rates of implant-supported fixed partial dentures with cantilevers: a systematic review. Clinical Oral Implants Research, 20, 59-66. doi:10.1111/j.1600-0501.2009.01773.x
