Cantilever FPDs, especially distal cantilevers, are discouraged in the texts and are prescribed with many precautions. What type of FAILURES are associated with them? Are the Forces and Biomechanics (and hence, the design considerations) similar for the lower and upper arches?
I would say conservative option of restoration. However careful case selection and treatment planning is necessary. E.g you may restore a central using a central but not a central using a lateral as an abutment. Good crown root ratio is a requirement. Reasonable success rates but less than a fixed fixed conventional.
This one is a good read
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3313584/
Cantilevers pose a great deal of stress on the abutments. It depends on what type of abutment u r using ( tooth or implant) for tooth abutments it can be used to restore a tooth providing it is not larger than a premolar. If u wanna restore upper 7 for example u make a premolar sized 7 so as not to increase the torque on the abutments. For the previous reply: u can't take a central for a central as the shape of the root will lead to extraction of the abutment. however, in some cases especially when implants are used, distal cantilevers can be used more extensively
I refer to my paper on the topic:
Dogus et al JPros 2011
This describes implant cantilever-teeth maxillary laterals can routinely be cantilevered from natural canines with full coverage or they can be cantilevered from minimally prepared teeth see Hussey et al & Kern et al as these are conservative resin bonded solutions in both metal ceramic or all ceramic resin bonded FPDs (Maryland Bridges)
When considering relatively classical dental literature the names of Laurell and Lundgren come to mind. These authors used long cantilevers in the natural dentition with excellent long-term success which was most likely secondary to careful management of occlusion and the beneficial effect of tooth mobility as a "stress relief" mechanism. Not long after these authors we started to see more common descriptions of cantilever usage with implant retained dental prostheses were the implants, by necessity, were placed between the mental foramen and the cantilever was extended distally and bilaterally. Perhaps with the implant prosthetic approach the situation benefited from the fact that many of those early prostheses were opposed by complete dentures which then created the, thought to be, relief system. Over time however cantilever usage in the combination with implant supported bilateral prostheses has been quite efficacious and eventually effective.
I mentioned previously, perhaps in response to another similar question, that there are number of critical factors and need to be considered when cantilevers are used in combination with implant retained prostheses. The situation must be curvilinear relative to the placement of the implants, there must be an appropriate relationship between the distance from the fulcrum to the anterior most abutment and its relationship to the length of the cantilever, there must be an appreciation of the type of material that is used for the framework that supports the cantilever, occlusion must be managed very carefully, the anticipated forces exerted by the patient must be considered, etc. it is not as simple situation where we can simply state that cantilevers work or that cantilevers don't work. When the myriad of considerations are managed appropriately cantilevers indeed do work but ignorance of or disregard to some of the critical factors will doom the treatment.
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