All-on-4, All-on-n, what’s in a name?

I was at a dental implant conference last Saturday afternoon moderating a session where the speakers were presenting their respective protocol. Listening to a lecture after lunch was always a challenge regardless of who the speaker was. As such, with the consent of the speaker, I told the audience to put their hand up at any point during the presentation if they want to ask any question or make a statement. Hopefully, with audience feedback, the session can be more lively and engaging. It was indeed but the downside was that we digressed a lot. At one point, someone mentioned the term “All-on-6” which drew a sharp retort from another member in the audience that there is no such thing as “all-on-6” and there was only “all-on-4”. So, who is right?

“All-on-4” is a registered trademark of Nobelbiocare, a company that manufactures dental implants of the same name, commonly referred to as “Nobel” within the dental profession. Technically, this is the only “All-on-anything” that has been trademarked. So, by default, there is no such thing as “all-on-6” or “all-on-n” for that matter. However, while you can trademark the name as a slogan, it is not possible to trademark a clinical practice. Indeed, many patients have been treated with full arch 4-dental implant supported fixed prostheses for a long time, which is what the “All-on-4” dictates. Granted, there are special features that the protocol dictates, such as angulating the implants to maximize bone to implant contact, increase the spread of the implants across the jaw, and to reduce the extent of the cantilever of the prosthesis beyond the last implants on each side.

The idea behind the concept is to simplify treatment and to eliminate the need for grafting. This reduces the cost of treatment as well as morbidity of surgery. In theory, it makes good sense and is a practical solution to rehabilitating a fully edentulous patient with a fixed dental prosthesis. However, is this something that can replace the conventional method of using a minimum of 6-8 implants for one arch?

One of the major disadvantages of the All-on-4 is that the minimalist approach leaves no room for contingency. Four implants to support a full arch prosthesis is the bare minimum and should one of the implants failed, the prosthesis will need to be reconstructed from scratch. While most implant manufacturers today will replace failed implants with minimal cost, the prosthesis are custom made and dental laboratories do not redo prostheses due to failed implants for free. Hence the natural development is to add more implants for contingency and accordingly, call them “all-on-6” or “all-on-8” as the case may be. The idea is to embrace all other features of the original concept sans the number of implants.

With the addition of more implants, the cost goes up but it gives the reassurance that a complete redo is not needed should one implant fails. However, with higher cost, is it better to do implants in the usual way, ie placing them straight instead of tilted. While biomechanical research indicates that success rates of splinted full arch prosthesis supported by tilted implants are as good as axially loaded implants, maintenance is better achieved by the patient with the latter. Furthermore, abutment screws of angulated abutments are smaller than the standard ones and hence more susceptible to breakages and hence higher maintenance cost.

After 20 years of doing implants in Singapore, I do not think that this concept is able to replace conventional treatment. The majority of patients who have been fully edentulous for a long time do not have the bone mass to even place four implants in whatever angle. These patients are severely lacking in bone and require a lot of bone grafting to just house four implants. And if bone grafting is going to be done anyway, it is natural to add more implants to ensure a better survival of the implants and by extension, the prosthesis. With advances in the understanding of bone grafting and the use of non-autogenous sources, the morbidity of bone grafting is significantly reduced today. Bilateral sinus bone grafting with simultaneous placement of six implants is a time-tested method with a comparable morbidity level.

Nevertheless, the concept is an excellent way to simplify treatment of the fully edentulous patient who is a suitable candidate. In my practice, the patient who potentially is the most suitable candidate is the newly edentulous patient, or one for whom all remaining teeth are to be extracted. In this group of patients, the likelihood of having sufficient bone to house the four implants in the way that the protocol prescribes is highest.