The practice of dentistry is getting complicated. There has been a lot of new development in the past ten years especially in the field of implant dentistry. In fact, sometimes, implant manufacturers create new products faster than dentists can incorporate them into their practice. In the past, dentists are the gatekeepers of what technological innovation is suited for their patients. When dental product manufacturers produce new products, they need to prove to dentists that the new products have undergone stringent tests over several years before a dentist will use it in his practice. This is usually a slow process as dentists usually view these new products with a healthy dose of skepticism. Some manufacturers have taken a different route. They advertise directly to the consumer with catchy names and slogans. All-on-four, which by the way is a registered trade mark own by a particular implant manufacturer even though the term has been used rather loosely, is basically a treatment concept that replaces full dentures with a full arch fixed prosthesis supported by four implants that are placed in a tilted fashion. In Singapore, the company has not marketed the concept aggressively but elsewhere, particularly in the USA and China, many patients are aware of it through the lay media. I have patients who comes in asking for All-on-four on their own. So, what’s the big fuss about All-on-four®?
Traditionally, a patient who has lost all his teeth or who is going to lose all his teeth and want to replace them with dental implants will require a rather complicated treatment process. Most patients who reached this state usually lose their teeth through periodontal disease. Along with the loss of teeth, these patients also lose a lot of bone that supported the teeth. As such, when restoring the dentition with dental implants, bone grafting is usually needed, especially for the upper jaw. The treatment plan will typically go through one round of bone grafting, waiting a few months before implants are placed. Usually six to eight implants are used for the upper jaw and four to six implants for the lower.
For the lower jaw, there is a pair of nerves at the back of the jaw that runs within the jaw, exiting at the region of the premolars to provide sensation to the lower lip. Implant placement in the lower jaw is often limited to the front of the jaw due to severe bone loss in the back of the jaw above the level of the nerve, leaving insufficient bone height to house dental implants. To place implants at the back of the lower jaw, additional surgery to move the nerve aside or to graft bone to rebuild the height is needed.
The All-on-four treatment concept was introduced to circumvent these problems of having insufficient bone. It is a rather different concept from traditional implant dentistry. Traditionally, it was thought that implants should be placed perpendicular to the jaw, similar to natural teeth. This is to allow biting forces to be transmitted to the implant axially, ie along its long axis, where it is best able to withstand maximum forces. When placing multiple implants in a fully edentulous jaw, these implants are placed parallel to each other for ease of connection of the prosthetic teeth. However, research has shown that implants that are placed in a tilted angle instead of being perpendicular, are equally successful, especially when use in full arch cases. Furthermore, the development of angulated abutments to compensate for the tilting of the implants has also neutralized the problem of fixing the prosthetic teeth to tilted implants.
All-on-four treatment concept is a graftless technique. Most edentulous jaws do have bone mass. It is just that the bone is not sufficient in areas where the implants are needed. Implant position is usually determined by the design of the prosthesis, which is the final product that the patient sees and bites on. With the All-on-four treatment, implants are placed in parts of the jaw where bone is available instead of where we would normally want them. This usually results in the implants being placed in a tilted angle, which was previously thought of as unfavourable. However, this allows the implants to engage more of the good quality bone, which in turn maximizes the bonding of the implant to bone. With full arch prostheses, all the implants are splinted together and the biomechanical load is well balanced regardless of the implant angulation. As such, the prostheses can be fixed onto the implants on the same day of implant surgery without having to wait for a few months for osseointegration.
Overall, All-on-four treatment concept reduces the treatment duration as well as cost as fewer implants are used. However, it does not replace the traditional treatment protocol of bone grafting and other adjunctive procedures combined with implant placement. There are cases whereby the jaws are so resorbed that even tilting the implants will not engage sufficient bone for the implant to support a prosthesis. Some patients may also have significant discrepancy in the jaw position whereby the upper jaw has resorbed significantly more than the lower and bone grafting is needed to restore that jaw relation prior to implant placement.