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All-On-Four Dental Implants

All-On-Four Dental Implants

To say that Dental Implants is becoming a fast trend in the world of Dentistry is really an understatement. The Science of replacing not just the coronal portion of a tooth has long been the thrust of every human being in the history of mankind. In fact, being the second oldest discipline in dentistry, second only to surgery-extraction, which dates back to the time of the ancient Chinese, man has continually searched for a replacement of his or her teeth. The discovery of titanium as a viable material with excellent biocompatibility to human tissue has certainly led to a series of studies and researches that brought about a revolution to know more about dental implants.

The All-On-Four Dental Implants Technique was developed by a dentist in Portugal in cooperation with Nobel Biocare. It is an attempt to allow dentists to place an almost full arch of teeth (no molars are included) in patients with poor bone levels by using highly angled implants in only the anterior portion of the jaw, where there is more bone density. The idea is to provide a shortcut around bone grafting.

Many periodontists believe patients should be cautions and well informed about the risks associated with this technique. His primary concern is the gigantic risk that if one of the dental implants fail, the entire restoration fails and has to be redone. A common saying at dental implantology conferences is “all on four but none on three”.

Today, we have now established a lot of surgical and prosthodontic protocols that has standardized the way we manipulate dental implants and maximized its use on our patients. Long term studies and observations have already been proven and have been generally accepted already. The numerous books on Dental Implants, Guided Bone Regeneration, Bone Grafts, Journals and the development of machines such as the Dental CT Scans is a testimony on how far we have already gone.

The diagram above (taken from a Nobel Biocare training manual) clearly shows that there are no molars in an All-On-Four restoration. Remember, back teeth (molars) do 80% of your chewing.

Here is a panographic x-ray of the four angled implants that have been placed.

A second concern when this technique is used is the jaw atrophy that occurs in the posterior region of the jaw. (For more information on this jaw atrophy, please see our page on facial collapse). This atrophy creates a risk of jaw fracture. Since the All-On-Four technique only places implants in the anterior of the jaw, the bone in the posterior is not stimulated and thus continues to be resorbed by the body. The presence of implants, on the other hand, has a piezoelectric effect that prevents bone resorption.

Another risk is the possible loosening of the screws of the prosthesis, leading to infection and failure.

Please see more information in this website on dental implant failure.

The all-on-four dental implants technique is promoted as a way to simplify providing dental implants for patients with no remaining natural teeth. Often these patients are missing a lot of bone. The theory is that by using only four dental implants, with two of them at extreme angles, the patient can eliminate the need for expensive and time-consuming bone grafting surgery.

One of the weaknesses is in the structural strength of the restorative system. Come doctors have serious questions about whether this treatment is appropriate for patients with large facial muscles that can generate heavy biting forces. Below is an enlarged photograph of a screw used to fasten a conventional implant to an implant overdenture, next to a screw used to fasten an all-on-four dental implant to its overdenture. The dime is used to help you judge the actual size.

You can see that the length of the threads of the all-on-four screw is half that of the conventional dental implant screw, and that the threads aren’t as deep. Over time, under the heavy stresses of chewing, these factors increase the risk of the screws coming loose. Dr. Carl E. Misch, author of the authoritative textbook, Dental Implant Prosthetics, lists twelve possible causes of screw loosening. Eleven of those twelve possible causes are related directly to the ability of the components of the dental implant system to resist the forces of the function of the replacement teeth (Misch, Dental Implant Prosthetics, p. 454). And a loose screw will lead to the trapping of foreign matter, subsequent infection, and the failure of the restoration.

Also notice that the diameter of the shank of the all-on-four screw is about 70% that of the conventional dental implant screw. This means that the cross-sectional area and thus the shear strength of the screw is slightly less than half that of the conventional screw. Over years of function under the heavy stresses of biting that are present in the mouth, these screws will be subject to metal fatigue and weakening.

The package has strong sales appeal. The patient can have the entire treatment done in one appointment. And it’s profitable for the dentist, because it commands a handsome fee without taking a lot of the dentist’s time.

A prominent implant dentist, has done extensive study of the all-on-four dental implants technique. He sees some weaknesses that would be helpful for prospective patients to know about. In some cases, the all-on-four technique may be appropriate for the patient. However there needs to be considerable judgment and discretion in its use. The patient also needs to be aware of the potential risks before agreeing to the treatment.

Implant Dentistry has certainly evolved throughout the years. This giant leap caused by many researches and findings have contributed to the advancement of this discipline in Dental Medicine.