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 »  Home  »  Dental Implant 1  »  Restoration of the Atrophied Mandible Using Basal Osseointegrated Implants and Fixed Prosthetic Superstructures
Restoration of the Atrophied Mandible Using Basal Osseointegrated Implants and Fixed Prosthetic Superstructures
Introduction.

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Stefan Ihde, Dr med dent
Senior Dentist, Gommiswald Dental Clinic, Uetliburg/SG, Switzerland.


In crestal implantology (crestal implantology: Implants are referred to as crestal-type implants if they are inserted into the jawbone coming from the crestal alveoli and whose main load-transmitting surfaces are vertical. The term thus covers screws, cylinders, and blade implants.), it is standard practice today to insert screws at least 10 to 13 mm in length in the anterior segment of the mandible because this part of the mandible usually offers sufficient vertical bone. Depending on how many screws this area can accommodate, patients will receive intramucosal abutments, bar attachments, or bridges with cantilevered pontics.
Patients with very little available vertical bone are at a particular disadvantage. The prosthodontic structures in these patients are usually planned so that only a small percentage of the masticatory load will be directed to the implants. Anterior crestal implants will often offer only rudimentary support for a removable denture that is essentially borne by the oral mucosa. Superficially, this approach seems to reduce the problem of support. However, providing removable dentures does not actually resolve the underlying process of debilitating tooth and jawbone loss. This therapy concept is probably still considered viable today because the debilitation is more or less not noticeable.
These considerations have prompted the author to forego the “conventional” approach in favor of basal osseointegration (basal osseointegrated implants: These implants are inserted into the jawbone coming from the lateral aspect. Masticatory load transmission is confined to the horizontal implant segments and, essentially, to the cortical bone structures.), especially in extremely atrophied mandibles. Over the years, based on clinical experience, a precise, fast, and inexpensive treatment procedure has been developed to optimize the implants, the surgical technique, and the dental treatment and follow up. (We have exchanged and continue to exchange our insights and results with the members of the German Implantoral Club (ICD).) (German Implantoral Club: Professional association of prosthodontists working with basal osseointegrated implants, oral surgeons, and maxillofacial surgeons. Founded in 1989.)
It is precisely the heavily atrophied mandible that is, in principle, best suited for fixed dentures. The mandible with its tubular structure has to accommodate strong muscular action. Hence, it features a high bone turnover rate that is stress-related, affording optimal bone regeneration after each osteotomy and very good regeneration in osteolysis of different etiological origins.
It does not take many implants to set up an implant-based fixed denture system that can support a stable, immobile bridge on a twisting and rather unstable underlying mandible— similar to an external fixating device. Even as Linkow3 developed his tripod subperiosteal and ramus frame implants, he had realized the principle that potentially favorable and stable long-term implant positions are not only found between the mandibular foramens, but also, and specifically, in the well-ossified distal aspect of the horizontal mandibular ramus, as well as in the transitional zone toward the ascending ramus. Spiekermann4 coined the term “strategic implant placement,” even though he was presumably referring to the maxilla and, specializing in screwed implants, he lacked suitable implants for fixed dentures for the atrophied mandibular ridge.
Our own treatment approach to extremely atrophied ridges based on basal osseointegration draws on the results of Linkow,3 Roberts,5 and Spiekermann.4 It has developed into a viable long-term therapeutic concept.
In recent years, two schools of thought have emerged in the area of basal osseointegration:

  1. The French school of Scortecci and others favors restoring even severely atrophied mandibular ridges by using a large number of basal osseointegrated implants (BOI), usually 7 to 12 implants. This school combines BOI with screw implants, both in the maxilla and in the mandible. The implant systems thus established are immobile and do not allow jaw regions to change their relative orientation.
  2. In the German-speaking countries there is a tendency to favor restoring the edentulous mandible using only a few BOIs, usually inserting four implants in regions 47, 43, 33, and 37, even when providing fixed dentures. This type of implant system is referred to as “flexible” because it permits mandibular shifts and flexion below the fixed superstructure, despite the fact that the load-transmitting segments of the basal implant osseointegrate. The long threaded pins between the load-transmitting osseointegrated disks and the bridge serve as flexible interfaces.

The atrophied mandibular ridge rarely offers enough vertical bone for implant insertion, but, as can be readily palpated, there is usually sufficient available bone in the horizontal plane. The bone is optimally utilized by BOI implants inserted horizontally. In the past, clinicians attempted to maximize the number of implants inserted in the mandible, following general custom in dental implantology and the French school. It was shown, however, that BOI suffered from the influence of jaw flexibility in the regions of the second premolars and first molars, resulting in inferior osseointegration of the force-transmitting disks. But because this had no consequences on the stability of the overall design, the prosthodontic structures could be preserved in all cases. As a rule, 2 to 3 implants can be inserted in the anterior segment, whereas one implant can be accommodated in each distal mandibular segment.