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BOI implants are used almost exclusively to support fixed prosthetic restorations. Occasionally, they are also used for bar attachments. BOI implants combine well with natural abutments and other enossal implant designs. The fundamental question is whether a rigid or an elastic implant-restoration system should be established. How these systems differ and what implications they have in terms of structural integrity will be discussed later in this chapter.

Two essential treatment alternatives are available for dealing with cantilever situations in the posterior segment: Structures that are supported by implants only (including single-tooth implants). Bridge structures supported by both implants and natural teeth.

This chapter deals with patients exhibiting intermaxillary relationships that can be defined as disto-oclusion by orthodontic criteria. These cases are usually associated with a large ANB angle and an intercuspidation in which both the canine and the first molar in the mandible are located too far distally in relation to their maxillary antagonists. Both for orthodontic and for implantological purposes, it is important to look not only at the ANB angle but also at the «Wits appraisal» in these cases. The ANB angle is the angle between points A, B, and N (nasion) in the teleradiograph. The ANB angle is large if the mandibular point is located far behind the maxillary point, indicating the presence of a Class II jaw base relationship. However, the ANB angle does not shed light on the relative position of the jaws: this is where the Wits appraisal comes in.

We are often faced with patients showing any or all of the following symptoms: Class III skeletal relations characterized by maxillary micrognathia, true mandibular prognathism, or both factors combined Edentulism in one of both jaws Sagittal resorption of the maxillary ridge as a result of early edentulism

It is standard procedure in crestal implantology today to insert screws with a minimum length of 10–13 mm in the anterior mandibular region, provided there is enough vertical bone height. Depending on how many screw implants there ultimately is room for, the patients may receive ball abutments, bars, or – in favourable situations – cantilevered-pontic bridges according to Brånemark. When it comes to distributing forces into the interior of the bone, patients with minimal bone height at the outset are at a disadvantage. It is precisely in these patients that only a small fraction of the overall masticatory forces will be directly toward the implants when designing the superstructure. In most cases, the crestal implants in these cases will offer only rudimentary support for a removable denture that, for the most part, will be periodontally supported. While this initially seems to alleviate the problem of denture retention, the disabling loss of teeth and jaw substance is not actually addressed. We as dentists have been able and continue to be able to make money on this type of «therapy» only because this disability is relatively invisible and because patients are ashamed and unwilling to bring their problem out into the open. As the most recent publication by Godbout et al. (2002) shows, subperiosteal implants are sometimes used – despite the fact that they are difficult to produce and difficult to insert and that they require a two-stage surgical approach – to treat situations of extreme vertical atrophy of the distal mandible.

Since panoramic radiographs are obtained by sectional imaging, they will only reveal the structures located in the focused plane. The X-ray system is adjusted in such a way that both the maxilla and the mandible are depicted about equally well in the same image, despite the fact that both jaws are not in the same vertical plane even in patients with intact dentitions. This discrepancy is even greater in edentulous situations, as the maxilla and mandible are characterized by a centripetal and centrifugal resorption pattern, respectively. The discrepancy is greatest in the tuberosity region, since the maxilla almost appears round in that area, and the distalmost parts as well as the palatal bone and the muscular processes of the sphenoid bone fall completely outside the OPG plane. Therefore, inability to depict bone in the tuberosity area using conventional panoramic radiographs does not furnish any evidence of bone resorption but constitutes a typical false-negative finding. The distal maxilla is just as stable to resorption as the mandibular anterior segment because it harbours attachments of powerful chewing muscles. The bone volume in that area is usually abundant as well, so that long screw implants with high anchorage potential can be readily inserted. We do think that this strategy is indicated because implants of this type will help to improve stability and support in this area of high masticatory forces.

Implants have been widely used to support fixed prosthetic restorations since the early 1980s. Implantological treatment options were, and still are, a highly controversial issue in situations characterized by advanced ridge resorption and severe forms of periodontitis. After all, these conditions usually involve both the maxilla and the mandible, and dysfunctions associated with loss of the vertical dimension are routinely present.

The fact that tooth loss is usually accompanied by vertical bone loss adds to the problems of crestal implant therapy in the distal maxilla.

Implant treatment to support removable restorations is the exception rather than the rule but may be desirable in some patients for a number of reasons. The following factors may prompt the dentist to take this route in specific cases.

In situations of advanced bone resorption, it is necessary to discuss with the patient whether the treatment should consist solely of replacing the missing teeth or whether additional measures should be taken to compensate for the missing bone volume along the ridge. Such augmentative techniques are expensive and time-consuming. The spectrum of applicable techniques ranges from relatively simple procedures based on extraneous grafting materials up to extensive surgical protocols in which autologous bone is harvested from the hip (iliac bone) or cranium (parietal bone). Osseodistraction is another technique to modify the shape of bone structures.