A situation in which the prosthetic structure shows early contacts at one or several implant sites may be defined as primary overload. These situations are addressed by carefully reducing the affected jaw segments with abrasive instruments.

A situation in which the spatial position of the mandible changes as a result of altered muscle function may be defined as secondary overload. These situations usually occur within the first months after inserting a restoration. Secondary overload situations develop naturally while the masticatory function is undergoing adaptive processes. They are addressed in the same way as primary overload situations by reducing the affected segments or by raising other segments. They are not a result of incorrect treatment but of muscular reactions. The clinician should inform the patient of this eventuality in advance so as to avoid misunderstandings.

Secondary overload situations are caused by short-term interactions between chewing muscles and their neuronal control. They can also develop as a result of changes in the jaw morphology, which is a response to altered functional patterns and the situation of nourishment and drainage of the bone. Secondary overload requires frequent adaptations of the occlusal platform, by far more than one would expect from the experience of work on natural abutments.

As a result of ongoing long-term functional adaptations while engrams governing the control of the masticatory and postural muscles are being redefined, the bimaxillary positional relations may undergo substantial changes that require correction even years after insertion. As far as implant-supported restorations are concerned, these situations may be described as tertiary overload situations. They are corrected by reducing the affected areas or, if necessary, by replacing the entire restoration. This worst-case scenario may come to pass if regular dental relations and a normal masticatory function cannot be reestablished by simple abrasive adjustments or if the vertical dimension has been excessively reduced by numerous adjustments.

Once again, this type of situation is not due to treatment errors but is caused by long-term normalization of the masticatory function as well as age-related alterations in jaw morphology.

The extent and the consequences of secondary and tertiary overload situations, as well as the timeframes involved, were not fully appreciated and analysed before dental implantology was included in the therapeutic spectrum (Book et al. 1992). Long-time users of BOI implants have learned how to deal with this type of problems. Novices, on the other hand, must pay close attention to the specific circumstances to avoid treatment failure. TMJs are routinely observed to move up to 5 cm (and sometimes as much as 1 cm) as functional abnormalities resolve. Patients with skeletal Class II relations and greatly altered TMJ morphology typically exhibit greater positional variability. Since BOI implants are the only option for patients with advanced jaw resorption to receive a fixed restoration in a single procedure, the experience of conventional restorative procedures cannot be readily transferred to the BOI concept, and it certainly cannot be transferred without qualifications. We continue to be faced with the problem that many non-authorized experts are unaware of or underestimate the consequences of these adaptation processes, so that their formal opinions are often marred by unfortunate misjudgements.

Nevertheless, these trains of thought are being increasingly pursued by crestal implantologists as well. Interestingly, even the University of Bern, Switzerland, seems to have abandoned the absolute concept of “bite registration” in favour of “bite testing” (Mericse-Stern 2002).

Issues concerning the registration of joint position are beyond the scope of this communication. Extreme jaw resorption is virtually always accompanied by painful or asymptomatic myoarthropathy. Facebow registration is therefore a questionable measure (Carlsson and Magnusson 2000) as its result would just reflect a pathological situation. There is a risk that this pathological situation is perpetuated by transferring these facebow data to the new restoration without getting to the bottom of the problem. Since a symmetrical prosthetic outcome is an essential treatment objective, other techniques including a plane record have proved to be a useful alternative to arbitrary registration (Schöttl 1997). The HIP-mount system developed for this purpose has the advantage that the HIP plane determined in the model can be checked by a plane record with the help of the Head Lines measuring device. Since the model is always mounted in the articulator parallel to the occlusal plane, it is easier for the dental technician to fabricate a horizontally correct restoration, which, in turn, will expedite the adaptation of masticatory function. In our view, the HIP technique enables optimal horizontal adjustment of the masticatory plane. Its users will immediately notice any elongations in the maxilla, and they can easily verify the absolute horizontal plane in a reliable manner. Even this technique cannot, however, change the fact that extensive subtractive adjustments or contralateral crowning of teeth will be necessary in the presence of greatly divergent AFMP angles on both sides of the jaw. Furthermore we always have to consider the vertical and horizontal bone level around teeth, around implants and between teeth, implants and even in edentulous sections of the jaw as highly unstable and adapting to function. The joints show a large range of adaptation to many of the changes, and thus compensatory elongations, the buildup of new trajectories, age- and extraction-related bone loss, changes in chewing force and morphological changes, which are followed by changes in the chewing pattern. Even a “correct” centric registration is bound to change considerably over time, which will lead to overload on teeth and implants. In our experience the changes are greater in cases where the bite is not balanced or constructions are unsymmetrical.

These situations include ill-advised occlusal adjustments, usually made by other dentists who are not sufficiently aware of the problems involved, after ossification of the basal plates has been completed. In contrast to the regular secondary and tertiary overload situations, which evolve gradually, iatrogenic tertiary overload situations occur abruptly and involve an even higher risk of implant fracture. After all, there is not enough time left for the well-ossified BIO implant to react to the problem by way of overload osteolysis.

Iatrogenic overload situations, as the name implies, are to be blamed on incorrect dental treatment. It is only fair to add, however, that patients who wear implant-supported restorations in both jaws will not be able to notice and report any premature contacts as readily as patients with natural dentitions.

In patients who received a first BOI restoration in one jaw, followed by a second BOI restoration in the opposite jaw at a later time, the jaw that was treated first may be subjected to iatrogenic tertiary overloading while the jaw that was treated second may be affected by regular types of primary, secondary or tertiary overload. Cases such as these require meticulous follow-up examinations and functional adjustments by additive and subtractive means.

Incidentally, osteolytic phenomena may remain confined to individual disks of an implant or indeed to specific portions of a disk. With the old double-disk implants that still featured a disk-to-disk distance of 3 mm, the crestal disk used to be more susceptible to osteolysis. In this situation, the dentist must consider removing the disk because there is a risk that the osteolytic area may become infected and that this infection may even spread to the basal disk. As long as the infection remains confined to the crestal disk, the implant as such can be preserved.

Figure 11.1 illustrates how BOI implants work. This specific implant was inserted into the crestal part of the alveolus immediately on extracting tooth 46. In other words, the threaded pin was never surrounded by bone. While the remaining space of the alveolus was filled with newly formed bone due to functional stimulation, the area of the threaded pin remained non-ossified. The picture was taken 5 years after the implant had been inserted and immediately loaded.

Figure 11.2 shows a similar case in which the implant was, however, inserted considerably more deeply.

The clinical developments in these examples attest to the fact that a clear-cut line between the initial treatment and the maintenance phase cannot always be drawn. This eventuality must be pointed out to the patient to avoid misunderstandings when he or she is charged for additional dental treatments that may become necessary after the cost ceiling for the initial treatment has been reached. In some patients, notably in those with myoarthropathies, it is downright impossible to draw a line between the initial treatment and the maintenance phase. After all, myoarthropathies are chronic diseases that may require lifelong therapy.