In the 1980s, an implantation technique was introduced in connection with disk implants to treat the area of the maxillary sinus in the presence of insufficient vertical bone volume. This is achieved by first elevating the membrane before installing the basally osseointegrated implants. The procedure is started by performing an incision in the upper mesial area of the anterior vestibular sinus wall (e.g. in the canine fossa), then the membrane is carefully elevated in a dorsal, caudal and cranial direction. After drilling the implant bed and inserting the implant, the cavity created in the sinus is filled with a grafting material, sometimes mixed with autologous cancellous bone tissue. By and large, this procedure has yielded good results over the past 20 years. Sometimes the membrane ruptures when elevated. In that case, the surgeon must decide whether the augmentation procedure should be continued and an attempt be made to repair the membrane. In smokers, the membrane is very thin and therefore ruptures more frequently. By contrast, such tearing rarely occurs in membranes that are thickened by chronic inflammation. Also, the increased blood supply associated with inflammations may arguably promote the healing process.

In theory, it would be advantageous not to open the sinus completely. In practice, however, we have observed infections in the augmentation area separated by the bony sinus where they are particularly difficult to manage.

Anyhow, since load transmission is confined to the ring area of the disks, the customary approach used with crestal implants of introducing a filling material in order to create a load-transmitting implant bed does not even offer theoretical advantages.

One disadvantage of this technique is that the (yet unorganized) augmentation material is in continuous contact with the oral cavity as the mucosa is penetrated by the threaded pin. In our experience, inorganic augmentation materials are better suited for this approach, since any postoperative contact of human bone grafts with the oral cavity is absolutely contraindicated.

Another problematic factor is that the integrity of the membrane inside the sinus itself cannot be verified too well during the procedure. A useful approach to sinus grafting is the technique described by Donsimoni (2003) in which the membrane is only dislodged in the small area immediately surrounding a previously prepared bone cover. Subsequently, suction is applied through the nose, which will gradually elevate the membrane in the absence of direct manipulation. This technique is said to involve a lower incidence of membrane rupture.

In situations where ventilation conditions are inadequate, an additional ventilation pathway must be considered. One way of creating such a pathway would be to fenestrate the area of the lower nasal meatus. Some otorhinolaryngologists have qualified this approach as obsolete, arguing that the drainage pathway for mucus by the defined cilium beat is not affected by this lack of ventilation. This viewpoint is correct with regard to chronic sinusitis. In connection with sinus grafting, however, the eventuality of acute infection and retention must be averted. Therefore, a fenestration as suggested above is absolutely indicated as a precaution against acute events occurring in the sinus both during and after the augmentation procedure. More recently, some otorhinolaryngologists have advocated the use of a drainage tube, to be inserted in the lower nasal meatus as a preoperative measure.

Regarding the medium- and long-term mobility of the implant-restoration complex, the results of transsinus implantation with augmentation may vary substantially. The following outcomes may occur in any combination:

Depending on the situation, even successful implants are likely to involve some mobility of the implant-restoration complex. This is true especially if papyraceous thin bone structures were present before the treatment was started, as these do not tend to favour a uniform interconnection between the cortical and the augmentation material. Another factor to consider is that the functional stimuli on cortical bone areas may be reduced by the implant being so firmly integrated in the augmentation material that the native bone structure in the area may disappear.

Trans-sinus installation of BOI implants is today a routine procedure in dental implantology (Konstantinovic 2003). The most important requirement in this approach is that the opposite cortical structure (i.e. the palatal ridge or the lateral nasal wall) is safely reached and that primary stability of the BOI implant is ensured both on the vestibular and on the opposite side (see Video 9). The harder part is to obtain primary stability in the vestibular bone because the numerous cutting procedures may quickly give rise to inadvertent expansion of the vestibular osteotomy gap. The number of cutting procedures can be reduced by using the newer generation of cutters operated with contra-angle handpieces. The risk of placing the osteotomy too high is greatly reduced with these cutters. Treatment under anaesthesia should still be considered in alveolar ridges characterized by poor accessibility and strong resorption, since anaesthetized patients will not perform uncontrolled movements, so that the surgeon can devote his whole attention to the osteotomy. Today the technical indications for anaesthesia are greatly reduced by the availability of contra-angle handpieces.

The case report in Fig. 18.4a–c illustrates the potential of the BOI system in the non-augmented sinus maxillaries:

Even most BOI users at one time attempted to circumvent the maxillary sinus. This approach has been abandoned, however, based on long-term observations and improvements made to the implant design:

This development was triggered by growing evidence that the healing process after inadvertent opening of the sinus during BOI implantation procedures was generally uneventful. In this way, surgeons were gradually encouraged to routinely use the non-augmented maxillary sinus as an implantation site.

In our experience, the surface structure of the implant in general and of the threaded pin in particular is especially important in this type of procedure. The former disk implants with their surface-enhanced shafts used to favour cross-contamination from the oral cavity to the sinus in the manner of a candle wick. Screw implants are known to involve similar problems. In BOI implants, which feature a smooth surface along the thin shaft (threadholders), this type of problem is almost non-existent. Using this concept, there is no need to create an additional ventilation pathway in the maxillary sinus unless the patient has a history of sinus problems or, more importantly, if intraoperative verification shows that adequate ventilation is present. Note that the vertical implant segments do not osseointegrate, which is why inflammations in this area will not primarily spread to the bone. This is where BOI implants differ from osteosynthesis plates, where osseointegration along the screw thread is an obvious requirement. Although this integration is achieved in the early phase, osteosynthesis in the craniofacial region (and especially in the area of the frontal sinus) will frequently involve loosening of the screws and a pronounced tendency towards osteolysis down the road because there is no soft-tissue layer between the screw and the bone offering nutrition and spatial limitation at the same time.