General principles of surgical reconstruction and technics of horizontal ridge augmentation for placement of brånemark implants

Tooth loss is almost always followed by reduction in the amount and quality of the hard and soft tissue. Hard tissue loss proceeds in different directions in the two jaws-posterosuperiorly in the maxillae and inferolaterally in the mandible (^{fig. 1a} and ^1b) (^{Starshak and Sanders, 1980}). Moreover, resorption is often irregular, differing in degree and direction between sites or even within sites (^{Seibert and Cohen, 1987} ; ^{Jensen, 1989}). As a result, the ridge may be narrowed and flattened, with complex irregularities, and the soft tissue may abnormally thick or thin. Sites where such adverse changes have taken place are said to be « compromised ».

In the past, osseointegrated implants often were placed in such sites. Inevitably, however, these implants had to be placed in the lingual position at an angle that did not duplicate the direction of the roots of the lost teeth. The result was phonetic limitation, an overcontoured restoration, and loss of orofacial support. The dentition was then reconstructed with a bar prosthesis or a denture-supported restoration, and the soft tissue loss was disguised by a flange overdenture. Alternatively, overcontoured ceramometall crowns and angle abutments were introduced.

Because of the greater demands of the therapist and the patients to duplicate the previous dentition and soft tissue with the restoration, surgical reconstruction was introduced. To achieve a functionally, esthetically, and phonetically optimal result, the hard and soft tissue often undergo some degree of reconstruction prior to, during, or after implant placement (^{table I}) (^{Bahat et al., 1993}).

Evaluation and surgical planning

The success of an implant-base reconstruction requires the stable placement of a sufficient number of implants of optimal length at the proper angle to support the occlusal load without nonaxial loading. Placement that satisfies these criteria necessitates adequate bone to cover all the threads of each properly positioned implant with at least a 1 mm collar of bone.

Evaluation and planning for an implant-based reconstruction consists of four steps :

- definition of the normal anatomy ;

- identification of all deviations from the normal anatomy ;

- conceptualization of the precise details of the final restoration ;

- development in reverse order of all of the steps needed to produce that restoration (^{table II}).

Each site must be examined individually, both clinically and with the aid of reformatted CT scans. The elements to be considered are the shape of the residual ridge (direction, type, and extent of loss), bone quality, the relations between the alveolar ridges, and the degree of ridge resorption in relation to the desired orofacial soft tissue profile. The limiting structures must be studied : lip length ; vestibular depth ; the position of the gingiva, mucosa, sinus, and neurvascular bundel ; and the position and prognosis of the adjacent dentition.

The bone of the ridge may be deficient in various ways. Most dramatically, there may be insufficient bone for implant placement. If implants are placed nevertheless, either they will be misplaced or misaligned, or mechanical modifications will be needed to permit completion of the reconstruction. Numerous adverse consequences may follow :

- overloading or nonaxial loading, leading to ischemia, infection, and further bone resorption ;

- metal fatigue that predisposes the implants and prosthetic reconstruction to fracture (^{Piattelli et al., 1998}) ;

- poor access for oral hygiene.

The short-term and long-term prospects for such a reconstruction are less than optimal (^{Roberts et al., 1989} ; ^{Kopp, 1989} ; ^{Jemt and Lekholm, 1995} ; ^{Bahat and Handelsman, 1991}).

Options for reconstruction of the hard tissues

If restoration of the hard tissue is necessary, the method must be selected : grafting (autogenous bone, allografts of freeze-dried bone, alloplastic materials, or xenografts) (^{Bernard, 1991}), a split crest technic, or application of an exclusion membrane.

Autogenous bone is the gold standard for reconstructing the hard tissues because of its safety, guaranteed biocompatibility, and well-documented long-term success (^{Bahat et al., 1993}). Its principal drawback is the need to create a donor site, which, like the recipient site, may suffer complications. Autogenous bone may be obtained intraorally (palate, chin, ramus, tuberosity, tori) or extraorally (cranium, iliac crest). Grafts that contain marrow or trabecular bone have stem cells and therefore possess considerable osteogenic potential. If an autogenous graft is to be used, surgical planning must include identification of a sutable donor site.

In patients in whom the bone is nearly optimal in configuration and location and who require only facial enhancement to increase orofacial support and improve the ridge shape, hydroxyapatite or other alloplastic material can be used (^{Kenney and Lekovic, 1991} ; ^{Shetty and Han, 1991}). Nonresorbable materials are preferred to avoid late deterioration.

The exclusion membrane technic (guided tissue regeneration) is designed to permit the formation of new bone by preventing ingrowth of connective tissue and epithelial elements (^{fig. 2a} and ^2b). It has been studied extensively in animals and humans (^{Scantlebury, 1993} ; ^{Linde et al., 1993}) and shown to be most useful for repairing concavities or small dehiscences. It may be combined with graft placement. Because of the blood supply limitation, a membrane is less effective in the correction of extensive horizontal or vertical bone loss (^{fig. 3a}, ^3b, ^3c, ^3d, ^3e and ^3f).

Types of autogenous grafts

Horizontal reconstruction can improve implant angulation, esthetics, access for hygiene, and coronal contour. A veneer graft is ordinarily indicated when the bony ridge is satisfactory on the palatal side but not the facial aspect. Occasionally, it can be placed on the lingual aspect of the ridge as well. These grafts permit placement of implants more facially, thus reversing the result of bone resorption. A veneer graft also restores support for the orofacial soft tissue, an important contributor to an esthetic outcome. A split crest graft with an interposition may be used to repair a horizontal defect if the remaining ridge is at least 4 mm wide. Split crest and veneer grafts are sometimes combined.

A saddle (inverted-J) graft is used when simultaneous horizontal and vertical reconstruction is desired and the interocclusal space is increased. This graft can consist of one or more pieces of corticocancellous bone that are reshaped as needed to suit the site (^{fig. 4a}, ^4b and ^4c). The graft is often harvested from the iliac crest. Augmentation or reconstruction of the sinus floor (^{Tatum, 1986} ; ^{Kent and Block, 1989}) may be carried out at the same time.

Technic of autogenous grafting

Initially, the intended recipient site is exposed widely and cleared of soft tissue, residual tooth roots, and small irregularities. The mesiodistal and apicocoronal dimensions and the curvature are determined with the help of the hard-tissue stent created during the prosthetic and surgical planning phase.

It is desirable to harvest a graft that is slightly larger than the recipient site in order to have sufficient material for customization. Between manipulations, it is kept in iced saline. The piece of bone is studied to determine the best orientation, and the apicocoronal and mesiodistal dimensions are established. Irregularities are then removed from the graft with rongeurs or burs, and the cancellous portion is trimmed as approppriate. This sculpting is monitored by frequent placement of the graft at the recipient site. To ensure that the developing graft is placed in the same position each time, a minimum of three grooves in different planes can be etched into the graft and recipient site with a sharp bur. These grooves are then aligned with each placement.

In some cases, it will be necessary to adjust the curvature of the graft to ensure a tight fit. This can be done by creating vertical grooves through the cortical bone with a reciprocal saw and gently bending the graft with forceps until it has the desired shape. The saw must not penetrate the cancellous bone.

When the graft has been appropriately sculpted to fit tightly to the recipient site, a small round bur is used to create entries in the cancellous portion of the bone of the recipient site. This intramarrow preparation will facilitate vascularization of the graft. A pilot hole is drilled and countersunk in the graft to allow a fixation screw to engage the alveolus without having the fixation screw protrude underneath the soft tissue coverage (^{fig. 5}).

Long-term viability of the graft requires the establishment of a new vascular supply, which will not develop if the graft does not fit tightly and is not immobilized. Thus, several fixation screws should be inserted, preferably in different planes. When a one-stage procedure is contemplated, extra care is critical to avoid traversing the future implant site. Any voids between the graft and the recipient site are packed with bone marrow. As a final step, the edges of the graft are smoothed with a round bur to protect the overlying soft tissues.

A relatively new technic to improve the integration and quality of bone grafts is treatment with platelet-rich plasma (^{fig. 6a}, ^6b, ^6c and ^6d). This material, prepared by density gradient centrifugation, contains high concentrations of platelet-derived growth factor and transforming growth factors beta 1 and beta 2. In a recently reported controlled study (^{Marx et al., 1998}) treatment with platelet-rich plasma was associated with faster maturation and greater density of bone grafts used to reconstruct mandibular continuity defects.

Soft tissue reconstruction

Any grafting procedure should be accompanied by transfer of a soft-tissue flap without tension. Overstretching of the flap may compromise viability and esthetics. An anterior advanced flap is the most versatile and commonly used option in these circumstances (^{Bahat and Handelsman, 1991}).

To create a flap, the lip is placed under tension, and the exact direction of flap advancement is marked. The mucosa is incised as far as the gingiva. The flap can be held by two pick-up forceps and is used as a tape measure to ensure that it is long enough to reach the intended recipient site. The flap is then advanced, with care not to twist it. A trial closure is performed to ensure that excessive tension is not present. It is often beneficial to run two parallel suture lines to be certain the flap is closed without any distortion. All manipulations must be gentle to protect the blood supply, which is critical for continued viability.

Controlled tissue expansion may be necessary if there has been severe soft tissue loss compounded by limiting anatomic structures such as a shallow vestibule (^{fig. 7a}, ^7b, ^7c, ^7d and ^7e). These technics and their applications have been discussed elsewhere (^{Bahat and Handelsman, 1991}).

Conclusion

In the initial years of implant use, restoration of function was the only consideration. Today, with greater the esthetic demands, it is appropriate to improve our surgical technic to obtain optimal esthetics and phonetics as well as successful function. Horizontal reconstruction of the hard tissues is one of the steps that may be needed to reach this goal.

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