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Double-Layer Technique for Alveolar Ridge Augmentation

Endosseous implants have been documented to be a successful treatment option for restoring missing or failing teeth. Implant success, as measured through fixture osseointegration and restoration of function, has been reported to be high and stable over time.1,2 The predictability of implant procedures and the maintenance of long-term implant stability in function are directly related to the quality and quantity of the available osseous tissue for implant placement. Implantation of endosseous devices in areas where the dimensions of the alveolar bone are equal to or less than those of the implant results in parts of the implant surfaces and/or threads not being covered by bone. In the dental literature, it is still unclear whether exposed implant threads hamper the long-term prognosis of endosseous implants.3

With respect to dental aesthetics, uncovered implant threads may be seen in concordance with the observations made following facial displacement of a tooth4 and can lead to soft tissue recession, which is subsequently followed by an aesthetic failure of the fixture. For an optimal outcome, several authors recommend at least 2 mm of bone structure on the buccal aspect of the implant shoulder.5,6  In the aesthetic zone, however, the anterior alveolar ridge is often devoid of this amount of bone structure. Therefore, in many instances, the bone structure on the buccal aspect of the implant shoulder has to be created using augmentation procedures.6

The most widely used technique to increase the alveolar ridge width is to exclude the invasion of nonosteogenetic soft tissue cells by guided bone regeneration (GBR). The efficacy of the GBR technique both in rebuilding the atrophic alveolar bone prior to implant placement and around exposed implant surfaces has been well established in the literature.7,8

Most GBR procedures initially used nonresorbable barrier membranes composed of expanded polytetrafluoroethylene. Despite encouraging results,9-11 there are several limitations on the use of nonresorbable membranes for GBR. Besides the need to remove the barrier, a premature exposure of a nonresorbable membrane has been associated with diminished treatment results.12,13 Simion et al reported significantly less bone gain when the membranes were exposed compared to nonexposed membrane treated sites (41.6% versus 96.6%).14

Unlike nonresorbable membranes, biodegradable or bioresorbable barriers undergo resorption in the body, so that secondary surgery for membrane removal is obviated.15  Barrier membranes made of bovine or porcine collagen are the most widely studied bioabsorbable materials for GBR.16 Collagen has several desirable properties, including its hemostatic, chemotactic, and cell-adhesion functions, and it has yielded favorable results in clinical trials for GBR.16  Collagen’s fast absorption rate, however, remains a concern to many clinicians.

The following case presentation shows an approach using two different biodegradable collagen membranes with various degradation times in order to combine the advantages of each.

Case Presentation

Pretreatment

A 49-year-old, nonsmoking male patient presented for tooth extraction and implant placement in the position of tooth #9. The patient had a noncontributory medical history (Figure 1). Following periodontal and prosthetic evaluation, tooth #9 was extracted and socket preservation was performed (Figure 2).

Surgical Protocol

Following the administration of local anesthesia, a midcrestal incision was performed and extended intrasulcularly to the buccal aspects of the adjacent teeth (Figure 3). One vertical releasing incision was positioned on the distobuccal line angle of the distal tooth, extending far beyond the mucogingival junction. After elevation of a buccal and a minute palatal mucoperiosteal flap, the extraction socket was curetted to remove granulation tissue and remaining bone substitute particles (Figure 4). The buccal full-thickness flap was then released using a periosteal dissection in order to improve its mobility for primary wound closure (Figure 5). Additionally, a subepithelial connective tissue graft (CTG) was harvested from the palate and fixed to the internal coronal part of the buccal flap.17 The CTG extended past the mucoperiosteal flap by approximately 4 mm to 5 mm (Figure 6). After implant placement (Figure 7), a GBR technique was performed to cover the exposed coronal implant threads.

Initially, the residual cortical bone was perforated to induce bleeding from the marrow vascular spaces and to provide a mechanical interlocking of the bone graft (Figure 9). A porcine collagen membrane was trimmed to size to overlap the defect margins by approximately 3 mm. The surgeon ensured direct contact of the membrane with the adjacent teeth was avoided (Figure 9).

The membrane was stabilized to the alveolar bone at its apical basis using resorbable tacks. Contrary to the manufacturer’s recommendations, the membrane was positioned with its rougher surface facing externally. Consecutively, a deproteinized bovine bone material was located on top of the exposed implant threads to entirely cover the implant (Figure 10). A second porcine collagen membrane was then trimmed to a shape identical to that of the porcine collagen membrane, yet in a smaller dimension (Figure 11). The porcine membrane was then gently located on top of the bone substitute. The membrane was moved coronally over the complex and positioned under the palatal flap to achieve initial stabilization of the membrane.

In order to enhance the probability of primary wound closure, the connective tissue extension of the mucoperiosteal flap was initially attached beneath the palatal mucosa using a 5-0 suture material. The CTG covered the coronal and buccal aspects of the augmented area (Figure 12). The buccal flap and the palatal flaps were consecutively readapted, and the vertical releasing incision was closed using 7-0 and 5-0 suture materials (Figure 13).

Following surgery, the patient was instructed to rinse with 0.2% chlorhexidine digluconate three times daily for at least two weeks. In order to reduce swelling caused by the surgical procedure, ibuprofen 600 mg was prescribed. During the healing period, the missing tooth was replaced by a provisional resin-bonded fixed partial denture (Figure 14). Removal of the sutures was performed seven days postsurgery. The healing period was uneventful, and primary healing was observed.

Six months after implant placement and augmentation, second-stage surgery was performed utilizing the modified roll-flap technique to uncover the implant (Figures 15 and 16).18  After six weeks of soft tissue healing, the definitive all-ceramic restorations were placed (Figures 17 and 18).

Discussion

This case report displays the use of two different collagen membranes in order to overcome the general disadvantages of resorbable barrier membranes for GBR procedures. Guided bone regeneration procedures utilizing collagen membranes have been widely reported.19-22 Recent investigations have demonstrated that bilayered collagen membranes have a high potential for tissue integration and vascularization without any observable foreign body reaction, thereby providing ideal conditions for uneventful soft tissue healing.23,24 Biodegradation starts to occur after about four to six weeks, and histologic differentiation between membrane and host collagen has been proven to be impossible after 12 weeks.24  

For periodontal indications, four to six weeks of barrier function are thought to be sufficient for guided tissue regeneration (GTR). It has also been reported that during GTR procedures, bone and/or periodontal ligament cell migration reach their peaks two to seven days postsurgery, with a decrease in mitotic activity to almost normal levels by the end of the third week.25 For bone augmentation procedures, however, no study has defined the actual time needed for GBR barriers. Nevertheless, a long-lasting barrier effect of up to six months appears to be desirable.23,26,27 In this context, the porcine collagen membrane might be an ideal barrier: a recent clinical and histological study in humans evaluated the osseous membrane for GBR procedures in combination with deproteinized bovine bone mineral.28  It was reported that collagen layers could still be observed seven months following healing.28

 

Conclusion

This case presentation demonstrates a modification of the conventional GBR concept. The modifications involve the application of two different kinds of bioresorbable collagen membranes in combination with a xenogenous bone substitute. As the biodegradation of the membrane might be regarded as too rapid for bone regeneration, a long-lasting osseous membrane with a biodegradation of up to six months was mounted above the bone substitute, but beneath the membrane. With this concept, the ideal behaviour of the membrane towards soft tissue and the lasting durability of the osseous membrane can be combined.

 

* Clinical Associate Professor, Department of Operative Dentistry and Periodontology, Albert Ludwigs University, Freiburg, Germany; Clinical  Associate Professor, University of Texas, Dental Branch, Houston, TX; private practice, Munich, Germany. 

†Private practice, Munich, Germany. 

‡Clinical Assistant Professor, Department for Periodontology and Implant Dentistry, Arthur Ashman College of Dentistry, New York University College of Dentistry, New York, NY; private practice, Munich, Germany. 


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