Objective: Vertical and horizontal bone insufficiency in both the maxilla and mandible has long been a contraindication for implants. This review provides an overview of the long-term survival rates of implants in augmented alveolar bone after the guided bone regeneration (GBR) technique. Results: GBR in a combination of allogeneic or xenogeneic graft material with a barrier membrane and simultaneous or delayed placement of dental implants has proven to be a very effective and feasible treatment option in long-term studies up to 35 years. Conclusion: Bone reconstruction with various materials is a standard therapy in implantology today.
Key points
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The guided bone regeneration (GBR) technology in combination with a bone filling material requires a surgical procedure under local anesthesia only.
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Resorbable membranes are preferable to nonresorbable membranes as they do not require a second surgical procedure.
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The indications for GBR technology are very diverse. However, they always refer to a limited bone defect.
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The combination of GBR and simultaneous implant placement has proven to be feasible with a high long-term survival rate of the implants.
Introduction
The consequences of complete tooth loss are a profound event for affected patients. First, there is a loss of oral function and the shape of the mouth. Quality of life and self-esteem are severely impaired. In addition, prosthesis instability leads to problems with eating and chewing function. Poor oral hygiene, especially in older people, can be a trigger for further, sometimes life-threatening complications and diseases.
Another complication is the resorption of the alveolar bone because of tooth loss. Resorption is the physiologic consequence of bone atrophy due to nonloading of the tooth-bearing bone. Due to various preprosthetic surgical measures, the rehabilitation of an atrophied alveolar bone in combination with dental implants to rehabilitate the masticatory organ with a stable fixed or removable denture has now become a standard therapy. Dental implants have high success and survival rates.
Different augmentation techniques have been developed depending on the localization, extent, and configuration of the bone defect. Autologous bone grafting is still considered the gold standard.
Stimulating bone formation through guided bone regeneration (GBR) has proven to be an effective treatment alternative for both the maxilla and mandible. This concept was described by Hurley and colleagues in 1959. However, the clinical possibilities were not investigated until 20 years later by the research group led by Nyman and colleagues , in various experimental and clinical studies on periodontal regeneration using barrier membranes. A little later, the membrane technique was tested in experimental studies on bone regeneration. From the end of the 1980s, the clinical use of membranes in implant patients was started and systematically investigated. , The membrane used was a bioinert, nonresorbable membrane made of expanded polytetrafluoroethylene (e-PTFE). The membrane creates a sealed space. This allows angiogenic and osteogenic cells to grow from the existing bone marrow space into the bone defect without the formation of fibroblasts. A frequent complication was the collapse of the membrane, resulting in insufficient bone formation. The combination of the e-PTFE membrane with a bone filling material—autologous, allogenic, xenogenic, or alloplastic—was the logical consequence. Autologous bone stimulates the formation of new bone best. However, the removal of the bone graft prolongs the operation time, and autologous bone is also subject to unpredictable resorption. The nonresorbable e-PTFE membrane requires a secondary surgery for removal. The development of resorbable membranes made of different materials—especially collagen membranes of animal origin—in order to avoid a second intervention was the logical consequence. ,
The development of bone regeneration materials took place in parallel with the development of resorbable membranes. In addition to autologous bone, the following replacement materials are used: allogenic bone replacement material consisting of human foreign bone; xenogenic material from animal—bovine, porcine, and equine—or plant tissue—red algae; and alloplastic material consisting of bioactive glass ceramics, metals or polymers, and minerals.
The indications for the GBR technique are diverse: remodeling of bone and soft tissue after tooth extraction; smaller and larger bone augmentations or horizontal and/or vertical after tooth loss, trauma, or after tumor resection; sinus floor elevation; soft tissue regeneration; and peri-implantitis and periodontal treatment ( Fig. 1 ).
This review provides an overview of the long-term survival rates of implants in augmented alveolar bone with the GBR technique.
The literature search was conducted in PubMed and BASE. The search strategy was based on the following terms: “implant survival,” “bone allograft,” “alveolar bone graft,” “autogenous bone graft,” and “bone augmentation.” The search terms were linked with AND or OR (“bone grafting” OR “alveolar bone grafting” OR “alveolar ridge augmentation” AND “dental implants” OR “dental implantation” AND “graft resorption” OR “survival rate” AND “grafting, autogenous” OR “grafting, homologous”).
Results
In the treatment of tooth and bone defects, the combination of GBR with dental implants represents a key clinical approach. Restoration of insufficient alveolar bone volume can be difficult due to local factors—periodontitis, trauma, and localized alveolar process resorption. GBR in combination of allogenic or xenogenic graft material with a barrier membrane and simultaneous or delayed placement of dental implants has proven to be a very effective and feasible treatment option in long-term studies. The following main parameters were investigated in various studies: peri-implant bone gain or loss, , crestal remodeling after vertical augmentation, , use of resorbable or nonresorbable membranes, , and survival rate of implants up to 25 years.
Peri-implant Bone Loss and Bone Gain
Chappuis and colleagues investigated the effective bone gain after extraction, immediate implant placement and augmentation as well as the esthetic gain of soft tissue dimensions in the maxillary anterior region. The follow-up period was 10 years. The patient cohort included in the follow-up consisted of 5 men and 15 women with an average age of 53 years. Only one patient experienced implant loss due to smoking and the use of bisphosphonates as a result of osteoporosis. This patient was excluded from the study. Overall, the other 19 patients had an average horizontal bone gain of 0 to 1.67 mm. The mean vertical peri-implant bone loss was 0.35 mm over a 10 year average. The authors conclude that early implant placement in combination with GBR technology can lead to stable bone conditions over a longer period. The risk of mucosal recessions, particularly in the esthetic area, is classified as low.
GBR in combination with autogenous block grafts or filling with anorganic bovine bone mineral particles has proven successful not only for vertical jaw defects but also for very pronounced horizontal alveolar ridge defects. Pistilli and colleagues treated 49 patients with horizontal bone defects in the posterior part of the maxilla and mandible simultaneously with GBR and implants. The average age was 55.86 years; 38 patients were women and 11 were men. Thirty-nine patients were nonsmokers, 10 patients were smokers. After placement of the implants, a mixture of autogenous bone particles and anorganic bovine bone mineral was placed in all patients and covered with a resorbable collagen membrane. The membrane was fixed buccally with titanium pins. The aim was to achieve a bone width of 2 mm around the implants. The healing time for the augmentation and the implants was 6 months. This was followed by definitive prosthetic treatment. Two patients experienced temporary paresthesia postoperatively (lasting 7–21 days) and 5 cases showed incomplete bone augmentation. Overall, the complications occurred in smokers. The alveolar ridge width was initially 5.19 ± 0.72 mm, after 6 months 7.95 ± 0.51 mm. Within the first 3 years, the peri-implant bone loss was 0.65 ± 0.40 mm. In the follow-up years 3 to 7, the bone loss was 0.30 ± 0.21 mm. This means that bone loss is significantly greater in the first 3 years than in the later years. The peri-implant bone loss correlated positively with the smokers. The authors conclude that horizontal augmentation should only be performed in one direction up to a maximum of 3 mm in order to minimize the complication rate.
Resorbable Versus Nonresorbable Membranes
Titanium-reinforced polytetrafluoroethylene (e-PTFE) has proven to be a suitable material for nonabsorbable membranes. It is characterized by biocompatibility, high strength and rigidity, low density, low weight, corrosion resistance, and the ability to withstand high temperatures. The use of a titanium-reinforced polytetrafluoroethylene (e-PTFE) membrane alone or together with a bone substitute material has proven to be an effective procedure for localized alveolar ridge augmentation. In 2009, Urban and colleagues reported on their results in vertical alveolar ridge defects prepared for implant placement using GBR in combination with a titanium-reinforced e-PTFE membrane after a healing phase of between 6 and 9 months. A total of 35 patients were included in the study who underwent surgery between June 1999 and October 2004. Of the 35 patients, 14 were men and 21 were women with an average age of 44.9 years. All patients were treated with autogenous bone from the mandible and a nonresorbable e-PTFE membrane. The membrane was fixed with titanium pins. After the healing phase, the e-PTFE membrane was removed, the implants inserted and covered with a resorbable collagen membrane to prevent premature bone resorption. Removal of the e-PTFE membrane resulted in very good new bone formation. The augmentation performed in vertical alignment averaged 5.5 mm with a standard deviation of 2.29 mm. With regard to the bone quality of the new bone obtained by augmentation and GBR, no difference was found compared to the existing bone. During the entire study period, there was no pronounced resorption of the newly formed alveolar ridge. The marginal bone loss around the implants was 0.39 mm after insertion of the abutments, 1.01 mm after 1 year and decreased by 0.05 to 0.02 mm during the following 6 years of follow-up. The survival rate of the implants was 100% after 1 year and 94.7% after 4 years. In another study, Urban and colleagues reported on a case series of 19 patients who were treated for a vertical alveolar ridge defect with augmentation using anorganic bovine bone mineral and autogenous bone and a titanium-reinforced, dense PTFE membrane in both the maxilla and mandible. The implant insertion took place at a later stage. A bone biopsy of the augmented bone was taken from 8 patients immediately before the implants were inserted and examined histologically. The implants were inserted after an average healing phase of 9.72 months with a standard deviation of 3.02 months. Of the 19 patients, 4 were men and 15 were women with an average age of 43.4 years. In 5 patients, a sinus lift was performed at the same time as the bone augmentation. The autogenous bone was mainly harvested in the posterior region of the mandible. In one case, bone was harvested from the posterior region of the maxilla, and in another case, bone was harvested from the chin region. All augmented areas showed very good bone regeneration. The vertical bone increase was 5.45 mm on average (standard deviation 1.93 mm). No bone resorption was observed in the subsequent period. The healing phase was without complications. Opening of the operated areas for implant placement revealed healthy bone tissue surrounded by periosteal tissue. The histologic preparation of the biopsies showed that the autogenous bone particles exhibited continuous remodeling. The anorganic bovine bone mineral accounted for approximately 17% of the augmented bone, but more than 46% of the bone marrow. The treatment of vertical alveolar ridge defects with GBR using a mixture of autologous bone and anorganic bovine bone mineral and a nonresorbable titanium membrane can, therefore, be considered promising. The histologic results have shown that the anorganic particles have bonded with newly formed bone of varying degrees of maturity.
In a recent study, Li and colleagues compared the effectiveness of a resorbable collagen membrane with the use of a digital titanium mesh. Preoperatively, the ideal position of the implant, the subsequent prosthetic restoration and the reconstructed alveolar bone around the implant were evaluated according to the data of an intraoral scan and Digital Imaging and Communications in Medicine data. The digitally reconstructed model was printed. The titanium mesh was molded on the printed model, autoclaved, and prepared for surgical use. To prevent stimulation of the soft tissue by the titanium mesh, it was covered with a resorbable collagen membrane. The authors treated 20 patients and 34 implant sites with a resorbable membrane and 20 patients with 31 implant sites with the digitally prepared titanium mesh. The implant survival rate was 100% during the observation period. Sixty implants were placed in the maxilla and 5 implants in the mandible. Postoperative bone augmentation in the horizontal and vertical directions was assessed as good in both groups. However, the average bone gain was significantly better in the titanium group (Ti group vs resorbable membrane: horizontal 5.41 ± 2.26 mm vs 4.10 ± 1.95 mm, vertical 2.56 ± 1.98 mm vs 1.75 ± 1.06 mm). The resorption rate of the built-up alveolar bone was significantly lower in the patients treated with a digital titanium mesh after 1 year than in the comparison group. The exposure of the titanium mesh during the healing phase is seen as a disadvantage of using a titanium mesh. However, the exposure rate was only 10%. The advantage of creating a titanium mesh using 3 dimensional (3D) technology is that the titanium mesh is only 0.2 mm thick, which means that it is relatively plastic. Another advantage is the exact bone augmentation volume, which is determined preoperatively using the digital design phase. Overcontouring of the bone arch is avoided.
In their randomized study, Cucchi and colleagues compared bone augmentation after the GBR technique with a nonresorbable, high-density, and titanium-reinforced PTFE membrane (d-PTFE, group A) with a titanium membrane covered with a membrane made of cross-linked collagen (group B). Thirty-nine patients with a total of 106 implants in the lateral edentulous mandible were treated with implants and bone augmentation with autologous bone (20 patients group A, 19 group B). A total of 7 complications occurred (3 group A, 4 group B). In the group with titanium-reinforced d-PTFE membrane, 34 implants showed supraimplant bone growth, necessitating an osteotomy to insert the healing screws. Incomplete bone regeneration was observed in one-fifth of group B. Similar figures were reported for group B. In this respect, there is no clear difference between the treatment groups. Bone growth and bone formation was similarly good in both groups.
Long-Term Survival of Implants in Augmented Bone
Various criteria have been used in the past to assess the success of implants in augmented bone structures, including absence of mobility and subjective discomfort and absence of recurrent peri-implantitis. Long-term follow-up provides valuable information on the effectiveness and feasibility of GBR and implants. In their systematic review from 2012, Clementini and colleagues reported the long-term survival of implants in augmented jaw areas to be between 61.5% and 100%. Even though a meta-analysis could not be performed due to the heterogeneity of the studies, the authors concluded that GBR is a reliable method with a high implant success rate. In a long-term study over almost 24 years, Jung and colleagues investigated the effectiveness of GBR in implants using resorbable and nonresorbable membranes. Implants placed in bone that had been pretreated without GBR served as a comparison. With regard to the follow-up period, this study is a follow-up study of the study by Jung and colleagues, in which the authors reported a follow-up period of 12 to 14 years. In this respect, the population in both studies was identical at the beginning of the investigations. The original patient cohort was treated between 1994 and 1996 and comprised 72 patients. Of these 72 patients, 54 were women and 18 were men. The average age of the patients was very high at 67.5 years. The 72 patients received a total of 265 implants. Of these, 112 implants were treated with a resorbable membrane and 41 with a nonresorbable membrane. A total of 112 implants were placed in untreated bone. The implants treated with GBR were additionally treated with anorganic bovine bone mineral. The resorbable membrane was a native collagen membrane, the nonresorbable membrane consisted of e-PTFE. For the follow-up after almost 14 years, 58 patients were recruited (6 patients had died in the meantime, 8 patients could not be reached due to geographic changes or illness). Of 265 implants, 18 implants were lost within 14 years. Most of the implants had been restored with fixed prosthetic restorations. Only 14.3% had been treated with removable overdentures. The implant survival rate was almost identical in all 3 study groups (control group: 94.6%; collagen membrane: 91.9%; and e-PTFE: 92.6%). Radiographically, all but 2 implants showed complete bony integration; 2 implants showed almost complete bone loss. These implants were evaluated as implant failures. The mean distance between the implant–bone contact and implant–abutment connection was 2.40 mm in the group with resorbable collagen membrane, 2.53 mm in the e-PTFE group, and 2.36 mm in the control group. For the follow-up examination in 2021, 39 of the original 72 patients were recruited. The average age was 75.8 ± 10.5 years. Twenty-three patients had died in the meantime, 10 patients could not be followed up due to geographic changes or serious illnesses. The implant survival rate was almost identical in all 3 groups (resorbable membrane: 89.3%; nonresorbable membrane: 90.2%; and control group: 93.8%). Smoking, in particular, was a limiting factor for implant survival. The marginal bone loss after an average of 23.5 years was almost identical in all 3 groups (bone level at the beginning: −0.3 ± 0.7 mm; bone loss after 23.5 years: resorbable membrane: −2.3 ± 1.4 mm; nonresorbable membrane: −3.0 ± 1.5 mm; and control group: −2.3 ± 1.5 mm). Patient satisfaction with the implants and the prosthetic restoration averaged approximately 100%, with 24 patients reporting a satisfaction index of 100%. Based on the results, the authors conclude that GBR—regardless of the type of membrane—leads to implant survival rates of between 89.3% and 93.8% after 23.5 years. However, smoking has a negative effect on implant survival. In a retrospective long-term study, Knöfler and colleagues investigated the long-term survival of implants in augmented and nonaugmented jaw areas. The patients were treated in 3 private dental clinics in the period from 1991 to 2011. The follow-up period was up to 20 years. A total of 10,158 implants were inserted in 3095 patients during this period. One thousand six hundred ninety-three patients were women (54.7%) and 1401 were men (45.3%). The mean age at the time of implantation was 52.4 years. In terms of age and gender distribution, there was no difference between patients with and without augmentation. Various graft materials were used for augmentation: autogenous bone blocks from the chin, maxillary tuberosity, retromolar region, and iliac crest; autogenous bone particles were collected during bone drilling for implantation and used as augmentation material; and allogenic and xenogenic bone mineral. Absorbable and nonabsorbable membranes were used as membranes. If a titanium mesh was used, the membranes were placed over the mesh. During the observation period, 460 (4.53%) implants were lost. Thirty-five implants had to be removed before insertion of the prosthetic superstructure. A further 198 implants with previous augmentation and 227 implants without augmentation had to be removed within the observation period of 20 years. The statistical analysis showed that 96.33% of the implants with augmentation survived, whereas the survival rate of the implants without augmentation was 94.27%. The overall survival rate of all implants was, therefore, 95.47%. The most common augmentation procedure was lateral augmentation (3210 implants) and external sinus floor augmentation (1101 implants). Other procedures included bone spreading, internal sinus lift, bone block grafting, and 3D augmentation with titanium mesh. The most common graft combination was autogenous bone particles with anorganic deproteinized bovine bone mineral. In the authors’ opinion, it is not possible to determine the superiority of an augmentation procedure—graft material, membrane, and surgical procedure—despite the large number of patients, the implants inserted, and the long follow-up period in some cases. After analyzing the data, however, it can be said that the survival rate of implants in augmented bone may be slightly better than in nonaugmented bone ( Fig. 2 ).
