**9. Guided bone regeneration (GBR)**

The treatment and rehabilitation of edentulism with dental implants has become a routine treatment modality in contemporary dental practice. Nevertheless, tooth loss is frequently associated with subsequent bone loss, often resulting in inadequate bone dimensions for ideal dental implant placement. Alveolar ridge resorption in partially and totally edentulous patients may interfere with the safe and correct positioning and placement of implants. When ridge resorption occurs, bone augmentation is essential to guarantee adequate bone volume, to provide patients with proper inter-arch dimensions, and to insure a satisfactory aesthetic result.

#### **9.1. Classic GBR**

Guided bone regeneration (GBR) is an important concept concerning restoration of deficient alveolar sites (e.g., an extraction site or deficient alveolar ridge) for implant placement. GBR uses an occlusive membrane interface between gingiva and the alveolar bone tissue to promote osteogenic tissue regeneration. The occlusive membrane acts as a barrier when placed into the surgical site, preventing connective and epithelial tissue migration into the defect. Progenitor cells located in the adjacent alveolar bone or blood are then able to recolonize the root area and differentiate into a new osteogenic tissue with the formation of new bone.

The strategy to isolate the bone defect with a material that will function as a physical barrier to avoid gingival cell invasion led to the development of GBR membranes. These membranes need to exhibit: (1) biocompatibility to allow integration with the host tissues without eliciting inflammatory responses, (2) proper degradation profile to match those of new tissue formation, (3) adequate mechanical and physical properties to allow its placement in vivo, and (4) sufficient sustained strength to avoid the membrane collapse and perform their barrier function. GBR membranes are divided into two groups, nonresorbable and resorbable, according to their degradation characteristics.

**Indications.** The most popular application of GBR is in dehiscence and fenestration type defects with simultaneous implant placement (Figure 16).

**Figure 16.** A, GBR is an efficient technique in correcting the dehiscence bone defects around implants. B, Exposed threads of the fixtures are covered by bone materials and a membrane to promote the osteogenic cells to generate new bone according to the guided regeneration concept.

The exposed threads of implants may be covered by bone materials and a membrane to prevent migration of the epithelial and connective tissue cells to the surgical site. So the osteogenic cells have the opportunity to migrate into the defect site and promote new bone formation. The bony dehiscence after installation of fixtures can be treated successfully by using GBR technique [43].

The other indication for GBR is an atrophic ridge either before or during implant surgery. The important consideration in reconstruction of ridge atrophy is appropriate case selection. Based on a general guide it is suggested to perform GBR procedure in A1, A2 or B1 defects of Khojasteh et al. classification. Application of GBR technique in these defects is associated with high implant survival rates [8]. Studies on installation of implants simultaneously with GBR showed a survival rate of 92.2% in horizontal defects. Others have reported the success rate of implants after the GBR procedure (non-simultaneous implant placement) reported 100% success in horizontal defects. The mean bone augmentation in these defects was 3.31 mm [43].

**Advantages.** GBR allows for the re-growth of the bone and the tissue. GBR is a relatively easy and predictable method which can be used under local anesthesia for small defects. In large defects due to trauma or resection of tumors the combination of this technique with bone grafting is an appropriate procedure for bone augmentation [43.[

**Disadvantages.** As the procedure takes approximately six months to heal completely, the likelihood of failure is higher if the patient does not take appropriate care. Apart from this, the success is also defect specific as the chances of success may be smaller if the condi‐ tion is severe [44].

The patient can contribute to the success of the procedure by maintaining good plaque control, nonsmoking, anti-infective therapy, and systemic health maintenance.

#### **9.2. Cortical tenting (Osteogenic GBR)**

**Advantages.** The risk of damage to IAN during the installation of fixtures is reduced by retracting and repositioning the nerve. The surgeon is able to use a longer fixture which may engage the inferior cortex of the mandible. The fixtures have more stability due to their bicortical insertion. This procedure is performed simultaneously with implant fixture instal‐

**Disadvantages.** The risk of damage to the IAN is a prominent disadvantage of nerve trans‐ positioning; Traction on the nerve usually causes temporary sensory loss [40]. Mandibular fracture, implant loss, hemorrhage, and osteomyelitis are other possible complications in long implant installation, associated with the transposition and lateralization of the IAN [38, 41, 42].

The treatment and rehabilitation of edentulism with dental implants has become a routine treatment modality in contemporary dental practice. Nevertheless, tooth loss is frequently associated with subsequent bone loss, often resulting in inadequate bone dimensions for ideal dental implant placement. Alveolar ridge resorption in partially and totally edentulous patients may interfere with the safe and correct positioning and placement of implants. When ridge resorption occurs, bone augmentation is essential to guarantee adequate bone volume, to provide patients with proper inter-arch dimensions, and to insure a satisfactory aesthetic

Guided bone regeneration (GBR) is an important concept concerning restoration of deficient alveolar sites (e.g., an extraction site or deficient alveolar ridge) for implant placement. GBR uses an occlusive membrane interface between gingiva and the alveolar bone tissue to promote osteogenic tissue regeneration. The occlusive membrane acts as a barrier when placed into the surgical site, preventing connective and epithelial tissue migration into the defect. Progenitor cells located in the adjacent alveolar bone or blood are then able to recolonize the root area and

The strategy to isolate the bone defect with a material that will function as a physical barrier to avoid gingival cell invasion led to the development of GBR membranes. These membranes need to exhibit: (1) biocompatibility to allow integration with the host tissues without eliciting inflammatory responses, (2) proper degradation profile to match those of new tissue formation, (3) adequate mechanical and physical properties to allow its placement in vivo, and (4) sufficient sustained strength to avoid the membrane collapse and perform their barrier function. GBR membranes are divided into two groups, nonresorbable and resorbable,

**Indications.** The most popular application of GBR is in dehiscence and fenestration type

differentiate into a new osteogenic tissue with the formation of new bone.

lation with or without bone grafting.

530 A Textbook of Advanced Oral and Maxillofacial Surgery Volume 2

**9. Guided bone regeneration (GBR)**

according to their degradation characteristics.

defects with simultaneous implant placement (Figure 16).

result.

**9.1. Classic GBR**

A usual limitation in reconstruction of the oral and maxillofacial region is the resorption of bone grafts due to contraction of overlying soft tissue. Excessive bone grafting is not always the ideal technique to compensate for resorption. We are not able to harvest a large amount of graft in all cases. Sometimes the defect size is larger than the harvested bone graft. In some cases we prefer to harvest the bone graft from an intra-oral recipient site rather than an extraoral site because of its morbidity. The *cortical tenting technique* has been suggested as an alternative method.

Cortical tenting is a reconstruction method in which a block bone graft together with bone substitutes are used to augment the horizontal and vertical deficiencies [45]. The first step in this method is to harvest an appropriate block graft for the recipient site. There are several intraoral sites to harvest a block graft; however the ideal graft should be prepared after weighing the advantages and disadvantages. The lateral ramus of the mandible is a popular donor site and is used in most studies [46-48]. The cortical nature of this bone graft is the reason for its high resistance to resorption, although prolong neovascularization and the risk of damage to IAN are important disadvantages of this block graft [46, 49]. The other useful donor sites are maxillary tuberosity and chin. A retrospective study by Khojasteh et al. showed that the greatest vertical bone gain was in the defects where tuberosity was used as a block graft [46]. The simplicity of bone harvest and lower risk for nerve damage are other advantages of this donor site.

After preparing a block graft it must be adapted to the recipient site and fixed properly with a gap from the surface of the defect (Figure 17A). Then bone materials are used to fill the gaps (Figure 17B).

**Figure 17.** A, An anterior mandible defect after retracting the soft tissue flap. Lateral ramus bone block is harvested as a block graft and fixed with micro-screws with a gap from the buccal surface. B, The gap between the bone graft and alveolar bone is filled with bone materials. C, The defect has filled with new generated bone after 20 weeks.

The bone substitute could also be used to cover the bone block. With this technique we anticipate the bone resorption and prevent this complication by tenting the periosteum [50]. Then a membrane is used to cover the site. The soft tissue flap is sutured last (Figure 18).

**Indications.** This technique is most useful in horizontal defects of the anterior maxilla. After extracting the maxillary incisors a saucer-shaped defect may present in the premaxilla. This kind of defect could be properly corrected with the tenting technique [46, 50]. This method is also applicable in atrophic posterior mandibles [45]. Three-dimensional reconstruction with this technique is possible in atrophic ridges [51].

**Figure 18.** A, The defect of anterior maxilla is obvious after retracting the soft tissue flap. B, Lateral ramus bone block is harvested as a block graft and fixed with micro-screws. C, The surgical site is ready for implant surgery after 20 weeks. D, The deficiency is corrected and installation of the implant was performed without any problems.

**Advantages.** This technique decreases the patient's morbidity and is relatively simpler than other procedures. This procedure can be performed under local anesthesia. The bone partic‐ ulates in the tenting technique promote the vascularization in the graft and improve bone regeneration and remodeling [52.[

**Disadvantages.** The tenting technique is not suitable in most combined horizontal and vertical defects. This method is not suitable for large defects resulting from severe trauma or resection of pathologic lesions. Complications including hematoma and nerve damage due to bone harvesting from chin and lateral of mandibular ramus respectively are some other disadvan‐ tages of this procedure. Inflammation, infection, graft exposure, and graft failure are other complications mentioned in the literature [46].

#### **9.3. GBR in combination with onlay bone graft (OBG)**

graft in all cases. Sometimes the defect size is larger than the harvested bone graft. In some cases we prefer to harvest the bone graft from an intra-oral recipient site rather than an extraoral site because of its morbidity. The *cortical tenting technique* has been suggested as an

Cortical tenting is a reconstruction method in which a block bone graft together with bone substitutes are used to augment the horizontal and vertical deficiencies [45]. The first step in this method is to harvest an appropriate block graft for the recipient site. There are several intraoral sites to harvest a block graft; however the ideal graft should be prepared after weighing the advantages and disadvantages. The lateral ramus of the mandible is a popular donor site and is used in most studies [46-48]. The cortical nature of this bone graft is the reason for its high resistance to resorption, although prolong neovascularization and the risk of damage to IAN are important disadvantages of this block graft [46, 49]. The other useful donor sites are maxillary tuberosity and chin. A retrospective study by Khojasteh et al. showed that the greatest vertical bone gain was in the defects where tuberosity was used as a block graft [46]. The simplicity of bone harvest and lower risk for nerve damage are other advantages of

After preparing a block graft it must be adapted to the recipient site and fixed properly with a gap from the surface of the defect (Figure 17A). Then bone materials are used to fill the gaps

**Figure 17.** A, An anterior mandible defect after retracting the soft tissue flap. Lateral ramus bone block is harvested as a block graft and fixed with micro-screws with a gap from the buccal surface. B, The gap between the bone graft and

The bone substitute could also be used to cover the bone block. With this technique we anticipate the bone resorption and prevent this complication by tenting the periosteum [50]. Then a membrane is used to cover the site. The soft tissue flap is sutured last (Figure 18).

**Indications.** This technique is most useful in horizontal defects of the anterior maxilla. After extracting the maxillary incisors a saucer-shaped defect may present in the premaxilla. This kind of defect could be properly corrected with the tenting technique [46, 50]. This method is also applicable in atrophic posterior mandibles [45]. Three-dimensional reconstruction with

alveolar bone is filled with bone materials. C, The defect has filled with new generated bone after 20 weeks.

this technique is possible in atrophic ridges [51].

alternative method.

532 A Textbook of Advanced Oral and Maxillofacial Surgery Volume 2

this donor site.

(Figure 17B).

Reconstruction of combined defects with representation of both horizontal and vertical bone deficiencies requires specific consideration. Decision- making in rehabilitation of these kinds of defects involves the patient's preferences, defect size, and cost considerations [53].Combi‐ nation of GBR and OBG is an appropriate technique in reconstruction of small combined defects before implant surgery. By applying this procedure the surgeon is able to use longer and wider implants, increasing the surface area resulting in a higher survival rate. In this technique a block bone graft is harvested and fixed in the defect area usually for vertical augmentation followed by using classic GBR procedure to restore the remaining defects (Figure 19).

**Figure 19.** A, The atrophic ridge of posterior mandible is selected as the recipient site. B, Lateral ramus bone graft is harvested as an OBG. C, The OBG is fixed to augment the defect vertically. D, Bone materials are used to reconstruct the horizontal defect by GBR procedure. E, The surgical site is ready for insertion of implant fixtures.

Approximately after 6 months the surgical site is ready to install the implant fixtures. The average bone gain presented in the literature is 4.3 mm after performing this procedure [43].

**Indications.** This procedure is suitable for small to moderate defects in partial edentulous patients. This technique is usually indicated in combined defects to reconstruct horizontal and vertical defects. The common indication of this technique is in the anterior maxilla.

**Advantages.** This procedure can be performed under local anesthesia. This technique removes the need for harvesting extraoral bone grafts and reduces discomfort of the patient.

**Disadvantages.** This technique is not for large defects. The high failure rate of this technique in posterior of mandible is one of the major drawbacks of this technique [54].
