The standard of care regarding tooth loss replacement is evolving towards the use of dental implants. The practice of fixed bridges and partial prosthesis can be and are iatrogenic to the existing teeth and bone. Prosthetics in the restoration of partial and complete edentulous conditions with implants has become the most important determinant. Because of this principle the emphasis has focused on optimization of the alveolus to receive a root form implant. Dental implants are a viable treatment option when there is sufficient quantity and quality of bone to achieve the desired functional and esthetic results. The reduction in bone volume has many etiologies. The most common are a result of: Periodontal disease, pneumatization of the maxillary sinus, long term ill-fitting dentures, and the general progression of osteoporosis with aging. Initially, malposition or short implants were used in areas of deficient bone volume. This often resulted in compromised prosthetic design and poor long term treatment outcomes. Today’s treatment plans first consider the prosthesis options. This necessitates reconstruction and modifications of the pre-existing anatomy provide the ideal environment needed for optimal implant placement. The deformity is often a composite loss of both bone and soft tissue. The alveolar bone loss frequently occurs in a three dimensional pattern. Multiple options and techniques have been advocated for correction and reconstruction of the atrophied alveolar bones. They include the following: Guided bone regeneration (GBR), onlay bone grafting (OBG), interpositional bone grafting (IBG), distraction osteogenesis (DO), ridge- split (RS), and sinus augmentation techniques (SA). [1-3] The complexity of the defect dictates the selection of the appropriate technique. The reconstruction must also take into account the three dimensional spatial relation of one arch to the opposing arch.
2. Considerations for reconstruction
2.1. Bone density
The quality of bone in the jaws is dependent on location and position within the dental arches and alveolus respectively. The most dense bone is observed in the anterior mandible, followed by the anterior maxilla and posterior mandible. The least compact bone is typically found in the posterior maxilla. Misch classified these bone densities into a spectrum of four categories, ranging from D1 through D4. D1 bone primarily consists of a dense cortical structure. D4 on the other hand, is the softest, consisting primarily of cancellous bone with a fine trabecular pattern with minimal crestal cortical anatomy. The density of bone is an important quality in the initial stabilization of the implant and in the loading profile of the prosthesis. Literature review of clinical studies from 1981 to 2001 reveals that poor bone density may decrease implant loading survival rates. The decrease survival ranged from 16% to 40 %. The primary cause of these failures was directly attributed to the bone density, strength and a lower percentage of bone to implant contact. Bone in the posterior maxilla was found to be five to ten times weaker in comparison to bone in the anterior when compared to other bone densities. Lesser bone densities also influence stress pattern distribution. Stresses in “soft bone” demonstrate patterns which migrate further towards the apex. Bone loss is more pronounced and occurs along the implant body rather than crestally, as in denser bone. D4 bone exhibits the greatest difference in biomechanical modulus of elasticity when compared with titanium. Therefore, afterload results in higher strain conditions at the bone-implant interface accelerating bone resorption and implant failure (Fig. 1).
2.2. Bone graft materials and mechanism of bone regeneration
Various bone augmentation materials are used for alveolar reconstruction, they include: Autografts, allografts, alloplasts, and xenografts. Autogenous bone grafts can regenerate bone through all three mechanisms:
2.3. Types of bone grafts
Allogenic bone is principally osteoconductive, although, it may retain some osteoinductive capability. This quality is dependent upon how the material is processed. Urist in 1965 described the process of acid demineralization of bone before implantation by using hydrochloric acid. The organic bone matrix contains bone morphogenic proteins (BMPs). These proteins are responsible for the de novo bone formation. BMP is not acid soluble, however the calcium and phosphate salts of the HA can be removed from the bone in the acid- reducing process. This results in demineralization of the freeze-dried bone (FDB) and an increased exposure of the BMPs with its osteopromotive effect. FDB is primary osteoconductive while demineralized freeze dried bone (DFDB) is believed to be osteoinductive.  Results of studies performed using DFDB are conflicting. Controversy still exists about the osteopromotive effects of DFDB. Some reports raise the question of the concentration variability of BMPs in commercially available grafts. Osteoinductive properties of DFDB vary from one cadaver to another. The product fabrication may also have an effect on the osteoinductivity of the allograft where the demineralization process is very technique sensitive. For example, it has been shown that the osteoinductive properties of the grafts are removed, if the calcium content is less than 2% by weight. In addition, controversy persists about the use of ethylene oxide for sterilization of the graft materials and its possible destructive affects on the BMPs. Demineralized cortical bone was found to have higher concentrations of BMPs than trabecular bone. Membranous cortical bone exhibits greater concentration of BMPs than endochondral cortical bone, consequently; the skull and facial bone represent a better source of inductive proteins than the remaining appendicular skeleton.
Routine studies are performed to evaluate the safety of allografts. According to the American association of tissue banks the probability of DFDB to contain HIV virus is 1 in 2.8 billion. When compared with the risk of 1 in 450,000 for blood transfusions, the risk of infection from allografts seems infinitesimal. Rigorous background checks are performed on the donor and his/her family before the donor is accepted into the program. Occasionally biopsy specimens of sites containing allograft from human patients sometimes show chronic inflammatory cells. These histologic appearances of a non-specific inflammatory condition cannot be attributed to an immune reaction with certainty.6
A concern over the risk of disease transmission from cattle to humans through the bone graft material derived from bovine bone used for dental implants has been suggested. The recent incidents of
Another popular alternative xenograft is
|DFDB (Demineralized)||Pacific Tissue Bank|
|Collagen + Growth factors||Mainly Osteoinduction varies based upon processing method||+/- 6 months|
|Minerals + Collagen||Mainly Osteoconduction||1 Yr +|
|Deprotenized bovine bone mineral||Bio-Oss||Cancellous or cortical|
|Anorganic bovine HA+ cell binding peptide||PepGen P-15||Peptide + microporous HA|
|Osteograft N||Micro + Macroporous|
|Coral ( Ca carbonate)||Biocoral|
Interpore 200 (Coralline)
|β-tricalcium phosphate (β-TCP)||Methylmethacrylate (HTR synthetic bone)|
|Hydroxyapatite (HA), (Bone source, Norian)||Poly- α- hydroxy acids (PLA,PLGA)|
|Ca2So4 (Plaster of paris)|
|Calcium phosphate cements (Ceredex, α-BSM)|
|Bioactive glass ( PerioGlass, BioGran)|
2.4. Properties of graft materials
It is important to consider the physical and chemical properties of the graft materials used in the augmentation procedures.
Close matching of the resorption rate to the bone deposition rate is important. Selection of graft material should be based on location of graft site, soft tissue environment, and its possible role in promoting and supporting future implant osseous integration. A rapidly resorbing scaffold might reestablish a void filled with connective tissue, whereas one that resorb too slowly, or not at all, would impede bone deposition and limit creeping substitution. There are, however clinical indications in which resorption is not desired, but rather, a permanent implant is preferred, such as craniofacial onlays for cosmetic augmentation.
2.5. Bone growth factors
The term growth factors comprises a group of polypeptides of approximately 6-45 KD (kilo Dalton) which are involved in cellular proliferation, differentiation and morphogenesis of tissues and organs during embryogenesis, postnatal growth, and adulthood.  Factors that are involved in the regeneration and induction of bone tissue have attracted attention as they possibly can facilitate skeletal reconstruction. These factors include platelet derived growth factor (PDGF), vascular endothelial growth factor (VEGF), insulin like growth factors (IGF), transforming growth factor β (TGF β), bone morphogenic proteins (BMPs), and platelet rich plasma (PRP).
The apparent strong desire of clinicians for the use of growth factors to facilitate reconstructive surgical procedures by obviating the need for procurement of autogenous grafts is contrasted by their limited availability for clinical application. This has prompted the application of autogenous growth factors by using
|BMPs approved for clinical use and indications|
InductOs (CHMP approved)
Open tibia fracture, 2002
Interbony spinal fusion, 2005
INFUSE Bone Graft (FDA approved)
Interbony spinal fusion, 2002
Open tibia fracture, 2004
OP-1 Implant (FDA HDE & CHMP approved)
Recalcitrant long bone nonunions, 2001/2004
OP-1 Putty (FDA HDE approved)
Osteolateral (intertransverse) lumbar spinal fusion revision, 2004.
Bioactive proteins Gem 21S (Osteohealth), Periodontal defects
3. Treatment plan for bone augmentation
The treatment planning sequence for implant dentistry begins with the design of the final prosthesis. After the determination of the type of restoration, number and position of teeth to be restored and the patients force factors are then evaluated. The bone density in the region of the implant placement is then considered. The key implant positions and the number and ideal implant sizes are then selected. Finally the available bone volume is evaluated for implant placement according to the proposed treatment plan. Previous studies have shown that the most common cause of implant failures are stress-related failures especially after loading. Mechanical stress can have both positive and negative consequences for bone tissue and, thereby, also for maintaining osseointegration of oral implants. Dental implants function to transfer occlusal loads to the surrounding biological tissues. If occlusal loads are within the bone physiologic tolerance zone, osseointegration will be maintained. On the other hand, if occlusal loads are excessive and beyond the bone physiologic tolerance limit, bone will ultimately resorb and failure of osseointegration result. Thus, as a general rule the goal of treatment planning should be to minimize and evenly distribute the mechanical stress in the implant system and the surrounding bone.  The magnitude of stress depends on two variables which are: The
3.1. Rationale for bone augmentation
From the previous discussion sufficient amount of bone volume should be available to provide the optimum biomechanical foundation for implant placement. Sufficient bone volume will allow placement of wide diameter implants with sufficient length and number as needed by the treatment plan instead of using small sized, short implants that were only used because of insufficient bone volume compromising the treatment outcome. Adequate bone volume allows placement and alignment of implants with optimum axial inclination to receive occlusal forces in a more favorable axial direction. In addition to providing optimum bone volume, bone augmentation procedures offered a solution in the avoidance of injuring vital structures that were present as obstacles when considering implant therapy as a treatment option, such as close proximity to the inferior alveolar canal and the maxillary sinus. It is worth mentioning that proper selection of the implant design is of paramount importance in achieving long term success.  Some areas in the oral cavity require special considerations, like the poor density maxillary posterior edentulous area. Wide diameter, threaded implants with optimum length should be used to increase the bone to implant contact ratio and the surface area, allowing proper stress distribution at the bone implant interface. This can only be done in the presence of sufficient bone volume to accommodate the selected implants otherwise bone augmentation procedures are mandatory. When considering esthetics, sufficient bone volume is also necessary to achieve the desirable aesthetic outcome especially in the aesthetic (anterior) zone. The emergence profile is greatly dependant on the bone surrounding dental implants allowing optimum soft tissue drape around the abutments for ideal esthetic results. Also, the presence of sufficient bone volume allows flexibility in choosing the properly sized implant for better abutment emergence profile. 
4. Bone augmentation techniques
4.1. Socket preservation/ Guided bone regeneration
Physiologic bone resorption results in unpredictable loss of bone following teeth extraction. This can lead to less than ideal bone volume available for implant placement especially in prolonged cases of edentulism. Multiple types of grafting materials have been used to fill the extraction sockets immediately after extraction in order to maintain the space of the extraction site and prevent its collapse. This will allow for more organized bone healing maintaining the bone height and width necessary for implant placement. Following grafting the socket, barrier membranes are used to provide guided bone regeneration by protecting the underlying grafted site during healing from undesirable cellular population from the overlying soft tissues that might compromise the outcome (Figs. 5,6).
4.2. Block bone grafting technique
Block grafting approaches can be used to reconstruct significant deficiency in the vertical and horizontal dimensions of the alveolar ridge. Autogenous block grafting procedures remain the gold standard for ridge augmentation. However, donor site morbidity associated with graft harvest has turned the attention to using allogenic grafting materials. The locations for harvesting intraoral block grafts include the external oblique ridge of the posterior mandible (ramus), symphysis. With bone defects >2 cm, an extraoral donor site is warranted for harvesting larger bone volumes. The iliac crest (anterior and posterior), cranium, or tibia is often used as extraoral harvest sites. The detailed description of the harvesting techniques is beyond the scope of this chapter. Case reports have demonstrated success with FDBA and DFDBA block graft material. However, further research is warranted to evaluate the healing of these blocks histologically (Figs. 7-12).
4.3. Ridge expansion (split) technique
With a narrow ridge, splitting the alveolar bone longitudinally, using chisels, osteotomes, or peizosurgical devices, can be performed to increase the horizontal ridge with, provided the facial and lingual plates are not fused and some intervening bone is present. With adequate stability of the mobile segment, sufficient interpositional grafting and soft tissue protection, comparable results to alternate techniques can be obtained. The decision to place the implants simultaneously with the split procedure or delayed placement following bone healing depend on the degree of stability of the expanded segment and the volume of remaining bone (Figs. 13-17).
4.4. Sinus augmentation
The most commonly used technique use to access the maxillary sinus is the lateral window technique modifying the Caldwell-Luc operation, also called the hinge osteotomy technique, originally described by Tatum then first published by Boyne and James.
A window is then created using a round bur on the lateral wall of the sinus till the bluish hue of the sinus membrane reveals itself. Using specially designed sinus elevation curettes the sinus membrane is elevated from the bony floor and is freed anteriorly, posteriorly and medially to create a tension free elevation to minimize the possibility of perforation. The trap door (window) is intruded medially forming the new sinus floor and the space created below it is then grafted to provide the platform for implant placement. The flap is then repositioned and closed. Implants are placed either simultaneously with the graft (one- stage) or after a delayed period of up to 8 months to allow for graft maturation (two- stage). The decision about the two options mainly depends on the preexisting residual amount of bone required for initial primary stability of an implant. It was found that if the bone thickness is 4 mm or less, initial implant stability would be jeopardized. In 1994, Summers published a new less invasive conservative technique for sinus floor elevation using osteotomes in an attempt to overcome the drawbacks of the lateral window approach. The technique begins with a crestal incision to expose the alveolar ridge. An osteotome of the smallest size is then tapped into place by a mallet into the bone just shy from the sinus membrane fracturing and moving the sinus floor superiorly. Osteotomes of increasing sizes are introduced sequentially to expand the alveolus and with each insertion of a larger osteotome, bone is compressed, pushed laterally and apically. Summers stated that the very nature of this technique improved the bone density of the posterior maxilla. Bone graft material is then introduced via the osteotomy followed by implant fixture insertion. The implant fixture should be slightly larger in diameter than the osteotomy site “tenting” the elevated maxillary sinus membrane. A minimally invasive antral membrane balloon elevation (MIAMBE) which is a modification of the osteotome technique has also been introduced with satisfactory results. It comprises the introduction of a balloon into the osteotomy site which is then slowly inflated to elevate the sinus membrane. This procedure showed predictable results and required a short learning curve. Recently, some authors have reported the use of a piezoelectric device in maxillary sinus surgery. Ultrasound has been increasingly used in many fields of medicine such as tumor enucleation, fragmentation of renal calculi and lithotripsy of gall bladder stones. Ultrasonic dissection has been classified as tissue-selective technique that might improve the efficiency of dissections and at the same time reduces the morbidity rate resulting from iatrogenic injuries. In addition, ultrasound energy can induce a cavitational effect in water containing tissues, which can in turn facilitate the tissue separation (Figs. 18,19).
4.5. Distraction osteogenesis
Distraction Osteogenesis (DO) uses the phenomenon that new bone fills in the gap defect created when two pieces of bone are slowly separated under tension. Distraction of the segment can be achieved in a vertical and /or horizontal direction on the basic principles involved in distraction which include a latency period of 7 days for initial soft callus formation, a distraction phase during which the 2 segments of bone undergo incremental gradual separation at a rate ~ 1 mm per day to stretch the formed soft callus, and a consolidation phase that allows healing of the regenerated bone between the 2 segments. The prerequisites for optimal bone augmentation of defects using DO are minimum of 6-7 mm of bone height above vital structures, such as neurovascular bundles or air passages/sinus cavities, a vertical ridge defect of > 3 -4 mm, and an edentulous span of three or more missing teeth (Figs. 20,21).
4.6. Tent- Pole technique
Marx et al in 2002 advanced the approach of soft tissue matrix expansion using corticocancellous bone grafting with dental implants to treat severely resorbed mandibles that were shorter than 6 mm. Using this transcutaneous submental approach, 4 to 6 dental implants were placed to act as “tent poles” to maintain the height of the overlying mucosal soft tissue and prevent it from sagging around the iliac crest graft (Figs. 22, 23). 
4.7. Bone ring technique
Three dimensional bone augmentations with immediate dental implant placement can be done using this technique. Using trephine burs corresponding to the extraction socket diameters, bone rings can be harvested from the chin or iliac crest regions. The harvested rings can then be secured to the extraction socket using the dental implants restoring the deficient bone at the crestal portion in a 3D fashion (Figs. 24,25). 
4.8. Reconstruction of segmental bony defects
Ablative loss of both bone and associated soft tissue from treatment of neoplastic or other pathologic processes represent a far different task from loss of bone from physiologic resorption, trauma or infection. The goals of reconstruction are to restore jaw continuity, provide morphology and position of the bone in relation to its opposing jaw, provide adequate height and width of bone, and provide facial contour and support for soft tissue structures.
Graft malpositioning result in occlusal problems and presents a formidable task to the restorative dentist. The site of the graft harvest depends mainly on the size of the residual defect (Figs. 26-28).
4.9. Combination grafts
In large defects, the use of grafting materials from different sources can be beneficial. Some techniques aim to combine the osteogenic potential of autogenous bone with the osteoconductive and space maintaining properties provided by the allogenic or alloplastic sources. Allogenic materials can provide constructs that are close in morphology as the resected part providing superior esthetic outcome following the grafting procedure (Fig. 29,30).
4.10. Future augmentation approaches
Future bone augmentation approaches likely will use molecular, cellular, and genetic tissue engineering technologies. Gene therapy is a relatively new therapeutic modality based on the potential for delivery of altered genetic material to the cell. Localized gene therapy can be used to increase the concentration of desired growth or differentiation factors to enhance the regenerative response. Cellular tissue engineering strategies that include the in vitro amplification of osteoprogenitor cells grown within three dimensional constructs is currently of particular interest. The use of mesenchymal stem cell for construct seeding showed promise for bone regeneration. These approaches may lead to further refinement and improvement in alveolar bone augmentation techniques.
5. Surgical caveats for bone grafting
There are several factors that may improve the success and predictability of bone graft procedures, they include the following:
5.1. Surgical asepsis and absence of infection
Contamination of bone grafts due to endogenous bacteria, lack of aseptic surgical technique, inadequate soft tissue closure and salivary exposure may lead to infection with subsequent lowering of the pH. Solution –mediated resorption will follow with resultant graft loss. Some clinicians prefer including antibiotics locally within the graft materials to guard against bacterial contamination as no blood supply is present early in the graft. Primary soft tissue closure is also mandatory for the success of the grafting procedure. It allows healing by primary intension protecting the graft from any surrounding contamination until healing. Dehiscence with graft loss is one of the most common complications in bone grafting procedures. Therefore, careful surgical flap planning which ensures adequate blood supply to the site with minimal trauma and primary soft tissue closure without tension are required.
5.2. Space maintenance
Creation of a desired contoured space for bone formation is very important in the grafting procedure. If the graft material resorbs too rapidly compared with the time required for bone formation, the site may fill with connective tissue rather than bone. Therefore, the space must be maintained long enough without collapse for bone to fill the desired area. Titanium-reinforced barrier membranes, tent screws elevated above the bone at the desired height covered by a membrane, block grafts (covered by membrane or not) are all used to create and maintain space for bone growth.
5.3. Graft stability
For predictable bone augmentation, graft stability is a paramount. Bone remodeling and graft healing requires rigid interface for blood clot adhesion with its associated growth factors. If a graft become mobile its vascularity will be compromised followed by fibrous encapsulation and often sequestrate. If block grafts are used fixation can be achieved using titanium screws or the graft can be fixed using the inserted implants itself. If particulate graft is used, it can be covered with a barrier membrane fixed with membrane tacks to avoid dislodgement of the graft particles.
5.4. Regional acceleratory phenomenon (RAP)
The host site during bone augmentation procedures should be decorticated to establish bleeding points in the cortical bone prior to graft placement. This procedure will provide access for trabecular bone vessels, encourage revascularization, bring growth factors to the graft site and increase the availability of osteogenic cells promoting graft union and shorten the healing time.