The treatment planning process must start with a reasonable assessment of the extent of the bony deficiency and the capacity of a regenerative procedure to create adequate support for implants in their ideal positions for comfort, aesthetics, function, and support. As the extent of bone regeneration is evaluated, care must be taken from the beginning stages to identify the expected positions of each restoration or prosthesis using accurate restorative wax-ups. Evaluation of the relationship between the required restorative positions and the bony deficiency will then provide insight into the volume and shape of the bone that will need to be generated. At this stage, the most predictable surgical approach and bone graft material (e.g., autograft, allograft, xenograft) is selected to ensure adequate bone support can be developed for ideal implant placement.
In site assessment treatment planning, complications often result when the clinician fails to understand the relationship between the limitations of various regenerative grafting techniques and the predictable development of the required bone contours and bone volume needed for overall restorative success. It is not possible to treat every defect with simple or limited techniques because this discipline requires a variety of approaches to meet the reality of advanced bone resorption. When the incorrect technique is utilized, inadequate bone volume will be regenerated, leading to either compromised restorative results or a potential failure of the prosthesis. These problems not only compromise the local grafting site, but they can also destroy bone around surrounding teeth, creating a worse situation than was originally encountered.
In an ideal setting, prevention starts with total awareness of ridge preservation and limiting bone loss before major ridge defects occur. This starts with atraumatic extraction techniques, aggressive socket grafting, and communication with the whole implant team in respect to the need for timely preservation of the ridge. The longer the patient remains without an implant in an extraction site, the greater the chance that adjunctive grafting procedures will be necessary. For patients with long-term edentulism, the surgeon needs to be fully aware of the mechanisms of bone resorption to understand the current underlying bony architecture and to correctly choose a grafting protocol that will build the correct volume for the intended prosthesis. A working knowledge of ridge resorption and expertise in the use of effective diagnostic imaging to accurately assess bone volumes gives the clinician the opportunity to correctly organize a reasonable and predictable implant treatment plan (Fig. 12.2).
Failure to Understand the Need for Bone Grafting
Success in any implant prosthesis requires the implants to be placed in positions that provide ideal aesthetics, function, comfort, and support. To be successful in the development of a favorable prosthesis, the number and positions for implants in an edentulous space must be determined with a careful analysis of the relationship between the restorative prosthesis and the forces that will be exerted on the final prosthesis. This is then associated with the functional and esthetic aspects of the case, ultimately dictating the relationship between the implants, bone, and opposing forces. All of these factors must be considered in planning support for a prosthesis that functions well while maintaining the bone volume around its implant abutments. Clinicians too often try to bypass the grafting process, either to save time or because they are not experienced in advanced grafting techniques. Insufficient bone in recipient sites leads to placement of implants with inadequate diameters, short lengths, or in insufficient numbers. Compromises like these eventually lead to significant damage around an implant and the prosthesis it supports. Due to the fact that resorption occurs in every edentulous site, the need for adjunctive bone grafting is very common and is often vital for a successful outcome (Fig. 12.3).
Failure to recognize the need for bone grafting leads to numerous treatment issues, ranging from esthetic complications to implant and prosthetic failure. Placing implants of suboptimal sizes or in less than ideal numbers to bypass the grafting process is a compromise that often leads to force-related failures of implant components, the prostheses itself, or accompanied bone loss. Ultimately, prosthetic and implant morbidities may result.
A multidisciplinary approach should be taken to assess the optimal prosthetic solution for the patient, based on the patient’s wishes, available bone, and other factors. When the prosthetic plan has been established, the clinician should begin planning the implant positions required to execute the prosthetic option. Once the sites for implants have been determined, the associated sites are evaluated for foundational support in the required positions. If inadequate bone is available to successfully place an implant in a key location for the prosthesis, grafting should then be included in the treatment plan to build the appropriate bone volumes.
Underestimation of Bone Required for Grafting of the Defect
One of the most difficult components of bone augmentation treatment planning is learning how to predict the amount of bone that will actually be required to develop the proper foundational support that the restorative treatment plan requires. Evaluation of the clinical situation, review of two-dimensional radiographs, assessment of models with restorative wax-ups, and information from cone beam computed tomography (CBCT) imaging all play a role in determining where bone will be required and how much bone will be needed to successfully graft the site. This is important when autogenous bone is incorporated into the regenerative process, and failure to clearly consider the difficulty of this bone harvest can lead to an eventual shortfall in the graft’s success.
In cases where the implant clinician fails to properly develop adequate bone volumes for grafting and implant positioning, reflection of tissue over the grafted site will reveal inadequate bony support for the intended implant size and position. At this time, critical decisions must be made to prevent the chance of compromising the overall case success due to this shortfall. The best solution is to stop and regraft the site, but this causes inconvenience for the patient, embarrassment for the surgeon, and an overall increase in the treatment time and expense. The alternative is to ignore the deficiency, placing the implant in a deficient site that ultimately limits the implant size or forces improper placement of the implant in an alternative position. Successful restorative cases require discipline and cutting corners leads to disappointed patients.
The use of CBCT imaging along with proper diagnostic casts allow the clinician to implement a proper prosthetic plan. The restorative wax-up can easily be interlaced into the CT imaging software for assessment of the bone volumes needed for proper implant support in key positions. Once the dimensions and volume of the graft have been determined, proper application of bone grafting techniques and materials is necessary to ensure that the intended volume can be achieved. At this point, the patient should be educated on the details of the regenerative procedures and a timeline of treatment. Advanced grafting procedures delay completion of the final prosthesis, and patients should be aware of the extent of the inconvenience that will need to be tolerated during this surgical sequence. Sites for autogenous grafts should also be evaluated to ensure there is adequate donor bone available to produce the bone foundation needed to execute the treatment plan (Figs. 12.4 and 12.5).
Failure to Evaluate the Tissue Biotype in Treatment Planning
Patient-to-patient comparisons of the soft tissue drape surrounding the natural teeth often demonstrate significant differences in color, surface consistency, tissue thickness, and overall aesthetics. This is emphasized when a very thin and friable tissue drape surrounds an anterior tooth. Differentiation of patients into either a “thick biotype” or a “thin biotype” is a critical tool that can be used during anterior implant–related treatment planning. Cook and Mealey demonstrated the most simple way to determine tissue biotype is through the visibility of a periodontal probe in the sulcus of an anterior tooth. A patient with a thick biotype will not show any translucence of the probe through the sulcular tissue. In contrast, a thin biotype will allow visualization of the coloration of a probe through the sulcular tissue. A patient with a thick biotype has tissue with a robust pink, stippled appearance. This dense tissue drape forms a thick layer of tissue that is very forgiving when dental restorations are placed around natural teeth and when dental implants are involved. The thin biotype patient, however, presents a much more difficult challenge. These patients have a thinner labial plate thickness, a narrower keratinized tissue width, a greater distance from the CEJ to the initial alveolar crest, and there is visibility of a periodontal probe through the sulcus. As teeth migrate out of position or rotate in the arch, the prominence of the roots can increase, complicating the soft tissue situation even more. Thin layers of tissue around the maxillary anterior teeth require meticulous planning to hide underlying crown margins. In the case of implants, problems related to the translucence of the dark hue of the implant body and the abutment can significantly complicate the aesthetics surrounding the final restoration (Fig. 12.6).58
When there is no consideration of the biotype of a patient, esthetic complications can occur, especially in the anterior regions. Thin biotype patients tend to be more prone to recession, and thin tissue may result in a bluish-gray hue at the gumline of the implant restored tooth. If recession or slight bone loss occurs, the facial aspect of the implant can be exposed, leaving a similar dark hue to the overlying tissue and the patient with a poor esthetic and embarrassing presentation.
When a clinician is aware of tissue biotype, it is possible to plan ahead procedurally to maintain or possibly change the biotype, leading to optimal esthetic outcomes. Patients with a very thin biotype can be evaluated for intra-operative supplementation using connective tissue grafts and facial bone grafts to create a more forgiving tissue drape over the implant site. As thicker cortical bone volumes promote thicker biotypes, the bony architecture and soft tissue drape may be modified in an esthetic zone prior to implant placement and restoration. Advance planning also provides the implant team an opportunity to inform the patient about these issues and to point out potential esthetic complications prior to commencing treatment. A patient’s expectations must be addressed, especially if they are not interested in grafting to modify the tissue type (Fig. 12.7).
Correction of thin biotypes requires tissue augmentation to create a thick, dense layer of fibrous tissue over the implant body and any deficiencies involving the adjacent natural teeth. Connective grafting procedures are readily available to increase the thickness of the tissue drape in situations like this. Subepithelial connective grafting procedures may utilize either palatal connective tissue or acellular dermal matrix (i.e., AlloDerm [BioHorizons IPH, Inc.]) as the source of donor tissue. The thick layer of connective tissue is inserted into the deficient regions with tunneling procedures, allowing the repositioned tissue flap to provide the blood supply to the developing graft site. The use of the subepithelial approach allows the implant clinician to produce a final tissue tone and color that matches the adjacent natural tissue. Earlier applications of “free tissue grafting procedures” utilized the epithelial layer of the palate as the donor site. This usually creates zones of thicker keratinized tissue with a distinctly white color that is not acceptable from an aesthetic standpoint when utilized in the anterior maxilla. Most anterior treatment plans today also incorporate the addition of layers of allograft or bovine graft particles with membrane coverage to limit excessive bone remodeling in these critical regions. These concepts are critical in “immediate implant” cases where many cases require both soft tissue and hard tissue supplementation (Fig. 12.8).
Procedural Technique Complications
Successful ridge augmentation requires consistent development of bony foundational support that allows the restorative prosthesis to be placed in an ideal position for proper aesthetic and functional success. As the regenerative technique is chosen, grafting materials and isolation techniques must be clearly understood from the surgeon’s standpoint to prevent inadequate graft development or unpredictable stability of the graft site as the prosthesis is loaded and maintained. The current approaches to ridge augmentation consist of a variety of techniques including guided bone regeneration (GBR), onlay block grafting, ridge splitting, distraction osteogenesis, or a combination of these techniques.5,6,8,9 GBR with autogenous bone, bone harvested from the same individual, is considered by some to be the gold standard for alveolar ridge augmentation.10 The use of allografts requires timely substitution of these primarily osteoconductive particles with vital bone, and the consistency of the resulting ridge must be dense enough to withstand the forces generated during the preparation of the osteotomy and insertion of the implant. Incorporation of osteoinductive graft materials into the procedure promotes the development of strong bony ridges, and the overall substitution process can be shortened. Autogenous bone provides the most active osteoinductive properties, as does the use of bone morphogenic protein (BMP) and other growth factors.55
A clinician who is not well versed in the limitations of the variety of graft materials may fall into the trap of a “one size fits all” approach to treatment. When significant defects require large volumes of bone, autogenous grafting may also be necessary. Allograft procedures are often used to spare the patient potential discomfort related to a secondary donor site. However, allograft in some cases will not develop a sufficient volume of bone to allow ideal implant placement and an aesthetic restoration. Complications usually arise when a graft is placed using a technique or with materials unsuited for the demands of the bone defect. Poor results eventually lead to increased treatment times, a loss of patient confidence in the surgeon and increased treatment costs.
The prevention of potential graft failures and poor augmentation volumes starts with a clear understanding of the anatomical, restorative, and aesthetic requirements for this specific defect. These factors must be matched to the best utilization of available grafting materials, membrane choices, techniques for space maintenance, and site protection. An effective bone regenerative material that has been matched with a predictable membrane creates the foundation for the rest of the restorative treatment plan.
The ideal GBR membrane is a biocompatible material capable of excluding epithelium without eliciting an immune reaction that might interfere with bone regeneration. Membranes are typically classified as resorbable or nonresorbable. Nonresorbable membranes include titanium foils, expanded polytetrafluoroethylene (e-PTFE) and dense polytetrafluoroethylene (d-PTFE) with or without titanium reinforcement. Studies of GBR procedures utilizing titanium-reinforced nonresorbable membranes have shown great success with horizontal and vertical alveolar ridge augmentation because of their ability to maintain space, minimize graft mobility, and exclude epithelium.11–21 Disadvantages of nonresorbable membranes include the need for reentry procedures for membrane removal and frequent postoperative infections that may follow premature membrane exposure.20,22 Various studies have shown premature membrane exposures typically result in increased morbidity and decreased bone regeneration in GBR procedures. Recent reports of d-PTFE use have demonstrated that membrane exposure does not always dictate failure of the developing graft. If the d-PTFE membrane can be maintained for at least 6 weeks, removal at that time or later will often be followed with development of a reasonable bony ridge. This is different than earlier cases, where e-PTFE membranes allowed bacterial invasion of the entire graft site through the larger pore sizes found in the e-PTFE membranes. The smaller pore size in the d-PTFE membrane prevents direct passage of bacteria through the membrane. Subsequently altered bone development may tend to be limited to the surrounding margins where the membrane was exposed (Fig. 12.9).22,54
In order to overcome these limitations, resorbable membranes have become a popular alternative because they are biodegradable and are less likely to become infected in the event of an exposure.23–26 Resorbable membranes are typically made of polyesters (e.g., polyglycolic acid [PGA], polylactic acid [PLA]) or tissue-derived collagens (e.g., AlloDerm GBR, Ossix Plus). AlloDerm is an acellular dermal matrix originally developed in 1994 to be used as a skin allograft for burn patients.27 It has been used in the medical and dental literature as an allograft for various procedures because of its ability to rapidly vascularize and to increase soft tissue thickness. In the dental literature, AlloDerm has been successfully used for root coverage, thickening of soft tissues, and guided bone regeneration.24,28–30 AlloDerm GBR is a thinner version (thickness ranges from 0.5–0.9 mm) of the original AlloDerm product (thickness ranges from 0.9–1.6 mm), specifically designed for GBR. AlloDerm GBR has been successfully used as a barrier membrane and has also been shown to significantly increase soft tissue thickness by 45% and 73% from baseline at 6 months and 9 months, respectively (baseline 0.55 ± 0.16 mm to 0.80 ± 0.26 mm at 6 months and 0.95 ± 0.28 mm at 9 months; p < 0.0033), when used as a barrier membrane for GBR of horizontal alveolar ridge deficiencies.29
Aside from soft tissue exclusion and clot stability, space maintenance is key to the success of GBR and can be accomplished in various ways using titanium-reinforced membranes, titanium mesh, particulate graft material, block grafts, dental implants, or tenting screws/pins.5,31,11,12,32–35 Nonresorbable5,19,34–37 and resorbable tenting screws38 have been used to aid in space maintenance in various horizontal and vertical ridge augmentation studies. The tenting screws are typically used as “tent poles” to support the membrane, decrease graft mobility, and relieve external pressure on the graft55 (Fig. 12.10).
Types of Bone Grafting Material
Autogenous bone is still considered by many to be the gold standard graft material for GBR because of its osteogenic, osteoinductive, and osteoconductive properties.6,10,39Autogenous bone is commonly harvested intraorally from the ramus and symphysis, but is associated with increased morbidity related to a second surgical site, unpredictable graft resorption, and graft mobility.5,10,13,40–44 The anatomy of the posterior edentulous ridge can limit the shape and volume of donor bone available for harvesting autogenous blocks.44 Many times the autogenous block and recipient site require such extensive preparation in order to obtain intimate contact between the graft and recipient site that a large percentage of the harvested bone cannot be utilized.43 Some clinicians have advocated crushing the autogenous block graft into a particulate autogenous graft to allow for more conservative recipient site preparation, complete utilization of the harvested bone, and a decreased volume of bone that will need to be harvested, thereby decreasing the morbidity of the procedure (Fig. 12.11).17,45
In order to overcome the limitations related to the availability of autogenous bone volume, various bone substitutes, including xenografts (material harvested from another species), alloplasts (inert synthetic material), and allografts (material harvested from another individual of the same species), are being used as adjuncts for GBR with successful clinical and histologic outcomes.6,8,13 Some clinicians have advocated combining autogenous bone with the various bone substitutes.16,23,45,46 The potential benefits of adding particulate autogenous bone to an allograft are the addition of osteogenic and osteoinductive growth factors to the osteoconductive properties of a bone substitute. The use of this combination allows for a reduction in the amount of autogenous bone harvested, decreasing the morbidity and postoperative discomfort for the patient.
Xenografts are graft materials that are taken from a donor of one species and grafted into a recipient of another species. This type of graft material heals via osteoconduction. Simian et al found that the addition of deproteinized bovine bone mineral (Bio-Oss) to autogenous particulate resulted in greater vertical augmentation than particulate autogenous material alone. Urban has combined bovine particles with autogenous bone in the development of large volumes of vertical and horizontal bone in severely compromised regeneration sites. The incorporation of the bovine product is planned for extended support of the graft volume, following with a timely turnover into vital bone as the graft matures (Fig. 12.12).16,47
The use of alloplasts is not currently recommended for major ridge augmentation. Successful grafting requires that the source of the grafting particles be readily available for consistent replacement with vital bony cells. Alloplastic approaches tend to leave a very granular ridge form that tends to fall apart as the osteotomy is prepared and the implant is inserted. Approaches have been utilized where alloplasts were added to FDBA (freeze dried bone allograft) or DFDBA (demineralized freeze dried bone allograft), but overall, the use of alloplasts is not recommended when significant regeneration is required.55
Incorrect Choice of Regenerative Technique in Respect to the Severity of the Defect
The literature today provides a multitude of surgical approaches that are available for regeneration of deficient implant sites. These would typically include particulate grafts, BMP graft combinations, block grafts, and the use of ridge-splitting techniques. The implant team must carefully consider each clinical situation to determine which technique will most predictably develop the needed bony support for the restorative treatment plan. In this assessment, the anatomy of the defect will often lead to the choice of a particular approach due to the ease of graft placement or the limitations of using a rigid graft in a highly irregular recipient site. Recipient sites with a very irregular surface are preferably approached with a particulate approach, and cortical blocks are best utilized where a smooth bed can be prepared for close adaptation of the block to the underlying defect.
The depth of the vestibule is a significant factor when evaluating defects. The use of an autogenous block is much easier when the vestibule is very deep and there is adequate room for adaptation of the entire length of the cortical graft. Placement of a block in a shallow defect can sometimes be difficult because of anatomic limits that will force graft placement higher above the ridge than the bone on the adjacent natural tooth. This can result in incision line opening, graft exposure, and a compromised healing process (Fig. 12.13).
If a particulate graft is utilized, lateral support of the graft will need to be incorporated into the procedure to provide and maintain space for the regenerative process to be completed. This same spacial support and protection prevents the graft particles from slipping laterally during the healing process (Fig. 12.14).
The use of a “ridge splitting” approach should only be considered when the apical region of the site is thick enough to allow expansion of the cortical wall laterally without fracturing the expanded cortical plate at the most inferior point of the split. This is particularly relevant in the maxillary anterior region where the thin width at the base of the site is often not substantial enough for a predictable split. Care must be taken to ensure the ridge split and graft will allow enough width for an implant with the required diameter. Ridge splits in a maxillary anterior region that is shaped with a proclined angulation can often lead to the placement of an implant with a severely angled emergence profile. This emergence angle then requires the use of an angled abutment to compensate for the malpositioning. Cases like this are better suited for use of an augmentation approach that thickens the ridge in both the coronal and apical regions. The additional apical augmentation developed in these techniques will create a better emergence profile for the implant and the restoration, leading to better patient satisfaction (Fig. 12.15).
Failure to choose the proper regenerative approach will often result in a poor postoperative ridge form that will not be amenable to an ideal implant placement and an acceptable emergence profile. Choice of the incorrect technique may lead to a graft that is susceptible to complications related to continuous isolation and stabilization of the graft during the entire healing process. These problems usually stem from issues related to strain on the incision line, movement of the temporary prosthesis, migration of the graft materials, or overzealous attempts to over-grow bone.
The implant clinician must develop a familiarity with the indications for each of the different types of grafting procedures, and incorporating that knowledge into a working treatment plan. With the aid of 3-D imaging, the clinician can complete a comprehensive evaluation of the extent of the bony defect. A treatment plan must then be developed, taking into consideration the overall size of the defect, the ability of the recipient site’s tissue to be expanded, and the presence of a temporary prosthesis, and the overall size of the defect. Included in this strategy would be the choice of possible donor sites, graft materials, suture type and technique, and the space maintenance method (Figs. 12.16 to 12.18).
Incision design is one of the keys to a predictable regenerative result. Ideal incision designs provide complete access to the surgical site without compromising the integrity of the surrounding tissue. As the incision is planned, the anatomy of the adjacent papilla must be considered to prevent any damage that will compromise the aesthetics and function of the tissue postoperatively. The patient’s biotype and the amount of keratinized tissue is always reviewed, and any deficiencies of attached tissue must be accounted for in the incision design. The incision must be planned in a way that keeps incision lines away from critical regions where graft particles or blocks could become exposed. Observation of sound surgical principles in preparation of incisions is critical for maintenance of the blood supply to all of the involved tissues. Wide-based incisions are always important to prevent interruptions in the vascular supply to the flap.
Failure to properly plan the incision design of a flap during grafting can pose numerous issues, chiefly related to incision line opening postoperatively. Incision line opening exposes the regeneration site to an influx of oral pathogens, soft tissue ingrowth, and loss of the graft materials that were intended to be isolated during the maturation process. Failure to preserve the integrity of the papilla during incision line design eventually leads to compromised aesthetics around the final restoration. An initial incision without a consistent depth may create a split-thickness flap, leading to tissue shredding and the involvement of vital structures located within the flap. Incisions through zones with limited keratinized support can leave large expanses of mucosa along the incision line. Thin mucosa is very difficult to predictably suture to the adjacent flap, often leading to an open incision days later. Lastly, failure to make broad-based releasing incisions may compromise the blood supply to the flap, causing tissue ischemia.
The coronal incision is usually placed on the crest of the ridge, favoring a location closer to the palatal aspect if possible. In regions where the keratinized tissue is limited, the incision should at least “split” the distance between the two edges of the keratinized tissue. It is always best to try to keep incision lines away from areas that are key to regenerative volume and protection. When possible, the papillae should be preserved. If there is a good papilla present, the incision should be designed to avoid involvement of the papilla or it should be moved to the adjacent interproximal space. If the papilla is absent or is flat, the incision can be directly adjacent to the root approximating the graft or it can be moved to the adjacent space. Moving the releasing incision to the adjacent interproximal space also moves the incision line away from the grafting site, limiting complications if the wound opens up postoperatively. Extending to the adjacent interproximal space can sometimes lead to difficulty in advancement of a tension free flap over the graft site, but this can be released with additional steps.
The releasing incision should always be prepared with a wider base than its coronal width to preserve the apical blood supply to the flap. As the flap is reflected, it is critical that the complete periosteal layer be reflected with the flap, avoiding maceration of the tissue during the releasing process. Attention to the thickness of the flap and careful use of the scalpel and instruments is important at this stage. By keeping instruments firmly against bone during the flap-releasing process, the clinician ensures a proper full-thickness flap release.
Incision lines should be prepared with vertical releasing incisions that are several millimeters away from the lateral border of the graft site. When an incision line opens around a graft site, the open region can directly contaminate the underlying graft particles, preventing proper regeneration of the bony defect. By moving the incision away from the critical regeneration site, the possibility of this type of contamination can be limited to some degree (Figs. 12.19 to 12.22).
Torn Lingual Flap
The tissue thickness on the lingual aspect of the mandible is very thin and friable. This tissue can be easily torn during reflection of the flap and manipulation of the tissue during the grafting procedures. Resultant “buttonhole” openings may compromise the blood supply to the surrounding tissue that is needed for coverage over the graft site, leading to compromised results postoperatively.
Tearing or buttonholing the lingual flap leads to exposure of the graft site and the possibility of margin necrosis coronal to the tear. This exposure may lead to total graft failure (Fig. 12.23).
If the lingual flap is torn during the procedure it can sometimes be repaired using 5-0 chromic suture, approximating the edges of the tear and preventing tension on the weak site. It is recommended to use a collagen membrane below these fenestrations to assist with healing and to isolate the graft materials. Maintenance of the blood supply to the tissue flap is important; thus tension should be minimized to the flap.
Preparation of the initial incision line must be extended completely through the tissue and through the periosteum. At the time of the initial separation of the flap margin from the bone, care must be taken to obtain a clean release of the complete flap margin from the bone. Shredding the flap margin at this time leads to poor control during the rest of the flap release and ultimately to increased chances of tearing the partial-thickness flap. Curettes or retractors must be utilized to create an even release and reflection of the full flap throughout this process.
Difficulty Releasing the Flap for Tension-Free Closure
Successful augmentation procedures require maintenance of an intact tissue closure along the incision line during the healing process. One of the most common surgical complications that a clinician will experience early in their learning curve is incision line opening. The failure of maintaining this union is directly related to an inadequate release of all tension on the tissue flap as it is stretched over the widened graft space. Clinicians will find that it is impossible to pull a tissue flap over any sizeable graft site without first altering the integrity of the flap itself. Examination of the exposed inner surface of a reflected flap reveals a smooth shiny layer called the periosteum. The periosteum is comprised of a thin firm layer of dense tissue that has no elastic fibers. This binding layer limits any significant elongation of the flap as it is stretched over a graft site. A simple incision through this dense tissue “releases” this tight band of pressure on the underlying tissue flap. The tissue directly below the periosteum is primarily comprised of elastic-type fibers, and once the periosteum has been released, the entire flap can be stretched. This simple releasing incision ultimately allows tension-free closure over the graft site.
A flap covering a graft that does not have complete release of pressure on the two margins of the flap will often pull open during the healing process (incision line opening). Tension on the flap compromises the blood supply to the tissue along the suture line that is under pressure. This pressure leads to necrosis and eventual separation of the two edges of the flap closure. Once this has occurred, the flap cannot be sutured back into place and the graft site is open for contamination and tissue ingrowth. The success of bone grafting is largely dependent on the maintenance of space for bone development and isolation of the graft particles during the slow process of osteogenesis. Soft tissue ingrowth, bacterial contamination, and migration of graft particles predictably compromise regenerative results.
The typical graft site requires that the overlying flap be released enough for extension of the flap at least 5 mm beyond the edge of the adjacent margin for a tension-free flap closure. The only way to achieve this free flap release is the use of a shallow incision though the periosteal layer, allowing the elastic fibers of the underlying flap to stretch over the graft site.
Tension-free flap release technique: A scalpel with a #15 blade is used to prepare a very shallow incision through the periosteum from the anterior to the posterior border of the graft site. As the incision is prepared, a clear separation of the borders of the incision line can be seen. It is not necessary to make a deeper incision because the underlying tissue can be freely released with the tip of sharp scissors (e.g., Metzenbaum). The closed scissor tip is placed into the incision, parallel to the flap itself. The ends are then opened, spreading the tissue as the ends separate. This is repeated until the flap can be freely extended at least 5 mm past the border of the lingual incision line of the graft site. The use of the spreading scissor tips reduces the need to cut underlying tissue and possibly vital structures like vessels or nerves. Tissue flaps in the maxillary and mandibular anterior regions usually require extensive release of the flap for tension-free closure over most graft sites. The posterior regions do not typically require extensive release and dissection. Care must be taken to prevent over thinning the flap or perforating the flap with a “buttonhole” (Figs. 12.24 to 12.26).
Inadequate Vertical and Horizontal Space Maintenance in Graft Sites Utilizing Membranes
The field of advanced implant dentistry went through a complete paradigm shift when the first augmentation procedures were introduced. Until that time, implants were placed in the islands of bone that were discovered at the time of flap reflection. This limited preoperative treatment planning to a great extent and subsequently the role of the restorative dentist was at many times very difficult. Implants often emerged at odd angles creating a variety of long-term support and restorative issues. The majority of bone grafts initially were designed around block grafting techniques where significant volumes of bone were regenerated horizontally and in limited cases in a vertical dimension. Block grafting is still used by many surgeons, but these procedures require surgical expertise and the morbidity can sometimes be an issue from the patient’s standpoint.
Particulate grafting was initially introduced utilizing non-resorbable e-PTFE membranes. This approach used titanium struts to prevent collapse of the membrane into the critical regenerative space. The titanium could be trimmed and shaped into contours that produced the bony support required for the predetermined restorative plans. Nonresorbable membranes were used to some extent, but they were generally limited to production of 1–3 mm of bone thickness. These limitations were directly related to the limited number of ways that the space between the recipient bone and the suspended membrane could be supported. In most cases, one or two bone fixation screws were placed in strategic sites, maintaining enough space for smaller graft sites.
In recent years, alternative approaches have centered around expanded use of membrane/fixation screw techniques, introduction of nonresorbable d-PTFE membranes with titanium struts, titanium mesh, temperature molded and welded membranes, along with other similar approaches. The key principle in each one of these techniques centers on the use of an occlusive membrane to maintain a defined space between the recipient bone and the overlying gingival/connective tissue flap. This space must be isolated from outside cellular downgrowth, and the flap covering the defined space must be completely supported throughout the regenerative process. Each technique has its own advantages in relation to defining the final shape of the ridge, and each approach has its own issues in respect to maintaining a sealed layer over the graft site while the bone is developed. All of these graft techniques require 5 to 6 months for maturation of the graft site. Over this timeframe various situations contribute to pressure on the graft site and breakdown of the incision lines and membrane edges.
Deficient ridges occur when one or more of these principles is violated. Any mobility of the membrane will disrupt the cellular development process, beginning with interruption of the initial clot stability. Graft particles that are not confined or protected will tend to shift to a region that has less pressure or movement. The coronal aspects of all graft sites are very important because the bone around the platform of an implant carries a great deal of the occlusal load. Failure to define and maintain this dimension leads to a narrow width at the coronal aspect. A deficient ridge width like this will many times create a dehiscence on the facial or lingual aspect of an implant. This bony deficit subjects the remaining bone to additional stress and also disrupts the delicate soft tissue attachment around the abutment. Success in all of these approaches requires development of large volumes of bone, overbuilding regions where possible. Under-estimation of the required bony support often leads to thin facial bony coverage over an implant body. It is our experience that you really never have too much bone. All bone will go through a constant remodeling process and all too often, facial bone will thin over time. This facial thickness will eventually tend to thin out over the threads of the implant, altering aesthetics and possibly implant support. Membranes that are not rigidly fixed in place tend to move out of position and some varieties resorb early in the regenerative process, allowing invasion of tissue, bacteria, or movement of the graft materials. Each one of these seemingly small issues can compromise the whole regenerative process.
Areas where a particulate graft shifts or where a supporting membrane collapses typically heal in a manner that does not provide the expected ridge shape and dimension established during the restorative planning process. The clinician is forced to either compromise the implant position or abort the implant aspect of the procedure. This delays implant placement until adequate supporting bone can be developed with additional grafting. Implants that are placed in compromised recipient sites are prone to complications when the prosthesis is loaded and bone remodeling occurs.
GBR techniques utilize an occlusive barrier membrane between the alveolar bone and the gingival epithelium/connective tissue to prevent epithelial down-growth into the alveolar ridge defect. The occlusive barrier membrane allows for osteogenic cells from the adjacent alveolar bone to colonize the blood clot and to induce bone regeneration.31,47 Aside from soft tissue exclusion and clot stability, space maintenance is the key to the success of GBR. Screw-supported barrier membranes may be utilized for development and maintenance of this regenerative space. This same vertical support can be achieved using titanium-supported membranes, titanium mesh, or any other approach that creates and holds an open, isolated space for bone to occupy.
Bone fixation screws.
Space maintenance can be accomplished utilizing bone fixation screws as vertical and horizontal supports for isolation of bone graft particles and support of occlusive membranes. The required graft volume and spatial dimensions determine the number and positioning of these screws. Screws are anchored in the recipient site as needed to form a dome over the graft site that matches the height of bone needed for proper implant placement. Placement of graft materials without defining space maintenance will usually lead to variable postoperative bone volumes and often deficient bony support on the facial and lingual aspect of the coronal aspects of the implant platform. A thin or granular bone consistency at the coronal aspect will lead to a dehiscence on the facial or lingual aspect of the implant platform.
Titanium supported d-PTFE.
The use of titanium supported d-PTFE membranes has demonstrated development of significant amounts of bone in everything from minor defects to extensive vertical defects with through-and-through cortical destruction. Earlier use of e-PTFE (Gore Tex [W. L. Gore & Associates, Inc.]) membranes showed serious compromises in final graft volumes if any portion of the membrane was exposed. This failure was largely related to the large pore size in the e-PTFE membrane. The pores in the e-PTFE were large enough for bacterial passage through the membrane itself, resulting in altered bone growth throughout the region (5–25 μ). The success in grafting with d-PTFE can be related to the small (<2 μ) pore size of d-PTFE, where bacterial invasion though the membrane itself is blocked.58 Exposed sites in d-PTFE cases show no side effects related to invasion of bacteria directly through the membrane and into the developing bone. Exposed sites can still present problems related to invasion around the edges of the exposed membranes. It has been described that d-PTFE membrane exposure cases need to be maintained for at least 6 weeks before the membrane can be safely removed. Removal of the membranes earlier than this exposes the contents to bacterial ingrowth and this usually results in a significantly altered final graft result. Exposed d-PTFE should be maintained with chlorhexidine rinses and careful hygiene around the exposure sites. Care should be taken to prevent any movement of the membranes with temporary appliances.54,56
Mesh support techniques use a piece of thin titanium mesh that is shaped into the external form of a desired ridge shape required for implant positioning. The advantage of this technique is directly related to providing rigid fixation of a formed template over a volume of grafting material, assuring maintenance of space required for graft development. It is used with either a particulate graft or with BMP that has been mixed with a graft and sponge mixture. If the integrity of the soft tissue flap can be maintained throughout the healing process, significant bone volumes have been consistently reproduced. If the flap margin or other region of the overlying flap exposes the titanium mesh, the predictability of the final graft volume can be compromised.
Treatment for dealing with an inadequate ridge follows one of two approaches. The first option involves placement of implants in the compromised bony foundation, grafting additional bone over the exposed implant threads at the time of implant placement. This technique often leads to varied results. If the exposure of the implant body is within the contours of the surrounding basal bone, grafting will be much more predictable than in cases where the implant contour extends beyond the surrounding basal bone. The presence of a blood supply, supporting bony protection, and adequate coverage of the remaining surfaces of the implant are critical. The second option requires postponement of the implant insertions, attempting additional augmentation, and placement of the implants after adequate bone has been regenerated. This approach is the most predictable for a successful long-term result. (Figs. 12.27 to 12.32).