Ridge Augmentation: Understanding the Power and Potential of Particulate Grafting

INTRODUCTION
The field of restorative dentistry has been through a paradigm shift as the introduction of implants has changed the prospects for reconstruction of severely compromised dental cases. The use of dental implants in most treatment plans today offers the possibility of restorative success in many situations that would have previously been impossible. This success has been largely related to the advent of bone augmentation techniques that allow for the regeneration of an ideal ridge form and placement of implants in their ideal functional and aesthetic positions.^1-5

As attempts to restore more difficult cases are made, the severely compromised bony ridge defects that are encountered require interdisciplinary team members to routinely offer new and predictable bone grafting techniques.

Although many significant ridge defects can be attributed to developmental defects and trauma, bone deficiencies most frequently occur due to the normal physiologic process that happens after tooth loss or extraction. Studies have shown that resultant bone resorption after tooth removal can be approximately 1.5 to 2.0 mm vertically, and 3.8 mm in the horizontal plane, within 6 months.^6,7 Guidelines have been established in regard to proper implant numbers and positioning based on the specific demands of the proposed prosthetic design. With the development of immediate implant protocols and the pressure to deliver a prosthesis on an instant basis, patients and dentists will constantly be tempted to avoid pre-restorative bone grafting, potentially compromising the final prostheses. The only predictable path to long-term restorative success in the resorbed dentate case is based on the development of a stable and long-lasting bony foundation prior to placement of the implants and prosthesis.

Planning in advanced cases requires a realistic assessment of the final restorative plan in relation to the foundational bony support. Interdisciplinary planning with CBCT 3-D imaging integrated into digital imaging allows a reasonable and accurate assessment of the existing bony architecture and potential deficiencies involved in key abutment positions. This critical analysis is then used to direct the development of adequate bone in deficient regions and to specify key abutment sites that need additional soft-tissue or bony supplementation for proper abutment emergence profiles and foundational support (Figure 1). The surface topography of a bony deficiency is usually irregular, and the application of regenerative techniques should be centered around specific techniques that ensure adequate bone development in volumes and contours that complement the restorative plan.

Regeneration of bone in a specified area requires the creation of a protected zone where the cellular development process can be completed without interference from an outside invasion of fibrous tissue and bacteria.⁸ Common regeneration techniques today include block grafting, GBR, the use of titanium mesh, ridge splitting, BMP, and distraction osteogenesis.^5-8

In general, membranes in GBR procedures act as biological and mechanical barriers, preventing the invasion of non-bone-forming cells (eg, connective tissue/epithelial cells), while slower-migrating bone-forming cells are drawn into defect sites.8 As bone defects heal over time, there is a competition between soft-tissue and bone-forming cells that are trying to migrate into the area. Soft-tissue cells tend to migrate at a much faster rate than bone-forming cells, and, if left unchecked, they will infiltrate the developing site. Therefore, the primary goal of barrier membranes is to allow for selective cell repopulation and to guide the proliferation of various tissues during the healing process.^9-11

Key components in space maintenance include an effective barrier membrane, a rigid supporting technique to maintain the “space” required for graft development, and the grafting materials themselves.3,8,10,11 Membranes are typically classified as resorbable or nonresorbable. Nonresorbable membranes include titanium foils and dense polytetrafluoroethylene (d-PTFE) with or without titanium reinforcement. Resorbable membranes have become a popular alternative because they are biodegradable and less likely to become infected in the event of an exposure. AlloDerm GBR Regenerative Tissue Matrix (BioHorizons) will be used as the primary membrane in this article, demonstrating the general use of Acellular Dermal Matrix membranes in GBR.^12-17

Space maintenance in large defects is typically maintained with tenting screws, titanium struts, titanium mesh, bioresorbable molded materials, or simply with particle support.³ Tenting screws and titanium-supported PTFE membranes were used in this series of cases for support of the membranes. The selection of grafting materials is a very important component in the success of a regenerative result, and choices include autologous bone grafts, allografts, xenografts, and alloplasts. The incorporation of some autologous bone in major bone grafting is highly recommended, and all cases in this article utilized at least 50% autogenous bone in the grafts. Allografts must be carefully considered from the standpoint of cortical bone vs cancellous bone and whether the bone is mineralized or has been demineralized. A significant variety of allograft combinations are found on the market today, and careful selection of allografts must be considered as the size and type of bony defect is evaluated.

Guided Bone Regeneration Technique
The cases shared here describe a guided bone regeneration technique following the principle of “Space Maintenance and Tissue Exclusion” in defined bone development. Unique parts of this surgical approach center around the use of multiple tenting screws or titanium-supported PTFE to establish a ridge form; space isolation with an acellular dermal matrix; and, primarily, the use of autogenous particulate in the grafting protocol. The allograft utilized in these cases was MinerOss Freeze Dried Cortico-Cancellous Mineralized Bone Allograft (BioHorizons).

Materials and Methods

Step 1: Incision.

a. Crestal, full-thickness incision, preserving the keratinized tissue band
b. Broad-based, maintaining blood supply
c. Papilla-sparing, where possible
d. Vertical incisions should be separated from the proximity of the graft material

Step 2: Reflection—Full thickness with no buttonholes in flap.

Step 3: Removal of all soft tissue from the recipient site.

Step 4: Decortication of the cortical bone covering the recipient site.

Step 5: Periosteal releasing incision in the vestibular portion of the flap, allowing tension-free closure.

Step 6: Membrane selection and placement.

a. Membrane selection—resorbable vs non-resorbable
b. Apical fixation of the membrane with tacks or sutures
c. Final coverage of the graft with membrane (lingual/palatal membrane fixation, if possible)

Step 7: Space Maintenance—the horizontal and vertical contours/dimensions for the graft should be established with the elevated heads of tenting screws or through the shaping of titanium-supported PTFE barriers.

Step 8: Choice of particulate graft particles.

a. Layer 1—autogenous cortical/cancellous particles or cortical shavings
b. Layer 2—mineralized allograft (70% cortical/30% cancellous) (MinerOss)

Step 9: Flap closure over the graft.

a. Mattress sutures for primary support (5-0 cytoplast)
b. Interrupted sutures and figure 8 sutures for tissue leveling (5-0 cytoplast)
c. Vertical incisions (5-0 chromic gut)

Step 10: Healing time—5-month healing timeframe with > 50% autogenous bone/< 50% allograft. If autogenous bone is not included, healing time is extended to 9 months.

CASE EXAMPLES
Case 1
A 63-year-old female presented with severe resorption of the maxillary anterior ridge following the loss of a long-standing fixed bridge. The restorative wax-up indicated significant horizontal deficiency. Tenting screws were placed in strategic sites for support of the graft and membrane for implants in the positions of teeth Nos. 7 and 9. A GBR Alloderm membrane was fixed apically, and the graft was filled to the level of the screw heads. Autogenous particles from the ramus were used for 70% of the graft volume, and they were placed directly against the recipient site bone. MinerOss Mineralized Cortical/Cancellous Allograft was used for the remainder of the graft. The Alloderm was draped over the entire graft site and was fixed on the palatal aspect with 2 tacks. After 5 months of maturation, re-entry showed that the regenerated ridge was filled to the level of the screw heads with a dense and stable ridge form. Two implants were placed in the sites of teeth Nos. 7 and 9 without any complications (Figure 1).

Cases 2 to 4
Case 1 and the remaining 3 cases presented in Figures 2 to 4 show the results of extensive clinical experience in the field of bone regeneration. As years have passed and different materials and techniques have been used, this protocol continues to be the most predictable approach at this time. The addition of various products and growth factors over the years have included PRP, PRF, GEM 21S (ZymoGenetics), Emdogain (Straumann), and a variety of bovine products/allografts. Although most of the growth factors promoted the healing of soft-tissue wounds, none demonstrated significant changes in overall bone development. As the particulate consistency was altered, very distinct changes were noted, and this protocol remains distinctly more predictable.

DISCUSSION
Predictable ridge augmentation is an important part of all surgical practices. The amount of bone that can be produced can vary significantly as each step in the process is altered and as specific materials are changed from case to case. On a long-term basis, completed cases are subjected to loading forces and a continual process of bone remodeling. The quality of bone that is produced with each procedure should be carefully evaluated from the standpoint of initial density, granular consistency, and resistance to expansion as implants are inserted. Any weakness in the initial graft support will almost certainly lead to potential complications or failure in the future.

Space maintenance in GBR procedures is absolutely necessary for success. Tenting screws in these cases were used in large numbers to literally “form or sculpt” a specific final ridge contour that matched the restorative plan’s prescribed dimensions. By using multiple tenting screws in compromised portions of severe defects, the surgeon is able to create a planned regenerative surface contour. This is critical in areas where the recipient bed has an irregular surface and is not amenable to easy adaptation of a bulky graft. The use of a titanium-supported PTFE membrane allows for the definition of a ridge shape, but these membranes are difficult to drape around a bend in an arch or around other surrounding structures or teeth. The tenting routine with a membrane provides a simple and predictable means of producing predictable ridge forms without the potential for complications related to membrane exposure in titanium-supported, non-resorbable membranes. Titanium mesh offers another option for shaping ridges, but extensive surgical experience and meticulous soft-tissue management is required for a predictable success.

The use of autogenous bone has always been considered the gold standard in graft procedures.^10,11,17-20 The use of autogenous bone in these cases creates a substantial and very dense ridge that has been shown to resist long-term remodeling and restorative loading, as shown in these case reports. The grafts shown in these cases have maintained ridge height over long periods of time in regions where large vertical ridge defects have been regenerated. The use of allografts without autogenous bone is a common practice because it eliminates the need for a secondary donor site where the autogenous bone is harvested. Although eliminating the autogenous particulate is convenient, completed cases without the help of autogenous bone must be carefully reviewed as cases are completed to document how much actual bone volume is being regenerated and what quality of bone is produced. The graft maturation window in cases using 100% allograft must be increased from 5 months to 9 months to allow sufficient substitution of non-vital graft particles with “vital” bone.

An important concept to understand is the need for regenerated ridges to withstand the long-term effects of restorative loading and bone remodeling. In 2013, Sterio et al²¹ studied augmentation using mineralized bone and a collagen membrane with no supporting tenting screws or titanium struts. One of the most significant findings in that research was related to the fact that over the 6-month maturation process, up to 66% of the graft width was resorbed. In 2015, G. Caldwell et al²² presented findings from cases using autogenous bone/allograft vs allograft alone. An acellular dermal matrix with tenting screws was used for space maintenance and, at 6 months, they produced an average ridge width of 3.6 mm in both graft types. When resorption of the width was reviewed, only 13% resorption was found in both treatment groups, demonstrating a sharp contrast to Sterio et al’s²¹ results. Others recommend at least 50% autogenous bone in grafts exceeding 4.0 mm and in vertical ridge regeneration.^10,11,23

The density in the final ridge in Case 3 shows a visible difference in consistency and granular surfaces when compared to the other cases where large amounts of autogenous bone were used. There was a reduction of autogenous particles used in Case 3, and it was concluded that the granular variation was directly attributed the lack of substantial amounts of autogenous bone and the 6-month graft re-entry time frame.

The specific barrier used in major augmentations is a critical factor in the predictability of the final graft quality. For successful production of regenerated bone volume, the isolating membrane must remain throughout the process. If a resorbable membrane tears at the fixation point or dissolves too soon, fibrous ingrowth of tissue into an immature graft can lead to fibrous encapsulation. If a non-resorbable membrane is exposed along a suture line or membrane border, bacterial contamination and fibrous in-growth can compromise graft quality. Once a membrane is exposed during the maturation process, the possibilities of eventual closure are not favorable.

An advantage of using Alloderm as the barrier is the fact that in the case of a membrane exposure, Alloderm will actually promote soft-tissue growth across the zone of exposure. Acellular dermal matrices are used throughout the field of soft-tissue grafting for this same tissue development process, and all exposures encountered have closed over a 4-week time frame. The predictable strength of the membrane, the extended graft isolation time, and its assistance in tissue growth over exposed regions makes acellular dermal matrix in GBR thickness a recommended barrier.

CLOSING COMMENTS
Restorative cases today demand not only functional success in implant-supported prostheses but also aesthetically pleasing results. These expectations therefore require that implants be placed in proper positions for acceptable emergence profiles and aesthetically designed restorations. Ridge defects are common in most advanced restorative cases, and the predictable augmentation of compromised regions must be offered by the interdisciplinary implant team.

Guided bone regeneration with membranes supported by tenting screws or titanium-supported membranes offers a predictable solution for even the most challenging situations. Acellular dermal matrices and d-PTFE membranes allow for long-term isolation of graft sites and the ability to shape and contour ridge forms. The inclusion of autogenous particulate in larger graft sites is an important component of this particular technique and should not be avoided due to related harvesting issues.

It is the continued challenge of every implant team to master hard- and soft-tissue management, and as this is accomplished, the ultimate recipient of these successes is the patient who will enjoy a life-changing dental experience.

References

1. Clementini M, Morlupi A, Canullo L, et al. Success rate of dental implants inserted in horizontal and vertical guided bone regenerated areas: a systematic review. Int J Oral Maxillofac Surg. 2012;41:847-852.
2. Hämmerle CH, Jung RE, Feloutzis A. A systematic review of the survival of implants in bone sites augmented with barrier membranes (guided bone regeneration) in partially edentulous patients. J Clin Periodontol. 2002;29(suppl 3):226-231.
3. McAllister BS, Haghighat K. Bone augmentation techniques. J Periodontol. 2007;78:377-396.
4. Jensen SS, Terheyden H. Bone augmentation procedures in localized defects in the alveolar ridge: clinical results with different bone grafts and bone-substitute materials. Int J Oral Maxillofac Implants. 2009;24(suppl):218-236.
5. Nevins M, Mellonig JT. The advantages of localized ridge augmentation prior to implant placement: a staged event. Int J Periodontics Restorative Dent. 1994;14:96-111.
6. Van der Weijden F, Dell’Acqua F, Slot DE. Alveolar bone dimensional changes of post-extraction sockets in humans: a systematic review. J Clin Periodontol. 2009;36:1048-1058.
7. Schropp L, Wenzel A, Kostopoulos L, et al. Bone healing and soft tissue contour changes following single-tooth extraction: a clinical and radiographic 12-month prospective study. Int J Periodontics Restorative Dent. 2003;23:313-323.
8. Polimeni G, Koo KT, Qahash M, et al. Prognostic factors for alveolar regeneration: effect of a space-providing biomaterial on guided tissue regeneration. J Clin Periodontol. 2004;31:725-729.
9. Pellegrini G, Pagni G, Rasperini G. Surgical approaches based on biological objectives: GTR versus GBR techniques. Int J Dent. 2013;2013:521547.
10. Caldwell CS. Particulate membrane grafting/guided bone regeneration. In: Resnik RR, ed. Misch’s Contemporary Implant Dentistry. 4th ed. Elsevier; 2020:933-986.
11. Dattilo DJ. Extraoral bone grafting for implant reconstruction. In: Resnik RR, ed. Misch’s Contemporary Implant Dentistry. 4th ed. Elsevier; 2020:1088-1111.
12. Buser D, Dula K, Hirt HP, et al. Lateral ridge augmentation using autografts and barrier membranes: a clinical study with 40 partially edentulous patients. J Oral Maxillofac Surg. 1996;54:420-432.
13. Buser D, Dula K, Hess D, et al. Localized ridge augmentation with autografts and barrier membranes. Periodontol 2000. 1999;19:151-163.
14. von Arx T, Cochran DL, Hermann JS, et al. Lateral ridge augmentation using different bone fillers and barrier membrane application. A histologic and histomorphometric pilot study in the canine mandible. Clin Oral Implants Res. 2001;12:260-269.
15. Simion M, Dahlin C, Rocchietta I, et al. Vertical ridge augmentation with guided bone regeneration in association with dental implants: an experimental study in dogs. Clin Oral Implants Res. 2007;18:86-94.
16. Simion M, Fontana F, Rasperini G, et al. Vertical ridge augmentation by expanded-polytetrafluoroethylene membrane and a combination of intraoral autogenous bone graft and deproteinized anorganic bovine bone (Bio Oss). Clin Oral Implants Res. 2007;18:620-629.
17. Fontana F, Santoro F, Maiorana C, et al. Clinical and histologic evaluation of allogeneic bone matrix versus autogenous bone chips associated with titanium-reinforced e-PTFE membrane for vertical ridge augmentation: a prospective pilot study. Int J Oral Maxillofac Implants. 2008;23:1003-1012.
18. Misch CM. Autogenous bone: is it still the gold standard? Implant Dent. 2010;19:361.
19. Trombelli L, Farina R, Marzola A, et al. GBR and autogenous cortical bone particulate by bone scraper for alveolar ridge augmentation: a 2-case report. Int J Oral Maxillofac Implants. 2008;23:111-116.
20. Urban IA, Nagursky H, Lozada JL. Horizontal ridge augmentation with a resorbable membrane and particulated autogenous bone with or without anorganic bovine bone-derived mineral: a prospective case series in 22 patients. Int J Oral Maxillofac Implants. 2011;26:404-414.
21. Sterio TW, Katancik JA, Blanchard SB, et al. A prospective, multicenter study of bovine pericardium membrane with cancellous particulate allograft for localized alveolar ridge augmentation. Int J Periodontics Restorative Dent. 2013;33:499-507.
22. Caldwell GR, Mills MP, Finlayson R, et al. Lateral alveolar ridge augmentation using tenting screws, acellular dermal matrix, and freeze-dried bone allograft alone or with particulate autogenous bone. Int J Periodontics Restorative Dent. 2015;35:75-83.
23. Urban IA, Nagursky H, Lozada JL, et al. Horizontal ridge augmentation with a collagen membrane and a combination of particulated autogenous bone and anorganic bovine bone-derived mineral: a prospective case series in 25 patients. Int J Periodontics Restorative Dent. 2013;33:299-307.

Dr. Caldwell received his DDS degree and completed a residency in periodontal surgery at the University of Texas Health Science Center at Houston School of Dentistry. He continued his studies by pursuing implant surgery at the Misch International Implant Institute, where he currently serves as a faculty member. Dr. Caldwell is a Diplomate of the American Board of Oral Implantology/Restorative Dentistry and the International Congress of Oral Implantology and Implant Dentistry. He is a Fellow of the American College of Dentists, the International College of Dentists, and the American Academy of Implant Dentistry and an implant Fellow at the Misch International Implant Institute and the Mastership Misch International Implant Institute. Dr. Caldwell is the author of 2 chapters in the 2 most recent Misch implant surgical textbooks. He can be reached at drscaldwell@mac.com.

Disclosure: Dr. Caldwell reports no disclosures.

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