Sustainable Development

The dimensions of the alveolar ridge are inevitably altered after a tooth is extracted, which often results in the placement of an implant in a site that has undergone a reduction in soft- and hard-tissue volume when compared with its neighboring dentate sites.^1,2 Hard-tissue defects at implant sites include intra-alveolar, dehiscence, fenestration, horizontal ridge, and vertical ridge defects.³ Soft-tissue defects affecting implant sites include those involving deficiencies in volume and quality (eg, lack of keratinized mucosa).⁴ These are all common clinical findings that if left unaddressed can lead to complications and ultimately compromise implant survival due to marginal bone loss, soft-tissue inflammation, and/or soft-tissue recession.^5-7

Soft-Tissue Grafting

The success of implant rehabilitation, particularly in the esthetic zone, relies heavily on the preservation or augmentation of the peri-implant soft tissue by means of periodontal surgical procedures.⁸ Free gingival grafts (FGGs) or subepithelial connective tissue grafts (SCTGs) can be used to improve tissue thickness to reconstruct the buccal dimension as well as to create the illusion of root prominence and increase the width of the crestal peri-implant mucosa for an esthetically pleasing result.

FGGs provide a reliable and efficacious way to augment peri-implant soft-tissue defects. Although they are not typically esthetically ideal, FGGs are the gold standard for increasing the amount of keratinized tissue. "We know that a robust zone of keratinized tissue around implants will help us, in a sense, combat the serious risk of peri-implant complications, such as peri-implant mucositis or peri-implantitis," says Sonia Leziy, DDS, Dipl Perio, a periodontist with a private practice in Nanaimo, British Columbia. "A more robust zone is more protective of the underlying bone, and to some degree, it helps reduce bone remodeling that can occur around implants." SCTGs are used to augment alveolar ridge contours for improved soft-tissue volume and optimized esthetics.^9,10 In an effort to avoid the postoperative morbidity associated with autologous grafting, xenogeneic soft-tissue substitutes have been developed as alternatives to SCTGs.

More specifically, porcine-derived acellular dermal matrices composed of noncrosslinked natural type I and type III collagen have been introduced and found to be successful for gingival augmentation and root coverage.^11-13 These materials can serve as substitutes for autogenous grafts, increasing soft-tissue thickness under closed healing conditions. In addition to reducing the morbidity associated with graft sites and the length of operative times, xenogeneic collagen matrix has been shown to quickly stabilize the blood clot while promoting rapid vascularization, root coverage, the reduction of recession, and the regeneration of keratinized gingiva in both width and thickness. It may also be an effective alternative to regenerate keratinized gingiva around implants.¹⁴

Adequate peri-implant soft tissue is critical in preventing inflammation and the onset of peri-implant disease as well as promoting long-term stability of the gingival margin.

Bone Grafting

The success of dental implant placement in the restoration of edentulous sites and ridges largely depends on the quality and quantity of alveolar bone available in all spatial dimensions. There are a variety of materials and techniques available to improve available bone; however, the search continues for treatment protocols that are less invasive and that result in vertical and horizontal bone augmentation with better reproducibility.

There are various options available for alveolar bone grafting, which are divided into natural materials (eg, autografts, allografts, and xenografts) and synthetic materials (eg, alloplasts). Depending on a graft material's origin, it will possess varying degrees of osteogenic, osteoinductive, and osteoconductive properties. Although autografts supply the most osteogenic organic materials, their disadvantages include donor site morbidity, increased postsurgical recovery time, and a limited amount of available graft volume. "Autografts are ideal because in addition to being autogenous, they contain living cells and vascular channels that are immediately put to use," explains Jason C. Stoner, DDS, MS, a periodontist and implantologist with a private practice in Columbus, Ohio. "Therefore, there's no delay in obtaining a blood supply to the site." Alternatively, allografts from donated tissue also work well, but there is a delay in healing when compared with autografts due to the need for neovascularization and angiogenesis.

Xenografts, which are derived from animal tissues, work well to maintain space because their resorption rate is slower, but that slower rate can result in increased healing times, and histomorphometric studies demonstrate that they result in a lower percentage of vital bone formation when compared with other materials.^15,16 "For a pontic site, I might want a xenograft with very slow or no breakdown over time because I know that the bone will stay stable in its architecture relative to the time it is placed," explains Leziy. "Conversely, if I am doing a ridge preservation procedure to place an implant in that area, I would want to consider a material that will break down to be replaced by autogenous bone. In situations in which I might be hoping to augment a ridge around an implant, and I want some additional structural stability, I will often use composite grafts containing a variety of materials in combination, such as autogenous shavings built in with an allograft and possibly a xenograft."

Alloplastic materials are usually osteoconductive without having any osteogenic and osteoinductive potential; however, they have been used successfully in periodontal reconstructive applications. They are fabricated in various forms with varying physicochemical properties and can be either resorbable or nonresorbable.

Patient-Derived Blood Products

Autologous blood products, such as platelet-rich plasma (PRP) and platelet-rich fibrin (PRF), are used as adjuncts in tissue development procedures because they are believed to help promote regeneration and accelerate the healing of bone and soft tissue through the release of cytokines and other growth factors that influence tissue repair. Deriving autologous PRP from patient blood is a safe, low-cost procedure to facilitate the delivery of growth factors to grafted sites. In addition to accelerating healing, the use of autologous blood products has also been shown to reduce the incidence of inflammation and pain following oral surgery.¹⁷ "The early results of PRP were very promising; however, it was never clear that we were achieving superior results to those cases treated without PRP," explains Barry P. Levin, DMD, a periodontist and implantologist with a private practice in Jenkintown, Pennsylvania. "The addition of growth factors gave us another way to increase the biologic activity of our osteoconductive and osteoinductive grafts. It was also a less-invasive procedure for our patients." Loading various growth factors and proteins on the implant surfaces can help to promote osteogenic differentiation and the mineralization of bone marrow stem cells.

"Most of us who are performing surgeries are using these products today. I work with PRF, whether it is an injectable version or in the form of sheets, such as L-PRF or A-PRF," notes Leziy. "We certainly use these materials with our bone grafting products. In addition to providing a slow release of growth factors and cytokines to help fast-track healing, they also have a significant positive influence on graft material handling. When we can take a particulate product and combine it with a morselized PRF membrane and exudate to create a consolidated sheet, the handling characteristics really improve for us." Platelet-derived growth factor, insulin-like growth factor, fibroblast growth factor, vascular endothelial growth factor, bone morphogenetic protein, and other materials are being studied to determine their potential benefit in these applications.

In Advance or at the Time of Placement?

Some immediate implant protocols require no mucoperiosteal flap and arguably produce some of the most favorable clinical and patient-centered outcomes when compared with other approaches to manage extraction sockets. Conversely, when indicated, the use of guided bone regeneration at dental extraction sites can result in substantial gains in alveolar ridge dimensions; however, this treatment may adversely influence the mucosal architecture and comes with an increased risk of postoperative morbidity. Therefore, when favorable bone and mucosa are present at a dental extraction site, immediate implant placement may be the treatment of choice.

There are various factors involved in deciding whether to develop a site in advance or upon implant placement. "If an implant can be placed in its ideal position regarding the emergence profile and restorative/occlusal requirements and in the presence of adequately thick hard and soft tissues or if reconstruction and preservation of the existing soft tissue architecture would benefit from immediate placement, this is the desired choice," Levin says. "However, if any of these parameters are lacking, it may be prudent to develop the site before implant placement."

Strengthening Our Understanding

Hard- and soft-tissue deficiencies at implant sites can result from a multitude of factors. Thankfully, advances in dental implant therapy have strengthened our understanding of the implant/soft- and hard-tissue interfaces, with site-specific implications ranging from marginal tissue management to esthetic enhancement. The techniques and materials used to develop the hard and soft tissues at edentulous sites are critical to the long-term success of implant therapy. As our understanding continues to evolve, the breadth of options available to offer predictable therapy for the rehabilitation of partially or fully edentulous patients is certain to continue to evolve as well.