Managing a Deficient Site: How to Augment Prior to Implant Placement in the Esthetic Zone

The loss of teeth in the esthetic zone can result in hard- and soft-tissue loss that can pose considerable clinical challenges for implant reconstruction. Bone augmentation is often required to create ideal gingival contours and esthetics. Increasing patient demand for natural-looking esthetic outcomes has redefined the definition of implant success. Success is no longer solely equated with implant survival, yet most studies on implants fail to include criteria for esthetic success. Up to 16% of single implant restorations in the esthetic zone reportedly fail for esthetic reasons due to tissue loss or failure to adequately restore this lost volume.¹ Achieving an ideal esthetic result in a compromised site is often elusive, and in many cases not possible.² With any surgical procedure, the potential for unexpected complications that can compromise the result always exists, and this consideration should be a part of the initial discussion with the patient and dental team regarding expectations.

Even procedures with a high level of predictability have esthetic failures, which are defined by significant tissue recession, long clinical crowns, open gingival embrasures, and/or exposure of the abutment margin.³ Given the complexity of hard- and soft-tissue reconstruction, the author recommends using the five simple criteria, abbreviated "FATTT," listed in Table 1 to assist clinicians in assessing the risk of an unesthetic outcome with hard- and soft-tissue reconstruction.

Favorable Gingival Level (F)

Because gingival recession is common after prosthetic delivery,¹ it is critical to assess the preoperative gingival margin height of the tooth or implant site. This margin is usually dictated by the underlying facial bone level. A free gingival margin that lies coronal to the planned restorative margin offers some protection against recession and is considered more favorable than a free gingival margin that is less coronal (Figure 1 and Figure 2). Ideally, the implant platform should be placed 3 mm to 4 mm below the planned gingival margin with an abundance of soft-tissue height for prosthetic sculpting to achieve a harmonious gingival margin with the adjacent teeth. In clinical cases where the gingival margin is in an unfavorable position, a primary goal of bone augmentation should be to bring the gingival margin and bone into a more coronal level prior to implant placement. A pictorial case report demonstrating management of a compromised extraction defect and socket augmentation is presented in Figure 3 through Figure 17, with Figure 11 and Figure 12 specifically illustrating this point.

Attachment on the Adjacent Tooth (A)

Predictable papilla formation is dependent on gingival biotype and the proximal bone height of the adjacent teeth. When treatment planning for vertical bone gain, the clinician must understand that this proximal height adjacent to a compromised site is also the determinant for the coronal limits of augmentation for the buccal bone crest level and its overlying gingival margin level. Because it is difficult to predictably graft bone beyond this compromised attachment, this limitation should be anticipated so that patient expectations can be appropriately addressed. For optimal esthetic outcomes, consideration must be given to options to increase interproximal bone height, including orthodontic extrusion and retention of the affected tooth or extraction of the affected tooth with vertical bone augmentation.

Thick/Thin Biotype (T)

Patients exhibit differences in their gingival phenotypes, often termed "gingival biotypes." Most patients fall into two categories: slender teeth with thin gingiva and scalloped periodontium or square teeth with thick gingiva and blunted periodontium. The thinner biotype is more prone to recession and loss of interdental papilla.⁴ Furthermore, there is evidence that thick soft tissue (>2.5 mm) may be protective against crestal bone loss.⁵ Some clinicians advocate the routine use of connective tissue grafts in the esthetic zone to transform thin biotypes into thicker tissue for enhanced esthetic outcomes.

If an implant site exhibits a thin biotype, a connective tissue graft or bone augmentation should be considered prior to or at the time of implant placement to reduce the risk of recession and graying of the tissue. Also, soft-tissue thickness around dental implants can be correlated with other factors not related to the patient's initial biotype. These factors include implant position, angulation, and the presence of labial bone. Le et al showed a high correlation between labial crestal soft-tissue thickness and underlying bone thickness, demonstrating that soft-tissue thickness around dental implants can be heavily influenced by the underlying labial bone thickness (Figure 18).⁶ Le et al studied the relationship between crestal labial soft-tissue thickness and implant buccolingual angulation.⁷ The buccolingual angulation was recorded as cingulum, incisally, or labially angled based on the position of the screw-access hole of the provisional restoration. Of implants with cingulum, incisal, and labial angulations, 3.4%, 20%, and 53.3%, respectively, had crestal labial soft-tissue thickness of <2 mm; mean crestal soft-tissue thickness was 2.98 mm for implants with cingulum angulation, 2.24 mm for implants with incisal angulation, and 1.71 mm for those with labial angulation.⁷

Thick/Thin Labial Bone (T)

A minimum buccal bone thickness of 2 mm is recommended for the maintenance of stable bone and soft-tissue level; any thickness less than this often necessitates bone augmentation. A high correlation has been reported between peri-implant labial bone thickness and labial crestal soft-tissue thickness in the esthetic zone.⁶ It is important to note that bone augmentation should always aim to correct not only buccal bone thickness, but proper buccal bone crest level to achieve a favorable gingival margin level.

Tooth Shape (T)

Extensive flap elevation can result in some loss of tissue to the teeth adjacent to the graft site. This can lead to either loss of papilla height or exposure of existing restorative margins or leave unesthetic black triangles in the final restorations.⁸ Because it is difficult to regenerate a missing papilla, alteration of the contact point of the adjacent teeth may become necessary to achieve a more symmetric appearance of the final restorations. Patients should be informed prior to bone augmentation of the possibility that additional costs may be incurred due to the need for additional restorations on the adjacent teeth.

It is important to note that the esthetic outcomes perceived by dental professionals and patients do not always match. Kocich et al compared the esthetic perception of dentists, orthodontists, and laypersons on various parameters.⁹ This was done by altering various parameters and asking each group to offer their esthetic perception of these altered parameters (eg, teeth length, gingival margin level, papilla height, etc). According to the authors, patients considered a discrepancy in gingival margin of more than 2 mm to be unesthetic, similar to general dentists. Conversely, while dentists had very low tolerance for any discrepancy in papilla height, most laypersons were unable to differentiate a severely compromised papilla height. Tymstra et al reported the results of placing two adjacent maxillary implants after autogenous block grafts in 10 consecutive patients.² They reported that in 40% of their cases, there was an absence of interdental papilla. Interestingly, all the patients in this study reported that their results were "acceptable" or better, supporting the findings of Kocich's study.

The success of bone augmentation in the esthetic zone is dependent on numerous critical variables, including defect configuration, flap design, space maintenance, graft selection, membrane selection, and implant position.

Defect Configuration

With traditional guided bone regeneration (GBR), migration of graft particles during site healing often results in unfavorable healing and soft-tissue collapse/recession.¹⁰ The challenge in maintaining graft particles in a crestal position depends on several factors related to defect configuration (Table 2) and are described as follows.

Width of edentulous span-Single-tooth defects have a much better esthetic prognosis than multiple-teeth defects since particulate grafts placed in wider edentulous spans are more prone to apical migration due to the wider flap elevation required. Wider defects often necessitate the use of a containment barrier or space maintenance device, such as a mesh or membrane with tacks to contain bone graft material. One strategy to limit the amount of apical and lateral graft migration is to avoid making larger flap designs than necessary.

Number of walls-New bone formation mainly depends on the surface area of exposed bone and bone marrow since the osteogenic and angiogenic cells that form new bone reside in the bone marrow.¹¹ The number of bony walls available in a defect has significant influence on the success of a GBR procedure. With more bone walls available, the healing potential of a given defect increases.¹¹ In other words, three-wall defects (eg, extraction sockets) have better healing potential than two-wall defects, which are frequently found in post-extraction sites and have good potential for bone regeneration. One-wall defects, however, are more challenging because there is a greater distance for osteogenic cells to bridge. Three- to four-wall defects also have a better prognosis for graft containment.

Type of defect-Horizontal defects with bony concavities that will contain graft material have better prognosis than those with no concavities. Defects with vertical components are more challenging to manage due to the difficulty in space maintenance. The strategic use of flap design, space maintenance devices such as titanium mesh, and tenting screws is recommended for correction of small to medium alveolar ridge defects.¹² Distraction osteogenesis and segmental osteotomies also have been prescribed for the management of severe vertical defects.

Flap Design

Minimizing flap exposure to maximize vascular supply to the surgical site while creating adequate access for graft placement can be challenging. For small ridge defects (<2 mm), a flapless or sulcular incision may be adequate; but for larger defects, an open-book flap design will be needed to enhance visualization and access (Figure 6 and Figure 7). It is crucial to achieve tension-free adaptation of wound margins during wound closure, and this will require incising the periosteum of the flap before repositioning it. In addition to allowing primary tension-free wound closure, scoring of the periosteum promotes angiogenesis by creating bleeding into the graft.

Graft Materials and Barrier Membranes

Various materials have been described for alveolar ridge augmentation. Autogenous bone has long been considered the gold standard for bone grafting due to its biocompatibility and osteogenic properties. Allografts, xenografts, alloplasts, and bone morphogenetic proteins can also be used successfully as a bone substitute for bone augmentation.¹³ Cost, ease of use, biocompatibility, bone formation, and resorption are all properties to consider when choosing a graft material. The use of mineralized allograft may provide earlier bone formation leading to earlier implant placement and restoration. However, a potential drawback observed with allografts is increased resorption. Overcorrection of ridge contours should be performed in anticipation of bone resorption and remodeling.

Ridge augmentation can be performed with or without barrier membranes. A systematic review concluded there is insufficient evidence regarding the effects of membranes on bone augmentation procedures to support any definitive conclusions.¹⁴ GBR can successfully be performed using either resorbable or nonresorbable membranes. Nonresorbable membranes, particularly those made from expanded polytetrafluoroethylene, have significant risk of premature membrane exposure.¹⁵ They also have higher irritation and infection rates compared to resorbable membranes.¹⁶ Collagen membranes are the most widely used resorbable membranes and are derived from modified bovine tendon, bovine dermis, calf skin, or porcine dermis.¹⁷

Surgical Technique

Various techniques and site development protocols are available for the management of common alveolar ridge defects. This section will focus on staged augmentation and simultaneous augmentation with implant placement to enhance esthetic outcomes for extraction defects and localized ridge defects in the esthetic zone.

Staged augmentation of extraction socket with labial wall defect-Teeth with periapical radiolucency or labial fistula or are lost due to trauma often have compromised labial walls (Figure 3 through Figure 17). Without intervention, these defects can lose significant bone. Augmentation with an open-flap approach is recommended for sockets with labial wall defects, as this yields predictable peri-implant tissue, bone stability, and contour.¹⁸ Opening extraction sockets with labial defects facilitates access for removal of tenacious granulation tissue and fibrous scar tissue that is often associated with chronic long-standing infection. The author prefers to use the "open book" flap for augmentation of these defects. Raising a flap allows for overcorrection of the anatomical defect and tension-free expansion of the soft-tissue matrix. The flap design enables coronal advancement of the gingival margin to achieve a favorable gingival margin level by minimizing the apical migration of the graft material away from the buccal bone crest.

The open-book flap (Figure 6 and Figure 7) is developed with a crestal incision followed by a distal, curvilinear, vertical incision that follows the gingival margin of the distal proximal tooth. A subperiosteal tunneling is made to expose two to three times the treatment area, and the papilla is reflected on the mesial side of the edentulous site. The soft tissue is released and advanced by deep split-thickness dissection of the periosteum to allow for expansion of the soft-tissue matrix and tension-free closure. Mineralized bone allograft material is packed into the defect and overcontoured by approximately 30% to compensate for the anticipated apical migration and partial resorption of the material. Prior to use, the allograft material should be hydrated and mixed with the patient's blood, which serves as a coagulant.

After graft placement, the material is covered with a resorbable membrane and the flap is advanced coronally. The amount of flap release should coincide with the amount of graft material used so there is little room for graft migration once the soft-tissue margins are closed. A 4-month healing period is allowed for graft maturation in most socket defects. Interim prostheses should be carefully adjusted to allow space for coronal migration and maturation of the soft tissue over the graft (favorable gingival level).

Implant placement with simultaneous augmentation (esthetic contour augmentation)-When there is adequate basal bone and the lateral ridge deficiency is mild (<4 mm), implants can be placed simultaneously with the augmentation procedure.¹⁹ Multiple authors have demonstrated predictable results with simultaneous GBR of facial wall defects with immediate implant placement.^20,21 Le et al assessed the outcome of single-stage (nonsubmerged) implant placement and simultaneous augmentation of 156 sites with vertical buccal defect using a mineralized particulate allograft covered with a collagen membrane.²⁰ The vertical buccal defects were classified as small (<3 mm in depth), medium (3 mm to 5 mm in depth), and large (>5 mm in depth). The initial vertical buccal wall defect was recorded by measuring the amount of vertical implant platform's rough surface exposure after implants were placed. Sectional CBCT scans were used at 36 months after graft healing. The site of the original vertical bone defect was evaluated for the presence of any residual vertical bone defect. The results showed the presence of bone in 100% and 79.3% of small- and medium-sized vertical defects, respectively. The likelihood of wound dehiscence, graft exposure and resorption, and subsequent implant thread exposure is increased when larger defects are treated simultaneously. A two-stage bone augmentation procedure followed by implant placement is recommended for predictable results with large (>5 mm) defects.

The surgical technique consists of an open-book flap design with a wide subperiosteal tunnel reflection to expose two to three times the treatment area, and the papilla is then reflected on the mesial side of the edentulous site. The author prefers this flap design because the site-specific vertical incision limits excessive flap elevation, promoting graft containment at the buccal crest. During implant placement, the implant's restorative platform is positioned to the desired level, and a healing abutment is attached to the implant. The peri-implant soft tissue is released and coronally advanced by scoring the periosteum so that tension-free closure is achieved around the healing abutment.

To induce bleeding in the graft site, periosteum release is performed as the last step just before graft placement. Human mineralized bone allograft is packed into the defect and overcontoured around the neck of the healing abutment to compensate for anticipated apical migration and resorption of the material. The graft material is covered with a long-acting resorbable membrane, and the soft tissues are approximated and sutured around the healing abutment. This creates a tenting effect over the allograft and, together with the healing abutment, helps to develop the labial soft-tissue contour. Some surgeons recommend perforating the recipient bone bed to enhance healing. By perforating the cortical bone with a small round bur, the marrow cavity is opened and bleeds into the defect. Clinical studies have shown that such perforations may improve healing in a membrane-protected defect.²²

Multiple missing teeth with labial crest defect (screw tentpole augmentation)-Most post-extraction losses of alveolar ridge dimensions occur in the horizontal (width) rather than the vertical (height) plane. Even when there is adequate bone to place implants, if irregular ridge anatomy does not get corrected an unnatural appearance of the soft-tissue emergence profile of the final restoration can result (Figure 18). Bone augmentation in the esthetic zone prior to or simultaneous with implant placement should have as its primary objective the correction of the buccal bone crest to provide for long-term peri-implant soft-tissue stability. Secondary bone augmentation may still be required in larger defects with multiple missing walls. Tenting screws may be used to facilitate and guide bone augmentation toward the buccal bone crest and for overcorrection of the defect and support of the overlying tissue.¹² Because most bone graft procedures inherently result in secondary remodeling and resorption, it is important to factor in the amount of anticipated resorption by overcorrecting the defects to a high buccal crest so that a critical 2 mm to 3 mm threshold of labial bone is achieved at the buccal crest after long-term remodeling (Figure 9 and Figure 10).

Single-tooth implant restorations are more likely to have predictable soft-tissue anatomy compared to multiple-implant restorations, which often have compromised soft-tissue anatomy.²³ Recreating natural ridge contours in adjacent implants is difficult.²⁴ Formation of papilla between two adjacent implants will follow the same principles as previously described. If intercrestal bone is present, papilla between the implants will be present. However, achieving formation or maintenance of intercrestal bone height between implants is more challenging. In a series of 136 interpapillary height measurements between adjacent implants, papilla height from the crest of the bone to the height of the papilla averaged 3.4 mm.²⁵

The use of a pontic may improve the overall esthetic outcome when replacing multiple teeth with implants. Some authors have suggested that the papilla height between pontic and implant can be greater than 5 mm, compared with 3.4 mm between adjacent implants.²⁶ Techniques to augment the pontic site include leaving submerged roots or augmenting with a connective tissue graft or slow-resorbing bone graft.²⁶ Submerged roots, however, may lead to future problems, and patients should be made aware of potential esthetic failures if future removal of the root is required.²⁷ More long-term studies in pontic site development are necessary to assess the longevity of augmentation techniques in conjunction with implant therapy.

The goals of minimally invasive dental implant therapy include minimizing surgical interventions and achieving shorter healing times while producing predictable and long-term functional and esthetic results. The decision on which technique to employ should be based largely on the comfort level of the surgeon. Failed guided tissue regeneration done with simultaneous implant placement may lead to exposed implant threads or crown margins. Single-stage implant placement and simultaneous grafting with particulate bone graft and membrane coverage is more predictable on alveolar ridges with small- to medium-sized horizontal and vertical labial wall defects. This technique becomes less reliable and more technique sensitive as the length of the edentulous span increases and if multiple implants are being placed. In wide spans, tenting screws are needed to prevent collapse of the tissue and graft resorption. The use of a limited flap design to maintain vascular supply and optimize attached tissue and vestibular depth and tension-free closure also are important for the success of this technique.

Bach Le, DDS, MD
Clinical Associate Professor, Oral and Maxillofacial Surgery, Herman Ostrow School of Dentistry, University of Southern California; Private Practice in Oral Surgery, Whittier, California