Sequential Ridge Augmentation Protocol for Hard and Soft Tissue Grafting in Alveolar Ridge Deficiencies: A Proposed Evidence-Based Algorithm

The success of implant-based therapy depends on surgical placement of implants in restoratively driven locations with adequate importance to soft tissue profile, hard tissue volume, and optimal occlusion. Implant placement in an ideal 3-dimensional position is extremely important for the restorative outcome.¹  Before an implant can be placed in the correct restorative position, it is crucial to perform an assessment of the local soft- and hard tissue profiles. In the absence of adequate supporting hard and soft tissue, augmentation procedures are required to develop deficient implant sites.

Although there have been several studies that have discussed hard tissue and soft tissue augmentation techniques for implant-based treatment,^2–6  the traditional emphasis of implant site development in previous treatment protocols has always been hard tissue assessment prior to soft tissue assessment.⁷  Bone-grafting techniques and materials have been extensively evaluated and compared in the literature.^6,8–10  In the past few years, there is growing evidence indicating that the presence of keratinized tissue around implants helps to maintain optimal implant health in terms of lower plaque accumulation and tissue inflammation.^11–15  While a few publications have stressed the importance of keratinized tissue around dental implants and described techniques to augment this tissue,^5,16,17  the timing and sequencing of soft tissue grafts have not been adequately addressed. Currently, there is a need for a concrete treatment sequence for hard and soft tissue augmentation procedures in a clinically relevant manner. Therefore, the aim of this article was to establish a step-by-step evidence-based protocol for the decision-making process involved in the hard and soft tissue augmentation procedures during implant treatment planning with special emphasis on keratinized tissue assessment. This, in turn, will help in ensuring a better prognosis for the final prosthetic outcomes. To the best of the authors' knowledge, this is the first article that provides a structured, evidence-based algorithm to perform hard and soft augmentation procedures for implant placement, which places importance on the evaluation of soft tissues around implants prior to hard tissue assessment.

The traditional literature on grafting procedures has always been focused on development of alveolar hard tissue dimensions to allow implant placement in restoratively driven positions, without adequate stress on the available keratinized tissue around implants. There have been instances in which implants have been placed in regions without sufficient keratinized tissue (Figure 1). The anatomy of the mucosal attachment around implants is substantially different than that around natural teeth.^18,19  Unlike natural teeth, a direct anchorage of the connective tissue to the implant surface is not possible because of the absence of periodontal ligament and cementum. Instead, collagen fibers run parallel to the implant surface, and the mechanical quality of this attachment is low.^18,19  On a biologic level, it would be favorable to have a zone of keratinized tissue around dental implants. However, the need for keratinized tissue around implants is a debated topic. Multiple studies have documented positive associations between the presence of adequate keratinized mucosa around implants and improved soft tissue health.^20–22  In addition, the absence of keratinized mucosa around implants has been shown to make the peri-implant region more susceptible to plaque-induced tissue destruction.²³  Oral hygiene has been reported to be painful because of the absence of the keratinized tissue surrounding implants, and this has been attributed to the mechanical irritation caused by the mobility of the nonkeratinized tissue under function.^22,24  Conversely, limited evidence in support of the need for keratinized tissues around implants to maintain health and tissue stability has been demonstrated as well.²⁵  However, it must be noted that most systematic reviews have indicated a positive relation between the presence of keratinized tissue around implants and clinical parameters such inflammation and plaque accumulation.^11–15  Thus, the present literature indicates that keratinized mucosa around implants would improve the predictability of implant-based treatment for long-term maintenance.

The main aim of the sequential ridge augmentation (SRA) protocol is to provide an evidence-based guideline in treatment planning the soft tissue and hard tissue requirement at the proposed implant site with significant importance placed on keratinized tissue evaluation before implant placement. Prior to the application of the SRA protocol algorithm, a thorough clinical and medical examination of the patient needs to be completed. After this, a working treatment plan for implant therapy based on the restorative requirements needs to be formulated. Once the number, design, location, and implant diameter is selected according to prosthetic requirements, the SRA protocol algorithm is applied. The steps involved in the clinical assessment and treatment planning can be seen in Figure 2.

The protocol involves 3 major steps in the treatment-planning process. The first and the most critical step is to assess the amount of keratinized tissue present at the proposed implant site. This is followed by the second step, which involves the assessment of hard tissue and alveolar ridge dimensions at the proposed implant site. The third and final step involves the formulation of a treatment sequence depending on the type and amount of augmentation requirement. As keratinized gingiva is significantly more resistant to mechanical stresses than alveolar mucosa,²⁶  a band of this tissue would improve the prognosis in terms of flap dehiscence, especially in cases requiring vertical or large horizontal bone augmentation. Also, higher buccal crestal bone loss and a more apically located soft tissue margin has been reported in implants when placed in bone surrounded by alveolar mucosa as compared with keratinized mucosa.²⁷  For these reasons, soft tissue assessment is given priority over hard tissue assessment in this protocol.

Although the need for keratinized mucosa around dental implants for success is controversial, several published systematic reviews have shown that its presence around implants is essential to maintain optimal implant health.^11–15  A higher alveolar buccal crest resorption and a more apical soft tissue position is expected in implants placed without surrounding keratinized mucosa as compared with a 2-mm band.²⁷  A band of 2 mm of keratinized tissue has been shown to have a better prognosis in terms of plaque accumulation, tissue inflammation, mucosal recession, and attachment loss.^11,12  In addition, there is significantly less crestal bone change in bone-level implants placed in an initial keratinized tissue thicknesses of 2 mm or less.²⁸  Other than maintaining adequate soft tissue health, considerable soft tissue reconstruction may also be necessary for an esthetic result, especially in the anterior zone. A soft tissue deficiency would necessitate vertical or horizontal reconstitution to improve the ridge morphology and the contour of the implant restoration. Thus, retaining a minimum of 2 mm (1 mm on the buccal and lingual aspect each) of keratinized tissue around implants would not only be advantageous for long-term maintenance but would also provide an esthetic profile.

Once the clinical assessment is complete, if a major correction of soft tissue is required (ie, more than 2 mm of keratinized mucosa needs to be augmented at the proposed implant site), a soft tissue augmentation procedure needs to be performed first. Such a procedure can be carried out at the time of implant placement. Several systematic reviews have compared available soft tissue augmentation procedures.^5,16,17  In general, all the compared techniques have provided adequate results, with no technique demonstrating significant superiority over others. Free gingival grafts as well as connective tissue grafts in combination with an apically positioned flap/vestibuloplasty have demonstrated good results to increase the width of the keratinized gingiva^7,29  and can be used when a major soft tissue correction of more than 1 mm is required. For minor soft tissue corrections, in which a total of less than 1 mm of the soft tissue needs to be augmented, grafting can be carried out in the second stage at the time of implant uncovering. Techniques such as roll envelope flap can also be successfully used at second-stage implant surgery for minor corrections.²⁹ 

Thus, the critical first step of the treatment algorithm is to identify whether adequate keratinized tissue of at least 2 mm is available at the implant site (1 mm each on the buccal and lingual flaps) and plan the treatment for the necessary soft tissue augmentation procedure if it is insufficient.

Once the soft tissue assessment is complete, the width of the alveolar bone needs to be examined. The suggested amount of bone required on the facial and lingual aspect for optimum maintenance ranges from 1.4 mm up to 2 mm in the anterior region where esthetics are critical and at least 1mm in the posterior region.^30,31  Therefore, the width of the alveolar bone is required to be at least 3 mm more than the planned implant diameter. In addition, the choice of simultaneous implant placement along with ridge augmentation depends significantly on the amount of native bone available for primary stability. If horizontal bone dimension is 4 mm or greater, the native bone is sufficient to provide primary stability for the implants, and excellent results can be obtained with simultaneous implant placement along with ridge augmentation.^32,33  For cases in which the horizontal ridge dimension is less than 4 mm (major hard tissue correction), a staged approach, wherein the grafting in the first stage followed by implant placement in the second stage is recommended.^32,33  The duration between both stages ranges from 3 months to 6 months and depends on the type of graft material (autogenic, allogenic, or xenogenic), graft particle size, and nature of the grafting technique (eg, block or particulate) used for the augmentation process. Various techniques and bone graft materials have been proposed to augment the horizontal and vertical dimension of the alveolar ridge, such as guided bone regeneration (GBR); onlay/veneer grafting; combinations of onlay, veneer, and interpositional inlay grafting; distraction osteogenesis; ridge splitting; free and vascularized autografts for discontinuity defects; mandibular interpositional grafting; and socket preservation.^6,8–10  Systematic reviews comparing these procedures have demonstrated satisfactory results in terms of implant survival, and no technique has been demonstrated to be superior as compared with others.^6,8–10,34  Any of the grafting procedures, after giving due consideration to their advantages and disadvantages, can successfully be used for ridge augmentation. In addition, the PASST principles (primary wound stability, angiogenesis, space maintenance, stability of wound, and tension-free closure) need to be borne in mind for predictable bone regeneration at deficient sites.³⁵ 

Once both the soft and hard tissue assessment is complete and the required augmentation technique is selected, a treatment sequence for grafting and implant placement is formulated depending on the requirement of each case. Figure 2 provides a guideline for treatment planning the augmentation sequence. In cases in which soft tissue grafting is required first, it is advisable to wait at least 6 weeks following a free gingival graft and up to 8 weeks following a subepithelial connective tissue graft,^36,37  before hard tissue grafting and/or implant placement, to allow for complete healing and remodeling of the soft tissue graft.

After clinical and medical examination of the patient, a prosthetic plan that involved placement of implants in the region of No. 20 and 21 and fixed partial units for No. 19 and 22 was decided (Figure 3). Prior to implant placement, analysis of soft and hard tissue requirement was performed according to the SRA protocol (Figure 4). Following step 1 of the SRA protocol, assessment of the soft tissue was done, and the amount of keratinized tissue was found to be less than 2 mm (less than 1 mm each on buccal and lingual flap) and was determined to be inadequate; however, the deficiency was minor. Step 2 of the SRA protocol, which involved the hard tissue examination, revealed adequate bone for implant placement at the proposed site. At step 3 of the protocol, it was decided that the soft tissue defect was minor, and therefore, it was to be augmented at the time of implant uncovery (second-stage surgery) using a free gingival graft from the palate (Figure 4). A treatment plan was decided that involved implant placement first (Figure 5a), followed by a free gingival graft to augment the keratinized tissue at the second stage (Figure 5b and c). The final restorations were placed 3 months following the second-stage surgery (Figure 5d). Thus, the SRA protocol provided a clear guideline to treatment plan the grafting process.

Following clinical and medical examination of the patient, a prosthetic plan that involved placement of implants in the region of No. 18 and 19 and fixed partial units for No. 18 and 19 was decided (Figure 6). An analysis of soft and hard tissue requirement was performed using the SRA protocol (Figure 7). Following step 1 of the SRA protocol, assessment of the soft tissue was done, and the amount of keratinized tissue was found to be less than 2 mm (less than 1 mm each on buccal and lingual flap) at the proposed implant sites along with a strong frenal pull requiring major soft tissue correction. Step 2 of the SRA protocol revealed inadequate bone for implant placement at the optimum restorative site. A cone-beam computerized tomography scan revealed inadequate width of the alveolar ridge ranging from 3.8 mm to 4.6 mm at the planned implant site and required major hard tissue correction (Figure 8). Following step 3 of the protocol, it was decided that the soft tissue defect needed to be corrected first using a free gingival graft from the palate, followed by hard tissue grafting and, finally, implant placement (Figures 7 and 8). A treatment plan was decided that involved free gingival graft first (Figure 8a), followed by horizontal buccal ridge augmentation after 6 weeks of healing (Figure 8b). Implant placement was planned 8 weeks after ridge augmentation using a surgical stent (Figure 8c). The implant sites showed excellent soft and hard tissue volume at the time of fixture level impressions 12 weeks after implant placement (Figure 8d).

If the SRA protocol was not followed, it is quite likely that the GBR procedure would have become more challenging and the implant prosthesis would have been left with inadequate keratinized tissue around it, which would have been undesirable.

Without a well-organized sequence, treatment planning the soft tissue and hard tissue augmentation for implant site development becomes difficult. The SRA protocol enables the clinician to follow an evidence-based treatment plan, which would help in the long-term success and implant site stability. The emphasis of the protocol on soft tissue assessment and, if required, augmentation prior to hard tissue assessment and grafting would improve the prognosis of the treatment in terms of implant maintenance over a long period of time.

Abbreviations

GBR

guided bone regeneration

PASST

primary wound stability, angiogenesis, space maintenance, stability of wound and tension-free closure

SRA

sequential ridge augmentation

There was no support in the form of funding for this study; the authors declare that there was no conflict of interest.