Guided Peri-Implant Autogenous Soft-Tissue Grafting: A Case Report

The reliability of implant therapy can no longer be questioned, with a success rate of more than 95% at 10 years.^1,2  The profession must now recognize and correct the elements identified in implant failures. Many factors can influence this; among them,³  the presence of peri-implant keratinized tissue seems to be of importance.⁴  Although the role of keratinized tissue in the prevention of peri-implant soft-tissue inflammation remains relatively controversial in the literature,^5–8  keratinized tissue does facilitate plaque control for the patient^9–13  and thus contributes to the maintenance of peri-implant soft-tissue health.^14–19 

Various techniques are available to correct a peri-implant keratinized tissue defect: (1) autogenous soft-tissue grafts (free gingival or connective tissue graft),^20,21  (2) acellular dermal matrix, or (3) xenogenic collagen matrix. Free gingival graft is one of the techniques of choice.^22,23  It is indicated when the esthetic demand is not preponderant and/or when there is an important need to increase the height or thickness of the keratinized mucosa. This mucogingival surgical technique has shown good results²²  but sometimes can prove difficult to perform (sites difficult to access, presence of dental- or implant-supported prosthesis, or management of the greater palatine artery). Computer-assisted surgery may overcome this last limitation.

Digital intraoral scanners and their software suites have revolutionized implant dentistry. They allow the final prosthetic project to be planned precisely and the various stages of treatment to be optimized accordingly (determination of implant emergence profiles, axes, and preparations for prosthetic crowns or veneers). Digital planning could also be an asset for performing a peri-implant free gingival graft. The clinician could accurately plan the keratinized tissue augmentation project. With better anticipation of both surgical recipient and donor sites and an understanding of the greater palatine artery anatomic environment, digital planning could facilitate the correction of peri-implant soft-tissue defects. It could also improve the outcome by reducing the operative time and thus favoring primary wound healing. The proof of concept of a guided peri-implant free gingival graft has never been reported.

The aim of this case report was to present for the first time the use of digital planning for a peri-implant free gingival graft.

A 65-year-old nonsmoking patient in good general health presented to rehabilitate his posterior right mandibular edentulism (tooth site Nos. 30 and 31). The implant-supported prosthetic solution was chosen as the best therapeutic option for the patient. Preimplant evaluation showed favorable bone volume but a reduced keratinized mucosa height in the edentulous area (Figure 1a). Implant placement was assisted by a full surgical drill guide (Figure 1b). During implant surgery, the crestal incision was shifted lingually (Figure 1c and d) to compensate for the keratinized tissue defect. Two implants were placed (Tissue Level Roxolid SLActive Standard Plus Wide Neck length 10 mm; Straumann AG Institute, Basel, Switzerland).

After 3 months of osseointegration, the mucosal environment of the implants was assessed at their vestibular sites; between 0.25 and 1 mm of keratinized tissue at the No. 30 site and less than 0.5 mm at the No. 31 site (Figures 2a and b). A free gingival graft was thus indicated to increase the amount of keratinized tissue. Examination of the sites nevertheless presented some operative difficulties. The recipient site presented with complicated access: (1) posterior location, (2) presence of external oblique ridge and (3) zygomatic tension, (4) low vestibular depth, and (5) healing caps. The donor site presented with (1) deep palate and (2) marked bunoid papillae (Figure 2c).

To help overcome these surgical difficulties, a guided surgical approach was chosen. Because cone-beam computerized tomography (CBCT) and maxillary digital impression had already been performed for the guided implant surgery, no additional examination was required. The mandibular digital impression was updated by removing the previously edentulous area and by rescanning it with the healing caps in place. Planning of the guided free gingival graft consisted of 3 successive steps (Figure 3).

Step 1 consisted of planning of the recipient site. The digital model made with the intraoral scanner (Trios 4; 3Shape, Copenhagen, Denmark) allowed for both information on the patient's teeth and mucous surfaces but also for color evaluation of the different tissues.²⁴  Therefore, it was possible to reposition the mucogingival line. Based on this information, the clinician could draw the contours of the intended recipient bed (margin line tool of the Implant Studio software, 3Shape; Figure 3a). The aim was to obtain a peri-implant keratinized tissue strip 2 mm in height.^12,13,25  The contours were defined as follows: at the crestal level along the healing caps in an apical direction 3 mm from the cap. This was done to compensate for possible postoperative graft retraction of 30%.²⁶  The proximal boundary was 2 mm in the mesial and distal directions to the healing caps to afford a sufficient vascular supply. This file was then sent to the info-prosthetist.

Step 2 comprised planning for the donor site. The CBCT provided the location of the greater palatine foramen from which the great palatine artery emerges as well as the palatal gutter in which this artery runs (Figure 3b). The bunoid papillae, gingival collars, and depth of the palate were studied. By superimposing the CBCT and digital model, the thickness of the entire palatal mucosa was measured (difference between the surface of the digital impression and the bone surface determined on the CBCT). These data are of great interest when selecting the site for graft harvesting (Figure 3c).

Step 3 was the design of the mandibular and maxillary surgical guides. With the help of the 3Shape Appliance designer and 3Shape Removable Partial software (3Shape), the info-prosthetist designed the surgical guides. The complete mandibular surgical guide was first traced, then the digital pattern corresponding to the future recipient bed was individualized and subtracted to the guide (Figure 4a–c). For the maxillary surgical guide, the surface mesh of the pattern, initially convex, was inverted (Exocad, Exocad GmbH, Exocad America, Inc, Woburn, Mass) to fit to the concavity of the palatal recipient site while perfectly maintaining the designed shape. As this digital design is innovative, each step was checked to make sure that no inaccuracies were introduced into the digital flow. The digital pattern was printed (Max series, Asiga, Alexandria, Australia) with a biocompatible resin (Keyguide, Keyprint, Keystone, Gibbstown, NJ) and clinically positioned to the harvesting site. For this, the practitioner took into account the (1) course of the greater palatine artery and (2) location of the gingival collars, bunoid papillae, and varying thicknesses of the palatal mucosa. The contours of the digital pattern were marked using a flowable composite before being scanned (Figure 4d). The maxillary surgical guide with a window corresponding to the harvesting site was then designed accordingly (Figure 4e, f). This guide served both as an incision guide and as a palatal protection plate once the inverted digital pattern was repositioned in the guide window after surgery.

Once the surgical guides had been received (Figure 5a), the free gingival grafting procedure was performed. Following administration of local anesthesia (infiltration anesthesia, 4% articaine with 1:200 000 epinephrine injection solution; Septanest, Septodont, Saint-Maur-des-fossés, France), the recipient bed was prepared. The mandibular guide was accurately positioned due to the presence of the adjacent teeth and the healing caps (Figure 5b). The incision was made with a micro-blade (Viper blade SB004; MJK, Marseille, France) following the contours of the guide window. After removal of the guide, the recipient site was prepared by reflecting a partial-thickness flap (Figure 5c). The various fibrous or muscular insertions were dissected to ensure the immobility of the future graft during healing (Figure 5d). A compress soaked in physiological saline was then applied to protect and hydrate the recipient site during the graft-harvesting phase.

In the second step, the maxillary surgical guide was inserted (Figure 6a). The incision that delineates the graft was made with a microblade following the guide window. The graft was then dissected in partial thickness and harvested (Figure 6b, c). Since the thickness of the palatal mucosa was known after planning, it was possible for the surgeon to harvest the graft with an optimal thickness (greater than 1.5–2 mm while keeping a distance from the great palatine artery and leaving sufficient connective tissue to avoid postoperative complications). The adipose tissue present on the graft's inner surface was removed. The graft was then positioned in a physiological saline solution to prevent dehydration. A compress was firmly applied to the donor site to ensure initial hemostasis.

In the final stage, the graft was placed at the recipient site. It was held in place with sutures (Monosof 5.0 and 6.0; Covidien, Dublin, Ireland) to allow for immobilization and good coaptation with the recipient site (Figure 7a). Hemostasis of the donor site was completed. A sterile type I collagen compress (Pangen; Urgo Surgical, Chenôve, France) was cut to the exact dimensions of the site using the digital template and sutured to the mucosa. The window of the palatal plate was then closed with the printed pattern, and the entire unit was assembled with flowable composite (Figure 6d). This full palatal plate was then used as a protective plate for the operative donor site to limit hemorrhagic risk and postoperative pain. A prescription (amoxicillin 2 g/d for 7 days, paracetamol 4 g/d for 3 days, paracetamol with codeine as needed, chlorhexidine mouthwash 0.2% to be diluted [chlorhexidine/chlorobutanol 0.5 mL/0.5 g per 100 mL, 20 mL of solution diluted with 25 m: of water), postoperative directions, and oral hygiene instructions were given to the patient. The patient was seen 2 weeks postoperatively to remove the sutures. The postoperative pain was tolerable due to the wearing of the palatal protection plate. At 6 weeks, healing was satisfactory, and a band of more than 1.75 mm of keratinized tissue surrounded the 2 healing caps (Figure 7b). One year after surgery, the patient presented with a stable band of keratinized tissue (3 to 4 mm around the implant at the No. 30 site and 1.75 to 3 mm around the implant at the No. 31 site; Figure 7c). The peri-implant environment showed no deposits of bacterial plaque or signs of inflammation either on probing (no bleeding, probing depth 3 mm). Radiologically, the peri-implant crestal level was constant (Figure 7d). Digital measurement tools 1 year postsurgery demonstrated a gain of 1 mm of tissue thickness (Figure 7e) and a thickness of keratinized tissue close to 2.7 mm (Figure 7f). Regarding the patient's reporting, there was greater comfort during brushing and a high degree of satisfaction following the intervention.

This case report provides for the first time the proof of concept of a guided free gingival graft around a dental implant. The guided surgery approach permitted the clinician to (1) anticipate and execute the intervention, (2) decrease operative time, (3) improve the practitioner's comfort, and (4) potentially enhance the free gingival graft outcome. In addition, this report outlines the technical steps performed in detail and with illustrations, so that practitioners can easily reproduce this surgical protocol.

The first authors to have highlighted the importance of the keratinized tissue on periodontal health were Lang and Loë in 1972.²⁷  In their longitudinal clinical study, they showed that in the presence of less than 2 mm of keratinized tissue, residual inflammation is present despite good plaque control. This finding has long been extrapolated to the field of dental implantology. However, from the years 1990 to 2000, some authors questioned this assertion.^5–8 

Due to the excessive heterogeneity of the clinical parameters of the clinical studies, it is difficult to determine the real contribution of the keratinized tissue to the maintenance of the peri-implant health.²⁸  Nonetheless, in cases presenting with an insufficient volume of keratinized tissue, clinicians may use this protocol as a possible favorable factor to be considered along with other factors such as the patient's systemic health, periodontal history, implant site (presence of an abnormal frenum, fibrous scar tissue, and vestibule depth), oral hygiene compliance, and accessibility for dental brushing.

The role of the keratinized tissue in maintaining peri-implant soft-tissue health has been debated.²⁹  Indeed, it is difficult to determine a link between a keratinized mucosa height threshold and an improvement in the peri-implant inflammation index.²⁶  Nevertheless, looking at the literature as a whole, taking into account study designs, sample sizes, and length of patient follow-up, keratinized mucosa appears to have a positive role in maintaining peri-implant health.^{13,23,25,30–32} 

Moreover, one element seems to bring consensus among the authors: the defect of peri-implant keratinized tissue can hinder the execution of oral hygiene and favor the accumulation of dental plaque.^9–13  It could be stated that peri-implant keratinized tissues provide greater resistance to external aggression and increased oral comfort for patients during plaque control procedures. They also contribute to soft-tissue stabilization and improve the esthetic results of implant-supported rehabilitations (reduced soft-tissue discoloration and decreased risk of peri-implant recession).^{14–16,33–35} 

There are many soft-tissue augmentation procedures: (1) autogenous soft-tissue grafts (free gingival or connective tissue graft), (2) acellular dermal matrix, or (3) xenogenic collagen matrix. Each technique has its advantages.^23,36–38  Connective tissue grafts are the techniques that offer the greatest predictability in terms of recession recovery and esthetic results and tend to increase soft-tissue volume. Xenografts or allografts can be a good alternative, with the main advantage of reducing intraoperative and postoperative morbidity and decreasing the number of surgical sites. The free gingival graft remains the approach of choice in situations in which esthetic demand is not paramount and there is a need to increase the keratinized mucosal height or soft-tissue thickness. It may show a more predictable increase in the width of the keratinized tissue.²³ 

Free gingival grafts were first described by Nabers³⁹  in 1966 and used to increase the height of keratinized gingival tissues. Logically, one of the conclusions of the systematic review of Thoma et al²³  in 2018 corroborated this fact: in the nonesthetic zones, to increase the height of peri-implant keratinized tissue, the best technique would be the free gingival graft. This was confirmed in the recent systematic review and network meta-analysis conducted by Tavelli et al²²  in 2021. However, Zucchelli et al,⁴⁰  in their review of the state of the art in 2020, alerted the reader to the difficulties inherent in the use of this technique, such as poor preparation of the recipient site, a graft of inadequate size or thickness, and a lack of graft stabilization. It is also important that the clinician keep in mind the significant shrinkage (approximately 30%) of the free gingival graft during the healing process.²⁶  Graft shrinkage forces the harvesting of a larger graft, which implies an increased risk of comorbidities for the patient.

The clinician could perform a keratinized tissue augmentation before, during, or after implant placement. There is no consensus on the best time to perform this surgical procedure.^{22,37,40–42}  The advantage of performing the procedure prior to implant placement is that there is no implant component or implant-supported prosthesis to be bypassed at the recipient site.⁴²  Nevertheless, it can sometimes be difficult to predict the future height of peri-implant keratinized tissue in edentulous sites where keratinized tissue is moderately present. In the situation in which a lack of keratinized tissue is detected after implant placement, it is preferable to perform the procedure prior to the placement of future supra-implant prosthesis, since the caps could be easily removed at this stage to facilitate the handling of the surgical blades or micro-blades. Another option could have been to use temporary crowns or customized healing abutments. The temporary crowns or customized healing abutments could reshape the gingival contour around the implants to some extent and leave the gingival tissue more esthetic and stable. In our case, these solutions were not chosen because of the cost to the patient and the profile of the implants. The effectiveness of mucosal remodeling by temporary crowns or customized healing abutments is indeed more limited with tissue-level implants than in the case of bone-level implants.

The contribution of computer-assisted technology to dentistry is major: it allows clinicians to enter into a new logic. Because of this technology, it is possible to anticipate with precision the surgical intervention or the dental preparation by putting the rehabilitation project at the center of the reflection. In this first description of guided mucogingival surgery, the contribution of the digital solution is multiple.

First, the clinician will be able to anticipate the surgical procedure. The areas to be grafted and harvested will be determined with a precision exceeding that allowed by clinical examination alone. The height, width, and thickness of the soft tissues could be perfectly determined by the computer-assisted technology. The future recipient bed may be designed with full knowledge because of the data. The incision windows of the guides save time and enhance the execution of the procedure. The perfect match between the recipient bed and the graft facilitates the repositioning of the graft and promotes healing by primary intention. This first wound healing occurs faster than secondary wound healing and carries a lower risk of infection or scar tissue formation.

Then, the practitioner may secure the surgical gesture. In the case of a free gingival graft, the main risk is hemorrhagic during palatal graft harvesting. It occurs in the case of injury to the greater palatine artery or collateral vessels. A recent systematic review has defined a probabilistic safety zone for graft harvesting while minimizing the risk of arterial injury.⁴³  However, instead of estimating the position of the greater palatine artery, it is possible to visualize its emergence from the foramen and its routing gutter because of the CBCT. It is then possible to draw the contours of the artery with implant-planning software to avoid injury during graft harvesting.

Finally, as with any guided surgery, the practitioner would find a real comfort of work and a reduction of surgical stress since the intervention had been carefully planned and secured. Nevertheless, this guide is a tool, and the practitioner must remain vigilant and in control of the surgical intervention.

It is important to note that this guided mucogingival surgery did not require an additional tomographic examination since the CBCT had been performed for implant treatment planning. If the patient had not already undergone a CBCT, it would have been necessary to assess the scan's benefit-risk ratio. In cases of a small graft harvesting, the benefit-risk ratio could be unfavorable given the radiant nature of the CBCT and the lower risk of injury to the greater palatine artery. In cases of a large graft harvesting, the location of this artery may be of greater interest since the size of the harvesting area must be optimized.

For the patient, the benefits are multiple: reduction in operative time, minimization of postoperative discomfort due to the palatal protection plate, and, above all, increased ease and comfort during the oral hygiene procedures over the long term.

This case report has shown the feasibility of guided mucogingival surgery, but it does not allow readers to make definitive conclusions regarding potential decreases in postoperative morbidities or on an improvement in the outcome compared with conventional surgery techniques. Further clinical research is needed to validate this protocol and to assess its long-term impact on peri-implant health.

Like guided implant surgery, guided periodontal or peri-implant soft-tissue surgeries present multiple advantages and could become a tool perfectly adapted to the exercise of the implantologist or the periodontist. The practitioner could retrieve the data from the clinical examination and then have access to supplemental data such as the needed measurement of the height, width, and especially thickness of the soft tissues at the area to be harvested and grafted. In addition, the clinician could locate the greater palatine artery, thus limiting the risk of injury and hemorrhage. Guided mucogingival surgery makes it possible to (1) anticipate and secure the surgical procedures, (2) save operating time, and (3) obtain a better adaptation of the graft to the recipient bed. Clinician and patient comforts are also improved. This promising novel approach merits further investigation to determine its impact on free gingival grafts outcomes and patient feedback.

Abbreviation

CBCT:

cone-beam computerized tomography

We thank Dr Thibaud Clee and Dr Alexandre Liman for their advice, Yannick Gourrier (Digital-labs, La Roche sur Yon, France) for having concretized our ideas, and the patient for his kindness.