Guided Bone Regeneration and Implant Placement in Association With a Coronally Positioned Palatal Sliding Flap: A 17-Year Follow-Up Case Report

The use of osseointegrated dental implants for replacement of missing teeth is considered a reliable treatment option, with a cumulative survival rate of almost 88% after a 36-year follow-up.¹  Comparable long-term outcomes have been reported for implants inserted in either pristine or augmented bone in terms of interproximal bone levels and dimensions of buccal bone and mucosa.²  Interestingly, implant survival of up to 20 years after insertion seems to be higher for implants placed in augmented sites,³  stressing the importance of an adequate amount of supporting bone circumferentially around the implant. Guided bone regeneration (GBR) technique has been developed to assist and promote bone healing by preventing nonosteogenic cells from migrating into a bone defect by means of barrier membranes.⁴  When applied to localized alveolar defects, GBR allows restoration of an adequate contour of the atrophic alveolar ridge and ensures a proper quantity and quality of supporting bone for a predictable, prosthetically driven implant placement.⁵  However, the most common complication of this technique is the membrane exposure, which has detrimental effects on the final outcome of bone regeneration.⁶  Furthermore, the absence of keratinized mucosa (KM) has been reported as a risk indicator that is strongly correlated with the occurrence of peri-implantitis.⁷  For such reasons, soft tissue management is regarded as the main component to avoid postoperative complications, thereby influencing the success of the GBR procedure and implant-supported rehabilitation. In this context, a split-thickness palatal flap, displaced coronally, has been described as an alternative flap design that facilitates primary intention healing and increases the zone of KM adjacent to the implants.⁸  A similar technique has also been used in the augmentation of soft tissues during second-stage implant surgery to achieve optimal function and esthetics, particularly in case of single-tooth implants in the anterior maxilla.⁹  That said, the long-term stability of hard and soft tissues following guided bone regeneration, implant placement, and simultaneous soft tissues management is seldom evaluated in literature. Thus, the purpose of the present case was to report hard and soft tissue stability at the 17-year follow-up evaluation after GBR and simultaneous implant placement in association with a split-thickness, coronally positioned palatal flap.

A 52-year-old nonsmoking male patient presented with complaints of pain and gingival bleeding in the posterior region of the right maxillary arch. The medical history was noncontributory. The initial clinical and radiological examination revealed a periodontally compromised upper right first molar, supporting a bridge connected to the upper right canine, replacing the first and second premolars lost several years earlier due to unspecified reasons (Figure 1). The natural element #3 was judged hopeless in view of the advanced periodontal breakdown, and the possible treatment options were discussed with the patient, including the possibility of a removable partial prosthesis. The patient was seeking a fixed solution; therefore, the proposed rehabilitation project consisted of GBR and implant-supported fixed dental rehabilitation. After acceptance of the treatment plan, the patient signed an informed consent for all surgical procedures. The ethical principles of the Helsinki Declaration were observed during all phases. The bridge was carefully separated from element #6, and the extraction of element #3 was carried out gently, adopting a minimally invasive approach.

After three months of uneventful healing, implant placement and simultaneous GBR were planned. The clinical examination showed a residual ridge resorbed in both width and height (Figure 2). The initial orthopantomograph was used to plan the length of the implants to reduce the exposure of the patient to additional radiation doses. A computed tomography scan was not performed, as it was not available at that time. Two weeks before surgery, the patient underwent a professional oral hygiene session and received oral hygiene instructions. One day before the appointed surgical session, the patient was given antibiotic therapy consisting of amoxicillin 1 g twice daily for 6 days. The surgery was conducted on an outpatient basis under local anesthesia (Figure 3). Prior to the start of the surgery, the patient was instructed to rinse with 0.2% chlorhexidine digluconate for 1 min, and a perioral skin antisepsis was accomplished with benzalkonium chloride degerming agent. Local anesthesia was achieved with mepivacaine 2% with epinephrine 1:100 000. A slightly palatal crestal incision was made to connect 2 divergent vertical releasing incisions without involving element #3 mesially, and a mucoperiosteal flap was raised. Clinically, the bone crest appeared irregular, with knife-edge morphology and a severely resorbed buccal plate. To regularize the alveolar ridge at the location of the implant sites, a triangular-shape bone block was carefully harvested and preserved in saline solution. The height, width, and thickness of the bone block were 10 mm, 6 mm, and roughly 2 mm, respectively. The implant sites were prepared in positions #3, #4, and #5 according to the manufacturer's recommendations in a prosthetically driven position guided by a surgical stent. Subsequently, 3 stepped-screw, internal-hex, 4.5-mm diameter dental implants with a sandblasted, and acid-etched surface (Frialit-2 implant system, Friatech AG, GmbH, Mannheim, Germany) were inserted with an insertion torque of ≥25 Ncm. Perforations of the cortical plate were performed using a small round surgical bur under copious irrigation with saline solution to facilitate vascularization of the graft and mesenchymal cell colonization from the bone marrow. A nonresorbable titanium reinforced expanded polytetrafluoroethylene (e-PTFE) barrier membrane (Gore-Tex, W. L. Gore & Associates, Flagstaff, Ariz) was trimmed and shaped extraorally to fit the defect size and was then fixed to the palatal side of the residual ridge with 2 endosseous pins. The harvested bone block was placed buccally with respect to the implant in position #4, approximately in the center of the defect. The rest of the missing hard tissue contour was reconstructed with prehydrated deproteinized bovine bone mineral (DBBM) particles (Bio-Oss, Geistlich AG, Wolhusen, Switzerland). The heterologous graft was overcontoured by approximately 20% to compensate for the resorption of the bone substitute during the remodeling phase. The e-PTFE membrane was then folded over and fixed to the vestibular side with 3 endosseous pins to secure and stabilize the bone graft. At this point, a coronally positioned palatal sliding flap was performed as originally described.⁸  In brief, 2 full-thickness vertical parallel incisions were extended approximately 2 to 3 mm longer than the desired coronal reposition. The palatal flap was thinned in a corono-apical direction without reaching the most apical part of the 2 vertical releasing incisions. A split-thickness mesiodistal incision was performed to connect the vertical incisions at a deeper layer to split the palatal tissue in another plane. As the palatal dissection proceeded, it was possible to mobilize the palatal flap toward a more coronal position. Periosteal horizontal releasing incisions were performed to passivate the buccal flap to allow tension-free closure. Primary wound sealing was obtained with horizontal mattress and single stitches using nonresorbable sutures (Gore-Tex, W. L. Gore & Associates).

In addition to the antibiotic therapy, medication prescribed for postoperative use by the patient included 600 mg ibuprofen twice daily for 2 to 3 days according to individual needs, and 0.2% chlorhexidine digluconate 15 mL mouthwash rinsing for 1 min 3 times daily up to suture removal, starting the day after the surgery. The patient was instructed to refrain from mechanical plaque removal of natural element #3 for 14 days. Moreover, the patient was not allowed to wear interim prosthesis during the healing time to prevent micromovements and soft tissue compression.

Sutures were removed 14 days after the surgery. The patient was recalled once a week for the first month, and then monthly thereafter to assess the healing process. No local adverse events, such as soft tissue dehiscences or membrane exposure, were observed. After 8 months from the reconstructive procedure, a clinical and radiological evaluation was performed to assess the healing process (Figure 4). No complications occurred; hence, the second stage of surgery was carried out to remove the nonresorbable membrane and cortical pins, and to evaluate the regeneration outcome. After membrane removal, it was possible to observe a very thin soft tissue layer of periosteal-like tissue occupying the space between the membrane and the regenerated bone-like tissue. The entire defect was completely filled by newly formed bone in an apparent ongoing maturation phase. The regenerated bone appeared firmly integrated within the surrounding hard tissue and well vascularized. In few areas, residual DBBM particles embedded in bone-like tissue were noticed. The physiological contour of the alveolar ridge was reestablished both in horizontal and vertical dimensions (Figure 5). After remodeling the bone in excess to expose the cover screws of the implants, healing abutments were connected. The mucoperiosteal flap was finally adjusted and sutured to fit around the neck of the healing abutment. Impressions and prosthetic phases began 1 month after implant uncovering, and implant-supported temporary resin restoration was provided (Figure 6). The temporary acrylic resin prosthesis was left for a period of 6 months, after which the definitive metal-ceramic definitive restoration was delivered to the patient. All temporary and definitive prosthesis were cemented with temporary zinc oxide-eugenol cement (Temp-Bond, Kerr Dental, Scafati, Italy). The patient was enrolled in a strict oral health maintaining program consisting of professional oral hygiene procedures, scaling and root planing every 3 months the first year and twice a year thereafter. Clinical follow-up recalls were planned yearly, while radiological exams consisting of orthopantomographs and intra-oral radiographs were performed at 1 year, 8 years, 12 years, and 17 years after the implants insertion (Figure 7). The latest follow-up visit performed after 17 years from the bone augmentation procedure showed clinically stable gingival levels. An acceptable slight apical migration of the buccal gingival margin was observed in correspondence with the implant element #5 and natural element #6, while a coronal adaptation of the soft tissues was detected in correspondence with the implant in position #3. Most importantly, the peri-implant soft tissues appeared clinically healthy, with peri-implant probing depths <4 mm circumferentially around the implants and no signs of bleeding on probing. The clinical outcome was corroborated by the radiological evaluation. No radiographic signs of peri-implantitis were observed. Mesial and distal marginal bone levels remained almost unchanged within the physiological threshold reported in the Albrektsson et al success criteria¹⁰  (Figure 8). The patient was satisfied from both functional and esthetic aspects.

The management of soft tissues is a critical aspect when performing GBR procedures and implant rehabilitations. A tension-free primary closure along the incision line might prevent the occurrence of wound dehiscences and membrane exposure. Furthermore, primary closure results in decreased discomfort and faster healing of the surgical wound.¹¹  In addition, the presence of at least 2 mm of KM around dental implants has been reported to have beneficial influence on implant health due to greater tissue stability, lower biofilm accumulation, and higher cleansability.¹²  Nonetheless, the long-term hard and soft tissues stability around dental implants after GBR is still underreported. In view of this, the goal of this present clinical case was to report the 17-year follow-up of a GBR procedure and implant-supported rehabilitation in the posterior maxilla. The focus was to show the stability of hard and soft tissues after the execution of a coronally advanced sliding palatal flap. This technique was developed to cover implants that have been inserted in compromised positions and augmented with barrier membranes. A series of incisions were used to split the thickness of palatal tissue so that the layers were capable of sliding and rotating one over the other toward a more coronal position.⁸  In the present case, this technique was applied simultaneously with the implant placement and reconstructive surgery with several purposes. The rationale was to decrease the tension of the buccal flap by reducing the gap between the vestibular and palatal margin of the surgical wound. This was accomplished by mobilizing the palatal flap more coronally, obtaining a bucco-palatal gain of 2 to 3 mm. In this way, the secondary aim of increasing the KM buccally was self-achieved by limiting the coronal advancement of the vestibular flap and, thus, the coronal displacement of the buccal KM in a more palatal position. It is worthy of note that the initial incision line dislocating slightly palatal might have contributed to increase the final amount of KM. Another advantage related to this aspect was to prevent an excessive decrease of the buccal vestibule when the vestibular flap was advanced to attain primary closure. Hence, there was no need for secondary vestibuloplasty procedures to deepen the buccal sulcus. This technique has been applied also in consideration of the poor soft tissue quality and quantity observed as inevitable consequence of the long-lasting edentulous ridge and the physiological healing after tooth extraction. A diminished distance between the palatal and buccal incision margins allowed reducing periosteal horizontal releasing incisions needed to mobilize the buccal flap. As a direct consequence, the periosteal blood supply was preserved without interfering with early soft tissue healing and revascularization of the grafted area. This is particularly true in the presence of a barrier membrane, which can further compromise the vascularity of the surgical area. In view of the split-thickness dissection performed to advance the palatal flap, it is noteworthy that the apical extension of the incisions on the palatal side must be limited to respect the anatomical course of the greater palatine artery.

Following this approach, the healing proceeded without complications. Healthy soft tissues characterized by firm and stable KM allowed placing the incisions during second stage surgery in an ideal anatomical condition. Avoiding membrane exposure with a tensionless closure throughout the entire 6-month healing period was an essential prerequisite to achieve successful regeneration. The importance of flap integrity was highlighted by the amount of bone regeneration obtained at the re-entry surgery. We noticed newly formed bone, well vascularized and firmly integrated into the surrounding hard tissue, filling the defect. In some parts of the regenerated volume, we found residual granules of DBBM, confirmation of the slow resorption rate of this bone substitute. In addition to the osteoconductive potential, the slow remodeling pattern of the DBBM has been exploited to retard the resorption of the autogenous bone block. Such technique showed the capability to preserve the original bone volume of corticocancellous blocks from clinical and histological perspectives.¹³  The results obtained in the present case are in agreement with other clinical studies supporting the use of DBBM eventually combined with autogenous bone, and e-PTFE membranes in the three-dimensional reconstruction of peri-implant defects.^14–16 

From a clinical and radiological standpoint, none of the implants failed nor was a significant bone loss observed on the radiographic images. Interestingly, this result was maintained over a 17-year follow-up, highlighting the efficacy of this technique even in demanding clinical defects over a long-term period.

Abbreviations

DBBM

deproteinized bovine bone mineral

e-PTFE

expanded polytetrafluoroethylene

GBR

guided bone regeneration

KM

keratinized mucosa

The authors report no conflicts of interest related to this study.