The Prosthetic Rehabilitation of Maxillary Aesthetic Area Guided by a Multidisciplinary Approach: A Case Report with Histomorphometric Evaluation

Abstract

Background: The rehabilitation of complex bone defects in the anterior maxilla presents significant challenges in restoring both function and esthetics. A multidisciplinary approach integrating guided bone regeneration (GBR) and connective tissue grafting (CTG) has proven effective in addressing such cases. Methods: This report describes the case of a 60-year-old female patient who presented with severe alveolar ridge resorption and peri-implant bone loss, necessitating an advanced regenerative strategy. The treatment protocol involved the use of autologous and xenogeneic bone grafts in combination with hyaluronic acid and polynucleotides to enhance osteogenesis and tissue integration. A six-month healing period was observed before histological and clinical evaluations were conducted. Results: The results demonstrated a significant increase in lamellar bone formation and vascularization in sites treated with biomodulators compared to conventional GBR techniques. Subsequently, CTG was employed to optimize peri-implant soft tissue volume and stability, leading to improved keratinized tissue thickness and enhanced esthetic outcomes. This case underscores the importance of a comprehensive surgical and prosthetic plan that integrates bone regeneration with mucogingival management for optimal results in implant rehabilitation. Additionally, histological analysis revealed that the incorporation of hyaluronic acid and polynucleotides resulted in improved cellular activity, reduced inflammatory responses, and enhanced overall bone quality. Conclusions: These results highlight the potential role of biomodulators in regenerative procedures. While the findings suggest promising clinical applications, further long-term studies are necessary to validate the outcomes and establish standardized protocols for the integration of advanced biomaterials in implantology.

1. Introduction

The alveolar bone may undergo resorption following the loss of dental elements due to infectious, traumatic, or rehabilitative causes [1]. This phenomenon can result in significant volumetric changes in the bone substrate, leading to morphological deficits of the alveolar ridge. The correction of alveolar defects through bone regeneration techniques is now essential for implant success [1]. Guided bone regeneration (GBR), introduced by Dahlin in 1988, is a regenerative bone surgery technique aimed at correcting bone defects, restoring the correct volumes and thicknesses of the dento-maxillofacial district, and creating an adequate bone substrate for implant placement [2].

The GBR surgical protocol involves the use of resorbable or non-resorbable membranes in association with autologous or heterologous graft materials. The membrane, acting as a barrier, promotes cell selectivity criteria by preventing the migration of non-osteogenic cells within the site to be regenerated [3]. At the same time, it promotes the stabilization and isolation of the grafted material by supporting the soft tissue overlying the bone defect [1]. For GBR to be successful, the coexistence of three fundamental biological factors is essential: the presence of osteogenic cells, the availability of growth factors that stimulate cell proliferation, and a scaffold, which is essential for clot stability. Hereby, bone substitutes act as scaffolds, promoting cell proliferation and supporting bone regeneration processes [4].

Wang and Boyapati outlined four key clinical principles for successful GBR, such as primary surgical wound closure, angiogenesis, bone defect isolation, and blood clot stabilization [5]. Over time, the integration of biomodulators with regenerative bone surgery techniques has shown increasing success, significantly enhancing the quality of regenerated tissue, accelerating healing processes, and optimizing clinical outcomes. In this context, hyaluronic acid (HA) has proven particularly effective in down-regulating inflammation, stabilizing clot formation, and accelerating angiogenesis and cell proliferation. From a biological standpoint, HA strongly promotes the growth of osteoprogenitor cells while preserving their stemness, potentially regulating the balance between self-renewal and differentiation during bone regeneration following oral reconstructive surgery [6]. HA incorporation into deficient bone areas or bone defects during implant or periodontal reconstructive surgery represents a potentially predictable approach to promote proliferation and differentiation of osteoprogenitor cells [6]. Therefore, the biological and physical properties of hyaluronic acid make it capable of effectively supporting bone regeneration techniques by promoting faster healing, integration, and maturation of graft biomaterials.

Polynucleotides are biocompatible, highly purified DNA-derived polymers with regenerative and anti-inflammatory properties. When applied to surgical sites, they stimulate fibroblast proliferation, promote extracellular matrix remodeling, and enhance angiogenesis. Their trophic effects contribute to improved soft tissue healing and volumetric stability, making them a valuable adjunct in oral regenerative procedures [4].

In cases of significant bone defects, particularly in highly esthetic areas, bone regeneration alone may not ensure implant success or an optimal esthetic outcome. In such circumstances, bone regeneration techniques are often followed by additional mucogingival surgical procedures aimed at increasing or restoring peri-implant soft tissue volume, reducing the risk of recession and deformities, especially in the upper jaw [7]. In this context, periodontal surgery focuses on enhancing both the esthetic and functional aspects of the anterior regions by increasing the amount of attached gingiva and optimizing tissue thickness when needed. Although it has not yet been unanimously accepted that the presence of an adequate band of keratinised tissue (KT) around implants is essential for their long-term survival [8,9], it has been widely demonstrated that their absence may expose them to increased risks of gingival recession and greater difficulties in maintaining oral hygiene. Furthermore, an adequate width of KT in vestibular areas provides several benefits, such as masking the implant abutment and preventing an uneven appearance of the dentition in the transition between natural teeth and implant prosthetic crowns. Conversely, peri-implant soft tissue augmentation is indicated to reduce possible mucogingival deformities, especially in areas of high esthetic impact. Connective Tissue Grafting (CTG) refers to the harvesting of autologous disepithelialized connective tissue, surgically removed from its original site (donor site) and subsequently applied at another site (recipient site) [9]. As extensively described in the literature by Zucchelli et al. [9], the use of a connective tissue graft with a bilaminar technique, placed directly on the exposed root or implant surface and subsequently covered by a coronal mobilized mucosal flap, is now a predictable technique in increasing the volume of keratinized mucosa and peri-dental or peri-implant soft tissue, especially in esthetic areas [7,8]. The bilaminar technique provides the connective tissue at the level of the recipient site, making it possible to modify the gingival phenotype by increasing the thickness of the marginal tissues, while improving the post-surgical stability of the newly formed peri-dental or peri-implant tissues [7]. The coronally advanced flap, provided in the bilaminar technique, gives the grafted connective tissue adequate vascular support, stability, and protection, thus reducing the risk of exposure or necrosis. Covering the graft with a coronal advanced flap let the establishment of the healing process that will allow a correct integration and maturation of the graft with the surrounding soft tissues. Generally, the connective tissue graft is harvested from the palate or retromolar area. To obtain a clutch from the palate, the trap door technique, the parallel-incision technique, and the single-incision technique were initially proposed [10,11]. Recently, it has been demonstrated that soft grafts can be obtained by harvesting and disepithelializing a free gingival graft (FGG) [11]. Numerous clinical studies supported CTG as the actual technique of choice for the gingival recessions’ treatment of dental elements or implant sites [12], as it promotes the correct volumetric restoration of soft tissue and allows the coverage of visible roots or implant components [10], especially in esthetic areas.

The aim of this case report is to illustrate the clinical and histomorphometric outcomes of a multidisciplinary approach, integrating guided bone regeneration and connective tissue grafting for the prosthetic rehabilitation of a complex anterior maxillary defect, with a focus on the potential regenerative benefits of incorporating hyaluronic acid and polynucleotides.

2. Methods

2.1. Case Presentation

A 60-year-old female patient, a nonsmoker with no relevant medical history, presented with a mixed implant-supported prosthetic rehabilitation involving both natural dentition and implants. Clinical and periodontal assessment revealed advanced probing depths around the natural teeth, consistent with active periodontal disease, and clinical signs of peri-implantitis affecting the implants in regions 12 and 22. Furthermore, the entire anterior segment exhibited abscess-like inflammatory manifestations. A preliminary radiographic examination (Rx panorax) revealed the presence of an endodontically treated tooth (2.1) with a history of apicoectomy, adjacent to a needle-supported implant (2.2), displaying an apical radiolucent area consistent with an extensive bone defect caused by peri-implantitis. The presence of clinical hypermobility and radiographic evidence of significant bone loss warranted the removal of the implant (Figure 1b). Therefore, a multi-step treatment plan involves the removal of hopeless implants and teeth, thorough elimination of the local infection and subsequent bone regenerative therapy to support implant-prosthetic rehabilitation in a high-esthetic-impact area. Tooth 1.1 exhibited a deep periodontal pocket measuring 10 mm on the palatal aspect and presented with grade 3 mobility, indicative of advanced periodontal breakdown and compromised attachment. Similarly, tooth 1.3 showed a 9 mm probing depth on the mesial surface and grade 2 mobility, reflecting moderate periodontal involvement with potential bone loss in the interproximal area. Tooth 2.1 was characterized by an 11 mm periodontal pocket on the distal surface and also demonstrated grade 3 mobility, further confirming the presence of severe periodontal disease and a poor long-term prognosis for the affected element.

2.2. Surgical Procedure

Local anesthesia was administered using an articaine hydrochloride/adrenaline solution at a concentration of 1:100,000 (Septanest, Saint-Maur-des-Fossés, Cedex, France), followed by the extraction of dental elements 1.3, 2.1, and the implant in the second quadrant (Figure 2a). The surgical site was then carefully debrided (Figure 2b) to remove all granulation tissue and stimulate bleeding from the bone marrow to promote faster and proper healing of the cavity while minimizing bone resorption. A temporary prosthesis was placed to promote proper tissue healing and meet the patient’s esthetic demands (Figure 2c).

Three months after the tooth extractions, a thorough radiographic evaluation (Cone Beam CT) was performed to assess the extent of the bone defect. The adjacent tooth was maintained in order to the initial bone defect increased the predictability of the subsequent bone regeneration procedure. The presence of adjacent bony peaks around the remaining teeth ensured a margin of vertical bone gain, essential for restoring adequate bone volume for implant placement. (Figure 3a–c) [13,14,15]. Following the elevation of a trapezoidal flap, the collapse of the vestibular bone wall and a substantial residual bone defect occurred.

The implant at site 1.2 was carefully removed due to inadequate osseointegration [16]. At this stage, following thorough decontamination of the surgical site, the guided bone regeneration (GBR) procedure was started. As described by Simion et al. [16], in cases of extensive and non-space making defects, non-resorbable titanium-reinforced membranes are used to ensure stability of the bone graft, and adequate space for selective cellular repopulation [17,18]. Conversely, in the presence of space making defects, resorbable membranes are employed [19]. A good amount of soft tissue is desirable in order to promote a good healing of surgical site without membrane exposure [20,21].

For these reasons, a resorbable membrane was applied to the defect in the first quadrant, while an e-PTFE membrane was placed in the second quadrant defect. At this stage, a mixed bone graft consisting of autologous bone and deproteinized bovine bone (DBBM, Bio-Oss^®, Geistlich, Wolhusen, Switzerland) was applied to the larger bone defect in the second quadrant. In contrast, for the smaller defect in the first quadrant, a composite graft incorporating autologous bone, deproteinized bovine bone (DBBM, Bio-Oss^®, Geistlich, Wolhusen, Switzerland), hyaluronic acid, and polynucleotides (REGENFAST^®, Geistlich, Wolhusen, Switzerland) was utilized. (Figure 4a). The grafting material was harvested using a safe scraper from the autologous bone portion in the anterior maxilla. Once the graft was inserted into the defect, membranes were adapted palatally and vestibularly with pins, according to the technique described by Urban et al. [3]. An attentive periosteal release facilitated proper flap passivation for the correct horizontal mattress and interrupted sutures (Figure 4b). Finally, at the conclusion of the first surgical stage, a provisional resin crown prosthesis was placed to meet the patient’s esthetic needs during the healing period.

After 5 months from the first surgical step, a CBCT scan was performed to plan the implant placement and analyze the bone augmentation. Radiographic images revealed an increase in the horizontal portion and effective bone regeneration, allowing for implant insertion (Figure 5a).

The implant surgery procedure included local anesthetic infiltration (1:100,000 Septanest, Saint-Maur-des-Fossés Cedex France), a crestal incision, and release incisions distal to elements 13–23. Once the full-thickness flap was detached, the reconstructed area was visible, allowing for the removal of the stabilization pins and the non-resorbable membrane placed during the bone regeneration procedure (Figure 5b–d). At the site where the implants were to be placed, a bone core was harvested (using trephine drill, internal diameter 2.5 mm, external diameter 3.0 mm) to histologically evaluate the difference in healing time and quality between the two regenerated sites, both treated with the same GBR procedure but different biomaterials. Once the implants were placed following a prosthetically guided approach [22,23], cover screws were positioned, and the flap was meticulously sutured to ensure optimal implant osseointegration (Figure 5c). The following images illustrate the procedural sequence of clinical steps in implant surgical phase.

Six months after the implant surgical phase, a follow-up visit was performed to assess proper tissue healing. In the anterior maxillary region, a significant mucogingival deformity was observed, characterized by a limited amount of keratinized mucosa and different gingival margin levels (Figure 6), which have a considerable esthetic impact [24].

As extensively described in the literature by Zucchelli et al. [9], a connective tissue graft with a bilaminar technique can be employed to enhance tissue thickness and the width of keratinized mucosa, particularly in esthetic areas where gingival scalloping and harmonious soft tissue relationships are a constant focus in clinical esthetic treatments [7,9,10,11]. Hence, according to current bibliographic evidence, the bilaminar technique is the preferred approach for correcting mucogingival defects in esthetic areas. The flap was elevated split-thickness, and all muscle insertions were eliminated to permit its coronal displacement (Figure 7a). The facial and occlusal portions of the anatomical papillae were de-epithelized to create connective tissue beds to which the surgical papillae of the coronally advanced flap were secured at time of suturing. The CTG was harvested from the palate and derived from the de-epithelization with the blade of a free gingival graft [22]. The mesio-distal length was 6 mm greater than the width of the dehiscence defect and the apico-coronal dimension was 3 mm more to the depth of the bone dehiscence (measured from the length of the clinical crown (CCL) of the contralateral tooth reference point to the buccal bone crest). The graft was positioned to cover the implant–abutment surface from the CCL reference point and secured at the base of the anatomical papillae with two resorbable interrupted sutures and in the apical portion with two single sutures anchored to the periosteum (Figure 7a–c). Flap mobilization was considered “adequate” when the soft tissue management (STM) was able to passively reach a level coronal to the CTG. The flap was sutured in a coronal position to cover the CTG without tension. All the sutures were performed in 6-0Vicryl. Subsequently, a digital impression was taken for the fabrication of a screw-retained resin provisional prosthesis, which will be placed upon tissue healing. At the same time, healing caps were placed to guide tissue healing and ensure optimal adaptation of the provisional prosthesis in the subsequent phase.

One month after the grafting procedure, it was decided to extract element 1.1 (Figure 8a) to allow the placement of a screw-retained resin provisional restoration. Before the handover, composite modifications were made at the cervical third of the prosthesis to shape the gingival tissue and achieve an appropriate gingival contour. (Figure 8b,c). This outcome is attributed to the substantial conditioning effect of the provisional restorations during the healing phase, as extensively documented in the literature by Loi et al. [25,26,27]. Composite modifications of the cervical third of the provisional prosthesis were performed to shape the peri-implant mucosa by applying gentle pressure to the soft tissues during the healing phase. This technique aimed to guide soft tissue maturation and contouring through the creation of a ‘biological polygon’, a tailored emergence profile that mimics natural anatomy and supports the formation of stable gingival architecture.

After 45 days, there was evidence of tissue healing around the provisional crown, a suitable situation for the preparation of the final prosthesis. Once the provisional prosthetic device was removed, the good amount of keratinized mucosa around the implant, adequate soft tissue thickness and harmonious relationship among vestibular gingival margins were observed (Figure 9).

At the end of the tissue conditioning phase, a second series of provisional crowns was inserted in order to promote the good healing and architecture of the soft tissue.

The final prosthetic restoration is successfully delivered after 3 months, achieving excellent esthetic and functional rehabilitation of the anterior maxillary region (Figure 10a,b).

The final prosthetic restoration is successfully delivered after 3 months, achieving excellent esthetic and functional rehabilitation of the anterior maxillary region (Figure 11 and Figure 12).

2.3. Tissue Processing

Immediately after harvesting, bone samples were immersion-fixed in 4% formalin/0.1 M phosphate-buffer saline (pH 7.4) and processed for histological analysis without prior decalcification. Employing the technique elucidated by Donath and Breuner (1982), the biopsy specimens were systematically dehydrated in ascending concentrations of ethanol (ranging from 70% to 100%), infiltrated under agitation and vacuum, and embedded in Kulzer Technovit 7200 VLC (Bio-Optica, Milano, Italy). Subsequently, each block underwent longitudinal sectioning via a diamond saw (Micromet Remet, Bologna, Italy). The two central sections were grounded, polished to a final thickness of 90 μm, and stained with hematoxylin and eosin (H&E). Each section was viewed and photographed at different magnifications: 500×, 200×, 100×, 20×, and 10× (Fisherbrand Serie AX-500, Fisher Scientific, Milan, Italy). Immunohistochemistry was performed for KP-1 (Ventana, mouse), actin (Ventana, mouse, clone 1A4), and SATB2 (Santa Cruz, mouse, clone G-11).

3. Results

Histological analysis revealed that, at low magnification, in the bone tissue treated with hyaluronic acid and polynucleotides, lamellar bone accounted for 45% of the total tissue volume (star), the inorganic matrix approximately 15% (arrows), and the interstitial spaces the remaining 40% (arrow) (Figure 10a). In the tissue treated using the conventional GBR technique, the amount of lamellar bone was lower, accounting for approximately 20% of the tissue (star), the inorganic bone matrix was around 10% (arrows), and the interstitial spaces represented the remaining 70% (dashed arrow) (Figure 10b).

All quantitative evaluations were performed using ZEN Blue software (Carl Zeiss Microscopy GmbH, Carl-Zeiss-Promenade 10, Jena, Germany).

At higher magnification, it is possible to observe that in the treated site, osteoblastic cells were easily found beneath fragments of lamellar bone (arrows), unlike the other site, where their presence was lower (circles). Regarding the interstitial spaces, both samples showed the presence of blood vessels and a variable number of fibroblasts and myofibroblasts mixed with fibrosis and inorganic matrix, the latter being more abundant in the sample not treated with hyaluronic acid.

Finally, immunohistochemistry was performed for SATB2, CD68, and actin to highlight the components within the sample. SATB2 (Special AT-rich sequence-binding protein 2) plays a role in osteoblastic differentiation and osteogenesis, while actin identifies pericytes, smooth muscle cells, and myofibroblasts. CD68, on the other hand, marks inflammatory cells such as histiocytes, macrophages, and monocytes. In the sample treated with hyaluronic acid, some myofibroblasts were found to be positive for actin and SATB2 (circles), and only a few macrophages were visible in the interstitial spaces (circles). In contrast, the main difference in the control sample was the large number of macrophages present in the interstitial spaces (circles).

4. Discussion

The multidisciplinary approach is a valid therapeutic solution for the clinical management of a complex bone defect in the anterior maxilla. The presented clinical case highlights the efficacy of the guided bone regeneration (GBR) technique in bone augmentation procedure, in the presence of the proper clinical condition [28,29,30]. The adopted protocol allowed for adequate bone morphology reconstruction, thanks to the use of resorbable and non-resorbable membranes combined with autologous and heterologous graft materials [26,27]. The membranes, acting as a barrier, promote cellular selectivity by preventing the colonization of the site by non-osteogenic cells, as described in the literature by Urban et al. [3]. Histological results showed a higher amount of lamellar bone in the site treated with hyaluronic acid and polynucleotides compared to conventional GBR, suggesting a potential benefit in integrating these substances into the regenerative protocol [31,32,33]. In fact, in experimental periodontitis [34], polynucleotides (PNs) act as biological stimulators of osteoblast activity and blood vessel formation, playing a fundamental role in bone regeneration. For these reasons, PNs have recently been proposed for clinical applications in regenerative medicine, including GBR [35]. Moreover, a recent literature review has shown that polynucleotides have the potential to boost the bone healing process and enhance the quality of regenerated bone when combined with graft materials [36]. Furthermore, as reported by Bartold et al., HA undergoes extensive degradation in tissues subjected to inflammatory processes, such as those involved in regenerative or implant therapies, leading to the formation of both high- and low-molecular-weight molecules [37]. High-molecular-weight HA suppresses the immune response, preventing excessive inflammation, while low-molecular-weight HA plays a crucial role in signaling tissue damage and mobilizing cells [38]. Additionally, research findings indicate that HA exerts osteogenic effects in bone regeneration processes, contributing to endochondral ossification, guiding osteoprogenitor cell migration, enhancing cell proliferation, and stimulating early vascularization [39]. Based on these considerations, it can be stated that HA, in combination with bone substitutes, can induce angiogenesis in vivo, thereby facilitating faster graft integration into the recipient bone [40]. Furthermore, this combination leads to higher portions of mineralized bone, increased bone volume density [41,42], and enhanced human osteoblastic activity [43]. Therefore, this case report, as demonstrated by clinical images and histomorphometry analysis results, aligns with the existing scientific evidence in the literature about bone regeneration procedures. However, a critical aspect emerged concerns the management of keratinized mucosa post-implantation, which required a connective tissue graft to improve esthetics and peri-implant tissue stability. Bone atrophies are frequently associated with a reduced amount of soft tissue, resulting in mucogingival anomalies after bone regeneration therapy. Therefore, integrating guided bone regeneration (GBR) with periodontal surgery can be beneficial in achieving optimal esthetic and functional rehabilitation in highly visible areas. In this context, according to the current scientific evidence, CTG with the bilaminar technique is the preferred approach for treating mucogingival deformities both at teeth and implant sites [13,44,45,46], as it increases soft tissue thickness, conceals discolored roots or visible implant components, and aids in interdental papilla reconstruction [11,47]. The bilaminar technique success is highly dependent on the quality of the CTG, which in turn is influenced by the harvesting technique, graft thickness, and the space available for soft tissue growth [26]. The emergence profile of the provisional restoration plays a fundamental role in the management of peri-implant soft tissues. A properly designed emergence angle, ideally below 30 degrees, minimizes tissue compression and facilitates biological width formation, reducing the risk of mucosal recession and inflammation. By gradually conditioning the soft tissue with provisional prostheses that replicate the ideal emergence profile, it is possible to promote a harmonious integration of the restoration with the surrounding mucosa, particularly in the esthetic zone. This strategy is crucial for optimizing both the esthetic and functional outcomes of implant-prosthetic rehabilitation. As demonstrated in this case report, reduced implant abutments and composite modifications of the provisional prosthesis were utilized to create a biological polygon, facilitating interdental soft tissue growth within the available space [27]. This approach may have contributed to the increased width and volume of the interdental soft tissue while enhancing vascular exchange between the graft and the surgical papillae of the covering flap. Regarding the surgical technique, a free gingival graft was utilized and subsequently de-epithelialized with a blade. This method offers several advantages: the grafted connective tissue is derived from the layer closest to the epithelium, which is denser, more stable, and less prone to contraction compared to the deeper connective tissue, which contains a higher proportion of fatty and glandular components [11]. The quality of the CTG becomes particularly relevant when harvesting thick grafts, as a greater proportion of glandular and fatty tissue is included. In contrast, the denser connective tissue near the epithelium remains within the primary flap when using the single-incision technique [48]. Finally, in light of these considerations, a multidisciplinary therapeutic strategy is essential for the effective management of complex osteomucosal defects.

5. Conclusions

A multidisciplinary approach, including the combined management of hard and soft tissues, along with precise prosthetic planning, is crucial to achieving optimal functional and esthetic outcomes in patients with complex rehabilitative needs. However, further studies with long-term follow-up and a larger patient sample will be necessary to confirm the obtained results and define standardized protocols for the use of innovative biomaterials in bone regeneration and peri-implant soft tissue management. Further long-term follow-up studies and the integration of patient-reported outcome measures (PROMs) would be valuable to comprehensively assess prosthesis survival and patient satisfaction over time.