Particulate Coral Hydroxyapatite Sheltered by Titanium Mesh for Localized Alveolar Rehabilitation After Onlay Graft Failure: A Case Report

In prosthetic-driven implant treatment, good quality and quantity of bone tissue is a prerequisite for favorable implant position, stability, and long-term success. Autologous bone grafts have routinely been used for bone augmentation, for better osseoinduction and osteoconduction properties to nonautologous alternatives.^1,2  However, because of the intrinsic limitations, such as donor site morbidity, unpredictable bone absorption, 5%–10% failure rate, and so forth, the outcomes of autologous bone grafts are not always satisfying.^3,4  Few studies have documented a bone augmentation strategy when encountered with autologous bone graft failure, since successful bone reconstruction relies on both the physician's diagnosis and surgical skills and the mechanism of bone regeneration.⁵ 

To avoid the secondary morbidity associated with harvesting autologous bone grafts, bone substitutes may be a better choice.⁶  Although products composed of allografts and xenografts are on the market, risks of immunologic rejection and disease transmission still cannot be denied.⁷  Besides, a systematic review pointed out that there were no significant differences in horizontal bone gain among particulate materials—allografts, xenografts, and alloplastic grafts.⁸ 

In the case of poor osteogenesis, coral hydroxyapatite, which exhibits slower degradation in vivo, may be beneficial. Coral hydroxyapatite is composed of calcium carbonate and hydroxyapatite. Applied as an osteoconductive scaffold with porous architecture, the inner structure of coral hydroxyapatite resembles cancellous bone, suitable for host osteoblasts to migrant and vascularize.⁹  However, the surrounding gingival epithelial tissue and connective tissue grow faster, which may interfere with bone formation.¹⁰  Hence, the absorbable or nonabsorbable membrane is coupled with the particulate substitutes by the rules of guided bone regeneration.

Since Boyne first reported titanium mesh for the reconstruction of large maxillary defects in 1969, this approach has been widely applied for bone augmentation in oral and maxillofacial regions.¹¹  Von Arx et al proposed the “TIME technique” for bone rehabilitation using micro-titanium meshes in 1996.¹²  Titanium meshes that exhibit excellent biocompatibility and biomechanical properties are a good choice for preventing the surrounding soft tissue from collapsing and forming static surroundings to facilitate osteogenesis in reconstructive bone intervention. Various reports have focused on preshaped or customized titanium meshes made by rapid prototyping to repair bone.^13,14  Some of these reports highlighted postoperative complications, particularly soft tissue dehiscence, which can result in surgery faliure.¹⁵  Most of these studies employed autologous bone in conjunction with an allograft or xenograft, sometimes accompanied by growth factors, and so on.^16,17  Few have investigated exclusively particulate coral hydroxyapatite in atrophy alveolar bone reconstruction.

With the above in mind, the objective of this report was to formulate a solution to onlay graft failure by reporting one severe alveolar bone defect reconstruction case of the anterior mandible using the titanium mesh technique with particulate coral hydroxyapatite, without using exterior growth factors or autologous bone graft. Furthermore, horizontal bone gain was assessed, and histologic and radiographic studies were undertaken.

A 50-year-old male patient with Nos. 6, 11, 14, 24, and 25 teeth missing attended our hospital for dental implant restoration. The 3 maxillary teeth were missing due to severe periodontitis, and 2 mandibular teeth were missing owing to childhood trauma. He had worn a removable partial denture for 25 years. After careful intraoral and radiologic examination, disease history inquiry, and receiving informed consent, under local anesthesia, the patient received onlay block grafts from the external oblique line of mandible in Nos. 11 and 24–25 regions simultaneously. Two weeks after autologous bone transplantation surgery, the autologous bone graft in the No. 11 region had healed uneventfully, while the bone block in the anterior mandible was infected for soft tissue dehiscence (Figure 1). After local anti-infection and oral antibiotic (0.25 g cephradine) administration over 7 days, the inflammation had not been alleviated. Thus, removal of the infected bone block was planned. Cone-beam computerized tomography (CBCT; NewTom VG, Via Silvestrini, Italy) showed that bone in the No. 24–25 region was obviously horizontally deficient. In addition, the bone quality was class I according to the Cawood and Howell classification (Figure 2). We virtually located 6 points that segmented the No. 24–25 region equally in the crest of alveolar ridge, to compare the bone gain pre- and postsurgery by the software NNT (New Tom VG). After being given full information on the proposed procedure, including the particulate coral hydroxyapatite (Bio-osteon, Yihuajian Commercial Co. Ltd, China) sheltered by titanium mesh (Medicon, Tuttlingen, Germany), bone augmentation surgery plan, and the possible complications and risks, the patient accepted the surgery.

After surgery preparation, under sterile condition and local anesthesia, a lingual crestal incision in the No. 24–25 region and gingival sulcus and vertical releasing incisions in the labial mucosa of Nos. 23 and 26 were made, following the suspension of the mucoperiosteal flap. Then, the inflamed bone block was taken out, the infected connective tissue was removed by curettage, and the wound was alternatively rinsed with 0.9% physiological saline and 3% hydrogen peroxide solution. The alveolar ridge was in the shape of a knife-edge (Figure 3). According to the contour of the anterior mandible, a titanium mesh of 5 × 5 cm dimensions was trimmed to cover the bone defect region from the mesiodistal to the labial-lingual. Before filling the defect with particulate coral hydroxyapatite, decortilization was performed by applying a fine-ball drill to the cortical bone surface to facilitate the mesenchymal stem cells' migration and improve vascularization. Blood was drawn locally and mixed with the particulate corals. Then, the preshaped titanium mesh was fixed with 3 titanium screws, 2 mm in diameter and 9 mm in length (Medicon; Figure 4). The particulate corals mixed with the blood filled the space. An absorbable collagen membrane (Bio-Gide, Geistlich Biomaterials, Switzerland) was used to cover the titanium mesh. Finally, the wound was closed carefully with a tension-free flap with incisions in the periosteum.

Fourteen days after surgery, a small buccal soft tissue dehisced, with part of the titanium mesh exposed. There was no obvious swelling or abscess (Figure 5). The wound was alternatively flushed with 0.9% physiological saline and 3% hydrogen peroxide solution, before being treated with minocycline hydrochloride ointment (Sunstar Inc, Tokyo, Japan). The patient was instructed on hygienic wound maintenance. After another 7 days, the wound had closed, and the alveolar ridge had become noticeably plumper. Six months later, after the margin of the basal and grafted bone and the edge of the mesh were defined, the bone width of the No. 24–25 region was measured linearly on 6 coronal sections by NNT. The results revealed that the bone width had increased significantly by 4.2 ± 0.5 mm (Figures 6 and 7). The titanium mesh was then removed. With the permission of the patient and the approval of the Ethics Committee of the Affiliated Stomatological Hospital of Guangzhou Medical University, a 2- × 5-mm cylindrical bone was harvested by the trephine bur during the implant site preparation for histologic and micro- radiographic evaluation (Figures 8 and 9). Afterward, a standard dental implant site was prepared, and a single Straumann implant (RN 3.3 × 12 mm) was inserted into the missing tooth area. Keratinized gingiva was found surrounding the neck of the dental implant. After a healing period of 3 months, a partially fixed dental bridge for Nos. 24 and 25 was fabricated and loaded. The patient was followed up for 3 years after the operation, with no infection of the peri-implant hard or soft tissues and no complaints of discomfort. The prosthesis functioned normally (Figures 10 and 11).

Pursuing less invasive surgical strategies to achieve a satisfying alveolar rehabilitation outcome remains a challenge in contemporary implantology. Tissue is the overwhelming factor to ensure the long-term prognosis of a dental implant therapy (eg, the first 1-mm bone ring around the dental implant).¹⁸  This article reported an efficacious method to reconstruct the severely atrophied alveolar bone with particulate corals stabilized by preconfigured titanium mesh after a failed autologous bone graft, aiming to provide a remedial solution for bone rehabilitation failure.

A variety of issues could result in autologous bone graft failure. It is difficult to reconstruct the bone because of the presence of inflammatory tissues, decreased viability of osteoblasts, and, above all, the fact that standardized procedures are yet to be established.

In this work, coral hydroxyapatite was chosen for its inherent slower adsorption properties; its capability of holding the microenvironment for osteoblasts to migrate, colonize, and proliferate; its porous structure, which offers a larger contact surface; and its ability to regain biological properties faster than cortical grafts.¹⁹  From the microcomputerized tomography (micro CT) and histologic results, the closer the coral hydroxyapatite was to the host bone, the more coral hydroxyapatite was resorbed within 6 months. There were plenty of mature lamellar bone structures, with evident residual coral hydroxyapatite. In addition, the specimen was divided into 3 parts: top, middle, and bottom virtually, with the top referring to the alveolar ridge, contrary to the bottom. The volume of new bone on the top was the smallest, as it was far away from the central bone remodeling area, which is in accordance with results reported by Ikeno et al.²⁰ 

The excellent mechanical properties of titanium mesh allow for 3-dimensional reconstruction of the bone contour. It acts as a protective shelter to maintain space for bone growth from the soft tissues and muscles, stabilizes the bone substitutes, and decreases the micro movement during bone healing. Uehara et al²¹  reported that compared with other nonabsorbable membranes, titanium mesh results in less infection in cases of wound dehiscence. Jensen and Terheyden⁴  reported that the average increase on the alveolar horizontal dimension is 3.6 mm after a mean healing period of 7.3 months, and a desired volume of bone augmentation in horizontal is more difficult than the vertical. Here, we obtained an impressive 4.2 ± 0.5 mm regenerated bone in the horizontal dimension. Multiple studies validated that this bone gain is excellent. Troeltzsch et al⁸  reported from 184 studies that the average horizontal bone gain of particulate graft is 3.7 ± 1.2 mm. Except for the bone substitutes, rhBMP-2 (about 1 mg) coupled with titanium mesh has been evaluated for 5 bone augmentation surgeries with an anterior maxillary bone gain of 3.8 ± 0.7 mm after 6 months.¹⁶  Although the measurement methods, the accuracy of CBCT, samples, and so on influence the results, our study demonstrated that titanium mesh with coral hydroxyapatite could successfully reconstruct bone defect.

The most common complication associated with the titanium mesh technique for bone augmentation is mesh exposure.¹⁵  Studies show that these nonabsorbable membranes carry a high (50%–70%) risk of exposure, which can result in about 15%–25% graft resorption.^21–23  In 23 cases of bone augmentation using titanium mesh, the success rate was 56.6%, which significantly correlated with the span of the augmentation site, while mesh exposure seemed to have no negative effect.²¹  Strict local hygiene and anti-inflammation treatment is a successful therapy for mesh exposure. Above all, a tension-free closure and careful attention to soft tissue are paramount. A related study of inorganic bovine bone with titanium mesh technique, together with or without platelet-rich plasma for bone regeneration, showed that platelet-rich plasma plays a decisive role in preventing mesh exposure.²⁴  Future work will concentrate on incorporating such factors with a view to system improvement. Overall, this approach to bone augmentation, without the need for any external growth factors, resulted in good osteointegration between the implant and the regenerated bone.

To salvage the bone graft failure is a formidable task. This report demonstrated that particulate coral hydroxyapatite coupled with customized titanium mesh technique is a practical and attainable mean to rehabilitate alveolar bone defect. In addition, the exposure of the mesh is not the critical factor for bone regeneration.

Abbreviations

CBCT

cone-beam computerized tomography

micro CT

microcomputerized tomography

This project was financially supported by the International Team for Implantology Grant (No. 881_2012), the National Nature Science Foundation of China (No. 81671029), National Science and Technology Major Project (No. 2016YFC1102900), Guangzhou Science Technology and Innovation Commission (201704030024), and Guangdong Provincial Department of Science and Technology (No. 2015B090920002).

The authors declare that they have no conflict of interests.