With the increasingly widespread use of dental implants, bone augmentation for high-grade alveolar bone resorption is being implemented using a variety of methods. An adequate structural base of osseous tissue is necessary for supporting the dental implant. Bone augmentation is needed to make the space before the embedding,1 if there is insufficient bone volume in the alveolar bone. Bone augmentation method using the space-making device2–5 is used to create space in the defect area, and the bone is augmented using autologous bone or artificial bone material such as hydroxyapatite or calcium phosphate. Commonly used materials for conventional artificial space-making device include absorbent material such as collagen and mesh-like, thin, flat titanium (Ti) that is manually adapted to fit the shape of the bone defect.6–10 However, adapting a flat titanium mesh sheet to complex bone defect areas comprising curved and flat surfaces requires a large amount of effort. In an attempt to simplify this process, we have been using a selective laser melting (SLM) Ti protocol11 to adapt the titanium mesh sheet to bone defects. Use of SLM to modify the Ti mesh sheet enables accurate shaping of the sheet to morphologically complex alveolar bone defects, which both shortens surgery duration and enables accurate augmentation of the bone form.
The aim of this report was to present the clinical feasibility of bone augmentation using SLM Ti mesh sheet.
Materials and Methods
Preoperative surgical simulation was implemented based on the number of implants and the embedding angle of the dental implants, as determined using BioNa, a 3-dimensional image analysis software (Wada Precision Dental Laboratories Co. Ltd., Osaka, Japan) and Digital Imaging and Communications in Medicine data obtained from CT. The bone shape and volume required at the implant embedding site were calculated based on this simulation, and the Ti mesh sheet was designed on a computer. The simulated Ti mesh sheet was then converted into data in a Standard Triangulated Language format. The mesh sheet was placed into a metal laminate molding apparatus, and the molding position was determined within the modeling range by the onboard internal software and metal additive manufacturing machine EOSINT M 270 (EOS GmbH Electro Optical Systems, Krailling, Germany). Pure Ti powder was scattered onto the shaping sheet and moved with a laser light, following the 2-dimensional data for each layer with respect to the molding position and modeling shape; only the powder irradiated by the laser light was selectively melted and coagulated into a 30-µm thick layer. This process was repeated to fabricate Ti mesh sheet 0.3 mm in thickness shaped to the simulated design (Fig. 1).12
The patient was a 50-year-old woman who had lost her maxillary central incisors and surrounding alveolar bone through trauma to the anterior maxilla. The design simulation was created from the preoperative CT images, and a 0.3-mm thick porous Ti mesh sheet was fabricated according to the method detailed above. An incision was made in the gingival periosteum, and the mucoperiosteum flap was reflected to reveal the bone defect (Fig. 2, A). There was bone loss in both the vertical and buccal directions corresponding to the defect seen on the preoperative CT scan (Fig. 2B). The SLM Ti mesh sheet was trial-fitted to the defect, and there was sufficient agreement (Fig. 2, C and D). The dental implant (Brånemark System MKIII Groovy RP 3.75 × 13 mm; Nobel Biocare, Zurich, Switzerland) was embedded into the remaining alveolar bone, and artificial bone13 (Bio-Oss; Geistlich Pharma, Wolhusen, Switzerland) was infiltrated into the space between the residual bone and the fixed SLM Ti mesh sheet using a 1.0- × 6.0-mm microscrew (KLS Martin Group, Tuttlingen, Germany). The mucoperiosteum was then sutured. Postoperatively, the mucous membrane was healthy. Six months after surgery, clinical examination of the patient revealed that the mucosa remained healthy and that the bone condition was sufficient (Fig. 3, A and B); bone morphology under the Ti mesh sheet was confirmed on CT images (Fig. 3, C and D). After considering the situation, we decided that retraction of the gingiva to remove the SLM Ti mesh sheet would influence mucosal volume, so the SLM Ti mesh sheet was left embedded to maintain esthetic appearance. The patient is currently free of any gingival malformations.
The patient was a 46-year-old man who had tooth loss on the left side from the maxillary canines to the premolars because of severe periodontitis associated with extensive resorption of the surrounding alveolar bone. As in case 1, a 0.3-mm thick porous Ti mesh sheet was prefabricated using the SLM method (Fig. 4, A–C). An incision was made in the gingival periosteum, and the mucoperiosteum was reflected to reveal the bone defect. There was bone loss in both the vertical and buccal directions, consistent with the defect seen on preoperative CT imaging. We trial-fitted the SLM Ti mesh sheet to the defect with sufficient result (Fig. 4C). The Ti mesh sheet was then fixed with 1 screw, and artificial bone (OSferion; Olympus, Tokyo, Japan) and autologous bone were infiltrated into the space between the residual bone and the SLM Ti mesh sheet and then covered with a collagen sheet material (CollaTape; Zimmer Biomet, INUS) (Fig. 4C). The mucoperiosteum was then sutured. There were no postoperative issues with the wound site.
The SLM Ti mesh sheet was removed 4 months later when the 3 dental implants (Brånemark System MKIII Groovy RP 3.75 × 11.5 mm, MKIII Groovy RP 3.75 × 11.5 mm MKIII Groovy RP 3.75 × 10 mm; Nobel Biocare) were embedded. There was some bone neoplasticity around the edges of the Ti mesh sheet, but the mesh was easily removed from the augmented bone. There was adequate bone morphology observed under the Ti mesh sheet (Fig. 5, A and B). Good bone regeneration was observed on the buccal side 4 months postoperatively on CT imaging (Fig. 5, C and D).
Bone augmentation is a method aimed at increasing bone mass through the use of artificial bone or an autologous bone graft to compensate for the bone defect at sites where implants cannot be inserted because of vertical or horizontal bone resorption of the jaw bone.14 The 3-dimensional space-making device was secured over the empty spaces in the compensated artificial or autologous bone grafts. The device can be categorized into 2 categories: absorbent sheet and nonabsorbent sheet; comparisons have shown that nonabsorbent sheets composed of metals such as Ti are superior to absorbent sheets composed of collagen because of their ability to retain their 3-dimensional morphology. However, the task of applying and adapting a nonabsorbent metallic sheet to a wound depends on the operator's skill and experience; lack of experience may slow down the process and lead to extended duration of the procedure. Use of an SLM titanium mesh may help solve operator issues related to conventional Ti mesh sheet.
In the 2 case reports, SLM of the Ti mesh sheet resulted in dramatically superior form fitting of the alveolar bone defect area. The SLM Ti mesh sheet fit well to the surrounding tissue immediately after implantation, and there was a complete absence of postoperative inflammation. In conventional surgery with Ti mesh, multiple pins are required to fix it in place. By contrast, we found that the SLM Ti mesh sheet was extremely stable after being passively fitted to the alveolar bone, and only 1 pin was required to fully fix the mesh in place. Sumida et al15 reported that the average number of screws used to maintain the space-making device was 1.31 for the custom-made Ti mesh sheet group and 3.23 for a conventional Ti mesh sheet group; this difference was statistically significant. The stiffness of the Ti mesh sheet may result in mechanical irritation of the mucosal flaps,16 with a subsequent risk of flap rupture. When designing the Ti mesh sheet onscreen from the CT scan data, it is necessary to also envision the placement of the mucosal incision and sutures. If the Ti mesh sheet is too large, there is a risk that the mucosal flap may rupture at the weak points of the mucosa, such as the suture line; therefore, if the mucosal flap is expected to be thin, it is necessary to design the implant to ensure that the mucosal suture line does not sit directly above the Ti mesh sheet. Furthermore, in conventional surgery, cutting, trimming, and bending of the conventional Ti mesh sheet can result in sharp edges, which may cause mucosal rupture.17 With our SLM Ti mesh sheet method, there was no need for intraoperative manipulation of the Ti mesh sheet; thus, the SLM Ti mesh sheet may be associated with less risk of mucosal rupture than is conventional Ti mesh sheet.
Recently, computer-assisted technologies (computer-aided design/computer-aided manufacturing) using CT images have made remarkable advances and have also contributed to developments in the fields of maxillofacial reconstruction18 and dental implants.19,20 With the 3-dimensional model construction device EOSINT M 270, the pure titanium powder layer (which is paved on the molding table) is sintered and melted using a laser beam. A pure titanium structure of any complex shape can be molded by adding a 30-μm layer in the direction of the vertical axis each time a layer is sintered and melted throughout the additive manufacturing process.21,22 However, a slight dimensional error is likely to occur between the original data in the computer and the Ti mesh sheet generated using layered manufacturing. According to a report published by Otawa et al,23 dimension errors found in the vertical direction (namely in the lamination direction) are believed to be greater than those found in the horizontal axis direction, but the average error is 139 μm and poses no issue when used for bone augmentation.
Customarily, the Ti mesh sheet used for bone augmentation in dental implants is removed after the bone augmentation is complete. However, removal of the mesh may create problems, such as reduction in gingival volume, removal of bone when a large amount of bone has been added to the Ti mesh sheet, and/or creation of a larger incision to remove the Ti mesh sheet. Considering the high degree of Ti biocompatibility, Ti mesh sheet could also be an option for deployment as a type of artificial bone embedded in the body after it has been used for space creation in bone regeneration. Given that Ti artificial knee joints24 and Ti brain artery clips25 are embedded in the body, expanding the use of Ti mesh from supplementary use as a bone defect space creation sheet to free-form artificial bone material embedded in the body is a logical next step. In a number of cases, Ti mesh sheet has been left embedded in the body (with consent from the patient) and has served to retain the esthetic appearance of the gingiva surrounding the front teeth. We are, therefore, investigating the application of laminate-molded Ti mesh sheet as embedded artificial bone in a wide range of mandibular and maxillary bone defects. Bone regeneration from residual bone can be expected when there is a comparatively small area of bone loss. However, when there is significant bone loss, concurrent use of artificial or autologous bone is essential. Ti has a high degree of biological affinity and, although bone synostosis occurs when it is in direct contact with the bone, adequate bone formation cannot be expected if there is a gap between the Ti and the bone. Various treatments12,26 have been proposed and applied in clinical practice to increase the bone-binding capability of the Ti surface when in direct contact with the bone.
Our study demonstrated the utility of bone augmentation using SLM titanium mesh sheet. SLM allows for molding a 3-dimensional shape that is ideal for the alveolar bone; it can also shorten surgery time and reduce the risk of postoperative infection. The SLM Ti mesh sheet protocol can be applied to various types of bone defects. SLM of the Ti mesh sheet should be considered as a new bone augmentation method.
The authors claim to have no financial interest, either directly or indirectly, in the products or information listed in the article.
Each patient provided informed consent for all the procedures. This study was approved by the Ethics Committee of Osaka Medical College (approval no. 2311).
Roles/Contributions by Authors
K. Inoue: Coauthor of this article. Prepared treatment plans using a titanium mesh generated through additive manufacturing, as well as the layout of the design and the insertion of the mesh into patients.
Y. Nakajima, M. Omori, Y. Suwa, N. Kato-Kogoe, and K. Yamamoto: Prepared treatment plans using titanium meshes generated through additive manufacturing, as well as the layout of the design and the insertion of the mesh into patients.
H. Kitagaki and S. Mori: Manufactured titanium meshes through additive manufacturing using a 3-dimensional molding machine.
H. Nakano: Prepared treatment plans using titanium meshes generated through additive manufacturing, as well as the layout of the design and the insertion of the mesh into patients.
T. Ueno: Study Executive Research Director. Invented the technique that uses titanium meshes generated through additive manufacturing; he prepared the treatment plans; and gave instructions regarding the layout of the design.
The authors thank Osaka Yakin Kogyo Co., Ltd., and Wada Precision Dental Laboratories Co, Ltd., for the manufacture of the titanium mesh, and Editage (www.editage.jp) for English language editing.
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