Customized Titanium Lattice Structure in Three-Dimensional Alveolar Defect: An Initial Case Letter

For some patients, dental implants would not be an option without horizontal or vertical bone augmentation. Alveolar bone defects may be treated with various bone regeneration techniques including block bone graft, guided bone regeneration (GBR), ridge splitting, and distraction osteogenesis,^1–4  as well as sinus floor augmentation procedures in the upper jaw.

Titanium meshes have been widely used for oral and maxillofacial defect reconstruction in terms of GBR technique.^5–9  They are rigid enough to maintain the grafted space and to avoid soft tissue collapse. Onlay osseous graft protected by a titanium mesh demonstrated significantly less bone resorption compared with an onlay bone graft alone.¹⁰  Titanium mesh is also an alternative to a (resorbable) membrane for ridge augmentation.¹¹ 

With its advantages, such as biocompatibility, corrosion resistance, and thermal effects, a titanium mesh has been proven to be useful in these indications,^12,13  and substantial bone augmentation can be achieved using the titanium construct in conjunction with bone grafting.^11,14  The inherent rigidity of stiff titanium membranes maintains the space needed to allow bone growth.¹⁵  Studies have demonstrated that titanium mesh supports the grafted space and prevents soft tissue collapse.^15,16  However, the clinical outcome of augmentation depends on the type of preoperative bone defect.¹⁷  In addition, titanium mesh has good mechanical strength,^18,19  and it can be shaped readily and fixed with suture or pins with resulting potential space. Titanium fiber mesh has proven to act as a bone regeneration scaffold, even with a thin hydroxyapatite coating of the mesh.²⁰ 

The conventional already established GBR method, which is based on nonindividualized mesh constructs, shows significant disadvantages such as manual cutting, bending, and trimming to achieve the desired shape for implant placement. These steps are time intensive and prolong surgery. Furthermore, the outcome of the mesh frequently does not reflect the entire anatomic characteristics in a satisfactory level.

New bone reconstructive techniques based on guided bone regeneration for localized three-dimensional hard tissue augmentation are discussed.^21,22  These techniques can result in significantly enhanced bone regeneration with minimal patient discomfort.²³  The effectiveness of a customized, three-dimensional, preformed titanium mesh as a barrier membrane for peri-implant alveolar bone regeneration has proven to result in satisfactory bone regeneration.²²  In general, the application of individual digital design and rapid prototyping in the reconstruction of bony defects seems promising.

This case report describes the three-dimensional reconstruction of a posterior mandible segment with the use of an individualized customized titanium lattice structure. After 24 months, clinical, radiologic, and histologic results are presented.

A 61-year-old healthy woman without any medical history showed a highly atrophied segment of the right lower posterior mandible (#29 and #28). The significant vertical and transversal deficit, as well as the challenging soft tissue situation, made a functionally and esthetically satisfying implant placement impossible (Figures 1 and 2).

After clinical examination of oral hard and soft tissue, radiographic analysis was performed. After the acquisition of cone beam computerized tomography (CBCT) data, the three-dimensional model of the bony defect proved to be an inadequate bony situation for implant placement. Augmentation procedure was planned by using a prefabricated titanium lattice structure (Yxoss CBR, ReOss, Filderstadt, Germany) and graft material. Comprehensive information about the individualized lattice structure, xenogenic allograft, and surgery were provided, and informed consent was obtained. Treatment alternatives such as removable prothesis were declined by the patient.

The patient-specific lattice structure was designed using computer-aided design/computer-aided manufacturing (CAD/CAM) technology by generating a three-dimensional model of the bony defect after CBCT with minimum artifacts from conventional digital imaging and communication in medicine (DICOM) files. The scan data were transferred and modified by reverse engineering software. The individualized lattice structure was designed according to the desired augmentation volume in the envelope (Figure 3). The final design was approved digitally by the surgeon and then manufactured. Costs depend on size of the defect and subsequent size of the lattice structure.

Surgery was performed under local anesthesia (Ultracain DS Forte, Ultracain, Hoechst, Germany). After elevation of a marginal soft tissue split flap starting in the vestibular gingival mucosa (about 12–15 mm vestibular from the mucogingival junction), scar tissue was removed, and the defect was visualized (Figure 4). The prefabricated titanium lattice structure was inserted with a passive tension-free fit keeping the biological precautions (1.5 mm to the adjacent teeth or nerve structures). Graft material from local bone obtained from the ramus of the mandible was mixed with xenogenic alloplastic material (Bio Oss, Geistlich Pharma, Wolhusen, Switzerland) in a ratio 1:1. Stable fixation of the lattice structure on the residual local bone was achieved by use of one osteosynthesis screw (Ø 2 mm/9 mm, Medicon eG, Tuttlingen, Germany) (Figure 5). Wound closure was achieved by suturing without tension. Postoperative instructions such as avoidance of the prosthesis were given to the patient, as well as detailed instructions about oral hygiene.

At suture removal (day 10) and during wound healing, a clinically healthy marginal area and full soft tissue coverage of the customized titanium lattice structure were present.

After a healing period of 6 months, a new CBCT dataset was collected to verify enhancement of the bone augmentation volume (Figure 6) and to plan implant surgery and removal of the lattice structure. For this second surgery, the same local anesthesia was used. After preparation of a mucoperiosteal full-thickness flap, the fixation screw was removed. By applying rotating focus with an elevator at the predetermined breaking point (Easy Removal Design, ReOss) the lattice structure is divided in two parts (Figure 7). The augmented bone volume was of stable dimension, well-vascularized, and without any signs of inflammation (Figure 8). The implant placement was performed following the standard procedures, and a cylindrical bone specimen was gained followed by a tension-free wound closure. The sutures were removed 1 week later.

The implants were functionally loaded after 4 months using a hybrid bridge according to the patient's wishes and preferred concept of the referral practice.

According to the patient's request, a closure of the interdental gap was necessary to improve the cosmetic and functional outcome. Therefore, an implant placement was required. Alternative treatment options such as conventional prosthetics (bridge #27 to #30 and #31) would have to deal with a wide range and may result in reduced mechanical stability. In this case, the posterior teeth (#30 and #31) were attached to the implant abutment. These teeth needed reconstruction because of an inherent insufficiency of the old crowns (as shown in Figure 1 compared with Figure 11). To avoid the neighboring healthy tooth being affected (#27), implant placement in region #28 offered the possibility to close the existing gap (#29 and #28).

Twenty-four months after reconstruction, the bone graft appeared well consolidated, and the implants were stable without clinical or radiologic signs of peri-implant bone loss (Figures 9–11). The patient-specific customized titanium lattice structure shaped the area to be augmented by backward planning for the implant position scheduled by the prosthetic need.

A sample histologic analysis showed newly formed bone including integrated xenogenic bone substitute material particles using toluidine blue staining (Figure 12). Higher magnification revealed newly formed bone tightly adherent to the residual bone plate. Bio-Oss particles appeared in green colors embedded in newly formed bone.

In this case report, a customized patient-specific lattice structure was used for horizontal and vertical augmentation in the posterior mandible. It offered a precise fit and high stability after screw fixation as already proven in recent studies for preformed meshes.^24,25  A customized mesh shortens duration of surgery^26,27  and offers all benefits of reduced time for intervention and improved surgical management,²⁸  as well as a decreased exposure time to general anesthesia, decreased blood loss, and shorter wound exposure. With its advantages such as biocompatibility, corrosion resistance, and three-dimensional stability, titanium meshes have proven to be useful in the reconstruction and augmentation of oral and maxillofacial defects.^12,13  Studies have demonstrated that the inherent rigidity of stiff titanium mesh supports the grafted space and prevents soft tissue collapse.^15,16  Six months after removal of the mesh, osseous grafts protected by a titanium mesh showed significantly less bone resorption compared with an overlay bone graft alone.²⁹ 

The round and blunt edges of the mesh used in this case prevents mucosal irritation. In the field of implant dentistry, a customized titanium mesh was already proven to be suitable for stabilization of bone regeneration.³⁰  A recent study proved a printed titanium mesh for alveolar bone reconstruction using a bone morphogenetic protein 2/absorbable collagen sponge 7 (BMP-2/ACS7) allograft to be a possible improvement to hand-configured mesh graft techniques.³¹  Ciocca et al²⁶  prepared a customized titanium mesh to augment the atrophic alveolar ridge and demonstrated satisfactory bone regeneration. A preliminary evaluation of a three-dimensional, customized, and preformed titanium mesh to regenerate alveolar bone proved its efficacy.²²  However, in these protocols, a possible loss of augmentation material in the course of mesh removal may occur. In this case, the removal of the lattice structure caused no fracturing of the augmented bone or damage to soft tissue because of the novel removal function. There were no signs of displacement or compression, and the augmented area showed no resorption processes. Additionally, the time of the second surgery was obviously reduced. Thus, the titanium lattice structure stabilized the defect area and its augmentation material and helped to rebuild the osseous defect to provide enough bone for implant placement procedures. The bony level remained stable even after a longer period, which may be due to the formation of “real new” bone. In addition, histologic examination revealed these new, mature bony structures tightly adherent to the residual bone.

The presented technique included three-dimensional planning and printing, allowing an easy application and convenient removal, together with a stable formation of local bone with no peri-implant bone loss. During the last few years, multiple techniques combining medical imaging and rapid manufacturing techniques^13,27  were published. The two most frequently used rapid prototyping technologies are stereolithography and three-dimensional printing (3DP). 3DP seem to be superior compared with stereolithography because this procedure provides better accuracy and quicker printing time.²⁸  In the novel protocol at hand, the surgeon is included into the designing process. This modern, digital workflow as part of daily augmentation procedures may result in an improved clinical outcome.

Dental implants bridged to a natural tooth represent a controversial topic in dentistry because of differences in resiliency. A natural tooth's periodontal ligament work as a shock absorber during clenching and chewing. This is not the case for well-osseointegrated dental implants. These differences in resiliency may lead to complications involving tooth eruption, failure of the bridge, fracturing of implant or screw components. Alternatives such as the placement of two implants or other bridge constructions were rejected by the patient.

This case report presents a novel patient-specific customized lattice structure made of titanium, which is suitable for shaping and rebuilding a bone defect in complex anatomic situations. Clinical and histologic results demonstrated this protocol as a successful and predictable procedure for rebuilding an atrophied bone defect. Further studies are needed to evaluate the effects and benefits of Yxoss CBR.

This protocol provides improved management to facilitate successful surgical augmentation of the jaw bones and provides sufficient quality to improve regeneration of bony defects. It offers a simplified handling, a removal option to keep the augmented bone in place together with reduced handling time. By confirming the design interactively, the surgeon is directly involved in the manufacturing process.

Abbreviations

BMP-2/ACS7

bone morphogenetic protein 2/absorbable collagen sponge 7

CAD/CAM

computer-aided design/computer-aided manufacturing

CBCT

cone beam computerized tomography

CBR

customized bone regeneration

DICOM

digital imaging and communication in medicine

GBR

guided bone regeneration

3DP

three-dimensional printing

The authors thank patients, nurses, and physicians for their support with patients' material and reports. Moreover, the authors thank all of our colleagues for helpful discussions. The authors thank Prof Dr Christoph Hämmerle, University of Zürich, for histologic examinations.

The authors declare that they have no competing interests. M.S. developed the methodology (owner of patent).