Vertical Ridge Augmentation With a Honeycomb Structure Titanium Membrane: A Technical Note for a 3-Dimensional Curvature Bending Method

Vertical ridge augmentation (VRA) is a major treatment option aimed at providing bone formation for the placement of dental implants and an esthetic outcome in an advanced bone resorption area. It is generally accepted that VRA is recognized as being more difficult as compared with horizontal ridge augmentation and internal bone augmentation, because of the lower supplement of osteogenic cells and proteins from residual bone. In addition, external pressure, such as occlusal force and labial pressure, is strongly significant in VRA. Furthermore, widespread flap expansion and tension-free flap closure are required over the grafted site with considerable risk of mucosal dehiscence and nerve injuries.¹ 

Previously, several augmentation techniques, such as distraction osteogenesis,²  block bone grafts,³  guided bone regeneration (GBR),⁴  and interpositional grafting⁵  have been introduced for VRA. A recently published systematic review and meta-analysis concluded that VRA procedures were in many studies shown to be effective in treating deficient alveolar ridges.⁶  Although no clear conclusion can be drawn regarding the superiority of any particular technique, GBR combined with a nonresorbable membrane offers effective VRA with low postoperative complication rates. Simion et al⁷  reported a VRA using titanium-reinforced expanded polytetrafluoroethylene (e-PTFE) membrane combination with a 1:1 mixture of deproteinized bovine bone mineral (DBBM) and autogenous bone graft. All implants appeared stable and submerged by augmented bone tissue at the timing of abutment connection. The histological analysis showed new bone formation and ongoing remodeling of the autogenous bone and the DBBM particles. Urban et al⁸  also reported a VRA with titanium-reinforced dense-PTFE (d-PTFE) membrane and the same bone substitute material. All augmented sites exhibited excellent histological bone formation, as in a previous report,⁹  with an average bone gain of 5.45 ± 1.93 mm. The d-PTFE membrane is considered to be advantageous in that it has a low porosity size, which creates a greater resistance to bacterial incorporation than that of the e-PTFE membrane.¹⁰  These PTFE membranes can be roughly adapted on residual bone by the bending of the supporting titanium framework. However, because of the elasticity of PTFE, morphological compatibility with residual bone can be achieved only by fixation with bone pins or screws. Therefore, it is difficult to shape the membrane to make a tray with an ideal form.

As with the other type, titanium (Ti) membrane (FRIOS Bone Shield [FBS], Densply Sirona, York, Pa) has been applied to GBR because of its high biocompatibility and excellent strength as well as its metal specific ductility, even when processed into thin sheets.¹⁰  Therefore, it can be easily given an ideal 3-dimensional morphology. In addition, because the smooth surfaces of the FBS are less susceptible to bacterial contamination, the risk of developing infections following membrane exposure is minimal.¹⁰  On the other hand, the Ti- membrane is a thin film that is 100-μm thick¹¹  and contains pores with a diameter of 40–60 μm; therefore, mechanical strength to maintain the morphology of the only membrane might not be enough for VRA.

Recently, an ultrafine-surface Ti membrane with a honeycomb shape was developed using laser processing technology (Ti-honeycomb membrane).¹²  The technique allows microperforations (diameter, 20 μm; pitch, 50 μm) into the Ti membrane, which is expected to prevent fibrous tissue ingrowth from outside the membrane. In addition to its honeycomb shape structure, by which the mechanical property of the membrane itself is enhanced, another type of membrane was developed, on which a titanium frame was jointed with welding to reinforce the space-making capacity (titanium flame–reinforced Ti-honeycomb membrane).¹³  For these reasons, the application of the titanium flame–reinforced Ti-honeycomb membrane to VRA is expected.

Currently, the Ti-honeycomb membrane is approved for clinical use in Japan, but no clinical reports have been reported in international journals. The purpose of this case report is to provide a technical note of VRA using the newly developed Ti membrane.

Written informed consent was obtained from the patient for publication of this case. A 53-year-old female patient was referred to the Hamamatsu Perio-implant Center, Hamamatsu, Shizuoka, Japan, in October 2016 for esthetic disturbance due to the detachment of an adhesive bridge in teeth Nos. 8 and 9 (Figure 1). An implant-supported restoration was considered for both occlusal and esthetic reasons. A diagnostic wax-up model was created to estimate the ideal amount of bone augmentation prior to surgery. The radiographic template with radiopaque material was fabricated from the diagnostic wax template. A cone-beam computerized tomography (CBCT) scan was performed after insertion of the diagnostic template (Figure 2).

The implant position was simulated for an ideal esthetic outcome. To allow for adequate prosthetic space, vertical implant positions were set up 4 mm apical to the free gingival margin at the facial aspect. Horizontal implant positions were set up 2 mm palatal from the free gingival margin of the ideal upper structures. To create interimplant papillae, the goal for vertical bone augmentation was estimated at the point 2 to 3 mm above the platform or the line connecting the bone peaks of healthy adjacent teeth. The point 4 mm below the contact area was also used to determine the bone height. As a result, simultaneous GBR using a titanium frame nonresorbable membrane was carried out.

The diagnostic template was transformed to an accurate surgical template. After administration of local anesthesia, an incision was performed from the middle of the alveolar crest of the No. 8 and 9 sites to the interproximal aspects of Nos. 7 and 10. The incision was extended intrasulcularly, and vertical releasing incisions were made in the distal aspects of teeth Nos. 5 and 12. Next, full-thickness flaps were elevated in the buccal and palatal aspects (Figure 3). The granulation tissue was completely removed by a curette. Two 11.5-mm-long, 4.0-mm-diameter implants (BIOMET3i T3 Tapered Implant) were placed after standard drilling protocol in sites 8 and 9 in the simulated implant positions. The rough surface of the implants was buccally exposed by only 1 mm in sites 8 and 9, respectively.

The Ti frame–reinforced Ti-honeycomb membrane (Ti-honeycomb membrane M1 [25 × 22 mm], Morita Mfg Corp) was used for GBR. The Ti membrane consists of 20-μm-thick pure Ti sheets with 20-μm-diameter pores and a pitch of 50 μm within regular hexagonal compartments, with an inscribed circle of 1.0 mm diameter (Figure 4). In addition, the Ti membrane is joined with a specific titanium frame by resistant welding.

The key to obtaining a successful bone augmentation into an ideal shape is trimming and appropriate 3-dimensional bending of the Ti membrane. The procedures are described in Figure 5.

1. After trimming the try-in paper (wrapping paper; Figure 5a), the Ti-honeycomb membrane can be trimmed likewise (Figure 5b). At this time, the edge of the membrane must be separated by 1 mm or more from the neighboring root surface.

2. The bending of the Ti-honeycomb membrane is performed from the alveolar crest area using curved pliers (mesh bending pliers, Proceed Corp; Figure 5c, d). The bending line can be determined by estimating the vertically and horizontally required bone volume to be obtained by GBR. However, it is limited inside the 2 Ti-reinforced frameworks (blue double arrow). When 4.0-mm-diameter implants are placed in the esthetic sites, a bone width of at least 8 mm is required at the bone ridge (2-mm buccal bone + 4-mm implant; 2-mm palatal bone). The 2 bend lines should be more than 8-mm apart (Figure 5e). The bend is gentle and without sharp corners to avoid mucosal dehiscence.

3. After adjusting the Ti-honeycomb membrane with the curved pliers to fit the palatal arch, gaps between the edge of the membrane and the bone just below the membrane should be confirmed (Figure 5f). The mesial, distal, and apical sides of the membrane are crimped in a V shape to create a curvature to adapt to the residual bone (red lines: bending lines; yellow area: crimping area; Figure 5g). Figure 5h shows the bending of the red line in the lateral sides of the membrane. Figure 5i shows the protruding area (yellow area of figure f) from the curve at a line angle being folded and crimped. The apical side in the membrane is also bent and folded as previously described.

Buccal (Figure 6a) and occlusal (Figure 6b) views show the 3-dimensionally bent membrane.

Intramarrow penetration of the recipient site was achieved with a small round bur. The bone defect was filled with the grafting materials (ratio of DBBM [Bio-Oss, Geistlich, Biomaterials]: autogenous bone particle = 50:50). The grafting site was covered with the Ti-honeycomb membrane packed with the filling materials (Figure 7). The membrane was attached to the palate with 2 bone pins (titanium screw pin, J. Morita Mfg Corp) and then buccally with 2 bone pins by tapping with a mallet.

The trimmed membrane edge fit well with the residual bone and was flush with the alveolar bone of the adjacent teeth. In addition, the edge of the membrane was separated by 1 mm from the adjacent roots. Finally, after periosteal-releasing incisions, flaps were sutured with 5-0 poliglecaprone sutures without flap tension. After the operation, antibiotics (azithromycin, a 15-membered macrolide antibiotic) were prescribed as 250 mg, once a day, for 3 days. Healing proceeded without any complications after GBR.

Thirteen months (February 2019) after GBR, the alveolar ridge extended vertically. However, the mucogingival junction was also moved coronally because of the periosteal releasing incision. In addition, since the postoperative labial mucosa became thinner compared with the preoperative labial mucosa, soft-tissue augmentation was required for an esthetic outcome. On the other hand, the radiopacity inside the titanium membrane was improved in the CBCT images (Figure 8). Mucoperiosteum flaps were elevated, followed by the palacrestal incision. After removal of the Ti membrane, significant vertical and horizontal bone gain was observed (Figure 9).

A subepithelial connective tissue band (SCTB) harvested from the mucosa of the right maxillary tuberosity was grafted on the alveolar crest (Figure 10). Then, a second SCTB harvested from the left maxillary tuberosity was covered in the interimplant area of the first SCTB for interimplant papillae construction. To prevent bone resorption, the bone-augmented site was covered with a resorbable cross-linked porcine-driven collagen membrane (OSSIX-Plus; OraPharma Inc). Buccal full-thickness flaps were repositioned and sutured apically. Therefore, the grafted SCTB was partially covered by the mucoperiosteal flaps.

At 1 month (March 2019) after SCTG, the mid-buccal alveolar ridge contour was significantly increased (Figure 11a). Abutment connection surgery was performed: a small circular incision was made, and provisional integrated abutment crowns were connected to the implants. Four months after the loading of the implant-supported provisional crowns, the interimplant papillae were reconstructed coronally with scalloped formation of peri-implant mucosa (Figure 11b). Thus, the provisional crown was replaced by a screw-retained all-ceramic crown (zirconia framework layered with glass-ceramic veneer material) in November 2019. The implant-supported final prosthesis and the peri-implant mucosa were harmonious with the proximal teeth and gum (Figure 12).

This technical note demonstrated a novel 3-dimensional curvature bending method of the newly developed honeycomb-like structure Ti membrane for GBR. The procedures made it possible to bend a membrane 3-dimensionally with an ideal shape without being crumpled and to adapt it to residual bone. As the results in this case demonstrated, implant treatment with 3-dimensional bone and soft-tissue augmentation achieved the optimal esthetic results in a case with multiple missing teeth and advanced bone resorption.

As for the histological and radiological evaluation of bone regeneration capacity, Hasegawa et al conducted 2 separate studies that evaluated a box-shaped ridge defect model of the dog mandible. Hasegawa et al¹²  compared the bone regenerative capacity in GBR using the Ti-honeycomb membrane, Ti frame–reinforced Ti-honeycomb membrane, and FBS (control). Regenerated bone tissue volume in the Ti-reinforced Ti-honeycomb membrane was statistically significantly higher than that in the FBS group. Although the calcific osseous area was similar among the groups, the tissue was highly vascular in the Ti-honeycomb membrane groups compared with the FBS group. In their second study, Hasegawa et al¹⁴  compared bone regeneration capacity using the Ti-honeycomb membranes + beta-tricalcium phosphate (β-TCP), Ti flame–reinforced Ti-honeycomb membrane with + β-TCP, and FBS membrane + β-TCP. Histomorphometric analyses revealed that the calcific osseous areas at 12 weeks after surgery were significantly greater in the Ti-honeycomb membrane + β-TCP group and in the Ti framework–reinforced Ti-honeycomb membrane + β-TCP group than in the FBS + β-TCP group. The fibrous area beneath the membrane at 12 weeks postsurgery was also significantly smaller in the Ti-honeycomb membrane groups than in the FBS group.¹⁴  Based on these results, the Ti framework–reinforced Ti-honeycomb membrane is considered to be equivalent to or greater than that of FBS.

In GBR of the esthetic area, the bending shape and installation position of the membrane tray are critically important. The diagnostic wax-up has to be visualized through CBCT scan with radiographic templates in place. It can highlight tissue deficiencies, and final teeth positioning can assist in the planning process. The ideal bone morphology should be estimated based on the following points.

The height and thickness of the facial bone wall affects important predictors of peri-implant mucosal levels. In cases with multiple implants, supporting the ideal crown form and soft-tissue profile, at least 2 mm of labial bone foundation from the implant platform is required.¹⁵  However, bone resorption occurs after bone augmentation. A systematic review evaluated the long-term effects of VRA with the GBR technique.¹⁶  Only 2 studies present the results for a follow-up period of 5 years.^17,18  The marginal bone level change between abutment connection and 1 year of loading varies between −1.01 and −1.86 mm and after 5 years of loading, between 0 mm and −0.22 mm. Therefore, augmenting the labial bone foundation beyond the implant platform by at least 2 to 4 mm is recommended to adequately compensate for the natural bone remodeling that occurs after restoration and loading.¹⁵ 

The challenge of creating esthetic papillae in multiple implant cases can be surmounted by implementing a careful combination of vertical bone support and prosthetic components. These esthetic papillae around implants require a VRA goal calculated by imagining a horizontal line running between the healthy interproximal bone peaks. In the esthetic zone, a palatal placement of the implants is quite common, so bone height calculated directly between the implants would result in a bone crest that is overly palatal. When calculating the necessary bone height for supporting esthetic papillae between implants, it is critical to shift the buccal target height location of the implants. With bone regenerated up to the buccally shifted imaginary line between bone peaks, it is likely that the recommended vertical amount of 2–3 mm of interproximal bone augmentation in the buccal area will be achieved, and an esthetic papillae can be maintained.

As mentioned previously, esthetic bone augmentation must be focused on the crestal area of the ridge, with the base providing only a supportive function. One of the most important requirements for successful VRA is to limit the area of bone augmentation to only the part that needs to be augmented. Otherwise, it will be difficult to achieve tension-free closure of the mucoperiosteal flaps, and this will hinder esthetic results. Therefore, it is necessary to bend and install the Ti membrane using a 3-dimensionally ideal form.

In conclusion, the Ti membrane is considered suitable for VRA with GBR because its mechanical properties are low elasticity and high formability. On the other hand, the membrane tends to be crumpled during the bending process because it is very thin, so it is necessary to perform the bending procedure carefully. The 3-dimensional curvature bending method is believed to improve usability of the newly developed honeycomb structured Ti membrane. However, there is still inadequate evidence to state this conclusively. Further optimization of surgical techniques and multicenter prospective studies are necessary for improvement of predictability.

Abbreviations

β-TCP:

beta-tricalcium phosphate

CBCT:

cone-beam computerized tomography

DBBM:

deproteinized bovine bone mineral

d-PTFE:

dense polytetrafluoroethylene

e-PTFE:

expanded polytetrafluoroethylene

GBR:

guided bone regeneration

SCTB:

subepithelial connective tissue band

Ti:

titanium

Ti membrane:

titanium membrane

VRA:

vertical ridge augmentation

The authors appreciate the gracious financial support of OJ (Osseointegration Study club of Japan) to assist in the publication of this article.

The authors have no conflicts of interest to declare.