Demineralized, Freeze-Dried Allogeneic Bone Blocks With Suture Fixation Technique for Reconstruction of Maxillary Alveolar Bone Deficiency: A Case Series

Reconstruction of severe horizontal alveolar bone deficiencies involving multiple consecutive teeth in the maxilla presents several challenges in clinical practice. Guided bone regeneration (GBR), bone block graft, alveolar ridge splitting, and other methods are often used to obtain bone mass according to different degrees of bone increment needs. According to the updated 2022 horizontal bone augmentation decision tree, allogeneic bone block grafting is a more appropriate option for patients with bone augmentation needs more significant than 3 mm.¹  Autologous bone block is considered the gold standard of bone grafts. Autogenous bone blocks have good osteogenic potential and biocompatibility due to the bone’s origin. However, problems include a second operation, long operation time, limited bone availability, and graft material absorption. Thus, allograft bone grafts have been used as a substitute in clinical practice.^2,3  Allogeneic bone blocks showed no significant differences in implant survival, bone regeneration, and esthetic effects compared with autogenous bone blocks. With block allografts, there is no need for a second surgery with a suitable quantity supply. However, it seems to present a higher risk of complications.^4–7 

The primary complications of allogeneic bone block transplantation are unpredictable bone resorption and postoperative soft tissue dehiscence. Bone resorption is related to the type of bone block and can be divided into cortical, cancellous bone, and a combination of both. However, it causes a higher rate of soft tissue dehiscence.^6,8–10  Depending on the treatment, it can be divided into fresh-frozen allogeneic bone blocks (FFABB); freeze-dried allogeneic bone blocks; and demineralized, freeze-dried allogeneic bone blocks (DFDABB). The freeze-drying technique allows the bone blocks to be preserved at room temperature instead of under deep freezing, and the demineralization process exposes organic matrix and growth factors that can promote cell proliferation and bone regeneration, providing a scaffold for new bone formation; however, it makes it less mechanically strong than deep-frozen bone.^2,11–13 

To minimize complications, the following principle should be strictly followed: primary wound closure, angiogenesis, space creation or maintenance, and stability of both the wound and implant.¹⁴  A flat alveolar ridge contour might make it more difficult to achieve stable graft fixation. The lack of a natural bone wall or inferior incision can affect the stability of the graft material during the healing period. Special techniques, such as titanium screw(s), titanium mesh, or suture fixation techniques, may be required to secure the graft and maintain its position during the healing process.^15–19  Compared with titanium screws, titanium mesh, and other fixation methods, suture fixation does not require secondary surgical removal and has achieved good clinical results in several cases. Urban et al¹⁷  report a clinical technique using vertical mattress sutures on the mesial and distal sides, which serve to immobilize the grafts through tension on the membrane and sutures, but this technique is only suitable for narrow defects; for broad defects, it is still necessary to fixate with the assistance of membrane tacks.

The objective of this case series was to provide a preliminary description and analysis of the clinical outcome of utilizing DFDABB in conjunction with the periosteal vertical mattress suture (PVMS) technique, evaluate its safety, and assess its overall impact on patient outcomes.

This case series comprises 7 patients with severe consecutive horizontal maxillary bone loss at multiple tooth sites, necessitating bone augmentation before implant placement. The inclusion criteria encompassed patients with a pronounced consecutive horizontal maxillary bone deficiency, requiring bone grafting before dental implant placement; aged >18 years; exhibiting good oral hygiene; being nonsmokers (or smoking fewer than 10 cigarettes per day); and not abusing alcohol. Exclusion criteria encompassed a history of recent infection, active periodontitis, use of oral or intravenous bisphosphonates, pregnancy, metabolic disorders, drug or alcohol abuse, and a history of radiation therapy in the head and neck. All patients provided informed consent; the study received approval from the ethics committee of Zhejiang Provincial People’s Hospital (approval No. 2021KY037) and Chinese Clinical Trial Registry (approval No. ChiCTR2300073739). The research was conducted in accordance with the revised Declaration of Helsinki (2013).

After local anesthesia (1.7 ml of atticaine with epinephrine 1:100 000), a full-thickness mucoperiosteal flap was made with 2 subtended vertical incisions to expose the buccal and palatal side of the maxilla and a portion of the maxilla (Figure 1a). Several alveolar bone nourishing hole bores were made on the buccal surface to ensure abundant vascularity (Figure 1b). Subsequently, an allograft bone block (XinKangcheng, Beijing, China) was selected based on the size of the defect area (Figure 1c) with options of either 10 × 10 × 5 mm or 20 × 10 × 5 mm. The 10-mm bone block was fixed with 1 titanium screw (Trausim, Suzhou, China), whereas the 20-mm bone block was fixed with 2 titanium screws (Figure 1d). The remaining space was filled with deproteinized bovine bone mineral (Bio-Oss, Geistlich, Switzerland) (Figure 1e). An absorbable collagen membrane (Bio-Gide, Geistlich, Switzerland) was applied to cover the surface of the graft material (Figure 1e). The collagen membrane and graft material were sutured using PVMS with 4-0 absorbable sutures (Coated VICRYL, Raritan, NJ) (Figure 1f).

The flap and membrane were sutured perpendicularly in a proximal and medial direction with the entrance and exit on the buccal side positioned at the root of the reduction incision. Additional stitches were placed in the middle if necessary.

After suturing was completed, to ensure tension-free closure of the wound, a tension-reduced incision was made on the buccal gingival flap using a 15-gauge C scalpel; the buccal flap was gently pulled to ensure complete fixation of the graft and membrane. Finally, the wound was sutured in 2 layers with 5-0 nonabsorbable sutures (Coated VICRYL, Ethicon) (Figure 1g), combining a horizontal mattress and single interrupted sutures. Vertical incisions were closed with single interrupted sutures (Figure 1g).

Cone-beam computerized tomography (CBCT, Planmeca ProMax 3D, Planmeca Oy, Helsinki, Finland; 60–90 kV, 2–15 mA, field of vision: 10 × 10 cm; slice thickness: 180 μm) imaging was performed preoperatively, immediately after bone augmentation surgery (Figure 1h). A significant increase in bone width was observed on CBCT in the immediate postoperative period (Figure 1i). Postoperatively, cefuroxime and metronidazole tablets were routinely administered for 1 week (cefuroxime, 0.25 g per dose, twice daily; metronidazole, 0.2 g per dose, 3 times daily) and 0.2% chlorhexidine gargled daily for 2 weeks. The wound was reviewed, and the sutures were removed after 14 days.

After 6–10 months of healing, implant placement was performed under local anesthesia. CBCT imaging was performed before implant surgery. Oral scans and virtual teeth arrangement were performed before surgery (Figure 2a and b). The flap was created the same way as for the bone graft; the entire graft was exposed, navigation pins were placed (Figure 2c and d), and the fixed titanium screws were carefully removed. Implantation in a predetermined position under computer-assisted dynamic navigation (Yizhimei computer-assisted dynamic navigation system DHC-D12, Digital-health Care Co., Ltd., Suzhou, China) and verification of the accuracy of the implant position with the use of prepared simple pirates and postoperative CBCT screenshot images (Figure 2e, g, and h). Subsequently, the soft tissue was sutured. The final restoration was finished after 3 months of healing (Figure 2f).

CBCT was taken before the bone-grafting surgery and after the implant surgery under the same conditions. It was performed on all patients by the same senior clinical radiologist. Both images were exported as DICOM format files and imported into image processing software (Mimics 21.0, Materialise, Leuven, Belgium). The procedure was as follows: Create a suitable bone mask through thresholds and regional growth tools in both images. Export the preoperative image as an STL file. Set a minimum distance filter of 1 mm to align the preoperative STL with the postimplant bone mask and manually adjust it to match the 2 (Figure 3a). After the complete registration was confirmed, the curve of the dental arch was drawn on the image to form a Panoramic radiograph so that the coronal section was perpendicular to the curve of the dental arch to prevent the alveolar width in the posterior region from becoming too long due to the cross-sectional orientation (Figure 3b). Data measurement methods—refer to Wang et al¹⁶ —make a reference line along the long axis of the implant center, create a line perpendicular to this reference line at 5 and 10 mm from the apex of the alveolar ridge, measure the width of the alveolar bone before the bone augmentation and after the implant procedure on this line, and calculate the difference between the 2 as the horizontal increase of the alveolar bone (Figure 3c). A single-blinded, experienced clinician performed the radiography data analysis to ensure consistency and accuracy. Intra-examiner reproducibility was assessed by taking measurements twice at a 1-week interval, and the intraclass correlation coefficient was evaluated, ranging from 0.80 to 0.95.

For patients who signed an informed consent form, bone tissue was removed by cylindrical biopsy perpendicular to the buccal surface using a 3.0-mm trephine bur (Changsha Tiantian Dental Co. Ltd., China) during implant surgery. The retrieved samples were fixed by immersion in 4% paraformaldehyde, after which they were subjected to gradient dehydration, decalcified, and embedded in paraffin. Sample sections were cut into 5-μm-thick slices and stained with hematoxylin-eosin (HE) and Masson’s trichrome. Sections were observed with histological analysis using a Leica DM500 light microscope (Leica Microsystems, Wetzlar, Germany), and histological images at magnifications of ×40, ×100, and ×200 were obtained using a Leica ICC50 high-definition digital camera (Leica) attached to it.

From May 2021 to February 2022, 7 patients aged between 31 and 69 were enrolled in this study. Each patient underwent restoration with 1–2 bone blocks and 1–4 implants. The present case series used 10 bone blocks and 13 implants. The surgical sites of 4 patients were located in the anterior region. At the same time, 2 were situated in the posterior region, and the last patient’s site encompassed both the anterior and posterior regions. The time interval between bone grafting and implantation in the patients was 6–10 months (Table 1). Demographic characteristics of the participants, the bone block size, and the titanium screws used for each patient’s defect area are detailed in Table 1.

During the postoperative follow-up, 1 wound experienced slight rupture without infection, whereas the remaining incisions showed no signs of rupture or infection. All of the patients exhibited localized swelling, which notably abated within approximately 1 week, and reported alleviation of discomfort within 2–3 days. The average alveolar ridge width at 5 mm was 4.52 ± 2.03 mm before bone graft and 9.79 ± 1.57 mm after implantation with an average increase of 5.26 ± 1.97 mm. At 10 mm, it was 7.23 ± 3.60 mm before the bone graft and 11.81 ± 2.90 mm after implantation with an average increase of 4.58 ± 2.01 mm (Table 2).

A significant amount of new bone formation surrounding the residual bone graft material is observed through HE and Masson’s trichrome staining of the jawbone tissue. This is particularly evident in the Masson-stained sections, in which the residual bone grafts appear blue with cavities devoid of cell nuclei. In contrast, the new bone appears red with visible cell nuclei within the cells, showing a gradual transition between the two, tightly connected without the intrusion of connective tissue. Haversian canals and the surrounding circular lamellar bone can be seen within the newly formed bone, indicating good bone integration. Connective tissue envelopment between the granules and vascular structures in the same area is also visible, suggesting good vascularization without any apparent signs of inflammation in the sections (Figure 4).

The observed mean bone width increase was about 4.92 mm in this study, and the result was similar to previous studies of allogenic bone blocks.²⁰  Traditional autogenous bone block grafting is shown in the literature to have a horizontal bone gain of approximately 5 mm.⁵  In contrast, the value of the horizontal bone gain with the classic GBR technique, which varies considerably depending on the size of the range, is approximately 1.5–5.5 mm.²¹  A body of literature underscores the well-established clinical efficacy of allograft bone;^22–24  notably, in comparison to autologous bone blocks, implant survival rates did not significantly differ between the two although allograft blocks exhibited a lesser extent of new bone formation.^4,5,7  Patients with maxillary continuous bone defects often imply a greater need for bone width gain and more difficult postoperative stabilization, which is more difficult to perform using GBR and fixate with postoperative grafts. At the same time, the damage caused by autogenous bone blocks is too significant and challenging to be accepted by most patients, so allogeneic allografts are a more appropriate choice for this type of patient, and they can satisfy the high need for bone gain as well as reduce the trauma to the patients.

Osseointegration of the graft material is essential for long-term stability and success. To achieve good osseointegration, there must be the largest possible contact area between the graft material and the recipient bone surface. Some studies personalize the bone blocks for different patients, and 3D matching and cutting were performed preoperatively better to match the bone defects in the operative area.^25–29  In the restoration of small bone defects, such as buccal single-wall bone defects on a sole anterior tooth, the personalized bone block achieves good retention in the mesial and distal directions using the difference in the horizontal thickness of the alveolar ridge between the defective area and adjacent dentition. However, in continuous horizontal defects, the difference in horizontal thickness may be more significant as the defect area lengthens. Still, the overall slope slows, so the retention force produced by the use of personalized bone blocks may be unanticipatedly reduced; the fixation of the bone block is mainly from titanium screws.

In some cases, the framing technique using cortical bone combined with bone graft particles has yielded results similar to autogenous bone block grafting. Still, there have been cases in which cortical bone was not mixed with bone graft, probably because the two have different remodeling rates.^30,31  We used DFDABB material with a compressible cancellous bone fraction in this case series to achieve more significant postoperative contact with the recipient bone surface. To fill the remaining void, DBBM also achieved this goal. On the other hand, because of the unpredictable postoperative resorption of DFDABB, the resorption rate of interstitially placed DBBM particles is slower, and they also play a role in space maintenance.

The PVMS technique was used to immobilize DBBM particles to maintain postoperative stabilization of grafts, and the suture was performed under a buccal flap reduction incision to minimize the influence of flap stretching on the graft. Fixed DFDABB also restricted the movement of particles to a certain extent. However, this technique also has inevitable disadvantages, such as particle transplantation material producing apicocoronal direction movement and the tensile strength of the suture decreasing with absorption.^16,17  Urban et al¹⁷  report that, according to data provided by the company, the tensile strength of the suture decreased by a quarter 1 week postoperatively and by 3 quarters 2 weeks postoperatively. Kamat et al¹⁵  describe the SauFRa technique, which involves a horizontal suture at the top of the suture based on vertical mattress sutures on both sides, avoiding apicocoronal direction movement but adding complexity and time to the operation. Johnson et al¹⁸  fixed the membrane sutures to the neighboring teeth on each side and at the base of the reduction inner flap and periosteum to form a triangular structure. Wang et al¹⁶  report that periosteal diagonal mattress sutures combined with 4 corner pins can maintain the space and stabilize the graft and membranes in severe continuous horizontal bone defects. It is worth noting that, no matter which suture method is used, reduced tensile strength after suture absorption is a problem for both, whereas selective cell colonization takes about 3–4 weeks. Complete degradation of the collagen membrane takes 4 weeks, which may have some effect on osteogenesis; future studies are expected to explore the specific differences.^32,33 

No disease transmission was observed in this study. With a rigorous donor screening and handling protocol, the risk of disease transmission from homogeneous bone blocks was almost negligible. However, some major histocompatibility complex molecules were still detectable in them,³⁴  and radiation sterilization leads to a decrease in osteoconductivity with a positive correlation over a range of time. In contrast, the freeze-drying technique preserves osteoconductivity over a more extended period.³⁵  Aslan et al¹²  report that the difference in postoperative resorption between DFDABB and FFABB was around 6%–8%, which suggests modest. FFABB has better mechanical and osteoinductive properties, but it may contain living cells, resulting in increased antigenic sensitivity and, thus, affecting bone remodeling.^22,36  Minerals in bone mask the proteins in it. Bone morphogenetic proteins (BMPs) act as small glycoproteins that promote osteogenesis through their effects on mesenchymal stem cells. At the same time, demineralization increases the utilization of BMPs in bone, and thermodynamic study surfaces that demineralized bone matrix release more heat, possibly associated with better hydration.³⁸  We chose DFDABB for this case series; the structure is cancellous cortical bone. The cortical bone somewhat compensates for the demineralization, the lack of strength after lyophilization, and also reduces late resorption, whereas the cancellous bone has a more lax structure that facilitates clinical plasticity and cellular growth. The lyophilization technique simplifies the preservation of the DFDABB and reduces the immunosensitization of the bone block.

This study still has several limitations. First, as this study is a case series report and not a randomized controlled trial, it is crucial to acknowledge that the outcomes reported in this study should be interpreted with caution due to the limited number of participants and the lack of long-term follow-up results; more comprehensive and statistically robust research, including clinical randomized controlled trials, is needed to evaluate the effectiveness of the treatment entirely. Second, this study did not provide quantitative histomorphometric data, which limits the ability to draw detailed conclusions about the bone remodeling process and the effectiveness of the treatment. Future research should include histomorphometric analysis to offer a deeper insight into the biological processes involved. Additionally, due to the inability of the cancellous bone portion to visualize on CBCT and the effect of DBBM particles on the image, changes in bone block volume cannot be measured accurately. Future studies should include measurements of graft material volume to provide a more complete understanding of the treatment outcomes.

DFDABB combined with PVMS demonstrated a superior horizontal bone gain in maxillary bone augmentation for cases with horizontal continuity deficiency. However, further studies are required to validate these findings.

The first 2 authors contributed equally to this work and share first authorship. Author contributions: Fan Yang and Linhong Wang, performed bone augmentation and implant surgery, review, and editing; Chengzhi Dong and Simin Zheng, original draft preparation and data collection; Zhuoheng Xia, Runzhi Chen, and Yuxin Zheng, selection and preparation of case pictures. All authors reviewed the manuscript. This study was supported by the Zhejiang Provincial Medical Science and Technology Planning Project (No. 2024KY008). The authors declare no competing interests.