Effect of enriched bone-marrow aspirates on the dimensional stability of cortico-cancellous iliac bone grafts in alveolar ridge augmentation

The study group consisted of patients who underwent vertical augmentation of the jaws via bone grafts harvested from the iliac crest enriched with bone-marrow aspirate concentrate. The cohort was compared to two control groups, which were evaluated in a former study by the same institution. The first control group (Control) included 40 patients underwent a vertical augmentation with autologous bone grafts from the iliac crest, which were recruited by the Department of Oral and Maxillofacial and Plastic Surgery at Friedrich-Alexander-University Erlangen Nuremberg [19, 20]. In the second control group, 40 patients received identical surgical procedure, whereas the autologous bone graft was covered with a thin layer of deproteinized bovine bone matrix and a collagen membrane (DBBM-group) (Table 1) [20]. This cohort was recruited by the Department of Oral and Maxillofacial and Plastic Surgery, University Hospital Schleswig–Holstein, Campus Kiel. The consistence of the surgical procedures was secured as the main surgeon moved from Erlangen to Kiel.

Comparative assessment was conducted and reported in accordance with the STROBE recommendations (strengthening the reporting of observations in epidemiology). It was undertaken with the understanding and written consent of each subject. It was carried out according to the ethical principles including the Declaration of Helsinki. Ethical approval was obtained by the by local ethical committee (AZ D494/18).

The data of the patients who presented with critical size defects of the jaws who underwent vertical or vertical–horizontal augmentation via autologous bone graft harvested from anterior iliac crest were included. Patients with any systemic conditions which could affect the bone healing, such as: uncontrolled diabetes, smoking habits, immunosuppression, malignancies of the maxillofacial structures, antiresorptive therapy and radiotherapy to the head and neck region were excluded. Clinical and radiographic evaluation was carried out after 4–6 months postoperatively in 33 patients, 12 months postoperatively in 16 patients and 24 months postoperatively in 10 patients.

The augmentation procedure was performed as previously described by Wiltfang et al. [20]. Briefly, under general anesthesia, cortico-spongeous bone grafts were harvested from the anterior iliac crest. The grafts were trimmed according to the form and size of the implant recipient site and fixed with titanium mini screws (Fig. 1). If a sinus floor elevation was indicated, the previously described lateral window technique was used [21]. During the same procedure and via the same access, bone marrow was aspirated with a bone cannula (PrepaPlus®E 11G, Peter Pflugbeil GmbH, Zorneding, Germany), which was screwed into the iliac crest 8 cm posterior of the anterior iliac spina (Fig. 2). 2500IE heparin per 20 ml syringe were added and a total of 50–60 ml of bone-marrow aspirate was gained. The stem cell enrichment was performed chairside using a laminar airflow bench according to the following protocol: centrifugation in 4 tubes at 1200g for 7 min (Centrifuge 5702, Eppendorf SE, Hamburg, Germany), removal of the serum supernatant, pooling of the cell-concentrates in one tube for second centrifugation at 1200 g for 3 min. Finally, the supernatant was removed. Approximately ten milliliters of enriched stem cells were used for each recipient site. The stem cells were mixed with autogenous bone chips and DBBM to cover and contour the bone-blocks. The augmentation was covered with resorbable membranes (Bio-Gide®, Geistlich Pharma AG, Wolhusen, Switzerland). Ampicillin/sulbactam (3 × 1.5 g/day) was administered intravenously at the day of surgery and 2–3 days postoperatively and then continued as oral antibiotics (2 × 750 mg/day) for five additional days. The surgical wounds were sutured primarily closed layer-by-layer and in a tension-free manner. A postoperative “as-needed” analgesic regimen was performed. The implant insertions were made after 4–6 months.

Clinical evaluation was carried out immediately after augmentation, after 6, 12 and 24 months postoperatively (Fig. 3). The evaluation included complications, such as wound dehiscence, abscess, transplant failure and implant survival.

Panoramic radiography was carried out with a ‘Kavo Pan eXam’ device (tube voltage: 66 kV (female patients) or 70–73 kV (male patients), current: 7.5–9.6 mA, exposure time: 10 s). The consecutive panoramic radiographs were processed by digital superimposition (Fig. 4). This method ensured the comparison of the bone height of each patients’ radiographs at different timepoints. By this method all radiographs of each patient were adjusted to each other for each single augmented quadrant. The different radiographs of one patient were opened in one file in several layers. The most recent served as a standard format. The other radiographs were adjusted to the standard format using a layer transparency of 40–45% and the formatting functions. This technique was performed for each single quadrant with augmented bone graft for a high degree of accuracy. The height of the bone was determined as the distance of the crestal edge of the residual alveolar bone and the graft surface. The known size of an implant in the examined quadrant served as a reference for the millimetre scale. The resorption was determined in millimetre compared to the initial height of the graft.

In ten patients treated with augmentation from iliac crest with additional BMCA, a specimen of the augmented bone was harvested using a 1.8 mm trepan bur at the time of implant insertion. The histological specimens of the control group included ten biopsies with conventional clinical standards with grafts from the iliac crest, absorbable membrane and particulate bone substitute material. The histological bone quality was evaluated using toluidine-blue staining. Clinical bone quality, density and structure, was assessed by intraoperative determination of the drilling resistance and classified by the Lekholm–Zarb classification system D1–D4 (D1: oak, D2: beech, D3: balsa, D4: polystyrene).

The resorption of the bone height was determined for each single augmented quadrant for each patient (63 quadrants after 4–6 months; 32 quadrants after 12 months; 25 quadrants after 24 months). The resorption was determined in millimetre and compared to the initial bone height. The mean resorption rate with standard deviation of all patients were calculated. The data was compared to the control groups. A two-sided t test was performed and p < 0.05 was considered significant.

As the acquisition of the stem cells was performed ipsilateral to the donor site, patients did not report any additional discomfort caused by the aspiration–procedure. No differences in terms of implant survival were observed in the groups. No abscess or loss of bone graft occurred. In total, two out of 188 implants had to be removed due to failed osseointegration. With 186 implants successfully osseointegrated after 2 years the implant survival rate was 98.9% (DBBM: failed osseointegration of three of 248 implants, survival rate: 98.8%; control: failed osseointegration of 2 of 237 implants, survival rate 99.2%) (Fig. 5).

In the study group, a total of 188 implants were inserted 4–6 months after augmentation. Patients of the control group received 237 implants, whereas patients of the DBBM group received 248 implants. Residual bone height at the augmented area was preoperatively 8.8 ± 2.7 mm. The average residual bone + graft height has reached to 14.2 ± 2.6 mm immediate postoperatively. The highest bone resorption rate was observed in the first 12 months postoperatively. In the stem cell group, the resorption after 4–6 months was 1.2 ± 1.3 mm and significantly lower than the resorption of the control group with 1.9 ± 1.6 mm (P = 0.029). The resorption in the DBBM group was a little bit higher but statistically not significant (1.4 ± 1.2 mm) (Fig. 6).

After 12 months, the resorption in the stem cell group was 2.1 ± 1.6 mm and significantly lower compared to the control group (4.2 ± 3.0 mm, P = 0.001) and significantly lower compared to the DBBM group (resorption 2.7 ± 0.9 mm, P = 0,012). The resorption rate in the second year was lower compared to the first year and was measured as 2.7 ± 1.7 mm in the stem cell group (1-year bone loss in the time period of 12–24 months of 0.6 mm compared to 2.1 mm in the first 12 months). The resorption was significantly lower compared to the control group (4.7 ± 2.9 mm; p = 0.003) but not significantly lower compared to the DBBM group (resorption 3.1 ± 0.5 mm, P = 0.075) (Fig. 6).

The clinical and histological bone quality were evaluated at the moment of implant insertion 4–6 month post-augmentation. Relative amounts of bone area vs total tissue of the spongious bone were measured (Fig. 7) [22]. The measured mean bone area (bone density) was 27.3 ± 10.9% in the stem cell group compared to 20.3 ± 13.4% in the control group. A higher clinical bone density (D1, 8, vs D2, 4) of the transplants with enriched bone-marrow aspirate treatment (p = 0.02) correlated with a better histological bone quality (p = 0.03).