The aim of this study was to analyze the success rate of dental implants and the graft shrinkage rate after vertical ridge augmentation and simultaneous implantation with an allograft bonering. Fifty-one patients (81 augmentations and simultaneous implantations) were included. The bonering technique followed a standardized protocol. The alveolar ridge was prepared using a congruent trephine, and depending on the defect size, an allograft bonering with an outer diameter of 6–7 mm was placed. The height of the bonering was trimmed with a diamond disc to the required length. The average height of vertical augmentation was 5.5 mm. Implants were inserted through the bonering into the native bone of alveolar ridge. After 6 months, dental implants were exposed, and dental prosthetics were placed. Of 81 implants placed with the bonering technique, two failed during a 12-month follow-up, corresponding to a success rate of 97.5%. One year after surgery, the allograft bonering exhibited an average vertical graft shrinkage rate of 8.6%. In conclusion, the allograft bonering technique was associated with a favorable outcome, and in cases with large vertical defects, both treatment time and donor site morbidity could be reduced.
Periodontitis, trauma, tumors, or resorption following tooth extraction can cause alveolar bone defects.1 In these cases, bone augmentation of the alveolar crest may be required before inserting dental implants.2,3 The principle aim of treatment is to create a sufficient implant site, inserting dental implants for optimal biomechanical function and in optimal esthetic position.4
To augment bone volume, several operative methods using autogenous or allogenous bone grafts have been described.3,5,6 Although autogenous bone is still considered the gold standard grafting material, it is associated with donor site morbidity at the second surgical site for bone graft harvesting.7–9 Furthermore, intraoral bone grafts are limited to the size and shape of the graft.10,11 Several bone substitute materials, such as allogenic, bovine, xenogenic, or alloplastic, are available,12,13 with no limitation of size and without donor site morbidity.
A definite conclusion of whether the survival and success rate of dental implants inserted in autogenous and allogenous bone grafts are comparable cannot be reached due the lack of controlled clinical trials.14 However, several studies have shown that bone allografts can be successfully used for the augmentation of alveolar ridge defects.15–19
In 2003, the bonering technique was decisively developed by Bernd Giesenhagen (Kassel, Germany).20 With the bonering technique, a cylinder of bone is used to surround a dental implant in case of an alveolar ridge defect. A congruent trephine prepares the recipient side, so that the allograft bonering and the implant can be placed. Prefabricated allograft bonerings (cancellous bone from living donors, harvested from femoral heads during total hip arthroplasty, chemically processes, sterilized, and lyophilized) were used.20
The bonering technique was found to be a reliable alternative to reconstruct severe defects of the alveolar crest and to insert a dental implant in a one-stage surgery.21 The bonering technique shortens the treatment time and enables an implantation with primary stability, including atrophied local bone.22–26
The purpose of this retrospective study was to describe in detail the bonering technique, assess the 12-month survival rate of dental implants, and appraise the amount of peri-implant bone loss after implantation using allograft bonerings.
Materials and Methods
This is a retrospective mono-centric study on all patients who were treated with the bonering technique between January 2013 and July 2015 in a private dental clinic. All patients were followed up for 12 months, and the medical records and radiographs had to be complete for the patients to be included in the retrospective evaluation.
Surgical procedure of the bonering technique
After reflecting the flap, the bony defect was measured using a trephine drill with an outer diameter of 6–7 mm to determine the appropriate size of the bonering. Maxgraft bonerings (Botiss Biomaterials GmbH, Berlin, Germany) are made from cancellous bone from explanted femoral heads provided by living donors subjected to hip arthroplasty treatment. At least 1-mm mesiodistal distance between the ring and adjacent teeth must be kept (Figures 1 through 3). Next, the ideal implant position was determined by pilot drilling (Figure 4). For preparing the bed for the bonering, a trephine (dependent on the chosen ring size) was used for a circular osteotomy at the defect side. A pin at the center of the trephine helped follow the pilot drill hole in ideal implant position. The depth of the osteotomy was defined by the defect (Figure 5). If the bonering bed was not bleeding, small drills were be used to create small bleeding points. As a next step, the bonering was trimmed with a diamond disc to the required length. The bone level of the neighboring teeth was used as reference for the height of bonering (Figure 6). Then, the bonering was inserted into the bed. A precise congruence and press-fit in the prepared bed are critical for the primary stability of the bonering and implant (Figure 7). As a next step, the osteotomy for dental implant was prepared through the bonering according to the surgical procedure of the implant system. The implant was inserted at least 3 mm deep into the local bone through the bonering into the native bone. The implant shoulder was placed about 1.5 mm below the cranial surface of the bonering to compensate for possible resorption. If no stable seating of the bonering was reached, the bonering was secured with a special screw with a head larger than the diameter of the implant (Figure 8). Then, the edges of the bonering were smoothed, using a diamond tulip bur to prevent perforation of the soft tissue. Next, the defect was covered with a mixture of autologous bone particles and bovine resorption–stable bone graft particles. After that, the augmented ridge was covered with a porcine pericardium barrier membrane, which was fixed with titanium pins. A tension-free closure of the wound was done at the end of the surgery (Figure 9). The surgery was done using systemic antibiotics (amoxicillin 1000 mg and metronidazol 400 mg), twice a day, beginning 1 day before surgery, until 5 days after surgery (in cases of penicillin allergy, clindamycin 600 mg was used twice a day).
Data collection and follow-up
A single clinical data manager, who was independent of the surgeon and the prosthodontist, extracted the data for this retrospective evaluation from medical records and radiographs. X-rays and clinical checkups were collected at the following intervals: day of surgery (t0), 6 weeks after surgery (t1), and 6 (t2) and 12 months after surgery (t3). Re-entry and prosthetic restauration took place at t2.
Orthopantomograms were taken at each recall. The marginal bone level was traced mesially and distally of the implant at 600% optical magnification. The length of the implant was used for calibration. With this processing, a comparison between the different radiographs (t0–t3) was feasible.
The following distances were measured: (1) the height of bonering was measured mesial and distal parallel to the dental implant, and the mean value of the two measurements was used for further analyses; and (2) the distance between implant shoulder (IS) and the most coronal surface of the bonering (CBS) parallel to the implant was defined as IS-CBS and was measured mesial and distal; to calculate the loss of marginal bone, the mean of IS-CBS mesial and IS-CBS distal were taken and compared between t0 and t3. When IS was coronal to CBS, the distance IS-CBS was negative; if IS was apical to CBS, the distance IS-CBS was positive. All distances were measured in millimeters with one decimal place (Figure 10).
Statistical analyses were performed with IBM SPSS (version 25, International Business Machines Corp, Armonk, NY). For descriptive statistics, mean values and SDs were calculated.
Between January 2013 and July 2015, we treated 51 patients, who together received 81 augmentations with the bonering technique and who had a complete radiographic documentation. The mean age at surgery was 58.8 ± 11.7 years. Most patients (58.8%; n = 30) was women, and 41.2% of patients were men (n = 21). In most cases (66.7%; n = 54), the bonering technique was applied to the maxilla, and in 27 cases (33.3%), it was inserted into the mandible.
In 10 cases (12.3%), the bonering technique was used directly after dental removal (immediate implantation), in 20 cases (24.7%) it was used 4–8 weeks after tooth extraction, in 4 cases (4.9%) augmentation was performed after 12–16 weeks, and in 47 cases (58%) the operation was performed more than 16 weeks after dental removal.
In all but one case (n = 80; 98.8%), titanium implants with an average diameter of 3.6 ± 0.2 mm and an average length of 11 ± 1.6 mm were used. One ceramic implant with a diameter of 3.8 mm and a length of 8 mm was inserted (1.2%). The ceramic implant had a fixed abutment (open healing). A fixation cap for stabilizing the ring was required in 16 cases (19.8%). The allogenous bonerings had an outer diameter of 6 (54.3%, n = 44) or 7 mm (45.7%, n = 37).
On average, the height of the alveolar ridge in the defect area was 15.2 ± 3.9 mm. The average height of the allograft bonerings at the time of implantation was 5.5 ± 1.0 mm.
Graft resorption rates
At surgery, the implant shoulder was placed 1.6 ± 0.6 mm below the cranial surface of the ring (distance: IS-CBS at t0). Six weeks later (t2), the average IS-CBS distance was 1.4 ± 0.9 mm, and 6 months later, it was 1.3 ± 1.0 mm. After 12 months, the implant shoulder was still 1.2 ± 1.2 mm below the cranial surface of the ring. The mean vertical loss after 12 months was 0.43 mm.
After 6 weeks, the vertical graft resorption rate was 5.6 ± 9.7%. After 6 months, the vertical graft resorption rate was 8.0 ± 11.8%. After 12 months, the vertical graft resorption rate was 8.6 ± 8.3%.
Implant success rate
After 12 months, 76 of 81 implants (93.8%) were successfully integrated without significant bone loss. In addition, three implants (3.7%) were well integrated, showing no mobility, pain, or exudation, but exhibited a loss of bone of 2–3 mm. Two implants (2.5%) from the maxilla showed no osseointegration and had to be removed. Therefore, the 12-month implant survival rate was 97.5%.
The 12-month survival rate of dental implants in this study was 97.5% and was thus perfectly in the range of other published implant survival rates without simultaneous augmentation.27,28 However, if the bonering augmentation fails, it requires the removal of the dental implant as well.
The vertical 12-month graft shrinkage rate of 8.6% found in this study fitted well into other observations made with allogenic bone materials used for alveolar ridge augmentation. Aslan and colleagues29 reported a mean percentage of vertical graft resorption of 5.4% following the use of a cortical block allograft for augmentation of the alveolar ridge after 5 months of healing. Kloss and colleagues19 reported a mean percentage of vertical graft resorption of 5.9% using maxgraft allogeneic bone blocks. Pereira and colleagues30 found that the mean horizontal bone resorption of cortico-cancellous fresh-frozen allogeneic bone blocks between the augmentation procedure and re-entry for implantation was approximately 7.1%. Spin-Neto and colleagues31 reported an average horizontal graft resorption of 8.3% at 6–8 months after cortico-cancellous fresh-frozen allograft placement.
The sample size of 81 bonering augmentation procedures and the follow-up period of 12 months can be considered as strengths of our study. For comparison, Giradi and Saifi32 analyzed the results of autogenous bonering augmentation and simultaneous implantation in 15 cases over a period of 9 months. Omara and colleagues21 studied the results of autogenous bonering augmentation and simultaneous implantation in 12 cases over a period of 6 months. In addition, this is the first retrospective evaluation of allogenic bonering augmentations in a clinical setting. Thus far, allograft bonerings were only studied in animal models.33,34
The retrospective character of this study can be considered a limitation. With retrospective studies, hypotheses on associations can only be formulated but not be proven or rejected. In addition, we treated more patients than those presented here, but they were not included into this evaluation, because of a lack of X-ray pictures. Thus, our sample can be considered a convenience sample. Therefore, the next logical step would be the planning of a prospective clinical study for investigating the long-term behavior of allograft bonerings. Furthermore, in this study, a three-dimensional alveolar crest structure was imaged in a two-dimensional X-ray, and the measurement of surrounding bone was only feasible at two points: mesial and distal to the implant, using the lowest point of contact between bone and implant. Although each implant was calibrated using individual corresponding X-ray pictures, we must assume that distortion and overlay resulted in imprecise measurements. Measurement of dental X-rays showed an inaccuracy of 0.2 mm.35 Newer studies used three-dimensional measurements on cone beam computed tomography images,19 so this is also an important issue to consider for future studies. However, our study is the first to give a long-term evaluation on clinical survival rates of dental implants inserted simultaneously with massive vertical alveolar ridge augmentation.
In this retrospective evaluation, we showed that alveolar ridge augmentation with allograft bonerings and a simultaneous implantation was associated with a 12-month implant survival rate of 97.5%, and an average vertical bone resorption rate of 8.6%. Predictable outcomes, decreased treatment time, and reduced morbidity for the patient are advantages of this technique. Regarding complications and loss of bone, allogenous bonerings can be considered a reliable alternative to autogenous bone augmentation.
The authors whose names are listed certify that they have no affiliations with or involvement in any organization or entity with any financial interest. This study is approved by the ethics commission of Hamburg, Germany, No.: PV5301, July 19, 2016.