Original study - ZZI 01/2015

Clinical results of one-stage augmentation with autologous bone rings and Ankylos implants after 5 years of loading in an atrophied mandible

The procedures were all performed under local anesthesia. The retromolar region acted as donor region for 4 of the 25 bone rings and the remaining 21 were harvested from the mandibular symphysis. X-rays were taken before and immediately after the procedure.

The rings were prepared using trephine drills (Helmut Zepf Medizintechnik GmbH, Seitingen-Oberflacht, Germany). In dentate patients, harvesting was to be performed at least 3 mm from the apices of the inferior incisors and canines and also 3 mm from the edge of the chin, and without producing fenestration of the opposite cortex during drilling of the bone ring. Preoperative determination of the maximum drilling depth is not possible but contact with the opposite cortex becomes apparent during drilling by a perceptible change in drill performance. Before finally drilling the bone ring and separating it from the opposite cortex with the so-called ring knife, a roughly 1 mm pilot hole is first drilled with the trephine, which serves as a marking for the donor region. Initial implant bed preparation is then carried out in the marked region with the standard Ankylos implant system instruments.

Preparation of the recipient site to receive the graft is also performed with a trephine drill, the diameter of which should be 1 mm smaller than the diameter of the trephine drill used to remove the graft from the donor region. This enables a good fit and close contact between the implant bed and the bone ring. To prevent overheating of the bone during trephine drilling, the final drilling must be intermittent and at a slow speed (maximum 200 rpm) with constant cooling.

After dividing them from the opposite cortex and removing them, the bone rings are positioned on the insertion site and preparation of the implant bed is repeated through the bone rings. It is advisable to place the rings in the patient’s blood until they are positioned in the recipient area to prevent them from drying out. Following implant insertion, the mucosal margins in the graft region must be sutured closed without tension to prevent dehiscences and postoperative complications.

All of the implants healed closed and were exposed again 6 months later for restoration with fixed crowns and bridges.

X-rays were taken again after 5 years for visual comparison of the position of the crestal bone relative to the implant shoulder with the postoperative X-rays. At the same time, the X-rays were used to measure the distance between the periimplant margin of the alveolar bone and the implant shoulder for quantitative determination of crestal bone loss.

The statistical methods employed were t-test statistics, the chi2 test (Fisher test) and the Kruskal-Wallis H-test. The significance level was set at ? = 0.05. For case examples, see figures 1–9.

Results

Significant associations between insertion site and donor region and the occurrence of postoperative complications were not identified (p = 0.157). A significant influence of postoperative complications on bone loss 5 years postoperatively was not found either (p = 0.578).

With bone rings harvested from the chin, a mean postoperative gain in height of 6.14 mm was found. The mean height of bone rings from the retromolar region was 6.00 mm (tab. 1). Using test statistics, no significant difference in mean postoperative gain in height depending on the donor region was found (p = 0.822).

No loss of height after 5 years was found with bone rings from the retromolar region. With bone rings removed from the chin region, a mean loss of height of 0.28 mm was measured, with a mean residual height of 5.86 mm, but this did not differ significantly from the bone rings from the retromolar region (p = 0.827) (tab. 2).

The greatest gain in bone height was achieved in the anterior region, followed by the molar region and premolar region (tab. 3). Large differences in height was found with the bone rings in the anterior region, which are apparent from the greater standard deviation compared with the premolar and molar region. The smallest differences were found in the molar region (tab. 3, fig. 10). Significant differences in the height of the postoperative bone level depending on the insertion site were not found (p = 0.058).

Five years postoperatively, a reduction in the crestal bone level in the area of bone ring insertion was measured. The mean differences from the initial level were 0.17 mm in the molar region, 0.29 mm in the premolar region and 0.25 mm in the anterior region (tab. 4). Depending on region, there were no significant differences with regard to bone loss (p = 0.073). 5 years postoperatively, the lowest standard deviation was also found in the molar region with regard to the bone level. While an obvious reduction in the difference in height was found in the anterior region, an increase in the height differences between the bone rings was found in the premolar region (tab. 4, fig. 11).

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