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 mean loss of bone height 5 years after the procedure differed significantly over the entire group of patients without differentiating it according to tooth regions (p = 0.01), even if the losses of height had occurred in only 2 patients and with 4 implants.

When the mean loss of height 5 years after the procedure was compared in relation to the mean baseline value, classified according to donor region, however, the differences were no longer significant (molar region: p = 0.081; premolar region: p = 0.172; anterior region: p = 0.110).

As several studies in humans and in animal models have shown, remodeling processes in crestal bone and the redistribution of the individual components of the biological width can differ depending on whether implants are inserted next to each other or as solitary implants or beside natural teeth. How single and adjacent multiple implants can affect the bone rings or lead to postoperative complications was therefore of interest. In this study, no associations were found between single or multiple implants and postoperative complications (p = 0.071).

Significant associations between single and adjacent multiple insertions of bone rings and implants and loss of crestal bone were also not found 5 years after the treatment (p = 0.395).

Discussion

This study was conducted in order to measure the rate of success or failure of simultaneous insertion of bone rings and Ankylos implants. Implant losses and radiographically measurable loss of crestal bone height at the implant shoulder were the parameters of failure. No special software was used for exact comparison of the X-rays but only a non-standardized visual comparison. Other clinical parameters such as probing depths, bleeding indices and recessions or loss of attachment were not included in the study, either immediately postoperatively or 5 years later.

The study was conducted with 5 male and 9 female subjects. The age range was between 25 and 87 years. The independent variables age and sex were not included because of the small number of subjects. The parameter “smoking” was not included as a variable although smoking represents a major risk factor for postimplant complications [12].

One problem is that no special software was used for exact comparison of the X-rays but only a standardized visual comparison was performed. In addition, imprecision in the visual assessment and measurement of the distance between implant shoulder and crestal bone due to distortions of the X-rays cannot be excluded. Thus, objective parameters that might allow exact statements regarding the extent of bone loss are lacking.

The retromolar region and the symphysis region of the chin are classic donor regions that are suitable for harvesting both bone blocks and bone rings. Removal of bone blocks from the retromolar region appears to be associated with fewer complications than removal from the chin. While an increased and prolonged bleeding tendency and discomfort with chewing are reported as complications in the retromolar region in the first postoperative period, patients whose donor site is in the chin often complain of paresthesia in the external skin and mucosa and also of a loss of vitality of the lower anterior teeth [5, 6, 14, 16, 20, 22, 30]. Harvesting of bone blocks from the retromolar region is therefore favored by clinicians and is often described as more pleasant by patients [1, 5, 24]. There do not appear to be advantages regarding implant healing depending on the donor site [6].

By contrast with removal of bone blocks, obtaining bone rings from autologous bone in the retromolar region and mandibular symphysis is a procedure that leads to good clinical results along with low donor morbidity and is generally well accepted by patients on account of its relatively low invasiveness [4, 19, 21, 24, 27].

Harvesting of bone rings from the chin rather than the retromolar region has the advantage that very good bone quality is usually found there with adequate cancellous bone and more autologous bone grafts (up to 5 rings) are available for augmentation for more than one implant.

In this study, 21 bone rings were obtained from the chin region and 4 from the retromolar region of all patients. In the case of bone rings harvested from the retromolar region, no loss of height was found 5 years after the procedure, while a mean loss of height of 0.28 mm was found with bone rings from the chin. However, this was of no clinical relevance and did not differ significantly from the retromolar group. However, the results of comparison between the donor regions should be interpreted with caution on account of the small number of cases and particularly because of the small number of bone rings from the retromolar region and also because of the nonvalidated and nonstandardized measurement method.

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