The influence of bicortical or monocortical anchorage on maxillary implant stability a 15-year retrospective study of Brånemark system implants

Aim of the study

To study the survival rates and the performance of the marginal bone around Brånemark implants with mono- or bicortical anchorage, after 15 years.

Materials and methods

A sample of 37 patients who were totally edentulous in the maxilla was selected from 351 patients who were treated between 1977 and 1983. They received 207 Brånemark implants, 10 mm in length. The anchorage of 110 of them was monocortical and the remaining 97 was bicortical. They were evaluated at the time of loading and subsequently at 1, 5, 10 and 15 years.

Results

Implants failure was 4 times greater with bicortical anchorage compared with monocortical anchorage. The same was true for fractures. It seems that the causes of failure are due to an increase in stress in the apical part of the implant, errors in occlusion or prosthetic design (poor inter-arch relationships). The remodelling of the marginal bone was identical in the two groups tested, suggesting that the mode of cortical anchorage does not significantly affect the performance of the peri-implant bony tissues.

Conclusion

Bicortical anchorage has been recommended (Adell et al., 1985) and some workers have indicated the need for using this technique for the long term stability of Brånemark implants. Bony remodelling is identical, no matter which type of anchorage is used.

Commentary

One should consider the results of this study as supplemental to the scientific body of evidence already obtained for Brånemark implants. However surprising they are, whether they confirm or deny other observations, they merit our attention.