WEAR RATE OF THE RETENTION SYSTEM OF A TWO-IMPLANT-RETAINED OVERDENTURE

Objectives: The wear of the implant attachment system is a success factor for OVDs. This study evaluates the correlation between implant angle and wear of an overdenture attachment system supported by two implants. The research is based on the creation of a reproducible and standardised system that permits a three-dimensional analysis of the relationship between the position of the two implants and the wear of the attachment. Methods: The implant attachment system, provided by Keystone Dental® and Rhein83®, is represented by simulated implants positioned in 26 models of different angular combinations, connected to simulated prostheses by two ball attachments. Processes of prosthesis insertion and removal by a patient throughout the period of one year are simulated in the lab. During this study, 1460 cycles (4 manoeuvres per day for one year) of insertion/removal will be carried out manually on the models. An Instron® linear force dynamometer is used to evaluate the variation in retention of the implant attachment system. The data is validated by ANOVA statistical analysis. Results: At this point in the study, six of the eight planned periodical measurements have been taken after the completion of 995 from 1460 extractions. In most cases, there is a reduction in retention with continued usage, however the pattern of this reduction varies. In some cases, there is a steady, decline in retention force. In other cases the retention force drops steeply during the first 135-260 insertions before stabilising. Certain models showed a significant lack of consistency between tests. The retention forces measured during the first test prior to the usage simulation varied from 47.0N to 11.1N and after 995 extractions had dropped to between 14.4N and 2.3N. Conclusions: The preliminary results agree with the literature. The results indicate that parallel inserts show a more consistent behaviour over time.