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LETTERS TO THE EDITORDr. J. de Lange, Isala Clinics, Dept. of Oral and Maxillofacial Surgery, Groot Wezenland 20, 8000 GM Zwolle, The Netherlands; lotte.jan{at}wxs.nl To the Editor: RE: Stoker GT, Wismeijer D, Van Waas MAJ (2007). An eight-year follow-up to a randomized clinical trial of aftercare and cost-analysis with three types of mandibular implant-retained overdentures. J Dent Res 86:276–280. We read the article by Stoker et al. with great interest. This study is unique in the length of adequate follow-up of the cohort that has been achieved. It is therefore possible to compare three types of overdentures in various aspects. The main conclusion of the article, however, after careful evaluation of the presented data, seems not completely in accordance with the results. The authors state that the cost-effectiveness of the single-bar attachment on two implants is better than that of the ball attachment. This conclusion is mainly based on the rather artificial division of the check-up episodes, with or without simple treatment. Simple treatment consisted, in most cases, of activation of the ball attachment, which takes a very short time. It is therefore not surprising that the total treatment time of the check-ups was not significantly different in the three groups (with the largest total treatment time in the single-bar group!). In our view, dividing the check-ups into two groups leads to incorrect conclusions and should not be done. Total costs after 8 years were 4.5% lower in the group with ball attachments compared with the group with 2 single-bar implants. This does not seem to be a very large difference, but when taking into account the thousands of patients who receive these overdentures every year, it makes a considerable difference in Euros and should therefore be considered as an important item. Since the groups were not normally distributed, statistical significance is of lesser importance. Only when evaluated in a greater number of patients is it more likely to achieve a normal distribution of data from which firm conclusions can be drawn. Patient satisfaction, published in an earlier report (Timmerman et al., 2004), is also mentioned. Despite the fact that, after 8 years, general satisfaction was high and not dependent on treatment strategy, in the patients’ opinion the ball attachment was found to be decreasing in retention and stability over the years. However, the clinical significance of this finding remains unclear and is not discussed in the article. In conclusion, the authors are to be commended for this very important and valuable study, but the final conclusions should be considered with some care. REFERENCES
The authors replyThe main conclusion of the article (Stoker et al., 2007)—that an overdenture on 2 implants interconnected by a single bar might be the first treatment of choice, with high cost-effectiveness and efficacy and proven stability for a long-term period—is based not only on the aspects of costs but also on patient satisfaction (Timmerman et al., 2004). De Lange and van Gool state that this conclusion is not in accordance with the results and is mainly based on a rather artificial division of check-up episodes. The costs of aftercare are not different for the 3 treatment groups when analyzed in an eight-year follow-up. The difference in total cost between the groups with a single bar and with 2 ball attachments was only 4.5% due to the initial cost involving placement of the implants, and the manufacture of the denture and the suprastructure. This means that this percentage is expected to decrease in time. Thus, the differences in cost are expected to decrease and so probably will play a minor role in the choice between 2 implants with a single bar or with 2 ball attachments. It is a misunderstanding that the groups were not normally distributed. Cost was a continuous variable, but the costs of aftercare per patient were not normally distributed. Despite the use of non-parametric tests, statistical significance can still be revealed. The conclusion that the group with the ball attachments needs more check-ups with simple treatment than the group with the single bar is drawn after analysis of all data. The division in check-up episodes with and without simple treatment especially shows simple intervention by the prosthodontist—for instance, re-activation of the retentive system. All experienced prosthodontists know that when the patient lacks the retention of the lower overdenture, it takes time before the patient contacts the practice and schedules an appointment. This means, for the patient, a longer period with less retention than desired, and thus leads to annoyance and patient dissatisfaction. The finding that the group with the ball attachments scored significantly lower in satisfaction for the item of retention and stability of the lower overdenture (Timmerman et al., 2004) confirms this conclusion. In this same paper, the clinical significance of this finding is discussed. In the literature, a majority of studies (e.g., Chaffee et al., 2002; Walton, 2003) reported that ball attachments needed more aftercare than a single bar, regardless of the implant system used. More short visits did not result in significantly more total treatment time. This is due to the fact that a non-scheduled visit with a simple treatment often leads to a rescheduling of the next already-planned regular check-up visit. This might explain why the total number of visits during the follow-up period hardly differs. REFERENCES
Journal of Dental Research, Vol. 86, No. 10,
920-921 (2007)
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