Common Longitudinal Studies Are Unsuitable To Guide Clinical Restorative Dentistry

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SYSTEM Initiative: New findings show that the results of common longitudinal studies without control treatments are misleading when choosing the correct type of tooth restorations in clinical dental practice.

Since decades, restorative dentistry has been informed by volumes of clinical longitudinal studies that do not include control treatments but only investigate the success and failures of novel tooth restorations over periods of time. In order to establish which dental restoration type performs best, particularly when placed in posterior load bearing teeth, prestigious expert reviews have traditionally offered advice to the dental profession on basis of simply comparing the success rates between different longitudinal studies with each other.

The SYSTEM Initiative of the Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, has investigated the accuracy of comparison results from longitudinal studies with that from randomised control trials (RCT). RCTs are considered the gold standard in investigating the merits of clinical interventions. SYSTEM’s investigation shows that there is very poor agreement between both results. While comparisons within an RCT would show that the number of treatment failures of two treatments is exactly the same, the comparison between different longitudinal studies would erroneously show a 64% higher failure rate of one type of treatment above the other. Accordingly, expert reviews would mistakenly recommend the merit of placing one type of tooth restorations above that of another.

Largely for this very reason, high-viscosity glass-ionomer restorations have been regarded as clinically inferior to that of silver amalgam in dental practice. When the results of all longitudinal studies, published during the last ten years, for high-viscosity glass-ionomer restorations were compared with that of amalgam restorations placed in posterior load bearing teeth a largely higher performance for amalgam was found. However, no difference between high-viscosity glass-ionomer and silver amalgam was found in all randomised control trials, published during the same time period.

Owing to the lack of a randomly selected comparison group, longitudinal studies are vulnerable to many sources of error. These may include misleading factors whose effects may increase with the length of the study period. Longitudinal studies of tooth restorations suggest thus wrongly that their results are only due to the chosen restorative material type and not to any other influencing factors. Longitudinal studies with longer follow-up periods are commonly regarded as of higher clinical value than those with shorter periods. The irony is that the results of the former may be even more misleading than those of the latter.

Ease and relative low costs make clinical longitudinal studies ideal for the collection of first information concerning new fields of investigation and thus are most suitable in the preparation of complex and costly randomised control trials. However, clinical longitudinal studies are not suitable for guiding clinical practice and may become cause for the fallacious condemnation of one type of intervention above others, as it has been the unfortunate fate of tooth restorations placed with high-viscosity glass-ionomers for years.

SYSTEM’s findings suggest that clincial longitudinal studies are unsuitable to guide clincial practice and that clincial decisions should be based on the results of well conducted randomised control trials instead.

The published full reports of the new findings are available online:

Mickenautsch S, SYSTEM Research note on: How should competing clinical interventions be compared in dentistry? – A simulation-based investigation. J Minim Interv Dent 2013; 6: 73-80.


Mickenautsch S, Yengopal V. Direct contra naïve-indirect comparison of clinical failure rates between high-viscosity GIC and conventional amalgam restorations. An empirical study. PLOS One 2013; 8: e78397.

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Dr S Mickenautsch
SYSTEM Initiative, Univ. of the Witwatersrand, Johannesburg
+27 823363214
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