Commentary

The objective of this systematic review was to examine the effect of local and systemic risk factors on tooth loss during long-term periodontal maintenance. The authors conducted a thorough search of three databases and the grey literature up to September 2009, including publications in all languages.

As the clinical question deals with prognostication, the review included observational studies of patients with chronic periodontitis, who had received active periodontal therapy followed by periodontal maintenance care for at least 5 years. Specific inclusion and exclusion criteria were outlined a priori. Thirteen retrospective case series were included and the details of each were described. No cohort or case-control studies were reported.

The major flaw in this review is the application of an adaptation of the Newcastle-Ottawa Scale (NOS) to determine risk-of-bias for included trials (http://www.ohri.ca/programs/clinical_epidemiology/nosgen.pdf). Risk-of-bias assessment tools are used in systematic reviews in a number of ways - as a threshold for inclusion of studies; as a possible explanation for differences in results between subgroups of studies; by performing sensitivity analyses where only some of the studies are included; or by using a qualitative score as a weight in a meta-analysis of the results. However, empirical research does not support the use of these scales other than to describe the potential biases of each included trial. In fact, the Cochrane Collaboration, the group responsible for the majority of published systematic reviews in health literature, advises against the use of scales.1

The NOS assesses cohort and case-control studies and consists in terms of selection of participants (sources and selection of cases and controls), comparability of cases and controls and exposure (ascertainment of exposure and non-response rates). Thus, it was not intended for case-series. And while the face and content validity of this scale is established, criterion validity is not. Nonetheless, the authors are very clear about the limited quality of current evidence.

Furthermore, case-series studies were the best evidence available to the authors. Evidence-based dentistry is based on probabilities and rational decision-making. It is difficult to determine from case-series, with any degree of certainty, the probability of causality and prognosis, due to the serious risk of bias by potential confounders. Thus our decision making is less dependent on evidence, relying more on a determination of the balance between risks and benefits of a particular course of action.

In this case, the risks of regular periodontal maintenance (apart from time and financial costs) are altered aesthetics due to shrinkage of inflamed tissue and dentinally hypersensitive teeth. The benefits are improved aesthetics, reduced tooth mobility and a lower likelihood of future tooth loss.

The importance of this article is that it examines the patient-based outcome of tooth loss, as opposed to surrogate markers such as clinical attachment levels. Unfortunately, due to the weakness of the evidence, the only conclusion the authors can draw is that researchers (and funders) need to improve the design of future prognostication studies.