I would like to approach you regarding a recent article on the performance of the EQUIA system from GC published in Dental Materials , Volume 27, Issue 10, pp. 1031–1037, October 2011: Clinical performance of a new glass ionomer based restoration system: A retrospective cohort study by Katrin Friedl, Karl-Anton Hiller, and Karl-Heinz Friedl The study came to my attention because of GC’s advertising claiming EQUIA as a “permanent posterior restorative system” referring to the results from the above-mentioned article. There is no reason to doubt that the authors are diligent and skilled professional evaluators of dental restorations. Yet, after thorough and duly review I am left with concerns about the scientific rationale and coherence of the study.

Based on the presented results of the study the authors make the claim:

“Within the limitations of this study it can be concluded that EQUIA can be used as a permanent restoration material for any sized Class I and in smaller Class II cavities.”

Proving such indication for any restorative material is a tall task, and robust as well as comprehensive clinical data supporting restoration material performance is needed.

There seems to be reason to believe such data is not presented in the study. Main concern number 1:

The authors mention in their results that no failures were observed during the study. However, according to the data provided in Table 6, 10.6% of restorations were in need for repair or replacement.

In addition, the data from Tables 3–5 show that:

• 34.4% of all restorations showed volume loss (according to the authors mainly chipping “ seen in approximal contacts ”)

• 41.7% of all restorations showed surface roughness

• 22.6% of all restorations showed marginal disintegrity

• 1.

  It appears concerning to classify restorations in need for repair or replacement as non-failures.

• 2.

  Regarding chipping or marginal disintegrity as non-failure seems unusual.

• 3.

  It is not defined how restoration performance parameters (volume loss, marginal disintegrity, surface roughness) are translated into clinical consequences (repair or replacement).

Main concern number 2

The intention of the study is to draw a general conclusion about the success rate of EQUIA, but with the chosen method of patient recruitment, there is no data on performance of EQUIA restorations less than 18 months in situ.

“…patients with EQUIA Class I and Class II restorations which will have been at least 18 months old at the planned (second) evaluation visit were selected by the participating dentists using the practice administration software. Only patients, who attended the practice at a regular basis for periodic checkups, were included in the study.”

• 1.

  With this method of patient recruitment, it is not possible to record a restoration failure prior to 18 months. Retrospective data from patient records that might show failures at an earlier point in time are not taken into consideration. It appears concerning to draw conclusions about restoration material performance while deliberately excluding the evaluation period of 0–17 months.

• 2.

  There is reason to assume a positive selection of restoration survivor cases. Included patients are seen on a regular basis for periodic check-ups. It appears that at least one check-up with follow-up data after restoration placement took place. The dentists are advised to select “ restorations which will have been at least 18 months old ”, which excludes failures noticed at previous check-ups from the study.

Please consider my remarks as an effort to contribute to the development of evidence-based recommendations for dental practitioners.