Laboratory Trial Results Concerning High-Viscosity Glass-Ionomer Versus Amalgam Tooth Restorations Not Suitable For Clinical Guidance

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SYSTEM Initiative: Results from laboratory studies comparing high-viscosity glass-ionomer cement (HVGIC) with amalgam for tooth restorations do not share the same effect direction and magnitude of results from controlled clinical trials. Laboratory trial results may thus not correctly reflect clinical reality and should not be used for clinical guidance concerning HVGICs in daily dental practice.

SYSTEM Initiative

Laboratory trial results should not be used for clinical guidance concerning high-viscisty glass-ionomers in daily dental practice.

A large percentage of evidence concerning dental interventions is based on laboratory research. The apparent wealth of laboratory/in-vitro evidence is sometimes used as basis for clinical inference and recommendations for daily dental practice.

Traditionally, glass ionomer cements are considered as unsuitable for clinical use as a permanent filling material in the posterior dentition due to in-vitro measured poor mechanical properties. Specifically, in-vitro measured low material strength and wear resistance have been stated as reasons why glass-ionomers cannot rival amalgam as truly universal posterior restorative material.

The SYSTEM Initiative of the Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, conducted a systematic search of the current dental literature for laboratory and controlled clinical trials that directly compared the efficacy of high-viscosity glass-ionomer cement (HVGIC) with amalgam as the current gold standard for placing tooth restorations. These trials were identified through the search of main international data sources, such as CENTRAL accessed via the Cochrane Library; MEDLINE accessed via PubMed; Biomed Central; Database of Open Access Journals (DOAJ); IndMed; OpenSIGLE and Google Scholar.

After literature search, the laboratory and clinical results of the identified trials were analysed and their joint effect magnitudes and effect direction statistically compared. While the laboratory trials indicated inferiority of HVGIC to amalgam, no significant differences between both types of tooth restorations using either material were found in clinical trials.

For example, the in-vitro measured lower physical strength of HVGIC in comparison to that of amalgam might not translated into any clinically higher fracture rate, because placed glass-ionomer restorations are generally smaller than amalgam fillings, adhere to the tooth structure on basis of ion exchange between carboxylate and phosphate ions and thus do not require the preparation of macroretention areas in tooth cavities, like amalgam. Furthermore, HVGIC placed in tooth cavities may abrade out of contact due to its potentially lower wear resistance. For these reasons, HVGIC restoration may not be exposed to the same extent of daily masticatoric forces in the oral cavity than amalgam restorations are. Therefore, while in the laboratory measured material properties such as compressive strength, fracture toughness or microleakage of HVGIC may indeed be inferior to that of silver amalgam, these may not be sufficiently strong enough to translate into clinically meaningful differences, due to other influencing factors that are not present during laboratory trials.

The established evidence shows that laboratory results concerning HVGIC versus amalgam for tooth restorations have no similar effect direction and magnitude than that of controlled clinical trials. The reasons remain unclear but may be due to multifactor influences and confounding, particularly due to the lack of clinical factors that are absent in laboratory trials.

Hence, while laboratory trial results may provide valuable explanations for observed clinical phenomena and may serve during the hypothesis development process, they appear not be suitable as basis for clinical inference and clinical recommendations concerning HVGICs in daily dental practice.
The full published report of the findings are available online for free download:
Mickenautsch S, Yengopal V (2015) Do Laboratory Results Concerning High-Viscosity Glass-Ionomers versus Amalgam for Tooth Restorations Indicate Similar Effect Direction and Magnitude than that of Controlled Clinical Trials? - A Meta-Epidemiological Study. PLoS ONE 10(7): e0132246.

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Prof Dr S Mickenautsch
MI Compendium
since: 11/2014
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