A Commentary on

Gurgan S, Kutuk Z B, Yalcin Cakir F, Ergin E.

A randomized controlled 10 years follow up of a glass ionomer restorative material in class I and class II cavities. J Dent 2019; DOI: 10.1016/j.jdent.2019.07.013.

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Dental materials are continually evolving. Valuing aesthetic, predictable and minimally invasive options. 2017 saw the facilitation of the Minamata convention on mercury, and with it the age of amalgam phase down.1 Highlighting the need for a reliable alternative material. CR is a popular choice commonly used for class 1 and 2 cavities. With properties including high tensile strength and aesthetic benefits. Nevertheless, se nsitivity to water and high shrinkage rate mean it is not always a clear substitute.2

GI is commonly seen as a temporary restoration, with previous studies reporting susceptibility to water uptake, poor tensile strength and retention. Properties have been improved in recent years, creating good handling and the ability to be used with poor moisture control.3

This prospective, randomised, double-blinded controlled trial aimed to evaluate the longitudinal differences of these two restorative materials in class 1 and class 2 cavities over 10 years. Thus, the purpose of this clinical study was to investigate the durability of a glass ionomer in the restoration of Class I and Class II cavities in comparison to composite resins restorations after 10 years. It was hypothesised was that GI restorations would not be as durable as CR restorations.

Conducted in a methodologically appropriate manner this single centred 4-armed design study recruited local people who required dental treatment. All participants were screened for eligibly and randomly assigned to subgroups. However, no mechanisms were used to reduce the confounding of variants. Participant characteristics such as parafunction, the tooth or surface which required restoration or restorative material staining habits such as smoking were not accounted for by stratification, or other methods. Two calibrated clinicians placed the restorations it is unclear if this was accounted for by how the participants were divided.

Bias was minimised using participant blinding. Blinding of clinicians was not possible due to the nature of the study. The dropout rate was 14%, introducing an aspect of attrition bias, as the majority of patients were lost from the Class 2 cavity group.

A power calculation was performed which was not met, therefore the study was under powered. This could cause type II error, ie falsely rejecting the initial hypothesis. Though the inclusion and exclusion criteria were not revealed within the paper, it can be assumed it was strict due to the 32% (n = 27) of enrolled participants not being eligible. This could be in part due to only accepting those with class 1/2 cavities in two posterior teeth, those with less than four cavities and excellent oral hygiene. This in addition to the small geographical area from which participants were drawn, perhaps reduces the potential generalisability of the results as the participants did not necessarily reflect the typical patient attending for dental treatment with generalised dental disease.

The authors investigated the differences in durability and clinical performance between GI and CR restorations. The results indicated no significant difference between failure rates or marginal adaption of the two restorative materials or of the cavity type (p >0.05). However, two patients presented at 4 years with failed restorations but were not present for the 10-year review so were not included in this success rate. Significance was found in the marginal discolouration between both class 1 and 2 GI cavities (p = 0.022), colour match in GI restorations compared to baselines and colour change bravo scores of class 2 cavities between glass ionomer and composite resin restorations.

Overall the above concerns would suggest that the strength of evidence from this study is likely to be very low. However, differing from previous studies this paper provides prospective and longitudinal data on a topical subject and offers conflicting ideas to conventional knowledge. Nevertheless, the results could be misleading due to an inadequate sample size and poor control of confounding factors and bias. Therefore, future high quality randomised clinical trials are recommended to generate stronger evidence.