Commentary

Developmental defects of enamel (DDE) occur when there is disruption to the normal process of enamel formation; they can manifest either as defects in the quantity or quality of enamel.1 Enamel hypoplasia, or a defect in the thickness of enamel, commonly manifests as pits, grooves or missing areas of enamel.2 Opacities in enamel are often due to hypomineralisation, or problems with the quality of enamel.2 It is thought the prevalence of DDE, in any form, in high income countries such as the United Kingdom could be anywhere between 25-50%1,3 with a specific form of DDE, molar incisor hypomineralisation, thought to affect around 15% of children in the UK regardless of water fluoridation exposure.4 Enamel defects have commonly been attributed to ill health in the first years of life or poor maternal health in the later stages of pregnancy,3 but are also shown to correlate with socio-economic status and increased caries risk, as well as an increased need for dental treatment.1,3,4 The paper reviewed here attempted to analyse the evidence relating DDE to dental caries.5

The aim of the paper was clear, the authors endeavoured to evaluate the association between developmental defects of enamel and dental caries experience in the permanent dentition through a systematic review and meta-analysis. The search strategy used to identify papers was provided and encompassed a number of different sources, had reasonable language and date limits and utilised citation searching to obtain as wide a variety of papers as possible. Concerns could possibly be raised regarding the decision not to limit study designs accepted in the systematic review, as it is common practice to limit this to a single design, however all studies included in the final meta-analysis were of a cross-sectional design. In the PRISMA flow diagram6 indicating the number of studies included and excluded, it was noted that some studies were excluded as they provided ‘assessment of other type of enamel defect (MIH)’, it is accepted however that MIH is a form of developmental defect of enamel and therefore this exclusion criterion is contradictory to the research question posed by the researchers. The quality of the studies included was assessed but then not reported clearly, though the meta-analysis was stratified for study quality at a later stage.

The meta-analysis combined the results of seven studies, with sample sizes ranging from 245 to 3538 participants, reported between the years 1994 and 2014, and using a number of different examination techniques. The resulting odds ratio indicated a 2.21 increase in odds of developing caries for participants with DDE compared to those without the condition (95% CI 1.39-3.54). There was significant heterogeneity between the studies which was explained primarily by the quality of the studies (55% of variance explained) and adjustment for socio-economic factors within the studies (30.3% of variance explained) suggesting it may not have been entirely appropriate to combine all studies in this way. When the results were stratified by study type the heterogeneity reduced significantly, showing a more concise result when more similar studies were combined.

In conclusion despite the significant odds ratio presented in the overall meta-analysis (OR 2.21 CI 1.39-3.54) it is unlikely this paper will be of any immediate utility in routine dental practice within the UK. All except one of the studies was conducted in low or middle income countries, which have higher prevalence rates of both dental caries and DDE than most high income countries. Additionally it has been highlighted that DDE and caries share many similar risk factors such as low socio-economic status, and therefore the relationship observed may simply be due to these common risk factors and there is no specific causal relationship between the two conditions.

The authors make no attempt to explain the possible biological sequence which would lead to the proposed association or indeed assert that the caries observed was attributed to teeth displaying enamel defects. Finally, as we are unable to effectively predict the development of DDE in individuals, or prevent these defects, the importance of establishing this link is unclear. The authors themselves suggest that ‘a common risk approach should be more rational’ which is aligned with most caries preventive advice currently available.