We read with great interest a paper recently published in the European Archives of Paediatric Dentistry (2015) by MEC Elfrink, A Ghanin, DJ Manton and KL Weerheijm entitled ''Standardised studies on molar incisor hypomineralisation (MIH) and hypomineralised second primary molars (HSPM): a need''. It seems to be the first time that authors describe and discuss a standardised protocol for future MIH and HSPM prevalence and aetiology studies. We thank the authors for this contribution, which will improve future studies about MIH and HSPM in order to provide comparisons.We agree with the proposed guideline, with regard to the calibration, but we would like to comment about the age proposed by the authors for diagnosing HSPM (5 years old). Some studies reported that the teeth that are the most often affected by caries in the primary dentition are the second primary molars (Elfrink et al. 2006(Elfrink et al. , 2010. Hypomineralised molars frequently suffer posteruptive enamel breakdown and severe carious lesions (Elfrink et al. 2008(Elfrink et al. , 2010. Moreover, children with HSPM frequently display a more rapid progression of caries (Ghanim et al. 2013), and the lesions become more severe as the children increase in age (Ghanim et al. 2013). Consequently, severe carious lesions could leave some hypomineralised defects unnoticed and thus decrease their reported prevalence (Lunardelli and Peres 2005). Odontogenic differentiation of the second primary molars begins during the 19th week of gestation (Hu et al. 2014), and its eruption is completed by the 30th month of life (GunaShekhar and Tenny 2010). Therefore we suggest 3 years as the optimal age for diagnosing HSPM. References