Molar incisor hypomineralisation (MIH) and hypomineralised second primary molars (HSPM): do we need to alter terminology and definition? A scoping review

Purpose: Molar incisor hypomineralisation (MIH) is a developmental defect characterised by demarcated enamel opacities primarily affecting first permanent molars and often incisors. A similar clinical condition affects the primary dentition—hypomineralised second primary molars (HSPM). The aim was to map existing literature on the definition and terminology used to describe MIH and HSPM comprehensively. Methods: Reports of primary studies addressing definition and terminology of enamel developmental defects published in the period 1985–2025, in English and involving humans were considered for inclusion. PubMed/MEDLINE, EMBASE, Cochrane Library and Web of Science were searched. Two reviewers screened retrieved papers independently for eligibility and charted the data. The protocol was registered with the Open Science Framework—registration number 10.17605/OSF.IO/RY9K8. Results: Fifty-seven studies were included in the review. Most papers referred to the EAPD criteria (98.1%), in some cases combined with a second system for scoring severity (13.5%). The pattern of teeth involved showed heterogeneity, with highest prevalence in first permanent molars followed by permanent incisors, but also mentioning canines, premolars and second molars. In the primary dentition, canines and first molars were also included. Most studies reported the presence of an asymmetrical distribution of lesions in severity, location and colour. Evidence reviewed supports the view that MIH and HSPM represent expressions within a broader developmental continuum of enamel mineralisation disturbances, rather than distinct entities. Conclusions: It may be timely to reconsider the definition and terminology currently in use to include the concept of asymmetry and the involvement of other types of teeth.