ORIGINAL SCIENTIFIC ARTICLE Hypomineralised second primary molars: prevalence, defect characteristics and possible association with Molar Incisor Hypomineralisation in Indian children N. Mittal 1 • B. B. Sharma 2 Received: 23 January 2015 / Accepted: 29 April 2015 Ó European Academy of Paediatric Dentistry 2015 Abstract Aim To report on the prevalence, defect characteristics, and distribution of hypomineralised second primary molars (HSPM) in Gautam Budh Nagar, Uttar Pradesh, India and to report on possible association, if any, between HSPM and molar-incisor-hypomineralisation (MIH). Methods A cross-sectional survey included a random sample of 978, 6–8-year-old school children. EAPD diag- nostic criteria for scoring MIH defects on first permanent molars (FPM) were adapted and used to score hypomin- eralisation defects in both FPM and second primary molars (SPM) by a single calibrated examiner. Comparative statistics for HSPM versus hypomineralised FPM were computed using a Chi square test. An odds ratio (OR) at 95 % confidence interval (CI) was used to test and any association between HSPM and MIH. Results An overall prevalence of 5.6 % (55/978) was reported for HSPM in the study population. Prevalence of MIH as hypomineralised FPM was 7.4 % (72/978). Con- comitant presence of HSPM and MIH was observed in 32.73 % (18/55) of affected subjects. The presence of HSPM had significantly higher odds ratio for development of MIH (OR 7.82; 95 % CI = 4.18–14.65; p \ 0.001). A greater severity of defects was observed in HSPM com- pared with affected FPM as greater number of affected surfaces presented with post-eruptive breakdown (PEB) in former compared to latter (p \ 0.001). Conclusion The prevalence of HSPM in 6–8-year-old Indian children was 5.6 %. The severity of hypominerali- sation was milder in FPM compared to SPM. The presence of HSPM was reported to have significantly higher odds for development of MIH in future. Keywords Primary molar hypomineralisation Á Developmental defects of enamel Á Enamel hypomineralisation Á Hypomineralised second primary molars Á Molar incisor hypomineralisation Introduction Developmental defects of enamel are commonly encoun- tered clinical entities and may be qualitative (hypominer- alisation) or quantitative (hypoplasia) (Ja ¨levik and Nore ´n 2000; William et al. 2006). Enamel hypomineralisation is identified visually as a demarcated opacity with a clear border with varying extensions and can be white, yellow, or brown in colour (Ja ¨levik and Nore ´n 2000; Weerheijm 2003). These demarcated opacities may present with/ without breakdown (post-eruptive breakdown; PEB) (Weerheijm 2003). Although demarcated opacities may occur in any teeth of the dentition i.e., first permanent molars (FPM), permanent incisors (PIs), canines, premo- lars, second permanent molars, and second primary molars (SPM); FPM are the most commonly affected teeth (El- frink et al. 2008, 2012; Lygidakis et al. 2010; Ghanim et al. 2011; Ku ¨hnisch et al. 2014). FPM may be affected in isolation or concomitantly with PIs and this combination is named as Molar Incisor Hypomineralisation (MIH) (Weerheijm 2003; Lygidakis et al. 2010) while the & N. Mittal dr.neetipgi@gmail.com 1 Department of Pediatric and Preventive Dentistry, Santosh Dental College and Hospital, No. 1 Santosh Nagar, Pratap Vihar, Ghaziabad 201009, Uttar Pradesh, India 2 Santosh Dental College and Hospital, No. 1 Santosh Nagar, Pratap Vihar, Ghaziabad 201009, Uttar Pradesh, India 123 Eur Arch Paediatr Dent DOI 10.1007/s40368-015-0190-z