Structural and chemical enamel characteristics of hypomineralised second primary molars

Purpose Although hypomineralised second primary molars (HSPM) are considered belonging in the same entity as molar incisor hypomineralisation (MIH), the structure and chemistry of their defected enamel have not been described. We aimed to study these in justifying any similarities with MIH. Methods Nine HSPM and five first permanent molars with MIH were either fractured or sectioned longitudinally through their defective enamel and examined by scanning electron microscopy. Relative amounts of calcium (Ca), phosphorus (P), oxygen (O), carbon (C) and the Ca:P ratio were calculated in the primary molar samples by energy-dispersive spectrometry. Results Rod width was deficient in the defected enamel of HSPM resulting in wide interrod spaces and suggesting similarities to permanent enamel structure in MIH. In areas with breakdown, cracks and disrupted coherence between enamel rods were more marked. Differences in Ca, P, O, C and Ca:P ratio between hypomineralised and sound enamel in HSPM followed the same trend as in MIH without reaching statistical significance. Conclusion Marked structural differences between sound and hypomineralised enamel of HSPM and similarity to MIH enamel were verified.