Morphological, histological, and chemical analysis of first permanent molars with molar incisor malformation.

Purpose: Molar incisor malformation (MIM) is a dental anomaly rendering first permanent molar pulps inflamed/necrotic at a young age. It often affects permanent incisors, primary second molars and less frequently other teeth. The purpose of this study was to investigate the anatomy and histology of MIM in seeking insight into its pathogenesis.

Methods: Five MIM first permanent molars were examined with micro-computed tomography (micro-CT) for 3D morphology, with scanning electron microscopy for microanatomy, with energy-dispersive X-ray spectrometer (EDS) for chemical composition and for histology with optical microscopy. Composition differences were statistically determined using one-way ANOVA.

Results: Micro-CT confirmed dentin abnormalities in the middle and cervical third of the crown in the form of the radiodense 'cervical mineralized diaphragm' (CMD). This was peripherally intertwined with enamel fjords and projections severely disrupting the integrity of pulp chamber and its continuity with root canals. EDS showed increased Ca in CMD compared to dentin. The histological examination revealed anomalous osteodentin-like hard tissue with denticles in the CMD.

Conclusion: An interconnection of anomalous cervical enamel with crown CMD dentin preceded to the severe pulp chamber and root dysplasias in MIM molar teeth.