Molar Incisor Hypomineralization: Structure, Composition, and Properties
The first permanent molars in molar incisor hypomineralization (MIH) are characterized by localized demarcated lesions or opacities within the enamel. These lesions are often rough and plaque retentive and at risk of rapid caries and post-eruptive breakdown (PEB). There is increasing evidence to suggest that the physical, chemical and mechanical properties of MIH-affected enamel are different to those of otherwise healthy enamel. Studies suggest that the hardness and modulus of elasticity of MIH-affected enamel are reduced by between 50 and 75 % and are accompanied by a simultaneous 20 % reduction in mineral content. Furthermore, the protein content of affected enamel is up to 15 times higher than in sound enamel particularly in the darker brown opacities. These findings may explain why hypomineralized enamel fractures easily under occlusal function causing PEB. Scanning and transmission electron microscopic studies have shown that the microstructure of this enamel is more disorganized and, when etched with phosphoric acid, it does not show the typical etching pattern. This may contribute clinically to the compromised bonding of adhesive dental materials to affected teeth. Knowledge of the physical and mechanical properties and composition of developmentally defective enamel helps clinicians understand the challenges associated with treating affected individuals.
KeywordsHypomineralized enamel Mechanical properties Porosity Mineral content Microstructure Proteins
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