Prevalence of Hypomineralized Second Primary Molars in a Group of Egyptian Children and Its Association with Molar-Incisor Hypomineralization: a Cross-Sectional Study.

The highly mineralized tooth enamel consists of nearly 95% of hydroxyapatite crystals and are grouped into highly organized structures called enamel prisms. This structure gives the enamel an exceptional degree of mechanical resistance. Ameloblasts secrete the organic component during tooth formation, after which they polarize and are eliminated from the enamel's surface. Because it no longer contains any living supporting cells, adult enamel is incapable of regeneration.

Enamel formation by ameloblasts passes through several stages: pre-secretory, secretory, transition, maturation, and post-maturation. Depending on whether stage of the ameloblast's life cycle is affected, one can typically find either a normal volume enamel with inadequate mineralization or a fragile and quantitatively deficient enamel. When insufficient mineralization takes place, enamel defects like Molar Incisor Hypomineralization (MIH) and Hypomineralized Second Primary Molar (HPSM) can occur.

MIH is defined as hypomineralization of one to four first permanent molars presenting as well demarcated opacities, qualitative defects of enamel, atypical caries/restorations and extractions due to MIH. It's also frequently associated with the permanent incisors. As of present time, HSPM is defined as hypomineralization of one to four second deciduous molars including the presence of well demarcated opacities, post-eruptive enamel breakdown (PEB), atypical caries or restorations, and extractions due to hypomineralized second primary molars. Recently, these conditions have grabbed the attention of many clinicians across the world mainly because of the worrisome clinical picture and the challenges faced in the management of such conditions.

The etiology of HSPM still remains unclear. Despite that, some potential prenatal, perinatal and postnatal factors have been suggested. Several authors have studied the possible role of risk factors that can cause HSPM based on the medical history given by the parents using structured questionnaires. To date, not a single factor has been found to be an HSPM risk predictor. Furthermore, there is a recall bias potential because all the data obtained from the parents are history-based rather than evaluations of documented medical records.

In addition to this, multiple studies showed a positive correlation between HSPM and MIH, and HSPM being a predictor to MIH. A systematic review and a meta-analysis were done in 2018 aiming to know whether the children with HSPM are likely to have MIH or not and came up with a result that HSPM could be considered as a predictive value to MIH. It was concluded that HSPM can be considered as a specific but not a highly sensitive predictor of MIH which means that the absence of HSPM in primary molars doesn't rule out the potential development of MIH later.