Prevalence and Severity of MIH among Primary School Girls in Qassim Region

In 2003, the term Molar Incisor Hypomineralization (MIH) was introduced by (Weerheijm et al.) to describe white or yellow-brown demarcated opacities on first permanent molars, frequently associated with affected permanent incisors.

Clinically, the severity of the MIH lesion may vary. On the first permanent molars these defects range from simple whitish yellow opacities to severely dysplastic enamel, which frequently breaks down rapidly following an eruption. On the permanent incisors, however, the defective enamel usually seems less severely disrupted and less prone to break down.

It is essential to distinguish MIH from defects like Amelogenesis Imperfecta which are more generalised. For MIH, one or all the four first permanent molars are affected and sometimes together with one or more permanent incisors. It has to be noted that the crown calcification of the affected teeth usually takes place in the period from birth to three years. This could explain why the two set of teeth are affected at the same time.

The affected teeth are often, hypersensitive to temperature changes, brittle, predisposed to dental caries and difficult to anaesthetise. Children are reluctant to carry out oral hygiene and to accept dental treatment, therefore are at risk of developing dental phobias.

Because the prismatic morphology of the porous enamel is altered, patients with MIH often require multidisciplinary dental management; bonding to the enamel becomes difficult leading to frequent loss of fillings and repeated treatment. Children with affected molars receive more dental treatments than those without and a significant number of retreated teeth eventually require extraction.

As a rule, the defects cannot be related to well-known causes. It has not been possible to name one singular influence or even a combination of multiple influences working together as being responsible for the disease. Some of the factors associated with this condition have included oxygen deficiency at birth, prenatal and perinatal sickness, high fevers, nephritic diseases, respiratory infections occurring during the period from birth to three years of life. It has also been associated with toxins and antibiotic consumption, malnutrition, intestinal inflammation, diarrhea, and hypo-parathyroid occurring around the same period.

Reports of the prevalence of MIH vary considerably throughout the world, and rates range from 2.4% in China to 40.2% with the highest prevalence reported in children of Rio de Janeiro, Brazil. While these large variations may reflect real differences between regions and countries, differences in recording methods, indices used and populations investigated may also be contributory.

In Arab countries, for example Lybia the prevalence stands at 2.9% and 18.6% in Iraq. In Saudi Arabia, a study was conducted in the Dental Clinics at the Faculty of Dentistry, King Abdulaziz University in Jeddah, MIH showed a prevalence of 8.6%. This study aims to investigate Molar Incisor Hypomineralisation (MIH) in 7 to 12 years old school girls in Burayda, Qassim regarding prevalence, distribution and severity of defects.

An age group of 7 to 12 years school going children was selected because at this age, at least one of the first molars would have erupted and also the risk of a defect in the enamel being masked by sizeable carious region in later age would be minimised.

The overall prevalence of MIH was 24.5% among 7-12-year-old school children in Qassim. Although comparing epidemiological studies from different countries is not applicable because of variations in criteria, sample selection, lesions included and aetiological and environmental factors exist. This study showed that MIH in Qassim was highly prevalent by comparison with data for other middle-east countries where they reported a prevalence of 8.6% in Jeddah, 2.5% in Libya, 17.6% Jordan and 18.6% in Iraq.

The present study found 24.5% MIH prevalence, similar to the levels obtained in European countries such as Finland and Spain where they found rates of MIH up to 25% and 21.8%, respectively. In Denmark, the prevalence was found to be 15-25%. Also, a study done in China using the same method as the present study showed similar MIH prevalence rates of 25.5%.

Other reports also indicated when combined with incisors, the defects prevalence rose significantly; the relationship between the number of affected molar and incisor. However, in the study done by (Kotsanos et. al.) this relation was not found. This may be because of small sample size in their research. Also, 41.6%of the cases presented with only molars affected while the remaining 58.4% had both molars and incisors affected. This finding was in agreement with results from previous studies.

A higher prevalence was reported in 12-year-olds compared with 7 and 8-year-olds (21.8% vs 4% and 16.8% respectively). The present findings are in agreement with previous conclusions regarding the influence of age on MIH prevalence.

In agreement with previous studies, the present study found that demarcated opacities were the most frequent type of MIH, while the prevalence of post eruptive breakdown in our study was higher than that reported in Sweden, Italy, and Libya. This may partly be explained by the inclusion of older children in our study, as some of the demarcated opacities may break down over time. This explanation is supported by findings of (Wogelius et al.). WHO reported an increased prevalence of post eruptive breakdown by increasing age.Variation in the susceptibility of maxillary and mandibular molars to MIH was insignificant in this study. This was in agreement with previous studies that found a similar distribution of hypomineralised molars between arches .but contradicted other studies that found that Maxillary molars were more frequently affected than Mandibular ones or studies which reported that more mandibular molars were affected than maxillary. Several factors may explain the arch difference of MH prevalence as maxillary and mandibular molars may be examined under differing conditions. The sitting position of children during the examination, the lighting sources may obscure the MH lesions in maxillary molars, and whether teeth were examined wet or dry. Regarding incisors, maxillary incisors in total were much more frequently affected than mandibular, which was in agreement with similar findings reported in most of the previous studies.

Regarding severity, another report that investigated the same age group, recorded defects of mild severity of 57.4%. In our study, it was seen that as age increased, the clinical severity of affected teeth increases. This finding of age-dependent severity has been noted in previous studies. An explanation that fits this finding is that the presence of enamel defects for long periods in the mouth is more often related to an increase in a risk of enamel break-down, particularly with permanent molars heavily involved in mastication.