This was a descriptive, cross-sectional study undertaken in 2017, involving 8-11 year-old children from public basic schools in Khartoum state.
Determination of study population: The study sample was determined using the formula,

with n= sample size, z = critical value for achieving 95 % confidence level, p= the anticipated population proportion which is always chosen from previous studies,
q = 1-p, d = desired margin of error and deff= design effect chosen as 2.
As for p value, a Kenyan study of 2009 that reported MIH prevalence of 13.73% (16) was used. Assuming an error of 4% in applying the formula, a sample size of 568 children was arrived at.
Sampling technique: Four localities out of the seven Localities forming Khartoum State were randomly selected, and through a multi-stage cluster sampling technique. Twenty basic schools were randomly selected proportionally to the child population in the selected localities. Ethical approval for the study was obtained from the Research Committee of University of Khartoum - Faculty of Dentistry (HREC - 5/2015), besides receiving written approvals from the Director of primary school education for each locality and the Director of each primary schools in Sudan. A written informed consent was obtained from the parents/guardians of the participants, and each child also gave assent to participate in the study.
Inclusion criteria: Sudanese Children aged 8-11 years old, attending the primary schools in Khartoum State and having their MIH index teeth erupted (i.e. permanent first molars and incisors).
Exclusion criteria: Children who had enamel lesions smaller than 2 mms (12), those with other enamel defects (e.g. fluorosis and hypoplasia) and those who refused to participate or absent from the school at the time of study.
Data collection: The Principal Investigator was initially trained by an experienced paediatric dentist on MIH detection. The training involved the use of photographs and later the actual examination of children under field conditions who were not part of the study participants. During this phase and during the time of data collection, inter-examiner calibration was done and Kappa values calculated, with mean value of 0.83. The Principal Investigator also re-examined every tenth participant to determine intra-examiner value, which was calculated as 0.84.
In carrying out the study, the Principal Investigator was assisted by a trained and pre-tested recording clerk during the examination for the MIH of the 8-11 years-old children. Participants were selected from third, fourth and fifth classes from the 20 schools. A total of 640 consent forms were sent to the eligible children’s parents. From which, 23 were not signed. All the children whose parents consented were included in the study. Nonetheless, 49 of them were excluded for various reasons, like absence from the school on the day of examination and those who had other enamel lesions (e.g. fluorosis and hypoplasia). Consequently, a total of 568 children (284 boys, 284 girls) were included in the study. Socio-demographic data of each participant were first recorded using a modified World Health Organization oral health assessment form for children (2003) including child’s name, gender, age, locality and school level, prior to the documentation of the findings of the oral examination.
The oral examination took place in a room prepared for the purpose, in the respective schools of the participants. Each child was examined while sitting in up-right position in an ordinary chair facing a natural light source. The examiner used sterile mirrors, dental probes, tweezers, cotton rolls, in addition to single use of clean disposable examination gloves and face masks for each child. The probe was initially used to gently remove dental plaque and food remnants from the tooth surfaces. Cotton rolls were used to clean the teeth surfaces prior to examining them for MIH.
The index teeth (i.e. permanent first molars and incisors) for each participant were examined, while wet; for the presence of demarcated opacities, post-eruptive enamel breakdown, atypical restorations (AR) and extraction due to MIH (7). Hypomineralization defects were recorded in accordance with EAPD scoring criteria for MIH (19). Children were considered as having MIH when one or more PFMs were affected, with or without the involvement of incisors. Opacities occurring in permanent incisors but not in at least one PFM were not recorded as MIH. All children in the participating schools received free oral health education and the study participants who required dental treatment were referred for appropriate management to the Pediatric Department, Faculty of Dentistry/University of Khartoum.
Data analysis: Data collected were analyzed using Statistical Package for Social Science (SPSS) computer program Version 19. Descriptive data like frequency, means and relative distributions of MIH were displayed using Tables and Bar Charts. The Chi-square test was used to test the association between MIH and age, gender; the difference in proportions between two groups like molars and incisors, left and right, maxillary and mandibular teeth. Spearman rank correlation was used to test the association between the number of affected molars and incisors. In all these tests the P-value was pegged at < 0.05, which was considered to be significant.