This study was part of a prospective cohort study to evaluate the impact of a preventive programme on the oral health of Thuringian children in Germany (German Clinical Trials Register DRKS00003438). The Ethics Committee of Jena University Hospital approved the study (registration number 2759-02/10). The study was conducted in full accordance with the ethical requirements of the World Medical Association Declaration of Helsinki (2008).
The study was conducted in a medium-sized and well-situated city in Germany (Jena, Thuringia) with a relatively low proportion of families with a low socio-economic status (SES) or migration background. The children of the Jena birth cohort 7/2009 to 10/2010 (n = 1162) were invited to have a dental examination in the first year of life. Those families who accepted the invitation (n = 512) were included as participants of the preventive programme with caries-risk-related continuous dental care from birth up to the age of 3 years. A caries risk assessment was carried out to categorise the children using the Caries-risk Assessment Tool for infants, children and adolescents of the American Academy of Pediatric Dentistry (AAPD) . Children with an increased caries risk were reappointed every three months and children with a low or moderate caries risk every six months. High-risk children received fluoride varnish application biannually. A thin film of fluoride varnish was applied by a dentist in the dental practice, using <0.25 ml per child, limited to those surfaces at risk. The study population included all the children who had participated in the final examination of the preventive programme (n = 377, 32.4 %). The eligibility criteria were provision of written consent by the caregiver and availability of data relating to the caregiver’s interview and dental examination of the child. The exclusion criteria were no written consent and incomplete data.
The children were examined at the Department of Preventive and Paediatric Dentistry, Jena University Hospital, Germany. The examinations were conducted using a dental light, mirror and sterile gauze for teeth cleaning and drying. Dental caries was scored using the WHO diagnostic criteria expanded to the d1-level without radiography . Enamel defects were assessed according to the mDDE . The scoring was at surface level, with three surfaces (buccal/labial, lingual/palatal and occlusal/incisal) for each tooth. An enamel defect of ≤1 square millimetre was considered as sound . The visual clinical presentation of the DDE was assessed according to these types:
Demarcated opacity-a qualitative defect presenting alterations in enamel translucency and opacity. The defective enamel is of normal thickness and is white, creamy, yellow or brown in colour. There is a clear border with adjacent normal enamel . Demarcated opacities are relatively prone to caries and enamel substance loss (post-eruptive enamel breakdown) [4, 11, 12]. This category also includes HSPM [11, 12]. A child was classified to have HSPM when at least one second primary molar was diagnosed with HSPM .
Diffuse opacity-a qualitative defect presenting alterations in enamel translucency and opacity. The defective enamel is of normal thickness and is white in colour. It can have a linear, patchy or confluent distribution, and there is no clear border with adjacent normal enamel. It also includes opacities owing to fluorosis .
Hypoplasia-a quantitative enamel deficiency with a decreased enamel thickness such as pits, grooves or larger areas of missing enamel .
Combination of defects (demarcated and diffuse opacities, hypoplasia and opacities) .
Amelogenesis imperfecta (AI)-a range of genetically caused enamel malformations (hypoplasia, hypocalcification and hypomaturation) .
The size of the defect (lesion extension criteria) was recorded in thirds of the affected tooth surface area: less than one-third of the tooth surface affected, at least one-third but less than two-thirds of the surface area affected, and at least two-thirds of the tooth surface affected [9, 11].
All records were performed by the same calibrated clinician (YW), who had been trained and calibrated following WHO guidelines by an experienced epidemiologist . The training was performed using a set of photographs with different clinical situations (teeth with enamel defects, including MIH, HSPM, carious lesions, dental fluorosis, AI). A training exercise was then carried out, involving the clinical oral examination of 10 children in the same age group as those of the main study. Afterwards, the calibration was performed. The dentist examined a group of 25 pre-selected subjects twice on successive days to assess the consistency. The intrarater-reliability regarding the DDE prevalence was very good (k = 0.83).
During the main survey duplicate examinations at the beginning, after 1 year and at the end of the survey were conducted with 25 subjects each randomly selected. The intrarater-reliability regarding the DDE prevalence was very good and ranged from 0.81 to 0.84.
Furthermore, a standardised questionnaire was conducted, which was updated during each dental visit. The questionnaire collected the following information: age, gender, migration background, special health care needs, diseases during pregnancy, type of delivery (Caesarean, vaginal), preterm birth (<37 weeks of pregnancy), weight at birth (<2.500 grams), general diseases (cardiovascular, metabolic or kidney disease), hospitalisation in the first year of life, systemic infectious diseases (pneumonia, otitis media, viral gastroenteritis, chickenpox, etc.), breathing patterns, allergies, medication, systemic antibiotic medication, feeding behaviour, the use of vitamin D or fluoride supplements, oral hygiene, and the SES of the families. The SES was recorded using the Brandenburg social index . The index was computed for each child based on the education and employment status of the parents, and children were allocated to lower, middle or higher SES groups. For cases with missing values of one parent, the value of the other parent was double weighted, analogous for single parents .
The development of the questionnaire and the selection of items were based on the assumption that early childhood caries and DDE could share possible aetiological factors [36, 46]. The developed questionnaire was tested regarding face validity and content validity using a panel of experts (dentists of the Department of Preventive and Paediatric Dentistry, Jena University Hospital, Germany) and respondents (randomly selected parents attending the Department of Preventive and Paediatric Dentistry, Jena University Hospital, Germany for routine dental examinations). The revised questionnaire was then tested in a pilot test by collecting data from 25 randomly selected parents not included in the final sample.
Data were recorded in Microsoft Excel files (Office Version 2011, Microsoft Corporation, Redmond, WA, USA) and transferred to Statistical Package for Social Sciences (SPSS version 20) for analysis (IBM Corporation, Armonk, NY, USA). After correlation analysis (Pearson) and adjustment of variables that showed a strong or very strong correlation (correlation coefficient >0.5), the chi-square test (Pearson) or Fisher exact test was used to determine the statistical significant associations between the independent variables (low SES, ethnicity, diet, preterm birth, general disease, medication, use of vitamin D supplements, etc.) and the outcome variable enamel defects before the multivariate analysis was conducted. Variables that showed significant associations (p < 0.2) were included in the multivariate logistic regression analysis. A backward stepwise elimination was used in the logistic regression. A further calculation was conducted to determine whether there was a difference between the independent variables (gender, migration background, low SES, diseases during pregnancy, Caesarean type of delivery, preterm birth, low birth weight) of the participating children and the children who dropped out. The data were analysed using the t-test. A p-value ≤0.05 was set to indicate statistically significant differences.