The oral health environment and the equal environment assumption (EEA) among 1-8-year-old twins

The purpose of the present study was to describe the oral health environment in preschool children and to examine the extent to which paired twins experience the same oral health environment.

In collaboration with The Medical Birth Registry of Norway (MBRN) 100 twin families who participated in the Norwegian Mother and Child Cohort, were invited to take part in ongoing studies on oral health. Participating twin families lived in Oslo and the surrounding counties of the capital. The age range of the participating twins was 1-8 years. A clinical examination took place at The Institute of Clinical Dentistry, University of Oslo in 2008. The oral health environment was measured in two ways: 1) Interview. Mothers were interviewed by trained interviewers about oral health related habits of each of the twins. 2) Weekend diet log. Parents listed 84 different deserts, ice cream, sweets, cakes, cookies, fruits, snacks, and biscuits for each twin that were consumed on during the weekend. The statistical analyses comprised frequency distributions of the environmental variables and correlations between the variables within the pair of twins.

The results showed a parental involvement in early tooth brushing and also an indication of tooth brushing not always being easy. Use of fluoride toothpaste started early, and two thirds of the children also used fluoride tablets. Use of pacifier was prevalent; the duration of use of pacifier and feeding bottle was relatively long. Nearly 75% of the parents indicated that they had no problems relatively to the twins' meals, and 53% mentioned that the twin pairs were different with regard to meals. Nearly 70% of the kindergartens had a clear health profile. The correlations varied between r = 0.45 and 1.00.

The children in the present work were young, and the detailed information in this paper therefore adds to the knowledge of parental involvement in children's oral health. Generally the findings indicate a high level of involvement from the parents in the oral health environment at home. Altogether the results showed that the assumption of identical oral health environment cannot be supported by these data.