Abstract
The Signal Tandmobiel study is a dental study involving about 5000 schoolchildren in Flanders. They are annually examined by calibrated dentists from the 1st till the 6th class in primary school. Detailed dental information is collected: on mouth-, tooth- and surface level. A yearly questionnaire collects information on dietary as well as tooth brushing information. Hence, this unique database contains high quality dental data with a complex hierarchical structure, both spatially in Flanders (children in schools) as well spatially in the mouth (the specific location of teeth in the mouth). The longitudinal character of the data adds another dimension to the hierarchical structure. In the first part of the lecture the study will be described.

Dentists believe that there are spatial symmetries in the mouth with respect to caries. However, this has never been shown in a statistical sense. In the second part of the talk this question is treated for primary teeth using data from the Signal Tandmobiel study. It is shown that this problem can be tackled both by a pseudo-likelihood as well as with a GEE-1 approach. Our analyses confirm the dentist viewpoint.