Fig. 4

Scatterplot of the mean sub-occlusal dentinal thickness (SODT) of a specific tooth in function of the dental age (days). Values and fitted specific regression lines of the deciduous premolars, permanent premolars and molars are depicted in blue, grey and orange, respectively. A strong interaction between fixed effects ‘dental age’ and ‘type of dentition’ is evident. Mean SODT appears to increase with dental age in permanent premolars, whereas the opposite effect is noted in the other types of dentition