Estimating emergence sequences of permanent teeth in Flemish schoolchildren using interval-censored biplots: a graphical display of tooth emergence sequences

Objectives: The aim of the present study was to investigate the pattern of emergence of permanent teeth using nonparametric techniques. Materials and methods: Data were obtained from the Signal-Tandmobiel (R) project, a 6-year prospective dental study conducted in Flanders (Belgium) in which 4468 primary school children born in 1989 were annually examined. A new exploratory method for interval-censored data, the IC-biplot, was applied to estimate individual sequences of emergence. In addition, the method renders a nice graphical representation of both children and teeth in the plane where the individual sequences of emergence can easily be visualized. On the basis of the estimated individual sequences, their corresponding prevalences were calculated. Results: The study revealed that between 7 and 13 different sequences of emergence can be expected depending on gender and quadrant. The prevalences of the most frequent sequences in girls varied from 35% to 85% depending on the quadrant, while in boys they varied from 28% to 32%. Most sequences in the maxilla start with 6-1-2 and in the mandible with 1-6-2. Conclusions: The IC-biplot is a flexible procedure that allows an easy visualization of the pattern of emergence of permanent teeth. Rank orders derived from the IC-biplot confirm rank orders suggested earlier in the literature.