LONGITUDINAL ANALYSIS OF DECIDUOUS TOOTH EMERGENCE - II - PARAMETRIC SURVIVAL ANALYSIS IN BANGLADESHI, GUATEMALAN, JAPANESE, AND JAVANESE CHILDREN

We present a form of parametric survival analysis that incorporates ex act, interval-censored, and right-censored times to deciduous tooth em ergence. The method is an extension of common cross-sectional procedur es such as legit and probit analysis, so that data arising from mixed longitudinal and cross-sectional studies can be properly combined. We extended the method to incorporate and estimate a proportion of agenic teeth. While we concentrate on deciduous tooth emergence, the method is relevant to studies of permanent tooth emergence and other developm ental events, Deciduous tooth emergence data were analyzed from four l ongitudinal studies. The samples are 1,271 rural Guatemalan children e xamined every three months up to age two and every six months thereaft er as part of the INCAP study; 397 rural Bangladeshi children examined monthly to age one and quarterly thereafter as part of the Meheran Gr owth and Development Study; 468 rural Indonesian children examined mon thly as part of the Ngaglik study; and 114 urban Japanese children exa mined monthly in studies from 1910 and 1920. Although all four studies were longitudinal, many observations from the Guatemala and Banglades h studies were effectively cross-sectionally observed. Three different parametric forms were used to model the eruption process: a normal di stribution, a lognormal distribution, and a lognormal distribution wit h age shifted to shortly after conception, All three distributions pro duced reliable estimates of central tendencies, but the shifted lognor mal distribution produced the best overall estimates of shape (varianc e) parameters. Estimates of emergence were compared to other studies t hat used similar methods. Japanese children showed relatively fast eme rgence times for all teeth. Bangladeshi and Javanese children showed e mergence times that were slower than are found in most previous studie s, Estimates of agenesis were not significantly different from zero fo r most teeth. One or two central incisors showed significant agenesis that ranged from 0.1 to 0.8% in three of the samples; even so, failure to model the agenic proportion did not seriously bias the estimates. (C) 1998 Wiley-Liss, Inc.