Size and shape of the human first permanent molar: A Fourier analysis of the occlusal and equatorial outlines

Form can be viewed as a combination of size and shape. Shape refers to the boundary outline independently from its orientation, relation to reference planes, and dimension (or size). Shape and its changes could be quantified by mathematical methods such as the Fourier series. In this investigation, Fourier analysis has been used to quantify the morphologic characteristics (size and shape) of the outline of the occlusal surface and maximum circumf erence (equator) in 259 normal, healthy human first permanent maxillary and mandibular molars and to assess the effect of sex. Large within-group vari ability was found in the Fourier coefficients. Both equatorial and occlusal molar areas were on average larger in male than in female homologous teeth , but the difference was statistically significant only for the equatorial areas. The mean ratios between equatorial and occlusal dental areas were in dependent from arch (maxillary and mandibular), side, or sex. Both equatori al and occlusal outlines of left and right homologous molars within sex and arch were similar, without size and shape differences. Similarly, no sex d ifferences in shape were found in the comparison of homologous teeth. The m ethod used in the present study could supply information about dental shape in both its entirety and local variations. In particular, the method is ex tremely sensitive to local variations in dental shape, and it could be usef ully employed to compare single teeth to a standard. (C) 1999 Wiley-Liss, I nc.