Relations between the mesiodistal crown diameters of the primary and permanent teeth of Hong Kong Chinese.

Relations between these diameters were studied on serial dental casts of 112 Hong Kong Chinese (61 males, 51 females) taken at mean ages of 5.68 and 12.31 yr. Size relations were studied in terms of correlation coefficient, difference, and ratio between corresponding pairs of individual teeth and corresponding groups of teeth in both dentitions. The coefficients of correlation were low to moderate (0.2-0.8), with those between groups of teeth consistently higher. As for size differences, incisors and canines were larger in the permanent dentition in both arches by 1.2-2.0 mm. Premolars were smaller than their primary predecessors except for the upper first premolar. When the absolute values of the differences were ranked, the second premolar-second primary molar differences were the greatest (2.0-2.8 mm) while those between the first premolar-first primary molar were the smallest (0.3-0.7 mm). When tooth groups were assessed, the permanent teeth were larger than their predecessors in the anterior segments but smaller in the posterior segments. The leeway space was larger in the mandibular arch (2.2 mm) than in the maxillary arch (0.3 mm). When diameters of five teeth on one side of the arch were combined, the permanent exceeded the primary by 3.5 mm in the upper arch but only 0.5 mm in the lower. The ratios between the permanent and primary tooth sizes showed the same trend as the differences.