Individual variation in tooth-size/ arch-length changes from the primary to permanent dentitions

To determine the individual variation in the maxillary and mandibular tooth-size/arch-length relationships after the complete eruption of the primary dentition (mean age, 4.0 years) and at the time of eruption of the second permanent molars (mean age, 13.3 years).

Records of 32 males and 27 females were evaluated. Each subject had a clinically acceptable occlusion; that is, a normal molar and canine relationship at the time of eruption of the primary and permanent teeth. In addition, each subject had a complete set of data at the 2 stages of dental development. These selection criteria limited the number of subjects in this investigation to 59. The mesiodistal diameter of all primary teeth and their permanent successors, as well as various dental arch length parameters were measured in the primary and permanent dentitions. A total of 60 parameters were measured or calculated.

The findings from the present investigation indicated that of the total sample of 59 male and female subjects observed on a longitudinal basis, 29 (49%) maintained their relative tooth-size/arch-length relationship ranking in the 2 dentitions, while 30 (51%) changed to either a more favorable or less favorable relationship in the permanent dentition.

The cases with the lower ranking of tooth-size/arch-length relationship in the primary dentition, 50% maintained their relatively lower rank in the permanent dentition, while the other 50% changed to a relatively more favorable rank in the permanent dentition. There is a similar probability for maintaining the same ranking in the primary and permanent dentitions in the mandibular arch (51%), as in the maxillary arch (49%). The clinical implications of the findings are discussed.