Late lower arch crowding: the role of differential horizontal growth.

Eighty-five subjects, recorded soon after eruption of second permanent molars, were followed longitudinally for 3 or 4 years. Correlation and multiple regression analyses were used to examine the relationship between the change in lower arch space condition and (1) the horizontal component of the change in position of various points on or near the anterior borders of the maxilla and mandible, (2) the differential horizontal-vertical change in these points and (3) differences in horizontal change between maxillary and mandibular, and between intramandibular points. No significant differences in amount or direction of growth were found between the maxillary and mandibular teeth or jaws. Pogonion changed more in a horizontal direction than B point. Increased lower arch crowding was weakly associated with differential horizontal growth of the teeth and jaws. Reduced horizontal growth and greater vertical as opposed to horizontal growth of the maxilla and teeth, and increased growth of the mandibular base were to some extent related to the crowding increase.