Variability in the sequence and timing of emergence of primary and permanent teeth: discrepancies in norms and clinical significance

ABSTRACT

Norms of timing and sequence of emergence of primal], and permanent teeth are mostly based on old data. Discrepancies between studies put into question the applicability of these norms. The aim of this study was to evaluate specific discrepancies in emergence of human teeth, and determine potential clinical implications. We conducted a comprehensive literature search that extended from the seminal work of Kronfeld and associates [1929-1939] to 2002. All studies reported the same eruption sequence in the primal], dentition central [A], lateral [B] incisors; first molar [12]; canine[C]; second molar [E]. Mandibular teeth emerge before their maxilla?], counterparts, except fin- B. Gender differences do not appear significant in all studies. Although the initiation of emergence [usually mandibular A] ranged between 6 and 8 months, tabulated means from studies with primary data suggest that the last tooth in every sequence of like-teeth emerges within 3 months from the preceding set of teeth, the maxillary canine[C] emerging around 18months. The last tooth [mandibular E] follows 9 months later.In the permanent dentition, the prevalent emergence sequence was in the maxilla Ml, 11, 12, Pm1, Pm2, C, M2, M3; in the mandible M1, II, 12, C, Pm1 Pm2, M2, M3. The most common variation in the mandibular sequence seems to be the eruption of Pm1 ahead of the canine. Recent data indicate the tendency for the mandibular 11 to emerge before or at the same time as MI, and the maxillary canine to erupt before Pm2, a finding that may affect timing of treatment. The changes in pattern may indicate an evolutionary trend, or simply reflect variations inherent to the populations studied