Early diagnosis of tooth agenesis in childhood enables clinicians to improve occlusion in the patient. In addition to patient age, we speculated that the developmental stage of adjacent teeth could assist with tooth agenesis diagnosis. In the present study, development of the mandibular second premolar (P2) was compared with that of adjacent teeth, including the mandibular first premolar (P1) and first molar (M1) in 238 patients aged 3-8 years old, by examining the formation stages of each tooth shown by panoramic and dental radiographic imaging.

Our findings showed that when P2 was in the initial mineralization (Ci) stage, P1 was between the cusp outline complete (Coc) and crown half completed with dentine formation (Cr1/2) stages, while M1 was between the crown three-quarters completed (Cr3/4) and initial root formation with diverge edges (Ri) stages. Agenesis of P2 could be readily determined after P1 had reached the crown threequarters completed (Cr3/4) stage and M 1 when the root length was less than the crown length (R1/4) stage. The average age in which a P2 tooth germ could be confirmed in the mandible was 3.70±0.73 years (males : 3.82±0.89, females : 3.52±0.47 years), with a median value of 3.58 years (males :3.58, females : 3.41 years). In addition to patient age, information regarding tooth germ development in adjacent teeth may help to facilitate early diagnosis of congenital absence of P2, which would help clinicians with early implementation of appropriate management strategies to achieve healthy permanent occlusion.