How to predict the timing of eruption of mandibular second premolars.

Objective: To evaluate the relationship between the stages of dental formation and the timing of eruption of mandibular second premolars.
Materials and Methods: The sample comprised panoramic radiographs of 25 children, 7 to 12 years old, observed by space supervision during development of dentition. The initial radiograph (T1) was taken in the mixed dentition period and the progress radiograph (T2) close to the eruption of mandibular second premolars. The stages of dental formation were determined by the proportion between crown length and total length (CL/TL) as well by the Simpson and Kunos index. Average values between right and left sides (35, 45) were correlated to the time elapsed until dental eruption (T2-T1). Statistical analysis was performed by Pearson correlation analysis.
Results: The proportion CL/TL presented higher correlation index with time to eruption than the Simpson and Kunos index. The linear regression equation for prediction of timing of eruption showed high coefficient of determination, low deviation, and good accuracy. According to survival analysis, mean deviation at 95% confidence level was between 3.6 and 6.4 months. There was no difference in contralateral measurements, with high intraclass correlation coefficient for both CL/TL proportion and Simpson and Kunos index.
Conclusions: More advanced stages of dental formation indicate less time until dental eruption. The strong correlation with crown length/total length proportion (CL/TL) provides a linear regression equation for prediction of the timing of eruption of mandibular second premolars.