Comparison of the left and right first molar mesial root length. Estimated mean percentage difference between the length of the upper right and left first molar mesial roots. All experimental groups demonstrated a significant reduction in the final mesial root length of the upper right first molar compared to the untouched upper left first molar. Statistically, only the sham and NGF groups were significantly different. Error bars represent the standard error of the mean difference. *P < 0.05 and **P < 0.01.