Three‑dimensional measurement of tooth inclination: A longitudinal study

New tools have been introduced for tooth inclination measurement and assessment of its changes over time. This study aimed to measure the change in inclination of teeth after the periods of 2 and 4 years in adolescents with normal occlusion using three‑dimensional (3D) software. This retrospective longitudinal study was conducted on 54 pairs of dental casts of 24 adolescents between 9 and 13 years of age with normal occlusion. The inclination of teeth was determined by 3D measurements using OrthoAid software. After scanning the casts via stereophotogrammetric scanner, the mean and standard deviation of inclination of teeth were calculated at three time points. Change in these values was calculated after 2 and 4 years. The effect of sex, duration of follow‑up, and the jaw (maxilla/mandible) on change of inclination was analyzed using the Mann–Whitney and Wilcoxon tests. P < 0.05 was considered statistically significant. Incisor teeth torque was positive in the maxilla (9.72 ± 8) and mandible (4.22 ± 6.09), but it was negative for the canine (–7.73 ± 6.3 for maxilla and –9.9 ± 5.22 for mandible), premolar (–10.35 ± 6.84 for maxilla and –26.51 ± 9.94 for mandible), and molar teeth (–13.23 ± 6.22 for maxilla and –39.78 ± 9.5 for mandible) in both jaws. Maxillary lateral incisor in boys showed the greatest change of inclination in both 2 and 4 years (about 7°) and the mandibular canine tooth in girls showed the least change of inclination in 4 years (4°). Sex significantly affected the changes in the inclination of teeth throughout the period of study. The variation of changes in torque was considerable, and no consistent pattern was defined.