Objectives: To investigate factors associated with spontaneous mesialization of impacted third molars after second molar protraction to close the space caused by a missing mandibular first molar (L-6) or retained deciduous mandibular second molars with a missing succedaneous premolar (L-E).
Materials and methods: Panoramic radiographs of patients treated with mandibular second molar protraction to close the space due to missing L-6 or L-E (14 males, 36 females, mean age = 18.6 ± 4.4 years) were analyzed before treatment (T1) and after second molar protraction (T2). Factors associated with the amount of third molar mesialization were investigated using regression analyses.
Results: Mandibular second molars were protracted by 5.1 ± 2.1 mm and 5.8 ± 2.7 mm, measured at the crown and root furcation, respectively. After second molar protraction, third molars showed spontaneous mesialization by 4.3 ± 1.6 mm and 3.8 ± 2.6 mm, measured at the crown and root furcation, respectively. Nolla's stage of the third molar at T1 (B = 0.20, P = .026) and second molar protraction time (B = 0.04, P = .042) were significantly associated with the amount of third molar mesialization.
Conclusions: Greater third molar mesialization was observed when Nolla's stage of the third molar was higher before treatment and when the second molar protraction time was longer.
Keywords: Impacted third molar; Missing posterior teeth; Molar protraction.