Effects of Third Molars on Anterior Crowding and Relapse After Orthodontic Treatment

Abstract

Purpose: This study aimed to evaluate the effect of the absence or presence of third molars on the relapse of mandibular incisor crowding after orthodontic treatment and to determine the indication for prophylactic third molar extraction in orthodontic patients based on Ganss ratios. Material and Method: The study was conducted with the dental models, panoramic and lateral cephalometric radiographs, and intraoral and extraoral photographs of 42 patients (26 females, mean age 16.56±4.96 years; 16 males, mean age 17.52±4.39 years). Data were collected at three time points: before (T1), at the end of (T2), and at least 2 years after the end of orthodontic treatment (T3). The patients were divided into two groups: those with impacted or erupted third molars (Group 1, n=22) and those with agenesis or extracted third molars (Group 2, n=20). Panoramic radiographs were used to determine the presence or absence of third molars at the three time points and to calculate Ganss ratio (GR) (1). Dental models were scanned with the 3 Shape TRIOS oral scanner (3 Shape Co. Copenhagen, Denmark) and mandibular anterior crowding was assessed using Little’s Irregularity Index (LII) (2). Mann-Whitney U test was used to compare mandibular LII values between the groups. GR values of mandibular impacted third molars at T1-T3 were evaluated with repeated-measures ANOVA. Pearson correlation analysis was used to determine the correlation between LII and GR in Group 1. Statistical significance was set at P<0.05. Results: There was no statistically significant difference between the groups in terms of the relapse of mandibular anterior crowding and the presence or absence of mandibular third molars (P=0.940). In Group 1, GR increased significantly at T3 due to an increase in retromolar distance (P<0.05). There was no correlation between LII and GR in Group 1. Conclusion: The presence or absence of mandibular third molars did not affect the relapse of mandibular anterior crowding in orthodontic patients. Prophylactic third molar extraction after orthodontic treatment does not seem necessary.