Impaction of mandibular third molars after orthodontic treatment by the edgewise method: a retrospective study.

Lucas Garcia Santana,Maria Leticia Ramos-Jorge,Izabella Barbosa Fernandes,Leandro Silva Marques,Túlio Silva Pereira,Saul Martins Paiva,Margareth Maria Gomes De Souza

doi:10.1590/1807-3107bor-2020.vol34.0065

Abstract

This study aimed to determine the incidence of mandibular third molar (M3) impaction after orthodontic treatment by edgewise appliances, and identify possible determinant factors of M3 impaction. A retrospective cohort study was conducted with 1154 patients. Complete orthodontic records were analyzed pretreatment and posttreatment, considering the following variables: type of Angle malocclusion, treatment with or without extraction of first premolars, overbite, stage of dentition, M3 prior angulation and duration of orthodontic treatment. Impaction was determined after radiographic evidence of total closure of the root apex. The chi-square test and Poisson regression (p < 0.05) were used for statistical analysis with a hierarchical approach. Rate ratios (RR) and 95% confidence intervals (CI) were calculated. Mandibular M3 impaction incidence was 17%. Overbite equal to or greater than 4 mm (RR = 1.23, 95%CI: 1.11-1.26, p < 0.001), prior mesial angulation of M3 (RR = 0.59, 95%CI: 0.52-0.68, p < 0.001), non-extraction of first premolars (RR=1.06, 95%CI: 1.01-1.12, P=0.019) and orthodontic treatment time equal to or less than three years (RR = 0.94. 95%CI: 0.90-0.99, p < 0.014) were significantly associated with impacted M3. There was no correlation between the type of Angle malocclusion and the risk of impaction. In conclusion, the incidence of mandibular M3 impaction was considered low. The main pretreatment factors directly involved in impaction were mesioangulation of M3 and overbite equal to or greater than 4 mm. Orthodontic treatment with extraction of first premolars and treatment time greater than 3 years reduce the risk of impaction.

Highlights

The univariate analysis revealed that the dependent variable (M3 impaction) was associated with the non-extraction of the four first premolars (PR = 1.16, 95%confidence intervals (CI): 1.09–1.23), treatment time greater than three years (PR = 0.89, 95%CI: 0.85–0.95), overbite equal to or greater than 4 mm (PR = 1.37, 95%CI: 1.21–1.56), Class I (PR = 0.94, 95%CI: 0.89–0.99) and Class II Division 1 (PR = 1.09, 95%CI: 1.03–1.15), and prior mesioangular M3 (PR = 0.89, 95%CI: 0.81–0.99) (Table 2)
The following pretreatment dentition characteristics were associated with M3 impaction: overbite equal to or greater than 4 mm increases the risk by 23% (RR = 1.23, 95%CI: 1.11–1.26), and absence of mesioangular M3 reduces the risk by 41% (RR = 0.59, 95%CI: 0.52–0.68)
Orthodontic treatment without extraction of the first premolars increases the risk of M3 impaction by 6% (RR = 1.06, 95%CI: 1.01–1.12), whereas a treatment time greater than three years reduces the risk of impaction by 6% (RR = 0.94. 95%CI: 0.90–0.99)

Summary

Objectives

This study aimed to determine the incidence of mandibular third molar (M3) impaction after orthodontic treatment by edgewise appliances, and identify possible determinant factors of M3 impaction. The aims of the present study were to assess the incidence of M3 impaction in patients treated with the edgewise orthodontic method, and identify possible determinant factors

Methods

Results

Conclusion