The Effect Of Class III Orthopedic Treatment On Position And Development Of Impacted Mandibular Third Molar: A Longitudinal Study
THE EFFECT OF CLASS III ORTHOPEDİC TREATMENT ON POSITION AND DEVELOPMENT OF IMPACTED MANDIBULAR THIRD MOLARS: A LONGITUDINAL STUDY
1. Statement of the problem
The third molars, and particularly those in the lower jaw, are the most frequently impacted teeth. The reason for third molar impaction, particularly of the lower molars is not absolutely clear. Several factors such as morphology, mesiodistal width of teeth, alveolar arch space behind the second molars, unfavorable path of eruption, and unsatisfactory uprighting during eruption have been associated with third molar impaction. While different methods have been developed to predict whether a molar will erupt or become impacted, no model has been able to reliably predict whether a molar will erupt or become retained. Yet, the risk of third molar impaction was reduced by an increase in retromolar space due to mandibular first premolar extraction1 and mesial molar movement2 during orthodontic treatments. However, we are aware of no studies evaluating the effect of Class III orthopedic treatment on the position and development of mandibular third molars, and retromolar space. The purpose of this study is to evaluate and to compare the position, inclintion of mandibular right and left third molars after Class III orthopedic treatment and long term follow-up.
2. Materials and Methods:
The material consisted of pretreatment(T1), posttreatment(T2), and long-term(T3) follow-up panoramic radiographs of 19 skeletal and dental Class III patients (mean age:10.5 years) treated with orthopedic appliances. The average treatment time was 13 months. The average follow-up period was 2.4 years. Positions of mandibular right and left third molars were assessed by Winter's classification. Positions of third molars were also evaluated according to inclinations of first molars, as the eruption of second molars were not completed at the beginning of orthopedic treatment. Retromolar space (D6-J) was calculated as the distance between the J point and the point (D6) where a perpendicular line intersects the occlusal line from the most distal of mandibular first molar. Inclination of the third molar (µ angle), first molar (Ɣ angle), and the angle between the first and third molar (α angle) were calculated.
3. Methods of data analysis:
Statistical evaluation was made with SPSS 20.0 (SPSS, IBM, New York, NY) software. Two-way analysis of variance was used to compare the changes of measurements during time intervals. Measurements of right and left third molars were compared by the intraclass correlation coefficient. Descriptive statistics of Winter's classification were presented using frequencies and the percentages. p<0.05 was considered significant.
4. Results:
At the beginning of treatment, the most common position of third molars were mesioangular.
Five horizontal third molars became upright during Class III treatment.
The position of four horizontal third molars did not change during Class III treatment or follow-up period.
Retromolar space was increased significantly during treatment and follow-up period.
No significant differences were observed in the inclination of lower right third molars during Class III orthopedic treatment, and follow-up period. However, lower left third molar became upright during 2.4 years of follow-up.
5. Conclusions
Class III orthopedic treatment
Class III orthopedic treatment have no significant effects of position and inclinations of lower third molars. Also, positional changes and eruption of impacted mandibular third molars are unpredictable event during follow-up period.
The possibility of the change in the inclinations of third molars must be taken into account before the extraction decision of orthodontists.
6. References
1. Richardson ME. The effect of mandibular first premolar extraction on thirdmolar space. AngleOrthod. 1989;59:291–294.
2. Behbehani F, Artun J, Thalib L. Prediction of mandibular third-molar impaction in adolescent orthodontic patients. Am J Orthod Dentofacial Orthop. 2006;130:47–55.