Changes in the Vertical Dimension After Orthodontic Treatment in Response to Different Premolar Extraction Patterns

Premolar extractions in orthodontics can relieve dental crowding and affect incisor inclination. The aim of this retrospective study was to compare changes to the facial vertical dimension after orthodontic treatment with different premolar extraction patterns and non-extraction treatment.

This was a retrospective cohort study. The pre-and post-treatment records of patients with at least 5.0mm of dental arch crowding were accessed. Patients were divided into three groups: Group A, patients who had four first premolars extracted during their orthodontic treatment; Group B, patients who had four second premolars extracted during their orthodontic treatment; and Group C, patients with no extractions during orthodontic treatment. The pre-and post-treatment skeletal vertical dimension measured through the mandibular plane angle, as well as the incisor angulations/positions, were measured on lateral cephalograms and compared between groups. Descriptive statistics were computed and statistical significance was set at p<0.05. A one-way ANOVA test was conducted between groups to assess for statistically significant differences in changes to the mandibular plane angle and incisor positions/angulations. Post-hoc statistical analyses were performed between groups for parameters showing significant differences.

One-hundred twenty-one patients were included (47 males and 74 females) with ages ranging from 9 years old to 26 years old. Mean upper dental crowding ranged from 6.0 to 7.3mm and mean lower crowding ranged from 5.9-7.4mm across groups. There were no significant differences in mean age, mean treatment length, or mean dental arch crowding in each arch across groups. There were no significant differences in changes to the mandibular plane angle across all three groups regardless of the extraction pattern or non-extraction during orthodontic treatment. The upper and lower incisors were significantly retracted in groups A and B and significantly protracted in group C post-treatment. The upper incisors retroclined significantly more in Group A than Group B and proclined significantly in Group C.

No differences in the vertical dimension and the mandibular plane angle were observed when extracting first versus second premolars and in non-extraction treatment. Significant changes to the incisor inclinations/position were observed depending on the extraction/non-extraction pattern executed. Different premolar extraction patterns during orthodontic treatment do not influence changes to the vertical dimension. Clinicians should make extraction decisions based on desired outcomes for incisors rather than controlling the vertical dimension.