Three-dimensional analysis of the tooth movement and arch dimension changes in Class I malocclusions treated with first premolar extractions: a guideline for virtual treatment planning.

INTRODUCTION: Our objective was to analyze patterns of tooth movement and changes of arch dimension by superimposing 3-dimensional (3D) virtual models.

METHODS: The sample consisted of 24 Korean adults with Class I malocclusion and minimal crowding, treated by first premolar extractions, sliding mechanics (0.022-in MBT brackets [3M Unitek, Monrovia, Calif] with 0.019 × 0.025-in stainless steel wire) and moderate anchorage. The 3D virtual maxillary casts at pretreatment and posttreatment were superimposed with the best-fit method. Linear and angular variables were measured with 3Txer program (Orapix, Seoul, Korea). Wilcoxon signed rank and Mann-Whitney tests were used for statistical analysis.

RESULTS: There was no significant difference in the individual tooth movement between the right and left sides (P > 0.05). For the movement of each tooth, the maxillary central incisors (U1), lateral incisors (U2), and canines (U3) were significantly inclined lingually, extruded, and moved posteriorly and laterally. The maxillary second premolar (U5), first molar (U6), and second molar (U7) had significant mesial inward rotation, anterior movement, and contracted toward the midsagittal plane. The ratio of anteroposterior movement between the maxillary anterior and posterior teeth was 5:1. The amounts of contraction in U5, U6, and U7 were 1.4, 1.3, and 1.2 mm, respectively. When the amount of change between the adjacent teeth were compared, the linguoversion in U1 was significantly greater than that of U2. U3 and U5 showed significant opposite movements in all variables. There were differences only in angulation and vertical displacement between U6 and U7.

CONCLUSIONS: Superimposition of 3D virtual models could be a guideline for precise virtual treatment planning.