Conventional Anchorage Reinforcement vs. Orthodontic Mini-implant: Comparison of Posterior Anchorage Loss During the En Masse Retraction of the Upper Anterior Teeth

This study sought to compare the amounts of posterior anchorage loss during the en masse retraction of the upper anterior teeth between orthodontic mini-implant (OMI) and conventional anchorage reinforcement (CAR) such as headgear and/or transpalatal arch. The subjects were 52 adult female patients treated with sliding mechanics (MBT brackets, .022” slot, .019X.025” stainless steel wire, 3M-Unitek, Monrovia, CA, USA). They were allocated into Group 1 (N=24, Class I malocclusion (CI), upper and lower first premolar (UP1LP1) extraction, and CAR), Group 2 (N=15, Cl, UP1LP1 extraction and OMI), and Group 3 (N=13, Class II division 1 malocclusion, upper first and lower second premolar extraction, and OMI). Lateral cephalograms were taken before (T0) and after treatment (T1). A total of 11 anchorage variables were measured. Analysis of variance was used for statistical analysis. There was no significant difference in treatment duration and anchorage variables at T0 among the three groups. Groups 2 and 3 showed significantly larger retraction of the upper incisor edge (U1E-sag, 9.3㎜:7.3㎜, P<.05) and less posterior anchorage loss (U6M-sag, 0.7㎜~0.9㎜:2㎜, P<.05; U6A-sag, 0.5㎜:2㎜, P<.01) than Group 1. The ratio of retraction amount of the upper incisor edge per 1㎜ of anchorage loss in the upper molar made for the significant difference between Groups 1 and 2 (4.6㎜:7.0㎜, P<.05). Group 3 showed a relatively distal inclination of the upper molar (P<.05) and the intrusion of the upper incisor and first molar (U1E-ver, P<.05; U6F-ver, P<.05) compared to Groups 1 and 2. Although OMI could not shorten the treatment duration, it could provide better maximum posterior anchorage than CAR.