The purpose of this study was to investigate the micro-implant height and anterior hook height to prevent maxillary six anterior teeth from lingual tipping and extruding during space closure. We manufactured maxillary dental arch form, bracket and wire, using the computer aided three-dimensional finite element method. Bracket was .022" X .028" slot size and attached to tooth surface. Wire was .019" x .025" stainless steel and .032" x .032" stainless steel hook was attached to wire between lateral incisor and canine. Vi,-ngth of hook was 8mm and force application points were marked at intervals of lmm. Four micro-implants were implanted on alveolar bone between second premolar and first molar. The heights of them were 4, 6, 8, l0mm starting from wire. We analyzed initial displacement of teeth by various force application point applying force of 150gm to each micro-implant and anterior hook.
The conclusions of this study are as the following
1. When the micro-implant height was 4mm and the anterior hook height was 5mm and below, anterior teeth were tipped lingually. When the anterior hook height was 6mm and above, anterior teeth were tipped labially.
2. When the micro-implant height was 6mm and the anterior hook height was 5mm and below, the anterior teeth were tipped lingually. When the anterior hook height was 6mm and above, the anterior teeth were tipped labially. But lingual tipping of anterior teeth decreased and labial tipping increased when the micro-implant height was 6mm, compared with 4mm micro-implant height.
3. When the micro-implant height was 8mm and the anterior hook height was 2mm, the anterior teeth were tipped lingually. When the anterior hook height was 3mm and above, labial tipping movement of the anterior teeth incre ased proportionally.
4. When the micro-implant height was 10mm and the anterior hook height was 2mm and above, labial tipping of the anterior teeth increased proportionally.
5. As the anterior hook height increased, anterior teeth were tipped more labially. But extrusion occurred on canine and premolar area because of the increase of wire distortion.
6. Movement of the posterior teeth was tipped distally during maxillary six anterior teeth retraction using micro-im plant because of the friction between bracket and wire.
Based on the results of this study, we could predict the pattern of the tooth movement according to position
of micro-implant and height of anterior hook. It seems that we can find the force application point for proper tooth movement in consideration of inclination of maxillary anterior teeth, periodontal condition, oveijet and overbite
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