Relationship between vertical skeletal pattern and success rate of orthodontic mini-implants

The objective of this research was to determine which clinical and skeletal factors are related to the success rate of orthodontic mini-implants in the maxillary and mandibular posterior buccal areas.

A total of 778 orthodontic mini-implants (Dual-Top Anchor System, Jeil Medical, Seoul, Korea; 1.6 mm diameter, 8 mm length, cylinder shape, self-drilling type) in 306 patients were retrospectively examined. The success rate was calculated according to clinical variables (sex, age, soft-tissue management, placement position, sagittal skeletal classification, arch-length discrepancy, and side) and skeletal variables (articular angle, mandibular plane to palatal plane angle, Frankfort-mandibular plane angle, mandibular plane angle, gonial angle, upper gonial angle, and lower gonial angle). Analysis of variance (ANOVA), chi-square tests, and multiple logistic regression analysis were used for statistical analysis.

The overall success rate was 79.0%. Almost 80% of the failures occurred within the first 4 months. The clinical variables sex, age, soft-tissue management, sagittal skeletal classification, arch-length discrepancy, and side did not show significant differences in the success rate. Although the success rates were significantly different according to placement position (P <0.01), there was no significant difference in the odds ratios among placement positions. In the skeletal variables, average upper gonial angle (84.2%) had a significantly higher success rate than low (75.7%) and high (71.2%) upper gonial angles (P <0.01). High Frankfort-mandibular plane angle (P <0.05) and low upper gonial angle groups (P <0.05) showed significant lower odds ratios than did the other types.

Vertical skeletal pattern might be an important factor for the success of orthodontic mini-implants placed in posterior buccal areas.