Comparison of the differences in cephalometric parameters after active orthodontic treatment applying mini-screw implants or transpalatal arches in adult patients with bialveolar dental protrusion.

The purpose of this study was to compare the differences in cephalometric parameters after active orthodontic treatment applying mini-screw implants (G1) or transpalatal arches (G2) as anchorage in adult patients with bialveolar dental protrusion needing extraction of four premolars. A total of 34 Chinese patients (18-33 years) with bialveolar dental protrusion were randomly assigned to G1 and G2. Sliding mechanics and en-masse retraction of anterior teeth were applied to close extraction spaces. The changes in skeletal, dental and soft tissues were analyzed in both groups on lateral cephalograms before and after active orthodontic treatment. Independent samples and paired-samples t-tests were utilized to analyze the morphological changes in both groups. ANB angle was decreased in G1 and remained unchanged in G2 (P < 0.05). Upper incisors were retracted more in G1 than in G2 (P < 0.01). Upper incisors and molars were intruded in G1, but extruded in G2 (P < 0.01). Although the upper molars were found with no significant distalization (P > 0.05), there existed molars distalization in some patients. However, the maxillary molars in G2 were mesialized (P < 0.01). The intrusion of upper molars in G1 resulted in counterclockwise rotation of the mandible and decrease of SN-MP angle (P < 0.01). Upper lip linear measurements including UL-Y and UL-E were decreased more in G1 than in G2 (P < 0.05). Mini-screw implants provide absolute anchorage in vertical and sagittal directions. Better dental, skeletal and soft tissue changes could be achieved by mini-screw implants especially in hyperdivergent patients. Skeletal anchorage should be routinely recommended in patients with bialveolar dental protrusion.