A comparison of miniplates and teeth for orthodontic anchorage.

INTRODUCTION

In this study, we investigated orthodontic space closure of premolar extraction sites with miniplate anchorage compared with conventional tooth-borne anchorage in 8 adult beagle dogs.

METHODS

A split-mouth design with all 4 quadrants was used. Four premolars were extracted to create adequate space for premolar retraction. Retraction was performed with nickel-titanium coil springs. In the control side, the premolars were retracted against other teeth, and, in the experimental side, the premolars were retracted against miniplates. Each quadrant received 2 additional bone screws as bone markers for cephalometric superimposition. Lateral cephalograms were taken at initial activation, 6 weeks, and 12 weeks. Three parameters were measured and evaluated: linear space closure, angular tipping, and amount of anchorage slippage.

RESULTS

Overall, the miniplates had a high success rate of 93.8% (15 of 16) during the 12-week period of orthodontic loading. Similar amounts of space closure were observed in the control and the experimental sites. A statistically significant difference was observed for the amounts of tipping and anchorage slippage of miniplates vs tooth-borne anchorage. In the maxilla, the mean miniplate tipping was 0.1 degrees , whereas mean tipping of the anchor teeth was 9 degrees (P = .01). In the mandible, the miniplates tipped an average of 3.4 degrees , whereas the mean tipping of the anchor teeth was 13.3 degrees (P = .02). In the maxilla, the miniplates had 1% anchorage loss, whereas the tooth anchors had 37.1% anchorage loss (P = .001). In the mandible, the miniplates had a mean anchorage loss of 4.5%, whereas the tooth anchors had a mean anchorage loss of 31.1% (P = .001).

CONCLUSIONS

Although the total amount of space closure was similar in both the control and the experimental groups, the mechanism of space closure was different. In the control group, slippage of the anchor teeth accounted for approximately a third of the space closure. In the experimental group, the miniplates had minimal movement, and space closure was achieved almost entirely by movement of the target teeth. These results confirm that miniplates provide virtually absolute anchorage.