# Evaluation of the stability of immediately reinserted orthodontic miniscrews using a novel bioactive adhesive composite: an in vivo animal study

## TL;DR

A new bioactive adhesive composite improves the stability of orthodontic miniscrews reinserted after failure in a rat model.

## Contribution

A novel bioactive adhesive composite is proposed to enhance miniscrew stability after reinsertion.

## Key findings

- Reinsertion without adhesive reduced miniscrew stability, but adhesive use increased pull-out strength.
- Foam-form adhesive showed the highest pull-out strength compared to paste and control groups.
- Adhesive-treated groups showed greater bone-implant contact and bone volume, though not statistically significant.

## Abstract

To evaluate the effectiveness of a novel bioactive adhesive composite—comprising chitosan (CS), nanohydroxyapatite (nHA), β-tricalcium phosphate (β-TCP), and postbiotics—in enhancing the stability of orthodontic miniscrews immediately reinserted following failure in the same insertion site using a new miniscrew in an in vivo rat femur model.

Composite adhesives were prepared in two distinct forms: foam and paste. Orthodontic miniscrews were placed into the left femurs of 28 male Sprague‒Dawley rats, and a small hole was drilled 15 mm distal to the miniscrew site. Orthodontic force was applied via a 100-gram Ni‒Ti closed coil spring attached between the miniscrew and the drilled hole. After 4 weeks, the rats were divided into four groups: Group 1 (4-week control), Group 2 (8-week control), Group 3 (paste adhesive), and Group 4 (foam adhesive). Group 1 rats were euthanized to assess primary miniscrew stability. Groups 2, 3, and 4 underwent a second surgery in which miniscrews were carefully removed and reinserted without adhesive, with paste-form adhesive, and with foam-form adhesive, respectively. After an additional 4 weeks, miniscrew stability was evaluated through histological analysis and mechanical pull-out testing. The data were analyzed via one-way ANOVA followed by Duncan’s post hoc test. Normality was confirmed with the Shapiro‒Wilk test, and effect sizes (Eta Squared) were calculated due to the small sample size.

Reinsertion without adhesive reduced the stability of miniscrews. However, when adhesive was used during reinsertion, the maximum force required to extract the miniscrew from the surrounding bone significantly increased, with the foam group demonstrating the highest pull-out strength (PS). Compared with the control group, the paste and foam groups presented greater mean bone‒implant contact (BIC) and bone volume (BV) values, although these differences were not statistically significant (p > 0.05). Effect size analysis revealed large differences in the clinical effects of BV and PS between the control groups and the adhesive-treated groups.

The bioactive adhesive composite can improve the primary stability of orthodontic miniscrews immediately reinserted into the same site after failure. The findings suggest that such adhesives may serve as a temporary adjunct to support anchorage continuity, warranting further in vivo evaluation before clinical application.