Qualitative and quantitative evaluation of root injury risk potentially burdening insertion of miniscrew implants

Objective: Microscrew implants (MSls) offer many advantages, but some complications are known to occur during their insertion. One of the most commonly reported complications is root injury. Our aim was to identify factors associated with root injury and to evaluate their qualitative and quantitative values. Methods: Thirty-five orthodontists placed MSls (AbsoAnchor$AbsoAnchor^{(R)}$, Dentos Co. Ltd, Daegu, Korea) in the upper jaw of typodonts, labially between the second premolar and the first molar, in low and high vertical positions. Root contacts were counted, and distances between MSI apices and roots were measured. Fear level of the orthodontists was surveyed before and after the experiment. Wilcoxon's test, chi-square test, and Mann-Whitney test were used for statistical analysis. Results: Overall root contact rate of MSI insertion was 23.57%. The root contact rate was significantly higher in MSls inserted at $90^{\circ}$ (45.71%) than at $30^{\circ}$ (1.43%). The distance between the dental root and MSI also increased significantly in MSls inserted at $30^{\circ}$. Mean fear level before MSI insertion (4.6) significantly decreased after insertion (3.2); the causative factors were risk of injury to dental root and maxillary sinus or mandibular canal. Conclusions: Root injury is relatively rare, and oblique angulation reduces the risk of root and MSI contact.