# A Finite Element Analysis of Mandibular Anterior Intrusion Using Mini-Screws With Three Different Implant Insertion Angles

## TL;DR

This study uses finite element analysis to determine the best angle for placing mini-screws to intrude mandibular anterior teeth with minimal stress and tipping.

## Contribution

The study introduces a novel finite element analysis comparing three mini-screw insertion angles for mandibular anterior intrusion.

## Key findings

- Maximum intrusion occurs at 90° insertion angle, but with higher labial tipping.
- The 60° insertion angle provides optimal stress distribution and minimal tipping.
- Central incisors experience the most intrusion in both four- and six-teeth scenarios.

## Abstract

Background

Facial aesthetics is a growing concern among young individuals, which greatly depends on the underlying dentofacial harmony. Among the anomalies in the three-dimensional plane of space, the problems related to the vertical plane of dentition are the most arduous to treat. It is commonly associated with supra-eruption of anterior teeth that are frequently treated using mini-screws as a skeletal anchorage device. The various factors associated with the stability of mini-screws include the insertion angle of the mini-screw in effecting a true intrusion with uniform distribution of stress. This finite element study evaluated the von Mises stress generated on the periodontal ligament and displacement in labio-lingual and apical directions during the intrusion of four- and six- mandibular anterior teeth using bilateral mini-screws inserted at 90°, 60°, and 30° in relation to the bone surface directed apically.

Methodology

Six finite element models of mandibular four- and six- anterior teeth with bilateral mini-screws were simulated with insertion angles of 30°, 60°, and 90° with disto-intrusive force vectors. The von Mises stress and displacement along apical and labiolingual axes were assessed when the force levels were applied, and a non-linear static analysis was performed using ANSYS version 18.1 software.

Results

The highest von Mises stress was elicited at 30° insertion in both four-teeth (0.002028 MPa) and six-teeth (0.002856 MPa) intrusion scenarios, which decreased with 60° (0.001948 MPa and 0.002768 MPa, respectively) and the least at 90° (0.001885 MPa and 0.002675 MPa, respectively). The teeth showed maximum labial tipping at 90° (0.000353 mm in four-teeth and 0.000507 mm in six-teeth) and least at 30°. Maximum intrusion was elicited at 90°, followed by 60°, and the least at 30°. Central incisor underwent maximum intrusion in both four- and six-teeth scenarios.

Conclusions

The study findings suggest the oblique placement of bilateral mini-screws at around 60° with a disto-intrusive force vector to achieve a relatively true intrusion with optimal stress generation and minimal labial tip in four- and six- mandibular anterior teeth.