# Comparison of Postorthodontic Occlusal Force Distributions between Nonextraction and Extraction Treatment Approaches of Premolars for Orthodontic Treatment by Using T-Scan III System

## TL;DR

This study compares bite force distributions in patients who had orthodontic treatment with and without premolar extractions, finding mostly similar patterns except for second molars.

## Contribution

The study provides empirical evidence on occlusal force differences between nonextraction and extraction orthodontic treatments using the T-Scan III system.

## Key findings

- Bite force distributions in anterior and posterior regions were similar between nonextraction and extraction groups.
- Second molars in the extraction group had significantly higher bite force compared to the nonextraction group.
- The nonextraction group showed greater bite force on the right side, while the extraction group did not.

## Abstract

Objective
 To compare bite force distributions in corresponding mouth regions between postorthodontic patients who underwent nonextraction and extraction approaches using the T-Scan III system (Tekscan, Inc, Massachusetts, United States).

Materials and Methods
 Thirty-six postorthodontic patients were divided into two groups: (1) 18 subjects with the nonextraction treatment and (2) 18 subjects with the extraction of four first-premolar treatments. The measurements were performed using the T-Scan to collect the occlusal bite force at the maximal intercuspal position to generate the bite force in the anterior region (incisors and canines) and posterior region (premolars and molars), the bite force in individual teeth, and the anteroposterior bite force ratio (A-P ratio).

Statistical Analysis
 The mean bite force in each region, individual teeth, and the A-P ratio were compared between the two groups by the Mann–Whitney's
U
-tests. Within-group comparisons of the mean bite force in each region were performed using Wilcoxon's signed rank tests.

Results
 The bite force in anterior and posterior regions, and the A-P ratio of the nonextraction group show no significant difference compared with the extraction group (
p
 > 0.05). For individual teeth (central incisors, lateral incisors, canines, second premolars, first molars, and second molars), each tooth exhibited nonsignificantly different bite forces (
p
 > 0.05) except for the second molars. The second molars in the nonextraction group had significantly less bite force than in the extraction group (
p
 = 0.001). The comparison of occlusal bite force between the right and left sides showed that in the nonextraction group, the right side had significantly greater force (
p
 < 0.05). In the extraction group, there was no significant difference between the sides (
p
 > 0.05).

Conclusion
 Both nonextraction and extraction orthodontic treated patients exhibited the similar bite force distribution patterns in regions and individual teeth except for the higher occlusal force on the second molars in the extractions compared with the nonextractions.