# Stress estimation by serum cortisol release during rapid maxillary expansion in mice: validation of an experimental model

## TL;DR

This study validates a mouse model for measuring stress during rapid maxillary expansion by tracking cortisol levels in the blood.

## Contribution

The study introduces a validated experimental model using serum cortisol to estimate stress in mice undergoing rapid maxillary expansion.

## Key findings

- A 0.42N force applied for 7 days significantly increased cortisol levels compared to control and lower-force groups.
- Cortisol levels decreased after 14 days of 0.42N force, suggesting adaptation over time.
- The 0.42N force at 7 days was identified as a valid model for stress analysis in RME.

## Abstract

Rapid maxillary expansion (RME) is an orthopedic procedure used to correct maxillary transverse deficiencies by applying forces through specialized appliances. This intervention induces both dental and skeletal changes, which may potentially elicit physiological stress responses.

To validate a model for estimating stress by measuring plasma cortisol levels in mice subjected to rapid RME.

5-6-week-old male mice (C57BL6/J) were submitted to RME performed by an opening loop distractor at the mid palatal suture calibrated as follows (n = 5 per group): no force (control); 0.28 Newtons (N), 0.42N and 0.56N for periods of 7 and 14 days. Histomorphometry analyses were performed to analyze RME effect and serum samples were collected to measure cortisol by enzyme-linked immunosorbent assay (ELISA).

The forces applied at two different time points resulted in a successful RME pattern with the opening of the mid-palatal suture compared to the control group (P<0.05). The 0.42N force at 7 days resulted in a significant (P<0.05) increase in cortisol (pg/ml) compared to the control and 0.28N at 7 days (d) groups; the cortisol level in the 0.42N 7d group was statistically reduced when compared to the 0.42N 14d group. There was no statistically significant difference between the other groups.

The results suggest an increase in the stress response during the first days after the application of RME force with a force of 0.42N, with subsequent body adaptation. The force parameter of 0.42N at days proved to be a valid model for analyzing RME in mice.