# Evaluating the reliability of myotonometry for assessing masseter muscle hypertrophy in healthy subjects

## TL;DR

This study evaluates how reliable a device called MyotonPRO is for measuring masseter muscle hypertrophy in healthy people.

## Contribution

The study introduces MyotonPRO as a reliable tool for objectively measuring masseter muscle hypertrophy.

## Key findings

- MyotonPRO showed moderate to excellent inter-rater reliability in measuring masseter muscle properties.
- The hypertrophy group had higher tension and stiffness compared to the normal group during muscle contraction.
- Only muscle elasticity showed a significant difference between groups in the relaxed state.

## Abstract

Background: Masseter muscle hypertrophy is characterized by either
symmetrical or asymmetrical enlargement of the muscle, often associated with
bruxism and other parafunctional habits. Traditional methods for assessing muscle
hypertrophy, such as palpation and visual inspection, can be subjective and
heavily dependent on the clinician’s experience. In contrast, devices like
MyotonPRO offer a standardized, objective and reproducible approach, enhancing
the precision and reliability of clinical diagnostics. The primary aim of our
study was to evaluate the intra- and inter-rater reliability of the MyotonPRO
device in assessing the viscoelastic properties of the masseter muscle.
Additionally, we sought to investigate the potential correlation between
subjective assessments of masseter hypertrophy and objective measurements
obtained through myotonometry. Methods: A clinical
examination using muscle palpation was conducted to identify masseter
hypertrophy, categorizing participants into Normal Muscle Volume (NMV) and Muscle
Hypertrophy (MH) groups. The viscoelastic properties of their masseter muscles
were then measured using MyotonPRO in both relaxed and maximal contraction
states. Two experienced operators performed the myotonometry on the same day,
with the first operator repeating the procedure 7 days later. Results:
Among the 58 participants, 51.7% were female, with a mean age of 28.6 years. The
inter-rater reliability of masseter muscle measurements using MyotonPRO ranged
from moderate to excellent, both at rest and during contraction, while
intra-rater reliability ranged from moderate to good. The MH group showed higher
levels of tension and stiffness, along with reduced relaxation time and creep
during contraction, compared to the NMV group. The only statistically significant
difference in relaxation between the groups was observed in muscle elasticity.
Conclusions: The MyotonPRO device effectively detects statistically
significant differences (p < 0.05) between the MH and NMV groups for
certain viscoelastic parameters. However, these differences were primarily
significant during contraction, with elasticity being the only parameter showing
a significant difference in the relaxed state.