Reliability of EMG Activity versus Bite Force during Static Biting

Reliability is fundamental to any measurement, yet data on the reliability of electromyographic (EMG) amplitude with bite-force (BF) for masticatory muscles is sparse, although these measures are often used for model biomechanics. Objective: Our aim was to evaluate the reliability of EMG vs. BF over time. Methods: Fourteen subjects produce unilateral static bites at 5 different positions. These five positions were established by buccal to lingual indentations in acrylic copings temporarily cemented on the crowns of the maxillary and mandibular first molars. At each position the subjects bit down on a 5 mm steel sphere placed between the copings. Five bites of varying forces were obtained at each position. Surface EMG activities of bilateral anterior temporalis, masseter and suprahyoid group muscles were recorded at two sessions separated by a period of one to two weeks. Using regression, the slopes relating root mean square EMG amplitude with bite-force were calculated. Then, Intraclass Correlation Coefficients (ICC) and 95% confidence intervals (CIs) were obtained for the slopes from the two sessions. Results: are summarized in the following table.

Range of ICCs among the five bite positions
	Ipsilateral	Contralateral
Temporalis	0.87-0.93* 0.79-0.85* 0.05-0.96	0.74-0.91* 0.62-0.89* 0.71-0.92*
Masseter
Suprahyoid

* None of the 95% CI included 0; i.e., all were significantly different from zero.

Conclusions: EMG:bite-force relationships are reliable with narrower CIs for the masseter and temporalis  muscles when the bite force is generated in the molar region, but less reliable for the suprahyoid muscles. Reliability of EMG:bite force during static biting depends on the muscle and bite position. Thus, these reliable measures can be in modeling jaw biomechanics.

This study was supported by NIH  R01 DE16417-01A1