As speech-language pathologists (SLPs) we often make diet recommendations. The unfortunate reality is we have scant information to direct these decisions. There is some evidence concerning the impact of volume and viscosity on swallowing kinematics (Barikroo, 2015; Chi-Fishman, 2002; Miller, 1996; Nagy, 2015; Watts, 2015). However, a systematic review (Steele, 2015) revealed little evidence to guide practice with respect to different degrees of modifying solid foods for patients with dysphagia. This means SLPs must rely on the sound understanding of the mastication process to make these decisions. Unfortunately, the system is quite complex and difficult to evaluate. This article represents the first of a series related to mastication that will address how mastication works and some possible assessment methods. Armed with this knowledge, SLPs may formulate more informed recommendations as part of a comprehensive patient care plan.
Mastication is a rhythmical act in which the tongue, facial muscles, and jaw muscles act in coordination to move food in the oral cavity between the teeth for it to be ground, mixed with saliva and formed into a bolus before swallowing. It is a dynamic process as the chewing cycles are altered with the continual changes to the food (Lund, 1991). Differences in the type, number, and size of food pieces appear to impact all the parameters of mastication. The basic pattern of rhythmic jaw movements produced during mastication is generated by a neural network located in the brainstem and referred to as the masticatory central pattern generator (CPG). The network composed of neurons mostly associated with the trigeminal system is found between the rostral borders of the trigeminal motor nucleus and facial nucleus (Morquette, 2012). The CPG receives afferent information from the interaction of the effecter system (muscles, bones, joints, and soft tissues) with the food (Lund, 2006).
It is commonly understood that the way we chew depends on the food that is being chewed. However, studies indicate that the most important variable in how food is chewed is the subjects themselves (Hiiemae, 1996; Peyron, 2003; Peyron, 2004). These studies found great differences between subjects in all the parameters measured, including the number of cycles needed to chew up a standard food load, amplitude and velocity of jaw movements, and the area of electromyogram bursts. The studies also found significant differences between males and females and that the number of cycles per sequence increased gradually with age. In addition, the number of cycles and the amount of jaw-closing muscle activity increased with food hardness (Lund, 2006).
I hope this introduction whet your desire to join me on this journey for a greater understanding of the common event of mastication. In the next issue, I will discuss the physiology of mastication in healthy adults.
Barikroo, A., Carnaby, G., & Crary, M. (2015). Effects of Age and Bolus Volume on Velocity of Hyolaryngeal Excursion in Healthy Adults. Dysphagia, 30(5), 558-564. doi:10.1007/s00455-015-9637-y
Chi-Fishman, G., & Sonies, B. C. (2002). Effects of systematic bolus viscosity and volume changes on hyoid movement kinematics. Dysphagia, 17(4), 278-287. doi:10.1007/s00455-002-0070-7
Hiiemae, K., Heath, M. R., Heath, G., Kazazoglu, E., Murray, J., Sapper, D., & Hamblett, K.(1996). Naturalbites, food consistency and feeding behaviour in man. Archives of Oral Biology, 41(2), 175-189.
Lund, J. P. (1991). Mastication and its control by the brain stem. Critical Reviews in Oral Biology & Medicine, 2(1), 33-64. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/1912143
Lund, J. P., & Kolta, A. (2006). Generation of the central masticatory pattern and its modification by sensory feedback. Dysphagia, 21(3), 167-174. doi:10.1007/s00455-006-9027-6
Miller, J. L., & Watkin, K. L. (1996). The influence of bolus volume and viscosity on anterior lingual force during the oral stage of swallowing. Dysphagia, 11(2), 117-124. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/8721070
Morquette, P., Lavoie, R., Fhima, M. D., Lamoureux, X., Verdier, D., & Kolta, A. (2012). Generation of the masticatory central pattern and its modulation by sensory feedback. Progress in Neurobiology, 96(3), 340-355.
Nagy, A., Molfenter, S. M., Péladeau-Pigeon, M., Stokely, S., & Steele, C. M. (2015). The Effect of Bolus Consistency on Hyoid Velocity in Healthy Swallowing. Dysphagia, 30(4), 445-451. doi:10.1007/s00455-015-9621-6
Peyron, M. A., Blanc, O., Lund, J. P., Woda, A. (2004). Influence of age on adaptability of human mastication. Journal of Neurophysiology, 92, 773-779.
Peyron, M. A., Mishellany, A., & Woda, A. (2004). Particle size distribution of food boluses after mastication of six natural foods. Journal of Dental Research, 83(7), 578-582 doi:10.1177/154405910408300713
Steele, C. M., Alsanei, W. A., Ayanikalath, S., Barbon, C. E., Chen, J., Cichero, J. A., . . . Wang, H. (2015). The influence of food texture and liquid consistency modification on swallowing physiology and function: a systematic
review. Dysphagia, 30(1), 2-26. doi:10.1007/s00455-014-9578-x
Watts, C. R., & Kelly, B. (2015). The Effect of Bolus Consistency and Sex on Electrophysiological Measures of Hyolaryngeal Muscle Activity During Swallowing. Dysphagia, 30(5), 551-557. doi:10.1007/s00455-015-9635-0