Effects of Different Gum Hardness on Masseter Muscle Activity During Gum Chewing: An NIRS Oximetry Study

Gum chewing is used in orofacial therapy to improve oral functions, such as a patient's chewing ability, bite force, tongue pressure, and lip closure strength. However, its effects on masseter muscle oxygen dynamics and muscle activity may vary with the hardness and features of the gum base. Therefore, when considering gum chewing for therapeutic purposes, it is essential to select gum of an appropriate hardness. This study aimed to elucidate the impact of gum hardness differences on masseter muscle tissue oxygen dynamics and muscle activity. We conducted a 120-s gum chewing study using three types of gum with different hardness levels on 11 healthy adult males. Each patient's masseter muscle tissue oxygen dynamics, muscle activity, and heart rate were measured, and the extent of masseter fatigue was assessed using a visual analogue scale (VAS). Per our findings, as gum hardness increased, significant reductions in oxygen saturation (StO₂) and significant increases in deoxyhaemoglobin (Deoxy-Hb) concentrations were observed in masseter muscle tissue oxygen dynamics. Likewise, muscle activity, heart rate, and muscle fatigue (according to VAS) also increased significantly as gum hardness increased. The findings of this study reveal that increasing gum base hardness not only affects masseter muscle tissue oxygen dynamics but also increases muscle activity, masseter fatigue, and heart rate. When selecting gum for orofacial therapy involving gum chewing exercises, it is crucial to choose the appropriate gum.