Oral functions are essential for mastication, swallowing, and overall quality of life. The oral phase of swallowing—including mouth opening, bolus intake, chewing, and propulsion—relies on the synchronized actions of jaw-opening muscles and tongue functions, together with the coordinated activity of masticatory, suprahyoid, and perioral muscle groups that support jaw stabilization, bolus formation, containment, and effective oral transport (Matsuo & Palmer, 2009). Disruptions in this sequence may contribute to nutritional decline, mealtime anxiety, and social withdrawal, particularly in older adults (Tibbling & Gustafsson, 1991). Understanding the physiological basis of these functions is therefore fundamental to maintaining oral performance throughout life.

Jaw opening is primarily facilitated by the lateral pterygoid and hyoid-related muscles, which also contribute to tongue stabilization during swallowing and speech (Peck, 2016 Shaffer et al., 2014; ). The range of mouth opening is commonly measured by maximal interincisal opening (MIO),(Kolçakoğlu et al., 2023, Li et al., 2016) reflects the functional capacity of these muscle groups and has been used to assess temporomandibular mobility and age-related musculoskeletal changes(Kajisa et al., 2018 Schmitter et al., 2005; ). Reductions in jaw-opening capacity have been associated with impaired swallowing and decreased oral intake efficiency (Hara et al., 2018).

Tongue mobility is a critical determinant of effective mastication, bolus control, articulation, and safe swallowing. Reduced tongue movement can impair bolus propulsion, increase oral residue, and heighten the risk of dysphagia—especially in older adults (Steele & Van Lieshout, 2008). The tongue range of motion ratio (TRMR) provides a standardized, functionally relevant index by expressing tongue elevation relative to jaw opening, offering greater clinical insight than traditional structural measures such as free-tongue length or frenulum attachment (Jeong et al., 2017).

Tongue strength and endurance are commonly evaluated using the Iowa Oral Performance Instrument (IOPI),(IOPI Medical LLC, 2008) represent the tongue’s capacity to generate and sustain pressure against the palate, which provides validated and objective measurements (Kays et al., 2010 Preedeewong et al., 2024; Stierwalt & Youmans, 2007; Yoshikawa et al., 2020; ). Adequate tongue force is required to propel the bolus against the palate and into the oropharynx,(Chiba et al., 2003) while endurance reflects the muscle’s resistance to fatigue (Pizzorni et al., 2020). Together, these metrics serve as key indicators of oral and swallowing efficiency (Stierwalt & Youmans, 2007).

Age-related neuromuscular changes, often referred to as orofacial sarcopenia, can influence both tongue and jaw performance through declines in muscle mass, neural drive, and tissue elasticity (Crow & Ship, 1996 Mioche et al., 2002; ). These effects may differ between sexes due to hormonal and morphological variations in craniofacial musculature (Adams et al., 2013 Albani et al., 2009; ). Although previous studies have examined jaw and tongue performance separately, few have characterized their combined functional patterns across the adult lifespan using standardized quantitative measures. Moreover, reference data describing age- and sex-specific variations in these functions remain limited, particularly in non-Western populations.

To address this gap, the present study aimed to quantify jaw-opening performance (MIO), tongue mobility (TRMR), and tongue function (strength and endurance) across age groups and sex groups in healthy adults, and to explore their associations with body mass index (BMI). These data provide physiological reference ranges that contribute to understanding oral motor aging and its implications for orofacial function.