Aging and Sex Effects on Mastication Performance in Healthy, Nondysphagic, Community-Dwelling Adults

Abstract

Purpose

This study investigated the impact of age and sex on mastication performance in healthy, nondysphagic, community-dwelling adults as observed during videofluoroscopy.

Method

Videofluoroscopic swallowing study imaging and mastication performance metrics (cycles, duration) were used to evaluate 185 healthy individuals (102 women, 83 men) aged 21–89 years.

Results

A significant effect of age on mastication cycles was not observed; however, a significant but weak effect of age on mastication duration was found. Female participants were observed to have significantly more mastication cycles and longer mastication durations compared to male participants. Three behavioral patterns of mastication performance emerged.

Conclusions

The results of this study contribute to normative data of mastication performance. An individual's sex was found to have a significant effect on mastication performance, although, in contrast to previous studies, age was not observed to significantly alter mastication performance. Differences in study methodologies likely explain the latter finding.

Mastication, or chewing, is a multifaceted process and engages numerous oral structures that work harmoniously to achieve breakdown of food into smaller particles for ease of swallowing. The mature adult chews using a cyclical, rotary jaw movement that involves food transport to the teeth by the tongue, followed by a quick closing of the jaw to connect the teeth with the bolus, and, lastly, a power stroke, where the jaw ultimately closes against the resistance of the bolus (Meenakshi & Paul, 2017). These steps repeat as the food is mixed with saliva until the bolus is softly broken down for safe swallowing.

The striated musculature of the upper aerodigestive tract system, including those used during mastication, can be altered by the typical aging process. Sarcopenia, or a loss in body muscle mass and endurance, can occur as people age (Azzolino et al., 2019). When typical aging negatively affects the swallowing mechanism, it is known as “presbyphagia” (Azzolino et al., 2019; Ekberg & Feinberg, 1991). For example, masticatory muscles may weaken, elasticity of the swallowing mechanism may be diminished, and dentition may be lost—all of which can lead to altered masticatory performance (Azzolino et al., 2019; Ekberg & Feinberg, 1991; Humbert & Robbins, 2008; Kohyama et al., 2003). Dentition is a critical component of mastication, providing the necessary tool to efficiently break down food too hard or large to swallow. Yet, as we age, our teeth weaken and, generally, become fewer (Kohyama et al., 2003). The Centers for Disease Control and Prevention (2003) have shown an increase in older adults who preserve their teeth past the age of 65 years; however, other dental disorders, such as dental caries and periodontal disease, increase dental loss risk for those who have retained their teeth. These alterations may result in poor mastication efficiency requiring an individual to increase numbers of mastication cycles and mastication duration.

Several early studies investigated mastication performance in healthy, nondysphagic participants using both direct and indirect measures, including videofluoroscopy and surface electromyography, respectively (Dua et al., 1997; Hiiemae et al., 1996; Huckabee et al., 2018; Inokuchi et al., 2014; Kohyama et al., 2003; Nagasawa et al., 1997; H. S. Park et al., 2017; S. Park & Shin, 2015; Saitoh et al., 2007; Yoneda & Saitoh, 2018). Previous findings support significant differences in duration of mastication based on the food type (i.e., harder solids require longer durations; Hiiemae et al., 1996; Inokuchi et al., 2014; Saitoh et al., 2007). High variability in mastication performance in healthy adults has also been described (Inokuchi et al., 2014; Saitoh et al., 2007; Yoneda & Saitoh, 2018). The wide variability in mastication performance may suggest unique patterns of mastication in healthy, nondysphagic individuals.

Overall findings from previous literature support the theory that aging's effect on the upper aerodigestive tract musculature may affect mastication performance. Specifically, increasing age has been associated with increases in numbers of mastication cycles and durational measures. An inverse relationship between mastication performance and age has previously been reported (Huckabee et al., 2018; Kohyama et al., 2003), but there is disagreement in the literature likely related to variation in study sample sizes and methods such as nondirect visualization, behavioral measures, and Surface Electromyography. For example, H. S. Park et al. (2017) reported significant differences in numbers of mastication cycles but not duration. Sex effects have also been explored, with male participants demonstrating faster mastication, fewer mastication cycles, and greater muscle activation during mastication in male participants relative to age-matched female participants (Huckabee et al., 2018; Nagasawa et al., 1997; S. Park & Shin, 2015).

Few large-scale videofluoroscopic studies have been performed to elucidate mastication performance in healthy adult populations, whereas even fewer have stratified patients by age and sex (Huckabee et al., 2018; Kohyama et al., 2003; H. S. Park et al., 2017). Since patients with presbyphagia are otherwise healthy, sarcopenia has become the primary explanation for the observable changes in the swallowing and mastication systems as humans age (Ekberg & Feinberg, 1991; Humbert & Robbins, 2008; Mulheren et al., 2018). These changes, however, have not been well defined on videofluoroscopy, the most common method for visualizing oropharyngeal swallowing function. Understanding masticatory function across the healthy aging spectrum will assist clinicians in distinguishing normal from abnormal patterns and in anticipating the potential implications of these patterns in the context of oropharyngeal swallowing impairment(s). Previous studies assessing mastication under videofluoroscopy used barium powder (Inokuchi et al., 2014) and barium pudding (Saitoh et al., 2007) in order to add contrast to food. Other studies did not specifically state how or if barium was used during videofluoroscopy (Dua et al., 1997; H. S. Park et al., 2017).

The primary purpose of this study was to investigate the impact of aging and sex on the mastication performance observed during videofluoroscopy in a large cohort of healthy, nondysphagic, community-dwelling adults. Furthermore, this study explored the association between mastication performance measures and Modified Barium Swallow Impairment Profile (MBSImP) Component 3 (Bolus Preparation/Mastication) scores (Martin-Harris et al., 2008, 2017; Northern Speech Services, Inc., 2019). Lastly, the existence of characteristic patterns of mastication in healthy adults was explored.

Method

Participants

Data were derived from a large normative videofluoroscopic swallowing study (VFSS) data set of 195 healthy participants (109 women, 86 men) ranging from 21 to 89 years old. The original study received institutional review board approval at the Medical University of South Carolina and provided written informed consent. Participants were included in the original database project if they met the following criteria: (a) sufficient level of alertness, attention, and cognitive function as judged by study personnel or speech-language pathologists or by performance on the Montréal Cognitive Assessment (score ≥ 26; Nasreddine et al., 2005); (b) 21 years of age and older; (c) no current or history of dysphagia; and (d) ability to drink thin liquids and eat solid foods as part of total oral diet without restrictions (Functional Oral Intake Scale Level 7; Crary et al., 2005). Exclusion criteria included (a) known allergy or dietary restriction for food or barium contrast materials used during VFSS, (b) history of upper aerodigestive tract surgical procedures (e.g., oral, nasal, pharyngeal, laryngeal, and esophageal resections), (c) large hiatal hernia (> 2 cm), (d) pulmonary disease (e.g., chronic obstructive pulmonary disease), (e) history of head and neck cancer, (f) inability to self-feed, (g) neurological disease (e.g., stroke, Parkinson's disease), and (h) pregnancy or suspected pregnancy. Participants were included even if they had a history of tonsillectomy, adenoidectomy, sinus surgery, and dental extractions if all other inclusion criteria were met. Pregnant women or women who thought they might be pregnant were not allowed to participate in the study due to radiation exposure risks.

VFSS

All eligible participants underwent a VFSS performed in collaboration by a speech-language pathologist and a radiology assistant. Each participant was evaluated using a standardized and validated protocol (MBSImP) published (Hazelwood et al., 2017; Martin-Harris et al., 2008, 2017) and available online (Northern Speech Services, Inc., 2019). A high-resolution, videofluoroscopic device (Digital Swallowing Workstation Model 7100, Kay Elemetrics Corp.; TIMS Dicom System) was used. Fluoroscopy rate was continuous, and videofluoroscopic recordings were made with a resolution of 60 fields (30 frames) per second. All consistencies were administered as outlined in the MBSImP protocol; however, only the cookie trial was extracted for analysis. The cookie trial involved a half portion of a Lorna Doone cookie coated with 3 ml of barium paste. Participants were asked to eat the entire provided portion “as they normally would,” with participants taking the whole portion in one bite.

Mastication Performance

Mastication cycles and total mastication durations were calculated for each participant. A single mastication cycle was operationally defined from an open-to-open phase, or when the teeth open then close, and then return to open position during mastication (see Figure 1). Mastication performance measures (cycles, duration) were derived from when the teeth opened to initiate mastication to when the participant began to exhibit nonrhythmic, collecting behavior prior to the swallow. Total mastication duration was timed in seconds using a digital stopwatch and was the time it took participants to complete all mastication cycles. All VFSS videos were viewed in QuickTime player, using real-time and frame-by-frame analysis.

Figure 1.

Example of one mastication cycle. A rotary chew involves an opening phase during which the bolus is manipulated by the tongue (A), power stroke where the teeth close against the bolus (B), and another opening phase where the bolus is manipulated (C). These steps repeat until the bolus is sufficiently ground for the swallow.

MBSImP Component 3 mastication scores (see Table 1) were also extracted from the normative database. These scores were previously assigned by two dysphagia experts using consensus scoring based on criteria outlined in MBSImP protocol (Martin-Harris et al., 2008, 2017; Northern Speech Services, Inc., 2019).

Table 1.

Modified Barium Swallow Impairment Profile Component 3 Bolus Preparation/Mastication scores and corresponding description (Martin-Harris et al., 2008, 2017; Northern Speech Services, Inc., 2019).

Component score	Component description
0	Individual displays timely and efficient chewing and mashing.
1	Individual displays slow and prolonged chewing and mashing, but complete recollection or formation of the bolus is achieved.
2	A cohesive bolus is not formed during mastication, resulting in pieces of unchewed bolus remaining in the oral cavity after the initial swallow.
3	Individual displays nominal chewing and mashing, leaving most of the bolus unchewed.

Analysis

Participants were distributed across four age categories (21–39 years, 40–59 years, 60–79 years, and 80 years and older) and distributed between sexes (female and male). These age categories are roughly consistent with previous literature discussing aging's effect on mastication and other aspects of deglutition (Garand et al., 2019; Huckabee et al., 2018; Martin-Harris et al., 2005). Descriptive measures, including means, standard deviations, medians, ranges, and interquartile ranges, were calculated for both the number of mastication cycles and total mastication duration as a function of age and sex. The associations between the number of mastication cycles and total mastication duration of mastication and age (continuous variable) were analyzed using Pearson correlation coefficients. The relationship between age categories and number of mastication cycles and total mastication duration was tested using Kruskal–Wallis tests. Mann–Whitney U tests were used to compare differences in numbers of mastication cycles and total mastication duration between the sexes. Further analysis involved a regression model to control for the effects of sex on the relationship between age categories and linear age and number of mastication cycles and total mastication duration.

A stepwise multiple regression analysis was performed to assess the relationship between MBSImP Component 3 scores and mastication performance (cycles, duration). To determine intra- and interrater reliability of counted cycles and total mastication duration, 20% of VFSSs (n = 40) were re-assessed by the first author (E. M.) for intrarater reliability and between the first and last authors (E. M. and K. L. G., respectively) to determine interrater reliability. To further assess interrater reliability of counted cycles and total mastication duration, interclass correlation coefficient (ICC) testing was used. Two-tailed p values of < .05 determined statistical significance. All analyses were performed with Statistical Package for Social Sciences, v.24 (IBM Corp., 2016) and R (R Development Core Team, 2008).

Results

Participant Demographics

Of the 195 participants, 10 were excluded due to missing data, leaving 185 participants (102 women, 83 men) available for analysis. Videos were excluded due to missing fluoroscopic frames or “frozen frames” due to computer error, which might have impacted timing of mastication. Demographic information is provided in Table 2.

Table 2.

Participant demographics across four age categories.

Variable	21–39 years n = 66	40–59 years n = 66	60–79 years n = 45	80+ years n = 8
Age
M ± SD	28.3 ± 4.6	48.8 ± 6.2	66.4 ± 5.7	83.1 ± 2.9
Sex
Female	33 (50)	33 (50)	32 (71)	4 (50)
Male	33 (50)	33 (50)	13 (29)	4 (50)
Race
White/Caucasian	46 (70)	41 (62)	40 (89)	8 (100)
African American	16 (24)	22 (33)	5 (11)	0 (0)
Other	4 (6)	3 (5)	0 (0)	0 (0)
Ethnicity
Hispanic/Latino	2 (3)	1 (2)	1 (2)	0 (0)
Non-Hispanic/Latino	64 (97)	65 (98)	44 (98)	8 (100)

Note. Data reported in frequency (percentage) unless otherwise reported.

Overall Mastication Performance

The average number of mastication cycles across all participants was 14.2 (SD = 5.2, range: 4–36), and the average total mastication duration was 10.1 s (SD = 4.1, range: 3.2–31.1 s).

Analysis of Mastication Performance by Age

Descriptive statistics across age categories for mastication cycles and total mastication duration times are reported in Tables 3 and 4, respectively. A positive, general trend between age categories and number of mastication cycles and total mastication duration was observed. Thus, as age category increased, number of mastication cycles and total mastication duration appeared to also increase; however, only the differences in total mastication duration were found to be significant. A Kruskal–Wallis test determined no significant difference between age categories and numbers of mastication cycles, H(3) = 4.11, p = .250; meanwhile, a significant relationship was observed between age categories and total mastication duration, H(3) = 8.25, p = .041. After collapsing the two oldest age categories (60–79 and 80+ years), the effect of age category on number of mastication cycles was insignificant (p = .396), while the effect was marginally significant on the total mastication duration (p = .051). Regression models were used to control for the effects of sex and race on mastication performance due to the confounding effect of sex and race discovered during statistical analysis. When controlling for race and sex, a significant difference was observed in the number of mastication cycles between the younger age categories (79 years and younger) and the oldest age category (80+ years, p = .01), but the differences between the remaining age categories remained nonsignificant. When controlling for race and sex, the effect of age on total mastication duration remained significant (p < .01).

Table 3.

Mastication cycles across age categories.

Variable	21–39 years n = 66	40–59 years n = 66	60–79 years n = 45	80+ years n = 8
M ± SD	13.6 ± 4.6	14.8 ± 5.0	13.8 ± 5.6	18.0 ± 8.1
95% CI	[12.5, 14.8]	[13.6, 16.1]	[12.1, 15.5]	[11.2, 24.8]
Range	4–29	7–35	4–32	12–36
Mdn	13	14	14	15
Interquartile ranges	10–16	11–17	10–18	13.5–21.8

Table 4.

Mastication duration (in seconds) across age categories.

Variable	21–39 years n = 66	40–59 years n = 66	60–79 years n = 45	80+ years n = 8
M ± SD	9.1 ± 2.9	10.7 ± 4.3	10.4 ± 4.7	12.7 ± 4.8
95% CI	[8.4, 9.8]	[9.7, 11.8]	[8.9, 11.8]	[8.7, 16.6]
Range	3.9–18.9	4.9–31.1	3.2–29.5	6.5–20.9
Mdn	8.6	9.9	9.4	11.9
Interquartile ranges	7.0–10.7	7.9–12.6	7.3–13.0	9.1–16.2

Using Pearson correlation coefficient, age was assessed as a continuous variable against total mastication duration and number of mastication cycles. There was a weak, but significant, linear relationship between age and total mastication duration (coefficient = .187, p = .011). However, when age was evaluated against the number of mastication cycles with the Pearson correlation coefficient, a linear relationship between age and numbers of mastication cycles was not supported (coefficient = .11, p = .136).

Analysis of Mastication Performance by Sex Categories

Descriptive statistics across age categories for number of mastication cycles and total mastication duration are reported in Tables 5 and 6, respectively. Findings support significant differences in the number of mastication cycles (p = .01) and total mastication duration (p < .01). Women, on average, required more mastication cycles (average of two cycles) and longer durations (average of 2 s) than men.

Table 5.

Mastication cycles across sex categories.

Variables	Female n = 102	Male n = 83
M ± SD	15.0 ± 5.0	13.4 ± 5.3
95% CI	[14.0, 16.0]	[12.2, 14.5]
Range	5–36	4–35
Mdn	15	13
Interquartile ranges	11–18	10–15

Table 6.

Mastication duration (in seconds) across sex categories.

Variables	Female n = 102	Male n = 83
Mean ± SD	11.1 ± 4.4	8.9 ± 3.4
95% CI	[10.3, 12.0]	[8.2, 9.7]
Range	4.9–31.1	3.2–22.6
Median	10.4	8.1
Interquartile ranges	8.1–13.7	6.7–10.5

Prediction of Component 3 Scores Using Mastication Performance

In order to evaluate the relationship between MBSImP Component 3 scores, mastication performance, and other covariates (sex, age, race, and ethnicity), a variety of statistical models (classification and regression tree, support vector machine, and mixed-effects models) were used. Race and ethnicity were controlled covariates due to post hoc analysis revealing a significant effect on total mastication duration and cycles. Nevertheless, none of these tested models was able to reliably predict component scores greater than 70% accuracy.

Mastication Patterns

Mastication patterns were delineated by two primary features:

1. Total seconds of mastication

2. Ratio of mastication cycles and duration

Three patterns of mastication emerged. Those in Pattern 1, labeled “aggressive chewers/mashers,” chewed less than 10 s and had a ratio of 1.5 cycles to 1 s of mastication. Pattern 2 individuals, or “methodical chewers/mashers,” chewed longer than 10 s and also had a ratio of 1.5 cycles to 1 s of mastication. The individuals in Pattern 3, “random chewers/mashers,” included any participant with a ratio greater than 1.5 cycles per second. Aggressive and methodical chewers/mashers were considered “rhythmic” masticators, while random chewers/mashers were considered “arrhythmic” masticators. Participants who demonstrated a rhythmic pattern (i.e., aggressive or methodical chewers/mashers) comprised the majority of this sample, 117 participants (63%). There were 68 participants (37%) who were classified as aggressive chewers/mashers and 49 individuals (26%) as methodical chewers/mashers. The remaining 68 participants (37%) were considered random chewers/mashers.

Aggressive chewers/mashers were almost equally distributed between male and female participants, 49% and 51%, respectively; however, the aggressive chewers/mashers group consisted predominantly of the youngest age groups (i.e., 43% were under the age of 39 years). The next most common age group in the aggressive chewers/mashers category was the 40–59 years age category (31%), followed by the 60–79 years age category (25%). Methodical chewers were overwhelmingly female (80%), with almost 40% of individuals belonging to the middle-age category of 40–59 years. The remaining methodical chewers were composed of participants under 39 years old (22%), followed by 60–79 years old (33%), and, lastly, 80 years old and older (6%). The final group, the random chewers, was predominately male (59%). Random chewers were more evenly spread among the age categories: 38% under 39 years old, 38% between 40 and 59 years old, 18% between 60 and 79 years old, and 6% 80 years old and older.

Reliability

Interrater as well as intrarater reliability was assessed using intraclass correlation coefficient. There was high interrater reliability for number of mastication cycles (ICC = .99, p < .0001) and total mastication duration (ICC = .89, p < .0001), as well as high intrarater reliability for cycles (ICC = .99, p < .0001) and duration (ICC = .95, p < .0001).

Post Hoc Analysis

Influence of Mastication Cycles and Duration on Bolus Transport/Lingual Motion

The relationship between MBSImP Component 4, bolus transport/lingual motion, and mastication performance was assessed using an independent t test and Mann–Whitney U test. MBSImP descriptions for Component 4 scores are as follows: 0, brisk tongue motion; 1, delayed initiation of tongue motion; 2, slowed tongue motion; 3, repetitive/disorganized motion; 4, minimal to no tongue motion. A score of 1 or greater is considered impaired. Participants were divided into groups pertaining to scores of zero (n = 176) and nonzero (n = 9). No significant differences existed between the two groups in both cycles and total mastication duration (cycles, p > .05; duration, p > .05).

Influence of Mastication Cycles and Duration on Oral Residue

MBSImP Component 5 (oral residue) and mastication performance were assessed using Kruskal–Wallis tests. Participants were grouped based on the following scores: 0 (n = 16), 1 (n = 68), 2 (n = 91), and 3 (n = 3). Descriptions for these scores are as follows: 0, complete oral clearance; 1, trace residue; 2, collection of residues; 3, majority of bolus remaining. Scores 2 and greater are considered impaired. No significant effects were observed on the number of mastication cycles or total mastication duration. Furthermore, when participants who earned a score of 3 were considered outliers and removed from analysis, the results remained nonsignificant (p = .054). Further exploration revealed mastication cycle differences between participants with an impairment score of “1” and “2” (p = .02), with group “2” demonstrating more mastication cycles.

Discussion

The purpose of this retrospective study was to explore the effect of age and sex on mastication performance in a cohort of healthy aging individuals. Overall, this study did not find a significant age effect on the number of mastication cycles and found a weak, but significant, effect on total mastication duration. Significant differences, however, were observed between sexes. Female participants, when compared to male participants, were observed to have an increased number of mastication cycles and longer total mastication duration. Similar to previous studies, participants demonstrated wide variability for number of mastication cycles and total mastication duration (Inokuchi et al., 2014; Yoneda & Saitoh, 2018).

Effect of Age on Mastication Performance

Our findings revealed a significant aging effect on total mastication duration, with older adults presenting with longer total mastication durations than younger participants. Previous studies have reported significant increases in the number of mastication cycles and total mastication duration times in healthy aging adults (Huckabee et al., 2018; Kohyama et al., 2003), with the exception of a study published by H. S. Park et al. (2017). In contrast to the former study findings, H. S. Park et al. found significant differences in the number of mastication cycles but not total mastication duration; however, H. S. Park et al.'s study involved exclusively dentulous participants. Dentition was not accounted for in this retrospective study and may help explain differences in total mastication duration in older individuals, who are more likely to have fewer teeth. Individuals with fewer teeth, or no teeth, have been previously reported to have increased total mastication durations when compared to peers with complete dentition (Kohyama et al., 2003).

In contrast to the study of Huckabee et al. (2018), this study did not find significant aging effects on the number of mastication cycles, although a positive relationship, in that as age increased, the number of mastication cycles increased, was observed. This difference could be due to direct (i.e., videofluoroscopy) versus indirect (i.e., observing jaw movements, sEMG) visualization of mastication, sample size differences, age category differences, and difference in amount and type of food trials. Direct visualization allows for differentiation of true mastication cycles versus bolus gathering behavior by the tongue and jaw. While Huckabee et al. had an overall large sample size, each analyzed age group contained only 10 men and 10 women. Furthermore, Huckabee et al. used a variety of crisp crackers (e.g., saltines, saladas), which may have had a drying effect on the oral cavity, leading to difficulty in gathering a cohesive bolus. The crackers used were also administered without a coating (i.e., barium), as Huckabee et al.'s study did not involve VFSS. These methodological differences likely explain the differences observed in significance levels of aging effects on the number of mastication cycles.

Unlike Huckabee et al. (2018) and Kohyama et al. (2003), H. S. Park et al. (2017) used direct visualization (i.e., VFSS) to study the effect of aging on mastication performance. H. S. Park et al.'s study found significant differences in cycles, but not total mastication duration. Although similar instrumentation was used to study mastication behavior, there were other differences between the current study and that of H. S. Park et al. (2017), including dentition status of participants, foods administered, and sample size. Due to the retrospective nature of the current study, dentition was not accounted for. The foods used in H. S. Park et al.'s study included a variety of rice dishes compared to the hard solid (i.e., cookie) used in our study, which likely affected chewing behavior. The sample used in H. S. Park et al.'s study involved more restricted age categories and fewer participants overall, 20 young adults (mean age of 26 years) and 40 older adults (mean age of 79 years), as compared to the current study, which involved 195 participants with a wide range of ages from 21 to 89 years broken into four age categories. An advantage of the large age range in the current study is that it allowed investigators to evaluate the linear relationship between age and the number of mastication cycles and total mastication duration.

Effect of Sex on Mastication Performance

Results from the current study revealed sex differences in mastication performance consistent with previous reports (Huckabee et al., 2018; Nagasawa et al., 1997; S. Park & Shin, 2015). Female participants demonstrated, on average, higher number of mastication cycles and longer total mastication durations relative to their male counterparts. Differences in mastication performance may result from physiological differences in masticatory musculature. Male participants were observed to have increased masticatory muscle electrical activity and chewing power (μV) in the temporal and masseter musculature in studies by Nagasawa et al. (1997) and S. Park and Shin (2015), respectively. Gender role differences between the sexes, such as dining etiquette (e.g., consuming small bites and chewing food thoroughly), may also explain these differences observed in mastication performance (Rolls et al., 1991).

Mastication Performance and MBSImP Component Scores

Various statistical models were applied to predict MBSImP Component 3 scores using mastication cycles and total mastication duration with other covariates (e.g., age, sex). Unfortunately, no tested model was able to reliably predict Component 3 scores greater than 70% accuracy. This suggests that a given score for Component 3, bolus preparation/mastication, is affected by more than observation of mastication cycles and total mastication duration. This is consistent with the operational definitions provided for scoring Component 3, which include behaviors such as “recollection” of the bolus and pieces of the bolus remaining unchewed. These behaviors are not necessarily connected to the number of mastication cycles or total mastication duration. The relationship between Component 4, bolus transport/lingual motion, and mastication was found to have no significant differences between groups in both cycles and duration. Although it did not reach significance, it was noted participants with a Component 5, oral residue, score of “2,” a collection of oral residues, had generally more cycles than participants with less oral residue. Future research including patient populations with dysphagia may provide further information regarding associations between masticatory performance and MBSImP component scores.

Patterns of Mastication

Three patterns of mastication emerged and were labeled as aggressive chewer/masher, methodical chewer/masher, and random chewer/masher. The aggressive chewer/masher was an individual who exhibited fast, rhythmic mastication involving fewer cycles in a shorter total mastication duration. Those who would be labeled under the aggressive pattern had fewer than 10 mastication cycles and 10 s of mastication time, generally with a 1:1 ratio. This style was favored by individuals with dentition; however, nearly edentulous individuals were also observed to use this pattern. In contrast to the aggressive chewer, the methodical chewer/masher typically exhibited greater than 10 cycles of mastication but maintained a rhythmic pattern. Individuals with this pattern were occasionally observed to pause or talk during mastication, therefore increasing total mastication duration.

The final pattern was the random chewer/masher, which characterized an individual who demonstrated a mixture of aggressive and methodical pattern behaviors. This pattern usually had an asymmetrical ratio of cycles and total mastication duration, for example, fewer than 10 mastication cycles but required greater than 10 s. Random chewers/mashers may also show a lack of patterning, such as beginning mastication with short, quick cycles but transitioning to a slower pattern mid-mastication. Further descriptions of these varying patterns of mastication could aid in differentiating individuals with healthy mastication and those with disordered mastication.

Limitations and Future Directions

Due to the retrospective nature of this study, dentition of participants was not accounted for, which is known to affect the number of mastication cycles and timing (Kohyama et al., 2003). Accounting for dentition as a covariate could have affected significance of mastication performance. Second, only a single solid (cookie) bolus trial was administered. A single trial limits further exploration of variances in mastication (Yoneda & Saitoh, 2018). Next, the oldest age category (80+ years) contained the fewest participants (n = 8). There was also a sex imbalance in the 60- to 79-year-old category (71% vs. 29%), with more female participants present. There was little continuity in how food stimuli were prepared, with respect to barium, in previous studies, which could affect comparability of results. Furthermore, medications were not analyzed, and thus, potential medication side effects leading to dry mouth may have influenced results. Despite these limitations, this study provides important information related to mastication performance in a large representative sample of community-dwelling adults. The results of this study contribute to existing literature in describing typical mastication performance in adults and explore effects of age and sex on performance. Healthy adults may show demonstrable changes to the masticatory system, although this does not drastically impact their overall swallowing function or alter diet intake; in other words, all participants reported tolerating a full regular diet with thin liquids (FOIS Level 7). For individuals who display a higher score on Component 3 of the MBSImP (e.g., score of 1 – slow prolonged chewing/mashing), it is likely unnecessary to modify their diet if other physiological components of the swallow are functional for safe and efficient swallowing. Thus, “slow” does not necessarily equate to “disordered,” particularly in female participants where an increased number of mastication cycles and total mastication durations were observed to significantly differ relative to their male counterparts. Since identification of dysphagia often leads to diet alterations and restrictions, this may impede an individual's quality of life. It has been well established that an individual's ability to continue to enjoy one's favorite foods is paramount to quality of life, which may increase life span (Steptoe et al., 2014).

Future investigations should address limitations in the current study, including documentation of dentition status of study participants, recruiting sufficient participants aged 80 years and older, and targeting balance among racial and sex distributions. If balance is achieved, across-group comparisons would allow for further evidence either supporting or refuting current study findings. Additionally, future studies should further explore and differentiate patterns of mastication among normal and disordered cohorts using multiple food trials and in larger populations. Further detailing of the various patterns of mastication should be explored and how it impacts mastication performance. Such findings will provide additional normative data to continue to explicate the differences between healthy and disordered mastication and prevent unnecessary diet alterations in order to improve quality of life.

Conclusion

This retrospective study contributes to normative data of mastication performance in healthy, nondysphagic, community-dwelling adults. These findings support previous evidence revealing sex differences in mastication performance, with female participants observed to have an increased number of mastication cycles and longer total mastication durations relative to male counterparts. In contrast to previous studies, this investigation did not find significant aging effects on the number of mastication cycles but found weak effects on total mastication duration. This disparity could be attributed to differing sample demographics, sample sizes, food items, number of trials, and instrumentation method for studying mastication. Collectively, these findings can further delineate the distinction between healthy and disordered mastication. The results from this study should continue to challenge the understanding of how aging affects or does not affect mastication.

Funding Statement

This work was partially supported by the Veterans Affairs CDA-1 (RR&D 1IK1RX001628-01A1 to Kendrea Garand); the National Institute on Deafness and Other Communication Disorders of the National Institutes of Health (K24DC12801 to Bonnie-Martin Harris); the South Carolina Clinical & Translational Research Institute, with an academic home at the Medical University of South Carolina; the National Center for Advancing Translational Sciences (TL1 TR000061 to Kathleen Brady, Project PI: Kendrea Garand); and the American Speech-Language-Hearing Foundation (to Kendrea Garand).