Masticatory Functionality in Post-Acute-COVID-Syndrome (PACS) Patients with and without Sarcopenia

: Musculoskeletal symptoms are common in both acute COVID-19 disease and post-acute sequelae (Post-Acute COVID Syndrome). The purpose of this study is to investigate whether there are reduced levels of masticatory function in patients with PACS (Post Acute COVID Syndrome) who suffer from sarcopenia, under the hypothesis that the latter may also involve the masticatory muscles. This study includes 23 patients hospitalized for COVID-19 between February 2020 and April 2021 and currently suffering from PACS. Among these PACS patients, 13/23 (56%) suffer from sarcopenia, 5/23 (22%) complain of asthenia but do not suffer from sarcopenia and the remaining 5/23 (22%) do not present muscle symptoms (non-asthenic non-sarcopenic). Oral health indices of all patients were collected. The masticatory strength was assessed with a gnathodynamometer based on piezoresistive sensors, and the masticatory effectiveness was measured by administering the “chewing gum mixing ability test” by having patients perform 20 masticatory cycles on a two-color chewing gum and analyzing the outcome through the ViewGum© software. Moreover, we gathered data with a hand grip test and gait speed test. The data collected in this study show that PACS sarcopenic patients have decreased masticatory effectiveness and strength compared to PACS asthenic non-sarcopenic patients and PACS non-asthenic non-sarcopenic patients.


Figure 1.
Integrative model of post-COVID symptoms in hospitalized patients showin Transition Phase (green) and Phases 1 (yellow), 2 (orange) and 3 (red) of post-COVID symp [11]. PACS has been described as an expression of a modified aging trajectory induce SARS-CoV-2 [12]. Aging, defined as the accumulation of unrepaired changes gene in different cells, tissues and organs, depends both on internal and external adapt mechanisms [13]. At the immunological level, aging is an interaction between the in immune system, mainly represented by an inflammation cascade [14], and the ada immune system, represented by T-lymphocytes [15]. The interaction between in aging and immunosenescence may underlie the pathogenesis of PACS. The accumul of senescent cells that acquire a secretory phenotype associated with senescence (S [16] has been described, and it is suggested this a phenotypic change is the resu cellular stress secondary to cellular homeostatic mechanisms compromised by S CoV-2. SASP cells release cytokines, chemokines, proteases, reactive metabolites, gr factors, non-coding nucleotides [17], thus effectively activating a chronic inflamm state.
Further, respiratory fatigue associated with PACS may also be due to respir muscle dysfunction, especially the diaphragm [35]. Therefore, it has been suggested skeletal muscle may be the most affected tissue by the effects of a severe COVI infection. Hence, it is hypothesized that sarcopenia in PACS patients can also affec masticatory muscles causing fatigue in chewing and possible masticatory distress.
Previous studies have highlighted a link between masticatory dysfunction sarcopenia. Yoshida et al. reported in 2021 that almost half of the elderly living in K Japan has oral hypofunction, defined as a disease not only influenced by aging bu by various factors related to diseases and disorders significantly related to sarcopenia "frailty" [36]. Kugimiya, Y. et al. in a study of more than 800 elderly (76.5 ± 8.3 y reported that sarcopenia is observed with a higher frequency in patients diagnosed oral hypofunction compared to those without; consequently, oral hypofunction ap to be significantly associated with sarcopenia [37]. However, there is currently no evidence in the literature regarding the involve of the stomatognathic system in PACS patients. We aim to measure the bite force PACS has been described as an expression of a modified aging trajectory induced by SARS-CoV-2 [12]. Aging, defined as the accumulation of unrepaired changes generated in different cells, tissues and organs, depends both on internal and external adaptation mechanisms [13]. At the immunological level, aging is an interaction between the innate immune system, mainly represented by an inflammation cascade [14], and the adaptive immune system, represented by T-lymphocytes [15]. The interaction between inflam-aging and immunosenescence may underlie the pathogenesis of PACS. The accumulation of senescent cells that acquire a secretory phenotype associated with senescence (SASP) [16] has been described, and it is suggested this a phenotypic change is the result of cellular stress secondary to cellular homeostatic mechanisms compromised by SARS-CoV-2. SASP cells release cytokines, chemokines, proteases, reactive metabolites, growth factors, noncoding nucleotides [17], thus effectively activating a chronic inflammatory state.
Further, respiratory fatigue associated with PACS may also be due to respiratory muscle dysfunction, especially the diaphragm [35]. Therefore, it has been suggested that skeletal muscle may be the most affected tissue by the effects of a severe COVID-19 infection. Hence, it is hypothesized that sarcopenia in PACS patients can also affect the masticatory muscles causing fatigue in chewing and possible masticatory distress.
Previous studies have highlighted a link between masticatory dysfunction and sarcopenia. Yoshida et al. reported in 2021 that almost half of the elderly living in Kyoto, Japan has oral hypofunction, defined as a disease not only influenced by aging but also by various factors related to diseases and disorders significantly related to sarcopenia and "frailty" [36]. Kugimiya, Y. et al. in a study of more than 800 elderly (76.5 ± 8.3 years) reported that sarcopenia is observed with a higher frequency in patients diagnosed with oral hypofunction compared to those without; consequently, oral hypofunction appears to be significantly associated with sarcopenia [37].
However, there is currently no evidence in the literature regarding the involvement of the stomatognathic system in PACS patients. We aim to measure the bite force and masticatory performance in PACS patients hospitalized at our center between February 2020 and April 2021.

Materials and Methods
We offered a dedicated odontoiatric consultancy to patients diagnosed with PACS attending a dedicated multidisciplinary clinic at Modena University. Patients were selected independently of gravity of PACS and presence of dental signs and symptoms.
Data obtained from medical screening visits of PACS patients included Depression Anxiety Stress Scale (DASS) [38], Body Mass Index (BMI) [39], "dominant hand grip test" (measurement of hand grip strength thanks to a digital dynamometer), "chair stand test" (seconds used for getting up and sitting down 5 times) and "gait speed test" (seconds employed for walking 5 m). The latter two tests are widely used in geriatrics as indicators of motility and frailty among the elderly [40,41].
Asthenia was detected using a predefined checklist of symptoms in which the patient is asked to identify presence and intensity (low, moderate or severe) of muscular symptoms. Sarcopenia was defined according to the European Working Group on Sarcopenia in Older People as low muscle strength, low muscle quantity or quality and low physical performance, adjusted for age and sex [42].
All patients enrolled in the study have PACS symptoms. In our paper, patients are divided into 3 groups: (1) PACS patients with sarcopenia (sarcopenic patients); (2) PACS patients who complain of muscle fatigue but do not fulfill the criteria for diagnosis of sarcopenia (asthenic non-sarcopenic patients); (3) PACS patients without sarcopenia and who do not complain of muscle fatigue (non-asthenic non-sarcopenic patients).

Short Medical History Interview
Patients were initially subjected to a short medical history associated with COVID-19, including hospitalization, persistence of PACS symptoms, possible presence of temporomandibular disorders and presence of parafunctions.

Anatomo-Functional Analysis
A palpatory analysis was performed, according to Slavicek [43], to assess the presence of pain in the head and neck muscles and TMJ (Temporo Mandibular Joint) dysfunctions. An extra-oral palpation of the shoulders, neck, atlanto-occipital region, sternocleidomastoid, homohyoid, TMJ in static and opening, posterior joint space, anterior temporal, median and posterior, superficial and digastric masseter was performed.
Intra-oral palpation of deep masseter, medial pterygoid, lateral pterygoid, mylohyoid and tongue was also performed.
The palpation of the TMJ was carried out both at a superficial and intra-articular level to assess the posterior joint space. Any clicks and squeaks heard during jaw opening movements were noted.
The mandibular limit movements of each patient were assessed with the aid of a ruler. Zero was positioned at the incisal edge between 1.1 and 2.1; the mm of maximum opening, right and left lateral movement and protrusion were measured. Maximum opening of >40 mm was considered normal. Laterality assessments were personalized (single patient comparison) according to the movement of the jaw in either direction. Protrusion was measured in mm without any value considered normal. All measurements considered the patients' overjet. Any sagittal axis deviations in the opening and closing route were recorded.

Intra-Oral Examination
An intra-oral physical examination was performed for each patient. Any missing teeth, prosthetic teeth (crowns on natural teeth or implants, veneers, bridges, pontic elements or teeth in resin belonging to removable partial prothesis [RPP]), decayed teeth, filled teeth, teeth with non-carious cervical lesion (NCCL), heavily abraded teeth, the level of oral hygiene (excellent, good or poor) and the state of the mucous membranes (presence inflammation, erythematous or hyperplastic areas) were noted. Pockets or pathologies of the periodontium were assessed with periodontal probing. Probing <3.5 mm was considered physiological [44].

Bite Force Measurement
We measured bite force with the FlexiForce ® A201 piezoresistive force transducer (Tekscan, Boston, MA, USA), see Figure 2a. The transducer has a load range up to 440 N, which is suitable for use with adults, and a sensitivity of 0.01 V/N [45]. The force transducer is inserted into a homemade "sandwich structure," consisting of two 8 × 1 mm discs, made of thermoformed plastic material covered with an aluminum sheet, see Figure 2b. Discs are placed above and below the FlexiForce ® force sensor, held in place by a layer of doublesided adhesive tape, according to the manufacturer's recommendation in the FlexiForce ® user manual [46]. The function of the plastic disc is to ensure that all lines of force between the upper and lower teeth are conveyed through that area. Because the sensor does not tolerate heat and sterilization [45], the FlexiForce ® strip is placed in a disposable plastic shield, used in dentistry for digital intra-oral radiographs. Adequate expression of force is maintained by the maximum thickness of 4 mm, enabling muscle fiber movement at an optimal length [47,48]. Calibration of the sensor was based on data in the literature [45].
which is suitable for use with adults, and a sensitivity of 0.01 V/N [45]. The force transducer is inserted into a homemade "sandwich structure," consisting of two 8 × 1 mm discs, made of thermoformed plastic material covered with an aluminum sheet, see Figure  2b. Discs are placed above and below the FlexiForce ® force sensor, held in place by a layer of double-sided adhesive tape, according to the manufacturer's recommendation in the FlexiForce ® user manual [46]. The function of the plastic disc is to ensure that all lines of force between the upper and lower teeth are conveyed through that area. Because the sensor does not tolerate heat and sterilization [45], the FlexiForce ® strip is placed in a disposable plastic shield, used in dentistry for digital intra-oral radiographs. Adequate expression of force is maintained by the maximum thickness of 4 mm, enabling muscle fiber movement at an optimal length [47,48]. Calibration of the sensor was based on data in the literature [45].
The two FlexiForce ® sensors were connected to an electrical circuit with a voltage of 5 V, powered by a lithium battery. The circuit consists of an "Arduino Uno" controller, to which an LCD screen is connected and displays pressure data. This corresponds to the force expressed in Newtons (N) exerted by the patient during the chewing test. (Figure 3) During the design phase of the device, an update frequency of 1.5 Hz for the chewing value was established, and the numerical precision was set to a single decimal digit without approximation. A threshold of 20 N was determined to return a null value [45] and, given the instrumental linear response, measurable and admissible values without losing generality range between 20-320 N.
The sensors were bitten by the patients between the first molars, if present, or between the most posterior teeth. Measurements were taken in the rest position and the maximal chewing force, which was recorded three times.  The two FlexiForce ® sensors were connected to an electrical circuit with a voltage of 5 V, powered by a lithium battery. The circuit consists of an "Arduino Uno" controller, to which an LCD screen is connected and displays pressure data. This corresponds to the force expressed in Newtons (N) exerted by the patient during the chewing test ( Figure 3).

Chewing Gum Mixing Ability Test
Garfield ® 30 mm long strips of "blue raspberry" (blue) and "all fruits" (red) flavor gum were manually stuck together and used for the chewing gum test. Patients were asked to chew the two strips of gum for 20 mastication cycles [49][50][51] in a seated upright position. The chewed sample was spat in a plastic bag and temporarily stored in a During the design phase of the device, an update frequency of 1.5 Hz for the chewing value was established, and the numerical precision was set to a single decimal digit without approximation. A threshold of 20 N was determined to return a null value [45] and, given the instrumental linear response, measurable and admissible values without losing generality range between 20-320 N.
The sensors were bitten by the patients between the first molars, if present, or between the most posterior teeth. Measurements were taken in the rest position and the maximal chewing force, which was recorded three times.

Chewing Gum Mixing Ability Test
Garfield ® 30 mm long strips of "blue raspberry" (blue) and "all fruits" (red) flavor gum were manually stuck together and used for the chewing gum test. Patients were asked to chew the two strips of gum for 20 mastication cycles [49][50][51] in a seated upright position. The chewed sample was spat in a plastic bag and temporarily stored in a refrigerator (16 • C).
All gum samples were prepared for analysis by flattening them to a 1 mm thick disk. Then they were photographed from both sides with a Nikon reflex camera (300 dpi resolution) at a standard distance of 10 cm in the same room and with the same lighting conditions [52]. Digitalization of the chewed samples has always been performed within a few hours of the chewing test. Figure 4 shows two examples of chewed gum. Gnathodynamometer's electronics.

Chewing Gum Mixing Ability Test
Garfield ® 30 mm long strips of "blue raspberry" (blue) and "all fruits" (red) flavor gum were manually stuck together and used for the chewing gum test. Patients were asked to chew the two strips of gum for 20 mastication cycles [49][50][51] in a seated upright position. The chewed sample was spat in a plastic bag and temporarily stored in a refrigerator (16 °C).
All gum samples were prepared for analysis by flattening them to a 1 mm thick disk. Then they were photographed from both sides with a Nikon reflex camera (300 dpi resolution) at a standard distance of 10 cm in the same room and with the same lighting conditions [52]. Digitalization of the chewed samples has always been performed within a few hours of the chewing test. Figure 4 shows two examples of chewed gum.  We performed an opto-electrical analysis of the gum photographs to evaluate the degree of color mixing with the ViewGum© software [53] (Figure 5). Variance of hue (VOH), an indication of the logarithmic association with the number of chewing cycles, was used to assess the gum samples; a high VOH indicates poorly mixed colors from poor chewing, and a low VOH indicates well mixed colors from adequate chewing [52]. The results were displayed as "Ch 0 St. Dev" in the ViewGum© software [53]. We performed an opto-electrical analysis of the gum photographs to evaluate the degree of color mixing with the ViewGum© software [53] (Figure 5). Variance of hue (VOH), an indication of the logarithmic association with the number of chewing cycles, was used to assess the gum samples; a high VOH indicates poorly mixed colors from poor chewing, and a low VOH indicates well mixed colors from adequate chewing [52]. The results were displayed as "Ch 0 St. Dev" in the ViewGum© software [53].

Statistical Analysis
Statistical analysis was performed using STATA ® software version 17 (StataCorp. 2021. Stata Statistical Software: Release 17. College Station, TX, USA: StataCorp LLC.). The KolmogorovSmirnov test was used to evaluate the normality of the data, and Levene tests were used to assess the homogeneity of variances. We used the parametric tests when assuming the normality of the data distribution and homogeneity of variances. Descriptive statistics were presented for baseline demographic clinical characteristics for the entire group. Continuous variables were presented as mean, standard deviation (SD), minimum (min) and maximum (max) and were compared between subgroups using ANOVA test. A p < 0.05 was considered statistically significant.

Statistical Analysis
Statistical analysis was performed using STATA ® software version 17 (StataCorp. 2021. Stata Statistical Software: Release 17. College Station, TX, USA: StataCorp LLC.). The KolmogorovSmirnov test was used to evaluate the normality of the data, and Levene tests were used to assess the homogeneity of variances. We used the parametric tests when assuming the normality of the data distribution and homogeneity of variances. Descriptive statistics were presented for baseline demographic clinical characteristics for the entire group. Continuous variables were presented as mean, standard deviation (SD), minimum (min) and maximum (max) and were compared between subgroups using ANOVA test. A p < 0.05 was considered statistically significant.
Anxiety (DASS A), depression (DASS D) and stress (DASS S) indices in most patients were within normal ranges [38] (Table 1). Mean patient BMI was 29.5, with value ranges between 41.7 and 21.6. Interestingly, there was no relationship found between BMI and chewing efficacy/efficiency. There was also no relevant difference in BMI between sarcopenic and non-sarcopenic patients. The dominant hand grip test mean values were
Anxiety (DASS A), depression (DASS D) and stress (DASS S) indices in most patients were within normal ranges [38] (Table 1). Mean patient BMI was 29.5, with value ranges between 41.7 and 21.6. Interestingly, there was no relationship found between BMI and chewing efficacy/efficiency. There was also no relevant difference in BMI between sarcopenic and non-sarcopenic patients. The dominant hand grip test mean values were lower in sarcopenic subjects compared to non-asthenic non-sarcopenic ones ( Table 2).
Along with asthenic patients, sarcopenic patients had slower and more strenuous movements, as evidenced in lower gait speed test values compared to non-asthenic nonsarcopenic patients p = 0.001, see Figure 6 and Table 2. Along with asthenic patients, sarcopenic patients had slower and more strenuous movements, as evidenced in lower gait speed test values compared to non-asthenic nonsarcopenic patients p = 0.001, see Figure 6 and Table 2.

Short Medical History Interview
Only 9/23 (39%) were admitted to the Intensive Care Unit (ICU). All ICU admitted patients had post-intensive care syndrome (PICS), reporting general motor difficulties within the first few weeks after discharge [54,55].
Parafunctions were recorded in 8/23 (35%) patients, and one of them reported that nocturnal bruxism began right after discharge, when post-COVID symptoms arose. The Figure 6. Walking time of the three patient groups: sarcopenic (orange), asthenic non-sarcopenic (yellow) and non-asthenic non-sarcopenic (green).

Short Medical History Interview
Only 9/23 (39%) were admitted to the Intensive Care Unit (ICU). All ICU admitted patients had post-intensive care syndrome (PICS), reporting general motor difficulties within the first few weeks after discharge [54,55].
Parafunctions were recorded in 8/23 (35%) patients, and one of them reported that nocturnal bruxism began right after discharge, when post-COVID symptoms arose. The reason for the onset cannot be precisely defined, but it can be assumed that it is caused by anxiety and stress-in fact, this patient had very high DASS values. Table 1 reports results about the Depression, Anxiety, and Stress Scale (DASS) questionnaire.
Twenty-three percent of patients reported TMDs (Temporo Mandibular Disorders) before admission, and all of them belong to sarcopenic or asthenic groups. Among the 13 sarcopenic patients, 3 reported spontaneous or chewing pain in the masseter, which appeared shortly after discharge. Two of those offered additional information, specifying motor difficulties associated with the opening and closure of the jaw.

Anatomo-Functional Analysis
Pain on palpation was recorded according to the muscle location; sternocleidomastoid/occipital/trapexious in 26% (6/23 patients), the mid-anterior temporal in 22% (5/23 patients), mylohyoid in 13% (3/23 patients) and lateral pterygoid in 9% (2/23 patients). No particular areas of muscle tension or inflammation were detected. No patients reported muscle pain during the bite force measurement, so the pain on palpation reported by the subjects is not so severe that it could significantly affect the bite force measurement.
During mandibular movements, noises from the TMJ (Temporo Mandibular Joint) were detected in 11/23 patients (48%), and pain during the jaw opening and closing was recorded in 3/23 (13%). Mandibular opening was normal in 20/23 (87%) patients. Lateral movements were symmetrical, and protrusion was perceivable for most patients; only one patient (sarcopenic) had difficult control of all mandibular movements. There were no differences among the patient groups revealed in terms of any anatomo-functional analysis.

Intra-Oral Examination
The intra-oral dental examination revealed various critical issues. Oral mucosa showed a normal trophism. Marginal gingivitis was found in 6/23 (26%) patients characterized by the presence of plaque and calculus. Almost half of all patients (n = 11/23; 47.8%) had a poor level of oral hygiene, although periodontal probes were non-physiological in only 4/23 (17%) patients. Table 1 outlines the quantitative measurements from the oral investigations. The overall mean DMFT (Decayed Missing Filled Teeth) was 12.5 ± 7.1. According to study groups, sarcopenic patients displayed a worse overall dental health compared to asthenic non sarcopenic and non-asthenic non-sarcopenic patients.
Comparing the index of each subject, DMFT was higher in sarcopenic patients; no correlation between NCCL and symptoms of sarcopenia or asthenia in PACS patients was found.

Bite Force Mesurament
According to patient groups, bite force was lowest among sarcopenic patients and highest among the non-asthenic non-sarcopenic patients (Figure 7 and Table 2). In particular, sarcopenic patients have an average decreased bite force of 125.8 N compared to nonasthenic non-sarcopenic subjects and a decreased bite force of 86.1 N compared to asthenic non-sarcopenic subjects. Figure 7 shows the variations in bite force compared to dominant hand force. The difference in bite force among the three groups was much more evident than the hand force. We have registered a maximum bite force value of 332.8 N, while with the hand grip test, the maximum value measured was 47.2 N.
highest among the non-asthenic non-sarcopenic patients (Figure 7 and Table 2). In particular, sarcopenic patients have an average decreased bite force of 125.8 N compared to non-asthenic non-sarcopenic subjects and a decreased bite force of 86.1 N compared to asthenic non-sarcopenic subjects. Figure 7 shows the variations in bite force compared to dominant hand force. The difference in bite force among the three groups was much more evident than the hand force. We have registered a maximum bite force value of 332.8 N, while with the hand grip test, the maximum value measured was 47.2 N.

Chewing Gum Mixing Ability Test
The VOH ranged between 0.127 and 0.678. The highest values (inefficient chewing) were observed in sarcopenic patients, compared to non-asthenic non-sarcopenic and asthenic non-sarcopenic subjects ( Figure 8 and Table 2). Sarcopenic patients showed an average VOH of 0.403; non-asthenic non-sarcopenic patients showed an average VOH value of 0.22. This difference is statistically significant.

Chewing Gum Mixing Ability Test
The VOH ranged between 0.127 and 0.678. The highest values (inefficient chewing) were observed in sarcopenic patients, compared to non-asthenic non-sarcopenic and asthenic non-sarcopenic subjects ( Figure 8 and Table 2). Sarcopenic patients showed an average VOH of 0.403; non-asthenic non-sarcopenic patients showed an average VOH value of 0.22. This difference is statistically significant. We also compared the VOH with the DMFT and the number of teeth in the arch (prosthetic or natural). Figures 9 and 10 demonstrate how oral health, especially of the teeth, was correlated with patients' masticatory performance. We also compared the VOH with the DMFT and the number of teeth in the arch (prosthetic or natural). Figures 9 and 10 demonstrate how oral health, especially of the teeth, was correlated with patients' masticatory performance. We also compared the VOH with the DMFT and the number of teeth in the arch (prosthetic or natural). Figures 9 and 10 demonstrate how oral health, especially of the teeth, was correlated with patients' masticatory performance. Figure 9. Comparison between VOH (in blue) and the number of prosthetic/natural teeth present in the arches (in orange). As can be seen from the graph, patients with fewer teeth tend to have a higher VOH score. Figure 9. Comparison between VOH (in blue) and the number of prosthetic/natural teeth present in the arches (in orange). As can be seen from the graph, patients with fewer teeth tend to have a higher VOH score.

Discussion
This research includes both intra-oral and extra-oral physical examination. This choice is motivated by the need to observe a variety of possible effects of PACS or COVID-19 in the areas of dental interest (teeth, mucous membranes and periodontium).

Short Medical History Interview
Stress, anxiety and emotional factors can create parafunctional problems, such as nocturnal grinding or locking, or exacerbate those already present [56,57], and it is important to consider psychological factors when investigating dysfunctional problems.
The severity of COVID-19 affects the symptoms and incidence of PACS [12]. With the anamnestic interview, the patients who were admitted to intensive care unit reported the difficulties encountered after discharge. It is, therefore, evident that post-intensive care syndrome (PISC) can affect the stomatognathic system and can also leave chewing

Discussion
This research includes both intra-oral and extra-oral physical examination. This choice is motivated by the need to observe a variety of possible effects of PACS or COVID-19 in the areas of dental interest (teeth, mucous membranes and periodontium).

Short Medical History Interview
Stress, anxiety and emotional factors can create parafunctional problems, such as nocturnal grinding or locking, or exacerbate those already present [56,57], and it is important to consider psychological factors when investigating dysfunctional problems.
The severity of COVID-19 affects the symptoms and incidence of PACS [12]. With the anamnestic interview, the patients who were admitted to intensive care unit reported the difficulties encountered after discharge. It is, therefore, evident that post-intensive care syndrome (PISC) can affect the stomatognathic system and can also leave chewing problems.

Anatomo-Functional Analysis
Some patients responded positively to muscle palpation, indicating specific areas of pain. In many of them, dysfunctional signs and symptoms were found, often mild. In general, it can be said that the TMJ does not perform its function perfectly in all subjects. It is not known exactly the reason behind the slight dysfunctions highlighted in these PACS subjects because there is no data of the anatomo-functional analysis before the COVID-19 infection. It can be hypothesized that the pain in the cervico-facial muscles found post-COVID may be part of the musculoskeletal symptoms characteristic of PACS; nevertheless, further studies are needed to confirm this hypothesis.

Intra-Oral Examination
The surveys did not reveal periodontal problems in most patients. The only nonphysiological probes (>3 mm) were observed in those patients with a poor level of oral hygiene and were attributable to gingival inflammation due to tartar and plaque. No cases of obvious inflammatory gingival problems have been found, so it can be said that the systemic inflammation underlying PACS does not affect oral soft tissues.
Third molars were not taken into consideration, thus reducing the maximum DMFT value to 28. The mean DMFT was 12.5 ± 7.1, hence the oral health status of the PACS subjects under examination is worse than the values found in the literature [58]. The reason may be that the PACS patient shifted attention to more important health problems-even hospitalization did not help to maintain proper oral hygiene. Many of these patients had to wear an oxygen insufflation mask for some time and were intubated [59]. Most patients reported that they did not go to the dentist prior to the COVID-19 infection.
The NCCL results are in line with a 2020 meta-analysis [60]. Many studies were not able to confirm a positive association between occlusal loading and abfraction. The literature suggests that dentin demineralization promotes NCCL formation from an early stage, while occlusal stress is an etiological factor contributing to the progression of these lesions [61].

Bite Force Measurement
The FlexiForce ® device has already been used in the related literature [62,63]. When inserting a device between the first or second molar, the mouth opens no more than 2-3 mm interincisal distance. This means that the condyles remain almost centered in the temporal fossa, i.e., in a centric position.
During the measurement, it was difficult to ensure that the sensor remained correctly interposed between the cusps of the teeth. The occlusal table is not as flat as the sensor turns out to be. The thermoplastic material of the discs, which is elastic, helps to overcome this problem. The aluminum sheet allows the correct positioning of the cusps with respect to the sensor, but it can also represent a disadvantage; if during the first detection the thermo-molded disc is moved outside the sensitive area of the Flexi-Force ® , the subsequent measurements are invalid. To address this problem, when the aluminum housing undergoes a clear plastic deformation, it is replaced.
The measurement takes place simultaneously on the right and left side, thus allowing one to quantify any masticatory asymmetries. However, for the purposes of the study, the average value of bite force between the right and the left was considered of most interest.

Chewing Gum Mixing Ability Test
The most important predictors of chewing efficiency are the number of pairs of occluding teeth, the bite force, the flow of saliva, prosthetic reconstructions, the strength and coordination of the tongue and cheeks, as well as age and sex [64,65]. Cognitive status and intra-oral sensitivity are also associated with chewing function [52]. This study only considers age, number of teeth and bite force.
The two-color chewing gum test is documented as a simple and effective test that can be used in the clinical setting [66]. The literature recommends the chewing gum mixing test to evaluate interindividual differences in chewing efficiency in clinical and research settings, in both prosthetic and non-prosthetic patients [67]. The simplicity of the optoelectronic assessment could help establish widespread screening for masticatory deficiencies. Furthermore, application in geriatrics or special care could help visualize oral-functionality or dental comorbidities.
From the data obtained through Viewgum©, it is evident that sarcopenic patients have a lower degree of masticatory performance than those without muscle symptoms (non-asthenic non-sarcopenic patients). This may be due to both decreased muscle function, caused by PACS, but also an increased DMFT. Comparisons of the VOH against the DMFT ( Figure 10) or the number of teeth ( Figure 9) highlight that chewing efficiency depends on the state of the oral health. Since it can be difficult to increase the muscular performance of sarcopenic PACS patients, it is advisable to improve the state of oral health and to rehabilitate missing teeth.

Limits of the Study
The lack of data on the chewing performance of patients before COVID-19 infection and the small number of subjects prevent proving that PACS was the actual cause of the decreased chewing performance. Moreover, this study does not allow us to detect improvement or deterioration in muscle performance over time.
We do not have the possibility to do an X-ray examination. For this reason, we only conducted an intra-oral examination that does not allow us to collect data about interproximal caries, periapical lesions and root fractures.
In this study, we used Garfield ® chewing gums. We remark that these chewing gums are not the same used and validated in the previous studies. Validated chewing gums (either Hubba Bubba ® or HueCheck ® ) were not readily available in our country at the moment of the investigation. We selected Garfield ® chewing gums because they are the most similar to Hubba Bubba ® .
We remark that bite force is different from masticatory force because the clenching movement of the mouth is different from the chewing movement. For this reason, the study cannot affirm the correlation between PACS and masticatory force.

Conclusions
In conclusion, the study showed that PACS people with sarcopenia have an average bite force of 122.4 Newton (N). This value is 86.1 N lower than asthenic non-sarcopenic patients (average bite force of 208.5 N) and 125.8 N lower than non-asthenic non-sarcopenic patients (average bite force of 248.2 N), As regards chewing efficiency, sarcopenic patients showed an average VOH increase of 0.18 compared to non-asthenic non-sarcopenic ones. Patients who complained only of asthenia (asthenic non-sarcopenic) were found to have lower values of bite force and masticatory efficacy than those who did not have muscular symptoms (non-asthenic non-sarcopenic) but higher values than those who suffered from sarcopenia (sarcopenic).
The piezoresistive sensor gnathodynamometer proved to be a valid bite force measurement tool. This tool can be a good alternative to other motor tests used to evaluate muscle effectiveness (such as the dominant hand grip test). Further studies on larger groups of subjects will be needed to validate their clinical use.
Oral health in most PACS patients appears to be compromised; it is, therefore, advisable to direct these patients towards a multi-disciplinary-rehabilitation path, addressing dental issues as well as all functional problems already present or occurring in the posthospitalization.  Institutional Review Board Statement: All subjects gave informed consent for inclusion before participating in the study. This study was conducted in accordance with the Declaration of Helsinki, and the protocol was approved by the ethic committee of "Area Vasta Emilia Nord" with the project identification code number 396/2020.