How does the continued use of the mask affect the craniofacial region? A cross‐sectional study

Abstract Objective The aim was to compare the effects between pre‐pandemic mask‐free living versus pandemic‐related continuous mask use. Methods A retrospective study was carried out. This study was conducted with 542 face mask users. Assessments included presence, frequency and impact of headache, temporomandibular disorders, and quality of life (QoL). Results Continuous mask use had a large main effect on headache, temporomandibular pain, and QoL (p < .0001; d = 1.25), but this effect was nuanced by mask type. Participants who declared suffering from headache increased by 84% with cloth masks, and by 25% with FFP2 masks. Temporomandibular pain increased by 50% and by 39% when wearing surgical masks and FFP2, respectively (p < .06; d = .19). The mask type did not nuance the effect on headache impact (p > .05; d = .06). QoL decreased regardless of mask type (p < .05; d = .21), the decrease being 38% for surgical masks, and 31% for either cloth or FFP2 masks. Conclusions Continuous mask use, regardless of type, increased existence of headache, headache impact, temporomandibular pain, and reduced QoL.


F I G U R E 1 Flow chart of the study.
against the disease is necessary, CMU could have secondary repercussions in different health areas. In this regard, several studies have been carried out in health care professionals relating the use of facemasks and headaches. The most used facemasks are filtering face pieces (FPP2, N95, and KN95), as well as surgical facemasks. The relationship of facemask use with altered, dizziness, and headache has been demonstrated (Kyung et al., 2020). In fact, the "de novo" primary headache has been related to the impact of facemask use in the working, family, personal, and social spheres (Ramirez-Moreno et al., 2021), as well as with sleepiness, headaches, and psychological symptoms (Cigiloglu et al., 2021). However, other authors have observed that in health care professionals with preexisting headache, the pain increased when using facemask and was also related to symptoms, such as tachypnea, sleep disorders, and fatigue (Köseoglu Toksoy et al., 2021). Nevertheless, only health care professionals were included in these studies, thus no extrapolation to general population could be done. In addition, the relationship with quality of life (QoL) or with headache impact was not studied.
CMU can have an impact on the musculoskeletal system (Lim et al., 2006) and, specifically wearing this protective element may have myofascial effects on the craniofacial muscles. In this sense, CMU, as well as other health protective equipment, could create tensions and provoke or increase headache (Marfil Rivera et al., 2021), and as a consequence, produce a pain-related impact. On the other hand, previous studies have shown that a slight variation in the position of the tem-  Paolo et al., 2017;Reik & Hale, 1981). All this could have a global impact on peoples' QoL. To the best of our knowledge, there are no studies that assess the association of CMU with symptoms related to the TMJ.
Therefore, it is necessary to accurately establish consequences in the craniofacial sphere arising from CMU, not only in health professionals who wear CMU in their daily practice but in the general population,

Participants
Volunteers who participated in this study were over 18-year old and were wearing facemasks daily for the avoidance of COVID-19 during at least 2 h/day and had the ability to answer the questions and complete the questionnaires. Subjects with musculoskeletal injuries in the craniofacial region, institutionalized subjects, as well as subjects who wore masks for less than 2 h a day were excluded from the study.

Study design
A retrospective study was carried out during the months of February to March 2021 taking into account mandatory CMU due to the current pandemic. The study was conducted at the (blinded) and consisted of an online questionnaire which included sociodemographic characteristics, ad hoc questions, and specific evaluation instruments for each variable.
The study included an interview regarding aspects related to headache and its impact, TMJ pain and QoL. It was conducted according to Declaration of Helsinki and was recorded in ClinicalTrials.gov Identifier: NCT04727762.

Ethical considerations
The study was approved by the Human Research Ethics Committee of the (blinded) (UV-INV_ETICA-1517574) and followed the ethical principles according to the Declaration of Helsinki. Participants signed an informed consent guaranteeing confidentiality prior de starting the study.

Outcome measures
Sociodemographic characteristics were collected (age, gender, marital status, education, and occupation), as well as face mask type which participants used. In addition, the assessment included headache characteristics, TMJ discomfort and pain, impact of headache and QoL. All outcomes were assessed comparing current CMU against pre-pandemic MFL.

Headache impact
Measured by the Headache Impact Test-6 (HIT-6) (Kosinski et al., 2003;Ware, 1999), the HIT-6 was designed to provide a global measure of the adverse impact of headache. This questionnaire measures the adverse impact of headache on social functioning, role performance, vitality, cognitive functioning and psychological distress, and scores as follows: never (6 points), hardly ever (8 points), sometimes (10 points), very often (11 points), and always (13 points). A total of 49 or less points are considered "little-to-no impact," between 50 and 55 "moderate impact," between 56 and 59 "substantial impact," and 60 or more "severe impact." It has been shown to have a good internal consistency (Cronbach's alpha .89) and test-retest reliability (ICC ranging from 0.78 to 0.90) (Martin et al., 2004;Yang et al., 2011).

Temporomandibular discomfort and pain
The ad hoc questionnaire also included four questions about the existence of TMJ discomfort (awake bruxism, sleep bruxism, chewing discomfort, and TMJ pain) with a dichotomous response (yes, no).

Quality of life
Measured by Cantril's Ladder of Life scale (Cantril, 1965), participants were shown an image displaying a ladder numbered from zero to ten, where the upper part of the ladder represents the best possible life for the subject (10 points), and the lower part of the ladder represents the worst possible life (= 0 points). The question which was asked was: Where on the ladder do you feel that you are at the moment?
However, in our study we adapted it using two ladders. The question for one ladder was: In which step do you think you are on without using a mask? (the top step being 10 and the bottom step 0), and in the other, the question was: In which step do you think you are on using a mask? (the top step being 10 and the bottom step 0). The test-retest analyses showed acceptable agreement (Pearson's correlations between .58 and .70) in adolescents (Levin & Currie, 2014).

Statistical analysis
Sociodemographic variables of the participants were analyzed. The data was summarized using frequency counts, descriptive statistics, summary tables, and figures. Immediately after, Pearson's r for all study variables was calculated. Based on prior findings, it was expected for dependent variables to be significantly correlated. Accordingly, a repeated measures multivariate analysis of (co)variance, or RM-MANCOVA were applied, with IBM's SPSS 27.  , TMJ pain, headache intensity and QoL). Third, a significant p-value of the between-within interaction term would indicate that the effect of any within-subject factor (i.e., CMU) in the dependent variables will vary across the different between-subject conditions (i.e., mask type).
Lastly, because an RM-MANCOVA reports partial eta squared (partial η 2 ) as an indicator of effect size, any partial η 2 scores can be transformed into Cohen's d effect sizes to ease its interpretation.

RESULTS
The final sample consisted of 542 participants (Figure 1). No attrition was identified in the sample, and thus all participants were included in the analyses. Mean age of participants was 37.23 ± 14.98 years.

DISCUSSION
The main findings were that the CMU produced significant changes in headache, TMJ discomfort and pain, as well as in headache impact and QoL. In terms of mask type in CMU, it was noted that participants used surgical masks to a greater extent, followed by FFP2 and to a lesser extent, cloth masks. CMU affected to a greater or lesser extent the different variables, such as headache, headache impact, TMJ discomfort, and pain depending on the mask type, and all mask types affected QoL.
In addition, in the case of headache, onset was gradual with CMU, and the frequency mainly being at least one headache a week.
Headaches were of an oppressive type resembling a tension-type headache, although the specific type of headache was not collected.
Moreover, the intensity of the headache was mild and moderate, in a similar percentage, coincident with the symptoms of tension-type headache.
This study is in line with other authors, who assessed the impact of CMU on headache in health care professionals; however, our sample includes general population, with a greater sample than other studies (Cigiloglu et al., 2021;Köseoglu Toksoy et al., 2021;Ramirez-Moreno et al., 2021). It may be considered that the results obtained in this study could be taken into account in similar situations related with pandemic in the future, and thus adopt preventive measures and decrease the repercussion of CMU on QoL. With regard to the time of facemask use, previous studies have reported that headaches are most likely to appear in health care workers who wear N95-type masks for more than 4 h and had previously been headache sufferers (Lim et al., 2006).
The present study shows that these effects in the craniofacial sphere appear after CMU during at least 2 h a day.
Regarding the location of pain, this study details the concrete area of pain. In this regard, the pain location in our results was more focused on the frontal and facial region (anterior cranial region) followed by the occipital area, with mandibular disorders such as awake bruxism and sleep bruxism or chewing discomfort. In this sense, tension-type headache pain concentrates in the upper and frontal part, as well as the occipital area, while our results showed a pain concentration in the frontal and also facial ocular region. Therefore, although we have not evaluated the results by type of headache, the pain reported by participants both in the frontal area and in the occipital area is related with tension-type headache and with migraine, being both of them primary headaches. According to the results of the present study, headaches may be caused by the head straps which may create compression on the pericranial soft tissues (Arnold, 2018). This pressure could thus lead to an irritative effect on the underlying superficial sensory nerves (such as trigeminal or occipital nerve branches) which innervate face, head, and cervical region (Krymchantowski, 2010).
In terms of the TMJ pain, our results show significant differences on the VAS for CMU. To our best knowledge, there is no previous literature relating CMU with pain in this region. Orofacial pain can be related to TMJ continuous structures and mastication muscles (International Classification of Orofacial Pain, 2020). Accordingly, CMU may be related to facial pain, and/or ear lobe discomfort, due to tight-fitting facemasks. Traction forces from the mask and the straps may lead to local tissue damage and produce an irritative effect on the underlying superficial sensory nerves (Ong et al., 2020). In addition, being a foreign object and of recent daily use, it has been noted that people tend to remove it from the face by pushing the jaw forward ("Mask Jaw" and TMJ Discomfort [Internet]2023;Pilcher, 2020). This gesture could occur in an attempt to release the mask from the face. These aspects, although being mild, could affect daily life in the short or long term. Thus, taking into account the results of the present study, this biomechanical effect in TMJ may cause pain due to CMU.
Moreover, our results showed a correlation between TMJ pain and headache with CMU. Other authors linked TMJ pain and headache (Di Paolo et al., 2017;Reik & Hale, 1981). The present study reaffirms this relationship with CMU that could be derived from the myofascial tension produced by the strap and could relate both. In this regard, fascial restrictions in one part of the body can cause undue tension in another part, due to fascial continuity (Schleip, 2003). Therefore, it could be considered that this fascial relationship (Schleip, 2003) between craniofacial structures and CMU can have an impact on the fascia due to the mild but continuous stimulus causing the permanent viscoelastic deformation of fascia (Schleip, 2003). This effect should be considered by clinicians in the initial assessments of patients and may explain the possible alterations before proceeding to apply a clinical treatment, and therefore obtain better results. Therefore, the application of myofascial release-based techniques and similar techniques in headache (Ajimsha, 2011;Rezaeian et al., 2021) and in TMJ (Lecturer et al., 2016;Martins et al., 2016) could be taken into account by clinicians for the treatment of these CMU-related effects.
Myofascial clinicians believe that by restoring the length and health of restricted connective tissue, pressure can be mitigated on pain sensitive structures such as nerves and blood vessels (Ajimsha, 2011). In this regard, myofascial treatment on craniocervical muscles related to strap pressure in mask-wearers could be considered in future research.
In the present study, a specific questionnaire to evaluate the impact of headache on normal daily activities was used, and significant differences for headache impact were found. Considering that CMU is compulsory in work or social activities which usually last several hours, the straps could be pressuring the craniocervical muscles, thus producing myofascial pain and peripheral sensitization which could explain the impact of headaches in daily life. Headaches may influence the ability to concentrate at work (Monzani et al., 2016), and they may also affect social activities (Eskin et al., 2013). Although CMU is needed in order to reduce the impact of COVID-19 on everyday life, the influence of its use is affecting different aspects of people's life, and this should be taken into account by clinicians.
A novelty of the present study is that is has assessed QoL regarding mask use. The results showed that QoL is generally affected by CMU regardless of the mask type, and that it can be affected when using the mask 2 h or more. Taking into account that participants also reported an impact of headache, and that headaches have shown to affect QoL (Eskin et al., 2013) it is clear that CMU has an influence in daily life.
Moreover, our results have reported not only that with CMU headache and TMJ pain have a close relationship, but also and impact on activities of daily living and QoL.
Although all masks have an impact on the variables, it affects them differently depending on the mask type. Thus, cloth masks affect the onset of headache and headache intensity to a greater extent. This may be due to the fact that non-standardized materials transpire less than the approved types (surgical and FFP2), and because of lower quality gas exchange that could generate headaches. Other authors report that mask use involve decreased O 2 and increased CO 2 , although this refers to surgical facemasks (Kisielinski et al., 2021). In the present study, FFP2 masks affect headache, but to a lesser extent than cloth masks. On the other hand, surgical masks and FFP2 masks affect to a greater extent TMJ pain, probably because fastening is firmer so they exert greater myofascial tension for a tighter fit.
Regarding public health implications of this study, in times of pandemic, mask use is necessary, however, it seems plausible that, having established the reasons behind the increase in headache and TMJ pain, suitable physiotherapy or medicine-based solutions and treatments, exercises or corrective habits preventing mask use-related side effects can be approached. The repercussions of mask use are a public health concern and treatment specialists must bear in mind these findings.
Undoubtedly, COVID-19 has implied changes in daily life, different lifestyle has been adopted and several protection measures have been applied, among others, the regular use of EPP, provoking different symptoms. This relationship has been clearly studied in health care professionals, although it has not been studied in the general population. In this regard, Gurnani and Kaur (2021) suggested that it is a silent epidemic due to the increase of headaches. Thus, in line with Ong et al. (2021) there is an urgent need of addressing new designs and improve the existing options of EPP that, while complying with safety standards, also consider comfort and tolerance, including both health care professionals and general population.

Limitations and strengths
This study was carried out through an online questionnaire due to the pandemic to avoid travel and contact and to promote participants involvement for questionnaire completion. However, the process was not always completed by the subjects due to the amount of time required to answer. On the other hand, thanks to this tool it has been able to obtain a description of this problem, which is really an issue that requires attention and can explain symptoms that have increased with CMU. Future studies should consider using the Diagnostic Criteria for Temporomandibular Disorders (DC/TMD) (Schiffman et al., 2014) for TMD diagnosis and Oral Behavior Checklist (DC/TMD axis II) to evaluate bruxism more precisely. On the other hand, as strengths, it can be highlighted that this study focuses on general population and, for the first time, outcomes such as headache impact and QoL, location of pain and TMJ have been measured with valid tools. Thus, further studies could measure the same outcomes in health care professionals, in order to compare the results and therefore increase the knowledge, in professional or not professional areas, and adjust future treatments.