The link between sleep bruxism and oxidative stress based on a polysomnographic study
Oxygen is essential for the survival of aerobic organisms. However, as stated by Paracelsus ca. 500 years ago, the dose is what makes the poison. An abundance of O2 can result in the production of reactive oxygen species (ROS), which, beyond their natural physiological roles, can also induce adverse effects . In line with this concept, all living organisms that rely on respiration are continually exposed to the detrimental outcomes arising from the various transformations of oxygen . Oxidative stress results from a discrepancy between the production and accumulation of ROS in cells and tissues, and the ability to efficiently eliminate these reactive substances . However, cells have developed special repair procedures after exposure to ROS to regulate the oxidant-antioxidant balance . The direct ROS measurement in cells is difficult due to its short half-live. Therefore, to establish the antioxidant status, several products of oxidative stress are measured including total antioxidant status (TAS), thiobarbituric acid-reacting substances TBARS and advanced protein products (AOPP). TAS is used to obtain general antioxidant status of the body. Insufficent levels of TAS suggest expanded vulnerability to oxidative damage . TBARS is used to measure lipid peroxidation . AOPP is an innovative oxidative stress biomarker taking part in atherosclerosis development . There is impressive evidence that ROS are engaged with the pathogenesis of different human diseases, including pain-related temporomandibular disorders and sleep related disorders and behaviors such as sleep deprivation , obstructive sleep apnea (OSA) and possibly sleep bruxism (SB). Sleep bruxism is currently defined as “masticatory muscle activity during sleep that is characterised as rhythmic (phasic) or non-rhythmic (tonic) and is not a movement disorder or a sleep disorder in otherwise healthy individuals” that is characterized by a heterogeneous etiology and an inadequately elucidated pathophysiology . The perspective on sleep bruxism (SB) has evolved from viewing it as merely a pathological condition to understanding its role as potentially physiological or even protective . Consequently, SB should not be simply dismissed as a harmful habit of teeth grinding leading to tooth wear or other forms of oral structures damage , . The contemporary definition of bruxism, initially introduced in 2013 and later refined by the international consensus on bruxism in 2018 , describes SB as either rhythmic (phasic) or non-rhythmic (tonic) activity of the masticatory muscles during sleep. This definition clarifies that SB is not indicative of a movement or sleep disorder in individuals who are otherwise healthy . Clinical manifestations of SB are recognized in the third edition of the International Classification of Sleep Disorders, highlighting the occurrence of regular or frequent episodes of bruxism during sleep, alongside evidence of unusual dental wear, or experiences of pain or fatigue in the jaw muscles . Previous investigations into the etiological factors of sleep bruxism have identified dozens relatively well-understood risk contributors, including, but not limited to, emotional stress , tobacco use, high alcohol intake , obstructive sleep apnea , and anxiety disorders . There some new emerging risk factors that are taken into account, among which smartphone overuse , dietary fiber intake and coffee consumption are worth mentioning. In the systematic review examining the correlation between sleep bruxism and systemic chronic inflammation, there have been found data confirming the foregoing premise, although the available data are limited . A recent case-control study has indicated however that the correlation between inflammatory markers and the severity of sleep bruxism is not linear . There still remains a deficiency in the evidence required to establish a causal relationship. Given the significant prevalence of sleep bruxism and the potential for oxidative stress to diminish healthy life expectancy , we have performed a case-control study to further explore the link between oxidative stress and sleep bruxism. 

The aim of the study was to assess the relationship between oxidative stress markers and sleep bruxism using polysomnographic assessment in attempt to get better insight to this association. 

General characteristics of the performed study This was prospective observational study of 80 adults. Patients were admitted to the Sleep Laboratory in Department of Internal Medicine and Occupational Diseases, Hypertension and Clinical Oncology at Wroclaw Medical University in Poland in order to undergo polysomnographic assessment. The patients were admitted to the Sleep Laboratory by the dentists due to sleep bruxism suspicion. Eligibility criteria The inclusion criteria were age over 18 years, written informed consent to polysomnographic examination, sleep bruxism suspicion. The exclusion criteria were neurological disorders, neuropathic pain, active inflammation, confirmed active malignancy, severe cardiac and respiratory insufficiency, treatments affecting muscle function and sleep structure, severe mental disorders, cognitive disability, and lack of compliance during the study. The study was approved by the Ethics Committee at Wroclaw Medical University (consent no. ID KB-369/2022). All the patients signed voluntary written informed consent before the study. Polysomnography and sleep bruxism assessment Polysomnography All the included patients ( n = 80) underwent a single-night full polysomnography (PSG) examination using NoxA1 (NOX Medical, Reykjavik, Iceland) device. The examination was performed according to the patient’s natural circadian rhythm between 22:00 and 6:00. Electrodes were placed as indicated by guidelines set out by the American Academy of Sleep Medicine (AASM) . Fasting venous blood samples were obtained into polyethylene terephthalate (PET) plastic tubes (Becton, Dickinson and Company; Franklin Lakes, NJ, USA), with dipotassium ethylenediaminetetraacetic acid (K2EDTA) and blood samples were stored at − 70 °C until subsequent analyses use. Blood samples were analyzed at the Main Laboratory of Wroclaw Medical University. Laboratory tests were performed according to the standard laboratory protocols of Wroclaw University Teaching Hospital. Audio-video recordings, along with electrocardiographic, electroencephalographic, electrooculographic and electromyographic were included in the examination, as well as body position detection, thoracic and abdominal breathing activity. A WristOx2 3150 pulse oximeter (Nonin Medical Inc., Plymouth, MN, USA) was used to measure blood saturation (SpO2%), pulse and plethysmography data. In the examination sleep bruxism parameters were gathered together with respiratory and sleep parameters. As stated in American Academy of Sleep Medicine (AASM) standard criteria , sleep parameters were obtained and classified as follows: non-REM 1 sleep stage (N1), non-REM 2 sleep stage (N2), non-REM 3 sleep stage (N3), REM sleep stage, arousal index (ArI), sleep latency (SL), wake after sleep onset (WASO), sleep efficiency (SE), apnea-hypopnea index (AHI), oxygen desaturation index (ODI), and snoring. Sleep bruxism Sleep bruxism parameters were obtained as follows: bruxism episode index (BEI), phasic bruxism, tonic bruxism, and mixed bruxism. Tonic episode was categorized as constant burst episode lasting over 2s. Phasic episode was categorized as episode including 3 or more bursts lasting over 2s. Mixed episode was categorized when episode shows the characteristics of both tonic and phasic episodes. The definition of sleep bruxism episode according to the AASM guidelines is the rhythmic movement of masseter muscles that occurs at least 3s after previous muscle movement and electromyography (EMG) activity must be at least twice the amplitude of the background EMG. Bruxism episode index (BEI) is measured by counting number of bruxism episodes per hour of sleep. Three phenotypes of bruxism were distinguished: phasic, tonic, and mixed bruxism. Sleep bruxism intensity was categorized by the number of bruxism episodes per hour of sleep (BEI). Irrelevant SB refers to BEI < 2, mild / moderate to BEI 2–4 and severe to BEI > 4 17,29 . Blood sampling and ELISA Venous blood samples were obtained from the ulnar vein after twelve hours of fasting at 7:00 a.m. Fasting venous blood samples were obtained into polyethylene terephthalate (PET) plastic tubes (Becton, Dickinson and Company; Franklin Lakes, NJ, USA), with K2EDTA. Blood samples were stored at − 70 °C until subsequent analyses use. Blood samples were analyzed at the Main Laboratory of Wroclaw Medical University. Laboratory tests were performed as indicated by the standard laboratory protocols of Wroclaw University Teaching Hospital. The concentration of 8-isoprostane was determined in serum by ELISA method with using the Human 8-isoprostane BT LAB Kit (Cat. No.: E6776 Hu, Bioassay Technology Laboratory, China). The determination was conducted according to the manufacturer’s instructions. 8-isoprostane F2-α from the samples (added in duplicate into a 96-well plate) or standard solutions (0–640 ng/L) was bounded to human 8-isoprostane F2-α antibody immobilized to the wells. This complex was detected by addition of streptavidin–horseradish peroxidase (HRP) solution into all wells. After washing away unbound antibodies, the substrate Solution A and substrate Solution B in a 1:1 ratio to each well were added. Lastly, the stop solution was added into each well, and the absorbance of each well was measured at 450 nm by using a Multiskan GO microplate reader (Thermo Fisher Scientific, Finland). The human 8-isoprostane F2-α concentration was calculated based on the standard curve. Total antioxidant capacity was measured in serum (in duplicate) with using of Antioxidant Assay Kit (Cat. No.: 709001, Cayman Chemicals, USA). The assay is based on the ability of antioxidant included in the sample to inhibit the oxidation of 2,2’-azino-di-[3-ethylbenzthiazoline sulphonate] by metmyoglobin. Under the reaction condition, the antioxidant causes the reduction of the maximum of the absorbance at 750 nm proportional to their concentration. The capacity of the antioxidants in the sample to prevent oxidation of above-mentioned substrate was compared with that of Trolox, a water-soluble tocopherol analogue, and was quantified as millimolar Trolox equivalents. measurement was performed using a Multiskan GO microplate reader (Thermo Fisher Scientific, Finland). The intensity of lipid peroxidation process was assessed by measuring malondialdehyde (MDA) concentration in serum, under acidic conditions and high temperatures. The MDA reacted with thiobarbituric acid forming a colour adducts (thiobarbituric acid reactive substances, TBARS). Products of the reaction were measured at λ = 535 nm. The amount of MDA was calculated using an extinction coefficient (0.156 µmol-1 x l x cm-1). AOPP concentration was determined in serum by spectrophotometric method, based on the reaction of AOPP with potassium iodide. The absorbance of samples was measured at λ = 340 nm. The results of determination were expressed in micromoles per liter of chloramine T as equivalents. Statistical analysis The statistical analysis was performed based on the statistical program “Dell Statistica 13” (Dell Inc.). Arithmetic means (X) and standard deviations (SD) were calculated for quantitative variables. The distribution of variables was checked using the Lilliefors and W-Shapiro-Wilk tests. In the case of quantitative independent variables with a normal distribution, the t test was used for further statistical analysis. In the case of variables with a non-normal distribution, the Mann-Whitney U test was used. Optimal cut-off points for comparative analyzes were estimated based on ROC curves. Results at the p < 0.05 level were considered statistically significant. The study group included 80 patients. Group size was determined using a sample size calculator. The selection conditions were as follows: population size 2,8 million, fraction size 0.25, maximum error 10%, confidence level 95%. The required minimum size of the study group was 73. 

This was prospective observational study of 80 adults. Patients were admitted to the Sleep Laboratory in Department of Internal Medicine and Occupational Diseases, Hypertension and Clinical Oncology at Wroclaw Medical University in Poland in order to undergo polysomnographic assessment. The patients were admitted to the Sleep Laboratory by the dentists due to sleep bruxism suspicion. 

The inclusion criteria were age over 18 years, written informed consent to polysomnographic examination, sleep bruxism suspicion. The exclusion criteria were neurological disorders, neuropathic pain, active inflammation, confirmed active malignancy, severe cardiac and respiratory insufficiency, treatments affecting muscle function and sleep structure, severe mental disorders, cognitive disability, and lack of compliance during the study. The study was approved by the Ethics Committee at Wroclaw Medical University (consent no. ID KB-369/2022). All the patients signed voluntary written informed consent before the study. 

Polysomnography All the included patients ( n = 80) underwent a single-night full polysomnography (PSG) examination using NoxA1 (NOX Medical, Reykjavik, Iceland) device. The examination was performed according to the patient’s natural circadian rhythm between 22:00 and 6:00. Electrodes were placed as indicated by guidelines set out by the American Academy of Sleep Medicine (AASM) . Fasting venous blood samples were obtained into polyethylene terephthalate (PET) plastic tubes (Becton, Dickinson and Company; Franklin Lakes, NJ, USA), with dipotassium ethylenediaminetetraacetic acid (K2EDTA) and blood samples were stored at − 70 °C until subsequent analyses use. Blood samples were analyzed at the Main Laboratory of Wroclaw Medical University. Laboratory tests were performed according to the standard laboratory protocols of Wroclaw University Teaching Hospital. Audio-video recordings, along with electrocardiographic, electroencephalographic, electrooculographic and electromyographic were included in the examination, as well as body position detection, thoracic and abdominal breathing activity. A WristOx2 3150 pulse oximeter (Nonin Medical Inc., Plymouth, MN, USA) was used to measure blood saturation (SpO2%), pulse and plethysmography data. In the examination sleep bruxism parameters were gathered together with respiratory and sleep parameters. As stated in American Academy of Sleep Medicine (AASM) standard criteria , sleep parameters were obtained and classified as follows: non-REM 1 sleep stage (N1), non-REM 2 sleep stage (N2), non-REM 3 sleep stage (N3), REM sleep stage, arousal index (ArI), sleep latency (SL), wake after sleep onset (WASO), sleep efficiency (SE), apnea-hypopnea index (AHI), oxygen desaturation index (ODI), and snoring. Sleep bruxism Sleep bruxism parameters were obtained as follows: bruxism episode index (BEI), phasic bruxism, tonic bruxism, and mixed bruxism. Tonic episode was categorized as constant burst episode lasting over 2s. Phasic episode was categorized as episode including 3 or more bursts lasting over 2s. Mixed episode was categorized when episode shows the characteristics of both tonic and phasic episodes. The definition of sleep bruxism episode according to the AASM guidelines is the rhythmic movement of masseter muscles that occurs at least 3s after previous muscle movement and electromyography (EMG) activity must be at least twice the amplitude of the background EMG. Bruxism episode index (BEI) is measured by counting number of bruxism episodes per hour of sleep. Three phenotypes of bruxism were distinguished: phasic, tonic, and mixed bruxism. Sleep bruxism intensity was categorized by the number of bruxism episodes per hour of sleep (BEI). Irrelevant SB refers to BEI < 2, mild / moderate to BEI 2–4 and severe to BEI > 4 17,29 . 

All the included patients ( n = 80) underwent a single-night full polysomnography (PSG) examination using NoxA1 (NOX Medical, Reykjavik, Iceland) device. The examination was performed according to the patient’s natural circadian rhythm between 22:00 and 6:00. Electrodes were placed as indicated by guidelines set out by the American Academy of Sleep Medicine (AASM) . Fasting venous blood samples were obtained into polyethylene terephthalate (PET) plastic tubes (Becton, Dickinson and Company; Franklin Lakes, NJ, USA), with dipotassium ethylenediaminetetraacetic acid (K2EDTA) and blood samples were stored at − 70 °C until subsequent analyses use. Blood samples were analyzed at the Main Laboratory of Wroclaw Medical University. Laboratory tests were performed according to the standard laboratory protocols of Wroclaw University Teaching Hospital. Audio-video recordings, along with electrocardiographic, electroencephalographic, electrooculographic and electromyographic were included in the examination, as well as body position detection, thoracic and abdominal breathing activity. A WristOx2 3150 pulse oximeter (Nonin Medical Inc., Plymouth, MN, USA) was used to measure blood saturation (SpO2%), pulse and plethysmography data. In the examination sleep bruxism parameters were gathered together with respiratory and sleep parameters. As stated in American Academy of Sleep Medicine (AASM) standard criteria , sleep parameters were obtained and classified as follows: non-REM 1 sleep stage (N1), non-REM 2 sleep stage (N2), non-REM 3 sleep stage (N3), REM sleep stage, arousal index (ArI), sleep latency (SL), wake after sleep onset (WASO), sleep efficiency (SE), apnea-hypopnea index (AHI), oxygen desaturation index (ODI), and snoring. 

Sleep bruxism parameters were obtained as follows: bruxism episode index (BEI), phasic bruxism, tonic bruxism, and mixed bruxism. Tonic episode was categorized as constant burst episode lasting over 2s. Phasic episode was categorized as episode including 3 or more bursts lasting over 2s. Mixed episode was categorized when episode shows the characteristics of both tonic and phasic episodes. The definition of sleep bruxism episode according to the AASM guidelines is the rhythmic movement of masseter muscles that occurs at least 3s after previous muscle movement and electromyography (EMG) activity must be at least twice the amplitude of the background EMG. Bruxism episode index (BEI) is measured by counting number of bruxism episodes per hour of sleep. Three phenotypes of bruxism were distinguished: phasic, tonic, and mixed bruxism. Sleep bruxism intensity was categorized by the number of bruxism episodes per hour of sleep (BEI). Irrelevant SB refers to BEI < 2, mild / moderate to BEI 2–4 and severe to BEI > 4 17,29 . 

Venous blood samples were obtained from the ulnar vein after twelve hours of fasting at 7:00 a.m. Fasting venous blood samples were obtained into polyethylene terephthalate (PET) plastic tubes (Becton, Dickinson and Company; Franklin Lakes, NJ, USA), with K2EDTA. Blood samples were stored at − 70 °C until subsequent analyses use. Blood samples were analyzed at the Main Laboratory of Wroclaw Medical University. Laboratory tests were performed as indicated by the standard laboratory protocols of Wroclaw University Teaching Hospital. The concentration of 8-isoprostane was determined in serum by ELISA method with using the Human 8-isoprostane BT LAB Kit (Cat. No.: E6776 Hu, Bioassay Technology Laboratory, China). The determination was conducted according to the manufacturer’s instructions. 8-isoprostane F2-α from the samples (added in duplicate into a 96-well plate) or standard solutions (0–640 ng/L) was bounded to human 8-isoprostane F2-α antibody immobilized to the wells. This complex was detected by addition of streptavidin–horseradish peroxidase (HRP) solution into all wells. After washing away unbound antibodies, the substrate Solution A and substrate Solution B in a 1:1 ratio to each well were added. Lastly, the stop solution was added into each well, and the absorbance of each well was measured at 450 nm by using a Multiskan GO microplate reader (Thermo Fisher Scientific, Finland). The human 8-isoprostane F2-α concentration was calculated based on the standard curve. Total antioxidant capacity was measured in serum (in duplicate) with using of Antioxidant Assay Kit (Cat. No.: 709001, Cayman Chemicals, USA). The assay is based on the ability of antioxidant included in the sample to inhibit the oxidation of 2,2’-azino-di-[3-ethylbenzthiazoline sulphonate] by metmyoglobin. Under the reaction condition, the antioxidant causes the reduction of the maximum of the absorbance at 750 nm proportional to their concentration. The capacity of the antioxidants in the sample to prevent oxidation of above-mentioned substrate was compared with that of Trolox, a water-soluble tocopherol analogue, and was quantified as millimolar Trolox equivalents. measurement was performed using a Multiskan GO microplate reader (Thermo Fisher Scientific, Finland). The intensity of lipid peroxidation process was assessed by measuring malondialdehyde (MDA) concentration in serum, under acidic conditions and high temperatures. The MDA reacted with thiobarbituric acid forming a colour adducts (thiobarbituric acid reactive substances, TBARS). Products of the reaction were measured at λ = 535 nm. The amount of MDA was calculated using an extinction coefficient (0.156 µmol-1 x l x cm-1). AOPP concentration was determined in serum by spectrophotometric method, based on the reaction of AOPP with potassium iodide. The absorbance of samples was measured at λ = 340 nm. The results of determination were expressed in micromoles per liter of chloramine T as equivalents. 

The statistical analysis was performed based on the statistical program “Dell Statistica 13” (Dell Inc.). Arithmetic means (X) and standard deviations (SD) were calculated for quantitative variables. The distribution of variables was checked using the Lilliefors and W-Shapiro-Wilk tests. In the case of quantitative independent variables with a normal distribution, the t test was used for further statistical analysis. In the case of variables with a non-normal distribution, the Mann-Whitney U test was used. Optimal cut-off points for comparative analyzes were estimated based on ROC curves. Results at the p < 0.05 level were considered statistically significant. The study group included 80 patients. Group size was determined using a sample size calculator. The selection conditions were as follows: population size 2,8 million, fraction size 0.25, maximum error 10%, confidence level 95%. The required minimum size of the study group was 73. 

Group characteristic evaluation is presented in Table . The average age of the study group was about 33.96 ± 10.59 years old. 72.5% of the participants were male ( n = 58) and 27.50% of participants were female ( n = 22). 68,75% ( n = 55) of the patients presented normal body weight, 18,75% ( n = 15) were overweight (BMI between 25.0 and 29.9) and 7.50% ( n = 6) were obese (BMI over 30). The study group was evaluated using polysomnographic examination and divided into sub-groups according to the bruxism severity according to bruxism episode index (BEI) score . Bruxism severity was estimated by the number of bruxism episodes per hour. BEI < 2 was defined as mild in 18 patients (22.5%). BEI 2–4 was defined as moderate in 28 patients (35.00%) and BEI > 4 was defined as severe in 34 patients (42.5%). Oxidative stress indicators and its relations to bruxism severity were presented in Table . SB was divided into two groups regarding severity. BEI > 2 correlating with moderate symptoms and BEI > 4 correlating with severe symptoms. The use of classic cut-off points indicated the lack of relationship between sleep bruxism and oxidative stress indicators. Values representing the optimal cut-off points were determined based on successive ROC curves. In this way, correlations were obtained for moderate sleep bruxism (BEI > 2) and severe sleep bruxism (BEI > 4). Moderate sleep bruxism BEI > 2 In patients with moderate SB no correlation between 8-izoprostanol, AOPP, adiponectin and leptin serum levels were observed. However, the relationship between TAS and TBARS has been indicated. This relation has been marked in Fig. and showed in Table . A low serum level of TAS (≤ 0.14) differentiates the group with respect to sleep bruxism parameters. Figure ; Table present the relation between TBARS serum levels and moderate sleep bruxism parameters. The greater TBARS serum level, the higher are sleep bruxism parameters, including BEI and BBI. Severe sleep bruxism (BEI > 4) In patients with severe SB no correlation between 8-izoprostanol, adiponectin and leptin serum levels were observed. However, the relationship between TBARS, TAS, AOPP and severe SB parameters were observed. Figure ; Table present relation between TAS serum levels and severe SB parameters. Low TAS serum levels (≤ 0.16) differentiate the group in terms of severe sleep bruxism parameters. Figure ; Table present relation between TBARS serum levels and severe SB parameters. High TBARS (≥ 1585.45) serum levels differentiate the group in terms of severe sleep bruxism parameters. Figure ; Table presents relation between AOPP serum levels and severe SB parameters. High AOPP (≥ 82.44) serum levels differentiate the group in terms of severe sleep bruxism parameters. The use of non-classical cut-off points (estimated on the basis of ROC curves) indicates the relationship between bruxism and the examined parameters: TAS, AOPP and TBARS. Low TAS (≤ 0.14 and ≤ 0.16), high AOPP (≥ 82.44) and high TBARS (≥ 723.03 and ≥ 1585.45) serum levels result in significantly higher sleep bruxism parameters. 

In patients with moderate SB no correlation between 8-izoprostanol, AOPP, adiponectin and leptin serum levels were observed. However, the relationship between TAS and TBARS has been indicated. This relation has been marked in Fig. and showed in Table . A low serum level of TAS (≤ 0.14) differentiates the group with respect to sleep bruxism parameters. Figure ; Table present the relation between TBARS serum levels and moderate sleep bruxism parameters. The greater TBARS serum level, the higher are sleep bruxism parameters, including BEI and BBI. 

In patients with severe SB no correlation between 8-izoprostanol, adiponectin and leptin serum levels were observed. However, the relationship between TBARS, TAS, AOPP and severe SB parameters were observed. Figure ; Table present relation between TAS serum levels and severe SB parameters. Low TAS serum levels (≤ 0.16) differentiate the group in terms of severe sleep bruxism parameters. Figure ; Table present relation between TBARS serum levels and severe SB parameters. High TBARS (≥ 1585.45) serum levels differentiate the group in terms of severe sleep bruxism parameters. Figure ; Table presents relation between AOPP serum levels and severe SB parameters. High AOPP (≥ 82.44) serum levels differentiate the group in terms of severe sleep bruxism parameters. The use of non-classical cut-off points (estimated on the basis of ROC curves) indicates the relationship between bruxism and the examined parameters: TAS, AOPP and TBARS. Low TAS (≤ 0.14 and ≤ 0.16), high AOPP (≥ 82.44) and high TBARS (≥ 723.03 and ≥ 1585.45) serum levels result in significantly higher sleep bruxism parameters. 

Based on the current body of knowledge, this is the first study to determine the influence of major oxidative stress components including TAS, TBARS, AOPP, 8-izoprostane on sleep bruxism parameters. We showed, that the severity of SB may depend on oxidative stress markers. According to our results, sleep bruxism intensity is correlated with low TAS and high AOPP and TBARS serum levels. Within the scope of the adopted norms, no relationship was confirmed, but during additional analysis, the use of non-classical cut-off points (estimated on the basis of ROC curves) indicates a relationship between bruxism and TAS, TBARS, and AOPP. What is worth mentioning, in research investigating influence of oxidative stress markers on OSA intensity, it has been established that oxidative stress markers, low TAS and high TBARS serum levels correlated with OSA intensity . In general, oxidative stress plays significant role in the development of many health issues . It has been proven, that oxidative stress induces inflammatory pathways. In the review based on human and animal models, it has been proven that reactive oxygen species (ROS), underlie atherosclerosis, hypertension, restenosis after balloon angioplasty . Moreover, cardiovascular consequences related to obstructive sleep apnea (OSA), which tend to co-occur/accompany with SB , share common underlying mechanisms of development . Patients with OSA even before developing disease-related consequences tend to have subclinical atherosclerosis signs including increased carotid intima-media thickness , increased arterial stiffness , increased prevalence of calcified carotid artery atheroma possibly resulting in stroke . Oxidative stress has also been connected with sleep related disorders, including sleep architecture disruption such as sleep disturbances and sleep deprivation . The influence of oxidative stress on sleep deprivation has been previously studied. A systematic review on animal models has been investigating oxidative stress influence on sleep deprivation resulting in conclusion, that sleep deprivation promotes oxidative stress . Other comprehensive article focusing on the topic also confirmed this association . Oxidative stress plays a crucial role in influencing the metabolic activity of the brain and its overall health . Recent years have seen a heightened focus on analyzing sleep architecture in individuals who exhibit bruxism during sleep, following evidence that suggests successive micro-arousals may elevate the risk of cardiovascular issues . Moreover, sleep disturbances are frequently observed and seem to be significantly correlated with a progressively higher risk of stroke . Oxidative stress along with systemic inflammation could potentially serve as a mediator for cardiovascular and cerebrovascular events . A critical pathophysiological mechanism of bruxism is attributed to the activation of the sympathetic nervous system, which is similarly recognized as a primary factor in the development of arterial hypertension . Research has demonstrated that bruxism is associated with alterations in autonomic function, particularly characterized by dysfunction in sympathetic vasoconstriction . To our best knowledge there has not been performed any previous research concerning the link between sleep bruxism and oxidative stress. Systemic inflammation and oxidative stress are strongly associated together. Systemic inflammation has been identified as a significant factor associated with endothelial dysfunction and the progression of atherosclerosis, potentially resulting in the development of hypertension . The link between systemic inflammation and sleep bruxism is possible , however it remains unclear and requires further investigation. The relation between OSA and oxidative stress has been widely discussed in present scientific literature , . However, there is a lack of studies investigating the relationship between SB and oxidative stress. Due to emerging awareness of sleep related disorders, with SB prevalence estimated to be about 8–13% in general population , we took steps to evaluate this relation. To our best knowledge, no past studies based on polysomnographic examination on the relation of sleep bruxism parameters and oxidative stress markers were performed. Our study has several strengths improving the value of the research. The research was performed using full night audio and video polysomnography, the “gold standard tool” in sleep assessment. Moreover, venous blood was collected and evaluated from the whole study group. However, our study is not free from limitations. The major limitation of this study was no adaptive night before PSG examination. It was related to the restricted capacity of the sleep laboratory and limitations associated with hospital’s organization as well as national health service. Secondly, we acknowledge the potential confounding role of obstructive sleep apnea (OSA). Although we did not explicitly exclude patients with OSA from the study, OSA has been shown to influence oxidative stress levels, which could affect the validity of our findings. Future studies should consider excluding or controlling for OSA to avoid potential bias in interpreting oxidative stress markers in relation to sleep bruxism. Lastly, the omission of body mass index (BMI) considerations is another limitation of this study. Higher BMI is known to be associated with increased oxidative stress, and while we collected data on BMI, we did not include it in the final analysis. This oversight may have influenced the relationship between oxidative stress markers and sleep bruxism severity. Future research should address this variable to further refine the understanding of oxidative stress in different populations. 

Based on the results, the following conclusions were formulated: Sleep bruxism is related to oxidative stress markers. Elevated markers of lipid and protein peroxidation may be associated with endovascular damage and cardiovascular risk, but further research is needed in this topic. 

