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The relationship between bruxism, sleep quality, and headaches in schoolchildren

[Purpose] Present study aimed to evaluate the relationship between sleep bruxism and headache in school children. [Subjects and Methods] This study was conducted with 103 children aged 3–6 years. The exclusion criteria were early tooth loss, dental appliance was used, physical or psychological limitations, chronic disease and continuous medication. Sleep bruxism was diagnosed based on an indication by parents of the occurrence of teeth clenching/grinding and incisor/occlusal tooth wear, following the criteria of the American Academy of Sleep Medicine. Sleep quality was evaluated by a questionnarie, detailing the child’s sleep characteristics. [Results] Forty-nine children (47.6%) were diagnosed with sleep bruxism. Those with sleep bruxism were 3.25-fold more likely to present headache. Children whose parents were separated had a significantly greater frequency of sleep bruxism and primary headache. The relative risk of exhibiting primary headache was 13.1 among children with sleep bruxism whose parents were separated. [Conclusion] Children with SB demonstrated a greater risk of having primary headache and those whose parents were separated had a greater chance of having headache. Only sleep bruxism was associated with headache, clenching the teeth during waking hours was not correlated with primary headache.

INTRODUCTION masticatory muscles 18) . According to Carra et al. 19) SB in young children can also be associated with fatigue of the masticatory musculature, headaches, and noisy breathing during sleep [15][16][17] .
Headache refers to any pain in the cephalic segment, and is an extremely common manifestation that originates primarily from tension, often caused by prolonged muscle contraction. It is usually bilateral, predominantly temporal, occipital, or frontal, and can cause a dull, constant pain, with a characteristic tightness or pressure, often enveloping the head and giving the sensation of "wearing a helmet" 20) . Literature reports a relationship between presence of bruxism and headaches [21][22][23] . However, an association between SB, tension and migraine headaches in children does not yield sufficient evidence based on the available data.
This study aimed to evaluate the relationship between SB and headache in school children aged 3-6 years, by assessing clinical indicators and the patient's history.

SUBJECTS AND METHODS
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. This study was submitted for approval by the Research Ethics Committee of the Universidade Nove de Julho, n.361299, according to regulatory standards by law. All children guardians received information about the study, signed the informed consent form for participation in the research.
A convenience sample was comprised of children aged 3-6 years, who attended the Centro de Educação Infantil Noemia Fabrício dos Santos Gatto (Araras-SP-Brazil). Children with a complete set of primary teeth without occlusal changes were included in the study. Children with early primary tooth loss, those who used orthodontic appliances, those with physical or psychological limitations that would prevent the research procedures from being conducted, and children who were taking continuous medication, were excluded from research.
Individuals was divided into two stages. The first one consisted of a specific questionnaire, which was sent to parents through the school, and a chart, to be filled in over three days, detailing the child's sleep characteristics. Three days after the questionnaire had been sent out, parents were sent a reminder, asking them to return it. The second stage consisted of a clinical examination, which was performed by a single trained evaluator, during the child remained seated under artificial light and had their tooth surfaces dried with sterile gauze. During clinical examination, teeth were examined for presence or absence of wear facets, tongue was examined for bite marks, and the jugal mucosa was assessed for bites and linea alba.
SB diagnosis was according American Academy of Sleep Medicine criteria: parents related clenching/grinding of teeth, and if there was incisal and/or occlusal wear of the dental elements. According to SB diagnosis, two groups were evalutated: Children with SB and without SB (Control Group).
The sample size was calculated to ashure a test power grater than 80%, thus with 103 subjects and an effect size of 0.35, the test power is 0.899 while maintaining the significant level at α=0.05.
The data were analysed with BioEstat 5.3 program. The data was organized in contingency tables (yes/no answers to each of the aspects analysed) and subjected to the χ 2 . Complementary, the odds ration (OR) and confidencial intervals (CI) were calculated to determine the approximated relative risk associated to the risk factor.

RESULTS
One hundred and three children aged 3-6 years participated in this study. The sample was composed of 52 boys (50.5%) and 51 girls (49.5%). Forty-nine of these children (47.6%) were diagnosed with SB, 25 (51%) of them girls and 24 (49%) of them boys, with no gender differences.
About family environment, 18.4% of SB children came from homes where parents had separated, while this number fell to 11.2% among children without SB.
According to parental/guardian reports, 96.3% of children without SB slept well during night, while for the children with sleep bruxism, this number was slightly lower, with 89.8% sleeping well. The other sleep habits are shown in Table 1. We also observed that SB children slept an average of 10 hours a night, while without SB slept an average of 9.5 hours per night.
An average of 20% of children both with and without SB had a habit of biting their nails or chewing on objects, with In relation to presence of headaches, we observed a statistically significant difference (p=0.0086), whereby 59.2% of SB children had headaches, while among children without SB, this number fell to 31.4%. Headaches also occurred more frequently in the children with SB than in the children without SB (p=0.0369). In 100% of the cases of headaches in the children without SB, pain ceased with sleep, while for SB children, this figure was 89.6%. When evaluating the odds ratio, we observed children with SB were almost three times more likely to have headaches than children without SB (OR=3.07; confidence interval 1.36-6.9). The odds of headache was 3.15-fold (95% CI: [1.41, 7.05]) higher among individuals with sleep bruxism than those without SB. However, no correlation was found between clenching teeth during waking hours and headache (p=0.8213, Fisher test). Children whose parents were separated had an additional risk factor, which, when added to the presence of SB, increased the odds of exhibiting headache by threefold (95% CI= [1.25, 7.17]) in comparison to those without SB (p=0.0179, Fisher test). The same was not found to be true for patients whose parents were together (p=0.2877, Fisher test).

DISCUSSION
Headaches are a very common symptom, such as migraines and tension headaches 24) , last one is the most common 25) . It is the result of poor posture or stress. Stress has been associated with SB in literature 28) . Tension headaches and SB involve muscle contractions caused by constantly stress. In present study, an association between SB and headaches was observed, with a three times higher risk developing headaches in children with SB than in children without SB. This data corroborated with Motta et al., who observed that SB children have changes in posture, with the head in a more forward position 26) . Therfore, there is a greater and more intense contraction on masticatory muscles 27) favoring the occurrence of headaches.
Regarding children's sleep quality observed in present study, most of parents reported that their children slept well. However, in most of headaches reported, the pain ceased with sleep, which means a poor sleep quality, with a lack of restful sleep, corroborating with Herrerra et al. 28) who observed that SB children have a higher number of nocturnal microarousals, which seems to be associated with an increase in behavior and attention issues.
A higher incidence of linea alba and biting inside the cheeks in SB children than in children without SB was observed. Despites present data is composed by a convenient sample, this is an important finding to be considered, because in literature, there is no consensus with association with each other yet 29) . Other signs observed in present study, such as presence of noises during sleep and family environment were related with SB presence. Antunes et al. observed that childhood bruxism is related to clinical signs and behaviors too, even bruxism does not significantly affect life quality in this age yet 29) .
Althogh present study had had some limitations, such as an absence of control group, results presents positive statistical associations with clinical signs, which is important to evaluate at clinical practice. SB diagnosis is still controvesal in literature, both in children and adults [30][31][32] . Researches pointed to polysomnography as the gold standard for the SB diagnosis 32) . On the other hand, this is not feasible for the children diagnosis, and the parents' report is still the most acceptable 31) . Therefore, these results point to relevant clinical signs that may aid in a more accurate diagnosis of SB. This study concluded that there is an association between SB and headache in children, and both are related to poor quality of sleep. Thus, we suggest further studies to evaluate the associations between sleep bruxism and headache in children, as well as their therapeutic possibilities.

Conflict of interest
Carolina C. Bortoleto declares that he has no conflict of interest. Monica C. C. Salgueiro declares that he has no conflict of interest. Renata Valio declares that he has no conflict of interest. Yara D. Fragoso declares that he has no conflict of interest. Pamella B. Motta declares that he has no conflict of interest. Lara J. Motta declares that he has no conflict of interest. Fernanda Y. Kobayashi declares that he has no conflict of interest. Kristianne P.S. Fernandes declares that he has no conflict of interest. Raquel A. Mesquita-Ferrari declares that he has no conflict of interest. Alessandro M. Deana declares that he has no conflict of interest. Sandra K. Bussadori declares that he has no conflict of interest.

Funding
The work was supported by the Postgraduate Program in Rehabilitation Sciences and Biophotonics applied to Health Sciences of the University Nove de Julho, São Paulo, SP, Brazil.

Clinical trial registration
The protocol for this study was registered with Clinical Trials number NCT02757261 on 8 April 2016