Factors associated with bruxism in children with developmental disabilities

The aim of the present study was to investigate factors associated with bruxism in children aged from 1 to 13 years with developmental disabilities. A total of 389 dental records were examined. The bruxism analyzed was determined based on parental reports. The following variables were also analyzed: gender, age, International Code of Diseases (ICD), mouth breathing, history of gastroesophageal reflux, use of psychotropic drugs, gingival status, reports of xerostomia, hyperkinesis, pacifier use, thumb sucking and involuntary movements. For the purposes of analysis, the individuals were categorized as being with and without bruxism. Variables with a p-value < 0.25 in the bivariate analysis were incorporated into the logistic regression models. Females had a 0.44-fold (95%CI: 0.25 to 0.78) greater chance of exhibiting bruxism than males. Individuals with gastroesophageal reflux had a 2.28-fold (95%CI: 1.03 to 5.02) greater chance of exhibiting bruxism. Individuals with reported involuntary movements had a 2.24-fold (95%CI: 1.19 to 4.24) greater chance of exhibiting bruxism than those without such movements. Exhibiting involuntary movements, the male gender and gastroesophageal reflux are factors associated with bruxism in children with developmental disabilities.


Introduction
Bruxism is the involuntary act of clenching or grinding one's teeth, either while awake or asleep, in an occasional to constant manner.Sleep bruxism is more common than awake bruxism. 1 According to a systematic review, the prevalence ranges from 5% to 40% around the world.This discrepancy in prevalence is most likely due to the different measuring instruments used in bruxism diagnosis. 2In Brazil, the prevalence is 35.3% in the general pediatric population. 3In children and adolescents with mental health problems (emotional symptoms, behavioral problems, peer problems, hyperactivity, etc.), the rate ranges from 28.7% to 30.0%. 4 Among children with developmental disabilities, such as cerebral palsy, the prevalence ranges from 25.0% to 69.4%. 5,6,7,8In studies involving children with cerebral palsy and a control group, a higher prevalence rate has been reported in the former group, 9 whereas other studies have found no significant differences between groups. 6n individuals with cerebral palsy, bruxism has been associated with spastic quadriplegia, athetosis, 5 sucking habits, posterior crossbite, 6 gastroesophageal reflux 10 and Level III of the Gross Motor Functional Declaration of Interests: The authors certify that they have no commercial or associative interest that represents a conflict of interest in connection with the manuscript.
Classification System. 11Together with dental caries, bruxism has a negative impact on the quality of life of this group of individuals. 8nowledge regarding factors associated with bruxism among individuals with developmental disabilities can assist in broadening the understanding of this condition and the establishment of treatment options that are more suitable for this group of patients.Thus, the purpose of the present study was to investigate factors associated with bruxism in children aged 1 to 13 years with developmental disabilities treated at a reference service health care service for patients with special needs in the city of Belo Horizonte, Brazil.

Methodology
This study received approval from the Human Research Ethics Committee of of the Universidade Federal de Minas Gerais -UFMG (process no: ETIC 219/03).A cross-sectional, epidemiological study was carried out using information collected from dental charts obtained from a reference center for the rehabilitation of children with neuromotor disabilities, which is affiliated with the aforementioned university and the Associação Mineira de Reabilitação -AMR.
A total of 389 charts were examined of children aged from 1 to 13 years with developmental disabilities (cerebral palsy, intellectual disability) who were treated between January 1998 and December 2013.The sample size was calculated based on 95% confidence interval, 80% power, and frequency of bruxism between each of the covariates from the pilot study with 40 dental charts.This pilot study also allowed for the testing of the instruments.
The frequency of thumb sucking was used in the sample size calculation because it resulted in the highest number of individuals.Data on the outcome and independent variables were simultaneously extracted from the patient charts by the same trained observer without any need for reexamination.Although this study does not provide an exact measure of intra-rater agreement, the observer consistently followed the daily routine employed in this center.Examiners attended at least two hours of lecture and two hours of practical demonstrations before starting dental care.For analysis purposes, the individuals were categorized as being with or without bruxism experience based on reports by parents/caregivers (Does your child have audible teeth grinding?).Sleep bruxism was not differentiated from awake bruxism.The parental report of bruxism was used for the calculation of the prevalence rate, as performed in previous studies. 4,6,12,13,14,15,16,17The following variables were also analyzed: gender, age, International Code of Diseases (ICD), history of gastroesophageal reflux, use of psychotropic drugs, gingival status, reports of xerostomia, hyperkinesis, pacifier use, thumb sucking and involuntary movements.The ICD of the neurological condition of each patient was defined by the physician in charge.The different diagnoses of spasticity were pooled into a single category.Other developmental disabilities were grouped into another category.The remaining variables were dichotomized as being either absent or present.With the exception of the medical diagnosis, which was defined during neurological treatment, the other variables were measured on the first day of dental treatment and a clinical chart that was created to serve as a basis for the dental treatment proposed for each patient.
The data were submitted to simple logistic regression for the determination of associations, with the calculation of respective odds ratios (ORs) and p-values.Variables with a p-value < 0.25 in this analysis were incorporated into the multiple logistic regression models.Variables with a p-value < 0.05 were maintained in the final model.Adjusted ORs with the respective 95% confidence intervals (CIs) and p-values were calculated.All statistical analyses were performed using SPSS version 19.0 (SPSS Inc., Chicago, USA).

Results
A total of 389 charts of children aged from 1 to 13 years were analyzed.Among those, the information on bruxism was available in 369 (Response rate = 94.9%).Bruxism was reported by parents/caregivers in 36.3% of the cases.The simple logistic regression revealed that the following variables were associated with bruxism (p < 0.05): neurological diagnosis, gender, report of gastroesophageal reflux, mouth breathing and involuntary movements (p < 0.05).The multiple logistic regression model revealed that females had a 0.44-fold (95%CI: 0.25 to 0.78) greater chance of exhibiting bruxism than males.Individuals with gastroesophageal reflux had a 2.28-fold (95%CI: 1.03 to 5.02) greater chance of exhibiting bruxism.Individuals with reported involuntary movements had a 2.24-fold (95%CI: 1.19 to 4.24) greater chance of exhibiting bruxism than those without such movements (Table 1).The Hosmer-Lemersshow test demonstrated that the logistic regression model was adequate (p = 0.749).

Discussion
Gender, gastroesophageal reflux and involuntary movements were independently associated with parent/caregiver-reported bruxism in the children analyzed in the present study.
While a number of previous studies have reported no association between bruxism and gender, 13,14,15,18,19 one study found such an association and reported that the strength of the association with the male gender diminished with age. 12A similar finding was reported in another study in which the authors suggest that girls tend to be less aggressive and agitated than boys and, due to social impositions, boys are unable to express their feelings, whereas girls express their feelings mainly through crying. 4All studies cited involved questionnaires administered to parents/caregivers.With respect to self-perceptions regarding bruxism, female adolescents tended to report the problem more often. 1he association between gastroesophageal reflux and bruxism was in agreement with findings reported in previous studies 10,20 but differed from data described for individuals with cerebral palsy. 7An increase in the rhythmic activity of the masticatory muscles, salivary flow and swallowing has been demonstrated through experimental acidification in healthy adults.Based on these data, bruxism (especially sleep bruxism) may follow gastroesophageal reflux, with a consequent increase in the excitation of the masticatory muscles and swallowing reflex. 10Sleep bruxism also leads to excitation during sleep and increased swallowing.The aim of this increase in salivation is to neutralize the lower pH of the esophagus due to acidification from the stomach in cases of gastroesophageal reflux. 20he association between bruxism and involuntary movements may be explained by mechanisms of the central nervous system.Neurological impairment is common among individuals with developmental disabilities and can trigger biting behavior as a pattern of primitive oral reflexes. 9This mechanism seems to involve direct and indirect pathways of the basal ganglia, which consist of a group of five subcortical nuclei involved in the coordination of movements and are altered in individuals with bruxism. 21Despite the plausibility of this explanation, further studies are needed for a more complete understanding of this association.
Other factors measured in the present study, such as thumb and pacifier sucking, hyperactivity and the use of psychotropic drugs were not associated with the outcome.These findings are in disagreement with data reported in previous studies. 4,6,15,22No association with age was found, which is in agreement with findings described in previous studies. 1,3,6oreover, no association with mouth breathing was observed, although previous studies have found such an association. 16,23ome variables reported to be associated with bruxism in the literature were not addressed in the present study, such as stress, level of responsibility, 3,15,17,19 excessive salivation, sleep walking, heredity, 13,15 the habit of chewing gum, biting on objects, 19 headache, 24 occlusal factors, impacted food scraps and extensive tooth decay. 13he frequency of bruxism was similar to that reported in previous studies, 3,4,9,14 higher than rates found in Iran 13,15 and lower than rates found in studies involving individuals with cerebral palsy. 5,8,11The divergence between the rate in the present investigation and those reported in studies involving individuals with cerebral palsy may be due to the small sample sizes in the studies cited.A systematic review of the literature reports that the prevalence rate of bruxism ranges from 5% to 40%, with higher rates found in Brazil in comparison to rates reported throughout the world. 2 The 37.9% rate in the present study may have been influenced by the specific characteristics of the sample (individuals with developmental disabilities treated at a health care service).
Basing on the prevalence of bruxism on parental reports can be considered to be a limitation of the present study.In a previous study, the prevalence rate was 69.4% when based on a clinical exam and 57.0% when based on the reports of parents/caregivers. 5owever, the methodology employed herein has been previously used for groups with cerebral palsy as well as for the general population. 3,4,6,8,9,11,12,13,14,15,16,17,24ndeed, a diagnosis based on tooth wear should be interpreted with caution, as individuals who have recently acquired the habit are not likely to exhibit typical signs of tooth wear.The cross-sectional design is another limitation, as this type of study does not allow for the determination of cause and effect.Thus, prospective analytical studies are needed to gain a better understanding of this phenomenon.The nondifferentiation of sleep bruxism from awake bruxism is another limitation.However, many of these children clearly grind their teeth throughout the entire day and/or night.Indeed, a previous study found no significant differences in the comparison of groups with sleep bruxism, those with awake bruxism and those who exhibited both behaviors, and it found no increased risk for the temporomandibular joint, sleep disorders or behavioral complaints when sleep and awake bruxism coexisted. 24dentifying factors that may predict the occurrence of bruxism in children with developmental disorders are very important to identify groups with a greater chance of having this condition.The treatment of bruxism involves behavioral aspects, such as anxiety control and improving sleep.Psychotherapy, orthodontics, speech therapy, physical therapy and drug therapy can also assist in the treatment of this condition. 5,17,18The construction of bite plates is difficult due to the complex molding stages and the establishment of centric occlusion in these patients.Moreover, the use of the plate itself poses problems, as the growth of the dental arches is not yet complete in children and the plate may break or even be swallowed.Understanding the factors associated with this condition in a group that poses particular challenges to dental care is important to establish the best treatment approach.

Table 1 .
Associations between reported bruxism and independent variables *Some variables have missing data.