Many studies have explained temporomandibular joint (TMJ) sounds in children are frequent with TMJ disorder. In addition to multiple divergent findings are designed to evaluate the relationship between bruxism and TMJ disorder in children.

Aim: study was designed and conducted to assess the possible relationship between bruxism and joint sounds in schoolchildren.

Subjects and Methods: The sample comprised 60 schoolchildren participants between 6 to 10 years of age, of whom 30 children with bruxism as study group G1 and another 30 without bruxism as a control group G2 who were scheduled and randomly selected for treatment at (Outpatient Dental Clinics, Zagazig University Hospital). Examiner performed assessment who was blinded allocation of the groups. Assessment involved of (manual palpation, lateral and dorsal extra-auricular auscultation of TMJ by stethoscope for detecting of joint sounds, differentiating between joint sounds as a click/pop or crepitation) Three readings were performed on each participant. Collected data were checked, entered and statistically analyzed to test different variables by chi-square test with the level of significance (p< 0.05).

Results: There were statistically significant association between joint sounds with regarding to bruxism and age, which showed the higher prevalence rates of joint sounds were found in children aged eight to ten years in comparison to those aged sex and seven years. However, there were statistically insignificant association between joints sounds and type in relation to gender.

Conclusion: The bruxism in children may be associated with the symptoms of joint sounds with significant association regarding to age.

Keywords: Bruxism; Temporomandibular Joint; Child; bruxism; TMJ sound.

The prevalence of TMJ disorder is not well known, with a frequency ranging from 16.3 to 68% [1-3]. There are variations regarding the TMJ disorder prevalence from center to center and from country to another depending on evaluation and diagnosis methods of TMJ disorder that is beside the contributory variations such as sample size, sample selection, the age group heterogeneity and difference in method of examination used in each study [1,4,5]. The relationship between primary and mixed dentition and TMJ disorders in children aged 4 were evaluated by (Muhtarodullary M, et al. [6]) who found that the signs and symptoms such as headache, joint sound, pain in TMJ area, restricted mouth opening, deviation-deflection, palpatory tenderness in TMJ, masticatory muscle tenderness were increased from the primary to the mixed dentition group. Unfortunately, the differences not significant between the two groups except joint sounds, which was more significant in mixed dentition group. (Chauhan D, et al. [7]) reported that the TMJ disorder prevalence increased by increasing the age was evident but without statistically significant results (P< 0.12), it was 1.6% for the 9 years age group and 3.5% in 12 years age group. Females were affected eight times more than the males; 4.8% to 6%. Children belonging to urban background were affected more, 3.2% as compared with 2% of rural children (P< 0.21). However, it is statically not significant. The prevalence of TMJ disorder in southern Portuguese children and adolescents aged 5-19 years and its association with emotional stress was studied by (Minghelli B, et al.[8]) their results were showed high prevalence of TMJ disorder (25.2%). Regarding to the emotional stress those who considered tense or nervous had higher probability to develop TMJ disorder. Moreover, the girls significantly prevalence of developing TMJ disorder than boys (p< 0.001), also found the older aged group had higher probability of developing the disorder (p< 0.001) [9]. In Brazilian adolescents who had TMJ disorder symptoms showing the girls had a significantly higher prevalence of symptoms than boys. The girls also had a significantly higher prevalence of myofascial pain and disc displacement with reduction. The myofunctional pain appear the more prevalent symptom (10.3%), followed by disc displacement with reduction (8.0%) arthralgia (3.5%), and myofascial pain with opening limitations (0.2%). Tense or nervous considered the most common symptom[10]. Bruxism is a very common condition in 85%–90% of the population. [11] and the term is defined as a repetitive jaw muscle activity characterized by clenching or grinding of the teeth and/or by bracing or thrusting of the mandible[12]. To date, three definitions of sleep bruxism have been provided by the American Academy of Sleep Medicine (AASM). In 1990, the International Classification of Sleep Disorders (ICSD) defined sleep bruxism within the category of parasomnias (or disorders that intrude on sleep, but are not associated with complaints of insomnia or sleepiness) as a stereotyped movement disorder characterized by grinding or clenching of the teeth during sleep [13]. In the second edition of the ICSD in 2005, sleep bruxism was categorized as a sleep-related movement disorder and defined as an oral parafunctional activity characterized by tooth grinding or jaw clenching during sleep, usually associated with sleep arousals 14. Recently, an updated definition of general bruxism was adopted for the third edition of the ICSD: a repetitive jaw-muscle activity characterized by clenching or grinding of the teeth and/or by bracing or thrusting of the mandible15. Bruxism para functional activity has harmful effects on the teeth, periodontium, masticatory muscles and temporomandibular joint TMJ which is often found in children and adolescents which also have psychological effects [16-18]. The bruxism consequences has direct relation to the changes that occur in the masticatory muscles which often associated with discomfort and pain in joint are the main complaints, along with difficulty chewing, joint luxation, uncoordinated jaw movements, degenerative altera¬tions in the joint, restricted/deviated mandibular movements and joint sounds 19,20. Bruxism is a rhythmic or sustained contraction of the jaw closing muscles produces tooth movement without awareness of patient which has two types of with different etiopathogenesis: asleep and awake bruxism [11,21,22]. A repetitive sleep movement disorder primarily characterized by rhythmic masticatory muscle activity and by occasional tooth grinding and is associated with brief cardiac and brain reactivation23. Instead, awake bruxism is characterized by only clenching type activity and is associated with psychosocial factors [24]. Classification of joint sounds are proposed which takes into account the nature of the sounds as a single, explosive noise (click or pop) or a continuous grating noise (crepitus), their quality (hard or soft), their positions in relation to mandibular movement (near, middle or wide) and whether the sounds occur on opening or closing of the jaws. There is consensus of clicks are generally as the result of the impact between the condyle of mandible and the temporal component of the TMJ after its rapid passage through the posterior band of the joint disc 25. Crepitus is found in more advanced stages of TMJ disorder and is associated with a degenerative condition 25. However, many studies have explained sounds in the TMJ are frequent in children with TMJ disorder [26-29]. Moreover, divergent findings are reported to demonstrate the relationship between bruxism and TMJ disorder in children [29]. Considering the consequences of these aspects to the TMJ, the present study was conducted to investigate the possible relationship between bruxism and joint sounds in schoolchildren.

According to World Medical Association, declaration of Helsinki [30], study population and ethical local institutional approval for study sample comprised 60 participants aged from six to ten years, scheduled for treatment at (Outpatient Dental Clinics, Zagazig University Hospital, Egypt). Patients with debilitating diseases or neurological disorder, with any type of maloc¬clusion, undergoing orthodontic treatment orofacial asymmetry or who examined for possible ear infections were excluded from the study. All participants have the first permanent molars in the Angle Class I occlusal relationship as inclusion criteria. First group (G1) was composed of 30 children with some sign of bruxism based on the criteria of AASM [15] parental report of clenching and/or grinding of the teeth and incisal and/or occlusal tooth wear. Another group (G2) consisted of 30 randomly selected children with no signs or symptoms of bruxism. All parents or legal guardians received adequate information and written consent to participate in the study. The same examiner performed the clinical evaluation undergone a training exercise and allocated participants in both groups blindly.

1-Unfortunately, joint sounds were analyzed by occurrence of a click/pop and crepitus through lateral and dorsal extra-auricular exam. Digital palpation of both TMJs was performed along with auscultation by stethoscope with diaphragm-endpiece. Digital palpation is valuable in detection of irregular TMJ movements due for instance to displacement of the disc [31,32] and it is a valuable complement to auscultation but is not recording the same variable. 2- The participants were asked to open and close their mouth several times to detect the presence or absence of joints sounds and classify their type. Each child performed the different movements at least three times. 3- When one or more signs were detected by auscultation, the child was classified as positive for joint sounds.

Checked data were collected, tabulated, entered and analyzed by using SPSS (version 22) and presented as a quantitative variable. Chi-Square test used for detecting distribution that is expected between different variable (bruxism, age and sex) to presence and type of TMJ sounds. (P< 0.05) was considered statistically significant.

(Table 1,2): Shows a total 60 participant aged six to ten years were examined 26 participants were males (43.33%) and 34 participants were females (56.67%). There was no statically significant association was found between joints sounds and sex (P>0.05). However, a significant association was found regarding to age as a greater percentage of children at eight to ten years of age had joint sounds and a lesser percentage at six to seven years of age (P< 0.05).

(Table 3,4): shows that 45% (n=25) had joint sounds and 55% (n=35) exhibited no sounds during any of the auscultations and examination. There was statically significant association between joint sounds and bruxism (P< 0.05), as 56.67% (n=17) of the participants with joint sounds and had bruxism at the same time. Among those with joint sounds 88% (n=22) exhibited a click/pop and 12% (n=3) exhibited crepitus which has statically insignificant relation with gender (P>0.05).

Although, the lack of relation between TMJ dysfunction and clicking does not mean that variable is not important, the main methods used in recording TMJ sound are palpation and auscultation with or without stethoscope [33.34]. During palpation, the low frequency vibrations of high amplitude may be possibly felt and heard. However, the human ear is most sensitive for vibrations in the range 1000-3000 Hz that most probably cannot be felt by palpation. TMJ sounds frequencies involved in that range and higher [35,36] and without auscultation they pass unnoticed at palpation. Therefore, palpation cannot replace auscultation in recording of TMJ sound. TMJ sounds can sometimes be heard with the naked ear. In the present study, it could not be heard without the help of a stethoscope. The stethoscope does not amplify the sound but pass it to be possible for the examiner to hear the sound about as well as if he listens with the naked ear touching the skin over the TMJ area. Avoiding to touch the patient was actually the original rationale for using a stethoscope Although, the lack of relation between TMJ dysfunction and clicking does not mean that variable is not important, the main methods used in recording TMJ sound are palpation and auscultation with or without stethoscope [33.34]. During palpation, the low frequency vibrations of high amplitude may be possibly felt and heard. However, the human ear is most sensitive for vibrations in the range 1000-3000 Hz that most probably cannot be felt by palpation. TMJ sounds frequencies involved in that range and higher [35,36] and without auscultation they pass unnoticed at palpation. Therefore, palpation cannot replace auscultation in recording of TMJ sound. TMJ sounds can sometimes be heard with the naked ear. In the present study, it could not be heard without the help of a stethoscope. The stethoscope does not amplify the sound but pass it to be possible for the examiner to hear the sound about as well as if he listens with the naked ear touching the skin over the TMJ area. Avoiding to touch the patient was actually the original rationale for using a stethoscope palpation tenderness. The crepitus sounds with low prevalence of this joint noise in children explained by it often occurs in cases of osteoarthrosis of the TMJ that is very rare in children [25,50]. It is difficult to make accurate comparisons due to variations between studies in recording methods, demographic characteristics and definition of variables and that they are significantly associated with a high number of other signs of TMJ dysfunction and related pain.

Results demonstrate higher prevalence rates of joint sounds were found in children aged of eight to ten in comparison to those aged of six and seven. The main value of present study is that demonstrates a possible association between bruxism and joint sounds in schoolchildren which our clinical relevance finding suggests this direct relation between bruxism in children and the severity and progression of joint sounds’ symptoms.

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