INTRODUCTION

Bruxism may be defined as purposeless rhythmic, habitual tooth clenching or grinding movements that may occur either when awake or during sleep.1 Habitual tooth pressing or clenching has been termed diurnal bruxism, whereas tooth grinding, which usually occurs during sleep, has been called nocturnal bruxism.1

The etiology of bruxism has been attributed to systematic factors, such as intestinal parasites, subclinical nutritional deficiencies, allergies, and endocrine disorders23 to local factors, especially malocclusion,45 and to psychological factors.67 Ramfjord and Ash8 stated that there are three mechanisms that interact to trigger bruxism, ie, emotional tensions, pain or discomfort, and occlusal maladjustments. Nadler2 emphasized the causes of bruxism as local, systemic, psychological, and occupational. Meklas9 believed that psychogenic and local irritation factors such as orthodontic malocclusions outweighed other causes of bruxism.

The prevalence of signs and symptoms of temporomandibular disorders are described in the literature for various worldwide ethnic groups. However, few studies have attempted to survey the occlusal factors in relation to bruxism. It would be useful to know this relationship in order to prevent bruxism developed by occlusal disorders.

Nilner10 studied the relationship between occlusal factors and parafunctional activities in 440 children aged seven to 14 years. Statistically significant relationships were found between Class II and Class III malocclusion and bruxism. Widgorowicz-Makowerowa et al11 examined 2100 children (10 to 15 years old) and found statistically significant differences in the prevalence of bruxism between children with and without malocclusion, but the type of malocclusion was not defined in the study.

The aim of this study was (1) to investigate the relationship between occlusal factors (such as Angle classification of molars, anterior and posterior crossbites, excessive overjet, open and deep bite, functional shift, and anterior crowding) and bruxism among seven- to 19-year-old Turkish subjects; and (2) to identify possible sex differences between male and female subjects.

MATERIALS AND METHODS

A total of 965 pupils (472 boys and 493 girls) were selected randomly from four different schools in Konya, Turkey. The mean age for the total sample group was 12.8 years (range, 7–19 years). The mean age was calculated as 12.9 ± 4.1 years for boys and 12.7 ± 3.9 years for girls.

The distribution of age for all participants is shown in Table 1. The following inclusion criteria were used for the selection of the sample.

• Seven years of age or older

• All permanent first molars erupted

• Caucasian

TABLE 1.  Number of Female and Male Subjects by Age Group

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The examiner recorded the Angle classification for molars bilaterally, severity of anterior crowding, existence of anterior and posterior crossbite, open and deep bite, functional shift, and excessive overjet.

Four mutually exclusive anteroposterior (A-P) molar relationship groups were established: (1) Class I, (2) Class II division 1, (3) Class II division 2, and (4) Class III. Crossbites were designated as either present or absent. Anterior and posterior crossbite was recorded as a single tooth or multiple teeth. More than five mm of anterior crowding was designated as anterior crowding present. Overjet or the horizontal distance between the facial surface of the upper central incisors and the facial surface of the lower central incisors was recorded using a periodontal probe. Overjet exceeding six mm was recorded as extreme overjet.

The process of diagnosing a functional shift in occlusion consisted of deconditioning the subject's habitual biting pattern, thus making it possible to measure any functional shift of the mandible. In this way any functional shift caused by an occlusal interference resulting in a reflex alteration in the movement pattern at the occlusal interface was detected. Deconditioning was accomplished using cotton rolls to separate posterior teeth for three minutes before any measurement of a functional shift was attempted.

Similarly, three groups were derived from the overbite data:12 (1) open bite (negative overbite), (2) deep bite (overbite greater than the lower incisor crown's height), and (3) overbite less than the total overlap of the lower incisor's crown.

The study was conducted using bruxing and nonbruxing subjects. Subjects were divided into two groups of bruxers or nonbruxers as determined by the clinical examination and self-report. The subjects were characterized based on answers to several questions related to them or their families and to their awareness of their teeth clenching or grinding. A clinical examination of signs and symptoms of bruxing was also important. The bruxing patients were required to meet all the following predetermined criteria in order to be selected for this study: (1) a self-reported history of nocturnal bruxism; (2) bruxing currently or heard to brux by parents or someone else; and (3) confirmation of bruxism by the principal investigator with an intraoral examination (presence of wear facets on teeth; grade 0, no wear facets; grade 1, enamel only; grade 2, enamel and dentin; grade 3, wear of the cusp). The nonbruxist sample was selected based on the subjects answering “no” to all inquiries regarding clenching or grinding their teeth, as well as an intraoral examination that ruled out obvious signs of bruxing (grade 2 or 3 of the presence of wear facets on at least four teeth).

All statistical analyses were performed using the SPSS software package (SPSS for Windows 98, version 10.0, SPSS Inc, Chicago, Ill). The relationship between bruxism and occlusal factors was evaluated with chi-square analysis (χ²). Chi-square analysis was also performed to compare the changes observed in male and female samples.

RESULTS

The evaluation of the results showed that bruxism was registered in 12.6% of all subjects. It was determined that 12.4% of girls and 12.9% of boys have bruxism. The distribution of bruxism in seven- to 19-year-old Turkish subjects is presented in Table 2. The results indicate that the prevalence of bruxism in boys and girls is similar, and no statistically significant differences were found in this population (P > .05).

TABLE 2.  The Distribution of Bruxism in Seven- to 19-Year-Old Turkish Subjects

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The distribution of different occlusal factors in seven- to 19-year-old Turkish subjects is presented in Table 3. The results showed that no statistically significant relationships existed between bruxism and occlusal factors, such as Angle classification for molars, severity of anterior crowding, existence of anterior and posterior crossbite, open and deep bite, functional shift, and excessive overjet (Table 4).

TABLE 3.  Prevalence of Different Occlusal Factors Among Seven- to 19-Year-Old Turkish Subjects

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TABLE 4.  The Relationship Between Different Occlusal Factors and Bruxism

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Sex differences between occlusal factors and bruxism are shown in Table 5. No sex differences were found between occlusal factors in relation to bruxism.

TABLE 5.  Gender Differences Between Occlusal Factors in Relation to Bruxism

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DISCUSSION

Different techniques are suggested to record bruxism in epidemiologic studies.13 One technique is the evaluation of dental attrition, from direct visual observations in the mouth,14 from dental study casts,15 or from occlusal appliances. However, it is very difficult to be sure if the bruxing is a consequence of parafunctional or functional habits.16 Because the occlusal surfaces are worn physiologically in the deciduous dentition, the reliability of using only the evaluation of dental attrition is controversial.17 Another remarkable point is the timing of the attrition because there is a risk of recording no bruxism when the subjects have recently begun bruxism and may not show signs of attrition.17 The same risk exists if bruxism has stopped, but attrition is observed.18 Also, dental wear can be caused by many factors other than bruxism.19 Therefore, in this study the bruxism history was obtained by a combination of methods. Interview of the children and clinical examination were carried out by the clinician.

The prevalence of bruxism is difficult to determine because the activity is performed subconsciously and questioning alone without a clinical examination is therefore unreliable. Studies by questionnaire, however, have reported that approximately 15–20% of people are aware of bruxing or habitually clenching their teeth.1 Reports of the prevalence of bruxism vary, ranging from 5% to 96% of the population.2021

Egermark-Erikson et al22 reported a high prevalence of bruxism and of subjective symptoms and clinical signs of mandibular dysfunction in seven, 11, and 15-year-old children. In this study, the prevalence of bruxism was 13.27% among seven- to 19-year-old Turkish subjects. In addition, the results indicated that the prevalence of bruxism was similar in boys and girls.

In this study, bruxism was considerably less common than reported by Lindqvist.2324 She based her assessment on the presence of wear facets on the teeth and found an incidence of about 50% in 12-year-old children, although only 15% of the parents reported bruxism in their children. The findings of this study are more in agreement those studies of adults in which bruxism was recorded based on the subject's own appraisal.2526 However, people are often unconscious of their bruxism, and the occurrence is undoubtedly higher than that reported in the answers to questionnaires.

Henrikson et al27 indicated that bruxism was higher in the Class II malocclusion group than in the normal group, which suggests a relationship between parafunctions and orthodontic malocclusion. Nilner10 studied the relationship between occlusal factors and bruxism and found statistically significant correlations between Class II and Class III molar relationships and bruxism. Carlsson et al28 indicated that Angle Class II malocclusion and tooth wear in childhood predicted increased tooth wear in adulthood. However, Clarke29 asserted that occlusal factors are not involved in the etiology of bruxism. Gunn et al30 found no statistically significant relationship between any type of morphologic malocclusion and tooth clenching and grinding. In this study we also found that the molar relationships were not related to bruxism in both the mixed and permanent dentitions. The current findings are in accordance with Clarke29 and Gunn et al.30

In another study, Nilner31 examined the relationship between occlusal factors and bruxism in 309 adolescents. A statistically significant correlation was reported between deep bites and clenching and dental wear. Nilner31 also asserted the need for occlusal treatment in young people with occlusal interferences combined with oral parafunctions. Bailey and Rugh32 showed that occlusal adjustments do not stop bruxism. Brandt33 studied the associations between morphological malocclusion and bruxism in 1342 children and adolescents aged six to 17 years. Significant associations were found among molar relationship, excessive overjet, overbite, and bruxism. Sari et al17 found statistically significant relationships among overjet > 6 mm, negative overjet, overbite, open bite, and bruxism in the permanent dentition. The same investigators also found relationships among Angle Class I occlusion for the first molar teeth, overjet > 6 mm, overbite > 5 mm, scissor bite, crossbite for anterior-posterior multiple teeth, and bruxism in the mixed dentition. In contrast to Nilner,31 Egermark-Eriksson34 indicated that children with deep bite had less worn teeth than other children. In this study, no statistically significant relations were found between bruxism and severity of anterior crowding, existence of anterior and posterior crossbite, open and deep bite, functional shift, or excessive overjet.

Currently, it is widely accepted that temporomandibular disorders are multifactorial in nature and more prevalent in female subjects than in male subjects.35–39 Therefore, to elucidate the causes or relationships of bruxism, it is of great importance to examine sex differences in bruxism in response to the occlusal factors. Egermark-Eriksson et al22 stated that there were no significant differences between the sexes in the occurrence of bruxism. Similarly, in this study, no statistically significant sex differences were determined among the seven- to 19-year-old Turkish population.

CONCLUSIONS

Based on the results obtained, it can be concluded that

• The data obtained from the physical examination and questionnaire identified no statistically significant relations between bruxism and all occlusal factors investigated in seven- to 19-year-old Turkish subjects. No evidence that the occlusal factors studied play a role in the development of bruxism was found.

• No statistically significant sex differences were found between different occlusal factors and bruxism.

• There is a need for further longitudinal investigations with larger sample sizes to know if there is a relationship between occlusal factors and bruxism.