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Unilateral Posterior Crossbite is Not Associated with TMJ Clicking in Young Adolescents
1 School of Dentistry, Department of Oral, Dental and Maxillo-Facial Sciences, Section of Orthodontics and Clinical Gnathology, University of Naples "Federico II", Via Pansini, 5, I-80131, Naples, Italy; and Correspondence: * corresponding author, farella{at}unina.it
Unilateral posterior crossbite has been considered as a risk factor for temporomandibular joint clicking, with conflicting findings. The aim of this study was to investigate a possible association between unilateral posterior crossbite and temporomandibular disk displacement with reduction, by means of a survey carried out in young adolescents recruited from three schools. The sample included 1291 participants (708 males and 583 females) with a mean age of 12.3 yrs (range, 10.1–16.1 yrs), who underwent an orthodontic and functional examination performed by two independent examiners. Unilateral posterior crossbite was found in 157 participants (12.2%). Fifty-three participants (4.1%) were diagnosed as having disk displacement with reduction. Logistic regression analysis failed to reveal a significant association between unilateral posterior crossbite and disk displacement with reduction (odds ratio = 1.3; confidence limits = 0.6–2.9). Posterior unilateral crossbite does not appear to be a risk factor for temporomandibular joint clicking, at least in young adolescents.
Key Words: temporomandibular disorders • crossbite • malocclusion • cross-sectional study • young adolescents
Among different malocclusions, posterior crossbite is thought to have astronger impact on the correct functioning of the masticatory system. Indeed, previous findings have suggested that persons with unilateral posterior crossbite contracted their jaw muscles asymmetrically (Troelstrup and Møller, 1970; Ingervall and Thilander, 1975; Ferrario et al., 1999; Alarcon et al., 2000), and that they exerted lower bite forces than did control participants (Sonnesen et al., 1998, 2001b). A reduced thickness of the masseter muscle ipsilaterally to the crossbite side has also been reported (Kiliaridis et al., 2000). It has been suggested that, in persons with unilateral posterior crossbite, the altered morphological relationship between the upper and lower dentition may result in right-to-left-side differences in the condyle-fossa relationship (O’Byrn et al., 1995; Hesse et al., 1997; Nerder et al., 1999; Pinto et al., 2001), and may induce asymmetrical mandibular growth (Mongini and Schmid, 1987; Lam et al., 1999; Pinto et al., 2001). The proposed causal chain of events suggests that these asymmetries may also result in alterations of the disk-condyle relationship, which in turn are responsible for disk displacement and temporomandibular joint (TMJ) clicking (Wilkinson, 1991; Pullinger et al., 1993; McNamara et al., 1995b; Egermark et al., 2003). Indeed, positive associations between unilateral posterior crossbite and TMJ clicking are supported by several studies, the results of which suggest that the crossbite increases the risk of disk displacement by a factor of up to 3 (Kritsineli and Shim, 1992; Pullinger et al., 1993; Tanne et al., 1993; McNamara et al., 1995a; Thilander et al., 2002; Egermark et al., 2003). Nevertheless, the existing relationship between posterior crossbite and TMJ disk displacement has also been questioned, since other studies obtained different results (Keeling et al., 1994; Sonnesen et al., 2001a). The main reasons for such controversies may be ascribed to the different clinical criteria for the definition of TMJ clicking across studies, and to the different study designs. Indeed, several studies (Pullinger et al., 1993; List et al., 2001; Sonnesen et al., 2001b) investigating the relationship between occlusal factors and temporomandibular disorders have been carried out with small sample sizes, or have used dental students/staff as controls in case-control design; this might lead to selection bias, particularly if potential confounding variables have not been taken into account in the analysis. A population-based study of risk factors for temporomandibular disorders has the advantage that cases and controls are not selected according to patient referral. Controls come from the same population as the cases, which reduces the possibility of selection bias and confounding. The aim of this cross-sectional study was, therefore, to investigate the association between TMJ disk displacement and posterior crossbite by means of well-defined criteria for the assessment of TMJ clicking and unilateral posterior crossbite and a population-based approach in a large sample of young adolescents. The working hypothesis to be tested was the assumption that co-morbidity between the two conditions would not exceed that expected by mere chance.
Participants were recruited from among secondary schools by means of a two-stage cluster sampling. First, 3 schools were randomly selected from among the 9 schools found in the vicinity of the Dental Clinic, University of Naples "Federico II". In each school, students were selected from lists by means of an inclusion probability (80%) related to the school’s size. Details about the recruitment process are given in Table 1  .
The determination of sample size was based upon previous estimates of the prevalence of joint clicking (about 9%) and unilateral posterior crossbite (about 20%) in Europe (Ciuffolo et al., 2005; Gesch et al., 2005); calculations were performed with type I error set at 0.05 and power set at 80%; it was estimated that about 1100 people would be needed for the detection of an odds ratio between ’exposed’ and ’unexposed to the risk factor’ equal to or greater than 2. We aimed to recruit more than 1600 eligible participants, predicting a 20–30% refusal rate. The protocol used in this study was in accord with the requirements of the Local Ethical Committee and of the principles of the Helsinki Declaration.
Selected students (n = 1680) received an informed consent form to be signed by their parents. Informed consent, however, was obtained only from 1291 (76.8%) out of 1680 students. The sample included 708 males (54.9%) and 583 females (45.1%), with a mean age (± standard deviation) of 12.3 ± 1.1 yrs. The age range, the tenth, and the ninetieth percentiles of the whole sample were 10.1–16.1, 11.0, and 13.8 yrs, respectively. Distribution of participants by gender, age, and orthodontic treatment for each school is given in Table 2
All the participants underwent an orthodontic and temporomandibular joint functional examination, performed independently by two dentists (i.e., the first two authors), who where calibrated to a gold standard (for details, see International Consortium for RDC/TMD-based Research, 2006). Posterior crossbite was diagnosed when the participant had one or more teeth of the posterior group (from canine to second molar) in an irregular (at least one cusp wide) bucco-lingual or bucco-palatal relationship, with one or more opposing teeth (Daskalogiannakis, 2000). TMJ disk displacement with reduction was diagnosed according to the Axis I-Group II of the Research and Diagnostic Criteria for Temporomandibular Disorders (Dworkin and LeResche, 1992). Positive diagnoses of right, left, and bilateral TMJ disk displacement with reduction were grouped into one dichotomous variable.
We assessed agreement between examiners by calculating kappa coefficients (Cohen, 1960) from duplicate measurements obtained from a subgroup of 60 participants. The Data collected were first analyzed by means of conventional descriptive statistics. Chi-square tests and multiple logistic regression were used for subsequent statistical analyses. Age, gender, and self-report of current or previous orthodontic treatment were entered into the multiple logistic model as potential confounding variables. Statistical analyses were carried out by means of the statistical package SPSS software (Release 12.0, Chicago, IL, USA), with a probability level of 0.05 considered statistically significant.
Fifty-three participants (4.1%) out of 1291 were diagnosed as having disk displacement with reduction of the temporomandibular joint. Twenty-four participants had disk displacement with reduction of the right TMJ, 20 participants had disk displacement with reduction of the left TMJ, and nine participants had disk displacement with reduction of both TMJs. Even though several participants (n = 25; 1.9%) had joint pain on palpation, none of the participants of the whole sample reported ongoing TMJ pain on opening and excursions during the examination, or a history of significant limitation of jaw opening. An asymptomatic coarse crepitus in the right TMJ was found in one participant, who received a diagnosis of right osteoarthrosis. None of the participants was diagnosed as having other joint disorders. Disk displacement with reduction of the temporomandibular joint was found in 31 out of 708 males (4.4%), and in 22 out of 583 females (3.8%). The proportion of disk displacement with reduction did not differ significantly between genders (Chi-square = 0.30; degrees of freedom = 1; p = 0.59). Unilateral posterior crossbite was found in 157 out of 1291 participants (12.2%), 79 (50.3%) males and 78 (49.6%) females (Chi-square = 1.49; degrees of freedom = 1; p = 0.22). The association between disk displacement with reduction (DDWR) and posterior crossbite was not statistically significant (Chi-square = 0.44; degrees of freedom = 1; p = 0.50), and only eight participants out of 1291 (0.6%) were found to have, concurrently, disk displacement with reduction and unilateral posterior crossbite. Four out of eight participants had a clicking joint ipsilateral to the crossbite side, while the others had a clicking joint contralateral to the crossbite side.
We performed a multiple logistic regression, considering the disk displacement with reduction diagnoses as the response variable (two modalities: present, absent), and unilateral posterior crossbite (two modalities: yes, no), age (three modalities: upper, middle, and lower tertile), gender (two modalities: boys, girls), and orthodontic treatment (two modalities: yes, no) as independent variables. The results of logistic regression analysis suggested that none of the covariates included into the model was significantly associated with the TMJ disk displacement with reduction, with the odds ratios ranging from 0.8 to 1.3 (Table 3
The proportion of disk displacement with reduction cases and of unilateral posterior crossbite cases did not differ significantly between participants who never received any orthodontic treatment and those with previous or current orthodontic treatment (Table 4 ).
Neither the magnitude (odds ratio = 1.2) nor the level of significance (p = 0.30) of the adjusted odds ratio for unilateral posterior crossbite changed noticeably when the participants with previous or current orthodontic treatment were excluded from the sample investigated. A post hoc power analysis revealed that the power of the main statistical test was 63%, because only 53 cases diagnosed as disk displacement with reduction were found in our sample. The actual sample size, however, ensured a 95% power in detection of an odds ratio equal to 3 or higher.
The relative frequency of disk displacement with reduction found in our sample (about 4%) was considerably lower than that obtained in other studies investigating children of a similar age (Sonnesen et al., 2001b; Thilander et al., 2002; Egermark et al., 2003). This discrepancy may be partly ascribed to the differentsampling procedures used in previous studies, since we sampled participants directly from schools and not from a dental clinic, and partly to the young age of the participants recruited for the present study. The low frequency of disk displacement with reduction diagnoses found in our sample might also be explained by the different criteria we used to assess disk displacement (i.e., Research and Diagnostic Criteria; Dworkin and LeResche, 1992), which are more conservative for clicking diagnoses than simple auscultation methods or self-reported methods (John et al., 2002; Gesch et al., 2005). Indeed, based on these criteria, the prevalence of reproducible joint clicking in a random selected sample of German children/adolescents was estimated at 4.3% (Hirsch et al., 2005). This value was similar to the proportion of joint clicking found in our study (i.e., 4.1%). The relative frequency of posterior crossbite found in our study fits with previous prevalence estimates obtained in unselected participants of similar age (Thilander and Myrberg, 1973; Helm and Prydso, 1979; Ciuffolo et al. 2005). In contrast, as expected, the occurrence of crossbite in our study group was considerably lower than that found in studies with selected pre-orthodontic samples (Sonnesen et al., 1998). The present findings suggest that, in young adolescents, unilateral posterior crossbite is not a risk factor for TMJ disk displacement, since the tested working hypothesis could not be rejected. Indeed, both chi-square test and multiple logistic regression analysis failed to demonstrate a significant association between this factor and disk displacement with reduction, showing an odds ratio very close to 1. The same result was obtained even after we excluded participants with current or previous orthodontic treatment. Interestingly, these participants were found to have a frequency of joint clicking (i.e., 4.1%) identical to that of the other participants. From a theoretical point of view, however, the previous or current orthodontic treatment may represent a confounding factor, since persons affected by both joint clicking and unilateral posterior crossbite may be more likely to be referred to orthodontists. For this reason, these participants were considered in this study. The lack of association between TMJ disk displacement and posterior crossbite is in contrast to previous reports obtained from both young adolescents and adults (Brandt, 1985; Pullinger et al., 1993; Tanne et al., 1993; McNamara et al., 1995a; Thilander et al., 2002; Egermark et al., 2003). Several reasons may contribute to an explanation of our contradictory findings. First, the present study was a population-based cross-sectional study of the relationship between unilateral posterior crossbite and disk displacement, with independently measured exposure and outcome variables, demonstrated reliability of temporomandibular joint clicking and crossbite assessments, and controlled for potentially confounding variables, whereas most previous studies (Pullinger et al., 1993; Tanne et al., 1993; Sonnesen et al., 1998; List et al., 2001; Thilander et al., 2002) have been carried out in universities or dental clinics. Second, our examiners were calibrated and made diagnoses of disk displacement with reduction by means of standardized methods, which are internationally accepted (Dworkin and LeResche, 1992; John et al., 2005). It should be noted that we have investigated the unilateral posterior crossbite as a static occlusal feature. Crossbite malocclusions, however, may be associated with mandibular functional shifts (Nerder et al., 1999). Therefore, the effects of functional occlusion on joint clicking need to be further investigated. It must also be stressed that the frequency of TMJ disk displacement diagnoses found in our sample was lower than expected. This has reduced the power of our statistical test. Post hoc power analysis, however, allowed us to be highly confident (i.e., with 95% power) that there was no relationship between disk displacement with reduction and posterior crossbite for a potential strength of association between the two conditions (i.e., odds ratio) equal to 3 or higher. This strength of association had been suggested from previous studies carried out in adult participants (Pullinger et al., 1993; Egermark et al., 2003). Our findings were obtained from a sample of young adolescents; therefore, it cannot be excluded that the unilateral posterior crossbite may become a significant risk factor with increasing age. Future studies, possibly with population-based sampling, might help to clarify this point. The present findings, which indicate a lack of association between posterior crossbite and disk displacement, suggest that there is an initial optimal TMJ functional adaptation to unilateral posterior crossbite, at least until young adolescence, since most participants (about 95%) with this malocclusion did not have TMJ internal derangements. Based upon these observations, clinicians should be cautious in recommending early orthodontic treatment, in persons with unilateral posterior crossbite, aiming only to prevent joint clicking, since it seems unrelated to this occlusal condition. In conclusion, the findings of our study suggest that unilateral posterior crossbite is not a risk factor for TMJ disk displacement in young adolescents. Further studies are needed, however, to determine the long term-effect of this malocclusion on TMJ internal derangements.
This study was supported by the fund number 2001062735, PRIN 2001 from the Italian Ministry for University and Research and was awarded the "Gaetano Salvatore" prize. Received for publication February 22, 2006. Revision received October 14, 2006. Accepted for publication November 5, 2006.
Journal of Dental Research, Vol. 86, No. 2,
137-141 (2007)
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ABSTRACT
INTRODUCTION
coefficients for disk displacement with reduction and posterior crossbite assessments were 0.72 (standard error = 0.06) and 0.95 (standard error = 0.03), respectively, indicating good to excellent agreement.