Assessment of disk displacements of the temporomandibular joint

The aim of the present research was to evaluate disk displacements (DDs) of the temporomandibular joint (TMJ) among patients referred for magnetic resonance imaging (MRI) scans, and analyze the type and prevalence of DD, gender, age, side distribution, reciprocal clicking, presence of pain, range of mouth opening movement, and dental condition. The sample comprised 113 patients, 12-78 years old (the age average was 36.4 +/- 13.5 years), 92 females and 21 males, who underwent MRI between July 2001 and December 2002. A Signa Horizon system (GE) MRI scanner was used at a magnetic field magnitude of 1.5 T with a bilateral radiofrequency surface coil (6.5 x 6.5 cm). Twenty-three (20.4%) patients were found to be normal, whereas 90 (79.7%) presented with DD. Anterior DD (61.1%) was the most common type of articular disk displacement. Males and females were equally affected (no statistically significant difference). We did not find a statistically significant association between DD and increased age. Bilateral DD (70%) was the most common DD occurrence. We found a statistically significant association between reciprocal clicking and anterior DD with reduction. We did not find a statistically significant association between DD and pain, be it articular or facial pain, otalgia or cephalgia. We found a statistically significant association between anterior DD without reduction and mouth opening limitation. With regard to oral condition, we did not find a statistically significant association between DD and loss of teeth.


INTRODUCTION
Internal derangement (ID) of the temporomandibular joint (TMJ) is characterized by an abnormal relationship between the articular disk and the condyle, the glenoid fossa, and the articular eminence 20 .It is mostly caused by disk displacement (DD) and jeopardizes the function of the TMJ 9 , although DD may be present without TMJ dysfunction.In addition, there are other etiologic factors related to ID, such as adhesions, loose bodies inside the articular spaces, and inflammatory and degenerative diseases 9 .
Due to its accuracy, magnetic resonance imaging (MRI) has become the first choice examination for the diagnosis of alterations of the TMJ, mostly soft tissue alterations, making the precise evaluation of the articular disk position possible 13,15,18 , and thus allowing the diagnosis of disk displacement 3,18 .Furthermore, magnetic resonance (MR) images give information about the cortical and medullary bones 8,12,13 , disk degeneration and articular effusion 12 , and about the bilaminar zone 12,19 .For these reasons, MRI is now the gold standard for the diagnosis of ID 12,21 .
The aim of this study was to assess TMJ disk displacements in patients who had been referred for MRI scans.The following data were recorded: the type and prevalence, distribution according to gender, age and affected side, reciprocal clicking, pain, range of the mouth opening movement and dental condition.

MATERIALS AND METHODS
The MR images of the TMJ of 113 patients, 92 (81.4%) females and 21 (18.6%)males, ages from 12 to 78 years (mean age 36.4 ± 13.5), were appraised from July 2001 to December 2002.Images were obtained according to the parameters described in Table 1.
As a rule, the clinical examination included directing the anamnesis of all the subjects to the main complaint and TMJ palpation during maximum mouth opening movement.
The MR scans were made using a Signa Horizon system model scanner (General Electric, Milwaukee, WI, USA), at a magnetic field magnitude of 1.5 T, using a bilateral radiofrequency surface coil of 6.5 x 6.5 cm in size.
For the acquisition of the final scan in T1, an axial scout was performed.Based on that, the condyle was located and the right orientation of the parasagittal and paracoronal slice sequences was established.
The scans were interpreted by two experienced radiologists who used the same criteria for DD diagnosis as that proposed by Katzberg, Westesson 9 (1994) and Milano et al. 12 (2000).
The statistical analysis, with a level of significance of 5%, comprised the Pearson's chi-squared test to observe the relation between the variables, measured at the minimum on an ordinal scale, and the Cuzick's test to evaluate the tendency of the variable age (grouped in age ranges) between the groups with and without DD.The prevalence and prevalence reasons were estimated as occurrence measurements and epidemiological associations.

RESULTS
The results of this study are shown in Tables 2  to 9. Ninety (79.7%) patients presented with DD.Anterior DD, with or without reduction, corresponded to 55 (61.1%) of the cases with DD [45 (81.8%) females and 10 (18.2%) males].

DISCUSSION
Of the total sample of 113 patients, 90 (79.7%) patients presented with DD.This result is similar to the results of Ishigaki et al. 7 (1992) (72.2%) and Paesani et al. 14 (1992) (78%), who worked with arthrography and arthrography plus MRI, respectively.Due to its invasive and painful characteristics, and sometimes unsatisfactory results, arthrogra-      phy is not a current option for TMJ examination, although it provides high quality images for disk perforation.
The findings on disk displacement type were as follows: anterior DD, with or without reduction, was found in 55 (61.1%) of the cases with DD [45 (81.8%) females and 10 (18.2%) males].Our data agree with the results reported in the related literature 9 , which do not demonstrate a higher prevalence of anterior DD.In our opinion, the action of the lateral pterygoid muscle is a contributory etiologic factor and it determines a tendency towards anterior DD.
Even though the greater number of patients presenting with DD were female (Table 2), this difference was not statistically significant (p = 0.66).In contrast, some authors 4,6,7,17 found that DD is more common in females, while Kircos et al. 11 (1987) found that males are more frequently affected by the condition.With these conflicting results, environmental and even genetic factors may determine different characteristics in different populations.
A statistically significant association (p = 0.37) between DD and increased age was not observed (Table 3).According to Sanchez-Woodworth et al. 17 (1988), TMJ internal derangement may also involve children and Isberg et al. 6 (1998) observed a statistically significant incidence of symptomatic DD in male and female adolescents.In fact, 15.6% of our sample comprised patients in the 11-20-year-old age group, although the majority of the patients were aged 31-40 or > 41.
Regarding its uni-or bilateral occurrence (Table 3), DD was observed only on the right side in 13 (14.4%)patients; and on the left side in 14 (15.6%)patients.More than half the patients with DD (63 patients -70%) presented with bilateral DD, and this difference was statistically significant (p < 0.01).This result, in association with the observation of Milano et al. 12 (2000), who found that 80% of their patients were affected by bilateral DD, gives support to the inference of Crusoé-Rebello et al. 2 (2003), who stated that both TMJs constitute only one functional unit.Therefore, contralateral TMJs tend to be equally affected by DD.
Reciprocal clicking (RC) was observed in patients with and without DD.Seventy-three (64.6%) patients presented with RC.Sixty-two (54.9%) patients displayed DD with RC, while 11 (9.7%) patients showed RC without DD (Table 4).A statistically significant association (p = 0.004) between RC and anterior DD with reduction was observed (Table 5).Nevertheless, a statistically significant association (p = 0.38) between RC and anterior DD without reduction was not observed (Table 6).These data lead us to infer that RC strongly suggests anterior DD with reduction.As RC in association with anterior DD without reduction may occur, the existence of RC is not conclusive for anterior DD with reduction.On the other hand, RC may be present without DD, which is in agreement with Katzberg, Westesson 9 (1994), who found that morphologic alterations of the articular disk give rise to RC and may determine irregular movement of the mandible upon jaw opening.
There was no statistically significant association between DD and pain, be it articular or facial pain, otalgia or cephalgia (p = 0.63, 0.21, 0.15, and 0.3, respectively).
Anterior DD, the commonest type, may cause posterior disk attachment between the condyle and the temporal component.As a consequence, the condyle exerts pressure on the disk attachment, an enervated and vascularized structure, and thus, anterior DD is initially present in association with articular pain.With the evolution of the condition, there is usually, but not always, fibrosis of the disk attachment and the articular pain gradually disappears.However, in a few cases, fibrosis does not occur and it is possible to observe a hyperplastic, highly vascularized, and chronically inflamed posterior disk attachment associated with chronic articular pain.In addition, degenerative conditions related to articular pain are usually secondary to anterior DD without reduction 9 .Therefore, anterior DD may be painful at first, evolve to a painless period, and, rarely, become a chronic painful condition.
Among the cases with DD in or study, the high number of patients with symptomatic DD aged 11-20 years (14 patients -15.6%) is in agreement with the findings of Isberg et al. 6 (1998), who found that symptomatic DD mostly affects adolescents.In our opinion, the main reason for the lack of association between DD and pain is the number of patients (62.2%) aged between 31 and 60 years, when the articular condition is diagnosed in a chronic symptomless stage.
Jaw opening limitation (JOL) was found in patients with DD (26 patients -23%) and in patients without DD (6 patients -5.3%).There was no statistically significant association (p = 0.79) between JOL and DD (Table 7).Nevertheless, a statistically significant association (p = 0.01) between JOL and anterior DD without reduction was observed (Table 8).
Even though anterior DD without reduction is not a jaw opening limitation factor for some patients, we observed that, for a large number of patients, anterior DD without reduction is related to mouth opening limitation.This was also observed by Katzberg et al. 10 (1996).
Incomplete dentition was found in 66 DD patients and in 18 non-DD patients.This difference was not statistically significant (p = 0.629).These results (Table 9) minimize the importance of occlusal trauma as an etiologic factor.
In contrast with the findings of Harriman et al. 5 (1990), who observed a statistically significant association between TMJ dysfunction and loss of teeth, we believe, in agreement with the findings of Pullinger et al. 16 (1993) and Ciancaglini et al. 1 (1999), that loss of teeth is a contributory, but not determining, factor acting in the pathophysiology of TMJ internal derangement.

CONCLUSIONS
Based on our results, the following conclusions can be reached: 1. Anterior disk displacement is the most prevalent type of articular disk displacement.2. Males and females are equally affected by the condition.3.There is no statistically significant association between disk displacement and increased age.4. Bilateral disk displacement is the most prevalent occurrence. 5.There is a statistically significant association between anterior disk displacement with reduction and reciprocal clicking.6.There is no statistically significant association between disk displacement and pain, be it articular or facial pain, otalgia or cephalgia.7.There is a statistically significant association between anterior disk displacement without reduction and jaw opening limitation.8.There is no statistically significant association between disk displacement and dental condition (full or incomplete dentition).

TABLE 1 -
Parameters for obtaining TMJ T1-weighted and proton density-weighted sequences.

TABLE 2 -
DD distribution according to gender and affected side.

TABLE 3 -
DD distribution according to age.

TABLE 5 -
Distribution of the sample according to the presence or absence of RC and anterior DD with reduction.

TABLE 6 -
Distribution of the sample according to the presence or absence of RC and anterior DD without reduction.

TABLE 4 -
Distribution of the sample according to the presence or absence of RC and DD.

TABLE 8 -
Distribution of the sample according to the presence or absence of JOL and anterior DD without reduction.

TABLE 9 -
Distribution of the sample according to the oral condition and DD.

TABLE 7 -
Distribution of the sample according to the presence or absence of JOL and DD.