Temporomandibular Joint Effects of Activator Treatment: A Prospective Longitudinal Magnetic Resonance Imaging and Clinical Study
Abstract
The aim of this prospective longitudinal clinical and magnetic resonance imaging (MRI) study was to analyze the effect of Activator treatment on the disc-condyle complex and the posterior attachment of the temporomandibular joint (TMJ) considering the degree of compliance in the evaluation. The material was comprised of 30 class II, division 1 patients (nine girls and 21 boys) who underwent Activator treatment. The average pretreatment age of the subjects was 11.4 years. Parasagittal MRIs in closed mouth position from before and after one year of Activator treatment were analyzed metrically. Possible clinical and subclinical soft tissue lesions of the posterior attachment of the TMJ were assessed by passive joint loading before, after six months, and after one year of Activator treatment. The overjet was continuously documented as a clinical measure for treatment reaction. To assess patient compliance, the subjects had to perform daily wearing-time records. Furthermore, the Activator was clinically inspected for fitting accuracy and signs of wear. The results revealed the following: (1) during the one-year treatment period the sagittal dental arch relationship improved, but a class I occlusion could not be achieved in all patients; (2) on average, a physiologic position of disc, condyle, and fossa was present both before and after one year of Activator treatment; (3) a pretreatment physiologic disc-condyle relationship was unaffected by Activator therapy; 4) a pretreatment disc displacement could not be repositioned during Activator treatment; (5) the prevalence of a subclinical capsulitis of the inferior stratum of the posterior attachment increased during Activator treatment; and (6) the degree of compliance had no influence on the disc-condyle relationship or the reaction of the posterior attachment of the TMJ.
INTRODUCTION
The Activator1 is a removable functional appliance mainly used for the correction of class II, division 1 malocclusions. Based on the “bite jumping” principle introduced by Kingsley2 in 1877, the Activator produces an intermittent functional jumping of the bite. This means that the mandible is advanced to a protrusive position whenever the patient bites into the appliance.
In the course of Activator treatment the forces transmitted to the teeth and jaws by the appliance result in dentoalveolar and skeletal adaptive processes3–12 that cause the transformation of the distal malocclusion into the therapeutically desired neutral occlusion. The efficacy of the appliance is predominately compliance-dependent. Therefore, until the transformation process is completed, Activator patients take up different condylar positions in their habitual distal occlusion (condyle in the fossa) and the therapeutic mandibular jumping position given by the Activator (protruded condylar position).
Investigations in Herbst patients have shown that continuous mechanical jumping results in a temporary subclinical capsulitis of the inferior stratum of the posterior attachment because of its permanent expansion as a consequence to the jumped mandibular position.13 Whether intermittent functional bite jumping as in Activator therapy also induces a capsulitis of the posterior attachment has not been investigated previously.
A chronic capsulitis of the posterior attachment may result in a decrease in synovial fluid viscosity, thus causing increased friction in the upper joint compartment.14–17 Subsequently, the movement of the disc is delayed relative to the condyle at mouth closure, thus loading the inferior stratum of the posterior attachment that stabilizes the disc on the condyle. Chronic loading of the inferior stratum may lead to its elongation, and thus to disc displacement.1819
Thus it might be possible that Activator treatment in noncompliant patients may promote the development of TMD. It was, therefore, the aim of the present study to investigate the effect of Activator treatment on the condition of the posterior attachment of the TMJ and the position of the articular disc considering the degree of patient compliance in the evaluation.
MATERIALS AND METHODS
Patients
A total of 30 consecutive Activator patients (21 boys and nine girls) with a class II, division 1 malocclusion and an average pretreatment age of 11.4 years were examined prospectively. Their handwrist radiographic stages MP3-E to MP3-G indicated that all patients were in the acceleration or peak phase of the pubertal growth spurt.20 All patients were treated with an Activator that had a moderately high construction bite (approximately 5 mm). The mandible was repositioned to an incisal edge-to-edge position.
Magnetic resonance imaging
Magnetic resonance images (MRI) of all patients were obtained before (mean = 76 days before) as well as after 1 year (mean = 19 days after the end of 1 year) of Activator treatment. The images were obtained by means of a Magnetom Expert 1.0 Tesla (Siemens AG, Erlangen, Germany) equipped with TMJ coils for simultaneous imaging of the left and right joint. Parasagittal proton-weighted spin echo sequences in the closed-mouth position (TR 2000/matrix 224 × 256/FOV 150 × 150) were used. Slice thickness was 3 mm with no interslice gap.
Tracings of the MRIs of the right and left joints were made on acetate foil. The medial, central, and lateral slices were analyzed and evaluated separately. To minimize the measuring error, the tracings were enlarged 200% by means of a photocopier, and the enlargement was considered in the analysis.
Metric analysis of the MRIs
In order to assess possible changes in the relative position of the condyle, disc, and fossa, the MRIs were analyzed metrically by means of a modified method of Bumann and Lotzmann,21 Bumann and Vargas-Pereira,22 and Vargas-Pereira.23 The following reference points and reference lines were used (Figure 1):
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Cm: Midpoint of the condyle;
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Ca: Most anterior point of the condyle;
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Tm: Midpoint of the tuberculum articulare;
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Ti: Most inferior point of the tuberculum articulare;
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TP: Turning point of the protuberantia;
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Da: Most anterior point of the articular disc;
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Dp: Most posterior point of the articular disc;
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Dm: Midpoint of the articular disc (equals midpoint of the distance Da–Dp);
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S1: Point of the tuberculum articulare nearest to the condyle;
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S2: Anterior point of the condyle nearest to the tuberculum articulare;
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S3: Posterior point of the condyle nearest to the postglenoid spine;
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S4: Anterior point of the postglenoid spine nearest to the condyle;
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PT: Protuberantia-tangent (equals reference line);
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Cm/Tm: Line between the midpoint of the condyle and the midpoint of the tuberculum articulare (equals the reference line);
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Measurements and calculations
Except for the distances 5 and 6 (see below), all measurements were performed in relation to the PT by means of perpendicular projection of the reference points to PT. The projected reference points are marked with an apostrophe (').
Relative position disc to fossa (Figure 2):
1. Dm'–Ti'
2. Dm'–TP.
Relative position condyle to fossa (Figures 3 and 4):
3. Ca'–Ti'
4. Ca'–TP;
5. Ant: anterior joint space (distance S1–S2);
6. Pos: posterior joint space (distance S3–S4).
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Citation: The Angle Orthodontist 72, 6; 10.1043/0003-3219(2002)072<0527:TJEOAT>2.0.CO;2
For the distances 1 to 4, the following was defined: if the midpoint of the disc (Dm') or the most anterior point of the condyle (Ca') were located posterior to the reference points Ti' or TP, respectively, the measured distance attained a positive value; if they were located anterior to the reference points, the distance attained a negative value.
Furthermore, the position of the condyle was assessed by means of the following joint space index (JSI) using variables 5 and 6:
For the JSI the following was defined: an index value of zero (0) corresponded to a sagittally centered position of the condyle. A positive index (+) implied an anterior, and a negative index (−) a posterior position of the condyle.
Relative position disc to condyle (Figure 5):
7. Dm'–Ca'
8. Dm'–Cm/Tm.
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For the distances 7 and 8 the following was defined: if the midpoint of the disc Dm' was located posterior to the reference point Ca' or the reference line Cm/Tm, respectively, the distance attained a positive value. If it was located anterior to the reference point or line, the distance attained a negative value.
Normative values
The values from the metric MRI analysis were compared with the physiological values for the relative position of the articular disc, condyle, and fossa given by Bumann and Lotzmann,21 Bumann and Vargas-Pereira,22 and Vargas-Pereira.23 These normative values are based on the analysis of MRIs from 82 female and 33 male patients (mean age 36.7 years, age range 10–69 years) whose MRIs were rated “physiologically” by means of visual inspection. The table of normative values describes (1) the position of the articular disc relative to the fossa by means of the variables Dm'–Ti' and Dm'–Tp; (2) the position of the condyle relative to the fossa using the variables Ca'–Ti', Ca'–TP, and the JSI; and (3) the position of the articular disc relative to the condyle by means of the variables Dm'–Ca' and Dm'–Cm/Tm. The physiological range for each variable was defined as the mean value ± 1 standard deviation.
In the table of normative values, deviations from the mean in an upward direction imply a relative or absolute anterior displacement of disc or condyle to the fossa or to each other, respectively. Deviations from the mean in a downward direction imply a relative or absolute posterior displacement of disc or condyle to the fossa or to each other, respectively. In the present study the original normative value table given by Bumann and Lotzmann,21 Bumann and Vargas-Pereira,22 and Vargas-Pereira23 was slightly modified in terms of parameter nomenclature and mathematical sign definition.
Clinical examination
Possible clinical and subclinical inflammatory conditions (capsulitis) of the posterior attachment of the temporomandibular joint were assessed by passive joint loading.17212425 The joint loading was performed in a retrusive (to examine the medial segments of the posterior attachment) and a laterotrusive (to examine the lateral segments of the posterior attachment) position of the mandible (Figures 6–8). For the purpose of this study, capsulitis refers to intracapsular inflammation primarily affecting the posterior attachment. The term posterior attachment is used as described by Scapino2627 and refers to the vascular and innervated tissue lying behind the articular disc.
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The examination was performed before (mean = 70 days before), after six months (mean = 13 days before), and after one year (mean = 20 days after the end of one year) of Activator treatment.
Assessment of the treatment progress and patient compliance
To determine the degree of treatment progress, the overjet was measured clinically (in millimeters) at the start of Activator treatment as well as every six to eight weeks thereafter.
At the start of treatment the patients were instructed to wear the Activator at least 14 hours daily. To assess the degree of compliance, the patients had to perform daily wearing-time records on a special form. Furthermore, the Activator was clinically inspected for fitting accuracy and signs of wearing such as tartar deposits. Additionally, the way the patients handled their appliance was noted.
To minimize misinterpretations of the study results, each patient was interviewed at the end of the observation period with respect to jaw and face trauma, which might have induced TMJ changes.
Statistical methods
For all measured variables the arithmetic mean and the standard deviation were calculated.
Before the assessment of arithmetic mean differences, the data were tested for normal distribution using the Kolmogorov Smirnov test. In case of a normal distribution, intraindividual and interindividual changes and group differences were determined by means of the Student's t-test for paired and unpaired samples. The interindividual comparison of nonordinary variables was performed using the median test, and the intraindividual comparison using the sign test. Possible interrelations between the MRI and overjet changes were tested by means of the Spearman correlation. A correlation level below 0.30 was defined as weak correlation, and a correlation level between 0.30 and 0.70 as moderate correlation. Using cross-tabulation and Fisher's exact test, a possible interrelation between the variable compliance and capsulitis was assessed.
The statistical significance was determined at the 0.1% (***), 1% (**), and 5% (*) levels of confidence. A confidence level greater than 5% was considered statistically not significant (n.s.).
Method error
For the assessment of the combined MRI method (error of the imaging technique and the measurement error), the images of 10 randomly selected patients were traced and evaluated twice after a time interval of 14 days. The following formula was used for the method error (ME) calculation:28
where d is the difference between two measurements of a pair and n is the number of subjects. The results of the method error analysis are given in Table 1.
RESULTS
During the one-year Activator treatment a class I occlusion could not be achieved on a general basis; however, an improvement in the sagittal dental arch relationship was seen in all cases. None of the patients had a history of face or jaw trauma during the observation period. No statistically significant gender differences were found for any of the examined variables. Therefore, no gender differentiation was performed in the further analysis.
Metric MRI analysis
The evaluation of the relative position of the disc, condyle, and fossa before and after one year of Activator treatment revealed that on average all measured variables were within the physiologic range (Tables 2–4; Figures 9 and 10). The JSI had values corresponding to the upper end of the physiologic range both before and after one year of Activator treatment, implying a slightly anterior position of the condyle within the fossa. This was especially pronounced for the lateral slice of the right joint (JSI = 24.78). One year after treatment, however, the position of the left and right condyle was more or less identical (JSI right = 13.52; JSI left = 13.08).
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Citation: The Angle Orthodontist 72, 6; 10.1043/0003-3219(2002)072<0527:TJEOAT>2.0.CO;2
All changes in the relative position of the disc, condyle, and fossa during the treatment period took place within the physiologic range (Tables 5–7; Figures 9 and 10). Thus Activator treatment, on average, did not seem to influence these TMJ structures to a clinically significant extent. Nevertheless, the following statistically significant treatment changes were found: (1) the disc attained an anterior position in relation to the fossa in some slices of both joints (Dm'–Ti' and Dm'–TP; P < .05); and (2) the right condyle changed toward a more centered position within the fossa in the lateral slice (JSI; P < .001). Furthermore, there was a tendency toward a more anterior position of the disc relative to the condyle in the lateral slice of the left joint (Dm'–Ca; n.s.).
Individual patient changes
In the evaluation of individual patients the relative position of the disc to the fossa, the condyle to the fossa, and the disc to the condyle was only classified as displaced if two indicated a position outside the physiologic range.
It was found that 18 of the 30 cases (60%) exhibited a physiologic disc-condyle-fossa relationship both before and after one year of Activator treatment (Figure 11).
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In nine patients (30%) a physiologic relative position of the disc to condyle was found. However, these individuals presented displacements of the disc to the fossa in combination with displacements of the condyle to the fossa. Both anterior and posterior displacements were seen.
Case 3 had a posterior displacement of the condyle, which lead to an anterior position of the disc to the condyle. The position of the disc to the fossa was physiologic. During Activator treatment the position of the condyle normalized and the relative position of the disc to the condyle returned to physiologic values.
The remaining two patients (6.6%) exhibited anterior disc displacements relative to the condyle. Case 10 exhibited a tendency toward an anterior disc displacement before treatment (one variable outside the physiologic range). The position of the condyle to the fossa was physiologic both before and after treatment. After treatment the displacement had increased and both variables indicated an anterior position of the disc relative to the condyle as well as to the fossa. Case 17 had an anterior disc displacement both before and after one year of treatment because of an anterior position of the disc to the fossa and a posterior position of the condyle within the fossa. No improvement of the disc-condyle relationship during treatment could be seen.
Passive joint loading
In two patients, pretreatment data were missing; thus the evaluation in this section was confined to 28 patients. Before treatment, four patients had a capsulitis of the lateral and/or medial segments of the inferior stratum of the posterior attachment with a total of six painful sites. After six months of Activator treatment, 11 patients exhibited 18 painful sites, and after one year 10 patients showed 23 painful sites. Thus, during treatment, both the number of patients with capsulitis as well as the number of painful sites increased. Changes in the relative position of the disc, condyle, and fossa on the MRI were found to be independent from the existence or absence of a capsulitis of the posterior attachment.
Treatment progress
The average pretreatment overjet of 6.0 ± 1.5 mm was significantly reduced (P < .001) during treatment. An overjet of 2.9 ± 0.5 mm remained after one year of Activator treatment.
Interrelations between changes in the relative position of the disc, condyle, and fossa on the MRI and changes in overjet are given in Table 8. Increased reductions in overjet were associated with (1) a more anterior position of the disc in relation to the fossa (Dm'–Ti' lateral slice right and central slice left TMJ; Dm'–TP medial slice left TMJ); and (2) a more posterior position of the disc relative to the condyle (Dm'–Cm/Tm, medial slice). One variable (Dm'–TP lateral slice left TMJ), however, indicated that the disc became more posteriorly positioned with increased overjet reduction.
Compliance
The evaluation of the daily wearing-time records proved to be difficult as only half of the patients filled them out regularly and correctly. Based on the analysis of treatment progress and compliance parameters (overjet development, wearing-time records, clinical inspection of the Activator for fitting accuracy and signs of use, handling of the Activator by the patient), 15 patients were classified as compliant and 15 as noncompliant. The overjet reduction during the treatment period was twice as large (P < .01) in the compliant group (−4.3 ± 1.6 mm) compared to the noncompliant group (−2.0 ± 0.9 mm).
The analysis of possible interrelations between changes in the relative position of the disc, condyle, and fossa on the MRI and the degree of compliance revealed that compliant compared with noncompliant patients develop a more posterior position of the disc relative to the condyle (Dm'–Ti' central slice left TMJ, P < .05) and a more anterior position of the condyle within the fossa (Ca'–Ti' central slice left TMJ, P < .05). The existence or absence of a capsulitis of the posterior attachment was independent from the degree of patient compliance at all observation times.
DISCUSSION
The prerequisites for a good reaction to Activator treatment are mainly a class II, division 1 late mixed dentition, treatment during the pubertal growth spurt, nasal respiration, closed-mouth sleeping position, and good patient compliance (at least 14 hours daily wearing time). All present 30 patients fulfilled these criteria except for the compliance factor. During the one-year investigation period an improvement in the sagittal occlusal relationship with an average overjet reduction of 50% was observed. However, a class I molar relationship could not be achieved in all patients. This may be attributed to the limited length of the observation period and to the lack of cooperation in some of the patients.
Various methods for the analysis of the position of the articular disc using MRIs can be found in the literature. Most methods rely on a visual-descriptive analysis of disc position;29–35 however, metric analyses are also described.2336–39 The main pitfall of many of these analyses, whether visually descriptive or metric, is that they evaluate the position of the articular disc relative to the condyle with respect to the so-called 12 o'clock position. Thus the interrelation between disc position and the inclination of the articular slope is not considered.2340 This limitation can be overcome by using the method of Bumann and Lotzmann,21 Bumann and Vargas-Pereira,22 and Vargas-Pereira.23 Furthermore, using the normative values it is possible to differentiate between displacements of the disc, condyle, or disc and condyle.
The method error of the MRI analysis proved to be acceptable, although it was larger then that described by Vargas-Pereira,23 Bumann et al,41 and Bumann and Vargas-Pereira.42 A possible reason for this could be the fact that in the present study the method error was calculated using duplicate registrations of 10 randomly selected MRIs, whereas Vargas-Pereira,23 Bumann et al,41 and Bumann and Vargas-Pereira42 analyzed 21 different tracings 20 times each. Furthermore, they included only optimal MRIs in their study, whereas in the present investigation some of the MRIs showed slight movement artifacts. The manual functional analysis212443 was given the preference above other techniques of clinical functional analysis44–47 because it leads to a tissue-specific diagnosis.2125
The differentiation of patient groups with good and bad cooperation proved to be difficult despite the fact that several criteria (wearing-time records, overjet development, patient records, clinical inspection of the Activator for fitting accuracy and signs of use, handling of the Activator by the patient) were used. This was especially true because the wearing-time records were either lacking or incomplete in several patients. It must, therefore, be pointed out that the division into compliant and noncompliant groups may subconsciously have been influenced by the degree of improvement seen.
All changes in the disc-condyle relationship were within the physiologic range. Thus a physiologic pretreatment condition was, on average, unaffected by Activator treatment.
Both before and after one year of Activator treatment condylar position in the fossa was within the physiologic range according to all 18 parameters, but it showed a large interindividual variability, as has been reported for asymptomatic populations.2348–51 Furthermore, the JSI exhibited large inter- and intraindividual variations when comparing different joint sections.235253 Thus the variability in condylar position seemed partly to be an expression of natural variation.
Nevertheless, there was a tendency of an anterior condylar position within the fossa pretreatment. This could be characteristic for class II, division 1 malocclusions as has been reported earlier both in radiographic54 and MRI1355 studies. This tendency increased (nine of 18 parameters) after one year of treatment and might be an expression of the new sensory engram of the mandible56 induced by Activator treatment. Furthermore, in animal experiments Woodside et al4 found a proliferation of the posterior part of the disc that appeared to fill the space created by the condylar displacement. Vargervik and Harvold57 and Arat et al58 in Activator patients as well as by Chintakanon et al55 in twin-block patients also made similar observations. A slightly anterior condylar position after Herbst treatment has also been reported.13
The disc to condyle relationship did not change significantly. Both before and after one year of treatment an average physiologic relationship was found. However, after one year of treatment a tendency toward a slightly anterior position of the disc relative to the condyle was noted. This tendency was found to be due to an increase in the degree of displacement of the disc in those subjects with pretreatment disc displacement. In subjects with a pretreatment physiologic disc position, however, no changes of the disc-condyle relationship could be seen. This is in agreement with the findings of Keeling et al59 who, with the analysis of Bionator treatment, found that subjects with TMJ sounds at follow up were more likely those who had clicking pretreatment and that Bionator treatment did not place healthy children at risk for the development of TMD signs. In another MRI study, Arat et al58 reported a slight statistically insignificant protrusion of the disc relative to the condyle during Activator treatment compared with untreated controls. Pancherz et al53 and Ruf and Pancherz,13 on the other hand, found a slight retrusion of the disc after Herbst treatment, whereas Chintakanon et al55 did so for twin-block therapy.
There was no evidence of the Activator influencing a disc displacement present positively in terms of recapturing. The same has been reported for twin-block therapy.55 Furthermore, Foucart et al,60 using a removable Herbst appliance, reported that three out of 10 Herbst patients developed a disc displacement during Herbst treatment. Ruf and Pancherz,13 on the other hand, described that by means of Herbst therapy a repositioning of partial disc displacements was possible and remained stable until the end of the observation period one year after treatment. Thus a rigid stabilization of a recaptured disc might be a prerequisite for successful disc repositioning procedures in the course of functional appliance therapy. This of course would only be possible by means of fixed functional appliances.
Four out of 12 MRI parameters describing the relative position disc to fossa showed a significant change of the disc in the anterior direction. As the disc physiologically follows the condyle upon mandibular protrusion, this change would most likely be the result of the anterior position change of the condyle within the fossa. The anterior position of the disc relative to the condyle, however, will also have contributed to the anterior disc position relative to the fossa.
Passive joint loadings were performed to reveal possible reactions in the posterior attachment of the TMJ. It is important to note that all pain reactions described in this study were exclusively provocable upon passive joint loading and thus were solely subclinical. None of the patients reported pain from the TMJ or masticatory muscles at any time during the observation period.
During Activator treatment both the number of patients with provocable pain due to a capsulitis of the posterior attachment as well as the number of pain sites per patient increased. At normal jaw opening, when the condyle leaves the glenoid fossa, a negative pressure appears within the posterior attachment, resulting in its expansion by dilatation of the retrodiscal venous plexus, thickening of the trabeculae separating the veins, and expansion of the synovium in the posterior joint spaces.262761–64 At full jaw opening, the posterior attachment was expanded about four to five times when compared with its jaw-closed volume.63
When inserting the Activator, the mandible is jumped anteriorly into an incisal edge-to-edge position. The condyle is located on top of the articular eminence. Thus the posterior attachment is expanded during the wearing time of the Activator up to 14 hours a day, instead of only for a few minutes as would be the case during uninfluenced mandibular function. Although the expansion does not seem to have a long-lasting effect on synovial pressure,65 it will result in a mechanical irritation of the tissue leading to an inflammatory reaction.66–69 This could explain the increased prevalence of a capsulitis of the posterior attachment during Activator treatment.
The prevalence of a capsulitis of the posterior attachment has also been reported to increase during Herbst treatment.1370 In contrast to the present study, during active Herbst treatment a capsulitis of the posterior attachment was found on a regular basis in all patients. This discordance in findings is probably due to the difference in appliance design. The Activator, being removable, expands the posterior attachment only during the wearing time. This, however, is highly variable. The Herbst appliance, on the other hand, is fixed influencing mandibular function 24 hours a day with no variation between patients.
According to Petrovic and Stutzmann,71 the lengthening of the posterior attachment is associated with an increase in blood and lymph flow, resulting in a better supply with nutritive and growth-stimulating factors as well as a decrease in locally produced cell catabolites and other negative feedback factors. Instead of being interpreted as a pathologic condition in the classical sense, the capsulitis of the posterior attachment might more likely be the prerequisite for condylar growth stimulation when using means of functional appliances. This seems even more likely as Activator patients with or without a capsulitis of the posterior attachment showed no difference in MRI parameters.
The influence of the degree of compliance on the position of the disc-condyle complex during Activator treatment has not been addressed earlier; thus a comparison with other studies in literature was difficult. The reduction in overjet is one of the goals of Activator treatment. It can be the result of an inhibition of maxillary growth, a retroclination of the upper incisors, a proclination of the lower incisors, and/or a stimulation mandibular growth.3–12 In the compliant group the overjet decreased approximately twice as much as in the noncompliant group. Furthermore, a better cooperation seemed to be associated with a slight anterior position of the disc and condyle relative to the fossa, as well as a more posterior position of the disc relative to the condyle. However, it must be pointed out that no systematic group differences were found and there were also some contradictory findings (Dm'–TP lateral slice left TMJ). Thus based on the present results, the degree of compliance during Activator treatment does not seem to affect the disc-condyle complex either positively or negatively. Keeling et al,59 however, reported that unsuccessful Bionator treatment increased the risk for the development of TMD.
CONCLUSIONS
The findings of the present study revealed that during one year of Activator treatment (1) the sagittal dental arch relation improved, although a class I-occlusion could not be achieved in all patients; (2) a physiologic disc-condyle-fossa relationship was unaffected by Activator treatment, whereas (3) a pretreatment disc-displacement could not be repositioned; (4) the prevalence of subclinical capsulitis of the inferior stratum of the posterior attachment increased during Activator treatment; and (5) the degree of compliance had no influence on the disc-condyle relationship or the reaction of the posterior attachment of the TMJ.
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Citation: The Angle Orthodontist 72, 6; 10.1043/0003-3219(2002)072<0527:TJEOAT>2.0.CO;2
Reference points and lines used in the metric analysis of the magnetic resonance images
Measured distances for the evaluation of the relative position disc to fossa. (1) Dm'–Ti'; (2) Dm'–TP
Measured distances for the evaluation of the relative position condyle to fossa. (3) Ca'–Ti'; (4) Ca'–TP
Measured distances for the evaluation of the relative position condyle to fossa (5) anterior joint space and (6) posterior joint space
Measured distances for the evaluation of the relative position disc to condyle. (7) Dm'–Ca'; (8) Dm'–Cm/Tm
Passive joint loading. Dorsal compression from a retrusive mandibular position: (1) the clinician makes a fist and places the V-shaped area between the thumb and the forefinger on the protuberantia mentalis on the contralateral side to be investigated. (2) The patient performs an active retrusion and places the tip of the tongue as far back on the soft palate as possible. (3) The clinician pushes the condyle posteriorly by exerting posteriorly directed pressure in direction of the TMJ to be analyzed. The examination of the left and right TMJ is performed separately. (4) The clinician registers possible pain provocation
Table of normative values for the right TMJ in the closed-mouth position. The arrows represent the changes during one year of Activator treatment. The medial slice is given as a dotted line, the central slice as a broken line and the lateral slice as a straight line. Except for the joint space index (JSI), all measurements are in millimeters. The gray shaded area indicates the physiologic range
Table of normative values for the left TMJ in the closed-mouth position. The arrows represent the changes during one year of Activator treatment. The medial slice is given as a dotted line, the central slice as a broken line and the lateral slice as a straight line. Except for the joint space index (JSI), all measurements are in millimeters. The gray shaded area indicates the physiologic range
Case presentation of an 11-year-old girl. Parasagittal closed-mouth MRIs (central slice) of the right TMJ before and after one year of Activator treatment. The measurements for the relative position of disc to fossa, condyle to fossa, and disc to condyle are shown in the table of normative values. The gray shaded area indicates the physiologic range. A physiologic disc-condyle-fossa relationship can be seen throughout the observation period
Passive joint loading. Dorsal compression from a laterotrusive mandibular position: (1) the clinician makes a fist and places the V-shaped area between the thumb and the forefinger on the protuberantia mentalis on the contralateral side to be investigated. (2) The patient places the canines of the laterotrusive side on each other. From this position the patient opens the mouth slightly (approximately 1 cm interincisal distance). (3) The clinician pushes the condyle posteriorly by exerting posteriorly directed pressure in direction of the TMJ to be analyzed. The examination of the left and right TMJ is performed separately. (4) The clinician registers possible pain provocation
The effect of dorsal compression on the loading of the posterior attachment of the TMJ. (A) Unloaded anatomic section; (B) loaded anatomic section. Please note the compression of the posterior attachment (from Bumann and Lotzmann21).
Contributor Notes
Corresponding author: Prof. Dr. Sabine Ruf, Department of Orthodontics, School of Dentistry, University of Berne, Freiburgstrasse 7, Berne, Switzerland (sabine.ruf@zmk.unibe.ch)