Sagittal position of the temporomandibular joint disc
after treatment with an activator: an MRI study
Type of article: Original Article
Abstract:
Background:
The relation of cause and effect between orthodontic treatment and joint dysfunction,
especially disc displacement, is not proved yet. The orthodontic treatment
that imposes stress on the temporomandibular joint is the mandibular advance to
correct the classes II by mandibular retrognathia. The study aimed to explore the effect of mandibular
advancement using rigid activator associated with extra-oral forces on the
sagittal position of temporomandibular joint (TMJ) disc.
Methods: 63 children, 10.6 +/- 1 years old with class II and
mandibular retrognathia were selected from primary schools. An imaging magnetic
resonance exploration (MRI) was performed on 126 TMJ before treatment (t1) and
one year after treatment (t2). The data were analyzed by the Statistical
Package for the Social Sciences (SPSS). The error risk α was 5%. The Friedman’s Chi2 Test for paired data was used. The
difference p was considered significant if p<.05.
Results: At t2, the discs generally occupied a more anterior
position remaining within the bounds of normality and 5 of them have presented
a displacement.
Conclusion: Overall, after one year of mandibular advancement,
the discs have maintained a normal position.
KEY WORDS: Temporomandibular joint; Magnetic resonance imaging;
Activator; Class II.
Corresponding author:DrNadiraBenkherfallah, Dentistry Department, Faculty
of Medicine, Algiers, Algeria.
Email: nadirabenkherfallah@gmail.com
Received:
September 05, 2017, Accepted: October30, 2017, English editing: January 19, 2018,
Published: March 19, 2018.
Screened by
iThenticate. ©2018 KNOWLEDGE KINGDOM PUBLISHING.
1. INTRODUCTION
Activators of growth are used to treat Class II
division 1 malocclusion in children with mandibular retrognathia. They
represent the first phase of treatment, usually followed by a second phase with
fixed therapeutic. Although different in their design as explained in the
Lautrou [1] classification, activators are based on the same principle: the
mandibular advancement.
Many articles [2, 3, and 4] on their effectiveness and
efficiency are regularly published. Their effects on dental and maxillofacial
structures have been and continue to be the object of studies [6-10]. We found
among these effects an adaptation of the of the temporomandibular joint (TMJ)
components. However, the exploration of all the TMJ components, especially the
disc, was only possible with magnetic resonance imaging or MRI. In 1994 Buthiau
[11] devoted a book exploring the temporomandibular joint (TMJ) by magnetic
resonance imaging (MRI). The principles, indications and
contraindications of MRI of TMJ are found in various publications [12-15].
The relation of cause and effect between orthodontic
treatment and joint dysfunction, especially disc displacement, is not proven as
demonstrated by McNamara [16] in a review of the literature and Kim [17] in a
meta-analysis, but it wasn’t definitively refuted.
Our study is part of this reflection and was
interested in relationships established between TMJ disc and mandibular condyle
in children treated by rigid activator associated with extra-oral force using
MRI exploration. The study received the agreement of the medical experts
committee of medicine, Algiers faculty.
2. MATERIALS AND METHODS
Subjects
The sample consisted of 63 children (girls
and boys) from 23 primary schools. The age’s mean was 10.6 years +/- 1.
The subjects included had: skeletal mandibular retrognathia, ANB higher
or equal to 5 °, a higher or equal to 5mm over jet, Class II molar, facial
growth should be medium or horizontal type. On clinical examination, patients
had to be free of signs of joint dysfunction.
Before treatment, the TMJ MRI exploration
should objectify right and left joint without disc displacement. Patients who
have undergone orthodontic treatment or suffering from general illness were not
included.
Methods
Two orthodontic assessments were carried
out: at t1 before treatment by activator and at t2, a year after treatment. The
TMJ clinical examination was performed at t1 and t2. Profile radiographs were
taken at t1 and t2. Ricketts’s analysis complemented by some values of
Steiner’s analysis was used.
Appliance
The same type of activators, a rigid
activator associated with headgear [18, 19] was used in this study for all
patients; the aim was to promote the mandibular growth. Maxillary and mandibular tray, made in
resin, was solidarized after articulated models in mandibular advancement. Extra-oral
forces were added.
In this appliance, no wire accessories have
been included. The retention was ensured by the faithful reproduction of the
indentations and the sufficient recovery of the teeth by the resin.
MRI exploration
It was made with 1.5 Tesla imager at the
National Center of Imaging. The same imager was used at time t1 and t2. The
exploration was bilateral, using a double surface coil. The same radiologist
conducted reading MRI images. Concerning the reproducibility and accuracy of
measurements of the angles for the same patient, the kappa test was used. The
kappa value was k= 0, 81 for the intraobserver. The concordance was good. Each
study included:
- A sequence identification in the
transverse plane
- A T1-weighted sequences gradient echo
with contiguous cuts 1.5mm thick in the sagittal and coronal plane in the
closed mouth (CM). The same sequences were repeated in open mouth (OM), (Figure
1a,1b).
Fig.1: MRI image of TMJ of a 10 year old child. (1a CM
and 1b OM).
Coronal sections oriented along the long axis of the
condyle in OM and CM were also conducted in gradient echo, T1-weighted to
assess the transversal disc position and eliminating false negatives (Figure
2a, 2b).
1 a2 b
Fig.2: MRI coronal images of TMJ. 2a CM, 2b OM.
Evaluation criteria of the position
of the TMJ disc
The sagittal position of the disc was evaluated in the
CM by the angle formed by the vertical line passing by the estimated center of
the condyle, the Y-axis or 12 o'clock of Shannon [20] and the junction zone
between the zone bilaminar and posterior band, and the center of the condyle.
These two lines, constructed an angle which evaluated t disc position (Figure
3) were described by Drace [21]. In this study, the angle was appointed
sagittal angle. In the CM an angle in front of the axis 12 o'clock was
positively noted, a posterior angle to this axis was negatively noted. In OM
the disc was considered in normal position if it came between the condyle
temporal and mandibular condyle.
Fig.3:
Drawing of sagittal angle according to Drace [21]
The transversal position was considered normal when
the disc was situated inside the two lines tangent to the condyle.
Statistical study
The statistical unit was the temporomandibular joint.
The study was conducted by the software Statistical Package for the Social
Sciences (SPSS). The α granted error risk was 5%. The Chi2 test of Friedman
for paired data was used. The difference p was considered significant if p <.05.
3. RESULTS
Distribution of patients
The sample comprised 63 children, 35 girls and 28 boys
that is to say 126 TMJ joint discs. The gender distribution gave 55,
6% girls and 44.4% boys.
Sagittal angle before treatment mouth closed
At t1, the sagittal angle defining the position of the
disc presented values ranging from a minimum of - 11.3 ° to a maximum of +
14 °. The mean value was 2.7 ° +/- 7. To be able to represent the results in
tables and graphs (Table 1), values of the sagittal angle were grouped into two classes: ]-14,
0] and ] 0, 14]. using brackets according to mathematical standards.
(Tab.I) Distribution of sagittal angle values,
frequencies and proportions at the time t1 in CM
Mean of sagittal angle at t1: 2.7 ° +/- 7.
Sagittal angle after
treatment, mouth closed
At t2, new values outside of ]-14,
14] have been identified, with a minimum
of -30 ° and a maximum of 42.2 °. The sagittal
angle mean value was 10.4 ° +/- 15,2. The comparison of means revealed a
significant difference, p=10-6. At this stage, several sagittal
angles have therefore seen their value changed and new classes of angles were
established. They were also ordered into classes.
The new classes [-30; -14], ]14; 30] and ] 30; 43[ were
added to the two existing at t1:] - 14; 0] and ] 0; 14] (Table II).
It appears that after a year of treatment with
activator, 52 discs remained in the classes ]-14.0] and] 0, 14], representing
the initial positions of the disc and 74 left these two starting classes. Of
these 74 discs 11 were found in class [-30, -14], 58 in the class ]14, 30] and
5 discs in the class ] 30, 43 [.
(Tab.II): Distribution of sagittal angle values, frequencies and
percentages at the time t2 in CM
Mean of sagittal angle at t2: 10.4 ° +/- 15. Comparison of means: ****p <0, 05.
Position of the disc in
OM
All Discs have capped the mandibular condyle.
Correlative analysis
Only variables that revealed an “r”, indicating a
correlation were reported. The analysis revealed a moderate correlation of the
angular value at time t2 with gender (r = 0.241), over jet (r = 0.293) and
overbite (r = 0.251).
4. DISCUSSION
After the MRI protocol was explained to the children,
no child has refused it. We haven’t found 30% refusal as described by Franco [22].
The sample consisted of girls and boys, the ratio was 0.8. This ratio may
suggest a greater frequency of Class II division1 in girls.
In our study, joint function was satisfactory after a
year of mandibular advancement. For the function we agree with the findings of
Pancherz [23] and Foucart [24]. Bourzgui and al [25] haven’t found severe signs
of joint dysfunction on the clinical examination of patients treated
orthodontically. Some authors [26-28] spoke of moderate dysfunction. Clinical
examination of the TMJ could not alone identify disc displacement and it can be
observed in asymptomatic patients [29].
MRI allowed a more objective approach to the status of
TMJ and variations of disc position. Regarding the position of the disc,
the criterion of Drace [21], the most used, was often superimposed on the
visual criterion by Shanon [20]. The sagittal angle as defined in our study was
visually estimated in some studies, while in others it was measured. The
normality was always reported to the visual criterion where the border between
posterior band and bilaminar zone was in a position 11 to 12 o’clock. That is
to say the value of sagittal angle is normal if it is of -30° to 0°. Regarding
to the errors of drawing the 12 o’clock lines and the individual variations,
many authors showed other values [30-33]. In this study we have adopted the
value used by Aidar [34], the normal sagittal angle was estimated normal if the
famous board line between posterior band and bilaminar zone was between 11 and
1 o’clock. This may better describe individual variations and varying
situations of the condyle line axis. In our study, we chose the normal
value used by Aider (for the same reasons). In CM the position of the disc was
normal if the border between bilaminar zone and posterior band of the disc was
between 11 o'clock and 1 o'clock that is to say between -30 ° to + 30 °.
The mean of the sagittal angle at t1 and t2 showed a
significant difference in our results. However, the mean at t2 remained within
normal bounds. This suggests that the disc, while adopting a more forward
position, remained in the normal-physiological range. The wide confidence
interval showed many variations of the sagittal angle and comparison of means
alone was not enough Analysis of disc displacement was given by the details of
the of 126 disc position organized in value class.
Thus, the results showed that 52 disks have not
changed their position and sagittal angles remained in the starting classes.
The displacement has affected 74 discs. Among them, 69 discs remained in the
normal bounds and 5 discs showed anterior displacement in excess of + 30 ° or 1
o'clock and signing an anterior displacement for 5 joints with a difference p =
0.04. If we take into account variations due to the angle’s lines, this
difference does not express a frank significance. This trend in anterior
displacement of the disc after wearing an activator is found in the Ruf’s [35]
study, justified by a condylar retrieve effect and not by disc displacement.
We found 11 disks with posterior position and sagittal
angles ranging from - 30° to -14° but within the normal values. This disc
position was noted by Pancherz [23] who followed the disc position by MRI in
children carrying an Herbiest appliance. He explained that the disc returned to
its original position (before treatment) after fixed therapeutic.
Watted [30] found by MRI a mean sagittal angle of -
18.8 °. He concluded that there was not pathological disc displacement after
orthopedic treatment in patients with retrognathia.
In our study the mean of the sagittal angle increased
from 2.17 at t1 to10, 4 ° at t2. The disc had generally occupied a more
anterior position while remaining within the limits of the normality. We joined
the conclusions of Foucart [24] where the mean sagittal angle was increased
from 6.7° before treatment to 9.3° after treatment.
In our sample the five discs which have moved beyond
the normal position corresponded to a proportion of 4%. This result was
different from the results of Foucart [24] which was 20%. In addition, he found
that the disc obeyed to the law of all or nothing, or it was strongly moved or
it was not. In our study we found different subgroups: with large, moderate and
without change of disc position. This may be due to the individual response or
the MRI protocol.
In his investigation Franco [22] used MRI as
exploration. He found no disc displacement after treatment by Fränkel
activator. Mandibular advancement, less aggressive and longer over time, can
explain the difference with our previous study that found 5 disc displacements.
It also stresses that the criterion, 11 to 12 o'clock by Shanon [20], purely
visually estimated can cause misinterpretations. For this reason, he advised an
angular value for judging the disc displacement. However, it states that
variations can exist depending on the accuracy of the layout of the lines that
make up this angle.
Wadhawan [31] found posterior disc displacement after activator
treatment and the disc was returned to a more normal position after the fixed
therapeutic. Kinzinger [36] following
patients treated with fixed propulsive appliance concludes that no movement was
observed after mandibular advancement and that any disc displacement before
treatment could be corrected after bite jumping.
Aidar [34], while concluding the safety of treatment
by Herbst appliance, added that at the end of the orthodontic phase, changes
were observed in the disc shape and position and could expose some patients in
the future to joint problems. These findings were similar to those of our study
where we found five displaced discs. He emphasized that there was relationship
between occlusion and joint disorders. According to him, an increased overjet
could be the cause of a disc displacement. These conclusions were close to the
results of our correlations. They have shown a link between disc position with
overjet and overbite. As described by Patti [37], increased overbite maintains
the mandible and the condyles in a retrieve position and may cause the anterior
displacement of the articular disc.
Chavan [38] explored TMJ patients treated by Bionator
and Twin Block and found to retrieve the disc position on MRI images with a
more anterior position of the condyle after 6 months. The duration of treatment
in our study is double.
We found a correlation between sex and sagittal angle.
Girls were more prone to changes in the disc position. However, we must
consider the increased number of girls in the sample.
In OM, all discs covered the condylar head, even the
five displaced discs.
It is found that by comparing our results with those
of authors which included MRI in their protocol, the disc position was
different each time. The elasticity of normal values probably also has been the
source of various conclusions.
The studied populations were not homogeneous, and
appliances for advancing the mandibular were different. The MRI imager didn’t have
the same ability to visualize the disc. The studies used imaging at 0.5 Tesla
to 1.0 Tesla and 1.5 Tesla. Therefore, the disc visibility was not the same.
This heterogeneity in methodology was raised by
Michelotti [39] in his review of the literature on the relationship between
orthodontic treatment and joint dysfunction. The multifactorial joint
dysfunction and heterogeneity in methodology makes it difficult to identify its
cause and effect, if it exists.
5. CONCLUSION
The relationship
between disc displacement and orthodontic treatment is still discussed. In our sample
the analysis by MRI of the disc behavior in children treated with rigid activator
revealed an overall disc displacement which remains within the limits of
normality.
However, the wholeness does not reflect the individual
variations. Indeed, the supposed adaptability of the TMJ is not the same for
all children treated with rigid activator; the individual angular values at the end of treatment in our study were ranged from
-30° to + 43°.
As a preventive measure and in order to avoid any particular
dysfunction that could be related to mandibular advancement, the TMJ examination
before, during and after treatment must be made carefully. The objective of
reducing the over jet should not overshadow the TMJ condition specially the
disc position.
6. Declaration of conflicts
No conflicts
7. Authors’ biography
Nadira Benkherfallah: Lecturer in orthodontics, head of service
Beni-Messous university hospital. Lecturer in Orthodontics Faculty of Medicine
of Algiers, Dental Department since 2014. Head of the dentofacial orthopedics service
at the Beni-Messous University Hospital, Algiers, from 2016 up today. Graduate
degree in medical science in 2013. Assistant professor from 2003 to 2013. Specialist
Diploma in Orthodontics,1994. Specialized study in orthodontics from 1990 to
1994. Private practitioner from 1984 to 1990, Diploma in Dental Surgery in
1982.
Malika Djeraf: Lecturer in orthodontics, faculty of medicine, dentistry
department, Algiers University from 2014 up to day. Thesis in dentofacial orthopedics in 2014. Assistant professor at Béni-messous university
hospital, Algiers from 1999 to 014. Assistant professor from 1997 to 1999 at
Tizi-Ouzou university. Specialized study in orthodontics from 1996 to 1999. Dentist
surgeon from 1998 to 1992. Dental surgery diploma in 1987.
Safia Laraba: Professor in orthodontics, faculty of medicine, department
of dentistry Algiers university Professor
and head of service at Beni-Messous
university hospital from1991 to
2016. Lecturer from 1980 to 1991, assistant professor in Switzerland from 1976
to 1978, dentist surgeon in 1972. President of Algerian orthodontics society
from 2011 up today.
Boudjema Mansouri, M.D. Professor in Radiology at the Faculty of Medicine,
Algiers, University Hospital of
Bab El Oued,
Medical Imaging and
Radiology. Head of
Department of the
National Center for Medical
Imaging from 1989
to 2017, Head of the neuroradiology unit of
CHU Mustapha, Algiers
from 1983 to 1989,
Lecturer then professor
at the Faculty
of Medicine of
Algiers. 1987. Head Clinic then doctor associated with the
department of radiology
University Hospital Center
Vaudois (CHUV), Lausanne, Switzerland. from 1980 to 1983. Radiology specialist in 1979, Medical doctor in
1976. Skills: Radiology and Neuroradiology, Radiation Protection ,
member of the Commissariat for Atomic Energy (COMENA) Algiers, Algeria and IAEA
Vienna, Austria. Collaborator in the Telemedicine program in Algeria.
Lila Stof, M.D. Lecturer in Radiology,
Faculty of Medicine, Algiers, department of medicine Algiers university Private
practitioner from 2012 up today. Graduate
degree in medical science in 2010 Specialist Diploma in radiology in 2002 at
Bab El Oued hospital. skills: advance imaging at MRI and CT-scan.
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