Reproducibility of the Obtained Centric Relation Records in Patients with Disc Displacement with Reduction.

OBJECTIVE: The aim of this study was to investigate reproducibility of the position of centric relation in patients with disc displacement with reduction.
MATERIALS AND METHODS: The test group included 30 subjects, diagnosed with disc displacement with reduction in right, left or both joints. The control group included 12 individuals with no signs and symptoms of temporomandibular disorders. Using chin point guidance with a jig, centric relation record was made three times by every participant, in a single session. Left and right condylar position for each centric relation record was determined and recorded using the electronic ultrasonic measuring device. The data were transferred to the computer, processed and analyzed. Condylar distances between centric relation records were measured (anteroposterior, vertical, transversal and linear values), and the data were statistically analyzed using the t and the F tests.
RESULTS: No statically significant difference was found between the test and the control groups. Two thirds of study participants demonstrated condylar position of the repeated centric relation recording within the area of 0.3 mm in diameter. For more than 90% of participants that area was within 0.4 mm.
CONCLUSIONS: There is no difference in reproducibility of the centric relation between patients with disc displacement with reduction and healthy temporomandibular joint individuals (p>0.05). When doing centric relation record on a patient with disc displacement with reduction there is no need for previous splint therapy and standard precautions are acceptable. The obtained results must be interpreted within the experimental group, and not projected on the other groups of temporomandibular disorders.

Introduction

Centric relation is a basic mandibular reference position for evaluation and treatment in prosthetic dentistry. The Glossary of Prosthodontic Terms () offers seven different definitions of centric relation, which points to some controversies regarding the position. The last definition of the Glossary defines centric relation as the maxillomandibular relationship in which the condyles articulate with the thinnest avascular portion of their respective discs with the complex in the anterior-superior position against the shapes of articular eminencies ().

Temporomandibular disorders still represent one of the most controversial topics in dentistry (). Although centric relation is considered a reliable and reproducible position (), studies showed lower reproducibility of mandibular movements in patients with temporomandibular disorders compared to the control group (-). Accordingly, it is expected that patients with temporomandibular dysfunctions demonstrate lower reproducibility of the centric relation record. Yet, a small number of studies (, ) that investigated reproducibility of the centric relation in patients with temporomandibular disorders failed to confirm it.

Disc displacement is one of the most frequent temporomandibular disorders, with reported prevalence ranging from 18% to 35% in general population (). In disc displacement with reduction the disc is anteriorly displaced in the closed mouth position and reverts to a normal superior position during opening (). To the authors’ knowledge there were not many studies about centric relation reproducibility in subjects with disc displacement with reduction. Most of the reported studies combined disc displacement with reduction together with other temporomandibular disorders (, , ) within one experimental group.

The aim of this study was to investigate reproducibility of centric relation position in patients with disc displacement with reduction, compared to a control group of subjects with no signs and symptoms of temporomandibular disorders.

Material and methods

Subjects

The test group included 30 participants (24.0 ± 3.9 years), with disc displacement with reduction in right, left or both temporomandibular joints. Disc displacement with reduction was confirmed according to the Research Diagnostic Criteria for Temporomandibular Disorders () protocol. Apart from disc displacement with reduction, the participants in test group had no other signs and symptoms of temporomandibular disorders (TMD). 18 participants in the test group had monolateral disc displacement (12 in left joint, 6 in right joint), while 12 participants had bilateral disc displacement. The control group included 12 subjects (26.0 ± 3.8 years) with no signs and symptoms of the TMD. Each subject had to give written informed consent, which was approved by the Ethics Committee of the School of Dental Medicine, University of Zagreb, Croatia.

Procedure

The apparatus which integrates the ultrasonic sensor and computer technology (ArcusDigma II, Kavo, Biberach, Germany) was used for recording of condylar distances. The accuracy of the method has been confirmed in previous publications (). Mandibular movement recording instruments provide information on condylar position in real time period, and are standardly used for investigation of temporomandibular joint anatomy and function (, ). Obrez and Gallo () reported that assessment of condylar position with relative precision has been possible since the development of a three-dimensional device for mandibular recording with six degrees of freedom (mathematical transformation).

First, alginate impressions (Aroma Fine Plus, GC, Tokyo, Japan) were made for each subject at first visit. Afterwards a mandibular clutch was made from light-polymerizing acrylics (Unitray, Polident, Volčja Draga, Slovenia) for each subject. At the second visit, a centric relation record was made three times per every participant with thermoplastic registration material (Bite Compound, GC, Tokyo, Japan) using a chin point guidance with a jig method (). Centric relation records were recorded for three times using three different jigs. All three centric relation records were done by the same operator (Figure 1). After the recording of centric relation position for three times, an electronic ultrasonic mandibular recording instrument was used for measuring spatial position of the left and the right condyles at recorded centric relation (Figure 2). Each subject sat comfortably in a dental chair (upright posture). The mandibular clutch was fixed on the buccal side of mandibular teeth with acrylics for provisional restoration (Structur, Voco, Cuxhaven, Germany). It was not in touch with the maxillary teeth in the maximum intercuspation or at lateral movements, and it was firmly fixed on mandibular teeth. After fixation of the mandibular clutch, every centric relation record (Figure 3) was repositioned in the mouth to check if the paraocclusal tray was in contact with centric relation record. If there was contact, buccal impressions of centric relation record registration material were shortened with a scalpel. Upper bow of the ultrasonic measuring device was mounted. A comparison of condylar position of centric relation records was made using module “Electronic Position Analysis”, as recommended by the manufacturer. The module “Electronic Position Analysis” measures distance of the measured position of the left and right condyles in relation to selected reference position of the condyles. The selected reference position was mandibular position of randomly selected centric relation record, due to simplicity and precision. After the reference position had been recorded, every centric relation record was repositioned in the mouth, and the position of the condyles was recorded. Deviations between different centric relation records were measured (at condylar level) with software of the instrument (Kavo Integrated Desktop, Kavo, Biberach, Germany). Measured positions were copied to Microsoft Excel®, (Microsoft Corporation, Redmond, USA) using the option in the software “Copy points”. The reference position was representing zero point of the Cartesian coordinate system and condylar deviations of different centric relation records to the zero point were measured in three axis; anteroposterior (x), superoinferior (y), and lateral (z). After the condylar deviations of different centric relation records to the zero point had been measured, condylar distances between different centric relation records were calculated; between first and second, first and third, and second and third centric relation record. The distances were calculated for the left and the right joint in anteroposterior, superoinferior and transversal direction. After the condylar distances between different centric relation records had been calculated in the Cartesian coordinate system, linear values were also calculated. The linear values were calculated for the left and the right condyle between different centric relation records. For each participant, mean value of distances between different centric relation records was calculated for the left and the right condyle, and used for statistical evaluation. The data were analyzed statistically using the t and the F test (Statsoft, Tulsa, USA).

Figure 1

Registration of the centric relation position using a bite plate with a jig and a chin point guidance method.

Figure 2

Ultrasonic mandibular recording instrument with six degrees of freedom.

Figure 3

The obtained centric relation record.

Results

Table 1 shows the results of the t test between the experimental and control groups for obtained condylar distances between different centric relation records. The minimal distance between different centric relation records for the anteroposterior, vertical and transversal axis was 0 mm, while maximal distance was 0.47 mm for both, the experimental and control group. The minimal linear distance between different centric relation records was 0.07 mm for the experimental group and 0.13 mm for the control group. The maximal linear distance was 0.70 mm for the experimental group and 0.51 mm for the control group. The T test between left side of subjects with disc displacement with reduction and left side of those with healthy temporomandibular joint, and t test between right side of subjects with disc displacement with reduction and right side of subjects with healthy temporomandibular joint showed no statistically significant difference for obtained distances between different centric relation records. Table 2 shows results of the F test between all joints with disc displacement with reduction and all joints without disc displacement with reduction. Table 3 shows size differences for obtained values between participants.

Table 1

Results of the t test between experimental (E) and control (C) group for obtained distances between different centric relation records (mm); p<0.05. * X – anteroposterior direction; Y – vertical direction; Z – transversal direction; L – left condyle; R – right condyle; LL – linear distance for the left condyle; LR – linear distance for the right condyle.

Variable	‾XE (mm)	‾XC (mm)	SDE	SDC	p
XL	0.10	0.11	0.10	0.07	0.86
YL	0.16	0.21	0.10	0.11	0.12
ZL	0.08	0.11	0.07	0.06	0.31
XR	0.10	0.11	0.09	0.07	0.81
YR	0.17	0.14	0.10	0.09	0.39
ZR	0.08	0.11	0.07	0.06	0.36
LL	0.24	0.29	0.13	0.09	0.20
LR	0.26	0.25	0.12	0.09	0.85

Table 2

Results of the F test between all joints with disc displacement with reduction (E, N=42) and all joints without disc displacement with reduction (C, N=42), for obtained distances between different centric relation records (mm). The experimental and control group are one sample (p<0.05). * X – anteroposterior direction; Y – vertical direction; Z – transversal direction; L – linear distance.

Variable	‾XE (mm)	‾XC (mm)	SDE	SDC	p
X	0.10	0.11	0.08	0.09	0.56
Y	0.16	0.17	0.10	0.10	0.67
Z	0.08	0.10	0.07	0.06	0.16
L	0.24	0.27	0.11	0.11	0.33

Table 3

Size differences for distances between different centric relation records. The differences between all joints with disc displacement with reduction (E) and all joints without disc displacement with reduction (C) are shown. Left and right side are one sample (p<0.05).

Direction	TMJ with disc displacement with reduction (N=42)	Healthy TMJ (N=42)
≤ 0.1 mm, anteroposterior	23 (54.8%)	23 (54.8%)
≤ 0.1 mm, vertical	12 (28.6%)	10 (23.8%)
≤ 0.1 mm, transversal	27 (64.3%)	22 (52.4%)
≤ 0.2 mm, anteroposterior	40 (95.2%)	39 (92.9%)
≤ 0.2 mm, vertical	33 (78.6%)	29 (69.0%)
≤ 0.2 mm, transversal	41 (97.6%)	41 (97.6%)
≤ 0.3 mm, anteroposterior	42 (100%)	41 (97.6%)
≤ 0.3 mm, vertical	39 (92.9%)	39 (92.9%)
≤ 0.3 mm, transversal	42 (100%)	42 (100%)
Linear distance ≤ 0.1 mm	5 (11.9%)	2 (4.8%)
Linear distance ≤ 0.2 mm	18 (42.9%)	13 (31.0%)
Linear distance ≤ 0.3 mm	27 (64.3%)	27 (64.3%)
Linear distance ≤ 0.4 mm	40 (95.2%)	39 (92.9%)

Discussion

In this study, the authors investigated reproducibility of centric relation position in subjects with disc displacement with reduction and, also, subjects with healthy temporomandibular joints. Statistical analysis of the results showed no significant difference in obtained distances between different centric relation records, between the experimental and control groups.

Most authors (, -) studied condylar position discrepancies between different centric relation records at anteroposterior, vertical and transversal axes of the Cartesian coordinate system. The results of the present study (Table 1-3) revealed variations of repeated centric relation records in axis values and true linear values, where linear values were greater. The average axis values can mask true value of linear distortion between consecutive centric relation records, measured at condylar level.

Most similar experimental groups had investigations of Harper and Schneiderman () and Zonnenberg and Mulder (). Harper and Schneiderman () studied condylar movement and centric relation in patients with internal derangement of temporomandibular joints. The axis point of condylar rotation in centric relation had significantly greater within-subject variability in the horizontal plane for the control group, which is contrary to the results of this study (Table 1 and 2). Yet, their experimental group included a history of TMJ pain, clicking or restricted jaw movement, which is a larger experimental group than the group with disc displacement with reduction alone. Zonnenberg and Mulder () also had different experimental groups. The authors investigated centric relation reproducibility in TMD patients. The groups included patients with myofascial pain, myofascial pain with disc displacement with reduction, disc displacement without reduction, and osteoarthrosis. The results showed no variability in centric relation position between any group of TMD-patients and control subjects by means of the leaf gauge. Although there are not any similar study groups and techniques for obtaining the position of the centric relation, the results are comparable to the present study (Table 1 and 2). It is safe to conclude that there is no difference in reproducibility of centric relation position between patients with disc displacement with reduction and patients with healthy temporomandibular joints. In practice, some authors () suggest splint therapy in patients with internal derangement, in order that a correct and reproducible centric relation position can be recorded for the final restorative treatment. The results of the present study confirmed that when doing centric relation record on a patient with disc displacement with reduction, there is no need for previous splint therapy, and standard precautions are acceptable.

Schmitt et al. () studied reproducibility of the Roth power centric in determining the centric relation. The measured deviations of the condylar position between different centric relation records were from 0.2 mm to 0.68 mm (SD 0.17 till 0.52). However, the repeated centric relation records showed a positive split cast check (using shim stock foil 0.005 mm) for all participants, which is an indicator of clinical precision. The results of similar studies (, , ), which are in concordance with present study results (Table 1 and 2), suggest that minimal shifts at condylar level do not have clinical significance on precision of the centric relation recording.

Pieshlinger et al. () discuss the terms “centric in point” and “reference position area” for the centric relation position. The authors () state that the term “area” makes more sense in biological systems, where minimal dispersion is expected. Harper and Schneiderman () concluded that the concept of centric relation in normal temporomandibular joints must include a dynamic range of horizontal adaptation to the potential biomechanical and biological stresses related to oral function. Kogawa et al. () and Grasso and Sharry () also question the centric relation as a rigid position. The results of the present study support the claim that centric relation is one area rather than one point. Due to the normal variability in biological systems, it can be expected that the “centric area” cannot have the same distance for all temporomandibular joints. The results of the present study (Table 3) suggest that two thirds of participants will demonstrate condylar position of the repeated centric relation recording within the area of 0.3 mm in diameter. The area was within 0.4 mm for more than 90% of participants.

Conclusion

Recording of centric relation position in patients with disc displacement with reduction has same reproducibility as in patients with healthy temporomandibular joints. Prior splint therapy when recording centric relation position in patients with disc displacement with reduction is not needed. The results of the present study suggest that it is very likely that repeated centric relation recording will position condyles within a diameter of 0.4 mm.