Reproducibility of Centric Relation Techniques by means of Condyle Position Analysis

Abstract

Purpose

The aim of this study was to determine the reproducibility of clinical centric relation (CR) registration techniques (bimanual manipulation, chin point guidance and Roth's method) by means of condyle position analysis.

Material and methods

Thirty two fully dentate asymptomatic subjects (16 female and 16 male) with normal occlusal relations (Angle class I) participated in the study (mean age, 22.6 ± 4.7 years). The mandibular position indicator (MPI) was used to analyze the three-dimensional (anteroposterior (ΔX), superoinferior (ΔZ), mediolateral (ΔY)) condylar shift generated by the difference between the centric relation position (CR) and the maximal intercuspation position (MI) observed in dental arches.

Results

The mean value and standard deviation of three-dimensional condylar shift of the tested clinical CR techniques was 0.19 ± 0.34 mm. Significant differences within the tested clinical CR registration techniques were found for anteroposterior condylar shift on the right side posterior (Δ Xrp; P ≤ 0.012); and superoinferior condylar shift on the left side inferior (Δ Zli; P ≤ 0.011), whereas between the tested CR registration techniques were found for anteroposterior shift on the right side posterior (ΔXrp, P ≤ 0.037) and superoinferior shift on the right side inferior (ΔZri, P ≤ 0.004), on the left side inferior (ΔZli, P ≤ 0.005) and on the left side superior (ΔZls, P ≤ 0.007).

Conclusion

Bimanual manipulation, chin point guidance and Roth's method are clinical CR registration techniques of equal accuracy and reproducibility in asymptomatic subjects with normal occlusal relationship.

Introduction

Although the review of the scientific literature demonstrated that there are numerous disputes on centric relation (CR) reliability, it is still routinely performed on regular basis in dental clinics. Glossary of Prosthodontics Terms (1) defines centric relation (CR) as "the maxillo-mandibular 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 slopes of the articular eminences”. This position is independent of tooth contact. In addition, it is clinically visible when the mandible is directed superiorly and anteriorly. Centric relation is restricted to a purely rotary movement about the transverse horizontal axis". Recording and reproducibility of a stable CR position at condyle level play an important role in reconstruction of occlusion and masticatory system. The adaptive capacity of masticatory system allows utilization of structural and functional principles in treatment. According to the traditional gnathological principles, certain occlusal scheme, within defined anatomical limitations, permits condyles to adjust and function properly within the occlusal design (2-5). On the other hand, functional occlusion concepts are based on morphological variations in condyle anatomy and Posselt’s envelope stating that subunits of masticatory system are controlled by their dynamic biological capacity (5-8). In other words, the modern definition of CR balances between gnathological and functional occlusal theories. It can be concluded that occlusal concept for CR position remains unclear due to the lack of relevant clinical evidence (9).

The main characteristic of CR is its applicability in both healthy and unhealthy temporomandibular joints and masticatory muscles, as well as various dental statuses (dentate, partially dentate, edentulous patients). Mandibular guidance techniques are divided into active (performed by the patient) and passive (performed by the dentist) (10, 11). Generally, a guidance of the mandible into the CR position should be performed in physiologically reliable and unforced manner because an extensive guidance prevents positioning of the condyles in the CR position. There are many passive techniques (6, 12-19) which are used to determine the CR position. They include chin point guidance technique, three-digit technique, Roth's method, bimanual manipulation, anterior guidance technique using Lucia or the Pankey jig, spatula technique, the methods that employ “the best-bite“ devices, leaf gauge, anterior deprogrammer, nociceptive trigeminal inhibition device etc. Those who advocate the abovementioned techniques criticize “active or non-guidance techniques” because they believe that the maximum intercuspation position does not place condyles centrically and symmetrically in the glenoid fossa. On the other hand, the evidence of muscle imbalance (for example, painful masticatory muscles) caused by occlusal premature contacts does not ensure a reproducible and reliable CR position either.

The aim of the study was to determine the consistency and reproducibility of clinically determined CR positions that are routinely performed on prosthetic and orthodontic patients for diagnostic and therapeutic procedures. The following three clinical CR registration techniques were tested: bimanual manipulation (Dawson's grasp), chin point guidance and Roth's method (“power centric“). The above mentioned techniques are frequently used in clinical practice. Also, there is considerable discussion on these techniques in the scientific world. The research was conducted in order to determine the mean values of the three-dimensional condylar shift (mediolateral (ΔY), anteroposterior (ΔX) and superoinferior (ΔZ)) generated by the difference between CR and MI positions at the level of dental arches by using the mandibular position indicator (MPI) (Figure 1). The difference between genders was also investigated considering the examined variables. The design of the study allowed for determination of reproducibility and reliability within and between CR registration techniques by means of temporomandibular joint condyle shift analysis. The null hypothesis was that there is no difference between the three different clinical CR techniques.

Figure 1.

Mandibular Position Indicator (MPI).

Material and methods

32 fully dentate subjects (16 female and 16 male) with normal relations (Angle class I) participated in the study. All the participants signed an informed consent. The subjects ranged from 20 to 33 years of age (female 22.3 ± 4.1; male 22.9 ± 5.3). The subjects were all in good health and had no past history of any serious illness. They did not have any clinical signs or symptoms of temporomandibular disorder. Also, they were free of parafunctional habits, cervical spine disorders, and orthodontic abnormalities. They had never undergone prosthetic and/or orthodontic therapy. Each CR recording technique was performed four times per subject (at baseline, the following day, 1 week after and 1 month after at approximately the same time of the day), which resulted in a total of 384 measurements.

Mandibular Position Indicator (MPI, SAM Prazisionstechnik GmbH, Muenchen, Germany) was used to analyze the mandibular condylar shift (20). This modular device comprises of a modified upper part of the SAM articulator. It is characterized by sliding cubes positioned on the inner axis of the upper part of the SAM articulator in place of condyle housings and a gauge placed in between. Sliding cubes and the gauge recorded a three-dimensional spatial shift (anteroposterior (ΔX), superoinferior (ΔZ), mediolateral (ΔY)) in millimeters between the CR and the MI position relative to the predefined hinge axis position on the sliding cubes and the initial position of the incisal pin. Right and left anteroposterior and superoinferior shifts were measured on the sliding cubes, whereas bilateral mediolateral shifts (ΔY right, ΔY left) were displayed on the analog dial of the gauge. Displacements of the axis in the anteroposterior (ΔX right anterior, ΔX right posterior, ΔX left inferior, ΔX left superior) and superoinferior (ΔZ right anterior, ΔZ right posterior, ΔZ left inferior, ΔZ left superior) direction between CR and MI were registered.

Master casts made from hard dental stone plaster (Alpenrock type IV, AmannGirrbach, Austria) were fabricated upon the anatomical alginate impressions (Aroma fine plus, GC Corporation, Japan) of dental arches for each subject involved in the study. According to the CR registration, a record was prepared on each master cast depending on the clinical CR recording technique requirements. The quality of CR registration records greatly influences the diagnostic validity of the condyle position analysis. Bite records should be made of rigid material. They should be of high quality. The base layer of the CR bite record was made of hard wax (Beauty Pink, Moyco Industries, USA). Softer wax (Aluwax, Aluwax Dental Products, USA) was used to record impressions of mandibular teeth in three points (anterior, right and left lateral segment). Each subject was first “deprogrammed“ by biting into a cotton pellet (jig) between the anterior teeth for 5 minutes in order to stabilize the mandible during CR recording and delete the proprioceptive perception received from teeth and masticatory muscles (10, 21, 22).

The study was approved by the Ethics Committee of the School of Dental Medicine, University of Zagreb, Croatia.

Results

The data were saved to the database (Microsoft Office Excel 2010) and a statistical analysis using a licenced software package SPSS 12.0. for Windows was performed.

Table 1 shows descriptive characteristics (mean values and standard deviations) of bilateral three-dimensional condylar shifts (mediolateral (ΔY), anteroposterior (ΔX) and superoinferior (ΔZ)) for the following three clinical CR registration techniques (bimanual manipulation, chin point guidance and Roth's method).

Table 1. Descriptive characteristics of bilateral three-dimensional condylar shifts between CR and MI for tested clinical CR registration techniques.

	ΔYr	ΔYl	ΔXra	ΔXrp	ΔZri	ΔZrs	Δxla	ΔXlp	ΔZli	ΔZls	Tot
N x SD	384 0.19 0.23	384 0.14 0.25	384 0.15 0.29	384 0.28 0.49	384 0.18 0.32	384 0.18 0.34	384 0.25 0.34	384 0.18 0.43	384 0.18 0.33	384 0.18 0.33	384 0.19 0.34

ΔYr – mediolateral shift to the right; ΔYl – mediolateral shift to the left; ΔXra – anteroposterior shift right anterior; ΔXrp – anteroposterior shift right posterior; ΔZri – superoinferior shift right inferior; ΔZrs – superoinferior shift right superior; ΔXla – anteroposterior shift left anterior; ΔXlp – anteroposterior shift left posterior; ΔZli – superoinferior shift left inferior; ΔZls – superoinferior shift left superior; Tot - Total.

The value of the three-dimensional shifts averaged 0.19 ± 0.34 mm (asymptomatic subjects with an Angle class I). No statistically significant difference (p ≥ 0.05) for bilateral three-dimensional shifts between genders was found (Mann-Whitney test, Table 2).

Table 2. Mann-Whitney test values for bilateral three-dimensional condylar shift variables with respect to gender.

	Mann-Whitney U	Wilcoxon W	Z	Significance
Δ Yr	17513	36549	-0.89	0.372
Δ Yl	17053	35581	-1.49	0.135
Δ Xra	17453	35981	-1.18	0.236
Δ Xrp	17588	36116	-0.95	0.343
Δ Zri	18344	36872	-0.10	0.918
Δ Zrs	16596	35124	-2.17	0.03
Δ Xla	17587	36115	-0.89	0.373
Δ Xlp	18363	36891	-0.09	0.929
Δ Zli	17745	36273	-0.80	0.423
Δ Zls	17835	36363	-0.69	0.486

ΔYr – mediolateral shift to the right; ΔYl – mediolateral shift to the left; ΔXra – anteroposterior shift right anterior; ΔXrp – anteroposterior shift right posterior; ΔZri – superoinferior shift right inferior; ΔZrs – superoinferior shift right superior; ΔXla – anteroposterior shift left anterior; ΔXlp – anteroposterior shift left posterior; ΔZli – superoinferior shift left inferior; ΔZls – superoinferior shift left superior.

A non-parametric Kruskal-Wallis test was used to observe differences in bilateral three-dimensional shifts within and between the different clinical CR recording techniques. Table 3 of this paper shows statistically significant differences within the tested clinical CR registration techniques for anteroposterior condylar shift on the right side posterior (Δ Xrp; P ≤ 0.012) and superoinferior condylar shift on the left side inferior (Δ Zli; P ≤ 0.011). The same trend can be noticed in Table 4 with statistically significant differences in anteroposterior shift on the right side posterior (ΔXrp, P ≤ 0.037) and superoinferior shift on the right side inferior (ΔZri, P ≤ 0.004), on the left side inferior (ΔZli, P ≤ 0.005) and on the left side superior (ΔZls, P ≤ 0.007) between the tested CR registration techniques. The differences can be explained as aberration (anomaly) in results obtained during measuring rather than the tendency towards inconsistencies within and between CR registration techniques.

Table 3. Kruskal-Wallis test used in evaluation of CR registration techniques (bimanual manipulation, chin point guidance and Roth's method) within methods.

	Hi-square	Df	Significance
Δ Yr	3.770	3	0.287
Δ Yl	3.051	3	0.384
Δ Xra	1.775	3	0.620
Δ Xrp	11. 005	3	0.012
Δ Zri	3.848	3	0.278
Δ Zrs	1.069	3	0.785
Δ Xla	2.074	3	0.557
Δ Xlp	0.984	3	0.805
Δ Zli	11.068	3	0.011
Δ Zls	3.896	3	0.273

ΔYr – mediolateral shift to the right; ΔYl – mediolateral shift to the left; ΔXra – anteroposterior shift right anterior; ΔXrp – anteroposterior shift right posterior; ΔZri – superoinferior shift right inferior; ΔZrs – superoinferior shift right superior; ΔXla – anteroposterior shift left anterior; ΔXlp – anteroposterior shift left posterior; ΔZli – superoinferior shift left inferior; ΔZls – superoinferior shift left superior; df – degrees of freedom.

Table 4. Kruskal-Wallis test used in evaluation of CR registration techniques (bimanual manipulation, chin point guidance and Roth's method) between methods.

	Hi-square	df	Significance
Δ Yr	0.263	2	0.877
Δ Yl	0.593	2	0.744
Δ Xra	5.180	2	0.075
Δ Xrp	6.580	2	0.037
Δ Zri	11.284	2	0.004
Δ Zrs	2.409	2	0.300
Δ Xla	0.762	2	0.683
Δ Xlp	1.153	2	0.562
Δ Zli	10.574	2	0.005
Δ Zls	9.857	2	0.007

ΔYr – mediolateral shift to the right; ΔYl – mediolateral shift to the left; ΔXra – anteroposterior shift right anterior; ΔXrp – anteroposterior shift right posterior; ΔZri – superoinferior shift right inferior; ΔZrs – superoinferior shift right superior; ΔXla – anteroposterior shift left anterior; ΔXlp – anteroposterior shift left posterior; ΔZli – superoinferior shift left inferior; ΔZls – superoinferior shift left superior; df – degrees of freedom

Discussion

Different CR recording techniques have been described in the literature. The reliability evaluation of these techniques is extremely important in clinical practice in order to determine the most accurate and most accepted technique by both the dentist and patients. All methods of CR registration (bimanual manipulation, chin point guidance and Roth's method) tested in this study revealed a high reliability and reproducibility in accordance with the three-dimensional condylar shift measurements. The recorded results were expected due to the tested sample (young population with normal occlusal relations and healthy TMJ), the design of the study and mean values of three-dimensional condylar shifts. Although many scientific papers address the very same subject, a comparison between them should not be drawn since there is a difference in design in each study. Besides, different inclusion criteria are applied and different statistical analyses are performed. The studies (9, 19, 21, 23-28) in which only one CR registration technique was used (bimanual manipulation, Gothic arch tracing, chin point guidance, push-back technique, neuromuscular centric technique, Roth's technique and others) using different methodologies (not only mandible position indicator, but also axiography, Arcus digma diagnostics, radiographic techniques (computerized tomography, magnetic resonance)) mostly concluded that all the techniques were reproducible and reliable in both symptomatic and asymptomatic examinees. In the scientific literature, there are also studies (29-31) that examined the consistency of two or more CR recording techniques.

Swenson et al. (29) examined the condylar positions generated by the five CR registration techniques (Roth power centric bite, tongue tip to soft palate, chin point guidance, bimanual manipulation and leaf gauge) and concluded that all methods of CR registration resulted in a very small range of condylar positions. Keshvad and Winstanley (32) conducted a similar study to ours in terms of design and methodology. Instead of the “power centric” technique, they evaluated Gothic arch tracing. They found that bimanual mandibular manipulation and chin point guidance were more reproducible than Gothic arch tracing, which was least consistent of the three techniques. The results obtained in the mentioned study are somewhat in line with our findings. However, the present study shows the same accuracy for all of the three analyzed techniques. This strong consistency might be the result of a better subject “deprogramming” procedure prior to the CR record registration. Numerous scientific publications (21, 26, 32-36) have pointed out that bimanual mandibular manipulation with anterior deprogrammer is one of the most reliable and reproducible methods of determining CR in dentistry. However, there are also scientific publications that oppose this finding, as the one conducted by Paixăo et al (37). Their results showed that a Gothic arch tracing was a more reproducible CR registration technique than bimanual mandibular manipulation. Venturelli et al. tried to dispute the studies in which CR was considered a referent, but not physiological position (38). They observed the temporomandibular joint condyles using magnetic resonance, transcranial radiography and articulator terminal hinge axis analysis in asymptomatic subjects whose occlusion was additionally deprogrammed by occlusal bite and Lucia jig deprogrammers. Those deprogrammers did not cause any statistically significant difference in TMJ condyle shifts regarding their initial position. This contributed to the adaptive capacity of the temporomandibular joint and its capability to maintain the adapted position within physiological boundaries regardless of the environmental and iatrogenic impacts.

The idea for the study came from the fact that the CR is included in both educational and practical curriculum of pre and post-doctoral programs. A lack of relevant knowledge was noticed after the completion of degree programs. Some studies suggest that not only should there be concern over student knowledge of CR but also over some dentist knowledge and certain specialists (39). This is best shown in studies which examined the compatibility of dental curricula within different university study programs (40), as well as presentations on CR given by educators and existence of consensus among different specialists (in prosthodontics, orthodontics and maxillofacial surgery) who use CR in their clinical practice (41). Unfortunately, the results of those studies were in discrepancy and inconsistency within and between the tested techniques. Further studies on CR are needed (possibly randomized) in order to find the definition, position and usage of this controversial term.

Conclusions

Within the limitations of this study, the following conclusions can be drawn: Mean value of the three-dimensional condylar shift of the tested CR techniques was 0.19 ± 0.34 mm. This result could be considered a normal CR finding in young asymptomatic subjects with Angle class I occlusion. No statistically significant difference (p ≥ 0.05) between genders was found; Reliability and reproducibility of bimanual mandibular manipulation, chin point guidance and Roth's method (“power centric“), as clinical methods in CR registration technique determination, is proved by the three-dimensional condylar shift analysis. The null hypothesis was accepted. All three methods that were tested in the study are reliable and consistent and can be performed in daily clinical practice with the same accuracy.