Temporomandibular disorders (TMD) are defined as conditions producing abnormal, incomplete, or impaired function of the temporomandibular joint(s) (1). They comprise a diverse group of disorders. Some studies show different prevalence of TMD within population (2-5). In a study performed by Progiante et al (4), 36.2% of the population had some degree of TMD pain, wherein 5.1% of the population had severe limitations due to pain. The issue of relationship between dental occlusion, and temporomandibular disorders (TMDs) is a controversial topic in dentistry. Some authors have reported a consistent association between some occlusal factors and TMD (6). Other studies also confirmed the association between occlusal factors and bruxism (7, 8). Although a large number of studies on the relationship between the occlusal interferences and different types of TMDs have been carried out, there have been opposing opinions regarding the causal relationship between them. Most of the clinicians treating TMD agree that occlusal interferences have certain role in occurrence and progression of different types of TMDs (9), and that irreversible occlusal therapy (selective grinding) has its value and application in patients with TMD (10).
Literature findings about clinical measurement of the condylar position at various occlusal irregularities are scarce. Jaw tracking devices with six degrees of freedom allow learning about accurate lower jaw position and kinematics, and are standardly used in investigation of anatomy and function of the lower jaw (11-13). Obrez and Gallo stated that a relatively accurate assessment of condylar position has been possible since the development of a three-dimensional device for mandibular recording with sophisticated mathematical transformation of the obtained data (14).
The aim of this in vivo study was to determine the influence of occlusal interference on the condylar position within the temporomandibular joint, on studied sample using electronic ultrasonic recording device.
Materials and Methods
This study included 10 completely dentate subjects (apart from third molars) without signs and symptoms of the TMD (mean age 26.0 ± 3.7 years), and without previous orthodontic therapy. The subjects had Angle's class I relation of the permanent first lower molar, without crossbite/openbite and without previous extensive restorative treatment. In order to participate in the present study, the participants gave their signed written informed consent approved by the Ethics Committee of the School of Dental Medicine University of Zagreb.
All recordings were obtained using an ultrasonic jaw tracking device with six degrees of freedom (Arcus Digma II, Kavo, and Biberach, Germany). A recording device has transmitters which are attached to the lower jaw by means of a paraocclusal tray, and sensors which are attached to the head by means of a facebow (Figure 1). The recording device measures the real-time latency period between transmitted and received ultrasonic impulses. Based on the six degrees of freedom concept, software of the device calculates spatial position of the condyles, sagittal incisal point and/or occlusal determinants, depending on the module of the device.
Irreversible hydrocolloid impressions (Aroma Fine Plus, GC, Tokyo, Japan) were made for each subject, and individual paraocclusal trays were fabricated on stone casts using light curing acrylic resin (Unitray, Polident, Volčja Draga, Slovenia) according to the manufacturer's instructions. At the next appointment, recordings were made using the ultrasonic jaw tracking device with six degrees of freedom. Each participant was seated comfortably in a chair (upright posture). A paraocclusal tray was fixed on the lower teeth using acrylic resins for temporary restorations (Structur, Voco, and Cuxhaven, Germany). The paraocclusal tray was firmly fixed to the lower teeth, and it was not in contact either with the upper teeth in the maximum intercuspation position or during the jaw movements. After the paraocclusal tray fixation, the facebow was mounted (Figure 1). Recordings were made using the software module ‘Electronic Position Analysis’, according to the manufacturer's instructions (Figure 2). After mounting of the facebow, the maximum intercuspation position was recorded as the reference position for measurements of the condylar position. Using composite resin (Tetric EvoCeram, Ivoclar Vivadent, Schaan, Lichtenstein) an artificial occlusal interference was created on the lingual cusp of the lower left second premolar using composite resin with layer thickness of 1 mm, and polymerized without application of adhesive (for easier removing of the composite resin). Subsequently, the condylar deviations were measured (module ‘Electronic Position Analysis’). The subjects had to bite, and the condylar position was recorded at occlusal position defined by the contact with the artificial occlusal interference on the lower left second premolar.
Using the corresponding computer program (Kavo Integrated Desktop) deviations of the recorded left and right condylar positions were measured: deviation at anteroposterior axis (x), deviation at vertical axis (y) and deviation at lateral axis (z). Deviations of the left and the right condylar position were treated as one sample, much like in similar studies. Apart from the deviations at the axes of the Cartesian coordinate system, the linear deviations between the condylar position at the uninterrupted maximum intercuspation and the condylar position during bite with artificial occlusal interference were also determined. Descriptive statistics (SPSS Statistics 17.0) was used to analyze the obtained results .
Table 1 shows the values of deviations between the maximum intercuspation position and the position of the occlusion with artificial occlusal interference, for the left and the right condyle together (n=20), at the x (anteroposterior), y (vertical) and z (lateral) axis. Figure 3 shows deviations at the x (anteroposterior) and the y (vertical) axis for all participants for the left and the right condyle together (n=20). Three participants had identical values (x=0.2; y=-0.2) of condylar deviations. The average condylar linear deviation between the maximum intercuspation position and the position of the occlusion with artificial occlusal interference was 0.48 mm (SD 0.29, min 0.17 mm, max 1.19 mm). Table 2 shows direction of the condylar deviation between the maximum intercuspation position and the position of the occlusion with artificial occlusal interference on the lower left second premolar.
The study investigated condylar position within temporomandibular joints at occlusion with artificial occlusal interference. On average, superior condylar position during occlusion with occlusal interference at lower left second premolar was determined, with average linear deviation of 0.48 mm (SD 0.29).
Safari et al (15) studied premature occlusal contacts and bruxism, and found links between nonworking occlusal interferences and the bruxism. Manfredini et al (8) found a partial relationship between bruxism and slide from the retruded contact position to maximum intercuspation, laterotrusion interferences and molar asymmetry. Some authors (16, 17) found no relationships between nonworking/working interferences and TMD. Nevertheless, based on a few studies conducted on the function of the condyle and lower jaw with artificial occlusal interferences, it can be concluded that mandibular function has changed with the occurrence of interference (18, 19). Huang et al (18) investigated the influence of the laterotrusion interferences on the movements of the working condyle. The authors (18) concluded that laterotrusion interferences have a significant immediate influence on the working-side condylar movements. In contrast to the present study, which observed interferences in maximum intercuspation position, Huang et al (18) investigated the effect of the occlusal interferences on lateral movements. However, with respect to the determined differences (Table 1), the results of Huang et al (18) study can be interpreted in a fashion similar to the present study. It can be concluded that emergence of the occlusal interferences lead to changes of the condylar position during lateral movements of the lower jaw, and also during maximum intercuspation. Although some authors (13, 20) agreed that occlusal interferences result in changes of condylar position (also confirmed by the results of the present study, see Table 1), it should be emphasized that the changes caused by occlusal interference were confirmed by immediate recording of the lower jaw position. It is difficult to determine how (and whether) these changes affect the long-term balance of the temporomandibular joint, or how (and whether) they affect possible progression or occurrence of different types of the TMD.
Unlike the study carried out by Huang et al (18), wherein both condylar movements, the inferior and the anterior one, were recorded during the lateral movement of the working condyle with occlusal interference, only the superior condylar position (Table 1) was recorded in the present study. The superior condylar position (Table 1) confirms the occurrence of a lever within dental arches due to the occlusal interference at one tooth (clinically high prosthodontic restoration or dental filling).
Within the limitations of this study it can be concluded that the introduction of occlusal interferences leads to immediate changes of the condylar position in the occlusal position of maximum intercuspation. Determined superior condylar position at occlusion with artificial occlusal interference confirms the immediate lever creation within dental arches. Further research of the temporomandibular joint adaptation upon occurrence of the occlusal interference is necessary, especially in patients with different types of temporomandibular disorders.