Pain and salivary biomarkers of stress in temperomandibular disorders were affected by maxillary splints.

BACKGROUND: Longitudinal intervention studies on treatment options in temporomandibular dysfunction (TMD) including self reports and salivary biomarkers of stress are rare and the exact therapeutic function of occlusal splints widely unknown. METHODS: We examined the therapeutic effects of a Michigan splint with occlusal relevance in patients with TMD using a placebo-controlled, delayed-start design. Two intervention groups received a Michigan splint, while one of them had a placebo palatine splint for the first 3 weeks. We collected pain intensities (at rest and after five occlusal movements), salivary measures associated with stress (cortisol and alpha-amylase) and self-reported psychological distress (stress, anxiety, catastrophizing) at baseline and 3 and 7 weeks after onset of intervention. RESULTS: At baseline, we observed increased pain intensity and psychological distress in TMD patients compared to 11 matched healthy controls. Baseline anxiety was linked to movement pain intensity through stress. Over therapy reductions in pain intensity and morning cortisol were more pronounced in those patients starting immediately with the Michigan splint, while psychological distress decreased similarly in both groups. CONCLUSION: Our results suggest that perceived stress plays a role for the association between anxiety and TMD pain and underlines the need for an interdisciplinary perspective on the pathogenesis and therapy of TMD in a setting where psychotherapeutic knowledge is still scarce or rarely applied.

Association of decrease in insula fMRI activation with changes in trait anxiety in patients with craniomandibular disorder (CMD).

Patients with chronic pain and especially with craniomandibular disorder (CMD) show specific psychopathology in trait anxiety. In a previous longitudinal functional imaging study on CMD we found that the anterior insula was modulated by successful therapy intervention and pain relief. We here intended to investigate possible associations between anterior insula fMRI-activation during occlusal movements and trait anxiety over a splint therapy approach in patients with CMD. Three fMRI-investigations of a craniomandibular occlusion task were performed together with pain score evaluations and scoring of trait anxiety (State -Trait Anxiety Inventory; STAI) before, after two weeks and after three months of a DIR-mandibular splint therapy in a small group (n = 9) of CMD patients. Patients showed increased anxiety levels before therapy assessed with the STAI and the depression and anxiety scale (DASS). Besides of relevant reduction in pain the STAI decreased over time. Reduction in STAI was associated with anterior insular fMRI-activation reduction on both hemispheres. We conclude that the anxiety driven anticipation of pain related to occlusal trigger is processed in the anterior insula and might therefore be a main driver of therapeutic intervention by the splint therapy in CMD.

Symmetry of fMRI activation in the primary sensorimotor cortex during unilateral chewing.

OBJECTIVE: Functional magnetic resonance imaging (fMRI) is one of the most advanced techniques to analyze the cerebral effects on many behavior aspects of the oral system such as chewing and mastication. Studies on imaging of the cerebral representation of chewing demonstrated differential results with respect to cortical lateralization during unilateral chewing. The aim of our study is to clarify the effects of cerebral responses during unilateral chewing. MATERIAL AND METHODS: We used fMRI to compare brain activities during occlusal function in centric occlusion on natural teeth and chewing on a gum located on the right or the left teeth in 15 healthy subjects. Group data were performed by Talairach normalization and in addition by an assignment of activation maxima to individual anatomical landmarks in order to avoid possible loss of spatial preciseness of activation sites by normalization procedures. RESULTS: Evaluation of group data by Talairach normalization revealed representation sites for occlusal movements in bilateral primary (S1) and secondary (S2) somatosensory cortices, primary motor (M1) and premotor cortices, supplementary motor area (SMA) and medial cingulate gyrus, bilateral anterior cerebellar hemispheres and vermis, insula, orbitofrontal cortex, thalamus, and left pallidum. Right-sided chewing showed no differential activation to left-sided chewing, and both showed activation in areas also involved in bilateral occlusion. Both techniques, the one based on group normalization and the one based on an individual evaluation method, revealed remarkable low differences in activation maximum location in the primary motor, the primary and secondary somatosensory cortices, and the anterior cerebellar lobe. All chewing movements tested involved bilateral sensorimotor activation without a significant lateralization of activation intensities. CONCLUSION: Overall, a general lateralization of occlusion movements to the dominant side could not be verified in the present study. Chewing on the left or on the right side of teeth makes no difference for brain representation of chewing. CLINICAL RELEVANCE: The results describe the basic effects of what we can expect by evaluation of cerebral effects of chewing and mastication. Based on these results, clinical fMRI studies can be performed in different patient groups.

Standard and limit values of mandibular condylar and incisal movement capacity.

A clinical functional status was obtained and an instrumental analysis of functional movement patterns of the mandible using the ultrasonic Jaw Motion Analyzer (JMA, Zebris; Isny, Germany) was performed on 259 subjects (100 male, 159 female) who were part of an associated project of the representative population-based Study of Health in Pomerania (SHIP 0). Standardized bilateral "arbitrary" skin points based on anatomical skin references were assumed as posterior reference points in the joint area. The recorded movement patterns were evaluated for condylar movement capacity right and left upon mouth opening (COR and COL, in mm), the incisal right-lateral and left-lateral excursion capacity (IR and IL, in mm), the incisal opening capacity (IO, in mm), and the maximum opening angle (OA, in degrees). For the determination of the standard and limit, the following means were determined with standard deviations and 5th and 95th percentiles: COR 14.52 +/- 4.188 (7.70, 21.40); (33.40; 56.10); OA 32.16 +/- 5.954 (21.40; 41.80). The values for men vs women for IR and for OW and in the age group below 40 years vs 40 years and above for IR were statistically significantly different. Interestingly, the interval between the 5th and 95th percentile in the group with a Helkimo clinical dysfunction index of 1 and approximately the same mean value was significantly greater than in the group with Helkimo 0. Based on this standard and limit values or ranges, individually measured values of functional mandibular movement can be compared and differentiated with respect to hypomobility/limitation (< 5th percentile) or hypermobility (> 95th percentile). This serves to indicate the therapeutic direction for functional treatment to improve the jaw's movement capacity in terms of biomechanical optimization. Objective kinematic measurements can be used for additional documentation of the treatment progress during the treatment course.

Variability and reliability of muscle activity measurements during chewing.

The objective of this study was to test masseter muscle activity and its variability and reliability in terms of repeatable measurements in fully dentate and healthy volunteers during habitual chewing and deliberate unilateral chewing. Three sessions were performed on three consecutive days, each time recording kinematic data and masseter muscle EMG activities through a series of defined jaw exercises, including maximum voluntary contraction, habitual chewing, and left and right unilateral chewing. Asymmetry index (AI) and deliberate chewing index (DCI) scores were used to evaluate the activities of the left and right masseter muscles, which were separately recorded during each of these chewing exercises. DCI scores were side-specific, including two sets of values for left and right unilateral chewing. Reproducibility testing of the values obtained for all parameters revealed good to excellent reproducibility of masseter muscle activity under standardized recording conditions across the consecutive study sessions, with intra-class correlation coefficients (ICCs) ranging from 0.68 to 0.93. Different individuals were found to utilize different strategies of bilateral masseter activation during both habitual chewing and deliberate unilateral chewing.

SICAT function: anatomical real-dynamic articulation by merging cone beam computed tomography and jaw motion tracking data.

Diagnostic imaging and jaw motion tracking are among the most important technologies used to document and assess the functional status of the stomatognathic system and to plan complex prosthetic restorations. However, the two technologies have not been used together until now. This article introduces SICAT Function (SICAT, Bonn, Germany), a new software application that directly combines and merges three-dimensional cone beam computed tomography (CBCT) and electronic jaw motion tracking (JMT) data. The software can also import digital impressions acquired with intraoral scanners and integrate them in functional movement displays. The result is an anatomically precise yet real-dynamic rendering of jaw movement, ready for comprehensive evaluation and analysis. Moreover, changes in the joint space (gap between the condyle and mandibular fossa) at defined mandibular resting positions or during mandibular movements can be directly measured and displayed. Only one CBCT scan is needed for patient-specific assessment of condylar positions (centric and therapeutic), which are displayed together with the joint space. All other positions are derived via correlation with electronic measurements.

Occlusion of artificial teeth in partial dentures in the "chewing center"--first exploratory population-based evaluations.

Occlusal performance is a substantial determinant of the quality of dental prosthetic restorations. In the follow-up (SHIP 1) to the Study of Health in Pomerania (SHIP), a representative population of 3300 subjects was studied in the first exploratory evaluation of the occlusion of artificial teeth in the chewing center (first molar region) of partial dentures. A digital analysis of interocclusal records of habitual intercuspation position (ICP) was performed using the Greifswald Digital Analyzing System (GEDAS), a software package that identifies contact points as transparent areas. 562 subjects (280 men aged 61.7 ± 11.9 years and 282 women aged 60.7 ± 10.7 years) had maxillary removable partial dentures (RPDs), and 619 (271 men aged 65.0 ± 11.5 years and 348 women aged 62.4 ± 10.6 years) had mandibular RPDs. Most RPDs were retained with either attachment retainers (11.7% maxilla, 11.7% mandible), cast clasps (38.4% maxilla, 40.7% mandible), telescopes with double crowns (15.7% maxilla, 19.1% mandible), or wrought wire clasps (16.4% maxilla, 8.2% mandible). Some had a combination of different retention elements. The mean number of artificial teeth was 7.8 ± 2.9 in the maxilla and 7.5 ± 3.0 in the mandible. Only the artificial teeth (first molars) in mandibular partial dentures showed differences in the frequency of occlusal contacts between groups (chi-square test). Of these, telescopic crown-retained RPDs had the highest frequency of occlusal contacts (74.4% at tooth 36 and 77.1% at tooth 46), and wrought wire-retained RPDs had the lowest (48.4% at tooth 36 and 45.2% at tooth 46). The results for RPDs with a free-end saddle were comparable and analogous; contact frequencies for those with an interdental saddle did not differ significantly. Notably, the overall frequency of occlusal contacts was greater for tooth 46 (62.9%) than for tooth 36. In conclusion, when replacing teeth in the chewing center, particularly in the mandible, telescopic crown-retained RPDs offer a distinct advantage in terms of occlusal contacts and thus provide better occlusal stability.

Finite element analysis of the principles and loosening force of the conical telescopic crown: a computer-based study.

OBJECTIVES: The primary goal of the present finite element (FE) analysis of a special removable prosthesis, the conical telescopic crown (CTC), was to validate established results based on a rigid model of the CTC and to analyze its characteristic features as a function of the essential material and geometric parameters. Furthermore, the effectiveness of a new element, the composite stop (CS), was investigated. MATERIALS AND METHODS: The study used an axisymmetric FE model containing the inner and outer crown including resin or ceramic veneer, the CS, the cement layer between the interior crown and the tooth, and the upper part of the tooth itself. RESULTS: For a convergence angle (half-cone angle) α = 4 degrees and a moderate chewing force F = 150 N the loosening force decreased from - 50 N without to - 10 N with CS. Increasing α values yielded a decrease of the loosening force. Adherence between the inner (IC) and outer crown (OC) was achieved for all configurations (α = 2 degrees, 4 degrees, and 6 degrees), except for zirconium crowns with α = 6 degrees. In systems without CS, the maximum tensile stress in the veneer increased proportionally to F, but remained limited in those with CS. CONCLUSIONS: The angle a and the coefficient of static friction µ0 emerged as the decisive parameters of the CTC. The computed fitting/loosening behavior agreed well with results of a simple rigid-body model and experiments. The incorporation of a CS allows ceramic veneering of the outer crown. CLINICAL RELEVANCE: The optimal angle α of the CTC is ascribed to a number of customary material combinations for IC and OC. The CS limits the loosening forces of the CTC to values which guarantee non-traumatic removal of the prosthesis.

Surface EMG of the masticatory muscles (Part 3): Impact of changes to the dynamic occlusion.

The third part of this literature review on the clinical relevance of surface electromyography (EMG) of the masticatory muscles summarizes the results of clinical studies in patients with temporomandibular disorders (TMD), preferably randomized controlled trials, examining the impact of changes to the dynamic occlusion. Clenching in left and right laterotrusive positions results in decrease in EMG activity of masseter and temporalis muscles on both working and non-working side. Masseter muscle exhibits largely uniform bilateral activity in laterotrusive positions, independent of canine guidance or group function with and without non-working side contacts. There is a dominance of temporalis muscle activity on the working side and, in case of posterior contacts and balancing contacts, temporalis muscle activity increases and changes from an unilateral to a symmetrical pattern.

Surface EMG of the masticatory muscles (part 2): fatigue testing, mastication analysis and influence of different factors.

The second part of this review of the literature on the clinical significance of surface electromyography (EMG) of the masticatory muscles systematically examines the results of clinical studies in patients with temporomandibular disorders (TMD), preferably randomized controlled trials, investigating relevant aspects of EMG activity during prolonged chewing activity (fatigue effects), during the mastication process, and under the influence of different factors. Studies on the influence of factors such as gender, age, tooth status, orofacial morphology and (acute) pain, the significance of different occlusal relationships during static and dynamic occlusion, and the impact of changes in static occlusion on EMG activity of the masticatory muscles were included in the review.

Correlation between computer-assisted measurements of mandibular opening and closing movements and clinical symptoms of temporomandibular dysfunction.

197 subjects (74 male, 123 female) were evaluated in this Study of Health in Pomerania associated project (SHIP 0). Both a clinical functional status and an instrumental analysis of functional movement patterns of the mandible were performed in each subject, in the latter case using an ultrasonic jaw motion analysis system. Correlations between instrumental movement pattern features and clinical signs and symptoms of temporomandibular joint dysfunction (TMD), such as joint sounds, palpable impairment of jaw movement, and the termination of opening movement at the incisal point, were particularly significant (p <0.005). Correlations for TMJ crepitation sounds and joint pain on palpitation from the lateral or posterior aspect tended to be less significant (p < 0.1). No association was found for pain on jaw movement or muscle tenderness in response to pressure. A multivariate logistic regression model showed a significant correlation between Helkimo Clinical Dysfunction grades 2 and 3 and the following independent variables: frequent headaches (odds ratio [OR] 4.12; p = 0.032), frequent popping sounds in the jaw joints (OR 5.79; p = 0.012), incisal paths showing conspicuous signs of dysfunction such as deviation or deflection (OR 4.35; p = 0.05), and condylar path anomalies such as jumpy, straight/inverse or irregular tracings (OR 28.59; p = 0.006). Instrumental functional analysis of condylar path tracings allows one to draw statistically valid conclusions about the occurrence of TMD symptoms. It can be helpful to perform condylar path analysis when performing risk assessments for temporomandibular dysfunction in certain situations, particularly before prosthetic rehabilitation.

Clinical relevance of surface EMG of the masticatory muscles. (Part 1): Resting activity, maximal and submaximal voluntary contraction, symmetry of EMG activity.

Based on a comprehensive computerized literature search supplemented by a specific manual search of the literature, the present review article focuses on concrete aspects of the application of surface electromyography (EMG) for evaluation of the masticatory muscles in general and of the masseter and anterior temporal muscles in particular, and presents the current base of knowledge on the clinical relevance of surface EMG in dental applications. In the first stage of the review, publications from the year 2000 or later reporting the results of controlled clinical trials (randomized as far as available) of patients with craniomandibular or temporomandibular disorders (TMD) were analyzed. Data from the selected publications were systematically compiled and divided into subject areas as follows: Resting activity, maximal and sub-maximal voluntary contraction, symmetry of EMG activity, and fatigue effects; EMG activity during mastication, factors (including pain) that affect EMG activity, and the impact of adjusting static and dynamic occlusal relationships; Effects of occlusal splints and other occlusal treatments. Surface electromyography is in principle a suitable tool for neuromuscular function analysis in the field of dentistry. If used according to the specific recommendations and in conjunction with a thorough and conscientious clinical history and physical examination, surface EMG measurements can provide objective, documentable, valid, and reproducible data on the functional condition of the masticatory muscles of an individual patient.

Analysis of jaw movements and muscle activity during mastication with JawReports Software.

We are currently developing new software for simultaneous visualisation and analysis of computerized recorded masticatory function and masticatory muscle activity. With the software, motion data recorded using the Jaw Motion Analyser and EMG data on masseter muscle activity can be uploaded in order to evaluate chewing activity immediately proximal to the occlusal surfaces. The software successfully differentiated between jaw opening and closing movements and filtered out muscle activity peaks, which were graphically depicted in the respective movement trajectories. This tracking strategy made it possible to visualize the movement sectors where chewing forces were effective and to estimate the strength of these forces. In the future, this software should improve our ability to analyze and assess the development of chewing forces. Therefore, it could provide a tool for optimal planning of implant-supported or CAD/CAM restorations.

[Dental education in Germany: new concepts for the dental curriculum]. / Die zahnärztliche Ausbildung : Neue Lehrkonzepte im Studiengang Zahnmedizin.

In Germany, the dental curriculum is still based on dental licensing regulations ("Approbations-/Prüfungsordnung für Zahnärzte") from 1955. Essential changes of the dental licensing regulations have not been made for over 50 years-unlike the medical licensing regulations in Germany. Teaching and learning concepts have, nevertheless, changed considerably in medical and dental education over time. The present study delivers an analysis about reform initiatives in dental education in Germany and introduces examples of innovative projects. To be able to establish long-term and broad reforms in dental education, new licensing regulations for dentists are required. This should create a contemporary framework for education, which assigns resources and enables occupational profile development at specific locations. Thereby, compatibility with the medical curriculum has to be guaranteed just as required adaptations of admission and curricular capacity regulations for dentistry.

GEDAS II--new possibilities in digital contact point analysis.

The following article describes a method for the clinical depiction and documentation of the strength, extent, and location of occlusal contact areas on the basis of digitized bite records. Bite records made of low-viscosity, addition-cured silicone in centric occlusion are digitized in a document scanner using incident and transmitted light scanning. Layer thicknesses < 20 microm were interpreted as occlusal contacts and classified as belonging to the anatomical structures of the occlusal surfaces. This procedure is of particular significance for epidemiological studies, but also of interest for dental practices and laboratories, since it can be used as a simple method of continuous quality control, documentation, and archiving of the patient's current occlusal contact situation.

Do we need real-time MRI for diagnosis of temporomandibular joint disorders?

INTRODUCTION: Magnetic resonance imaging (MRI) has been approved as an appropriate radiological modality for temporomandibular joint (TMJ) diagnosis, whereas the results of international multicenter studies impressively show the limitations of static three-dimensional MRI. The state of the art for dynamic imaging of the TMJ in real-time are TrueFISP sequences in one sagittal plane. In order to support the diagnostics, a computer-assisted visualization procedure has been developed by the authors for both the static and dynamic MRI. METHODS: A number of validated sequences are available for the static 3D-MRI within the clinical routine. For dynamic MRI in real-time, True-FISP sequences in one sagittal plane with a slice thickness of 5-10 mm and 1.3 mm x 1.3 mm spatial resolution were applied. Both the dynamic and static MRI datasets are animated and visualized using the computer-assisted procedure. RESULTS: The computer-assisted procedure reliably supported the clinical diagnosis, especially the visibility of the articular disc was enhanced. On the basis of the static MRI, a 60-year-old patient was diagnosed with anterior disc displacement without reduction. In contrast, by the dynamic MRI, it was recognized how the articular disc was firstly somehow stretched and flattened before the mandibular condyle again glided under the disc, thus resulting in an anterior disc displacement with reduction. CONCLUSION: These results endorse the relevance of real-time diagnosis for the TMJ. The computer-assisted visualization has been approved as a reliable help for clinical diagnosis.

Variability of closing movements, dynamic occlusion, and occlusal contact patterns during mastication.

Virtual articulation makes it possible to overcome the limitations of mechanical articulation. Novel visualization techniques have great advantages. In this study, the occlusal surfaces of the upper and lower teeth were digitized with a 3D scanner, and real functional movements of the mandible were recorded using the Jaw Motion Analyzer (JMA), an ultrasonic measurement system. A coupling component designed for clinical use in the patient's mouth was utilized for precise referencing of the movement and scan data. Similar to a two-sided impression tray, the coupling tray is used to take a joint impression of the upper and lower arches. The JMA records the positions of the mandible and the coupling component in space. The virtual articulator was designed for visualization of jaw relationships during mastication. For analysis of intercuspation, the system generates dynamic images on which closing movements/ dynamic occlusion and contact areas are highlighted. The jaw movement data are plotted to create an envelope surface representing the maximum possible space occupied by the mandible. Such an envelope surface is a type of virtual FGP (functionally generated path) bite registration. It can be applied to design virtual tooth restorations and helps to quantify the occlusal space in a virtual environment. This system can be used to individually register and utilize the variability of occlusal function.

Comparison of computer generated occlusal surfaces with functionally waxed-on surfaces.

CAD/CAM methods are also being used ever more frequently to produce fully anatomical restorations. These automated, computer-assisted methods play an outstanding role in generating occlusal surfaces. This study examines whether such computer generated occlusal surfaces are comparable with those which an experienced dental technician functionally waxes-up in the individually controlled articulator. A comparison of the occlusal surfaces in twelve posterior teeth of eleven functionally healthy patients showed differences ranging from 380 to 530 pm related to the mean difference in volume between both types of occlusal surface. Furthermore, a mean pixel deviation of the superimposed occlusal surfaces of 5.12 +/- 1.951 microm (min: 2.49 microm, max: 9.16 microm) was observed. These deviations were found for both functionless surfaces and occlusal surface areas of the functional occlusion. Thus, comparable occlusal surfaces can be achieved with computer generated methods, but they do not quite achieve the result of functionally waxed-up occlusal surfaces in the individually programmed articulator.

3D-VAS--initial results from computerized visualization of dynamic occlusion.

Visualization of the dynamic occlusion is one of the central tasks in both clinical dentistry and dental engineering. Many aspects of dynamic occlusion, such as the interocclusal function in the posterior region, cannot be seen directly clinically and at best can be recorded with contact paper. Therefore, analyses of the dynamic occlusion using mounted models in the articulator are unavoidable in many cases for reproduction of dynamic occlusion. However, the reproduction of dynamic occlusion in the mechanical articulator has clear restrictions inherent to the process, but also caused by biological variability. Virtual articulators can expediently supplement mechanical articulators, since with them it is possible to display in relation to time unusual and extraordinary perspectives, such as sectional images and flowing, sliding contact points. One of the latest developments in the field of virtual articulation is the 3D virtual articulation system module of the Zebris company, D-Isny. By means of a specially developed coupling tray, 3D-scanned rows of teeth can be matched with computerized motion recordings of mandibular function. The software displays the movements of the 3D-scanned rows of teeth not only with jaw motion but also with chewing motion--therefore movements under chewing pressure--in real time and facilitates special analytical methods transcending mechanical occlusion analysis in conventional articulators: This includes displays of the strength of the contact points and surfaces, the occurrence of the contact points in relation to time, sectional images of the dentition, analyses of the interocclusal gap in the occlusal region, etc. This software and its possibilities are described and explained by reference to individual cases.