Orthopedic jaw movement observations. Part I: Determination and analysis of the length of protrusion

Preliminary clinical study of the accuracy of a digital axiographic recording system for the assessment of sagittal condylar inclination

OBJECTIVES

The aim of this study was to clinically evaluate the accuracy of a digital axiographic recording system in tracing the sagittal condylar inclination.

METHODS

An axiographic examination that records the sagittal condylar path during protrusive/retrusive movement was performed on ten patients. Each subject was registered five different times by two different systems: 1) the Cadiax Gamma Diagnostic 4 computerized system as the control; 2) the Zebris Jaw Motion Analyser+  Optic System as the tested digital axiographic recording system. The records obtained allow to calculate the kinematic terminal transverse horizontal axis and the sagittal condylar inclination (SCI) at 3 and 5 mm along the pro-retrusive path. A linear mixed model was used to analyze if there was a statistically significant difference between the two systems.

RESULTS

The mean left SCI value recorded by Zebris system were 49.81 ± 10.64° at 3 mm, 48.10 ± 11.04° at 5 mm, while the values recorded by Gamma system were 55.16° at 3 mm, 52.18° at 5 mm. The mean right SCI value recorded by Zebris system were 54.53 ± 10.26° at 3 mm, 51.85 ± 8.55° at 5 mm, while the values recorded by Gamma system were 49.68° at 3 mm, 48.23° at 5 mm. Linear mixed model showed no significant statistical difference between the two systems.

CONCLUSIONS

Based on preliminary results, the Zebris Jaw Motion Analyzer+ Optic System demonstrates comparable accuracy to the Cadiax Gamma Diagnostic 4 when measuring sagittal condylar inclination.

CLINICAL SIGNIFICANCE

The digital axiographic recording system enables to evaluate sagittal condylar inclination and to adjust virtual articulators in a digital workflow.

In vivo prediction of temporomandibular joint disc thickness and position changes for different jaw positions

Temporomandibular joint disorders (TMD) are common dysfunctions of the masticatory region and are often linked to dislocation or changes of the temporomandibular joint (TMJ) disc. Magnetic resonance imaging (MRI) is the gold standard for TMJ imaging but standard clinical sequences do not deliver a sufficient resolution and contrast for the creation of detailed meshes of the TMJ disc. Additionally, bony structures cannot be captured appropriately using standard MRI sequences due to their low signal intensity. The objective of this study was to enable researchers to create high resolution representations of all structures of the TMJ and consequently investigate morphological as well as positional changes of the masticatory system. To create meshes of the bony structures, a single computed tomography (CT) scan was acquired. In addition, a high-resolution MRI sequence was produced, which is used to collect the thickness and position change of the disc for various static postures using bite blocks. Changes in thickness of the TMJ disc as well as disc translation were measured. The newly developed workflow successfully allows researchers to create high resolution models of all structures of the TMJ for various static positions, enabling the investigation of TMJ disc translation and deformation. Discs were thinnest in the lateral part and moved mainly anteriorly and slightly medially. The procedure offers the most comprehensive picture of disc positioning and thickness changes reported to date. The presented data can be used for the development of a biomechanical computer model of TMJ anatomy and to investigate dynamic and static loads on the components of the system, which could be useful for the prediction of TMD onset.

Real-time three-dimensional jaw tracking in temporomandibular disorders

When a dysfunction occurs in any component of the stomatognathic system, temporomandibular disorders (TMD) may originate. The aim of this study was to compare the deviations, displacement and the execution speed of mandibular movements among asymptomatic participants and those with TMD. Convenience sampling was used; forty participants diagnosed by clinical evaluation following the Research Diagnostic Criteria for Temporomandibular Disorders were divided into three groups: arthropathy (GART, 10 participants, 40% men), myopathy (GMYO, 10 participants, 30% men), and the control group (CG, 20 asymptomatic participants, 25% men). Participants were asked to perform the movements of free maximal mouth opening and closing, right and left lateral excursions, and protrusion with sliding teeth contacts. The mandibular trajectory was recorded using opto-electronic devices tracking reflective markers placed in front of the 'soft tissue pogonion point'. The movements were analysed on the following axis: x - medial-lateral, y - vertical, z - antero-posterior. Significative differences were found in CGxGART - unassisted maximal mouth opening and closing projection on y-axis (OCY), CGxGMYO - unassisted maximal mouth opening and closing projection on x-axis (OCX), and in the measures Opening lateral deviation on x-axis (OLDX), closing lateral deviation on x-axis (CLDX) and in the measures of speed for both. In regard to GARTxGMYO, a significative difference was found in Protrusion lateral deviation on x-axis (PLDX) 'Conover-Iman Test of Multiple Comparisons Using Rank Sums' using Bonferroni correction (P < 0·05). In conclusion, the total opening movements in individuals with TMD tended to have higher deviation than in those asymptomatic individuals and a reduction in the speed of movements.

Disc displacement without reduction: a retrospective study of a clinical diagnostic sign

OBJECTIVE

The purpose of this retrospective study is to evaluate a clinical diagnostic sign for disc displacement without reduction (DDWR), the absence of additional condylar translation during opening compared with protrusion.

METHOD

Thirty-eight electronic axiographic and magnetic resonance imaging (MRI) examinations of the TMJ were analyzed in order to compare the opening/protrusion ratio of condylar translation between non-painful DDWR and non-DDWR.

RESULT

According to the Mann-Whitney U test, the opening/protrusion ratio in non-painful DDWR differs significantly from non-DDWR (p < 0.0001).

DISCUSSION

Among non-painful DDWR, there is no additional condylar translation during opening in comparison with protrusion, and this is probably also the case for DDWR without limited opening, which is a subtype that has not been validated by the Diagnostic Criteria for Temporomandibular Disorders (DC/TMD). Comparative condylar palpation can analyze this sign, and therefore, further comparative investigations between MRI and clinical examination are needed to validate the corresponding clinical test.

Compatibility of mechanical and computerized axiographs: a pilot study

STATEMENT OF PROBLEM

There is little known information comparing axiographic data obtained with a mechanical device and data obtained with a computerized device. However, long-term follow-up of patients may necessitate comparison of previously made mechanical axiographic data with records obtained through computer-aided axiography.

PURPOSE

The purpose of this study was to compare measurements between mechanical and computerized axiographs in recording the rotational and translation movements of the mandible.

MATERIAL AND METHODS

The study enrolled 31 subjects with no detectable clinical signs of temporomandibular disorders. A single operator obtained 3 separate axiographic tracings of right and left condylar paths for each subject, using repeated opening, closing, protrusive, and retrusive movements. Data were collected for both the mechanical (SAM Axiograph Axo 200), and the computerized axiographs (SAM Axiotron and Axo 500). Angular (degrees) and linear measurements (mm) for the mechanical axiograph were made from the tracings obtained on grid paper using a compass, ruler, and protractor. The computer performed the measurements for the computerized axiograph tracings. All parameters were compared statistically with a Wilcoxon signed rank test (alpha = .05). The same operator remeasured all mechanical axiographic tracings for 20 subjects 1 week later to evaluate measurement error. Chronbach's alpha was used as a measure of consistency between the 2 measurements.

RESULTS

Mean opening and closing angles varied between 52.4 and 54.2 degrees, and mean protrusive, and retrusive angles varied between 50.1 and 54.9 degrees. Mean opening and closing distances varied between 11.4 and 12.3 mm, and mean protrusive and retrusive distances varied between 8.2 and 8.7 mm. Comparison with the Wilcoxon signed rank test showed no significant differences for any parameter tested. There were high and medium inter-item correlations between repeated measurements of the manual device when Chronbach's alpha was applied, but these results were not sufficient to prove consistency between 2 consecutive measurements.

CONCLUSION

The results showed nonsignificant differences between the recordings of the mechanical and computerized axiographs tested. The authors hypothesize that minor differences may be attributed to hand-measuring errors for the tracings generated by the mechanical axiograph. This study is limited due to the impact of poor precision of the manual device on the study results when these recordings are compared to another instrument. Therefore, it is not possible to conclude that data from the manual and the computerized axiographs are compatible with each other.

Comparison of deep bite and open bite cases: normative data for condylar positions, paths and radiographic appearances

To compare normal overbite, deep bite and open bite cases with clinically healthy temporomandibular joints (TMJ) regarding the difference between condylar positions in centric relation (CR) and habitual or centric occlusion (CO), condylar paths and radiographic findings of condylar appearance in order to establish normative data. Three study groups of normal overbite, deep bite and open bite cases consisted each of 30 subjects with no detectable clinical signs of temporomandibular disorder. The CR-CO differences and axiographic tracings were recorded using the School Artikulator of Mack (SAM) diagnostic system. Condylar shape was evaluated on panoramic radiographs. The CR-CO differences were greater in the vertical plane in open bite cases, and direction of movements from CR to CO showed great variability. Open bite cases had significantly shorter condylar paths. Radiographic findings exhibited that 23% of the total sample showed evidence of erosion and 83% evidence of flattening of condyles. The erosion rates were higher in the open bite group, but flattening was seen more often in the deep bite group. Results of this study showed that open bite cases show larger vertical CR-CO slides and, shorter protrusion paths than normal and deep overbite cases. The radiographic appearance of condyles in non-patients may also differ significantly according to vertical incisor guidance type. Deep bite cases demonstrated a higher incidence of condylar flattening. This study indicates that the clinician should be paying special attention to the TMJ status of open bite patients.