Accuracy of a predetermined transverse horizontal mandibular axis point

Digital application of three-dimensional diagnosis and treatment with a virtual articulator

OBJECTIVE

The purpose of this article was to introduce a method for the digital application of three-dimensional (3D) diagnosis and treatment with a virtual articulator and 3D data.

CLINICAL CONSIDERATION

With the use of cone-beam computed tomography (CBCT) and intraoral and facial scans, we can create a virtual articulator and evaluate the mandibular position in maximum intercuspation and centric-related occlusion for the patient with an unstable occlusion and temporomandibular disorders (TMD). Based on this, we treated a case using a digital mandibular position indicator (MPI) and fabricated a stabilization splint using a 3D printer. This approach eliminates the traditional impression or model mounting process and the analog face bow transfer. Furthermore, the design of the stabilization splint is accomplished using software.

CONCLUSIONS

The approach outlined in this article offers the potential for a digital diagnosis and treatment process by seamlessly integrating CBCT, intraoral scans, and facial scans with a high degree of accuracy. This may enhance precision in diagnosis and treatment planning, especially for patients with complicated TMD, in addition to facilitating effective communication with orthodontic patients who require thorough attention.

CLINICAL SIGNIFICANCE

Utilizing a virtual articulator and digital MPI for the occlusal evaluation of patients with TMD and unstable occlusion makes it possible to diagnose and analyze the occlusal condition accurately. This approach also allows for precision and efficiency in treatment.

Pure rotation in the temporomandibular joint during jaw opening? A digital motion analysis

OBJECTIVE

In the temporomandibular joint two separate movements of rotation and translation occur in two articular spaces during mouth opening. Over the years, the approach has changed considerably, but it is still subject to controversy as to which of these movement is involved in the initial stage of mouth opening. In the present study, the extent of rotation and translation was investigated in the first 5 mm of mouth opening.

MATERIALS AND METHODS

The study was carried out on 46 volunteers. Anamnesis was taken and patients were examined. For the investigation, an ultrasonic digital motion analyser (KaVo Arcus Digma 2) was applied. The measurements were made after calibration to an arbitrary axis. Each participant performed three open-close movements in succession, starting from maximum intercuspal position.

RESULTS

Data were statistically processed using cubic spline interpolation. Linear regression was then used. The resulting line is significantly (p < 0.0001) different from the horizontal that represents only rotational movement.

CONCLUSION

The results show that during mouth opening from maximum intercuspal position, translation is present continuously in addition to rotation. Therefore, it might be time to re-evaluate the principle of a pure rotational approach.

The Role of Digital Facebow for CAD/CAM Implant-Supported Crowns Workflow

Recent advancements in digital technologies have transformed clinical workflows in dentistry, ensuring precise restorations. Custom-made crowns and fixed partial dentures (FPDs) now rely on virtual articulation. The digital facebow provides individualized data for CAD settings, streamlining the fabrication via digital workflow. For the purpose of demonstrating the differences observed during fabrication, we present a case report involving a 68-year-old patient seeking a replacement for missing teeth 24, 25, 26, and 27. The treatment plan involved the fabrication of an implant-supported FPD using monolithic zirconia (ZrO2). However, technical hurdles emerged during the planning phase, primarily due to spatial limitations posing a risk of mechanical failure over time. Consequently, we pivoted approach towards a porcelain fused to metal (PFM) FPD. For the PFM FPD, individual values from the digital facebow adjusted both virtual and conventional articulators. For comparison, two ZrO2 FPDs were milled-individual settings and average settings. All restorations underwent assessment for occlusion in maximal intercuspal position and eccentric mandible movements. In conclusion, the case report showed that individualized PFM FPD required minimal adjustments compared to milled ZrO2 restorations, whether using individual or average values. Utilizing individual values from the digital facebow reduced operator working time and minimized the intraoral adjustments.

Guided and unguided mandibular reference positions in asymptomatic individuals

OBJECTIVES

To determine the difference between guided and unguided mandibular reference positions assessed by articulator simulation.

SETTING AND SAMPLE POPULATION

This study was carried out at the Division of Orthodontics at Vienna Medical University. The sample population consisted of 19 men and 18 women aged 23-32 years and without temporomandibular disorder.

MATERIALS AND METHODS

Three examiners used bimanual operator guidance and unguided mandibular stationary hinging at final jaw closure before occlusal contact and made occlusal wax recordings. The examiners repeated both techniques after 8 and 17 days on the same subjects. Condylar positions were assessed using articulator-mounted casts and a three-dimensional electronic condylar position indicator.

RESULTS

Bimanual guidance positioned the condylar spheres, on average, 0.1 mm more right and 0.6 mm more posterior and superior to unguided hinging (p < 0.04). The repeatability of bimanual guidance by three operators and on 3 days resulted in inter-repetition standard deviations ranging from 0.19 to 0.4 mm and from 0.41 to 0.76 mm for unguided hinging. The highest fraction of the total variance came from the individuals, followed by days, then intra-operator and interoperator variability. Both methods showed considerable overlap of condylar sphere positions at the 95% confidence level.

CONCLUSION

Within the limits of an articulator study, the spatial variability of condylar sphere positions suggested a statistically but not clinically relevant methodological difference between bimanual guidance and unguided stationary hinging.

Midline correction by asymmetric reciprocal torque: a pilot study

OBJECTIVE

Can we correct dental midline discrepancies by systematic torque bends on all canines and premolars without extraction and mesiodistal tooth movement?

PATIENTS AND METHODS

Eight orthodontic patients (4 males, 4 emales, mean age 31 years) presented a dental midline discrepancy of 2-4 mm, moderate deviation of the chin, no skeletal asymmetry, and a horizontal orientation of the occlusal plane in the frontal aspect. On the side where the mandible was shifted medially, asymmetric torque bends moved the antagonist canine and both premolar crowns buccally, while palatal crown torque was used on the maxillary canine and premolars on the other side. Lingual crown torque corrected the medially shifted canine and premolars in the mandibular dental arch, and buccal crown torque the laterally shifted lower canine and premolars.

RESULTS

On average, torque effects altered the canine guidance by 6.5 ± 4.7°, the first premolar guidance by 7 ± 4.1°, and the second premolar guidance by 6.3 ± 3.7°. Correction of the dental midline shift averaged 1.6 ± 0.8 mm after the torque, and eliminated the midline discrepancy completely (n = 2) or partly (n = 6).

CONCLUSION

In this pilot study, asymmetric reciprocal torque represented a treatment option for midline corrections of approximately 2-4 mm and improvement in the chin position without mesiodistal tooth movement or extraction.

Variations in cyclic mandibular movements during treatment of Class II malocclusions with removable functional appliances

The aim of the study was to establish whether juveniles with a Class II malocclusion change the neuromuscular control of mandibular movements during the course of orthodontic treatment with removable functional appliances (RFAs). Neuromuscular control can be indirectly evaluated by recording cyclic planar mandibular movements which were freely carried out by the patients (28 girls, 14 boys, aged 11.1 ± 1.1 years at the start of treatment) and measured with an ultrasonic device before, during, and after Class II functional appliance therapy, with either an activator or a bite jumping plate. The cyclic movements represented simultaneous rotations of the mandible around a maxillary and mandibular fixed axis (MFHA) and could be characterized by μ(α)-diagrams (μ = swing angle of MFHA, α = mouth opening angle) and path length (L) of the MFHA. The μ(α)-diagrams clearly divided into four parts: movement representing protrusion, mouth opening, and two parts of backward closing as known from Posselt diagrams. Parameters from the Posselt and μ(α)-diagrams were checked by one-factor analysis of variance on a 5 per cent significance level for group dependency. For one-third of the patients investigated, no significant changes were seen in any parameter pre- or post-therapy. However, patients showing an initially large mouth opening capacity or a very short condylar path changed their neuromuscular control to that of Class I subjects. Analysis of μ(α)-diagrams provides the possibility of assessing changes in the neuromuscular control of the mandible during Class II treatment.

The mandibularly fixed hinge axis – investigation of patients with sound and pathological jaws

In former works, we had proved that test persons with sound temporomandibular joints (TMJs) used a mandibularly fixed hinge axis (MFHA) and were able to pilot the mandible by solely two kinematical degrees of freedom. We wondered if we could evaluate the MFHA the same way for patients who had problems with their TMJs. Actually, the MFHA could be determined likewise. The results could provide information on the reason for the distortion of the movement of the TMJs, which cannot be yielded by X-ray radiographs.

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.