Is dynamic occlusal design necessary for anterior guidance recovery in the computer-aided design process? An in vitro study

OBJECTIVES

This study aimed to assess the effectiveness of patient-specific motion in restoring anterior guidance and to investigate the influence of occlusal plane position within a virtual articulator on the design of the anterior guide slope for incisors.

METHODS

Twenty participants' intraoral scan, occlusal plane position, and jaw motion data were recorded. The maxillary anterior teeth were virtually prepared, and the crowns were designed based on average virtual articulator (AVR), personalized virtual articulator (ART), and patient-specific motion (PSM). The anterior guide slope of maxillary central incisors (S1, S2, Sc, Sp) and the mesio-distal angle (MDA) of the canine of prostheses were compared to that of natural teeth (NAT). One-Way ANOVA was utilized to evaluate the effectiveness of the three methods in restoring the anterior guidance of maxillary anterior teeth.

RESULTS

The comparison of Sp and MDA showed no significant difference between the PSM and NAT groups (p > 0.05). However, Sp of the ART group was significantly smaller, while MDA was higher than that of the NAT group (p < 0.05). Sp did not differ significantly (p > 0.05) when the angle of the occlusal plane (AOP) was small. As the AOP increased, Sp of the ART and AVR groups were significantly smaller than that of the NAT group (p < 0.05). With a large AOP, Sp of the ART group was notably smaller than that of the NAT group (p < 0.05), while there was no significant difference between the AVR and NAT groups (p > 0.05).

CONCLUSIONS

Occlusal design based on patient-specific motion proved more effective in restoring natural anterior guidance. The anterior guidance of prostheses designed using a virtual articulator was influenced by occlusal plane position.

CLINICAL SIGNIFICANCE

The utilization of a jaw motion tracer facilitated the transfer of personalized occlusal plane positions and recorded jaw motion, which can be integrated into the digital prosthetic workflow for virtual occlusion adjustment. Occlusal design based on patient-specific motion more effectively restored lingual guidance of maxillary anterior crowns.

A novel technique for implant-supported fixed complete rehabilitation based on a dynamic virtual patient

BACKGROUND

A digital workflow for implant-supported fixed complete prostheses (ISFCP) using photogrammetry (PG), virtual articulator (VA), and virtual facebow (VF) data remains a challenge.

METHODS

The novel ISFCP technique included four steps: (1) formation of a dynamic virtual patient, (2) integration of PG data, (3) fabrication of a diagnostic ISFCP, and (4) fabrication of a definitive ISFCP and test of the deviation.

RESULTS

Dynamic virtual patients were formed by integrating PG, VA, and VF data. The cumulative root mean square deviation between the designed data and actual definitive prosthesis was 140.4 µm.

CONCLUSIONS

The novel technique for ISFCP fabrication described in this paper can help optimise the clinical efficiency and quality of ISFCP but requires an initial learning curve.

CLINICAL SIGNIFICANCE

This technique provides a direct workflow, using PG, VA, and VF data, to fabricate ISFCP based on the provisional restoration.

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.

A Novel Technique to Align the Intraoral Scans to the Virtual Articulator and Set the Patient-Specific Sagittal Condylar Inclination

Customized cast orientations and parameter settings of the virtual articulator according to the patient's condyles are indispensable parts of today's digital workflows in prosthodontics. This article describes a digital technique to align the intraoral scans to a virtual articulator by using a facial scanner to locate the patient's cutaneous landmarks of the arbitrary hinge axis and the reference plane, and to customize the sagittal condylar inclination of the virtual articulator through a digital protrusive interocclusal record and a dental computer-aided design software program. It enables individual cast orientations and virtual articulator parameter settings without conventional facebow transferring and bite registration procedures and can be easily integrated with most virtual articulator systems on the market to allow clinicians and technicians to work in a complete digital workflow and facilitate customized treatment planning and dental prosthesis fabrication.

The Effect of Residual Dentition on the Dynamic Adjustment of Wear Facet Morphology on a Mandibular First Molar Crown

PURPOSE

To evaluate the effect of different residual dentitions on the dynamic adjustment of wear facet morphology on a single mandibular first molar crown with a virtual articulator.

MATERIALS AND METHODS

Gypsum casts (N = 12) of natural full dentitions were mounted on an articulator and scanned. The mandibular right first molar (#46) was prepared and a copy of the tooth before it was prepared and used to design the crown. The wear facets on the original #46 were selected and elevated by 0.3 mm in the occlusal direction to generate high points. The #46 with high points was segmented to create a digital wax pattern. Then different teeth were virtually removed to generate 4 types of residual dentitions: Type I (no teeth), Type II (adjacent teeth), Type III (ipsilateral posterior teeth and canine), and Type IV (all teeth). The crowns were adjusted dynamically with different residual teeth to guide mandibular movement of the virtual articulator. Three-dimensional deviations, negative and positive volumes between crowns and wear facets on the original #46 were analyzed. The Kruskal-Wallis test was used to analyze the results.

RESULTS

The mean deviation values and positive volumes decreased with the decrease in residual teeth, and the negative volumes showed an opposite trend. The mean deviation values, root mean square, and positive volumes were not significantly different. The negative volume of the crowns of Type I was different from that of Type IV (p = 0.031).

CONCLUSIONS

Residual dentition affects the dynamic adjustment of wear facet morphology. When there are insufficient residual teeth, mandibular movements should be accurately measured.

Complete assessment of occlusal dynamics and establishment of a digital workflow by using target tracking with a three-dimensional facial scanner

PURPOSE

To introduce a new and simple digital workflow to record dynamic occlusion, and apply it to occlusal analysis and prosthetic treatment in a virtual environment.

METHODS

A table-top scanner (Identica hybrid) was used to transfer fabricated casts into a virtual environment. A facial scanner (Rexcan CS2) was used for facial scanning and target tracking. Four targets were attached to each of the four incisors in the maxilla and mandible to track jaw movement. Target position data were recorded in real time during eccentric movement. The targets were replaced with maxilla and mandible cast scan data, and mandibular movement relative to the maxilla was reconstructed. Four types of antagonist meshes were reconstructed in computer-aided design (CAD) software (EzScan8). The CAD software (Exocad) enabled checking of occlusal contacts in the maximal intercuspation position during eccentric movement.

CONCLUSIONS

Target tracking data were transformed into video clips of dental cast scan data, which showed jaw movements in real time. Occlusal contact information was produced by the CAD software. Both dynamic and static occlusion analyses were performed with reconstructed eccentric movement antagonist meshes. Our new method for reconstructing eccentric movements of the mandible can reveal the occlusal dynamics of a patient within a virtual environment.

The influence of temporomandibular joint movement parameters on dental morphology

Association between tooth morphology, occlusal relations and mandibular condyle/glenoid fossa morphology is still a controversial issue in dentistry. The aim of the present study was to examine the influence of three important articular parameters on the dental morphology and the crown volume, quantifying the variation for each tooth group: incisor, canine, premolar and molar.

MATERIALS AND METHODS

All maxillary teeth from a set of basic study models were prepared for zirconia single crowns. The models were scanned and then, using a computer aided design software, they were mounted in a virtual articulator and specific mandibular movements were defined. The crown morphology was designed and statically adapted. Ten models were obtained by dynamical adjustment of the basic model for successively modified articular parameters: sagittal condylar inclination (SCI)=30°, Bennett angle (BA)=10°, Immediate side shift (ISS)=0.5mm - for control and SCI: 40°, 50° and 60° with BA and ISS as control, BA: 15°, 20° and 25° with SCI and ISS as control, ISS: 1.5mm, 1.0mm and 0.0mm with SCI and BA as control - for the nine test models. The following measurements were performed three times on the right side of each model: volume for each tooth group, slope (S) for the central incisor, S and mesio-distal angle (MDA) for canine, S, MDA and vestibulo-oral angle (VOA) for the first premolar and molar.

RESULTS

When SCI was varied, statistically significant changes as compared to the controls were found for incisor's and premolar's S, premolar's VOA and, for 50° and 60°, MDA and molar's MDA (for 50°) and VOA (for 60°). When BA was varied, significant changes were found for S (canine) and, in certain models, MDA (premolar, molar). Variations of ISS significantly changed mainly MDA for molars and, in two models, premolars.

CONCLUSIONS

Within the limits of this study, among the articular parameters, SCI mostly influenced the dynamic tooth morphology, but canine and molar morphology was stronger influenced by BA and/or ISS.

The role of virtual articulator in prosthetic and restorative dentistry

Virtual reality is a computer based technology linked with the future of dentistry and dental practice. The virtual articulator is one such application in prosthetic and restorative dentistry based on virtual reality that will significantly reduce the limitations of the mechanical articulator, and by simulation of real patient data, allow analyses with regard to static and dynamic occlusion as well as to jaw relation. It is the purpose of this article to present the concepts and strategies for a future replacement of the mechanical articulator by a virtual one. Also, a brief note on virtual reality haptic system has been highlighted along with newly developed touch enabled virtual articulator.