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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., (© 2020 by the American College of Prosthodontists.)

Purpose: To research and develop a novel virtual articulator system (the PN-300) based on computer binocular vision, raster scanning, and simulation technology and to conduct a preliminary evaluation of its accuracy., Materials and Methods: Two digital cameras were used to build the trajectory-tracking part of the virtual articulator system, and cameras combined with a projection module were used to form the scanning part of the system. The most prominent feature of the PN-300 is its ability to simultaneously obtain the 3D data of the subject's teeth and the movement trajectory of the mandible relative to the maxilla. The PN-300 recorded the linear, circular, and rectangular quadrilateral movements of a high-accuracy 3D electronic translation stage. The accuracy of measurement of the inclination of incisal guidance derived from the PN-300 based on the PROTAR evo7 articulator was also estimated., Results: The measurement error was below 100 μm for the linear and circular movements, and the angle error was within 0.2 degrees for the rectangular quadrilateral movements. The error of inclination of protrusive incisal guidance was 1.51 ± 0.68 degrees, and for incisal guidance was 0.82 ± 0.55 degrees. Trajectories and incisal 3D data obtained by the PN-300 were combined with data from plaster models and CBCT to simulate mandibular movement and to calculate the trajectories of the condyle., Conclusion: The PN-300 achieved a good accuracy for recording mandibular movement and can be expected to calculate the movement of the condyle.

Purpose: To research and develop a novel virtual articulator system (the PN-300) based on computer binocular vision, raster scanning, and simulation technology and to conduct a preliminary evaluation of its accuracy.Materials and Methods: Two digital cameras were used to build the trajectory-tracking part of the virtual articulator system, and cameras combined with a projection module were used to form the scanning part of the system. The most prominent feature of the PN-300 is its ability to simultaneously obtain the 3D data of the subject's teeth and the movement trajectory of the mandible relative to the maxilla. The PN-300 recorded the linear, circular, and rectangular quadrilateral movements of a high-accuracy 3D electronic translation stage. The accuracy of measurement of the inclination of incisal guidance derived from the PN-300 based on the PROTAR evo7 articulator was also estimated.Results: The measurement error was below 100 μm for the linear and circular movements, and the angle error was within 0.2 degrees for the rectangular quadrilateral movements. The error of inclination of protrusive incisal guidance was 1.51 ± 0.68 degrees, and for incisal guidance was 0.82 ± 0.55 degrees. Trajectories and incisal 3D data obtained by the PN-300 were combined with data from plaster models and CBCT to simulate mandibular movement and to calculate the trajectories of the condyle.Conclusion: The PN-300 achieved a good accuracy for recording mandibular movement and can be expected to calculate the movement of the condyle. [ABSTRACT FROM AUTHOR]

Purpose: The aim of this study was to explore the application of computer-aided design and rapid prototyping (CAD/RP) for removable partial denture (RPD) frameworks and evaluate the fitness of the technique for clinical application.Materials and Methods: Three-dimensional (3D) images of dentition defects were obtained using a lab scanner. The RPD frameworks were designed using commercial dental software and manufactured using selective laser melting (SLM). A total of 15 cases of RPD prostheses were selected, wherein each patient received two types of RPD frameworks, prepared by CAD/RP and investment casting. Primary evaluation of the CAD/RP framework was performed by visual inspection. The gap between the occlusal rest and the relevant rest seat was then replaced using silicone, and the specimens were observed and measured. Paired t test was used to compare the average thickness and distributed thickness between the CAD/RP and investment casting frameworks. Analysis of variance test was used to compare the difference in thickness among different zones.Results: The RPD framework was designed and directly manufactured using the SLM technique. CAD/RP frameworks may meet the clinical requirements with satisfactory retention and stability and no undesired rotation. Although the average gap between the occlusal rest and the corresponding rest seat of the CAD/RP frameworks was slightly larger than that of the investment casting frameworks (P < .05), it was acceptable for clinical application.Conclusion: RPD frameworks can be designed and fabricated directly using digital techniques with acceptable results in clinical application. [ABSTRACT FROM AUTHOR]

Objective: To quantitatively evaluate maxillary complete dentures fabricated from polylactic acid (PLA) using fused deposition modelling (FDM) technology. Methods: A digital maxillary complete denture was prepared based on a standard maxillary edentulous plaster model. The PLA pattern was printed by a FDM machine, with 5 repetitions, while another 5 wax patterns were printed as control group, using a high accuracy three-dimensional (3D) wax printer. The patterns were scanned with a 3D scanner. A light-body silicone film was made after each denture pattern had been totally seated on the plaster model, and was scanned to determine its thickness, which reflected the 3D space between the plaster model and the tissue surface of the denture pattern. The overall area was separated into four parts: primary stress-bearing area, secondary stress-bearing area, border seal area and relief area, and the average deviation of these four parts were measured. The values were analyzed by independent t-test. Results: The overall mean value and standard deviation of space between PLA denture patterns and plaster model was 0.277 ± 0.021 mm, while that of the wax denture patterns was 0.279 ± 0.045 mm, which showed a good fit overall. No statistically significant (푃 > 0.05) difference was observed between the PLA patterns and wax patterns. Conclusions: The adaptation of the PLA pattern of maxillary complete denture printed by FDM technology is comparable to that prepared by wax printer, and can satisfy the accuracy requirements. [ABSTRACT FROM AUTHOR]

The conventional technique for the fabrication of complete dentures is complex, with a long fabrication process and difficult-to-control restoration quality. In recent years, digital complete denture design has become a research focus. Digital complete denture tooth arrangement is a challenging issue that is difficult to efficiently implement under the constraints of complex tooth arrangement rules and the patient’s individualized functional aesthetics. The present study proposes a complete denture automatic tooth arrangement method driven by a reconfigurable rule; it uses four typical operators, including a position operator, a scaling operator, a posture operator, and a contact operator, to establish the constraint mapping association between the teeth and the constraint set of the individual patient. By using the process reorganization of different constraint operators, this method can flexibly implement different clinical tooth arrangement rules. When combined with a virtual occlusion algorithm based on progressive iterative Laplacian deformation, the proposed method can achieve automatic and individual tooth arrangement. Finally, the experimental results verify that the proposed method is flexible and efficient. [ABSTRACT FROM AUTHOR]

Objective: Developments in digital technology have permitted researchers to study mandibular movements. Here, the accuracy of a real-time, computerized, binocular, three-dimensional (3D) trajectory-tracking device for recording functional mandibular movements was evaluated. Methods: An occlusal splint without the occlusal region was created based on a plaster cast of the lower dentition. The splint was rigidly connected with a target on its labial side and seated on the cast. The cast was then rigidly attached to the stage of a high-precision triaxial electronic translator, which was used to move the target-cast-stage complex. Half-circular movements (5.00-mm radius) in three planes (XOY, XOZ, YOZ) and linear movements along the x-axis were performed at 5.00 mm/s. All trajectory points were recorded with the binocular 3D trajectory-tracking device and fitted to arcs or lines, respectively, with the Imageware software. To analyze the accuracy of the trajectory-tracking device, the mean distances between the trajectory points and the fitted arcs or lines were measured, and the mean differences between the lengths of the fitted arcs’ radii and a set value (5.00 mm) were then calculated. A one-way analysis of variance was used to evaluate the spatial consistency of the recording accuracy in three different planes. Results: The mean distances between the trajectory points and fitted arcs or lines were 0.076 ± 0.033 mm or 0.089 ± 0.014 mm. The mean difference between the lengths of the fitted arcs’ radii and the set value (5.00 mm) was 0.025 ± 0.071 mm. A one-way ANOVA showed that the recording errors in three different planes were not statistically significant. Conclusion: These results suggest that the device can record certain movements at 5.00 mm/s, which is similar to the speed of functional mandibular movements. In addition, the recordings had an error of <0.1 mm and good spatial consistency. Thus, the device meets some of the requirements necessary for recording human mandibular movements. [ABSTRACT FROM AUTHOR]

Background and Objective: To develop a real-time recording system based on computer binocular vision and two-dimensional image feature extraction to accurately record mandibular movement in three dimensions. Methods: A computer-based binocular vision device with two digital cameras was used in conjunction with a fixed head retention bracket to track occlusal movement. Software was developed for extracting target spatial coordinates in real time based on two-dimensional image feature recognition. A plaster model of a subject’s upper and lower dentition were made using conventional methods. A mandibular occlusal splint was made on the plaster model, and then the occlusal surface was removed. Temporal denture base resin was used to make a 3-cm handle extending outside the mouth connecting the anterior labial surface of the occlusal splint with a detection target with intersecting lines designed for spatial coordinate extraction. The subject's head was firmly fixed in place, and the occlusal splint was fully seated on the mandibular dentition. The subject was then asked to make various mouth movements while the mandibular movement target locus point set was recorded. Comparisons between the coordinate values and the actual values of the 30 intersections on the detection target were then analyzed using paired t-tests. Results: The three-dimensional trajectory curve shapes of the mandibular movements were consistent with the respective subject movements. Mean XYZ coordinate values and paired t-test results were as follows: X axis: -0.0037 ± 0.02953, P = 0.502; Y axis: 0.0037 ± 0.05242, P = 0.704; and Z axis: 0.0007 ± 0.06040, P = 0.952. The t-test result showed that the coordinate values of the 30 cross points were considered statistically no significant. (P<0.05) Conclusions: Use of a real-time recording system of three-dimensional mandibular movement based on computer binocular vision and two-dimensional image feature recognition technology produced a recording accuracy of approximately ± 0.1 mm, and is therefore suitable for clinical application. Certainly, further research is necessary to confirm the clinical applications of the method. [ABSTRACT FROM AUTHOR]