Angular Deviation Research Articles

Effect of Implant Analog Design and Additively Manufactured Casts' Printing Layer Thickness on the Linear and Angular Accuracy of Analogs for Direct Digital Workflow: An In Vitro Study.

To evaluate how implant analog design and printing layer thickness affect the linear and angular accuracy of implant analogs in additively manufactured casts, comparing with conventional implant analogs in stone casts. A reference cobalt chromium mandibular model with a single implant was digitized with an industrial optical scanner and scan bodies compatible with a pressure/friction fit (S) or a screw-retained (N) implant analog for direct digital workflow. These scans were used to fabricate casts with 50 μm (S-50 and N-50) and 100 μm (S-100 and N-100) layer thickness (n=10). Ten stone casts were made after single-step closed-tray polyvinylsiloxane impressions of the model (CNV). All casts were digitized with the same metal scan body and scanner used to digitize the master model, and these scans were superimposed over the scan of the master model to measure the linear (x, y, and z-axes) and angular (XY and YZ planes) deviations (Geomagic Control X). The precision of measured deviations was defined with the average deviation values. Generalized linear model analysis was used to compare the deviations within implant analogs for direct digital workflow, while 1-way analysis of variance and Dunnett's test were used to compare these analogs and conventional analogs (α = .05) Results. The analog design affected the linear deviations (y-axis), while the interaction between the analog design and the layer thickness, and the analog design affected the angular deviations (XY plane, P ≤ .030). S analogs had lower linear and angular deviations than N analogs, and S-50 led to lower angular deviations than N-50 (P ≤ .030). CNV led to higher linear accuracy (y-axis) than N-50, N-100, and S-100 and led to lower angular deviations than all test groups (XY plane) (P ≤ .025). The analogs in S-50 casts had positional trueness similar to or higher than those in other test groups and their accuracy was mostly similar to those in CNV casts. Implant analogs for direct digital workflow deviated more towards lingual and gingival, and conventional analogs deviated more towards buccal, occlusal, and distal. All analogs had a tendency to tilt towards lingual and distal.

Is bracket bonding with guided bonding devices accurate enough for crowded dentition?

This research aimed to study whether bracket bonding using guided bonding devices (GBDs) is accurate enough for crowded dentitions in vitro. Fifteen three-dimensionally (3D) printed resin model sets were included and divided into three groups: mild, moderate, and severe crowding. The resin models were scanned and virtually bonded with brackets. Corresponding GBDs were generated and 3D printed. Subsequently, the brackets were bonded to the resin models on adental mannequin using the GBDs. The models with bonded brackets were scanned, and comparisons were made between the positions of the actually bonded and the planned ones to evaluate possible deviations. There was no immediate bonding failure in any group. The bonding duration tended to increase with crowding severity (P > 0.05). Almost all linear and angular deviations in all groups were below 0.5 mm and 2°, respectively, and no statistically significant difference was found among the different crowding degrees (P > 0.05). In all groups, the brackets tended to deviate lingually and had buccal crown torque. Brackets in the groups with mild and severe crowding showed atendency for mesiobuccal rotation. GBDs provide high bracket bonding accuracy for dentitions with different crowding degrees and, thus, could hopefully be applied to uncrowded and crowded dentitions alike.

Error analysis and accuracy evaluation method for coordinate measurement in transformed coordinate system

Multiple coordinate system transformations are required for engineering measurements of multi-faceted components. Traditional engineering measurements neglect coordinate errors after transformations, leading to inaccurate accuracy evaluations for coordinates. In this study, the effects of angular deviation and coordinate value magnitude on coordinate errors during transformations are first analyzed. Additionally, the transformation deviation of the three-point method is examined. Subsequently, an accuracy evaluation method for coordinate measurements is proposed to determine the scale scaling factor and the formula for calculating the variance of measuring coordinate errors. Finally, a coordinate accuracy evaluation method and evaluation formula that consider coordinate system transformation errors are proposed by self-checking. The validity of the proposed accuracy evaluation formula is confirmed through experiments. The coordinate measurement accuracy of the low-cost binocular camera is higher than that of the total station, whether or not coordinate system transformations are considered. Stereo-vision measurement technology is more suitable for small-scale engineering measurements.

Scan accuracy of wireless intraoral scanners while digitizing a combined scan body-healing abutment system

ObjectivesTo investigate the accuracy (trueness and precision) of wireless and wired intraoral scanners (IOSs) when scanning an implant with the combined healing abutment-scan body (CHA-SB) system. MethodsA partially edentulous mandibular model with a CHA-SB at the right first molar site was digitized with 2 wireless (NeoScan 2000 (NW) and TRIOS 4 wireless (T4 W)) and 2 wired (NeoScan 1000 (N) and TRIOS 4 wired (T4)) IOSs 44 times in total (n = 11). The reference scan file was generated by digitizing the same master model and CHA-SB with an industrial-grade optical scanner. All files were imported into a metrology-grade analysis software program to evaluate the surface (root mean square, RMS), linear, and angular deviations of the top part of the SB. The average deviation values defined the precision of the scans. The data were statistically analyzed (α = 0.05). ResultsIOS type affected the surface and angular deviations and the precision (linear deviations on the x-axis) of the scans (p ≤ 0.043). T4 W had lower RMS than N and T4 (p ≤ 0.031). T4 had higher angular deviations than N on the XZ plane and had the lowest angular deviations on the YZ plane (p ≤ 0.011). T4 W scans had higher precision than N scans (p = 0.024). ConclusionDespite some differences in the trueness or precision of scans, tested IOSs mostly enabled similar scan accuracy. Regardless of the IOS, the implant scans had a tendency to tilt mesiobuccally, which can be considered clinically small. Clinical SignificanceTested wireless intraoral scanners may be suitable alternatives to their wired counterparts while digitizing an implant with a combined healing abutment-scan body system in the posterior region. However, the crowns fabricated from tested scans might require buccal, mesial, and occlusal surface veneering and distal surface adjustments.

A multifunctional scannable mounting device for computer guided implant surgery: An in vitro study

As part of the growing digitization of the dental field, clinicians are looking for ways to simplify digital workflow, reduce chairside time, and provide new work patterns for future applications. Whether scanning with a multifunctional apparatus (MFA) scan body results in improved scanning is unclear. The purpose of this in vitro study was to compare the horizontal, vertical, and angular deviations with the MFA scan body with a commercially available scan body (SBIO). Sixteen identically printed edentulous maxillary models were used to plan two Ø3.8×11.5-mm implants in the right maxillary first molar and left maxillary central incisor locations. Two implants in each model were installed using a surgical guide. The models were scanned using an intraoral scanner with MFA and then rescanned twice, with SBIO using the intraoral scanner and a laboratory 3D scanner. The implants were digitally positioned according to the scanned MFA and SBIO locations in standard tessellation language (STL) files. These STL files were superimposed on the reference laboratory 3D scanner STL files. Linear measurements included implant apex/cervical horizontal/vertical deviations, as well as implant axis angular deviations. Normality was evaluated with the Shapiro-Wilk test. Paired samples t tests (2 sided) were used for the mean SBIO-MFA deviation difference. To compare the molar/incisor sites, paired samples Wilcoxon tests were used (α=.05 for all tests). No statistically significant differences were found between the MFA/ SBIO deviations, for each of the 10 sites × deviation combinations (P>.05). Overall, the lowest endpoint of the 95% confidence intervals among the 8 linear measurement comparisons was -0.107 mm (coronal vertical deviation, right maxillary first molar site) and -0.30 degrees between the 2 angular measurement comparisons. The current in vitro study demonstrated high accuracy for the novel MFA device, similar to that of the standard SBIO scan body. Furthermore, the current study offers an alternative technique to evaluate the accuracy of implant placement by using scanning and back programming over the traditional postplacement cone beam computed tomography (CBCT) scanning.

Scan-body accuracy and angular deviation with different IOS

Scan-body accuracy and angular deviation with different IOS

A novel technique to resolve directional ambiguity for Particle Streak Velocimetry

In this study, a novel streak direction-resolving algorithm is introduced to determine the direction of the flow field for a single image frame with multiple streaks. The streak direction was resolved by varying its intensity from 100% to 50% of the total intensity of the streak image. This technique was applied to two main types of flows parallel and Hill’s vortex flows, parallel flows were divided into further two types constant velocity parallel flow and accelerating parallel flow. The purpose of using different types of flows was to test the robustness of the algorithm with easy and complex flows. The performance of the algorithm was checked by the angular deviation between the true and least-square fitted velocity vectors. The number of correct synthetic streak directions was measured with the success rate in percentage. A high success rate means low angular deviation and a high number of velocity vectors with correct direction was obtained. In this research, four different types of image formats were considered DP (double precision), 16-bit (without noise), 16-bit (1.0% noise), 16-bit (5.0% noise), and 8-bit (without noise) and the best results were obtained for DP and 16-bit image formats. The results of the parallel flows indicated a 100% streak direction success rate, Hill’s vortex was a type of complex flow therefore, the algorithm hard to resolve some streak directions due to very low velocities (less than 0.1 px (pixel)/interval) and very high-velocity gradients (greater than 52 px/interval). The observation shows that Hill’s vortex synthetic streak images were resolved with a success rate of 92.76% which means that the majority of the synthetic streaks were resolved. Experimental analysis was also done by using the PDMS microchannel setup. Intensity variation streaks were recorded with long camera exposure time and for maintaining the intensity variation, as the LED switched on maximum illumination was started, and continuous decrement in illumination was set by switching off at 50% of the total illumination intensity. The best results were achieved with a 94% success rate. Therefore, the proposed novel approach can be used with less expensive hardware for image processing with a single image frame and is useful for multiple applications.

A feedforward kinematic error controller with an angular positioning deviations model for backlash compensation of industrial robots

The accuracy of industrial robots, typically on the order of several millimeters, has inhibited their adoption in advanced aerospace manufacturing applications, such as robotic machining. For this reason, extensive investigations have been conducted to develop solutions to improve their accuracy. These solutions can be categorized into offline and online compensation strategies, both of which have advantages and limitations. Offline compensation has been shown to improve the accuracy of industrial robots by two to three orders of magnitude; however, the sensitivity of these solutions to environmental changes and external disturbances can degrade their performance. In contrast, online compensation, which utilizes real-time measurement and compensation, is robust to these changes; however, the performance of these solutions is limited by the causality of time, preventing them from compensating fast changing errors such as backlash. In this work, a novel kinematic modeling strategy, which models the robot’s angular positioning deviations to predict when backlash will occur, is integrated into a novel online kinematic error compensation framework to leverage the advantages of both solutions. By integrating the proposed kinematic model into the online compensation framework, backlash errors can be predicted and preemptively compensated to improve performance. The performance of the combined system was evaluated using ball bar measurements, where it was shown to improve the circularity of the ball bar motion by 25 %.

Accuracy of polyether and vinylpolysiloxane impressions when using different types of 3D-printed impression trays - an in vitro study.

To investigate dimensional accuracy of polyether (PE) and vinylpolysiloxane (VPS) impressions taken with manually fabricated and 3D-printed trays. To evaluate impression accuracy, highly precise digital data of a metallic lower jaw model with prepared teeth (regions 34 and 36), an implant (region 47) and three precision balls placed occlusally along the dental arch served as reference. PE (Impregum, 3M Oral Care) and VPS (Aquasil, Dentsply Sirona) impressions (n = 10/group) were taken with trays fabricated using different materials and manufacturing techniques (FDM: filament deposition modeling, material: Arfona Tray, Arfona; printer: Pro2, Raise3D; DLP: digital light processing, material: V-Print Tray, VOCO, printer: Max, Asiga; MPR: manual processing with light-curing plates, material:LC Tray,Müller-Omicron) including an open implant impression. Scans of resulting stone models were compared with the reference situation. Global distance and angular deviations as well as local trueness and precision for abutment teeth and scan abutment were computed. Possible statistical effects were analyzed using ANOVA. Clinically acceptable global accuracy was found (all mean absolute distance changes < 100μm) and local accuracy for single abutments was excellent. All factors (abutment type, impression material, tray material) affected global accuracy (p < 0.05). In particular with PE impressions, MPR trays led to the best accuracies, both in horizontal and vertical direction. Within the limitations of this in vitro study, impression accuracy was high in use of both polyether and vinylpolysiloxane combined with different 3D-printed and customized trays making them recommendable for at least impressions for smaller fixed dental prostheses. Manually fabricated trays were overall still the best choice if utmost precision is required. Based on the results of this study, use of innovative CAD-CAM fabrication of individual impression trays fulfills the perquisites to be a viable option for impression making. In the sense of translational research, performance should be proved in a clinical setting.

Spontaneous Alignment of Boron Nitride Nanotubes into Polycrystalline Film Arrays for Enhanced Piezoelectric Nanogeneration

1D nanomaterials feature distinct physical properties owing to their characteristic anisotropy and size‐induced quantization; yet, creating an ordered ensemble of the nanomaterials is nontrivial, marking it as a grand challenge in materials science. Herein, the spontaneous alignment of a model 1D nanomaterial, boron nitride nanotube (BNNT), into a highly ordered multidomain film is presented. A conventional, benchtop gravity filtration is employed, during which thickening of the BNNT dispersion leads to a formation of the liquid crystal (LC) phase that is readily isolatable. The spontaneity of the phase separation excludes notoriously persisting synthetic impurities to a degree &gt;99%, from ≈50% of the initial material purity. The LC‐based thin film features an aligned multidomain with an exceptionally low angular deviation of &lt;2.5° and a domain size of &gt;50 μm. A piezoelectric nanogenerator based on the thin film records a 1000‐fold increase in the piezocurrent compared to its random analog. This work demonstrates the first example of the spontaneous alignment of an unconventional nanotube system and the realization of the macroscopic properties therefrom, which can be readily expanded to 1D materials in general.

Effect of Storage Conditions and Time on the Dimensional Stability of 3D Printed Surgical Guides: An InVitro Study.

To evaluate the dimensional stability over time of additively manufactured surgical templates, fabricated by different resins, and stored by different methods. Using a 3D printer with DLS technology and two different resins (Surgical Guide (SG)-WhipMix and Key Guide (KG)-KeystoneIndustries), 96 surgical guides were additively manufactured. The guides were stored in three different environments: directly exposed to sunlight (S1), in normal interior room conditions (S2), and in darkness (S3). The guides were digitally scanned immediately after fabrication and post-processing, and after 1, 3, and 6 months of storage. For each group, the mean deviation of the root mean square (RMS) between guide's intaglio surface, as well as the axial deviation between sleeves' housings were calculated. The mean axial variations of angular axis deviation of sleeves' housings ranged between 0.09° and 3.99°. The mean deviation of the RMS discrepancy in guide's intaglio ranged from 0.1 to 0.18 mm. Variations were significant (p < 0.001) only for the S1 group and only for SG material. After 3 months, an additional storage time of 3 months did not have any further effect on dimensional stability. Within the limitations of the present study, storage time of a surgical guide for up to 3 months after manufacturing, as well as printing material can significantly affect surgical guide's dimensional stability, when they are exposed to direct or indirect sunlight conditions. Storage of guides in a dark environment is recommended in order to avoid an additional source of error in computer-guided surgery workflows.

On Self-Positioning and Self-Fixation of Parts Made of Alloys with Shape Memory Effect under Component Assembling

Introduction Violation of mutual positioning and fixation of parts worsens the operation of the equipment. Traditional approaches to solving the problem under consideration have been sufficiently studied: interchangeability of parts and the use of special equipment. Both methods involve a significant number of additional elements and assembly operations. Fixation is often provided by means of force fitting and welding. Disadvantages of these methods include assembly, residual and other stresses, engineering constraints, etc. To solve these problems, alloys with thermoelastic phase transformations are used, which provide shape memory effects (SME) to manifest themselves. This article describes, for the first time, self-positioning and self-fixation using the example of parts specially made from an alloy with SME. Materials and Methods. The pin element under pressing mandrels the blind hole of the cup and enters the seat. The alloy with SME was Ti-55.7wt%Ni. The temperature of the onset of its austenitic transformation was As = 95°C ± 5°C. The elemental composition was determined by a Shimadzu EDX-8000 X-ray fluorescence spectrometer, the phase composition — by a Shimadzu XRD-7000 diffractometer. The temperature was specified through differential scanning calorimetry. The range was 20–300°C, the heating rate was 5 deg/min. A Guide T120 thermal imager and a RangeVision DIY 3D scanner with structured illumination were used. After pressing the pin into the cup at different angles, the alignment and deviations between the axes of the cup and the pin were examined. Then, the cup was heated to 110–120°C, cooled, and control measurements were taken.Results. Values of the deflection angle after pressing were 0.2–11°. With a rigid structure and an installation angle of 0°, the pin deflected in the mounting hole by 0.2–0.5°. The axes shifted and did not intersect. The pin was not always completely pressed in. This indicated uneven deformation of the metal and different stress values around the hole. Such a unit would soon fail. The pin took the required position after heating the cup to 110–120°C (this temperature was higher than at the end of the reverse martensitic transformation). The angular deviation of the axes was noted to be 0.03–0.1°. The maximum misalignment (0.04 mm) corresponded to high positioning accuracy. Heating during the reverse martensitic transformation created internal stresses that returned the initial geometry of the cup. They also formed the forces that positioned and fixed the pin in the hole. That is, it is the parts that provide positioning and fixation (this is selfpositioning and self-fixation).Discussion and Conclusion. For self-positioning and self-fixation of parts due to the shape memory effect, it is necessary to avoid sharp transition lines between the surfaces of parts during design, select rounded corners or fillets, and get a clean surface without burrs. Self-fixation and self-positioning reduce defects and inaccuracies during assembly. The use of certain alloys increases the profitability of equipment production.

Closed reduction by robot with different modes: Experimental study on tibial fracture specimen

PurposeThis paper evaluates the accuracy and safety of a long bone fracture reduction robot under different surgical modes. MethodsA long bone fracture reduction robot system was developed, which can be controlled via an autonomous surgical mode or a master-slave surgical mode. Reduction experiments were conducted on a long bone cadaver specimen. The accuracy and safety of the robotic reduction were compared across the different surgical modes. ResultsWhen the fracture reduction was completed by the robot, the translational deviation was less than 2 mm, and the angular deviation was less than 3° The autonomous reduction time was 140 s, while the master-slave reduction time was 200 s. ConclusionsBased on CT imaging verification, the accuracy of the robot in both autonomous and master-slave surgical modes meets clinical requirements. Future work will focus on further optimizing the robot system.

The effect of arm muscle discrete relaxation training and fine-coordination training on proprioceptive control

Proprioception makes an important contribution to the regulation of speed, strength and spatial parameters of movements, determining the level of proficiency in motor skills. However, the effectiveness of various training approaches in relation to voluntary proprioceptive control of target muscles has not been sufficiently studied. In this paper, we investigated the effectiveness of three types of manipulative training: 1) fine coordination, 2) discrete muscle relaxation and 3) their combinations in relation to the accuracy of reproducing:а) the angular deviation of the joystick from the vertical and b) static muscle efforts during the pronation and supination of the joystick. The study involved 40 young (18-35 years old), physically active volunteers who randomly made up 4 groups of 10 people: “Control” (lack of training), “Coordination” (training of passing an analog of a slit maze with a thin probe), “Discrete relaxation” (training of discrete muscle relaxation of pronators and supinators of the forearm), “Combined” (combined training of maze passing and discrete relaxation). Before and after training (n = 10) we evaluated: 1) the accuracy of reproduction of the deviation of the wrist joystick from the vertical by 20, 50, 80 degrees and 2) the accuracy of reproduction of isometric contraction (0, 20, 50 and 80% of the maximum effort) in the descending, ascending directions as well as discrete achievement of any effort level by pronation /supination of the wrist joystick. It was found that coordination training increased the length of the traversed path in 3 minutes with a reduced number of errors, and increased the proprioceptive accuracy of reproducing the angle of deviation of the joystick by 20 degrees also. In the “Discrete Relaxation” group the average modulus of errors in reproducing descending, ascending and discrete forces during supination, as well as the average modulus of errors in reproducing descending, ascending and discrete forces during forearm pronation decreased after course training. At the same time, no changes in the accuracy of reproducing the angular positions of the joystick were found in this group. In the “Combined” group, training led to an increase in the accuracy of reproducing ascending and descending efforts during pronation, as well as the accuracy of descending efforts during supination of the forearm. In addition, in this group, a decrease in the error modulus during reproducing the tilt of the joystick by 50 degrees by supination was revealed. Correlation analysis did not reveal positive links between training changes in proprioceptive control of different modality. Thus, the training effects used on the target muscles of the forearm have a specific effect on the proprioceptive control of muscle effort and spatial position in the hand joints. The high efficiency of discrete relaxation training regarding the accuracy of voluntary efforts allows us to recommend its use in order to increase the level of mastery of the motor skills of the hand.

An on-machine measurement and calibration method for incident laser error in dual-swing laser heads

The dual-swing laser head is essential for five-axis laser machining, yet its precision is greatly affected by the incident laser beam. Any positional or angular deviation in the laser can cause the focus spot position of the head to change continuously during rotation, thereby severely compromise the manufacturing performance of the head. However, the current calibration methods for the incident beam of dual-swing laser heads have issues with low accuracy and insufficient engineering applicability. This paper proposes an on-machine measurement and calibration method for incident laser error in dual-swing laser heads. An error model for the incident beam with a dual-swing laser head was established, from which the law of spot position changes caused by incident beam errors during the head's rotation was derived. Subsequently, following this law, a precision calibration method for the laser head's incident beam error was proposed, based on the theory of optical image height. Afterwards, an on-machine error measurement system was established on the dual-swing laser head, and the calibration method was verified through experiments. The results show that the use of this calibration method can improve the accuracy of the incident beam for dual-swing laser head to 0.071 mm, which is approximately 3–4 times better than traditional calibration methods, thereby significantly enhancing the manufacturing precision of the laser head.

On the implementation of acollinearity in PET Monte Carlo simulations

Objective.Acollinearity of annihilation photons (APA) introduces spatial blur in positron emission tomography (PET) imaging. This phenomenon increases proportionally with the scanner diameter and it has been shown to follow a Gaussian distribution. This last statement can be interpreted in two ways: the magnitude of the acollinearity angle, or the angular deviation of annihilation photons from perfect collinearity. As the former constitutes the partial integral of the latter, a misinterpretation could have significant consequences on the resulting spatial blurring. Previous research investigating the impact of APA in PET imaging has assumed the Gaussian nature of its angular deviation, which is consistent with experimental results. However, a comprehensive analysis of several simulation software packages for PET data acquisition revealed that the magnitude of APA was implemented as a Gaussian distribution.Approach.We quantified the impact of this misinterpretation of APA by comparing simulations obtained with GATE, which is one of these simulation programs, to an in-house modification of GATE that models APA deviation as following a Gaussian distribution.Main results.We show that the APA misinterpretation not only alters the spatial blurring profile in image space, but also considerably underestimates the impact of APA on spatial resolution. For an ideal PET scanner with a diameter of 81 cm, the APA point source response simulated under the first interpretation has a cusp shape with 0.4 mm FWHM. This is significantly different from the expected Gaussian point source response of 2.1 mm FWHM reproduced under the second interpretation.Significance.Although this misinterpretation has been found in several PET simulation tools, it has had a limited impact on the simulated spatial resolution of current PET scanners due to its small magnitude relative to the other factors. However, the inaccuracy it introduces in estimating the overall spatial resolution of PET scanners will increase as the performance of newer devices improves.

Shape Anisotropy of Grains Formed by Laser Melting of (CoCuFeZr)17Sm2

For permanent magnetic materials, anisotropic microstructures are crucial for maximizing remanence Jr and maximum energy product (BH)max. This also applies to additive manufacturing processes such as laser powder bed fusion (PBF-LB). In PBF-LB processing, the solidification behavior is determined by the crystal structure of the material, the substrate, and the melt-pool morphology, resulting from the laser power PL and scanning speed vs. To study the impact of these parameters on the textured growth of grains in the melt-pool, experiments were conducted using single laser tracks on (CoCuFeZr)17Sm2 sintered magnets. A method was developed to quantify this grain shape anisotropy from electron backscatter diffraction (EBSD) analysis. For all grains in the melt-pool, the grain shape aspect ratio (GSAR) is calculated to distinguish columnar (GSAR &lt; 0.5) and equiaxed (GSAR &gt; 0.5) grains. For columnar grains, the grain shape orientation (GSO) is determined. The GSO represents the preferred growth direction of each grain. This method can also be used to reconstruct the temperature gradients present during solidification in the melt-pool. A dependence of the melt-pool aspect ratio (depth/width) on energy input was observed, where increasing energy input (increasing PL, decreasing vs) led to higher aspect ratios. For aspect ratios around 0.3, an optimum for directional columnar growth (93% area fraction) with predominantly vertical growth direction (mean angular deviation of 23.1° from vertical) was observed. The resulting crystallographic orientation is beyond the scope of this publication and will be investigated in future work.

Effects of facial forms and midline deviations and rolls on female facial beauty according to laypeople, orthodontists, and prosthodontists or restorative dentists

No study has examined the simultaneous effect of facial forms, midline deviations and midline angulations on facial beauty. Therefore, this comprehensive study aimed to evaluate these and many other hypotheses. This psychometric study was performed on 15,042 observations. A female frontal photograph was edited to 45 perceptometric images with controlled anatomical alteration: 3 facial forms (euryprosopic [brachyfacial], mesoprosopic [mesofacial], leptoprosopic [dolichofacial]), each having either 9 bidirectional midline deviations (0, 1, 2, 3, and 4 mm deviated to the left and right) or 7 bidirectional midline angular deviations (0°, 5°, 10°, and 15° deviated to the left and right). One of the photographs were repeated. These 46 images were esthetically judged by 327 participants (243 laypeople, 49 orthodontists, and 35 ‘prosthodontists or restorative dentists’). Hierarchical mixed-model multiple linear regressions and post hoc tests were adopted to evaluate the simultaneous impacts of the photomodel’s facial forms, midline deviations to the right or left, and midline rolls to the right or left plus sex, age, experience, and dental specialty of the referees on their perception of facial beauty as well as the tolerable zones of midline alterations. These were also done separately for each specialty group, and also for each facial face. Ideal combinations of anatomic features were determined using repeated-measures ANOVAs. Differences between esthetic preferences of different groups in terms of each image were assessed using one-way ANOVAs and t-tests (α = 0.05, α = 0.008, α = 0.001). All 5 anatomical features significantly and independently influenced perception of facial beauty. The tolerance threshold for midline deviations was 1 mm deviations to the right and left sides. For midline rolls, the only tolerable form was the no-roll (‘on’) midline; the judges preferred right-oriented defects over left-sided ones. The most beautiful facial form was mesoprosopic, followed by leptoprosopic. Men perceived the female face slightly more attractive than did women. The viewers’ specialty (or lack of it), their age, or their experience did not affect their esthetic preferences. Predictors of esthetic preferences were all 5 anatomical features plus views’ sex, but not their dental specialty, age, or experience. Zones of acceptability and also the ideal range of anatomical features were determined.

Calibration of rotary axis angular positioning deviations in a six-axis robotic manipulator by using the R-Test

Prediction accuracy of the kinematic model plays a pivotal role in offline numerical compensation for three-dimensional (3D) positioning error of a six-axis robotic manipulator. In addition to the Denavit-Hartenberg (D-H) error that was typically discussed in the analogous research, this paper proposes a novel scheme to identify the bidirectional angular positioning deviations of all the rotary axes without using the commercial laser tracker. This proposed scheme employs the R-Test, which is significantly more cost-efficient than a laser tracker employed in many past works. Compared to the conventional D-H model, significantly improved prediction performance of the proposed model was experimentally investigated on three rectangular paths covering the entire workspace. Experimental results indicate that the proposed scheme reduces the residual error from 505.2 to 215.2 mm, compared to 118.8 mm with a laser tracker, while maintaining a significantly lower cost that is 1/100 of a commercial laser tracker. Uncertainty analysis also clarify that when only the D-H error parameters are identified, as in many conventional works, the angular positioning deviations can be a major uncertainty contributor to the identification of the D-H errors. The proposed scheme does not require the R-Test locations to be calibrated, and its influence on the uncertainty in the identified errors is assessed.

Implant position accuracy using dynamic computer-assisted implant surgery (CAIS) combined with augmented reality: A randomized controlled clinical trial

Background/purposeComputer-assisted implant surgery (CAIS) is increasingly performed to reduce deviations in implant position. Dynamic CAIS or navigation systems provide instant display of implant drilling instruments and patient positions directly on the computer monitor. Augmented reality (AR) technology allows operators to visualize real-time information projected onto the lenses of AR glasses. Although AR is being used in medical applications, there are few clinical studies on applying AR glasses to dental implants. The purpose of this randomized clinical study was to compare the accuracy of implant position using the dynamic CAIS with and without AR glasses. Materials and methodsTwenty patients who needed a single dental implant were randomly divided into two groups: combined dynamic CAIS with AR glasses (AR glasses group, n = 10) and dynamic CAIS without AR glasses (non-AR glasses group, n = 10). Three-dimensional (3D) deviations of implant platform, apex and angular deviations were measured and analyzed using independent t-tests (P < 0.05). ResultsThe 3D angular deviations in the AR glasses and non-AR glasses groups were 1.47 ± 1.01° and 2.42 ± 0.76°, respectively. Mean 3D entry point and apical deviations were 0.75 ± 0.45 mm and 0.87 ± 0.45 mm in the AR glasses group, whereas the non-AR glasses group were 1.11 ± 0.44 mm and 1.18 ± 0.50 mm, respectively. There was no statistically significant difference between the two groups. ConclusionImplant position accuracy using dynamic CAIS with AR glasses was similar to dynamic CAIS without AR glasses during a single implant placement.