Stereolithography File Research Articles

Optimization of a Hydrogen-Fueled Parametric Strut Injector Using an Automated Workflow Computational Fluid Dynamics Method

Abstract A strut injector for burning hydrogen has been optimized using an automated workflow system. In order to choose the optimal set of injectors to cover the design space, an optimized design of experiments (DOE) method was used to automatically choose the parameters that best spanned the design space. One hundred candidate designs were chosen, and a script was used to generate a series of stereolithography (STL) files for each design. The STL files were then uploaded to a supercomputer for computational fluid dynamics analysis. For each of the 100 designs, a four step process was followed to generate the required data, and this included an automated mesh generation step, a field initialization step, a mesh adaptation step, and finally an large eddy simulation all within the yales2 numerical framework. In order to reduce the time required for postprocessing and the amount of data required, the simulations relied heavily on an on-the-fly postprocessing methodology, which reduced the complex time-unsteady flow fields to a small number of quantified outputs of interest that measured the suitability of each design such as the pressure drop across the injector and the efficiency of the mixing process. At the conclusion of these simulations, automated scripts translated these outputs into a smaller set of parameters that could be used to compare each design and allow subsequent optimization and surrogate modeling. Several surrogate modeling methods were attempted with mixed results; however, a simple classification methodology quickly identified the parameters of interest.

Comparing the Accuracy of Conventional Gypsum and 3D-Printed Dental Casts Using Three-Dimensional Analysis.

Dental impressions and casts play a critical role in dental care, facilitating diagnoses and the fabrication of prostheses. Traditional methods of fabrication involve elastomeric materials that are more prone to errors and patient discomfort. Digital advancements offer promising alternatives, yet their accuracy and applicability to military dentistry remain under-explored. This study evaluates the accuracy of digital casts produced with material available in the Military Health System compared to conventional methods. Using a digital (n = 10) and analog (n = 10) methodology casts were fabricated from a reference cast (n = 1). The reference and cast samples were scanned with a reference scanner to generate stereolithography files. These files were used to generate full arch, single crown, fixed dental prosthesis, and inlay digital casts which were then compared using a three-dimensional (3D) comparison software to evaluate accuracy. Root mean square values were obtained, giving a quantitative evaluation of the deviation of each sample from the reference cast. Statistical analysis consisted of a Shapiro-Wilk and Levene test to account for homogeneity of variances in each group. An ANOVA and Tukey post-hoc test were used to determine differences in accuracy among the full arch and a two-way ANOVA and Tukey post-hoc test evaluated differences in trueness among the casts of the individual preparations. Analog full arch casts had an average root mean square of 106 ±19.18 µm when examining trueness and 12 ±2.58 µm for precision. Digital full arch casts had an average root mean square of 51.9 ±5.39 µm when examining trueness and 4.2 ±1.57 µm for precision. Overall digital casts surpassed analog counterparts in accuracy. Fixed dental prostheses were found to be the only group, which showed no statistically significant difference between digital and analog. These findings validate the potential of digital workflows in enhancing the speed and accuracy of dental care in the Military Health System, while underscoring the need for further exploration and refinement in specific clinical contexts.

A novel methodology for analysing dental implant positional changes from virtual planning to placement without CBCT.

Introduction This paper introduces a novel methodology for analysing dental implant positioning in vivo, advancing beyond traditional methods that rely on post-placement cone beam computed tomography (CBCT) scans.Method The core of the methodology is comparing stereolithography (STL) files, representing pre-planned and actual post-placement implant positions. These STL files, exported from guided surgery planning and computer-aided design software, focus on clinically significant key points, like the apical and coronal midpoints. Additionally, the method uses pose detection, differing fundamentally from CBCT scan approximations.Discussion Relying on pose detection instead of scanner resolution, this method aligns with international standards and overcomes CBCT and intra-oral scanner limitations. It allows for a more precise and accurate assessment of implant positions, independent of scanner technology constraints. Further refinements include potential detailed reporting of apical deviations, enhancing implant placement accuracy.Conclusion This research has significant implications for dental implantology, enhancing implant placement precision and overall procedure success. Introducing an automated process for report generation through a batch script improves efficiency and precision, streamlining the analysis process. This innovation sets the stage for future technological advancements, improving both the accuracy and reliability of implant placement assessments.

Verification of mean dose in a tumor using 3D-printed tumor-model scintillators in anthropomorphic phantoms and a spherical phantom

To enhance treatment outcomes of radiotherapy, accurate verification of dosimetric parameters such as the mean, minimum, and maximum doses is essential. This study aimed to measure the mean absorbed dose in a tumor-shaped target and compare the results with the calculated value of the treatment planning system. Tumor model scintillators (TMSs) mimicking brain tumors were fabricated with a commercial 3D printer based on stereolithography files of tumors. The TMSs were irradiated following treatment plans made with the Leksell Gamma Plan® (Elekta AB, Stockholm, Sweden), and the mean dose in each TMS was measured three times and compared with the calculated value. Eleven TMSs were set at the center of a spherical solid water phantom. Two additional TMSs were fabricated according to images of vestibular schwannomas and were set at the tumor location in head model phantoms following each patient's head shape. The mean relative differences between the measured and calculated mean doses were less than one percent. This method provides an independent parameter for evaluating the accuracy of the treatment planning system.

Accuracy of Tooth Segmentation in the Digital Kesling Setup of Two Different Software Programs: A Retrospective Study.

Introduction Precise virtual setup creation and orthodontic appliance fabrication depend on accurate teeth segmentation from intraoral scans. This accuracy is also fundamental for successful orthodontic treatment, as it ensures correct diagnosis and optimal treatment planning. A number of software packages that facilitate the building of virtual setups have been made available in recent years. The performance of these software packages on automatic tooth segmentation has not been widely studied. Hence, the aim of this study was to evaluate the accuracy of automated teeth segmentation in the digital Keslingsetup of Ortho Studio (Maestro 3D Dental Studio, Bordeaux, France) and OrthoAnalyzer (3Shape, Copenhagen, Denmark) software systems. Materials and methods All the scans were taken from the same intraoral scanner (Runyes 3D intraoral scanner; Runyes Medical, Ningbo, China). The scans were stored and imported as stereolithography (STL) files into the Maestro Ortho Studio and 3Shape OrthoAnalyzer software systems. Subsequently, the digital photos underwent alignment in both software applications, an essential stage in each respective workflow prior to any further processing. The digitized images were automatically segmented in Maestro and 3Shape software by a single researcher. For each software interface, the accuracy of teeth segmentation was assessed. An independent t-test, with a significance level set at p < 0.05, was used to evaluate the statistical significance between the two software segmentations. Results The total number of teeth segmented by both software programs utilizing the 12 intraoral scans was 336 for both groups. Successful identification of the tooth segments was 98.21% (n = 330) for 3Shape software and 98.8% (n = 332) for Maestro software. There was no significant difference in the accuracy of determining the tooth segmentations between anterior and posterior teeth, respectively, between both groups, with a p-value of 0.523. Conclusion There were no statistically significant differences between the two software programs, and both demonstrated high success rates for auto-tooth segmentation. Although both programs had excellent success rates, Maestro 3D performed more accurately than 3Shape OrthoAnalyzer.

Infant bronchial tree simulator: Success of a built-from-scratch model for single lung isolation

BackgroundOne-lung ventilation in infants is a high-risk procedure. Complications include endotracheal tube occlusion, with grave consequences. Although there are commercially available bronchoscopy simulators, there are no realistic models of infant patients. This limits access to training opportunities that would ensure safe and efficient lung isolation. To bridge this gap, we developesd a realistic infant bronchial tree model for single lung intubation and evaluated preliminary validity evidence of its features and clinicians’ ability to perform critical skills associated with pediatric one-lung ventilation. MethodsUsing computed tomography imaging, a stereolithography file of an infant airway was generated to 3D print a model. This model was inserted into a commercially available airway trainer to allow lung isolation using standard bronchoscopy techniques. Ten experienced pediatric anesthesiologists independently evaluated the simulator’s physical attributes, realism, value, and relevance using a 29-item paper survey and rated using 4-point rating scales (4 = highest). Participants’ ability to complete 5 critical tasks was self-reported using 5-point rating scales (5 = too easy). Item and domain mean ratings were calculated, and comments reviewed. ResultsOverall, reviews were positive, with mean scores indicating adequate realism and high value. Specific challenges were associated with right mainstem bronchus and upper lobe takeoff. Performance scores indicated that most tasks were “somewhat easy to perform,” suggesting that the model’s anatomy did not hinder physicians’ ability to perform one-lung ventilation. ConclusionPreliminary findings indicate that the novel simulator holds promise for training in lung isolation techniques after refinement. Future research will target refinement, expanding evaluation, and developing a comprehensive curriculum and competency assessment program.

Rapid particle generation from an STL file and related issues in the application of material point methods to complex objects

In this paper, we focus on three issues related to applications of material point methods (MPMs) to objects with complex geometries. They are material point generation, compatibility of material points with a mesh, and sensitivity to mesh orientation. An efficient method of generating material points from a stereolithography (STL) file is introduced. This material point generation method is independent of the mesh used in MPM calculations. The compatibility between the material points and the mesh is then studied. We also show that the original MPM and the dual domain material point (DDMP) method are sensitive to mesh orientation. These issues are related to the calculation of the internal force and are concerns of the MPMs. They become more prominent when MPMs are applied to complex geometries. Our numerical results show that the recently developed local stress difference (LSD) algorithm (Perez et al. in J Comp Phys 498:112681, 2024) can be used to effectively address them.

Research and application discussion of cranial bone model preparation method based on three-dimensional reconstruction and 3D printing technology.

The aim of this study was to find an alternative method to meet traditional human anatomy teaching and clinical needs in order to solve the problem of cranial specimen attrition and specimen resource shortage due to long-term use. We performed a computed tomography (CT) scan of a well-preserved male cranial specimen and used Mimics 19.0 software for 3D reconstruction and cranial block separation. Subsequently, we compared the recognition ability of the processed cranial digital model with that of the 3D body digital model and used 3D printing to create the cranial model and compare it with the physical specimen. Twenty-two cranial bone block models were obtained, excluding the hyoid bone. Their 3D reconstructed digital models had better bony landmark recognition than the 3D body human digital models, and the differences between the 3D printed models and the physical specimens were minimal. In addition, only one stereolithography (STL) file was required to produce the cranial models, which facilitates repetitive printing at any time. By isolating cranial bone blocks through 3D reconstruction techniques and preparing high-quality cranial models in combination with 3D printing techniques, this study solves the problem of shortage of cranial teaching specimens for the sustainable development of clinical and medical schools.

Augmented Reality Improved Knowledge and Efficiency of Root Canal Anatomy Learning: A Comparative Study

Teaching root canal anatomy has traditionally been reliant on static methods, but recent studies have explored the potential of advanced technologies like augmented reality (AR) to enhance learning and address the limitations of traditional training methods, such as the requirement for spatial imagination and the inability to simulate clinical scenarios fully. This study evaluated the potential of AR as a tool for teaching root canal anatomy in preclinical training in endodontics for predoctoral dental students. Six cone beam computed tomography (CBCT) images of teeth were selected. Board-certified endodontist and radiologist recorded the tooth type and classification of root canals. Then, STereoLithography (STL) files of the same images were imported into a virtual reality (VR) application and viewed through a VR head-mounted display. Forty-three third-year dental students were asked questions about root canal anatomy based on the CBCT images, and then, after the AR model. The time to respond to each question and feedback was recorded. Student responses were paired, and the difference between CBCT and AR scores was examined using a paired-sample t-test and set to p = 0.05. Students demonstrated a significant improvement in their ability to answer questions about root canal anatomy after utilizing the AR model (p &lt; 0.05). Female participants demonstrated significantly higher AR scores compared to male participants. However, gender did not significantly influence overall test scores. Furthermore, students required significantly less time to answer questions after using the AR model (M = 4.09, SD = 3.55) compared to the CBCT method (M = 15.21, SD = 8.01) (p &lt; 0.05). This indicates that AR may improve learning efficiency alongside comprehension. In a positive feedback survey, 93% of students reported that the AR simulation led to a better understanding of root canal anatomy than traditional CBCT interpretation. While this study highlights the potential of AR in learning root canal anatomy, further research is needed to explore its long-term impact and efficacy in clinical settings.

Fracture resistance, marginal and internal adaptation of innovative 3D-printed graded structure crown using a 3D jet printing technology.

This in vitro study aimed to create a graded structured dental crown using 3D printing technology and investigate the fracture resistance and the adaptation of this new design. A dental crown with a uniform thickness of 1.5mm was designed, and the exported stereolithography file (STL) was used to manufacture 30 crowns in three groups (n = 10), solid (SC), bilayer (BL), and multilayer (ML) crowns using 3D jet printing technology. Marginal and internal gaps were measured using the silicone replica technique. Crowns were then luted to a resin die using a temporary luting agent and the fracture resistance was measured using a universal testing machine. One-way ANOVA and Tukey post hoc tests were used to compare the fracture resistance and the adaptation of crowns at a significance level of 0.05. Mean marginal and internal gap of the ML group were 80 and 82mm, respectively; which were significantly (p<0.05) smaller than BL (203 and 183mm) and SC (318 and 221mm) groups. The SC group showed the highest mean load at fracture (2330 N) which was significantly (p<0.05) higher than the BL (1716 N) and ML (1516 N) groups. 3D jet printing technology provides an opportunity to manufacture crowns in a graded structure with various mechanical properties. This study provided an example of graded structured crowns and presented their fracture resistance. SC group had the highest fracture resistance; however, ML had the best marginal and internal adaptation.

Post sterilization of intraoral scan body and the effect it has on the axes and distances between three adjacent implants: in-vitro study

BackgroundThe purpose of this pilot in-vitro study was to assess the effect of sterilization on the intra-implant axis, inter-implant axis, intra-implant distance and inter-implant distance of three implants in a straight line by using laboratory scanner (LBS) versus intra-oral scanner (IOS) with intra-oral scan bodies (ISB). Methods: A printed 3D model with three internal hex analogs in the positions 15#,16#,17# was used. Zirkonzhan (ZZ) intra-oral scan body (ISB), two-piece titanium was used. The ZZ ISBs were scanned by 7 Series dental wings (LBS) and 30 times by Primescan (IOS) pre sterilization and 30 times post sterilization. For each scan (pre and post) stereolithography (STL) file was created and a comparison between all the scans pre sterilization and post sterilization were superimposed on the laboratory scan by using a 3D analyzing software. A Kolmogorov-Smirnov test performed followed by Wilcoxon Signed Ranks tests. (p < 0.05) Results: Post sterilization of the ZZ ISB, the mean errors were significantly increased for the inter-implant distances (p < 0.0005), intra-implant distances 1,2,3 (p < 0.0005), intra-implant axis 1,3 (p < 0.0005) and inter-implant axes 13,23 (p < 0.05). In contrast, the mean errors for intra-implant axis 2 (p < 0.0005) and inter-implant axis 12 (p < 0.0005) were significantly reduced. Conclusions: ZZ ISB showed changes in all four parameters after sterilization. The middle ISB had the largest changes in mean error regarding all four parameters. Sterilization process may affect the three-dimensional (3D) structure of the ZZ ISB after three cycles. There is a lack in the literature in this field and there is a need for further studies to explore the effect of sterilization (multiple cycles) on different ISBs and for creating an approved guidelines regarding the amount of sterilization for each ISB in the industry.

A novel digital way to measure the vertical and horizontal dimensions of the supra-crestal peri-implant soft tissues.

To report on a novel digital superimposition workflow that enables measuring the supra-crestal peri-implant soft tissue dimensions all along implant treatment and afterwards. A preoperative CBCT and intra-oral scans (IOS) are successively taken before surgery, at the end of the healing period, at prosthesis delivery, and over time; they are digitally superposed on a dedicated software. Then, the stereolithography files (STL) of the healing abutment, of the prosthetic abutment and the crown are successively merged into the superposition set of IOSs. The workflow protocol of merging successively the STL of each item into the superposition set of IOSs enables capturing the dimensions of the height and width of the supra-crestal soft tissues, at every level of the healing abutment, the prosthetic abutment and the crown. In addition, it allows measuring the vertical distance that the crown exerts pressure on the gingiva and the thickness of the papillae at every level of the abutment. This novel digital superimposition workflow provides a straightforward method of measuring the vertical and horizontal dimensions of the supra-crestal peri-implant soft tissues, including the papillae, at each stage of the implant treatment process. It allows investigating a certain number of soft tissue variables that were previously inaccessible to clinical research. It should help enhancing our comprehension of the peri-implant soft tissue dynamics.

Design and characterization of 3D-printed hollow microneedle arrays for transdermal insulin delivery

The delivery of insulin to diabetic patients remains a challenge due to the limitations of current insulin delivery paradigms, including painful cannula insertion, potential infections, interference with activity, embarrassment, and sometimes cost. To address this problem, we designed and fabricated nine prototypes of stereolithographic 3D-printed microneedle arrays (MNAs) appropriate for the minimally invasive delivery of insulin. We characterized their transdermal penetration performance by delivering fluid at a constant rate to porcine skin through these MNAs. Moreover, we characterized the force required for these MNAs to puncture porcine skin using a mechanical testing apparatus. We developed an improved method of mechanical testing for the MNAs against porcine skin by incorporating an imitation soft tissue layer under the skin and compared the MNA results with those using a single microneedle and a hypodermic needle. In addition, we investigated the mechanical flexural strength of the MNAs by performing a flexural failure load test on them. We confirmed that the prototype MNAs are mechanically robust and do not fracture during skin penetration, setting the stage for future trials in vitro and in vivo. The final, optimized designs are freely available in stereolithography (STL) file format.

Design and Validation of a Novel 3D-Printed Retrograde Intrarenal Surgery Trainer

ObjectivesTo report on the design of a novel 3D-printed retrograde intrarenal surgery (RIRS) benchtop trainer and detail its validation against real-life experiences. MethodsDigital Imaging and Communications in Medicine (DICOM) files of two patients with normal computed tomography of the kidney and bladder were converted into stereolithography files to create 3D triangular mesh models. These images were further refined using Autodesk Meshmixer. These 3D models were fabricated through additive manufacturing, a process commonly known as 3D printing and assembled in a polypropylene case. After development, the model was validated by 40 experienced urologists and urology residents in their final year of training. They were asked to rate the components of the simulation using a nine-point questionnaire. ResultsThe model’s value in understanding the principles of RIRS and simulating contextual anatomy had mean scores of 9.43 (standard deviation [SD] = 0.74) and 9.21 (SD = 1.03), respectively. Mean scores for specific steps in RIRS were 8.07 (SD 1.47) for cannulating the ureteric orifice, 8.61 (SD 1.24) for inserting the ureteric access sheath, 9.29 (SD 0.97) for performing a renoscopy and evaluating all the calyces, 9.46 (SD 0.87) for laser lithotripsy, and 9.17 (SD 0.94) for manual stone retrieval. Participants scored the model with a mean score of 9.04 (SD 0.87) regarding realism and a mean score of 9.18 (SD 0.89) when evaluating its ability to enhance a trainee’s confidence in RIRS. ConclusionsThe model performed well for all components of RIRS. This model allows high fidelity of the simulation, and is cost-effective, portable, durable, reusable, and compatible with standard ureteroscopes.

Development of a 3D-printed nuchal translucency model: a pilot study for prenatal ultrasound training

BackgroundWe used two 3D ultrasound volumes of fetal heads at 13 weeks to create live-size 3D-printed phantoms with a view to training or assessment of diagnostic abilities for normal and abnormal nuchal translucency measurements. The phantoms are suitable for use in a water bath, imitating a real-life exam. They were then used to study measurement accuracy and reproducibility in examiners of different skill levels.MethodsUltrasound scans of a 13 + 0-week fetus were processed using 3D Slicer software, producing a stereolithography file for 3D printing. The model, crafted in Autodesk Fusion360™, adhered to FMF guidelines for NT dimensions (NT 2.3 mm). Additionally, a model with pathologic NT was designed (NT 4.2 mm). Printing was performed via Formlabs Form 3® printer using High Temp Resin V2. The externally identical looking 3D models were embedded in water-filled condoms for ultrasound examination. Eight specialists of varying expertise levels conducted five NT measurements for each model, classifying them in physiological and abnormal models.ResultsClassification of the models in physiological or abnormal NT resulted in a detection rate of 100%. Average measurements for the normal NT model and the increased NT model were 2.27 mm (SD ± 0.38) and 4.165 mm (SD ± 0.51), respectively. The interrater reliability was calculated via the intraclass correlation coefficient (ICC) which yielded a result of 0.883, indicating robust agreement between the raters. Cost-effectiveness analysis demonstrated the economical nature of the 3D printing process.DiscussionThis study underscores the potential of 3D printed fetal models for enhancing ultrasound training through high inter-rater reliability, consistency across different expert levels, and cost-effectiveness. Limitations, including population variability and direct translation to clinical outcomes, warrant further exploration. The study contributes to ongoing discussions on integrating innovative technologies into medical education, offering a practical and economical method to acquire, refine and revise diagnostic skills in prenatal ultrasound. Future research should explore broader applications and long-term economic implications, paving the way for transformative advancements in medical training and practice.

Advancement of 3D printing technology for the development of a training model in US-guided vesicoamniotic shunting for early LUTO therapy.

Prenatal lower urinary tract obstruction (LUTO) is a rare and challenging condition with potential severe morbidity and mortality. Prenatal shunting methods, specifically vesicoamniotic shunting (VAS) and fetal cystoscopy, aim to manage this condition. However, comprehensive education and training are hindered by the rarity of LUTO. To address this gap, we present a low-cost 3D-printed ultrasound training model for VAS in LUTO fetuses. The aim of the study was to evaluate ultrasound and haptic fidelity of the model. Ultrasound images of three LUTO fetuses at 12-14 weeks were utilized to create detailed 3D-printed models. Fusion360TM software generated stereo-lithography files, and the Formlabs Form3® printer, using Flexible 80A resin, produced the models. A simulation box mimicking uterine conditions and fetal anatomy was developed for testing. Ultrasound assessments determined model accuracy, and expert evaluations gauged fidelity for VAS placement. The 3D-printed model accurately replicated LUTO fetal anatomy, demonstrating structural integrity and realistic sonographic and haptic feedback during 20 punctures. Macroscopic visualization confirmed the model's durability and authenticity. This innovative 3D-printed model addresses the scarcity of LUTO cases and the lack of realistic training tools. Simulation models enhance skills, providing a controlled learning environment that bridges theoretical knowledge and clinical application, potentially improving patient outcomes. The 3D-printed training model for VAS in LUTO represents a significant advancement in surgical education, offering realistic anatomical simulation and tactile feedback. Future studies should assess its effectiveness in enhancing surgical skills and impacting patient outcomes in clinical practice.

Accuracy of implant placement using a mixed reality-based dynamic navigation system versus static computer-assisted and freehand surgery: An in Vitro study

PurposeThis in vitro study aimed to compare the accuracy of dental implant placement in partially edentulous maxillary models using a mixed reality-based dynamic navigation (MR-DN) system to conventional static computer-assisted implant surgery (s-CAIS) and a freehand (FH) method. MethodsForty-five partially edentulous models (with teeth missing in positions #15, #16 and #25) were assigned to three groups (15 per group). The same experienced operator performed the model surgeries using an MR-DN system (group 1), s-CAIS (group 2) and FH (group 3). In total, 135 dental implants were placed (45 per group). The primary outcomes were the linear coronal deviation (entry error; En), apical deviation (apex error; Ap), XY and Z deviations, and angular deviation (An) between the planned and actual (post-surgery) position of the implants in the models. These deviations were computed as the distances between the stereolithographic (STL) files for the planned implants and placed implants captured with an intraoral scanner. ResultsAcross the three implant sites, the MR-DN system was significantly more accurate than the FH method (in XY, Z, En, Ap and An) and s-CAIS (in Z, Ap and An), respectively. However, S-CAIS was more accurate than MR-DN in XY, and no difference was found between MR-DN and s-CAIS in En. ConclusionsWithin the limits of this study (in vitro design, only partially edentulous models), implant placement accuracy with MR-DN was superior to that of FH and similar to that of s-CAIS. Statement of Clinical RelevanceIn vitro, MR-DN showed greater accuracy in implant positioning than FH, and similar accuracy to s-CAIS: it could, therefore, represent a new option for the surgeon. However, clinical studies are needed to determine the feasibility of MR-DN.

A slicing and path generation method for 3D printing of periodic surface structure

Periodic surface (PS) model holds enormous potential in the field of lightweight, heat management, and biomedical implants. To achieve tunable mechanical strength and high surface area versus volume (SA/V) ratio, it is imperative to achieve solid representation of the PS models. However, because of the complex inner structure, converting the surface model to solid model with uniform thickness remains a major challenge. In the meantime, the most pervasive practice to achieve tunable wall thickness is by offsetting the contour with a constant value or setting a constant value difference between two implicit functions. However, these existing approaches cannot guarantee uniform wall thickness. In this paper, a novel method is proposed to define an adjacent implicit surface with a uniform offset distance to the original. By repeatedly generating implicit surfaces with uniform distance from each other, the solid representation of the PS model with uniform thickness can be achieved. Meanwhile, a new slicing method allowing for the slicing without stereolithography (STL) file is developed to slice the implicit surfaces and generate the printing path so that the accumulation of slicing errors introduced by meshing steps can be avoided. By slicing each implicit surface separately, the corresponding G-code file is generated. This developed method is demonstrated by fabricating typical PS with fused filament 3D printing.

Evaluating free segmentation tools for CBCT-derived models: Cost-effective solutions.

This study evaluated the segmentation accuracy and reliability of free software packages and compared them with commercial alternatives. A total of 36 stone models were scanned using a desktop scanner and then imaged by cone beam computed tomography (CBCT). The CBCT volumes were segmented using 2 free software packages (3D Slicer and Blue Sky Plan) and 2 commercial software packages (Mimics and OnDemand3D). Stereolithography (STL) files generated by the desktop scanner were used as the control group (reference models). The accuracy of segmentation was evaluated by (1) comparing 6 linear measurements taken from each STL model generated by the 4 software packages with that obtained by the scanner, and (2) deviation analysis of each STL model generated by the 4 software packages with that obtained by the scanner. Absolute error and percentage error, repeated measures anova and Friedman test followed by post hoc analysis, intraclass correlation coefficient (ICC), and Pearson's r were used to evaluate the accuracy of the tested software packages. There was no statistically significant difference in all intra-arch measurements obtained using the four software packages. Measurements obtained using the free software packages and the scanner showed excellent positive correlation, ranging from 0.825 to 0.988, confirming equivalence with commercial software packages. Within the settings of the current study, accurate and time-saving segmentations with high positive correlation could be performed using the tested free segmentation software packages (3D Slicer and Blue Sky Plan). Nevertheless, further evaluation is necessary to gage their accuracy using different CBCT modalities.

Development of ZTA (80% Al2O3/20% ZrO2) pre-sintered blocks for milling in CAD/CAM systems

The present work aims to develop a production method of pre-sintered zirconia-toughened-alumina (ZTA) composite blocks for machining in a computer-aided design and computer-aided manufacturing (CAD-CAM) system. The ZTA composite comprised of 80% Al2O3 and 20% ZrO2 was synthesized, uniaxially and isostatically pressed to generate machinable CAD-CAM blocks. Fourteen green-body blocks were prepared and pre-sintered at 1000 °C. After cooling and holder gluing, a stereolithography (STL) file was designed and uploaded to manufacture disk-shaped specimens projected to comply with ISO 6872:2015. Seventy specimens were produced through machining of the blocks, samples were sintered at 1600 °C and two-sided polished. Half of the samples were subjected to accelerated autoclave hydrothermal aging (20h at 134 °C and 2.2 bar). Immediate and aged samples were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Optical and mechanical properties were assessed by reflectance tests and by biaxial flexural strength test, Vickers indentation and fracture toughness, respectively. Samples produced by machining presented high density and smooth surfaces at SEM evaluation with few microstructural defects. XRD evaluation depicted characteristic peaks of alpha alumina and tetragonal zirconia and autoclave aging had no effect on the crystalline spectra of the composite. Optical and mechanical evaluations demonstrated a high masking ability for the composite and a characteristic strength of 464 MPa and Weibull modulus of 17, with no significant alterations after aging. The milled composite exhibited a hardness of 17.61 GPa and fracture toughness of 5.63 MPa m1/2, which remained unaltered after aging. The synthesis of ZTA blocks for CAD-CAM was successful and allowed for the milling of disk-shaped specimens using the grinding method of the CAD-CAM system. ZTA composite properties were unaffected by hydrothermal autoclave aging and present a promising alternative for the manufacture of infrastructures of fixed dental prostheses.