Computer-aided Manufacturing Systems Research Articles

BrepMFR: Enhancing machining feature recognition in B-rep models through deep learning and domain adaptation

Feature Recognition (FR) plays a crucial role in modern digital manufacturing, serving as a key technology for integrating Computer-Aided Design (CAD), Computer-Aided Process Planning (CAPP) and Computer-Aided Manufacturing (CAM) systems. The emergence of deep learning methods in recent years offers a new approach to address challenges in recognizing highly intersecting features with complex geometric shapes. However, due to the high cost of labeling real CAD models, neural networks are usually trained on computer-synthesized datasets, resulting in noticeable performance degradation when applied to real-world CAD models. Therefore, we propose a novel deep learning network, BrepMFR, designed for Machining Feature Recognition (MFR) from Boundary Representation (B-rep) models. We transform the original B-rep model into a graph representation as network-friendly input, incorporating local geometric shape and global topological relationships. Leveraging a graph neural network based on Transformer architecture and graph attention mechanism, we extract the feature representation of high-level semantic information to achieve machining feature recognition. Additionally, employing a two-step training strategy under a transfer learning framework, we enhance BrepMFR's generalization ability by adapting synthetic training data to real CAD data. Furthermore, we establish a large-scale synthetic CAD model dataset inclusive of 24 typical machining features, showcasing diversity in geometry that closely mirrors real-world mechanical engineering scenarios. Extensive experiments across various datasets demonstrate that BrepMFR achieves state-of-the-art machining feature recognition accuracy and performs effectively on CAD models of real-world mechanical parts.

Adaptive recognition of machining features in sheet metal parts based on a graph class-incremental learning strategy

The integration of computer-aided design (CAD), computer-aided process planning (CAPP), and computer-aided manufacturing (CAM) systems is significantly enhanced by employing deep learning-based automatic feature recognition (AFR) methods. These methods outperform traditional, rule-based approaches, particularly in handling the complexities of intersecting features. However, existing deep learning-based AFR methods face two major challenges. The initial challenge stems from the frequent utilization of voxelized or point-cloud representations of CAD models, resulting in the unfortunate loss of valuable geometric and topological information inherent in original Boundary representation (B-Rep) models. The second challenge involves the limitation of supervised deep learning methods in identifying machining features that are not present in the predefined dataset. This constraint renders them suboptimal for the continually evolving datasets of real industrial scenarios. To address the first challenge, this study introduces a graph-structured language, Multidimensional Attributed Face-Edge Graph (maFEG), crafted to encapsulate the intricate geometric and topological details of CAD models. Furthermore, a graph neural network, Sheet-metalNet, is proposed for the efficient learning and interpretation of maFEGs. To tackle the second challenge, a three-component incremental learning strategy is proposed: an initial phase of pre-training and fine-tuning, a prototype sampling-based replay, and a stage employing knowledge distillation for parameter regularization. The effectiveness of Sheet-metalNet and its complementary incremental learning strategy is evaluated using the open-source MFCAD++ dataset and the newly created SMCAD dataset. Experimental results show that Sheet-metalNet surpasses state-of-the-art AFR methods in machining feature recognition accuracy. Moreover, Sheet-metalNet demonstrates adaptability to dynamic dataset changes, maintaining high performance when encountering newly introduced features, thanks to its innovative incremental learning strategy.

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.

Verifying the seating of a 3D-printed removable die using elastomeric matrices: A dental technique.

Computer-aided design and computer-aided manufacturing systems enable digital designing and 3-dimensional (3D) printing of definitive casts with removable dies. However, the fit of the removable dies should be without interferences for their accurate positioning in the cast. Given that the accuracy of additive manufacturing depends on design- and manufacturing-related factors, verifying the accuracy of the position of 3D-printed removable dies in their cast is essential to fabricate positionally accurate definitive prostheses, which would enable minimal or no laboratory and clinical adjustments. This dental technique article presents a straightforward approach to verify the seating of a 3D-printed removable die by using verification matrices made of a polyvinylsiloxane interocclusal registration material.

A comparative evaluation of physical properties of CAD/CAM complete denture resins- an in vitro study

BackgroundIn dentistry, there is a growing preference for computer-aided design and computer-aided manufacturing (CAD/CAM) systems over traditional laboratory procedures. However, there is not much literature comparing various CAD/CAM materials. Thus, this study aimed to assess and compare the color stability and hardness of gingival and tooth colored milled and 3D-printed acrylic resins.Materials and methodsFour types of CAD/CAM materials were prepared: 3D-printed pink shade (PP), milled polymenthymethacrylate (PMMA) pink shade (MP), 3D-printed tooth shade (PT) and milled PMMA tooth shade (MT) (n = 6). For hardness, disc shaped samples of 15 mm × 2 mm and for color stability, bar shaped samples of 65mmx10mmx2.5 mm were prepared and polished. Vickers hardness test was performed in a microhardness tester. Color stability test was done by immersing in coffee solution and coca cola for 7 days. Day 0 and day 7 measurements were recorded using a digital spectrophotometer and the change in color was calculated. For statistical analysis, one-way ANOVA and Tukey’s post hoc tests were done.ResultsFor color stability, milled PMMA was superior to 3D-printed resin samples. Milled pink and tooth shade samples had similar color stability, whereas 3D-printed tooth shade samples were more color stable as compared to pink shade 3D-printed samples. For hardness, milled tooth shade PMMA was the most superior one, followed by 3D-printed tooth shade, whereas pink shade milled PMMA and 3D-printed resin samples had similar hardness values and were inferior to the tooth shade CAD/CAM materials.ConclusionColor stability of milled PMMA is superior to that of 3D-printed resins. Hardness of tooth shade milled and 3D-printed resins is more than that of pink shade milled and 3D-printed resins.

Fundamental Study of Press Molding Method for CFRP Preform Using a 3D Printer

Carbon fiber reinforced plastic (CFRP) is a composite material with high specific strength and is applied to transportation and aviation equipment. However, conventional processing methods require large-scale production apparatus or a high level of dexterity that only comes with extensive experience which makes it difficult to achieve high processing efficiency. The objective of this study is to develop a novel method for forming thermos-plastic CFRP (CFRTP) preforms implementing a 3D printer for press molding. Applying this method offers the advantage that continuous carbon fibers can be formed on a free-form surface. It also reduces the manufacturing time and operator skill required. The goal of this research is to establish a method for molding a free-form surface composed of continuous fibers by employing a 3D-printed preform designed to match the unfolded polygonised diagram of the free-form surface. Previous research introduced an unfolding approach for converting a three-dimensional shape to a plane surface based on a computer-aided design and manufacturing (CAD/CAM) system, enabling the generation of an unfolding diagram that maintains the continuity of fiber tow. Furthermore, the validity of unfolded diagram was confirmed by reproducing the objective three-dimensional shape from the unfolded diagram using thermos-setting CPRP (CFRTS) tow prepreg. In this study, the viability of the proposed molding process using CFRTP preform fabricated by a 3D printer was verified and an assessment of the formability of the molded parts was conducted.

Subtractive and Additive Technologies in Fixed Dental Restoration: A Systematic Review

Today, computers and digital devices are an indispensable part of our daily lives, and dentistry is no exception. Dentistry has adopted a number of digital technologies, including CAD/CAM (computer-aided design and manufacturing) systems. The goal of the current study is to evaluate the current state of knowledge on dental alloy manufacturing using subtractive and additive techniques for metal ceramic restoration. On this topic, an electronic systematic review was conducted in various databases (Science Direct, PubMed, Web of Science, and Google Scholar searches), as well as a hand search of the scientific literature. Published work was collected, analyzed, and relevant articles were chosen for inclusion in this review from 2008 to 2021. The online databases were searched for articles published that appeared between 2008 and 2021, with no time or language constraints we grouped relevant search terms together, such as "Computer-Aided Design, CAD/CAM, dentistry, dental fabrication, restoration, additive manufacturing." We recognized publications individually and systematically screened titles, summaries, and complete texts of the obtained publications. The findings indicate that current knowledge is sufficient to recommend subtractive manufacturing for crowns and fixed dental restorations for routine clinical use, with improvements in each of the current metal-ceramic veneering materials and procedures. According to the review, several digital technologies, such as systems of computer aided design and aided manufacturing were used in different dental specialties. Application of CAD/CAM technology provided numerous benefits while posing few limitations.

Comparative Analysis of the Fracture Resistance of a Polymeric Material for 3D Printing and a Milled Polymethylmethacrylate Material as Interim Material for Fixed Partial Dentures: New Material Updated

The aim of this study was to evaluate and compare the fracture resistance of a temporary three-unit fixed dental prosthesis (FDP) made of a new polymeric material obtained by an additive technique (3DPP) using a computer-aided design and manufacturing (CAD/CAM) system, comparing the prosthesis to the respective outcomes of temporary polymethylmethacrylate (PMMA) FDPs obtained by a subtractive technique (milling). Methods: Three-unit FDPs were 3D printed using a polymeric material (n = 20) or milled using polymethylmethacrylate (n = 20). After thermocycling at 5000 cycles at extreme temperatures of 5 °C and 55 °C in distilled water, each specimen was subjected to a compression test on a universal testing machine at a rate of 0.5 mm/min until failure occurred, recording the value in newtons (N). Results: There were statistically significant differences (p-value < 0.005) between the PMMA material (2104.7 N; SD = 178.97 N) and 3DPP (1000.8 N; SD = 196.4 N). Conclusions: The fracture resistance of the PDFs manufactured from milled PMMA showed higher values for fracture resistance. However, the resistance of the 3DPP showed acceptable values under mechanical load; this notable advance in the resistance of printed materials consolidates them as an important alternative to use in interim indirect restorations.

Enhancing Dental Cement Bond Strength with Autofocus-Laser-Cutter-Generated Grooves on Polyetheretherketone Surfaces.

Polyetheretherketone (PEEK) is widely used in dentistry owing to its exceptional properties, including its natural appearance; however, existing surface treatment methods for bonding PEEK have limitations. Autofocus laser cutters, known for their precise engraving and cutting capabilities, offer potential for surface treatment of PEEK; thus, the objective of this study was to investigate the creation of laser groove structures on PEEK to enhance its bonding capability with dental resin cement. A dental computer-aided design and manufacturing system was used to fabricate PEEK samples, and three groove patterns (circle, line, and grid) were generated on PEEK surfaces, with air-abrasion used as the control group. The surface characteristics, cell viability, and bond strength were evaluated, and the data were statistically analyzed using one-way analysis of variance and post hoc Tukey's tests (α = 0.05). Laser-treated PEEK exhibited a uniform texture with a groove depth of approximately 39.4 µm, hydrophobic properties with a contact angle exceeding 90°, a surface roughness of 7.3-12.4 µm, consistent topography, and comparable cell viability compared with untreated PEEK. Despite a decrease in bond strength after thermal cycling, no significant intergroup differences were observed, except for the line-shaped laser pattern. These findings indicate that the autofocus laser cutter effectively enhances the surface characteristics of PEEK by creating a uniform texture and grooves, showing promise in improving bonding properties, even considering the impact of thermal cycling effects.

A feasibility study of application of purpose-design frame and 3-D clinical ultrasound in assessment and design of spinal orthoses for adolescent idiopathic scoliosis.

The immediate in-orthosis correction of adolescent idiopathic scoliosis (AIS) is a useful prognostic parameter for the long-term orthotic treatment outcome. The 3-D clinical ultrasound technique is considered a noninvasive alternative to assess scoliotic deformities that could be applied in the orthotic treatment of AIS. This study aimed to investigate the feasibility of a purpose-design assessment frame in estimating biomechanical effects of the controlling pads of a spinal orthosis under the guidance of the ultrasound system. Twenty-six subjects with AIS were recruited and arranged to position inside the assessment frame, and controlling pads were applied strategically while the scoliotic deformities were assessed by clinical ultrasound to obtain at least 30% curvature correction, and the body shape was then captured using a computer-aided design and computer-aided manufacture system, and spinal orthoses were subsequently fabricated. The preorthosis and immediate in-orthosis coronal and sagittal X-rays were used for comparison. X-ray assessments showed that the mean coronal Cobb angle and lumbar lordosis of the subjects from the preorthosis to immediate in-orthosis visits decreased significantly (p < 0.05) from 29.6° to 16.6°, and from 47.2° to 35.3°, respectively. This feasibility study showed that the proposed method would have a good potential to improve orthotic treatment outcome in a documented approach that should be considered for implementation into routine clinical practice aiming to reduce the chance of deformity deterioration leading to surgical intervention. However, a controlled group study is required to compare the results.

Marginal fit and fracture resistance of polyetheretherketone, zirconia, and titanium implant-supported prosthesis frameworks for a partially edentulous arch after thermomechanical aging

Although polyetheretherketone (PEEK) and zirconia (Zir) have been used as implant-supported prosthesis (ISP) frameworks, the long-term effects of thermomechanical aging on the marginal fit and fracture resistance of PEEK and Zir ISP frameworks with titanium (Ti) bases for patients with a partially edentulous arch are not clear. The purpose of this in vitro study was to determine the marginal fit and fracture resistance of PEEK and Zir ISP frameworks with Ti bases and Ti ISP frameworks for partially edentulous arches after aging. A total of 30 ISP epoxy resin casts were obtained from a typodont with 1 straight implant (Nobel Biocare) in the mandibular right canine region and 1 implant with a 30-degree distal tilt in the mandibular right first molar region. All frameworks (n=10) were fabricated on their own epoxy resin cast with multiunit abutment replicas by using a computer-aided design and computer-aided manufacturing system (exocad-Yenadent). The PEEK and Zir frameworks were fabricated with Ti-bases. Primer (MKZ) and resin cement (DTK adhesive) were used to cement the frameworks to the Ti-bases under a static load of 10N. After thermomechanical aging (1.2×106 cycles, 120N, 5°C-55°C), marginal gaps between the Ti-bases and cemented frameworks and vertical and passive fits between the Ti-bases and framework and multi-unit abutments were measured by using a stereomicroscope (Euromex) at ×100 magnification. Fracture resistances and types were then determined by using a universal test machine and a stereomicroscope at ×40 magnification. Data were analyzed by using 1-way analysis of variance (ANOVA) and the Tukey HSD and Fisher-Freeman-Halton tests (α=.05). The marginal gaps of the PEEK and Zir frameworks were respectively 83.5 ±27.1 and 81.8 ±17.8µm. PEEK (23.7 ±4.6) and Zir (32.9 ±8.7) had a better vertical fit (µm) than Ti (52.5 ±10.6) (P<.001). Zir (49.3 ±16.2) (P<.001) and PEEK (70.9 ±19.6) (P>.05) frameworks had better passive fit (µm) than Ti (91.3 ±24.2). Ti had the highest mean fracture resistance (N) (14800.2 ±3442.3) followed by Zir (7318.7 ±1385.1) and PEEK (3448.9 ±486.6) (P<.001). Fracture types were different in different groups (P<.001). The PEEK and Zir frameworks with Ti baseshad better vertical and passive fit than the Ti frameworks. All ISP frameworks represented mean marginal fit below 92µm and withstood physiologic occlusal forces after thermomechanical aging.

Mixed tiny path smoothing method based on sliding convolution windows for CNC machining

The machining toolpaths of complex free-form surface parts are generated using computer-aided manufacturing (CAM) systems and programmed by a series of mixed tiny paths composed of tiny lines, arcs, and non-uniform rational B-spline (NURBS). The mixed tiny paths need to be smoothed to eliminate the tangential discontinuities at corners. This paper proposes a mixed tiny path smoothing method based on sliding convolution windows (MSSCW). In this method, the mixed tiny path is firstly converted into a positional signal along the travel length in the spatial domain, and then sliding convolution windows, which centered on each original interpolation point, are used to generate high-order continuous smoothed toolpath. Finally, the smoothing error is checked and corrected by modifying the length duration of the sliding convolution windows. Compared with conventional path smoothing method, the MSSCW method is suitable for various computer numerical control (CNC) machining toolpaths, and the continuity of the smoothed toolpath can be adjusted according to user requirements. Consequently, the feasibility and effectiveness of the proposed method are validated in simulations and experimental results which realize the improvement of the machining quality of complex free-form surfaces.

Three-Dimensional Analysis of Upper and Lower Arches Using Digital Technology: Measurement of the Index of Bolton and Correspondence between Arch Shapesand Orthodontic Arches.

Thanks to the great development of digital technology, viaCAD (computer-aided design) and CAM (computer-aided manufacturing) systems, digital models canbe used as an aid for orthodontic planning decision-making processes as there are numerous studies in the literature that support the validity ofthe digital model measurements of anterior teeth and the total coefficient of Bolton analysis. The aim of the present study isto compare the average length value of the current upper and lower arches with that of a hypothetical nickel-titanium wire and to confirm the reliability and accuracy of digitally taken measurements of the anterior and total Bolton coefficients.In this retrospective study, dental casts of 138 Caucasian adolescent patients were scanned with an extraoral scanner, and Ortho3Shape software was adopted for the following dental cast measurements: actual and ideal lengths of the lower arches and anterior and total Bolton coefficients.In the present study, we found that the mean value of the anterior coefficients of the Bolton index was compatible with those of previous studies, confirming the reliability of digital measurements.Therefore, digital CAD/CAM models may be a viable alternative to plaster models, as they can facilitate model preservation and recovery. For future studies, it would be better to use intraoral scanners (IOSs) to ensure greater accuracy, since they only require one step and allow obtaining better results for the patients.

Detection of misfits at the abutment-prosthesis interface in the esthetic zone: Implications of the radiographic technique and the magnitude of the misfit

Misfits in the abutment-prosthesis interface represent a setback for implant-supported prostheses. Periapical radiographs have been used as an auxiliary method in the evaluation of prosthesis fit to the abutments; however, the evidence supporting the use of this method is still restricted to studies of low to moderate quality. Furthermore, studies on the diagnostic accuracy of different periapical techniques used to detect misfits in the abutment-prosthesis interface, especially in the esthetic zone, are lacking. The purpose of this in vitro study was to assess the discrimination power of 3 periapical radiographic techniques in detecting misfits at the abutment-prosthesis interface in the esthetic zone and evaluate whether the magnitude of the misfit influenced the diagnosis. A total of 15 implants with an internal conical connection were installed in the central incisor region in polyamide jaws. Custom ceramic copings for cemented crowns were made by using a computer-aided design and computer-aided manufacturing (CAD-CAM) system. Misfits of 50, 100, and 150µm were simulated by interposing 1, 2, or 3 50-μm-thick polyester strips at the abutment-prosthesis interface; the absence of the strip represented the control group. Digital radiographs were obtained by using film holders for the following periapical techniques: bisecting angle (PBA), standard paralleling (PSP), and modified paralleling (PMP). Two radiologists and 1 prosthodontist evaluated a total of 180 radiographs. The values of the area under the receiver operating characteristic curve (Az) were regarded as a measure of diagnostic accuracy and subjected to the Friedman test with post hoc Durbin-Conover (α=.05). The PSP (Az=0.873) had higher Az values than the PBA (Az=0.753) for the 50-μm misfits (P<.05). Larger misfits resulted in greater accuracy than smaller misfits (P<.05). Interactions between the factors radiographic technique and misfit magnitude resulted in statistically significant differences for all comparisons (P<.05), except between the PSP for the 100-μm misfits (Az=0.976) and the PMP for the 150-μm misfits (Az=0.998). The PSP was more accurate than the PBA in detecting the 50-µm misfits at the abutment-prosthesis interface; larger misfits resulted in more accurate diagnoses, regardless of the technique used.

Defining challenging areas of the preparation finish line by using an open-source 3D modeling computer program: A tip to simplify margin identification by the dental laboratory technician

Intraoral data acquisition and computer-aided design and computer-aided manufacturing (CAD-CAM) systems have simplified and expedited the fabrication of dental prostheses. 1 Van Noort R. The future of dental devices is digital. Dent Mater. 2012; 28: 3-12 Crossref PubMed Scopus (801) Google Scholar ,2 Giuliodori G. Rappelli G. Aquilanti L. Intraoral scans of full dental arches: an in vitro measurement study of the accuracy of different intraoral scanners. Int J Environ Res Public Health. 2023; 20: 4776 Crossref Scopus (0) Google Scholar Contemporary dental CAD-CAM provides the freedom to design and fabricate diverse dental devices, including custom impression trays, surgical templates, and removable and fixed dental prostheses. 1 Van Noort R. The future of dental devices is digital. Dent Mater. 2012; 28: 3-12 Crossref PubMed Scopus (801) Google Scholar ,3 Revilla-León M. Özcan M. Additive manufacturing technologies used for processing polymers: current status and potential application in prosthetic dentistry. J Prosthodont. 2019; 28: 146-158 Crossref PubMed Scopus (217) Google Scholar ,4 Turkyilmaz I. Wilkins G.N. Varvara G. Tooth preparation, digital design and milling process considerations for CAD/CAM crowns: understanding the transition from analog to digital workflow. J Dent Sci. 2021; 16: 1312-1314 Crossref Scopus (8) Google Scholar These dental appliances are created from a digital file that recreates the surface geometry of the target object, typically a standard tessellation language (STL) file. 5 Grant G.T. Campbell S.D. Masri R.M. Andersen M.R. The American college of prosthodontist digital dentistry glossary development task force. Glossary of digital terms. J Prosthodont. 2016; 25: S2-S9 Crossref PubMed Scopus (27) Google Scholar A prerequisite for accurate manufacture is the exact capture and identification of the fine details in the target intraoral structures. An accurate capture can be challenging when the preparation finish line is subgingival, when abundant bleeding or salivation occurs, or when operator scanning skills and speed are still developing. 6 Mangano F. Gandolfi A. Luongo G. Logozzo S. Intraoral scanners in dentistry: a review of the current literature. BMC Oral Health. 2017; 17: 149 Crossref PubMed Scopus (308) Google Scholar Additionally, the location of fine details can be challenging for the dental laboratory technician to visualize when the CAD file is outsourced for the manufacture of the definitive restoration, since STL files lack attributes such as color and texture. 5 Grant G.T. Campbell S.D. Masri R.M. Andersen M.R. The American college of prosthodontist digital dentistry glossary development task force. Glossary of digital terms. J Prosthodont. 2016; 25: S2-S9 Crossref PubMed Scopus (27) Google Scholar These features help differentiate the tooth from its surrounding tissues when finish lines are subgingival or when displacement is limited. The present article presents a straightforward workflow that defines challenging areas of the preparation finish line by using an open-source 3D modeling computer program. This procedure can be used to communicate the finish line observed to the dental laboratory technician when STL files are used to design the definitive restoration and stops the technician guessing the finish line, since the hard-to-see areas are defined by the clinician. Additionally, this approach has advantages over the margin tracing and sculpting tools available in most 3-dimensional (3D) CAD computer programs since it allows selecting the critical areas around the finish line considering the mesh geometry of the 3D file. Visualizing the 3D mesh permits a more precise selection, which can minimize distortion as even the smallest changes in the mesh surface can be observed if transformation or sculpting procedures are used.

Digital working process in diagnosis, treatment planning and fabrication of personalized orthodontic appliances

ABSTRACT Until recently, the working process of personalized orthodontic appliances (POAs) is performed digitally with the use of virtual systems including diagnosis, treatment planning and remote monitoring. Based on the exponential development of digital technologies such as imaging systems, computer-aided design and computer-aided manufacturing (CAD/CAM) systems, three-dimensional (3D) printing and artificial intelligence (AI), orthodontists want to go further and create an almost automatic intelligent orthodontic procedure containing big data to assist orthodontists in clinical treatment and reduce therapy duration. Here, we review the latest studies illustrating the application of digital technologies during treatment and manufacturing process of POAs. In addition, we highlight the current challenges and future directions of digital technology in POAs to call for more attention to the (I) AI applications for image analysis and treatment designation, and (II) 3D printing technologies for precise fabrication of POAs like clear aligner, accessories of fixed orthodontic appliances.

Comparative Fracture Resistance Analysis of Translucent Monolithic Zirconia Dioxide Milled in a CAD/CAM System

The aim of this study was to evaluate and compare the fracture resistance of definitive zirconia dioxide restorations obtained using a computer-aided design and manufacturing (CAD/CAM) system. Methods: Two groups of ten samples were analyzed for each material (n: 20); the first group was Zolid Gen X Amann Girrbach (ZGX) and the second group was Cercon HT Dentsply Sirona (CDS). The restorations were designed with identical parameters and milled with a CAD/CAM system. Each specimen was load tested at a speed of 0.5 mm/min, with a direction parallel to the major axis of the tooth and with an initial preload of 10 N until fracture using a universal testing machine (Universal/Tensile Testing Machine, Autograph AGS-X Series) equipped with a 20 kN load cell. The results obtained were recorded in Newtons (N), using software connected to the testing machine. Results: Statistically significant differences were found, and the fracture resistance of the monolithic zirconia crowns was lower in the CDS group (1744.84 ± 172.8 N) compared to the ZGX group (2387.41 ± 516 N). Conclusions: The monolithic zirconia CAD-CAM zirconia crowns showed sufficient fracture resistance when used in posterior molar and premolar zones with either material, as they withstood fracture loads greater than the maximum masticatory force.

An analytical local tool path smoothing method with curvature control

In traditional multi-axis machining, the linear tool path generated by computer-aided manufacturing systems is still in a broad tool path format, resulting in discontinuities at the corners, which slow down tool motion, and also trigger tool vibration, reducing machining accuracy and surface quality. In order to ensure the C3 continuity of the tool during the multi-axis machining process, this paper proposes an analytical B-spline local smoothing method with curvature control. The tool position trajectory and tool orientation are both smoothed by a 5th spline curve with 9 control points. Optimal control points are determined for position and orientation splines to achieve C3 continuity at the junctions between the spline and linear segment while preserving the predefined geometric tolerance limits and minimizing the maximum curvature of the inserted B-spline curve. The smoothed tool path is expected to have less curvature fluctuation, which can significantly improve both the kinematic performance of the machine tool and the machining efficiency. Both computer simulations and physical printing experiments are carried out to demonstrate the improvements of our proposed method in motion smoothness and tracking accuracy in multi-axis machining tasks.

Construction of Local-Shape-Controlled Quartic Generalized Said-Ball Model

Said-Ball curves and surfaces are extensively applied in the realm of geometric modeling. Their appearance is only decided by the control points, which produces a great deal of inconvenience for the shape design of sophisticated products. To overcome this defect, we construct a novel kind of quartic generalized Said-Ball (QGS-Ball, for short) curves and surfaces, which contain multiple shape parameters, and the global and local shape can be easily modified via shape parameters. The specific research contents are as follows: Firstly, the QGS-Ball basis functions carrying multiple shape parameters are defined, and the correlative properties are proved. Secondly, the QGS-Ball curve is proposed according to the QGS-Ball basis functions, and the effect of shape parameters on the curve is discussed. Thirdly, in view of the constructed QGS-Ball curve, we further propose the combined quartic generalized Said-Ball (CQGS-Ball, for short) curves, and deduce the conditions of first-order and second-order geometric continuity (namely, G1 and G2 continuity). Finally, the QGS-Ball surface is defined by tensor product method, and the influence of shape parameters on the surface is analyzed. The main contribution of this article is to construct the QGS-Ball curve model, and deduce the G1 and G2 geometric joining conditions of QGS-Ball curves. Combined with some modeling examples, it further illustrates that the QGS-Ball curve as a new geometric model provides a powerful supplement for the geometric design of sophisticated form in computer-aided design (CAD) and computer-aided manufacturing (CAM) systems.

Biofilm Formation on the Surfaces of CAD/CAM Dental Polymers.

Dental polymers are now available as monolithic materials which can be readily used in computer-aided design and computer-aided manufacturing (CAD/CAM) systems. Despite possessing numerous advantages over conventionally produced polymers, the polymers produced by either of these systems fail to exhibit immunity to surface microbial adhesion when introduced into the oral environment, leading to the development of oral diseases. The aim of this study was to analyze the biofilm formation of six microorganisms from the oral cavity and its correlation to the surface characteristics of CAD/CAM dental polymers. A total of ninety specimens were divided into three groups: resin-based composite, polymethyl methacrylate, and polyether ether ketone. The experimental procedure included surface roughness and water contact angle measurements, colony forming unit counting, and scanning electron microscopy analysis of biofilm formed on the surface of the tested materials. The data were analyzed using the Kruskal-Wallis test, with a Dunn's post hoc analysis, and one way analysis of variance, with a Tukey's post hoc test; the correlation between the measurements was tested using Spearman's correlation coefficient, and descriptive statistics were used to present the data. Despite using the same manufacturing procedure, as well as the identical manufacturer's finishing and polishing protocols, CAD/CAM dental polymers revealed significant differences in surface roughness and water contact angle, and the increased values of both parameters led to an increase in biofilm formation on the surface of the materials. The CAD/CAM resin-based composite showed the lowest number of adhered microorganisms compared to CAD/CAM polymethyl methacrylate and CAD/CAM polyether ether ketone.