Influence of ceramic firing on marginal gap accuracy and metal-ceramic bond strength of 3D-printed Co-Cr frameworks.

STATEMENT OF PROBLEM: The marginal gap and ceramic bond strength of metal-ceramic restorations are important for success. However, studies evaluating the marginal gap and ceramic bond strength of fixed partial dentures (FPDs) produced with 3D printing technologies such as selective laser melting (SLM) are scarce. PURPOSE: The purpose of this in vitro study was to investigate the marginal gap of cobalt-chromium (Co-Cr) alloy frameworks produced by SLM technology before and after ceramic firing. Additionally, the metal-ceramic bond strength was evaluated with the Schwickerath crack-initiation test according to the International Standards Organization (ISO) 9693-1:2012. MATERIAL AND METHODS: Conventional impressions were made, and the definitive cast of a patient requiring a 4-unit FPD was scanned. After designing the FPD, the files were sent to a service center for the fabrication of a metal master model, 80 Co-Cr frameworks, and 80 flat specimens (25×3×0.5 mm) with SLM technology. The marginal gap between frameworks and the abutment tooth of the metal master model was nondestructively measured by using an optical coordinate-measuring machine. A total of 80 sets, consisting of 1 framework and 1 flat specimen, were sent to 80 dental laboratory technicians for ceramic firing. Detailed instructions for correct manipulation of the framework and flat specimen were provided. The marginal gap was remeasured, and the 3-point bend test was used to evaluate metal-ceramic bond strength. RESULTS: Only 28 of the 80 dental technicians returned the specimens within a prespecified time and/or in adequate condition. The mean ±standard deviation marginal gap of the framework before ceramic firing was 25 ±9 µm and 34 ±12 µm after firing. The difference was statistically significant (P=.001). The mean ±standard deviation 3-point bend strength was 33 ±9 MPa. CONCLUSIONS: Ceramic firing affected the marginal gap; however, all Co-Cr frameworks had a marginal gap lower than 120 µm, which is reported to be a clinically acceptable limit. Most of the specimens (80%) had a metal-ceramic bond strength value higher than the 25-MPa ISO 9693 requirement. Five of 28 dental laboratory technicians were not able to comply with ceramic firing instructions.

Manufacturing of Metal Frameworks for Full-Arch Dental Restoration on Implants: A Comparison between Milling and a Novel Hybrid Technology.

PURPOSE: To determine the trueness and precision of frameworks manufactured with a selective laser melting/milling hybrid technique (SLM/m) and conventional milling by comparing the implant-platform/framework interface with those of the original computer-aided design (CAD). MATERIALS AND METHODS: Using a virtual 6-implant-supported full-arch framework CAD drawing, 27 titanium replicas were manufactured by 3 independent manufacturing centers (n = 9/center) using a hybrid SLM/m technology (labs 1 and 2) or the conventional milling technique (lab 3). Using an opto-mechanical coordinate measuring machine, the frameworks' misfit distribution and patterns were analyzed, and the position error between paired platform positions within each framework was evaluated to calculate the misfit tendency for each group. A multilevel analysis using a mixed-effects model was conducted (α = 0.05). The trueness was evaluated as the dimensional difference from the original, while the precision as the dimensional difference from a repeated scan. RESULTS: The 3 dimensional misfits differed significantly among the 3 groups, with the milled group exhibiting the least accurate outcome (p = 0.005). The mean 3D positioning errors ranged from 8 to 16 µm and from 9 to 22 µm for the SLM/m technique (labs 1 and 2, respectively), and from 20 to 35 µm for conventional milling (lab 3). Regarding the misfit distribution pattern, the misfit increased with the distance between paired platform positions in all groups. CONCLUSIONS: All groups had 3D misfits well within the error limits reported in the literature. The 3D misfits of new hybrid (SLM/milling) and conventional (milling) procedures differed significantly among them, with the milling technique the less accurate and precise. The largest errors in all groups were found between the most distant implants, resulting in a correlation between the framework span and the inaccuracies.

Computation of Femoral Canine Morphometric Parameters in Three-Dimensional Geometrical Models.

OBJECTIVE: To define and validate a method for the measurement of 3-dimensional (3D) morphometric parameters in polygonal mesh models of canine femora. STUDY DESIGN: Ex vivo/computerized model. SAMPLE POPULATION: Sixteen femora from 8 medium to large-breed canine cadavers (mean body weight 28.3 kg, mean age 5.3 years). METHODS: Femora were measured with a 3D scanner, obtaining 3D meshes. A computer-aided design-based (CAD) software tool was purposely developed, which allowed automatic calculation of morphometric parameters on a mesh model. Anatomic and mechanical lateral proximal femoral angles (aLPFA and mLPFA), anatomic and mechanical lateral distal femoral angles (aLDFA and mLDFA), femoral neck angle (FNA), femoral torsion angle (FTA), and femoral varus angle (FVA) were measured in 3D space. Angles were also measured onto projected planes and radiographic images. RESULTS: Mean (SD) femoral angles (degrees) measured in 3D space were: aLPFA 115.2 (3.9), mLPFA 105.5 (4.2), aLDFA 88.6 (4.5), mLDFA 93.4 (3.9), FNA 129.6 (4.3), FTA 45 (4.5), and FVA -1.4 (4.5). Onto projection planes, aLPFA was 103.7 (5.9), mLPFA 98.4 (5.3), aLDFA 88.3 (5.5), mLDFA 93.6 (4.2), FNA 132.1 (3.5), FTA 19.1 (5.7), and FVA -1.7 (5.5). With radiographic imaging, aLPFA was 109.6 (5.9), mLPFA 105.3 (5.2), aLDFA 92.6 (3.8), mLDFA 96.9 (2.9), FNA 120.2 (8.0), FTA 30.2 (5.7), and FVA 2.6 (3.8). CONCLUSION: The proposed method gives reliable and consistent information about 3D bone conformation. Results are obtained automatically and depend only on femur morphology, avoiding any operator-related bias. Angles in 3D space are different from those measured with standard radiographic methods, mainly due to the different definition of femoral axes.

Modeling Materials Coextrusion in Polymers Additive Manufacturing.

Material extrusion additive manufacturing enables us to combine more materials in the same nozzle during the deposition process. This technology, called material coextrusion, generates an expanded range of material properties, which can gradually change in the design domain, ensuring blending or higher bonding/interlocking among the different materials. To exploit the opportunities offered by these technologies, it is necessary to know the behavior of the combined materials according to the materials fractions. In this work, two compatible pairs of materials, namely Polylactic Acid (PLA)-Thermoplastic Polyurethane (TPU) and Acrylonitrile Styrene Acrylate (ASA)-TPU, were investigated by changing the material fractions in the coextrusion process. An original model describing the distribution of the materials is proposed. Based on this, the mechanical properties were investigated by analytical and numerical approaches. The analytical model was developed on the simplified assumption that the coextruded materials are a set of rods, whereas the more realistic numerical model is based on homogenization theory, adopting the finite element analysis of a representative volume element. To verify the deposition model, a specific experimental test was developed, and the modeled material deposition was superimposed and qualitatively compared with the actual microscope images regarding the different deposition directions and material fractions. The analytical and numerical models show similar trends, and it can be assumed that the finite element model has a more realistic behavior due to the higher accuracy of the model description. The elastic moduli obtained by the models was verified in experimental tensile tests. The tensile tests show Young's moduli of 3425 MPa for PLA, 1812 MPa for ASA, and 162 MPa for TPU. At the intermediate material fraction, the Young's modulus shows an almost linear trend between PLA and TPU and between ASA and TPU. The ultimate tensile strength values are 63.9 MPa for PLA, 35.7 MPa for ASA, and 63.5 MPa for TPU, whereas at the intermediate material fraction, they assume lower values. In this initial work, the results show a good agreement between models and experiments, providing useful tools for designers and contributing to a new branch in additive manufacturing research.

3D Printing of Hierarchically Porous Lattice Structures Based on Åkermanite Glass Microspheres and Reactive Silicone Binder.

The present study illustrates the manufacturing method of hierarchically porous 3D scaffolds based on åkermanite as a promising bioceramic for stereolithography. The macroporosity was designed by implementing 3D models corresponding to different lattice structures (cubic, diamond, Kelvin, and Kagome). To obtain micro-scale porosity, flame synthesized glass microbeads with 10 wt% of silicone resins were utilized to fabricate green scaffolds, later converted into targeted bioceramic phase by firing at 1100 °C in air. No chemical reaction between the glass microspheres, crystallizing into åkermanite, and silica deriving from silicone oxidation was observed upon heat treatment. Silica acted as a binder between the adjacent microspheres, enhancing the creation of microporosity, as documented by XRD, and SEM coupled with EDX analysis. The formation of 'spongy' struts was confirmed by infiltration with Rhodamine B solution. The compressive strength of the sintered porous scaffolds was up to 0.7 MPa with the porosity of 68-84%.

Investigation of the Accuracy of Four Intraoral Scanners in Mandibular Full-Arch Digital Implant Impression: A Comparative In Vitro Study.

Background: We compare the accuracy of new intraoral scanners (IOSs) in full-arch digital implant impressions. Methods: A master model with six scan bodies was milled in poly(methyl methacrylate), measured by using a coordinate measuring machine, and scanned 15 times with four IOSs: PrimeScan, Medit i500, Vatech EZ scan, and iTero. The software was developed to identify the position points on each scan body. The 3D position and distance analysis were performed. Results: The average and ± standard deviation of the 3D position analysis was 29 µm ± 6 µm for PrimeScan, 39 µm ± 6 µm for iTero, 48 µm ± 18 µm for Mediti500, and 118 µm ± 24 µm for Vatech EZ scan (p < 0.05). Conclusions: All IOSs are able to make a digital complete implant impression in vitro according to the average misfit value reported in literature (150 µm); however, the 3D distance analysis showed that only the Primescan and iTero presented negligible systematic error sources.

Up-Cycling of LCD Glass by Additive Manufacturing of Porous Translucent Glass Scaffolds.

Additive manufacturing technologies, compared to conventional shaping methods, offer great opportunities in design versatility, for the manufacturing of highly porous ceramic components. However, the application to glass powders, later subjected to viscous flow sintering, involves significant challenges, especially in shape retention and in the achievement of a substantial degree of translucency in the final products. The present paper disclosed the potential of glass recovered from liquid crystal displays (LCD) for the manufacturing of highly porous scaffolds by direct ink writing and masked stereolithography of fine powders mixed with suitable organic additives, and sintered at 950 °C, for 1-1.5 h, in air. The specific glass, featuring a relatively high transition temperature (Tg~700 °C), allowed for the complete burn-out of organics before viscous flow sintering could take place; in addition, translucency was favored by the successful removal of porosity in the struts and by the resistance of the used glass to crystallization.

Digital Planning and Manufacturing of Maxillary Skeletal Expander for Patients with Thin Palatal Bone.

The miniscrew-assisted rapid palatal expansion approach has given new opportunities for the treatment of maxilla transverse deficiency by providing an alternative to the surgical approach for adult patients. However, the presence of a thin palatal bone can compromise the success of such approach. Recently, the digital planning of the miniscrew-assisted appliances has offered unique advantages in terms of safety and accuracy of the overall process. The aim of this study is to describe the digital planning and MSE fabrication with cad-cam technology using 6 mini-screws in cases with a palatal bone thickness of less than 2.5 mm.

A New Methodology for the Digital Planning of Micro-Implant-Supported Maxillary Skeletal Expansion.

INTRODUCTION: Miniscrew-assisted rapid palatal expansion (MARPE) appliances utilize the skeletal anchorage to expand the maxilla. One type of MARPE device is the Maxillary Skeletal Expander (MSE), which presents four micro-implants with bicortical engagement of the palatal vault and nasal floor. MSE positioning is traditionally planned using dental stone models and 2D headfilms. This approach presents some critical issues, such as the inability to identify the MSE position relative to skeletal structures, and the potential risk of damaging anatomical structures. METHODS: A novel methodology has been developed to plan MSE position using the digital model of dental arches and cone-beam computed tomography (CBCT). A virtual model of MSE appliance with the four micro-implants was created. After virtual planning, a positioning guide is virtually designed, 3D printed, and utilized to model and weld the MSE supporting arms to the molar bands. The expansion device is then cemented in the patient oral cavity and micro-implants inserted. A clinical case of a 12.9-year-old female patient presenting a Class III malocclusion with transverse and sagittal maxillary deficiency is reported. RESULTS: The midpalatal suture was opened with a split of 3.06 mm and 2.8 mm at the anterior and posterior nasal spine, respectively. After facemask therapy, the sagittal skeletal relationship was improved, as shown by the increase in ANB, A-Na perpendicular and Wits cephalometric parameters, and the mandibular plane rotated 1.6° clockwise. CONCLUSION: The proposed digital methodology represents an advancement in the planning of MSE positioning, compared to the traditional approach. By evaluating the bone morphology of the palate and midface on patient CBCT, the placement of MSE is improved regarding the biomechanics of maxillary expansion and the bone thickness at micro-implants insertion sites. In the present case report, the digital planning was associated with a positive outcome of maxillary expansion and protraction in safety conditions.

Accuracy of an automated three-dimensional technique for the computation of femoral angles in dogs.

AIMS: The purpose of the study was to evaluate the accuracy of a three-dimensional (3D) automated technique (computer-aided design (aCAD)) for the measurement of three canine femoral angles: anatomical lateral distal femoral angle (aLDFA), femoral neck angle (FNA) and femoral torsion angle. METHODS: Twenty-eight femurs equally divided intotwo groups (normal and abnormal) were obtained from 14 dogs of different conformations (dolicomorphic and chondrodystrophicCT scans and 3D scanner acquisitions were used to create stereolithographic (STL) files , which were run in a CAD platform. Two blinded observers separately performed the measurements using the STL obtained from CT scans (CT aCAD) and 3D scanner (3D aCAD), which was considered the gold standard method. C orrelation coefficients were used to investigate the strength of the relationship between the two measurements. RESULTS: A ccuracy of the aCAD computation was good, being always above the threshold of R2 of greater than 80 per cent for all three angles assessed in both groups. a LDFA and FNA were the most accurate angles (accuracy >90 per cent). CONCLUSIONS: The proposed 3D aCAD protocol can be considered a reliable technique to assess femoral angle measurements in canine femur. The developed algorithm automatically calculates the femoral angles in 3D, thus considering the subjective intrinsic femur morphology. The main benefit relies on a fast user-independent computation, which avoids user-related measurement variability. The accuracy of 3D details may be helpful for patellar luxation and femoral bone deformity correction, as well as for the design of patient- specific, custom-made hip prosthesis implants.

Full arch digital scanning systems performances for implant-supported fixed dental prostheses: a comparative study of 8 intraoral scanners.

PURPOSE: Compare the accuracy of intraoral digital impression in full-arch implant-supported fixed dental prosthesis acquired with eight different intraoral scanner (Ios). METHODS: A polymethyl methacrylate acrylic model of an edentulous mandible with six scan-abutment was used as a master model and its dimensions measured with a coordinate measuring machine. Eight different Ios were used to generate digital impression: True Definition, Trios, Cerec Omnicam, 3D progress, CS3500, CS3600, Planmeca Emelard and Dental Wings. Fifteen digital impressions were made. A software called "Scan-abut" was developed to analyse and compare the digital impression with the master model, obtaining the scanning accuracy. The three-dimensional (3D) position and distance analysis were performed. RESULTS: Mean value of the 3D position analysis showed that the True Definition (31 µm ± 8 µm) and Trios (32 µm ± 5 µm) have the best performance of the group. The Cerec Omnicam (71 µm ± 55 µm), CS3600 (61 µm ± 14 µm) have an average performance. The CS3500 (107 µm ± 28 µm) and Planmeca Emelard (101 µm ± 38 µm) present a middle-low performance, while the 3D progress (344 µm ± 121 µm) and Dental Wings (148 µm ± 64 µm) show the low performance. The 3D distance analysis showed a good linear relationship between the errors and scan-abutment distance only with the True Definition and CS3600. CONCLUSIONS: Not all scanners are suitable for digital impression in full-arch implant-supported fixed dental prosthesis and the weight of the output files is independent from the accuracy of the Ios.

3D surface imaging of abdominal wall muscular contraction.

BACKGROUND AND OBJECTIVE: The biomechanical analysis of the abdominal wall should take into account muscle activation and related phenomena, such as intra-abdominal pressure variation and abdomen surface deformation. The geometry of abdominal surface and its deformation during contraction have not been extensively characterized, while represent a key issue to be investigated. METHODS: In this work, the antero-lateral abdominal wall surface of ten healthy volunteers in supine position is acquired via laser scanning in relaxed conditions and during abdominal muscles contraction, repeating each acquisition six times. The average relaxed and contracted abdominal surfaces are compared for each subject and displacements measured. RESULTS: Muscular activation induces raising in the region adjacent to linea alba along the posterior-anterior direction and a simultaneous lowering along lateral-medial direction of the abdominal wall sides. Displacements reach a maximum value of 12.5 mm for the involved subjects. The coefficient of variation associated to the abdomen surface measurements in the same configuration (relaxed or contracted) is below 0.75%. Non-parametric Mann-Whitney U test highlights that the differences between relaxed and contracted abdominal wall surfaces are significant (p < 0.01). CONCLUSIONS: Laser scanning is an accurate and reliable method to evaluate surface changes on the abdominal wall during muscular contraction. The results of this experimental activity can be useful to validate numerical models aimed at describing abdominal wall biomechanics.

Geometric Modeling of Cellular Materials for Additive Manufacturing in Biomedical Field: A Review.

Advances in additive manufacturing technologies facilitate the fabrication of cellular materials that have tailored functional characteristics. The application of solid freeform fabrication techniques is especially exploited in designing scaffolds for tissue engineering. In this review, firstly, a classification of cellular materials from a geometric point of view is proposed; then, the main approaches on geometric modeling of cellular materials are discussed. Finally, an investigation on porous scaffolds fabricated by additive manufacturing technologies is pointed out. Perspectives in geometric modeling of scaffolds for tissue engineering are also proposed.

Precision of the Connection Between Implant and Standard or Computer-Aided Design/Computer-Aided Manufacturing Abutments: A Novel Evaluation Method.

PURPOSE: The aim of this in vitro study was to verify whether or not stock and computer-aided design/computer-aided manufacturing (CAD/CAM) abutments show similar precision in the connection with the respective implants. MATERIALS AND METHODS: Ten CAD/CAM titanium abutments were compared with 10 stock titanium abutments. Each abutment fit a regular-platform implant (Institute Straumann). Implants and abutments were measured independently and then connected. During the connection procedure, the torque was measured using a six-axes load cell. Then, outer geometric features of the implant-abutment connection were measured again. Finally, the assembly was sectioned to provide the analysis of inner surfaces in contact. The geometric measurements were performed using a multisensored opto-mechanical coordinate measuring machine. The following parameters were measured and compared for the CAD/CAM and stock titanium abutment groups, respectively: width of interference and interference length between the conical surfaces of the implant and abutment; and volume of material involved in the implant-abutment connection. RESULTS: Interference width mean ± SD values of 18 ± 0.5 and 14 µ 0.5 µm were calculated for the stock and CAD/CAM titanium abutment groups, respectively. The difference was statistically significant (P = .02). Furthermore, the interference length mean ± SD values of 763 ± 10 and 816 ± 43 µm were calculated for stock and CAD/CAM titanium abutment groups, respectively. The difference was also statistically significant (P = .04). Finally, the volume of material involved in the implant-abutment connection was compared between stock and CAD/CAM titanium abutment groups; the mean ± SD values of 0.134 ± 0.014 and 0.108 ± 0.023 mm3 were significantly different (P = .009). CONCLUSION: Both standard and CAD/CAM abutment groups showed a three-dimensional (3D) seal activation after the screw tightening. Nevertheless, stock titanium abutments showed a significantly higher volume of material involved in the implant-abutment connection compared with that of CAD/CAM titanium abutments.

In vitro assessment of the accuracy of digital impressions prepared using a single system for full-arch restorations on implants.

PURPOSE: This study describes a method for measuring the accuracy of the virtual impression. METHODS: In vitro measurements according to a metrological approach were based on (1) use of an opto-mechanical coordinate measuring machine to acquire 3D points from a master model, (2) the mathematical reconstruction of regular geometric features (planes, cylinders, points) from 3D points or an STL file, and (3) consistent definition and evaluation of position and distance errors describing scanning inaccuracies. Two expert and two inexpert operators each made five impressions. The 3D position error, with its relevant X, Y, and Z components, the mean 3D position error of each scanbody, and the intra-scanbody distance error were measured using the analysis of variance and the Sheffe's test for multiple comparison. RESULTS: Statistically significant differences in the accuracy of the impression were observed among the operators for each scanbody, despite the good reliability (Cronbach's [Formula: see text] = 0.897). The mean 3D position error of the digital impression was between 0.041 ± 0.023 mm and 0.082 ± 0.030 mm. CONCLUSIONS: Within the limitations of this in vitro study, which was performed using a single commercial system for preparing digital impressions and one test configuration, the data showed that the digital impressions had a level of accuracy comparable to that reported in other studies, and which was acceptable for clinical and technological applications. The distance between the individual positions (#36 to #46) of the scanbody influenced the magnitude of the error. The position error generated by the intraoral scanner was dependent on the length of the arch scanned. Operator skill and experience may influence the accuracy of the impression.

A Novel In Vitro Technique for Assessing Dental Implant Osseointegration.

By definition, osseointegration means close contact between bone and implant. Bone response is related to implant surface properties. Various surfaces have been studied and applied to improve the biological properties of the implant and thereby favor the mechanism of osseointegration. This strategy aims to promote osseointegration by means of a faster and stronger bone formation, improving stability during the healing process, and thus allowing for earlier loading of the implant. Dental implant osseointegration has so far been studied in various animal models. The development of a method based on tissue engineering for assessing the osseointegration process in vitro could prove a valid biomimetic alternative to sacrificing animals. In this study, flat cylindrical dental implants with moderately rough surfaces and machined implants were set in bovine bone blocks. Then, adipose-derived stem cells (ADSCs) were three dimensionally cultured onto these blocks in osteo-endothelial medium for up to 30 days to mimic the osseointegration process in vitro. Scanning electron microscopy (SEM) and gene expression were used to examine stem cell commitment. Mechanical pull-out tests were also performed. SEM analysis identified cells with an osteoblast morphology adhering to the surface of the implants after their removal. Gene expression analysis showed that ADSCs seeded onto the bone blocks were able to express osteoblast and endothelial markers. The implants with the moderately rough surface generated higher pull-out strengths when compared with the machined implants. Nevertheless, the pull-out test values were higher for implants placed in bone blocks with ADSCs than for those set in scaffolds without stem cells. Our results demonstrate the validity of the method adopted and its potential for use in the in vitro assessment of the biological behavior of dental implant surfaces.

In Vitro Implant Impression Accuracy Using a New Photopolymerizing SDR Splinting Material.

PURPOSE: The study aims to evaluate three-dimensionally (3D) the accuracy of implant impressions using a new resin splinting material, "Smart Dentin Replacement" (SDR). MATERIALS AND METHODS: A titanium model of an edentulous mandible with six implant analogues was used as a master model and its dimensions measured with a coordinate measuring machine. Before the total 60 impressions were taken (open tray, screw-retained abutments, vinyl polysiloxane), they were divided in four groups: A (test): copings pick-up splinted with dental floss and fotopolymerizing SDR; B (test): see A, additionally sectioned and splinted again with SDR; C (control): copings pick-up splinted with dental floss and autopolymerizing Duralay® (Reliance Dental Mfg. Co., Alsip, IL, USA) acrylic resin; and D (control): see C, additionally sectioned and splinted again with Duralay. The impressions were measured directly with an optomechanical coordinate measuring machine and analyzed with a computer-aided design (CAD) geometric modeling software. The Wilcoxon matched-pair signed-rank test was used to compare groups. RESULTS: While there was no difference (p = .430) between the mean 3D deviations of the test groups A (17.5 µm) and B (17.4 µm), they both showed statistically significant differences (p < .003) compared with both control groups (C 25.0 µm, D 19.1 µm). CONCLUSIONS: Conventional impression techniques for edentulous jaws with multiple implants are highly accurate using the new fotopolymerizing splinting material SDR. Sectioning and rejoining of the SDR splinting had no impact on the impression accuracy.