Rui B. Ruben

Preload loss and plastic deformation of titanium abutment screws under repeated tightening are clinically significant yet incompletely characterized across systems with differing head geometries and surface treatments. Two ISO 14801-certified titanium screws were evaluated: hexalobular-head gold-plated (Gold-Tite^®; 3i Zimmer Biomet, now ZIMVIE) and anodized star-shaped (Vega^®; Klockner^®). Six groups (n = 5 screws) varied by screw type, torque (20–40 N·cm), and cycle count (10 or 20). Reverse torque value (RTV) was recorded at every cycle and analyzed at the screw level; a linear mixed-effects model (screw as random effect) characterized how RTV evolved across cycles, with screw-level non-parametric tests for between-protocol contrasts. Micro-CT (19.9 μm; n = 3 per group) used Otsu segmentation. RTV was lower than insertion torque in every screw (30/30; 73–89% of applied torque). RTV declined significantly across cycles in the Vega/Klockner system (−0.17 N·cm per cycle, p = 0.006) but not in the ZFX/ZIMVIE system (p = 0.302), which showed greater between screw variability. Between protocol contrasts at n = 5 were null or underpowered. Micro-CT showed head localized change in both systems (mean cross-sectional area essentially unchanged); in the ZFX/ZIMVIE screws, this change appeared specifically under the over-use condition, whereas the Klockner screws showed comparable head change across all protocols. Preload loss is intrinsic to abutment screw tightening irrespective of design; RTV behaviour under repeated cycling is system-dependent, and abutment screws should be treated as limited-use components.

This exploratory proof-of-concept study aimed to develop and preliminarily evaluate a 3D-printed holder designed for reuse in cone beam computed tomography (CBCT) in dental research, particularly for comparative studies requiring pre- and post-intervention tooth assessment. The holder was designed using computer-aided design software and fabricated from polylactic acid using 3D printing. A conventional alginate-based holder was used for comparison. The comparison therefore concerned two complete positioning systems with different geometries and modes of adaptation to the CBCT headrest. The two positioning devices were independently placed by two operators with different levels of experience, and all CBCT scans were acquired by the same operator. The procedure was repeated after a 5-day interval. Root canal morphology was assessed using volumetric and surface measurements, as well as voxel counts. The independently segmented canal models were qualitatively displayed together in their native coordinate space to visualize positional consistency between acquisitions. Paired analyses showed substantially lower positional deviations with the 3D-printed holder than with the conventional holder in all four acquisition comparisons (Holm-adjusted p < 0.001). Mean deviations ranged from 0.126 to 0.172 mm for the 3D-printed holder and from 3.626 to 8.318 mm for the conventional holder. Morphometric parameters derived from 3D analysis remained identical across all acquisitions, regardless of operator, time point, or positioning method. Qualitative 3D analysis showed near-complete overlap for the 3D-printed holder and clear spatial discrepancies for the conventional holder. Under the evaluated conditions, the 3D-printed holder exhibited less positional variability than the conventional alginate-based holder.

Tissue engineering lies at the crossroads of biology, medicine, and engineering, playing a crucial role in developing advanced treatments for various pathologies

Objectives: Commercial artificial teeth (AT) and three-dimensional printed teeth (3DPT) have been increasingly used in preclinical endodontic education; however, limitations regarding anatomical realism, tactile sensation, and procedural simulation continued to be reported. This study assessed students’ and evaluators’ perceptions regarding AT and PolyJet™ 3DPT fabricated with RGD525™, compared with natural teeth (NT), together with the quality of endodontic procedures performed using both artificial models. Methods: Undergraduate dental students with no previous experience using AT or 3DPT performed standardized endodontic procedures on both artificial models. Students and evaluators completed questionnaires regarding anatomical realism, tactile sensation, radiographic characteristics, educational applicability, and model preference. Procedural quality and errors were independently assessed radiographically by evaluators. Results: AT received more favorable perceptions regarding external anatomy, whereas 3DPT were more positively evaluated for internal anatomy, radiopacity, resistance of root canal walls and tactile sensation during instrumentation (p ≤ 0.002). NT remained the preferred training model, followed by 3DPT, while AT received the lowest preference ratings (p < 0.001). Evaluators consistently perceived 3DPT as more similar to NT than AT. Regarding treatment outcomes, 3DPT showed significantly higher scores for endodontic preparation, verifier fitting, and root canal filling (p < 0.05), while presenting significantly fewer procedural errors than AT (p < 0.001). Conclusions: PolyJet™ 3DPT fabricated with RGD525™ demonstrated promising applicability for preclinical endodontic training, combining favorable perceptions, fewer procedural errors, and potential for low-cost large-scale in-house production. Nevertheless, improvements in material realism and tactile simulation are still required.

This study aimed to evaluate the aging effect (6 and 12 months), relative to baseline (0 months), on the dimensional accuracy, morphological stability, and shaping behavior of PolyJet™ 3D-printed teeth (3DPT) produced in two printing orientations (X and Y axes). Specimens (XA0, XA6, XA12, YA0, YA6, YA12) were analyzed using microcomputed tomography before and after root canal preparation with the ProTaper Gold^® system. Preoperative analysis included canal volume, centroid, total tooth volume, and total tooth area. Aging-related changes were observed, with significant differences between XA0 and XA12 (p < 0.05), whereas no differences were detected among Y-axis groups (p > 0.05). These findings indicate that X-axis specimens are not comparable over time, while Y-axis specimens maintain baseline consistency. Postoperative evaluation revealed significant differences across aging conditions for most endodontic preparation parameters. Within the limitations of this study, aging had a limited effect on dimensional accuracy but influenced the shaping behavior of 3DPT. Based on these findings, future studies using PolyJet™ 3DPT should report the printing batch and the storage time between fabrication and experimental use, as these factors may influence the comparability and reliability of the results.

The hammer throw is a complex discipline event in track and field sports, where Principal Component Analysis (PCA) has been applied as a key tool to analyse the details of movement patterns and identify crucial factors that affect performance. Therefore, this study aimed to use the PCA to analyse the hammer technique considering the age and performance. Thirty-nine male and thirty-two female hammer throwers who competed in the European Throwing Cup in 2018 and 2022 participated in the study. Three-dimensional kinematic analysis was used to process temporal and kinematic parameters associated with the hammer technique. The best throw from each athlete was chosen for analysis. The PCA facilitated the reduction and connection of the analysed parameters. In both groups except women U23, we observed higher correlations in velocity increase, hammer amplitude, and timing variables (double support, single support, and total time) in Turn 4. Lastly, differentiation factors were identified for each group. It was observed that a low initial velocity during Turn 1 was common in both men's and women's categories. Under 23 men should minimise the single support in Turn 2, and women should improve the velocity increase in Turn 4 to increase throw performance.

This study aimed to identify the optimal printing orientation (X, Y, or Z axis) and positioning of a mandibular molar presenting an isthmus using PolyJet™ technology. The influence of these parameters on dimensional accuracy and on the behavior of 3D-printed teeth (3DPT) during endodontic preparation with ProTaper Gold^® system was evaluated. Six groups (XA, XB, YA, YB, ZA, ZB; n = 10) were printed with different axis orientations and distinct isthmus positions relative to the build platform. All samples underwent micro-computed tomography scanning before and after endodontic preparation. Regarding preoperative analyses—canal volume, centroids, and total tooth volume and area—no significant differences were found between groups XA–YA or XB–YB (p > 0.05), supporting their comparability. In contrast, groups ZA and ZB differed significantly from all others (p < 0.05), failing to meet equivalence required for further comparison, and were therefore excluded. Postoperative evaluation—volume change, centroid displacement, transportation, and unprepared areas—revealed no significant differences between XA–YA and XB–YB. Within the limitations of this study, both printing orientation and position affected the accuracy and repeatability of 3DPT, with positioning exerting the greatest influence, while their behavior towards endodontic preparation remained consistent across orientations.

Material Extrusion (MEX) process is increasingly used to fabricate components for structural applications, driven by the availability of advanced materials and greater industrial adoption. In these contexts, understanding the mechanical performance of printed parts is crucial. However, conventional methods for assessing anisotropic elastic behavior often rely on expensive equipment and time-consuming procedures. The aim of this study is to evaluate the applicability of the impulse excitation of vibration (IEV) in characterizing the dynamic mechanical properties of a 3D-printed composite material. Tensile tests were also performed to compare quasi-static properties with the dynamic ones obtained through IEV. The tested material, Nylon 12CF, contains 35% short carbon fibers by weight and is commercially available from Stratasys. It is used in the fused deposition modeling (FDM) process, a Material Extrusion technology, and exhibits anisotropic mechanical properties. This is further reinforced by the filament deposition process, which affects the mechanical response of printed parts. Young’s modulus obtained in the direction perpendicular to the deposition plane (E₃₃), obtained via IEV, was 14.77% higher than the value in the technical datasheet. Comparing methods, the Young’s modulus obtained in the deposition plane, in an inclined direction of 45 degrees in relation to the deposition direction (E₄₅), showed a 22.95% difference between IEV and tensile tests, while Poisson’s ratio in the deposition plane (v₁₂) differed by 6.78%. This data is critical for designing parts subject to demanding service conditions, and the results obtained (orthotropic elastic properties) can be used in finite element simulation software. Ultimately, this work reinforces the potential of the IEV method as an accessible and consistent alternative for characterizing the anisotropic properties of components produced through additive manufacturing (AM).

Accurate contact and impact detection remain key challenges in computational mechanics. This work presents a methodology for non-conformal contact detection between rigid convex bodies with superelliptical boundaries, represented using their respective Signed Distance Fields (SDFs). A method for approximating the SDF of discretized superelliptical boundaries is introduced, along with the concept of the Gap Distance Field (GDF). Reformulating the contact detection problem as an unconstrained minimization over the GDF simplifies the computation of minimum distance and overlap, while the closest contact point is obtained by projecting the SDF gradients. Numerical experiments involving superelliptical contact bodies validate the accuracy and robustness of the proposed approach. Additionally, the common normal (CN) condition naturally arises within this framework, and together with the optimality of the GDF minima, provides a sufficient condition for determining the minimum distance between the interacting bodies.