Background/Objectives: The increasing clinical integration of 3D-printed definitive resins requires a comprehensive understanding of their physicochemical properties and adhesive behavior. However, there is limited evidence regarding the optimal surface treatment and bonding strategies for clear aligner composite attachments on these materials. This study aimed to characterize a 3D-printed definitive resin, evaluate the effects of surface treatments on its surface topography, and compare the shear bond strength (SBS) of the bonded attachments using different adhesive systems, both before and after thermocycling. Methods: A total of 120 rectangular specimens were fabricated from a 3D printed dental resin (Crowntec^®, SAREMCO Dental AG—Mexico City, Mexico). For physicochemical characterization, six samples underwent scanning electron microscopy/energy-dispersive spectroscopy, X-ray diffraction, and thermogravimetric analysis. To evaluate surface topography, 42 polished specimens were assigned to three groups: untreated (control), etched with 4% hydrofluoric acid (HFA), or sandblasted with 50 µm Al₂O₃ (AA). Each group was subdivided for SEM observation and surface roughness (Ra) measurement. For SBS testing, 72 additional samples received the same surface treatments and were further subdivided according to the adhesive system: Transbond™ XT Primer (TXT) or Single Bond Universal (SBU). Results: The AA group showed the highest Ra (2.21 ± 0.30 µm), followed by HFA (0.81 ± 0.20 µm) and control (0.07 ± 0.30 µm) (p < 0.001). The highest SBS was observed in the AA + SBU group, followed by AA + TXT. Conclusions: Sandblasting with Al₂O₃ particles, combined with a universal adhesive, significantly improved bond strength, suggesting a viable protocol for 3D printed definitive composites in aligner attachment applications.

Background: Metallic and metal oxide nanoparticles are increasingly explored as antimicrobial biomaterials in endodontics due to their multi-target mechanisms of action, largely mediated by metal ion release (e.g., Ag⁺, Cu⁺). However, bacterial metal resistance systems, particularly efflux-related proteins, may influence their antimicrobial performance. This study aimed to analyze the prevalence and distribution of metal resistance-associated proteins in bacteria involved in endodontic infections using a bioinformatic approach. Methods: An in silico, cross-sectional bioinformatic analysis was conducted using publicly available genomes from the Bacterial and Viral Bioinformatics Resource Center (BV-BRC). Bacterial species associated with acute apical abscess (AAA), symptomatic apical periodontitis (SAP), asymptomatic apical periodontitis (AAP), and post-treatment apical periodontitis (PTAP) were included. The presence of selected metal resistance-related proteins (CutC, CopA, CzcA, CusA, SilA, P-type ATPase, and PA3920) was assessed using a binary presence/absence framework. Prevalence, group comparisons (Fisher’s exact test), and co-occurrence patterns (Phi coefficient) were analyzed. Results: Metal resistance-associated proteins were widely distributed across all infection types, with prevalence ranging from 70.0% to 82.9% and no significant differences between groups (p > 0.05). CutC was the most prevalent protein, followed by CopA and CzcA, whereas SilA and PA3920 were not detected. Correlation analysis revealed consistent co-occurrence patterns among key taxa, including Porphyromonas gingivalis, Fusobacterium nucleatum, and Prevotella spp. Conclusions: Metal resistance-related proteins are broadly distributed in endodontic microbiota, indicating a conserved genetic capacity for metal tolerance. These findings suggest that microbial resistance determinants may influence, but do not directly determine, the antimicrobial performance of nanoparticle-based biomaterials. This study provides a hypothesis-generating, bioinformatic framework to support the design and optimization of antimicrobial biomaterials, highlighting the need for experimental validation and integration of phenotypic and biofilm-based analyses.

Objective: This in vitro study aimed to compare the layer-matched color compatibility of three 3Y/4Y/5Y multilayer zirconia grades marketed in shade A2. Materials and Methods: Disc specimens (18 mm × 1.5 mm) were milled from pre-shaded multilayer zirconia blanks (Katana™ Multi-Layered Zirconia; Kuraray Noritake Dental Inc., Tokyo, Japan) in three grades: UTML (5Y), STML (4Y), and HTML (3Y). Twelve discs per grade were polished and measured on a neutral-gray background (Munsell N7) using a dental spectrophotometer (VITA Easyshade Advance 4.0; VITA Zahnfabrik, Bad Säckingen, Germany) at the incisal, middle, and cervical thirds. Color differences were calculated using CIEDE2000 (ΔE₀₀). Yttria content (wt%) was determined using EDS (JSM-7800F; JEOL Ltd., Tokyo, Japan), and phases were assessed using XRD (X’Pert PRO; Malvern Panalytical, Almelo, The Netherlands); microstructure and grain size were examined using FE-SEM after thermal etching. Statistics: A two-way mixed-design ANOVA with Bonferroni adjustment (α = 0.05) was conducted. Results: A significant incisal-to-cervical gradient was observed within each grade (p < 0.001), whereas layer-matched inter-material differences were small (all ΔE00 < 1.0), i.e., below the commonly accepted perceptibility threshold. EDS confirmed the expected stepwise decrease in Y₂O₃ from UTML to HTML, accompanied by corresponding changes in phase constitution and grain size. Conclusions: Despite compositional and microstructural differences, the three multilayer zirconia grades showed no clinically perceptible layer-matched color differences, supporting their combined use in extended rehabilitations while maintaining the natural-like color gradient across the multilayer blank.