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In Vitro Shear Bond Strength of Additively Manufactured Denture Base Resins to Hard Chairside Reline Materials

2026-08-01T00:00:00Z

Title: In Vitro Shear Bond Strength of Additively Manufactured Denture Base Resins to Hard Chairside Reline Materials Authors: Yoo, Je-Hyeon; Kim, Jimin; Park, Yeseul; Kim, Jee-Hwan Abstract: Introduction and aims: Reliable bonding between additively manufactured denture base resins and hard chairside reline materials is essential for long-term clinical performance, yet evidence under simulated aging conditions remains limited. This in vitro study evaluated the shear bond strength (SBS) of two hard chairside reline materials to conventional polymethyl methacrylate (PMMA) and two additively manufactured denture base resins under thermocycling conditions simulating relining at denture delivery and after clinical service. Methods: One heat-polymerized PMMA resin and two additively manufactured denture base resins composed of urethane dimethacrylate (UDMA) and methacrylate ester monomer (MA) were bonded to Tokuyama Rebase II (R) or Ufi Gel Hard (U), forming six material combinations. Specimens were assigned to three conditions: non-thermocycling (NT), thermocycling before relining (TB), or thermocycling after relining (TA). Ten specimens were prepared per subgroup (n = 180). Specimens that exhibited complete debonding during thermocycling were assigned an SBS value of 0 MPa and included in the analysis. SBS was measured using a universal testing machine, and failure modes were classified. Data were analysed using appropriate statistical tests (alpha = 0.05). Results: SBS was significantly influenced by denture base resin type, reline material, and thermocycling condition (P < .05). U demonstrated higher SBS than R across all denture base resins. Under NT conditions, the MA-U group showed the highest SBS (6.78 +/- 1.57 MPa), and the UDMA-R group showed the lowest (1.41 +/- 0.49 MPa). After thermocycling, 80% of UDMA-R and 20% of MA-R specimens debonded, whereas no failures occurred in the U groups. R predominantly exhibited adhesive failures, while U mainly showed cohesive or mixed failures. Conclusion: Within the limitations of this in vitro study, bonding performance between denture base resins and hard chairside reline materials was influenced by material compatibility and thermal aging. U demonstrated greater resistance to thermally induced debonding than R.

Antimicrobial DMAHDM nanoparticle-modified resin for 3D printing: Composition-Property relationships

2026-08-01T00:00:00Z

Title: Antimicrobial DMAHDM nanoparticle-modified resin for 3D printing: Composition-Property relationships Authors: Jin, Gan; Liu, Yunqi; Lee, Dae Gyun; Shim, Min Suk; Cho, Seok Hwan; Lee, Du-Hyeong; Kim, Jong-Eun Abstract: This study aimed to determine the effects of the proportion of dimethylaminohexadecyl methacrylate (DMAHDM) nanoparticle to urethane acrylate (UA)-based 3D-printing resin on antibacterial and antifungal activities, biocompatibility, degree of conversion (DC), and mechanical properties. UA-based resin and DMAHDM were synthesized separately and mixed to prepare specimens at DMAHDM proportions of 0-1 wt%. The WST-8 viability assay was used to assess the antibacterial effects against Streptococcus mutans (S. mutans), and the growth of Candida albicans (C. albicans) was measured by OD600 to evaluate antifungal activity. Human gingival fibroblasts were used for biocompatibility assessment via WST-8 and EdU assay. The DC was analyzed using FTIR spectroscopy. Flexural strength, flexural modulus, and Vickers hardness were assessed. One-way ANOVA was performed (alpha = 0.05). The anti-S. mutans efficacy increased with the DMAHDM concentration, with the bacterial viability significantly decreasing from 85.76 f 14.78% (mean f standard deviation) at 0 wt% to 56.61 f 0.60% at 1 wt%. C. albicans growth was also inhibited in a dose-dependent manner, decreasing from 88.77 f 5.03% at 0 wt% to 44.00 f 14.72% at 1 wt%. No cytotoxicity was observed but the cell proliferation decreased as the DMAHDM concentration increased. The highest DC was recorded at 1 wt% (57.88 f 0.83%). The flexural strength was largest (118.59 f 19.89 MPa) at 0 wt%. The Vickers hardness was highest at 0 wt% (23.03 f 0.76 HV) and decreased slightly with increasing DMAHDM concentration. DMAHDM-incorporated UAbased 3D-printing resin exhibited strong antibacterial effects against S. mutans and antifungal effects against C. albicans, alongside excellent biocompatibility, improved polymer conversion, and competitive mechanical properties, highlighting its potential for dental applications.

Composition-dependent mechanical properties and viscoelastic behavior of a 3D-printable polyurethane-acrylate soft denture liner

2026-07-01T00:00:00Z

Title: Composition-dependent mechanical properties and viscoelastic behavior of a 3D-printable polyurethane-acrylate soft denture liner Authors: Ham, Sangmin; Min, Jinhong; Lee, Jiho; Park, Young-Bum; Kim, Hoon; Park, Jaehan Abstract: The long-term clinical performance of conventional soft denture liners is limited by microbial colonization, poor adhesion, and plasticizer leaching. This study developed a polyurethane-acrylate soft denture liner enabling moldless fabrication through digital photolithography-based 3D printing. Two urethane-acrylate oligomers with different molecular weights (1K: 12900 g/mol, 2K: 18500 g/mol) were synthesized and mixed in five different ratios to investigate compositional effects on mechanical and viscoelastic behavior. Increasing the proportion of the 2K oligomer enhanced tensile strength and elongation, with compositions >= 1:1 (GR-C) showing mechanical performance comparable to conventional silicone-based soft liners. Dynamic mechanical analysis showed storage modulus values (0.50-0.65 MPa) within the oral mucosal elastic range (0.37-5.93 MPa), indicating damping capacity. Shore A hardness of all compositions remained within the extrasoft range after 30 days, satisfying ISO 10139-2. Under compressive loading, higher 1K content increased resistance to deformation, while GR-C demonstrated intermediate compressive stress at 10-30% strain. In terms of dimensional accuracy, GR-A and GR-D showed greater deviations than the other groups, with higher deviations along the x- and y-axes compared to the z-axis, and group- and axis-dependent patterns were observed. Optical rheometry revealed that increasing the 2K oligomer content reduced the storage modulus while increasing the loss modulus and loss tangent, indicating enhanced viscous behavior. Water sorption (13.1-14.9 mu g/mm3) was within previously reported ranges, whereas solubility (12.3-16.2 mu g/ mm3) was comparatively higher. Near-surface degree of conversion approached 100% after post-polymerization. GR-C was selected as the optimized formulation and showed no cytotoxicity in an L929 cell assay. In the printability assessment using a novel digital workflow, GR-C exhibited a root-mean square (RMS) deviation of 0.619 mm. These results demonstrate that controlled oligomer composition enables tunable tensile, compressive, and viscoelastic properties in 3D-printable polyurethane-acrylate soft denture liners.

Sequential intraoral cementation for enhancing the retrievability of implant-supported fixed dental prostheses with screw access holes

2026-04-01T00:00:00Z

Title: Sequential intraoral cementation for enhancing the retrievability of implant-supported fixed dental prostheses with screw access holes Authors: Oh, Won-suck; Kim, Yongkun; Shah, Kumar C.; Lee, Damian J.; Kim, Jong-Eun Abstract: While innovative designs combining the advantages of screw and cement retention provide both retrievability and passive fit for implant-supported fixed dental prostheses, retrieval becomes challenging with nonparallel implants because of deeper hexagon engagement and antirotational features. This dental technique introduces a sequential intraoral cementation approach to address this limitation. The technique involves engaging each abutment to its hexagon intraorally by cementing the prosthesis first to the most angled implant, removing it extraorally to clean excess cement, and modifying the abutment hexagon into a nonengaging type. Subsequently, the remaining prosthesis is cemented to favorably angled abutments, ensuring both passivity and retrievability. This approach compensates for fabrication discrepancies and enhances the retrievability of these prostheses involving implants with varying angulations, ultimately improving patient comfort and long-term prosthesis maintenance. (J