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

Wed, 01 Jul 2026 00:00:00 GMT

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

Wed, 01 Apr 2026 00:00:00 GMT

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

Evaluation of blue-light model scanner trueness, precision, and surface detail reproduction with different rubber impression material colors

Sun, 01 Mar 2026 00:00:00 GMT

Title: Evaluation of blue-light model scanner trueness, precision, and surface detail reproduction with different rubber impression material colors Authors: Seo, Kyoungjin; Cai, Hongxin; Shin, Seung-Ho; Choi, Ji-Won; Seo, Young-Bin; Kim, Jong-Eun; Kim, Kwang-Man; Jiang, Heng Bo; Kwon, Jae-Sung Abstract: Objective Although the accuracy of scanning technologies has been extensively explored, a research gap still exists concerning the scanning results of dental impression materials, particularly regarding their color and gloss characteristics. This study aims to evaluate and compare the scanning capabilities of blue-light scanners for various dental impression materials characterized by different colors and gloss levels. Methods Blue (B), green (G), red (R), and yellow (Y) dental impression materials were selected for this study. Colorimetric analyses were conducted using a spectrophotometer. The gloss levels of the samples were quantified using a gloss meter. The accuracy and surface detail reproduction of a blue-light scanner were analyzed by scanning impression materials in four different colors. The four-unit crown-bridge model for accuracy analysis was based on International Standardization Organization (ISO) standard 12836. The data measured by the coordinate measuring machine (CMM) served as the gold standard and were used for parameter comparison (height, angle, and distance) and 3D fitting with the scanned files. Results Surface detail reproduction analyses revealed significant differences among the various groups. Notably, Group B consistently demonstrated superior scanning accuracy across all measurements, indicating its effectiveness as a dental impression material in blue-light scanning applications. Significant differences were observed in the rate of surface detail, angle parameters, and corner height across the various groups (p < 0.05). Additionally, the root-mean-square error values pertaining to trueness exhibited significant disparities in all the specimens (p < 0.05). Significance. The absence of significant gloss differences across all color variations indicates that color should be evaluated alongside other critical factors when employing blue-light scanners for measurement accuracy.

Quantitative assessment of tooth wear using intraoral scanners: A comparative analysis of two monitoring tools

Sun, 01 Mar 2026 00:00:00 GMT

Title: Quantitative assessment of tooth wear using intraoral scanners: A comparative analysis of two monitoring tools Authors: Higuera, Elizabeth Merino; Lee, Hyeonjong; Riera, Carme; Sailer, Irena; Ham, Sangmin; Zarauz, Cristina Abstract: Objectives: To evaluate the accuracy of a digital monitoring tool integrated in two intraoral scanners (Trios 3 and Trios 4) in detecting and quantifying tooth wear, using a validated ISO-based reference standard. Methods: An in vitro model was developed with a structured digital reference design incorporating vertically embedded slot structures to enable standardized sectioning and reduce operator variability. The Patient Monitoring Tool within the 3Shape IOS software was assessed by comparing its measurements to those obtained using a validated method conforming to ISO 20,896-1 Annex C. Tooth wear of varying depths (ranging from shallow to advanced) was simulated and measured across both systems. Measurement differences were statistically analyzed for accuracy evaluation. Results: The monitoring tool demonstrated clinically acceptable levels of accuracy in assessing moderate to advanced wear depths. However, the tool showed increased variability and decreased precision at lower wear levels, indicating limitations in detecting early-stage tooth wear. Conclusions: Intraoral scanner-based monitoring using the 3Shape Patient Monitoring Tool is a promising noninvasive method for longitudinal tooth wear assessment. Nevertheless, clinicians should interpret early wear measurements with caution due to limited accuracy in shallow wear detection. Further improvements in digital tool sensitivity are warranted to enhance early diagnostic capability. Clinical Significance: This study highlights the clinical potential of intraoral scanner-based monitoring for tooth wear. While effective in detecting advanced wear, clinicians should interpret minimal changes with caution. Understanding its limitations can aid in selecting appropriate tools for long-term, non-invasive wear assessment and early intervention in preventive and restorative dental care.