Online Dental Research Seminar

Online Dental Research Seminar Date: September 8, 2026 (Tuesday) Time: 12:00 p.m. - 12:30 p.m. (This presentation will be held virtually via Zoom.) Presenter: Miss Tin Yuet Chau, MPhil candidate Supervisors: Professor K.H. Tsoi (Primary Supervisor) & Professor K. Cho (Co-supervisor) Join Zoom Meeting https://hku.zoom.us/j/91356301390?pwd=fsb7x3Yj6ASGycMeoC9I5kRy1wBXqP.1 Meeting ID: 913 5630 1390 Password: 953462 Title: Novel polyurethane oligomers for 3D-printed dental aligners Abstract: The transition from conventional thermoforming to direct three‑dimensional (3D) printing via vat photopolymerization represents a transformative shift in clear aligner fabrication, offering significant advantages in workflow efficiency and clinical function. Despite these benefits, 3D‑printed aligners have yet to overcome critical limitations in mechanical performance essential for orthodontic force delivery, specifically insufficient elastic modulus and excessive stress relaxation, which restrict their clinical adoption for complex tooth movements requiring sustained force delivery. Moreover, the precise molecular structures of commercial resins remain proprietary, with Material Safety Data Sheets providing only generic descriptions such as "polyurethane methacrylate" or "aliphatic urethane acrylate oligomer", hindering rational design improvements. To address these challenges, this study designed and synthesised six novel polyurethane oligomers with systematically varied soft segment chemistries, including polyethylene glycol (PEG), polypropylene glycol (PPG), and polyetheramine (PEA), at two molecular weight ranges (400–600 and 1540–2000 g mol⁻¹). The oligomers were prepared from isophorone diisocyanate (IPDI) and 2‑hydroxyethyl methacrylate (HEMA) via a controlled multi‑step procedure, then formulated into photocurable resins and 3D‑printed into test specimens. Mechanical and thermal properties critical to orthodontic function, including tensile and flexural properties, stress relaxation, shape memory, glass transition temperature, and cytotoxicity, were evaluated and benchmarked against commercial 3D‑printed and thermoplastic aligner materials. PEG‑based oligomers exhibited higher stiffness and slower stress relaxation than PPG‑based oligomers, consistent with PEG's linear, symmetric structure. PPG, with its methyl side groups, imparted greater softness and faster shape recovery. PEA, which replaces urethane linkages with stronger bidentate hydrogen‑bonded urea linkages, provided increased stiffness, higher Tg, and lower stress relaxation, but with slower shape recovery. Higher molecular weight (1540–2000 g mol⁻¹) soft segments enhanced flexibility and shape recovery but lacked sufficient stiffness for orthodontic force generation. Among the six oligomers, PEAM‑400 uniquely combined stiffness (tensile elastic modulus of 1059.34 MPa), sustained force delivery (residual stress of 9.02 MPa after 1 hour), shape memory (91.6% recovery after 60 minutes), and cytocompatibility (>99% cell viability). This combination of properties was not simultaneously observed in any commercial aligner material included in this study. In summary, PEAM‑400 overcomes the key mechanical limitations of current 3D‑printed aligners by providing the stiffness and sustained force delivery required for effective orthodontic treatment. The structure–property relationships established in this study offer a rational basis for the development of next‑generation 3D‑printed clear aligners with optimised clinical performance. Date/Time: 08/09/2026 12:00-13:00 Organized by: Dental Faculty

Uploaded at 2026/09/05