Enhancing thermal and thermomechanical properties of 3D printed denture base resin with titanium dioxide nanotubes

Introduction: Three-dimensional printed dentures have poor thermal and thermomechanical properties, which hinder their clinical applications. Previous denture nanocomposite studies focused on mechanical and physical properties. In this study, the impacts of TiO₂ NT addition to 3D-printed denture based on some thermal properties were studied for the first time.

Methodology: Digitally formed specimens (DLP Asiga 3D printer) for 1) Hot-Disc (thermal conductivity (W/km), diffusivity (mm²/s), volumetric heat capacity (MJ/m³K) tests). 2)Thermomechanical-analyzer (TMA) (coefficient of thermal expansion (10^‒6/K), thermal strain (%) and elastic modulus (N/mm²)). 3) Glass transition temperature (Tg) (⁰C) (by DSC, DTA and TMA). 4) Thermal stability (weight%). 5) Degree of conversion (DC%) by ATR-FTIR. Following ISO (22007, 11359, 11357, 11358 and 10640), respectively. TiO₂ NTs (Diameter=30-70nm and length=2-4µm) were added at 1.0 wt.% and 2.0 wt.%. Ultrasonication (3 minutes) for nanotube dispersion, magnetic stirrer (8 hours) for TiO₂ NTs/ 3D liquid resin mixing. Printing settings: slice thickness=50µm, heater temperature=30°C, wavelength=385nm, 90-degree printing orientation and (65 watts/30 minutes) post-polymerization curing. The effective sample size was 30 specimens for each test (10 specimens for each group), which was calculated using G power (power=85%, alpha error=.05, effect size=0.25, groups=3, measurements=5 (30°C, 40°C,50°C,60°C,70°C)). Data analysis via SPSS and Prism 8.4. Shapiro–Wilk (normality), Levene (homogeneity), ANOVA and post-hoc tests were utilized. Significance level at α=.05.

Results: Increasing TiO₂ NT concentration improved all the tested thermal and thermomechanical properties. However, Tg increased for the 1.0 wt.% group and decreased for the 2.0 wt.% group. The Tg decreased due to the aggregation of the nanofiller and functioned as a plasticizer or impurity, thus increasing the mobility of the chains. The DC% increased in both 1.0 wt.% and 2.0 wt.% groups, although this increase was statistically non-significant with a P value of 0.9801).

Potential clinical impact: improvement in thermal perception. A marginal deterioration reduction between different denture parts interface, and improved ability to withstand wide range of intra-oral temperatures during eating.