Thermodynamic Control of Polymerization Kinetics and Mechanical Properties in Resin-Based Composites

To construct a quantitative framework elucidating the polymerization kinetics of resin-based composites (RBCs) by integrating thermodynamic, chemical, and mechanical parameters.

Three distinct RBC formulations (universal, flowable, bulk-fill) were polymerized under controlled thermal (4-50°C), irradiance (300-600 mW/cm²), and spectral (250-500 nm) conditions. A standardized differential scanning calorimetry (DSC) protocol was developed to quantify polymerization enthalpy (ΔH) and reaction kinetics. These thermodynamic metrics were correlated with degree of conversion (DC), Vickers hardness (VHN), and depth of cure (DoC) using non-linear regression analysis.

Temperature exerted a dominant influence on polymerization dynamics, following Arrhenius kinetics; raising the temperature to 50°C amplified ΔH (up to 67%), DC, and VHN, surpassing the magnitude of effects induced by irradiance or spectral variations. A critical radiant exposure threshold of 8 J/cm² was identified for thermodynamic saturation, beyond which kinetic gains plateaued. Logarithmic and power-law regression models revealed robust predictive correlations (R² > 0.90) between ΔH and physicochemical properties, establishing a direct mapping from thermodynamic energy to mechanical integrity.

The thermodynamic and mechanical properties of RBCs were significantly influenced by pre-heating, irradiance protocols, and material formulation, as nonlinear regression models confirmed a robust predictive relationship between ΔH and both DC and VHN.

Thermal energy drives polymerization kinetics more effectively than high irradiance, the study provides a quantitative basis for optimizing clinical protocols through pre-heating and defined energy thresholds.