Water sorption of dental resin composites: Is a new method the future?

Intraoral, diffusion-controlled water sorption leads to dimensional expansion and mechanical degradation over time. Measurement of small quantities of water in dental resin composites (RCs) is challenging, as current techniques rely on weighing approaches. Here, we evaluate Karl-Fischer Titration (KFT) and thermogravimetry (TG) as alternatives to ISO 4049 standard. Four indirect RCs, one polymer-infiltrated ceramic network (PICN), and one direct composite were soaked in water over 270 days, heated, and evaporated water was detected by KFT and TG. Dilatometric (DIL) and TG coupled with Fourier transform infrared spectroscopy (TG-FTIR) measurements were conducted to verify the methodology and to compare with ISO 4049 outcome. Initial water content was measured between 0.19 and 1.65 wt.%, which increased to 0.73-3.12 wt.% upon water sorption over 270 days. The direct RC performed well, indirect RCs showed significant differences, and the PICN performed comparable to indirect RCs. KFT correlated well with ISO, except for one RC. KFT proved slightly more sensitive than TG. DIL offered different linear expansion of high-versus-low-absorbing materials and confirmed the water sorption rate seen by KFT. In contrast to ISO, KFT has the potential to detect initial water content allowing for a precise and kinetic quantification of the water diffusion process.