The Effect of Brushing and Post-Processing Procedures on the Optical Properties of Printed Dental Resin

The optical stability and aesthetic performance of dental polymers are critical for the longevity of restorative treatments. This study aims to evaluate the influence of different polymerisation conditions and maintenance protocols—specifically the use of charcoal pastes and brushes—on the Whiteness Index for Dentistry (WID) of polymer samples. Four groups of polymer samples (Optiprint Lumina, Dentona, AG) were prepared under various conditions: Group I (Standard: 7 min, 22 °C), Group II (Thermal: 7 min, 60 °C), Group III (Extended: 20 min, 22 °C), and Group IV (Glycerin barrier: 7 min, 22 °C). The protocol consisted of brushing with standard or carbon-infused toothpastes and brushes for a period of 2 min. Between brushing, the samples were stored in artificial saliva at 37 °C to simulate the oral environment. The samples were divided into groups. The first group was brushed with a standard paste and a standard brush; the second group was brushed with a simple paste and a carbon brush; the third group was brushed with carbon paste and a standard brush; and the fourth group was brushed with carbon paste and a carbon brush. Changes in the Whiteness Index for Dentistry (WID) were recorded and analysed statistically using a paired t-test and Pearson correlation. Results: All groups showed a statistically significant increase in the WID (p = 0.0191). Group IV (glycerin barrier + carbon paste/brush) exhibited the highest increase, with a WID = 2.0, demonstrating a synergistic effect between oxygen inhibition control and activated charcoal. In contrast, Group II (thermal polymerisation) showed the highest chromatic stability (ΔWID = 0.6), remaining below the Whiteness Perceptibility Threshold (WPT = 0.72). No significant correlation was found between polymerisation time and WID changes (r = 0.087, p = 0.913), indicating that temperature and surface treatment are the primary drivers of optical modification. Conclusions: The heat parameter did not reveal a significant difference in the optical properties. Furthermore, the combination of a glycerin barrier and carbon-based hygiene products maximises the whitening effect while remaining within the Whiteness Acceptability Threshold (WAT < 2.60), providing valuable insights for both material processing and patient maintenance protocols.