Influence of Wavelength on Light Transmittance, Heat Generation and Pulpal Cellular Response Across Different...

This study aimed to evaluate the effects of different wavelengths on light transmittance, heat generation, and pulpal cellular response across different restorative procedures.

Standardized 5mmx5mm Class I preparations and dentin discs were prepared, leaving 0.5mm of dentin at the pulpal floor using extracted third molars. Direct restorations on the Class I preparations were performed using conventional or bulk-fill composites, and 1.5mm ceramic restorations were cemented onto the dentin discs with resin cement. Light-curing procedures were performed using blue (460nm), green (520nm), and red (620nm) wavelengths at 1000 mW/cm². The degree of conversion was assessed using FTIR-ATR (Nicolet iS20). Specimens were positioned above the input sensor of a spectrophotometer (MARC-LC) for the light-transmittance analyses or in a customized oral cavity chamber simulator for temperature variations analyses using an infrared thermal camera (FLIR ONE PRO), with measurements performed on the pulpal floor. Odontoblast-like cells (MDPC-23) were exposed to the same maximum radiant exposure that reached the pulp chamber, and cell viability was assessed using an MTT assay. A power analysis was conducted to determine the sample size to provide a power of at least 0.8 with =0.05. Statistical analyses were performed using one-way ANOVA and Tukey's test.

Degree of conversion did not differ across wavelengths/irradiance conditions (p>0.09). Across all restorative procedures tested, light transmittance to the pulpal floor increased with longer wavelengths (p<0.05). Increased material thickness resulted in significant reductions in transmittance across all wavelengths (p<0.001), with longer wavelengths less affected by this attenuation. Thermal analysis demonstrated that shorter wavelengths produced significantly greater temperature increases within the pulp chamber (p<0.05), while red light consistently produced the lowest changes (p<0.01). Cell viability analysis revealed that red light maintained cell viability at levels statistically similar to those of non-irradiated controls (p=0.23); blue and green light significantly reduced cell viability (p<0.05).

Within the limitations of this in vitro model, it was possible to conclude that longer wavelengths demonstrate increased light transmission, lower temperature rise, and higher cell viability compared to shorter wavelengths delivered at equal exposure.