The aim of this study was to investigate the antibacterial effect of a diode laser in deep root canal dentin. The microbial colonization of root canal dentin can lead to failures in conventional endodontic treatment if an inadequate bacterial reduction only is achieved through canal treatment and chemical disinfection. 100 microm, 300 microm and 500 microm bovine dentin slices obtained by longitudinal sections were sterilized and inoculated on one side with an Enterococcus faecalis suspension. Laser radiation was performed on the opposite side with the diode laser (810 nm) at a setting of 3 W in continuous mode (CW). Radiation was performed using a 400-microm tapered fiber tip at an angle of approximately 5 degrees to the surface over a period of 30 seconds. The output power at the distal end of the tip was 0.6 W. The bacteria were then eluted through vibration and cultured on blood agar plates. The colony count reflected the antibacterial effect of laser radiation as a function of the layer thickness. A mean bacterial reduction of 74% was achieved even with a 500-microm thick slice. This investigation indicates that the diode laser radiation reduces the number of bacteria in deep layers of infected root canal wall dentin.

Three-dimensional (3D) bioprinting is a promising technology for manufacturing cell-laden tissue-engineered constructs. Larger tissue substitutes, however, require a vascularized network to ensure nutrition supply. Therefore, tailored bioinks combining 3D printability and cell-induced vascularization are needed. We hypothesize that tailored hydrogel blends made of agarose-type I collagen and agarose-fibrinogen are 3D printable and will allow the formation of capillary-like structures by human umbilical vein endothelial cells and human dermal fibroblasts. Samples were casted, incubated for 14 days, and analyzed by immunohistology and two-photon laser scanning microscopy. The 3D printability of the hydrogel blends was examined using a drop-on-demand printing system. The rheological behavior was also investigated. Substantial capillary network formation was observed in agarose-type I collagen hydrogel blends with concentrations of 0.2% or 0.5% collagen and 0.5% agarose. Furthermore, storage moduli of agarose-collagen blends were significantly increased compared to those of the corresponding single components (448 Pa for 0.5% agarose, 148 Pa for 0.5% collagen, and 1551 Pa for 0.5% agarose-0.5% collagen). Neither the addition of collagen nor fibrinogen significantly impaired the printing resolution. In conclusion, we present a tailored hydrogel blend that can be printed in 3D and in parallel exhibits cell-induced vascularization capability.

Since erbium lasers were introduced in medicine and dentistry in the late 1980s and early 1990s, the understanding of the ablation of hard tissues using erbium laser wavelengths has essentially been based on the theory of thermomechanical interaction. Due to the high degree of absorption, the water component contained in the tissue is abruptly heated and evaporated. The pressure of the expanding steam blasts small particles of hard tissue out of the tooth structure.^{1, 2, 3} The absorption in hydroxyapatite, the main component of the hard tissues, plays only a subordinate role. This is clearly illustrated by the fact that ablation begins in temperature ranges well below the melting point of biological apatites.^{4, 5, 6}