# Penetration Depth of Initiated and Non-Initiated Diode Lasers in Bovine Gingiva
## 4 Discussion  
The purpose of this investigation was to compare the penetration depth of near-infrared (970 nm) and visible (445 nm) diode lasers in both pulsed and continuous emission modes using initiated and non-initiated tips in bovine gingiva ex vivo. The results showed that, overall, the pulsed mode displayed less thermal damage than continuous mode. This was explained by the fact that the pulsed setting allows for the thermal relaxation of the targeted tissues and therefore a lower thermal penetration depth. Additionally, the 445 nm laser wavelength displayed a higher thermal penetration depth than the 970 nm laser wavelength. This was consistent with another study displaying a higher temperature rise under a 445 nm compared to a 980 nm wavelength when uncovering implants in pigs [12]. This may have been because the 445 nm wavelength has a higher degree of absorption by both hemoglobin and melanin than the 970 nm wavelength [13]. Although this was exemplified in this study, it is still unknown how this effect translates to wound healing in vivo. In an in vitro study by [PERSON] et al. using cell cultures, the 445 nm wavelength demonstrated faster wound healing [6]. Additionally, it has been shown that periodontal pathogens such as _P. gingivalis_ can replicate in the host tissue [14; 15]. Therefore, it may be beneficial to have a deeper-penetrating laser to accurately remove all the contaminated soft tissues. Additionally, removing inflamed epithelium in periodontal pockets helps to create a stronger attachment apparatus [5; 16; 17]. It has been demonstrated that the pulsed Nd: YAG laser can be effectively used to remove pocket epithelium in humans [18]. Most commonly applied is a trademarked technique called the \"Laser-Assisted New Attachment Procedure\" (LANAP), which has one of the highest thermal penetration depths among commonly used laser wavelengths [1]. Despite this deeper penetration, it is usually applied under a specific protocol for regenerative periodontal therapy with histological evidence [19; 20]. Additionally, the 970 nm initiated laser group showed a significantly greater thermal penetration depth when compared to the non-initiated group. This was consistent with the study by [PERSON] et al., which highlighted a lower increase in temperature in the deep layers of the tissue when blue articulating paper was used to initiate the tip compared to when a non-initiated tip was used [9]. However, this phenomenon was not evident when comparing the 445 nm pulsed groups, as there was no difference in penetration depth between the initiated and non-initiated groups. This may have been due to the penetration of the 445 nm wavelength being dependent on the chromophores and, specifically, the presence of hemoglobin in the blood vessels of the connective tissue; whether or not an initiator was used seemed to have no influence in the pulsed mode. Since recent studies have shown that longer pulse widths are recommended in the case of long working distances and shorter pulse widths in the case of short working distances [21] due to changes in the fluence, there is ample opportunity to develop ideal pulse widths in periodonontology by considering the thermal effects and tissue phenotype. Regardless, further research withmore specific initiating protocols is necessary to fully compare the impact of initiated glass fibers in periodontal tissues using this novel blue laser light wavelength. Recent recommendations from the World Workshop of Periodontal and Peri-implant Diseases showed that subgingival curettage has no additional benefits in non-surgical periodontal therapy, and therefore there is no need for the utilization of lasers in addition to non-surgical instrumentation [22]. However, the clinical study by [PERSON] et al. [23] involving aggressive periodontitis patients determined better microbiological and clinical outcomes using the 2 W power setting.