# Long-Term Stability of Er:YAG Laser Non-Surgical Periodontial Treatment
## 4 Discussion
In addition, they observed that the level of clinical attachment varied from 6.3 \(\pm\) 1.1 mm to 4.4 \(\pm\) 1.0 mm, and bleeding on probing was reduced by 43% over the study period, where these changes although are slightly more significant in the laser instrumentation group compared to the conventionally treated group. Lack of bleeding on probing, as a sign of elimination of the inflammatory process, is an important clinical assessment parameter for effectiveness of periodontal treatment. Professional mechanical plaque control has been found to reduce BOP with an initial depth of the pockets between 4 and 6.5 mm to an average of 45% throughout the observed post-treatment period [21]. For comparison, the reduction in BOP in the test group in the present study is 75% one year after therapy, with final values of this index below 20%. In contrast, in the control group, the values of the bleeding index are over 30%, which requires additional instrumentation to control the inflammation [1]. The data from the present clinical study demonstrate that Er:YAG laser instrumentation leads to a significant improvement in all observed clinical parameters. [PERSON] et al. also observe the effectiveness of the Er:YAG laser in non-surgical periodontal therapy, with the follow-up examinations of their study again in the first, third, sixth and twelfth month after treatment [17]. However, they report a greater difference after therapy, which may be due to the greater initial depth of the pocket--about 6 mm, in contrast to the current study, where this depth was about 5 mm [15,25]. The early significant improvement of PPD and CAL in the laser group may be explained by the fact that there is not only mechanical disorganisation of the bacterial biofilm, but also photothermal light effect against periodontal pathogens, which in turn leads to a reduced inflammatory process, resulting in a significant reduction of bleeding and pocket depth [7,26]. Moreover, no side effects were observed for the treatment as well as for the healing period. The present study possesses some limitations. The time period could be further extended to examine the stability of the results in a longer period in comparison to the conventional treatment. Subgingivally, the root surfaces are instrumented only with the Er:YAG laser without using ultrasonic instrumentation previously which consumes more time. Further clinical studies with longer observation periods and the same parameters of laser instrumentation should be performed to clarify and confirm the abovementioned results. Conceptualization, B.Y. and G.T. ; formal analysis, E.K. ; investigation, B.Y. ; writing--original draft preparation, B.Y. ; writing--review and editing, G.E.R. All authors have read and agreed to the published version of the manuscript. This research received no external funding. The study was conducted in accordance with the Declaration of Helsinki and approved by the Ethics Committee of the Medical University of Plovdiv (protocol No 3/5 July 2012). **Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study. **Data Availability Statement:** The data presented in this study are available on request from the corresponding author. **Conflicts of Interest:** The authors declare no conflict of interest.