# Long-Term Stability of Er:YAG Laser Non-Surgical Periodontial Treatment
## 4 Discussion  
It has been proven in the literature that an initial probing pocket depth of 4-6 mm demonstrates a reduction of an average of 1.29 mm and a gain of clinical attachment of 0.55 mm after mechanical nonsurgical periodontal therapy with hand instruments or ultrasonic devices. In the periodontal pockets, where the PPD before treatment is greater than 7 mm, the greatest reduction of the depth is found--2.16 mm and, respectively, the gain of clinical attachment is 1.19 mm. Also, the greatest reduction in pocket depth is reported between the first and third month after non-surgical periodontal therapy, although the healing process lasts up to 9-12 months after treatment [21,22]. These data are also confirmed by the current clinical study with initial PPD between 3.6 and 6.4 mm, where a reduction in pocket depth of 1.55 mm was observed in the control group and 1.70 mm in the test group one year after the initial instrumentation. Although there is a minimal difference in the data between both groups, which is statistically significant, there is no real clinical significance. A more interesting observation is that in both examined groups, the most significant is the reduction of inflammation in the first 3 months. After that, deepening of the PPD is observed in the control group, which is within nearly 1 mm (0.91 mm) up to one year after treatment. In comparison, in the laser-treated group, the reduction in PPD after \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{3}{c}{**BOP**} & \\ \cline{2-5}
**Visit** & **Yes** & **No** & **Difference\%** & **X\({}^{2}\)** & \(p\)-Value** \\ \cline{2-5}  & **\%** & **\%** & & & \\ \hline
**Control\_3 months** & 27.7 & 72.3 & 9.7 & 14.700 & _0.00_ \\ Laser\_3 months & 18.0 & 82.0 & 1.8 & 0.458 & 0.50 \\ \hline
**Control\_6 months** & 25.8 & 74.2 & 1.8 & 0.458 & 0.50 \\ Laser\_6 months & 24.0 & 76.0 & 14.7 & 33.998 & _0.00_ \\ \hline
**Control\_12 months** & 33.8 & 66.2 & 14.7 & 33.998 & _0.00_ \\ Laser\_12 months & 19.1 & 80.9 & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 6: _Cont._ \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{3}{c}{**FMPS**} & \\ \cline{2-5}
**Visit** & **Yes** & **No** & **Difference** & **X\({}^{2}\)** & \(p\)-Value** \\ \cline{2-5}  & **\%** & **\%** & & & \\ \hline
**Control\_baseline** & 75.9 & 24.1 & \multirow{2}{*}{\(-0.6\)} & \multirow{2}{*}{0.090} & \multirow{2}{*}{0.76} \\
**Laser\_baseline** & 76.5 & 23.5 & & & \\ \hline
**Control\_1 month** & 40.9 & 59.1 & \multirow{2}{*}{5.0} & \multirow{2}{*}{4.767} & \multirow{2}{*}{_0.03_} \\
**Laser\_1 month** & 35.9 & 64.1 & & & \\ \hline
**Control\_3 months** & 30.9 & 69.1 & \multirow{2}{*}{4.6} & \multirow{2}{*}{4.664} & \multirow{2}{*}{_0.03_} \\
**Laser\_3 months** & 26.3 & 73.7 & & & \\ \hline
**Control\_6 months** & 44.2 & 55.8 & \multirow{2}{*}{3.9} & \multirow{2}{*}{2.400} & \multirow{2}{*}{0.12} \\
**Laser\_6 months** & 40.3 & 59.7 & & & \\ \hline
**Control\_12 months** & 40.2 & 59.8 & \multirow{2}{*}{4.7} & \multirow{2}{*}{4.210} & \multirow{2}{*}{_0.04_} \\
**Laser\_12 months** & 35.5 & 64.5 & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Comparison of full mouth plaque score between both groups for the whole study period. the third month remains almost unchanged until the end of the study period, which proves the long-term effectiveness of Er:YAG laser scaling and root debridement. Recent studies by [PERSON] et al. and [PERSON] report, although minimal, significant difference in favour of laser instrumentation 6 months after treatment [23,24]. The results of the present study correspond to those of [PERSON] et al., who found that the depth of the pocket decreases from 4.9 \(\pm\) 0.7 mm in the baseline to 2.9 \(\pm\) 0.6 mm six months after Er:YAG laser therapy.