## 4 Discussion  
In the literature, the ability of different types of lasers in sealing patent dental tubules has been evaluated, but studies carried out on which laser achieves the best outcome for the treatment of DH showed discordant evidence, which could be due to several factors such as the types of lasers, fibers, power output, exposure time, and radiation frequency [19]. Several studies have shown the efficiency of a diode laser [20; 21; 22; 23] and of its different wavelengths (780, 900, and 810 nm) in the treatment of DH [24]. A diode laser of 810 nm is a high-energy laser with thermal effects that develop in-depth by virtue of its physiological target. However, by acting on the energy powers of the laser and on the mode of use, the thermal effects can be limited at the surface layers of hard tissues when we use the laser with an energy power of 2 W and in pulsed mode (HPLT) with a non-contact fiber; by using lower powers, 0.2 W, with a non-contact fiber and in CW mode (LLLT), thermal effects can be avoided, and photo-stimulating activities for the tissues can be promoted instead. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Study Groups** & **t1** & **t2** & **t3** \\ \hline LLLT vs. HPLT & 0.0326 * & 0.0993 & 0.3740 \\ LLLT vs. LHLT & 0.0194 * & 0.0060 * & 0.0019 *** \\ HPLT vs. LHLT & 0.8485 & 0.0001 *** & 0.0001 *** \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Comparison of the mean values of VAS estimated at t1, t2, and t3 for the three pairs of study groups: LLLT vs. HPLT, LLLT vs. LHLT, and HPLT vs. LHLT. * = \(p\)-value < 0.05; *** = \(p\)-value < 0.005. LLLT: Low-Level Laser Therapy; HPLT: High-Power Laser Therapy; LHLT: Low-High combined Laser Therapy; CW: Continuous Wave. The rationale behind the use of two different output powers of the diode laser is based on the different interaction that each intensity of a laser has with the tissues: a photothermal effect with the thermodynamic behaviour of tissue water content and bio-stimulant effects on dental tissues. In the present study, we have appraised the effectiveness of three different treatments based on the use of a diode laser (LLLT, HPLT, and LHLT), focusing on the different percentage of pain reduction and on the persistence of the effect over time. Our results underline that more immediate improvements, obtained with a single-output power, are not long-lasting, while others that can be achieved over a longer period of time are more persistent [14; 25]. The effectiveness of each laser therapy was gauged by estimating the improvement of DH symptomatology on three different NCCLs by comparing the mean VAS score obtained at the end of treatment (t1), after 15 days (t2), and after 3 months (t3), with the mean VAS values at baseline (t0). A clear improvement, both in the short and long term, was documented for all the NCCLs in all study groups, with the best results obtained in LHLT. Immediately after the end of treatment (t1), HPLT and LHLT showed the same improvement of DH symptomatology compared to LLLT (59.29% and 60.12% vs. 49.38%). In fact, no significant difference was estimated between the mean VAS score of HPLT and LHLT at t1, while both averages were statistically different from the mean VAS score of LLLT for the same time point. After 15 days and after three months, the effectiveness of LHLT was still greater (56.44% and 50.62%, respectively) than the laser treatments based on the use of single-output power, applied in LLLT and HPLT, respectively. This result was supported by the fact that the averages of VAS scores of LLLT vs. LHLT and of HPLT vs. LHLT were statistically different. In HPLT, the lasers with high power can improve the symptomatology of DH mainly by the photothermal effect that melts the hard tissue on the surface with the smear layer occluding the tubules. In this way, the laser blocks the movement of the fluids in the denitnal tubules, which is the fundament of the hydrodynamic theory of DH pain.