## 3 Results
The group treated with an Er:YAG laser-Endo tip and a 2.5% NaOCl irrigation, the CFU was reduced more significantly than Er:YAG laser-Endo tip and saline irrigation (\(p\) < 0.001; Figure 4). The CFU of the samples treated with an Er:YAG laser-Endo tip and a 17% EDTA following a 2.5% NaOCl irrigation decreased even more than Er:YAG laser-Endo tip and a EDTA irrigation (\(p\) < 0.001; Figure 4). Figure 3: The number of _E. faecalis_ colonies after treatment of infected teeth was compared between control (untreated infected root canals) and 3 groups of 17% EDTA irrigation: Group 1: The CFU of control samples infected with _E. faecalis_ without receiving any treatment (black). Group 6: The CFU of _E. faecalis_ in the root canals after a 17% EDTA irrigation (blue). Group 3: The CFU of _E. faecalis_ after using an Er:YAG laser-Endo tip and a 17% EDTA irrigation (green). Group 8: The CFU of _E. faecalis_ after using an Er:YAG laser-Endo tip and a 17% EDTA irrigation, followed by a 2.5% NaOCl irrigation (red). N = 8 in each group. * \(p\) < 0.01 for treated samples compared to control. * \(p\) < 0.001 for treated samples compared to control. \(p\) < 0.02 for EDTA versus ER:YAG laser with EDTA. \(p\) < 0.001 for ER:YAG laser with EDTA and ER:YAG laser with EDTA and NaOCl. Er:YAG Laser-Endo Tip Treatment Alone Had Only a Partial Anti-Bacterial Effect on E. faecalis Biofilm in Tooth Root Canals  
It was also important to study the effect of Er:YAG laser-Endo tip treatment alone on the bacterial load of _E. faecalis_ in the infected root canals. Therefore, we compared the CFU of remaining bacteria in control, saline irrigated and Er:YAG laser-Endo tip-saline irrigated root canals. The average of colonies in the saline irrigation group decreased from 2.25 \(\times\) 10\({}^{6}\) CFU/mL to 1.5 \(\times\) 10\({}^{6}\) CFU/mL compared to the control untreated infected group (Figure 5), however, this decrease was not statistically significant (_p_ = 0.50). In the group treated with an Er:YAG laser-Endo tip and saline irrigation, the bacterial load was reduced to 1.25 \(\times\) 10\({}^{6}\) CFU/mL, which is a less bacterial burden compared to control infected samples, (_p_ = 0.01; Figure 5), but not significant when compared to the saline irrigated samples (_p_ = 0.13; Figure 5). It is clear that neither treatment group was effective alone in significantly reducing the bacterial load, although the Er:YAG laser-Endo tip protocol did have a certain anti-bacterial effect on _E. faecalis_ biofilms. Figure 4: The number of _E. faecalis_ colonies after treatment on infected teeth with Er:YAG laser-Endo tip and different irrigation solutions in comparison to the control group. Group 1: The CFU of _E. faecalis_ in control infected samples without treatment (black). Group 5: The CFU of _E. faecalis_ after using an Er:YAG laser-Endo tip and saline (blue). Group 4: The CFU of _E. faecalis_ after using an Er:YAG laser-Endo tip and a 2.5% NaOCl irrigation (green). Group 3: The CFU of _E. faecalis_ after using an Er:YAG laser-Endo tip and a 17% EDTA irrigation (yellow). Group 8: The CFU of _E. faecalis_ after using an Er:YAG laser-Endo tip and a 17% EDTA irrigation, followed by a 2.5% NaOCl irrigation (red). N = 8 in each group. * \(p\) < 0.01 for treated samples compared to control. ** \(p\) < 0.001 for treated samples compared to control.