## 2 Conditioning Solutions
### Prefabricated Conditioning Solutions  
Biopure MTAD (Dentsply Tulsa Dental Specialties) is an acidic solution, which consists of 4.25% citric acid, 3% doxycycline, and 0.5% Tween 80 mixture [52]. This solution has a pH of 2.15 and has the capacity to remove inorganic compounds, producing minimal erosive changes on the dentinal surface compared to EDTA [41; 42]. It acts as a calcium chelator by the tetracycline content, a chemical chelator similar to citric acid that produces dentin demineralization [41; 43]. The detergent Tween 80 produces a reduction in the surface tension of the irrigant and increases its capability to reach the apical area [41]. Altogether, this results in a partial SSL removal from the dentinal tubules, with similar bond strength values among cervical, middle, and apical section. However, it presents a 45% failure rate between resin cement and dentin [36]. QMix (Dentsply Tulsa Dental Specialties, Tulsa, OK, USA) is composed of antimicrobial agent CHX, a calcium chelating agent EDTA, saline solution, and cetrimide [53]. It has a slightly alkaline pH, and its use is recommended after NaOCI application during root canal instrumentation due to its effectiveness in SL removal [45]. Additionally, antibacterial activity has been reported [9; 54]. QMix was designed as a final irrigant in endodontic treatment to replace the 17% EDTA irrigation protocol [55], and its use has been proposed for post space preparation cleaning due to its capability of inhibiting the activity of metalloproteinases (MMP), such as MMP-2, -8, and -9 [44]. This action is due to the presence of CHX, which prevents decomposition of the hybrid layer and decalcification of the intra-radicular dentin [24]. Interestingly, using SEM, a complete elimination of the SSL and debris have been reported with QMix irrigation, opening dental tubules [22]. The above can be associated with the promotion of the bond strength of glass fiber posts to root dentine with or without 5.25% NaOCI before irrigation of QMix. However, higher bond strength values are found in the cervical compared to apical position, suggesting that the improvement of adherence is more in the shallower regions of the canal root [9; 22]. The results of smear layer removal with different conditioning solutions are summarized in Table 2, and of push-out bond strength test in Table 3. \begin{table}
\begin{tabular}{c c c} \hline \multicolumn{3}{c}{**Conventional Dentin Conditioning**} \\ \hline \hline \multicolumn{1}{c}{\multirow{2}{*}{**Protocols**}} & **Secondary Smear Layer** & \multirow{2}{*}{**Reference**} \\ \cline{2-2} \multicolumn{1}{c}{} & **Removal** & \\ \hline
**17\% EDTA** & Partial–Complete & [11; 22; 23; 42; 56] \\ \hline
**17\% EDTA (Gel)** & Without Removal & [46] \\ \hline
37\% phosphoric acid liquid & Partial & [30] \\ \hline
35–37\% phosphoric acid gel & Partial–Complete & [25; 30; 46] \\ \hline
7\% maleic acid & Complete & [20] \\ \hline MTAD & Partial & [36] \\ \hline \hline \multirow{4}{*}{**NaOCI**} & Without removal–Partial & [6; 7; 16; 18; 19; 23; 37; 45] \\ \cline{2-2} \cline{3-3}  & **17\% EDTA** & Partial–Complete & [9; 11; 20; 27; 36] \\ \cline{2-2} \cline{3-3}  & **10\% citric acid** & Partial & [9] \\ \cline{2-2} \cline{3-3}  & **Qmix** & Complete & [9; 22] \\ \hline
17\% EDTA & **37\% phosphoric acid liquid** & Partial & [16] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Results of the smear layer removal by conventional dentin conditioning with or without sonic or ultrasonic irrigant activation and dentin conditioning with laser.