# A New Design for Switched-Mode Dental Iontophoresis System Using a Dual-Return Probe
## 4 Results and Discussion  
Within the scope of experimental studies, the new switched-mode pulse DC method using a dual-return probe and the classical continuous and pulse DC methods are examined, and their performances are compared. The setup developed to conduct experimental studies with the SMDIS and CDIS methods is shown in Figure 10. For experimental studies, two different prototypes are prepared using the exemplary resistance and capacitor values shown in Table 2, according to the hand-to-tooth human body impedance model based on the R-RC lumped-parameter model. In the experimental setup, a dual channel oscilloscope is used for signal analysis of the system. In addition, a digital multimeter is used for current and voltage measurements. The dental iontophoresis test system used in the experimental study can operate as both an SMDIS and CDIS depending on the criteria such as current mode, voltage, frequency and duty cycle set in the GUI. The TP in the test system is applied to the tooth connection point of the prototype, and the RPs are applied to the RP-A and RP-B hand \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Prototype** & \(\mathbf{R_{S}}\) & \(\mathbf{R_{A}}\) **and \(\mathbf{R_{B}}\)** & \(\mathbf{C_{A}}\) **and \(\mathbf{C_{B}}\)** \\ \hline I & 1 k\(\Omega\) & 10 k\(\Omega\) & 100 pF \\ II & 1 k\(\Omega\) & 100 k\(\Omega\) & 100 nF \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Representative resistance-capacitor values for the prototype of the simplified human body electrical impedance model from hand to tooth according to the R-RC lumped-parameter model. Figure 10: Experimental setup. connection points of this prototype. The TP ensures that the negative pole of the DC source is applied to the tooth and has the same function regardless of whether the system operates as an SMDIS or CDIS. The RPs ensure that the positive pole of the DC source is applied to the hand but have different functions depending on whether the system operates as an SMDIS or CDIS. When the test system is used as an SMDIS, the RPs operate with phase shift. When used as a CDIS, the RPs work together, acting as a single probe regardless of whether the current is continuous or pulsed. In the first stage of the experimental study, dental iontophoresis current changes for the applied DC voltage are investigated. The iontophoresis average current (I\({}_{\text{avg}}\)) and peak current (I\({}_{\text{peak}}\)) changes obtained for different DC values between 0-5 V with 1 kHz and 50% duty cycle rate, applied to two different prototypes using the CDIS and SMDIS methods, are shown in Figures 11 and 12, respectively. For both prototypes, the I\({}_{\text{avg}}\) values obtained by the SMDIS pulse DC method are not lower than that of the CDIS pulse DC method. The SMDIS pulse DC method can provide the desired I\({}_{\text{avg}}\) current for dental iontophoresis treatment with lower I\({}_{\text{peak}}\) current compared to the CDIS pulse DC method. In the second stage of the experimental study, dental iontophoresis current changes in prototypes are investigated for different frequency values and duty cycle rates for SMDIS and CDIS applications. Firstly, average current changes for different duty cycle rates were obtained for 1 kHz, 3 V pulse DC application (Figure 13). According to these data, as the duty cycle ratio increases, the iontophoresis currents in the SMDIS and CDIS become more similar to each other due to the insufficient depolarization duration and also approach the current obtained with continuous DC. In practice, the time required for skin depolarization decreases inversely proportionally to the increase in duty cycle rate and becomes insufficient. In the other case, as the duty  
Figure 11: Average iontophoresis current changes depending on the applied DC voltages (0–5 V, 1 kHz, 50%) using the CDIS and SMDIS methods. Figure 12: Peak iontophoresis current changes depending on the applied DC voltages (0–5 V, 1 kHz, 50%) using the CDIS and SMDIS methods.