# A New Design for Switched-Mode Dental Iontophoresis System Using a Dual-Return Probe
## 3 The Designed SMDIS with Dual-Return Probe  
Within the scope of this study, a computer-aided embedded system is designed that would allow experimental comparison of the classical and new methods. In addition, a simplified electrical model is created for the hand-tooth connection and the performance of the SMDIS is compared with the CDIS. In the performance comparison of the SMDIS and CDIS methods, only the skin and internal organs are taken into account, and the effects of variables such as humidity, temperature, contact surface and pressure are ignored. The new developed dental iontophoresis test system to implement the SMDIS and CDIS methods is shown in Figure 6 and its general characteristics are given in Table 1. The block diagram of this test system consisting of basically a microcontroller, digital/analog (D/A) converter, analog switch, measurement unit, computer-based HMI, human body electrical impedance prototype and probes is shown in Figure 7. A prototype has been developed for the simplified human body electrical model between the hand and the tooth, according to the R-RC lumped-parameter model, in order to conduct experimental studies on the setup. This prototype has hand and tooth connections. The TP of the SMDIS is applied to the tooth connection point, while the RPs are applied to the RP-A and RP-B hand connection points. Figure 5: Simplified electrical equivalent circuit model between hand and tooth for switched-mode pulse DC method. Figure 6: CDIS/SMDIS test system: (**a**) with TP and RPs; (**b**) with human body electrical impedance prototype. In addition to switching the probes in the SMDIS, an 8-bit Arduino Nano with ATmega328 microcontroller is used for the necessary control and regulation. In addition, in order to complete the loop of the iontophoresis current through RPs, a 12-bit D/A converter and a two-channel analog switch chip are used. The D/A converter (which communicates with the microcontroller via the I\({}^{2}\)C method) is used to obtain a microcontroller-based adjustable analog voltage in the range of 0-5 V DC required for an iontophoresis application. In the design, while the TP connected to the negative pole of the DC source is touched to the negative pole of the DC source, the DC source is located at the negative pole of the DC source. \begin{table}
\begin{tabular}{c c} \hline
**Characteristics** & **Properties** \\ \hline Application field & Dentin sensitivity treatment \\ \hline Working method & Dental iontophoresis \\ \hline Solution polarity & Negative ion solutions \\ \hline Probes & Treatment probe: one piece (TP)/conductive brush tip \\ \cline{2-3}  & Return probe: two pieces (RP-A and RP-B)/conductive pipe \\ \hline User interface & PC-based GUI/C\# \\ \hline Voltage range & 0-5 V DC (resolution: 0.1 V) \\ \hline Frequency range & 0-1 kHz (resolution: 1 Hz) \\ \hline Duty cycle & 0-100\% (resolution: \%1) \\ \hline Current modes and & 1 k\(\Omega\) & 10 k\(\Omega\) & 100 k\(\Omega\) \\ iontophoresis currents & CDIS—Continuous DC & 5000 uA & 500 uA \\ (average) depending on & CDIS—Pulse DC (\%50) & 2500 uA & 25 uA \\ body impedance & SMDIS—Pulse DC (\%50) & 2500 uA & 25 uA \\ \hline \end{tabular}
\end{table} 
Table 1: General characteristics of the test system. Figure 7: The general block diagram of the developed SMDIS and prototype. the tooth, the RPs are connected to the positive pole applied via the analog switch chip. The analog switch chip allows the analog voltage received from the D/A converter to be quickly switched and transferred to the desired return probes. Thanks to the analog switch, only one of the RPs remains in contact and the other one is electrically disconnected from the DC source. Hence, the change of current direction, which is important for iontophoresis, is prevented and crosstalk between RPs, which would have a negative effect on the iontophoresis application, is not allowed. Iontophoresis current and voltage values obtained through the measurement unit are applied to the A0 and A1 analog inputs of the microcontroller with 10-bit resolution.