# A New Design for Switched-Mode Dental Iontophoresis System Using a Dual-Return Probe
## 2 Materials and Methods
### New Switched-Mode Pulse DC Method  
The principal schema of the newly developed switched-mode pulse DC method is shown in Figure 4a. In this new method, the TP connected to the cathode end of the DC source and two RPs connected to the anode end are used to apply the solution containing the negatively charged ionized drug to the tissue. While the solution-soaked TP is touched to the area where the DH is, two RPs are touched to different points on the body close to the tooth that do not pose a risk. With the application of electric current, the solution passes into the dental tissue with the help of the TP, depending on the ion flow provided by both RPs. Figure 3: Principle scheme of classical dental iontophoresis method. In the new dual-return probe switched-mode pulse DC method, the current completes its circuit by switching in different paths (\(I_{A}\) and \(I_{B}\)). In this method, the output is given from the two channels by switching according to the 180-degree phase-shifting principle, depending on the duty cycle ratio. In this way, while the body is depolarized by applying a pulse current, a continuous DC-like current is provided through the tooth by giving pulse currents that switch from two different paths. In this case, in the switched-mode pulse DC method where the dual-return probe is used, the total amount of electric charge (\(Q_{i}\)) carried during the iontophoresis process can be expressed as in Equation (6). On the other hand, switched-mode pulse DC method treatment duration (\(t_{sm}\)) can be expressed by Equation (7). \[Q_{i}=(I_{A}+I_{B})t_{i} \tag{6}\]  
\[t_{sm}=\frac{Q_{i}}{(I_{A}+I_{B})D} \tag{7}\]  
In the developed switched-mode pulse DC method with a dual-return probe, instead of waiting for the current to be cut off on the polarized skin as in the pulse DC method, the RP-A and RP-B return probes are switched periodically. In this way, in the switched-mode pulse DC method, the desired DC current for dental iontophoresis can be applied to the tooth with a lower peak current value than in the classical pulse DC method and in a form similar to continuous DC current. The low peak current value is an important factor in increasing the pain threshold against the DC current applied to the tooth in dental  
Figure 4: Developed switched-mode pulse DC method. iontophoresis treatment. Thus, in the new switched-mode pulsed DC method, where skin polarization is prevented, the treatment duration is shorter than that of the classical pulsed DC method as it allows higher currents to be applied to the tooth without causing pain. Figure 4b shows the probe switching voltages for the newly developed switched-mode pulse DC method. In this method, there are RP-A and RP-B return probes as well as the TP. The switching voltages of the probes change periodically depending on the treatment and depolarization times (\(t_{ta}\), \(t_{tb}\), \(t_{da}\) and \(t_{db}\)). During iontophoresis treatment, RP-A and RP-B return probes are periodically activated with the help of SA and SB switches. In this way, it is ensured that the iontophoresis current completes its circuit through the tooth and the ion flow is always from the dentin to the nerve. Iontophoresis treatment is provided via RP-A and RP-B return probes during \(t_{ta}\) and \(t_{tb}\) times of the applied current, and skin depolarization is provided during \(t_{da}\) and \(t_{db}\) times. During the \(t_{da}\) depolarization time, the \(S_{A}\) switch is open, and the \(S_{B}\) switch is closed, while during the \(t_{db}\) depolarization time, the \(S_{B}\) switch is open, and the \(S_{A}\) switch is closed. The dual-return probe prototype designed for the SMDIS is shown in Figure 4c. This prototype is for single-handed use, and the RPs of the prototype are designed to have more contact surface to reduce skin electrical resistance and to be as far apart from each other and as homogeneous as possible for skin depolarization.