# A New Design for Switched-Mode Dental Iontophoresis System Using a Dual-Return Probe
## 1 Introduction  
Dentin hypersensitivity (DH) is described as regional short-term and sharp pain originating from the exposed dentin surface due to thermal, chemical and mechanical stimuli [1, 2, 3]. The reason for the occurrence of DH is the exposure of the dentin layer and dentin tubules as a result of loss of enamel, gingival recession or loss of cementum tissue due to various factors, as shown in Figure 1[4]. The basic principle of DH treatment is to reduce the exposed dental tubules, close their mouths and narrow their diameters, as well as reduce fluid movement in the tubules and block nerve conduction [5]. Various methods and systems such as topical fluoride [6, 7], dental iontophoresis [8, 9, 10, 11, 12, 13] and laser [8, 14, 15, 16, 17] have been developed in order to treat DH without any risk to human health. The dental iontophoresis method is preferred more than other methods because it is painless, non-invasive, practical and effective for a long time in the treatment of DH [8, 12, 18, 19]. In the literature, the basic principle of topical fluoride applications used for the treatment of DH is the occlusion of open tubules by forming calcium fluoride (CaF\({}_{2}\)) precipitation on the enamel surface [6]. However, since the calcium fluoride precipitate on the enamel can dissolve from the surface in a very short time, the treatment effect lasts a very short time. Therefore, by using various methods such as dental iontophoresis, fluoride ions are transferred to deeper tissues in the dentin; thereby, CaF\({}_{2}\) precipitation is created and the treatment is provided to be effective for a longer time [6, 7, 10, 20, 21]. Iontophoresis is a method of improving the transfer of ions or ionized drugs in the contacted tissue by using low-value DC for various purposes such as treatment, anesthesia and blood sugar measurement [22; 23; 24]. Dental iontophoresis is a common treatment method based on the principle of occlusion of dentinal tubules by applying low-level direct current (DC), which is harmless to human health, with a special solution to the area of dentin sensitivity [20; 22]. The pain threshold due to the electric current applied to the tooth in dental iontophoresis treatment varies from person to person [25; 26]. The patient's pain threshold determines the level of current that can be applied for treatment, and it also plays an important role in determining the treatment duration. In the iontophoresis process, ion movement occurs depending on the direction of the current applied and the electrical charge of the solution used. Therefore, the current direction should be chosen correctly and should not change in order to deliver the solution to deeper tissues by ion movement from the dentinal tubules to the nerve. In this respect, in order to complete the treatment process successfully in a short time, it is of great importance to use continuous DC, whose current direction does not change. However, the use of continuous DC may result in skin polarization, which in turn reduces the efficiency of iontophoresis treatment [27]. Polarization, which occurs due to the capacitive effect of the skin, slows down the delivery of the solution to the tissue by reducing the effect of the applied DC current [28]. In addition, continuous DC application may cause discomfort such as itching, redness and burning on the skin [29]. For these reasons, thanks to the use of pulse DC in the classical method, depolarization of the skin is provided and the discomfort that occurs is minimized [29; 30; 31; 32]. However, there are cycles when the current is not applied periodically in pulse DC application, which adversely affects the quality of treatment and also causes the prolongation of the treatment period. In this study, a microcontroller-based switched-mode dental iontophoresis system (SMDIS) using a dual-return probe is designed, and its performance is investigated.