Many oral diseases, such as oral leukoplakia and erythroplakia, which have a high potential for malignant transformations, cause abnormal structural changes in the oral mucosa. These changes are clinically assessed by visual inspection and palpation despite their poor accuracy and subjective nature. We hypothesized that non-invasive bioimpedance spectroscopy (BIS) might be a viable option to improve the diagnostics of potentially malignant lesions. In this study, we aimed to design and optimize the measurement setup and to conduct feasibility testing on pork oral tissues. The contact pressure between a custom-made concentric ring probe and tissue was experimentally optimized. The effects of loading time and inter-electrode spacing on BIS spectra were also clarified. Tissue differentiation testing was performed for ex vivo pork oral tissues including palatinum, buccal mucosa, fat, and muscle tissue samples. We observed that the most reproducible results were obtained by using a loading weight of 200 g and a fixed time period under press, which was necessary to allow meaningful quantitative comparison. All studied tissues showed their own unique spectra, accompanied by significant differences in both impedance magnitude and phase (p ≤ 0.014, Kruskal-Wallis test). BIS shows promise, and further studies are warranted to clarify its potential to detect specific pathological tissue alterations.

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The diagnosis of oral potentially malignant disorders currently relies on histopathological examination of surgically removed biopsies causing pain and discomfort for the patient. We hypothesise that non-invasive bioimpedance spectroscopy (BIS) method would overcome these problems and could make possible regular screening of at-risk patients. Previously several handmade probes have been introduced in such BIS studies. However, for the first time, we aimed to design a 3D printed probe and test it with model samples (saline solutions, cucumber and porcine tongue). We found that it is extremely crucial to select proper printable materials and optimise electrode geometries to avoid electrochemical corrosion problems, short-circuiting and other signal instabilities related to miniaturised probe. However, our final prototype constructed with four high purity silver made electrodes showed a good linearity (R 2 ¼ 0.999) in diluted saline solution measurements over a wide conductivity range (0.25-8 mS/cm), which covers well the range of values for the different biological tissues. Moreover, our data show that high reproducibility of the manufacturing and measurement is one important merit in the present 3D printed probe. However, further studies are needed to clarify the importance of fixed pressure especially when the tetrapolar 3D printed probe is used as a hand-held apparatus.

Three-dimensional (3D) printing has a high potential in various biomedical applications. We hypothesise that 3D printing could be a viable option to construct bioimpedance spectroscopic (BIS) sensors suitable for electrochemical characterization of oral mucosal tissues. Previous BIS studies have been relied on hand-made probes possessing significant limitations related to single patient disposable use, great inter-probe differences and weak reproducibility of measurement. There is also uncertainty related to effect of varying loading pressure between the probe and biological tissue. Here, we introduced three different sized rectangular shaped 3D printed probes and test those using four-terminal measurement principle on various porcine oral tissue samples. We found that constructing fully 3D printed probe is a challenging task and prone to issues relating to short circuiting or electrochemical corrosion. However, our final protype version constructed with silver-coated copper electrodes showed favourable characteristics in BIS experiments. All three different sized probes were able to differentiate between different tissue types with excellent reproducibility. The effect of loading pressure was found to be almost negligible when using small and medium sized probes. However, further studies are needed to measure tissues with uneven surfaces, such as palatinum, and to avoid manual or electrochemical surface finishing steps.