Characterization and Analysis of Healthy and Carious Teeth Through Electrical Measurements

Caries of the enamel is a disease that still affects billions of people all over the world. This is primarily because of the consumption of fermentable sugars and poor hygiene practises, which allow oral bacteria to self-organize in biofilms (dental plaque) and produce acid as part of the acidogenic bacteria metabolism [1]. Enamel consists of hydroxyapatite (HAp), accounting for around 85 percent of its volume, together with water and a minor yet essential quantity of binding proteins. The components are organised in an intricate configuration [2, 3].

The capacity of biological tissue to impede the passage of an electric current is referred to as bioimpedance, or bioelectrical impedance. The bioimpedance spectroscopy (BIS) method can be used to measure the impedance of living tissue over a wide frequency range [4]. This is done by combining the two ways. Electric impedance spectroscopy (EIS) is a common method for characterising material electrical characteristics. BIS is methodologically comparable to EIS. EIS is a low-cost, non-destructive method for characterising electrical characteristics of different materials. Having said that, BIS is where the method is most often used on biological tissues [5]. The process involves measuring the impedance magnitude and phase difference at each frequency point while delivering a weak alternating current (AC)-like that present in human tissue-through the biological sample [6]. In some cases, like a full-body analysis, the "tissue" can be enormous; in others, like a microscopic section of the target tissue, like the mucosa, it could be incredibly tiny. In direct contact with the external environment, the mucosal membrane, also known as mucosa, borders several body cavities. When observed within the mouth, this membrane is known as the oral mucosa or oral mucous layer [7].

Spectral cameras work by detecting the light that is reflected off of an item after it has been illuminated by a light source [8]. Alternately, the object may be illuminated with a monochromatic light, and the light that is reflected back can then be filtered to identify certain wavelengths [9]. The kind of information that one seeks to extract from the item being investigated dictates the selection of the appropriate filter [10]. Imaging a sample's surface with a focused electron beam allows scanning electron microscopy (SEM) to produce images of the sample [11]. Scientists use these signals to study the sample in depth, determining surface shape, composition, and crystal structures through electron interactions with atoms in the sample. Elements and chemical compounds in a sample can be identified using chemical microanalysis techniques like EDS [12]. With a search engine optimization (SEM) tool, it is commonplace. Because each element has its own atomic structure, each X-ray signal created when blasted with electrons is unique, the characterisation capabilities of this technique are based on this basic premise. Micrometrical elemental compositions of a sample may be studied using this method [13]. A number of studies have been achieved recently that focuses the bioimpedance spectroscopy characteristics and importance. Emran et al. [1] developed a method for measuring electrical impedance utilising five distinct depth settings across a frequency range of 1 kHz to 1MHz. The impact of impedance magnitude and phase spectra is investigated by Lackovic and Stare [14] from 30Hz to 1MHz. Besides, Pathiraja et al. [15], Tatullo et al. [16] use the measurable impedance magnitude to identify the healthy teeth.

The LCR-meter electrical impedance analyzer was used in this study to measure the impedance change of various teeth with and without carious over a wide range of frequency [17-21]. The results demonstrated that the range of impedance value when the teeth are healthy is greater than when the teeth are carious. In addition, the SEM test was used to scan the surface characteristics of teeth.

Electrochemical impedance spectroscopy has been shown to be a powerful approach for evaluating the electrical properties of dentine, but in order to yield relevant data, it requires thorough sample processing and experimental set-up. The average impedance and phase shift of two from the carious teeth are shown in Table 2.

Table 2. Impedance and phase shift values of carious teeth

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Figure 6. The real part of average impedance changes of carious teeth

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Figure 7. Imaginary part of the average impedance changes of carious teeth

Figure 6 shows the real part of the average electrical impedance change of carious teeth. The results show that the impedance located in the range of (82.567 to 1.27E+05) Ω with increasing of the frequency for the range of (1.00E-02-1.00E+07) Hz, and decreasing in the phase shift of the tooth. Figure 7 shows an imaginary part of the average change of electrical impedance of the carious teeth which represent the measuring electrode of the bioelectric impedance meter of carious tooth for ten sub- jects by the relation between the phase shift angle of the teeth and the frequency of the meter. In the other hand, Table 3 shows the average impedance and phase shift of some of healthy teeth.

Table 3. Impedance and phase shift values of healthy teeth

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Figure 8. The average impedance changes of healthy teeth for real part

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Figure 9. The average impedance changes of healthy teeth for imaginary part

Figure 8 shows the real part of the healthy teeth. The results show the average impedance located in range of (3.63E+03 to 2.59E+06) Ω which are larger than the range of carious teeth. While the Figure 9 illustrates the imaginary part of the average impedance of the healthy teeth. With increasing the frequencies (1.00E-02-8.89E+06) Hz and decreasing in the phase shift.

The SEM results of healthy tooth surface with different range of magnification (500 µm-5 µm) are shown in Figure 10 which clearly shows the surface morphology of healthy tooth were very smooth and there is no wrinkles and holes appear on the surface. In contrast the SEM results of carious tooth were shown in Figure 11. The SEM surface morphology of carious tooth at different magnification show the surface has numerous of holes, grooves, and wrinkles due to the carious of tooth.

The EDX analysis of tooth surface before and after carious are illustrated in Table 4 and Table 5, also shown in Figure 12, and Figure 13 respectively.

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Figure 10. SEM image of healthy tooth at different magnification (a) at 500 µm, (b) at 200 µm, (c) at 100 µm, (d) at 50 µm, (e) at 20 µm, (f) at 10 µm (g) at 5 µm and (h) at 1 µm

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Figure 11. SEM image of carious tooth at different magnification (a) at 500 µm, (b) at 200 µm, (c) at 100 µm, (d) at 50 µm, (e) at 20 µm, (f) at 10 µm (g) at 5 µm and (h) at 1 µm

Table 4. The measurement of the EDX test on the healthy teeth

Table 5. The measurement of the EDX test on the carious teeth

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Figure 12. EDX spectrum of healthy tooth

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Figure 13. EDX spectrum of carious tooth

In Figure 12, EDX of healthy tooth shows the concentrations of chemical elements, which contain 54.22% of Antimony (Sb), 22.31% of Calcium (Ca), 16.42% of Phosphorus (P), 6.39% of Carbon (C), and 0.66% of Chlorine (Cl) which confirm the chemical composition of tooth. In contrast, EDX analysis of carious tooth show in Figure 13, which contains 40.82% of Antimony (Sb), 16.27% of Calcium (Ca), 18.47% of Phosphorus (P), 15.23% of Carbon (C), 2.16% of Chlorine (Cl), 3.02% of Sodium (Na), 1.70% of Aluminum (Al), 1.39 of Magnesium (Mg), and 0.94% of Silicon (Si). In this case, the error can be determined by using the formula:

$\operatorname{Error}(\%)=\mp 3 \frac{\sigma}{N} \times 100=\mp 3 \frac{\sqrt{N}}{N} \times 100$       (1)

where, N is the X-ray counts number after background subtraction in the peak. Generally, the increasing N is, the decreasing the error in the EDX analysis. And $\sigma=\sqrt{N}$.

The X-ray imaging test for healthy and diseased teeth is a fast and painless way to get images of the tooth structure for diagnosing issues with the jaw, mouth, or teeth. For the simple reason that a visual examination can't always reveal issues like cavities, tumours, bone loss, or hidden dental structures like wisdom teeth; X-ray scans can. Different densities of materials absorb X-rays to varying degrees as they travel through the tooth. Bone and metal, both of which are dense, seem white on X-ray pictures. It looks like the air within the lungs is dark. Muscle and fat show up as different colours of grey. Any physical measurement worth its salt will always be an average.

A few examples of the healthy teeth are shown in Figure 14. If a function f of one variable x describes the system's state, then the average of over a 2δ interval is:

$M_{\tilde{\delta}}(f)(x)=\frac{1}{2 \delta} \int_{x-\bar{\delta}}^{x+\bar{\delta}} f(y) d y$        (2)

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Figure 14. The X-ray test of the healthy tooth

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Figure15. The X-ray test of the carious tooth

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Figure 16. The X-ray test of the bone resorption

Tooth decay caused by acid produced by bacteria is known as carious teeth or dental caries. The buildup of bacterial debris and the subsequent development of caries are both caused by poor oral hygiene and the consumption of sugary foods and drinks. From yellow to black, there's a rainbow of possible cavity colours. Discomfort in eating and other related symptoms are possible. Tooth loss, inflammation of the tissues surrounding the tooth, infection, and abscess formation are all potential complications.

Figure 15 demonstrates different types of caries. In the subgraph (a) of Figure 15, The presence of spaces and indentation between the teeth, which leads to the accumulation of foods and the formation of bacteria that led to tooth decay and pain in the gums. For subgraph (b) of Figure 15, this tooth requires orthodontics or extraction because its indentation causes latensification in the adjacent tooth, pain in the gums, and erosion in the external texture, while the teeth in subgraph (c) of Figure 15 represent proximal caries mesial four and distal caries. Subgraph (d) of Figure 15 illustrates evidence of bone formation and bone resorption and change in periodontal with association.

In the other cases the X-ray test detect the bone resorption as in Figure 16 which demonstrates periodontics with lateral bone resorption caries on proximal surface of radiograph of mandibular teeth.

One of the most significant factor effects on the interpretation of the image and the diagnosis is the density of the teeth. Density is different in human teeth and according to the age, it is certain that in children it is less dense, and in adults it is a higher and constant amount, and sometimes there is a slight discrepancy according to the size of the tooth. What determines the dark and light colours is the duration of the X-ray radiation the present duration in this study is between 0.6-0.8 depending on the patient's circumstances or the condition of the tooth.

Also, another factor is the acidification period which is passing in three stages: Fixation, Cleaning, and Watering. Each stage has a specific time that is inversely proportional to the duration of the exposure that the film is exposed to it, that also gave us additional information about the reflection of rays from minerals such as the filling or orthodontic and the minerals of the tooth and the lack of its reflection in caries due to bacteria that feed on the ray-reflecting minerals.