Impedance spectroscopy of teeth with and without approximal caries lesions--an in vitro study

METHODS FOR DIAGNOSING DENTAL CARIES LESIONS

Tooth decay (dental caries) commonly occurs throughout the world and is one of the most widespread infectious diseases of lifestyle, globally affecting all age groups; up to 90% schoolchildren and almost 100% adults in both developing and developed countries. When left untreated, it can lead to disease outbreaks resulting in advere-health and life-threatening conditions such as endocarditis or sepsis. Undoubtedly, basic measures are thus required in both dental and GP practice to ensure that dental caries are detected early. This article presents the various diagnostic methods used to identify these disease outbreaks.

Assessment of demineralized tooth lesions using optical coherence tomography and other state-of-the-art technologies: a review

Tooth demineralization is one of the most common intraoral diseases, encompassing (1) caries caused by acid-producing bacteria and (2) erosion induced by acid of non-bacterial origin from intrinsic sources (e.g. stomach acid reflux) and extrinsic sources (e.g. carbonated drinks). Current clinical assessment based on visual-tactile examination and standardized scoring systems is insufficient for early detection. A combination of clinical examination and technology is therefore increasingly adapted. This paper reviews various procedures and technologies that have been invented to diagnose and assess the severity of tooth demineralization, with focus on optical coherence tomography (OCT). As a micron-resolution non-invasive 3D imaging modality, variants of OCT are now available, offering many advantages under different working principles for detailed analytical assessment of tooth demineralization. The roles, capabilities and impact of OCT against other state-of-the-art technologies in both clinical and research settings are described. (139 words).

A Comparative Study of Two Fractional-Order Equivalent Electrical Circuits for Modeling the Electrical Impedance of Dental Tissues

Background: Electrical impedance spectroscopy (EIS) is a fast, non-invasive, and safe approach for electrical impedance measurement of biomedical tissues. Applied to dental research, EIS has been used to detect tooth cracks and caries with higher accuracy than visual or radiographic methods. Recent studies have reported age-related differences in human dental tissue impedance and utilized fractional-order equivalent circuit model parameters to represent these measurements. Objective: We aimed to highlight that fractional-order equivalent circuit models with different topologies (but same number of components) can equally well model the electrical impedance of dental tissues. Additionally, this work presents an equivalent circuit network that can be realized using Electronic Industries Alliance (EIA) standard compliant RC component values to emulate the electrical impedance characteristics of dental tissues. Results: To validate the results, the goodness of fits of electrical impedance models were evaluated visually and statistically in terms of relative error, mean absolute error (MAE), root mean squared error (RMSE), coefficient of determination (R2), Nash–Sutcliffe’s efficiency (NSE), Willmott’s index of agreement (WIA), or Legates’s coefficient of efficiency (LCE). The fit accuracy of proposed recurrent electrical impedance models for data representative of different age groups teeth dentin supports that both models can represent the same impedance data near perfectly. Significance: With the continued exploration of fractional-order equivalent circuit models to represent biological tissue data, it is important to investigate which models and model parameters are most closely associated with clinically relevant markers and physiological structures of the tissues/materials being measured and not just “fit” with experimental data. This exploration highlights that two different fractional-order models can fit experimental dental tissue data equally well, which should be considered during studies aimed at investigating different topologies to represent biological tissue impedance and their interpretation.

Gauging electrical properties of bone with a bioimpedance-sensing drill

OBJECTIVE

Multiple surgical procedures require drilling through bone to access underlying anatomy or for device placement. In dental applications, iatrogenic injury caused by accidental perforation of cortical bone into critical anatomy occurs in a significant number of dental implant procedures. Limited real-time sensing methods are available to guide clinicians while drilling through cancellous bone towards cortical interfaces. Early interface detection could prevent accidental damage to underlying anatomic structures. This study aims to demonstrate that electrical impedance spectroscopy can be integrated within a standard surgical drill to distinguish between bone types.

APPROACH

A custom bearing and insulated drill bit were designed to collect 10 cortical and cancellous impedance measurements from ex vivo femurs (2 pigs) and 80 bone measurements from in situ femurs (4 pigs). In the in situ study, two return electrodes (simulating a lip-clip and shoulder pad) were used to assess impedance differences associated with return electrode geometry.

MAIN RESULTS

Significant ex vivo differences (p  <  0.05) between cortical and cancellous bone occurred in the real resistivity from 0.1 to 100 kHz and in the imaginary resistivity from 0.3 to 10 kHz, with a maximum cortical-to-cancellous impedance ratio of 1.48. Significant in situ differences (p  <  0.01) were observed in both real and imaginary resistivities from 0.1 to 100 kHz, with a maximum impedance ratio of 2.94. AUCs for classifying bone type based on the real resistivity ranged from 0.84 to 0.96 for ex vivo bone and 0.98 to 1.0 for in situ bone. Mean differences between return electrode geometries were less than 5%.

SIGNIFICANCE

The significant cortical-to-cancellous contrast observed indicates this system's potential to provide real-time tissue differentiation during bone drilling procedures.

Monitoring regression of post-orthodontic lesions with impedance spectroscopy: a pilot study

Objective

To investigate if the alternating current impedance spectroscopy (ACIS) technology could be used to monitor remineralization of post-orthodontic white spot lesions (WSLs) after debonding of fixed orthodontic appliances.

Material and methods

The study group consisted of 28 adolescents (aged 12–16 years) with at least two WSLs on their maxillary incisors, canines, or first premolars at debonding. Buccal surfaces (n = 194) were visually examined and scored with modified International Caries Detection and Assessment System (ICDAS) criteria and with the CarieScan Pro device by three examiners according to manufactures manual (test method). In addition, 31 surfaces with ICDAS = 0 were monitored by ACIS, serving as controls. Follow-up examinations were carried out after 8 and 16 weeks. Modified ICDAS scores, captured from digital photographs by three independent examiners, served as reference method. Four patients were lost to follow-up. Data were analysed in a mixed statistical model considering systematic effects of visit, tooth and observer, random effects of patients, and visits within patients.

Results

Over 50 per cent of all surfaces had marked WSL at baseline and the corresponding values at 8 and 16 weeks were 33 per cent and 22 per cent. The ACIS readings mirrored the visual scores; the baseline estimate (56.3) was significantly decreased after 8 weeks (P < 0.05). The lateral incisors exhibited the highest values whereas the lowest were recorded for the central incisors.

Limitations

ICDAS is not the same as a ‘true’ gold standard. The high prevalence of WSL may jeopardize the external validity.

Conclusion

The ACIS technology may to some extent be used to monitor the regression of post-orthodontic WSLs.

Performance of Different Methods for Detection of Incipient Occlusal Caries Lesions: An In Vitro Study

OBJECTIVE

The aim of this in vitro study was to evaluate the diagnostic performance of visual inspection (VI), laser fluorescence (LF pen), fluorescence camera (FC), and alternating current impedance spectroscopy technique (ACIST) for detection of incipient occlusal caries lesions. Histology was used as the gold standard to determine the interexaminer reliability of the methods, among three examiners with different levels of experiences (Examiner 1: 5 years; examiner 2: 10 years; and examiner 3: 25 years).

MATERIALS AND METHODS

One hundred two molar teeth were selected. The occlusal surfaces of teeth were evaluated with VI, LF pen, FC, and ACIST devices independently by three examiners. Diagnostic performances of methods were evaluated with binormal receiver-operating characteristics analysis. Interexaminer agreement of detection methods was assessed using Cohen's kappa coefficient values (p < 0.001).

RESULTS

Incipient enamel lesions were determined more successfully with VI by all examiners. All detection methods were presented with statistically acceptable interexaminer agreement (p < 0.001). For D₂ and D₃ thresholds, FC for examiner 1, VI for examiner 2, and both VI and FC for examiner 3 demonstrated statistically high sensitivity and specificity (p < 0.05).

CONCLUSIONS

It can be concluded that diagnostic performance of the methods was insufficient for detecting incipient occlusal caries lesions by itself. Performance can be improved by using them with VI as a traditional caries detection method.

Detection of questionable occlusal carious lesions using an electrical bioimpedance method with fractional electrical model

This in vitro study evaluated the diagnostic performance of an alternative electric bioimpedance spectroscopy technique (BIS-STEP) detect questionable occlusal carious lesions. Six specialists carried out the visual (V), radiography (R), and combined (VR) exams of 57 sound or non-cavitated occlusal carious lesion teeth classifying the occlusal surfaces in sound surface (H), enamel caries (EC), and dentinal caries (DC). Measurements were based on the current response to a step voltage excitation (BIS-STEP). A fractional electrical model was used to predict the current response in the time domain and to estimate the model parameters: Rs and Rp (resistive parameters), and C and α (fractional parameters). Histological analysis showed caries prevalence of 33.3% being 15.8% hidden caries. Combined examination obtained the best traditional diagnostic results with specificity = 59.0%, sensitivity = 70.9%, and accuracy = 60.8%. There were statistically significant differences in bioimpedance parameters between the H and EC groups (p = 0.016) and between the H and DC groups (Rs, p = 0.006; Rp, p = 0.022, and α, p = 0.041). Using a suitable threshold for the Rs, we obtained specificity = 60.7%, sensitivity = 77.9%, accuracy = 73.2%, and 100% of detection for deep lesions. It can be concluded that BIS-STEP method could be an important tool to improve the detection and management of occlusal non-cavitated primary caries and pigmented sites.

Assessment of tooth structure using an alternative electrical bioimpedance spectroscopy method

In the past few years bioimpedance has been used in many applications in dentistry, such as estimating the length of root canals and the physical properties of enamel. Despite the significant number of studies using bioimpedance to investigate the dental structure, many of them use only the real component of bioimpedance, i.e., the resistance, disregarding the information provided by the imaginary one, i.e., the reactance. Moreover, in different studies that investigate both parts of bioimpedance, the data are obtained by using single frequency or multifrequency methods based on sinusoidal sweep. The aim of this study was to investigate the use of an alternative bioimpedance spectroscopy (BIS) method based on step response in the assessment of tooth structure. To test the feasibility of the studied method we performed in vitro experiments that considered the successive removal of enamel layers of 22 healthy teeth, the accomplishment of the BIS method, and the estimate of bioimpedance parameter that were associated with the changes in the tooth structure. To deal with the variability of bioimpedance parameters a dental health index (DHI) is proposed. The findings include the behavior of bioimpedance parameters of intact teeth, as well as those associated with the successive removal of the enamel layer, and indicate that DHI is sensitive enough to detect changes of the enamel layer. The results point to the feasibility of the studied BIS method in evaluating tooth structure and that it might be used to assess dental health.

Detection of non-cavitated occlusal caries with impedance spectroscopy and laser fluorescence: an in vitro study

Objective:

To evaluate the performance of an impedance spectroscopy technology for detecting non-cavitated occlusal caries lesions in permanent teeth in vitro. The method was compared with a commonly used laser fluorescence device and validated against histology.

Material and Methodology:

A non-cavitated sample of 100 extracted posterior teeth was randomly selected and assessed for caries on enamel and dentin level with aid of CarioScan PRO (ACIS) and DIAGNOdent pen (LF pen) by three examiners. After the measurements, the extension of the lesion was histologically determined as gold standard. Sensitivity, specificity, accuracy and receiver-operating curves were calculated. Intra- and inter-examiner reproducibility was expressed by intra class correlation coefficients.

Results:

The histological caries prevalence was 99% and 41% exhibited dentin caries. The ACIS technique displayed high specificities but almost negligible sensitivities at readings >50. A similar pattern was noted for the LF pen at readings >30. The intra- and inter-examiner reproducibility varied between 0.47 and 0.98 and the values were generally lower for the ACIS technique than for the LF pen. The inter-examiner agreement reached excellent levels with both methods.

Conclusions:

In vitro,the ACIS technique showed a low ability to disclose occlusal caries lesions in the enamel and/or dentin of non-cavitated permanent molars. However, further in vivo studies of permanent occlusal surfaces are needed to mirror the clinical situation.

Dental caries and pulpal disease

This article reviews the diagnostic process, from the first clinically evident stages of the caries process to development of pulpal pathosis. The caries diagnostic process includes 4 interconnected components-staging caries lesion severity, assessing caries lesion activity, and risk assessments at the patient and tooth surface level - which modify treatment decisions for the patient. Pulpal pathosis is diagnosed as reversible pulpitis, irreversible pulpitis (asymptomatic), irreversible pulpitis (symptomatic), and pulp necrosis. Periapical disease is diagnosed as symptomatic apical periodontitis, asymptomatic apical periodontitis, acute apical abscess, and chronic apical abscess. Ultimately, the goal of any diagnosis should be to achieve better treatment decisions and health outcomes for the patient.

Monitoring bacterial-demineralization of human dentine by electrochemical impedance spectroscopy

OBJECTIVE

The purpose of this study was two-fold: (1) to monitor bacterial biofilm formation and bacteria-induced demineralization of dentine in situ by using electrochemical impedance spectrum (EIS); (2) to examine the relationship between EIS findings and changes in the chemical composition and ultrastructure of dentine during bacteria-induced demineralization.

METHODS

In this study, dentine demineralization was induced by Streptococcusmutans (ATCC 25175) in the presence of sucrose in culture medium and was monitored using two EIS measurement systems (Type A with a working electrode and Type B without a working electrode). Scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) and X-ray diffraction (XRD) were employed to examine the morphology, element contents and crystallinity of hydroxyapatite (HAP) on the dentine surface. Transverse microradiography (TMR) was used to characterize the lesion depth and degree of mineral loss during demineralization.

RESULTS

The resistance of the bulk dentine (R(d)) and the apparent resistance of dentine (R(a)) measured from the Type A and Type B EIS systems, respectively, decreased gradually with demineralization. The resistance of the biofilm formed on dentine surface was determined by fitting the EIS data with equivalent circuits. The presence of biofilm slightly increased R(a) of dentine before demineralization. However, the electrochemical behavior of biofilm did not affect the decreasing impedance of dentine with demineralization. The SEM, EDX, XRD and TMR results demonstrated that the surface and bulk dentine gradually became more porous due to the loss of minerals during demineralization, which in turn resulted in the decrease in R(d) and R(a) values obtained from EIS systems.

CONCLUSIONS

This investigation highlighted EIS as a potential technique to monitor biofilm formation and bacterial-induced demineralization in situ.

Age-related changes in ac-impedance spectroscopy studies of normal human dentine

Non-destructive methods, such as the ac-impedance technique, have recently been applied to early caries detection and to identify micro-leakage between tooth structure and filling materials. However, in vitro impedance measurements are affected by a number of external factors. The purpose of present study was to investigate the effect of the age of teeth on impedance measurements of human dentine by employing electrical impedance spectroscopy (EIS). Fully hydrated dentine samples were prepared from extracted third molars of 20 and 50 year old patients. Ac-impedance measurements were carried out over a wide frequency range. Impedance measurements showed that there were differences in impedance between young and older dentine. In their circuit models, both resistance and capacitance were found to be significantly different (p < 0.05) for the two age groups. One of the age-related changes in dentine is the formation of peritubular dentine on the inner walls of dentinal tubules and we propose that this is responsible for the differences in impedance. Sample or patient age therefore must be considered when making impedance measurements on any tooth.

In situ tracing the process of human enamel demineralization by electrochemical impedance spectroscopy (EIS)

OBJECTIVE

The purpose of this study was to in situ characterize the demineralization (namely dissolution of hydroxyapatite) on the surface of the human enamel using electrochemical impedance spectroscopy (EIS) technology.

METHODS

Fresh human third molars extracted without visible evidence of caries, were used in this study. After they were immersed in a demineralizing solution prepared from lactic acid and carboxy methyl cellulose sodium (Na-CMC) buffering at pH 4, demineralization happened on their surfaces. EIS of the specimens were measured at a series of immersed interval. X-ray diffractometer (XRD) were used to distinguish the microstructure of the surface layer of the specimens. The depositions that appeared in the demineralizing solution after 46 h immersion were analyzed by fourier transform infrared spectrometer (FTIR).

RESULTS

XRD analysis revealed that the percentage of intensity (I%) of HAP gradually decreased with the elapsed immersing time, which indicated the dissolution of HAP columns of enamel. Nyquist spectra were fitted with an equivalent circuit characterized by some parameters, such as Q and R(p) (error<0.1%). Changes of the parameters' values revealed that the rate of demineralization accelerated at the forepart of the demineralization, but slowed down beyond 70 h immersion.

CONCLUSIONS

The results suggested that EIS was proved to be a useful method for in situ investigating and in vivo detecting the demineralization of the enamel.

Caries detection and diagnosis: Novel technologies

Recent years have seen an increase in research activity surrounding diagnostic methods, particularly in the assessment of early caries lesions. The drive for this has come from two disparate directions. The first is from the dentifrice industry who are keen to develop techniques that would permit caries clinical trials (CCTs) to be reduced in duration and subject numbers to permit the investigation of novel new anti-caries actives. The second is from clinicians who, armed with the therapies to remineralise early lesions are now seeking methods to reliably detect such demineralised areas and implement true preventative dentistry. This review examines novel technologies and the research supporting their use. Techniques based on visual, optical, radiographic and some emerging technologies are discussed. Each have their benefits although systems based on the auto-fluorescence (such as QLF) of teeth and electrical resistance (such as ECM) seem to offer the most hope for achieving reliable, accurate detection of the earliest stages of enamel demineralisation.

Caries risk assessment: methods available to clinicians for caries detection

It is hypothesized that occlusal lesions are initiated on the fissure walls and can therefore be obscured by sound superficial tissue. Additionally, there is evidence that one effect of regular use of fluorides is greater opacity of enamel, which may obscure underlying lesions in dentin, the so-called 'hidden lesions'. Dental radiographs are inadequate for detecting decay in the occlusal surfaces until the lesion is well advanced through the enamel and into the dentin. The clinician relies on visual observation of texture and discoloration, clinical judgment based upon experience, and on tactile sense by probing with an explorer. An objective detection method to complement the traditional visual assessment is used by the clinician for arriving at clinical decisions on the management of the carious lesion: whether invasive therapy or a more conservative, noninvasive approach. Objective and reliable longitudinal monitoring of the lesion's response to preventive measures allow the selection of an appropriate therapy before the lesion progresses to the stage where invasive treatment is required. This paper discusses the problem of the lack of appropriate clinical methods for the detection and quantification of carious lesions. A few commercially available methods are described (the quantitative light-induced fluorescence method, the DIAGNOdent device, and electrical caries monitor) and some new techniques mentioned.

Temperature dependence of the electrical resistance of sound and carious teeth

Temperature variations are expected to influence measurement error in electrical resistance of teeth. It was the aim of this study to determine the changes in electrical behavior of extracted human teeth due to temperature changes in the range of room temperature to intra-oral temperature. Nine extracted teeth were selected, and the occlusal or an approximal surface was chosen for measurement. Carious involvement of the surfaces ranged from sound to cavitated. Electrical impedance spectroscopy sweeps in a frequency range of about 100 kHz to 10 Hz were completed at selected temperatures between 22 degrees C and 40 degrees C. After fitting the data to equivalent circuits that yielded parameter values for components of the equivalent circuit, we calculated the dc bulk resistance (Rh). The temperature dependence of Rb of the surfaces with different carious involvement was very similar, and the mean drop of Rb from 20 to 35 degrees C was 45% (SD 2%). It was concluded that the electrical resistance of sound and carious tooth surfaces is inversely related to temperature.

Enamel demineralisation assessed by computerised image analysis of clinical photographs

OBJECTIVES

To investigate the use of computerised image analysis to measure the area of demineralisation on the buccal surface of a tooth and to analyse the effect on that measurement of varying the angle at which a photographic image of the buccal surface of a tooth is taken.

METHODS

Twenty-two teeth with areas of incremental demineralisation on the buccal surface were photographed perpendicular to the buccal surface and at angles of 20 and 40 degrees, above (Cuspal) and below (Gingival) the perpendicular. The images were captured and analysed using computerised image analysis.

RESULTS

The Gingival views showed lower limits of agreement than the Cuspal views, probably due to the positioning of the masking on the lower part of the flash, to reduce reflection. There was a significant difference between the areas of demineralisation measured for the three angles from the Gingival views (p<0.001). The mean differences in areas measured were not linear, but there was a significantly greater reduction in area measured for the 40 degrees views.

CONCLUSIONS

Computerised image analysis to measure areas of demineralisation from a captured 35mm slide is reproducible. The position of the masking on the camera flash and the angle of the camera makes a difference to the area measured and the grey scales recorded. Images taken at a larger angle than 20 degrees to the perpendicular will record a significantly reduced area of demineralisation. Standardisation of photographs with the use of calibration markers and manipulation of images is discussed.

The effect of multiple examinations on the diagnosis of approximal caries and the restoration of approximal surfaces

OBJECTIVE

The aim of this study was to determine the effect of multiple examinations on sensitivity and specificity in the diagnosis and restoration of approximal caries.

STUDY DESIGN

In 2 studies, dentists examined bitewing radiographic films for approximal caries and the need for restoration. To model the clinical situation of multiple examinations over time, all groups of combinations of 2 to 10 dentists were constructed. Mean sensitivity and specificity were determined. In addition, 2 new variables were created: the first, "sensitivity any," was calculated by assigning a correct diagnosis for disease if any dentist in the group identified the diseased surface correctly; the second, "specificity all," was calculated by assigning a correct response only when all dentists in the group correctly identify a nondiseased surface.

RESULTS

The sensitivity and specificity means were the same for all group sizes. The "sensitivity any" means increased monotonically from group size 1 to group size 10, whereas the "specificity all" means decreased continually. There was a statistically significant difference between sensitivity and "sensitivity any" and between specificity and "specificity all" for all group sizes in both studies.

CONCLUSIONS

Multiple examinations increase the number of carious surfaces correctly diagnosed and the number of surfaces appropriately restored; however, multiple examinations also increase the number of sound surfaces diagnosed as carious and the number of intact surfaces receiving restorations.