Electrical conductance and electrode area on sound smooth enamel in extracted teeth

Electric-current-assisted Application of Self-etch Adhesives to Dentin

The use of electric current during the application of etch-and-rinse adhesive systems has been recently claimed to increase bonding of etch-and-rinse adhesives by enhancing substrate impregnation. The null hypothesis tested in this study was that electrically assisted application has no effect on bond strength of self-etching bonding systems. Three self-etch adhesives (Protect-Bond, Xeno III, and Prompt L-Pop) were applied with the aid of an electric signal-generating device (ElectroBond) and tested vs. controls prepared with the same disposable sponges but without electric current. Specimens bonded under the influence of electric current exhibited increased microtensile bond strength compared with the controls (p < 0.05). High-resolution SEM analysis showed that bonding under the influence of electricity reduced interfacial nanoleakage. It is speculated that resin infiltration may be improved by the attraction of polar monomers by an electric current or by modification of the dentin surface charges, resulting in better water substitution or evaporation.

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.

Detecting Short-Term Changes in the Activity of Caries Lesions with the Aid of New Technologies

This paper discusses the use of new technologies for the assessment of caries and more in particular changes in caries activity. Over the past decades, we have seen a shift from restorative treatment caries to a prevention-driven approach. Also there is a need for shorter and less expensive caries clinical trials. These demand earlier detection of lesions and the monitoring of lesion changes longitudinally in time, which has led to the development of new technologies to aid clinical visual examination. Also clinical visual inspection indices have been refined to fit this purpose. There is a constant flow of technologies emerging and disappearing. This review discusses the merits of recent developments regarding their respective uses for research purposes in testing new caries prevention strategies as well as in clinical caries management in dental private practice. Which technique to choose highly depends on the needed resolution of information.

An artificial multilayer perceptron neural network for diagnosis of proximal dental caries

OBJECTIVE

To evaluate if the application of an artificial intelligence model, a multilayer perceptron neural network, improves the radiographic diagnosis of proximal caries.

STUDY DESIGN

One hundred sixty radiographic images of proximal surfaces of extracted human teeth were assessed regarding the presence of caries by 25 examiners. Examination of the radiographs was used to feed the neural network, and the corresponding teeth were sectioned and assessed under optical microscope (gold standard). This gold standard served to teach the neural network to diagnose caries on the basis of the radiographic exams. To gauge the network's capacity for generalization, i.e., its performance with new cases, data were divided into 3 subgroups for training, test, and cross-validation. The area under the receiver operating characteristic (ROC) curve allowed comparison of efficacy between network and examiner diagnosis.

RESULTS

For the best of the 25 examiners, the ROC curve area was 0.717, whereas network diagnosis achieved an ROC curve area of 0.884, indicating a sizeable improvement in proximal caries diagnosis.

CONCLUSION

Considering all examiners, the diagnostic improvement using the neural network was 39.4%.

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 vivo enamel fluid movement

The aim of this study was to visualize fluid movement through dental enamel in vivo. Fifty permanent upper central incisors, from subjects aged 10-70 yr, and 5 permanent central just-erupted incisors, from subjects aged 6-7 yr, were included in the study. An impression was obtained by vinyl polyxiloxane, and replicas were then obtained by polyether impression material. The hydrophobic vinyl polyxiloxane material yielded a morphological image in situ of outward fluid flow through tooth enamel. The study confirmed in vivo that enamel is a permeable substrate, as shown by the presence of droplets on its surface, and demonstrated that age and enamel permeability are closely related. Samples from subjects of different ages showed a decreasing number and size of droplets with increasing age: freshly erupted permanent teeth showed many droplets covering the entire enamel surface. Droplets in permanent teeth were prominent along enamel perikymata.

The accuracy of electrical method for microleakage evaluation by a three-dimensional analysis

OBJECTIVES

This in vitro study aimed to investigate the accuracy of an electrical method for the evaluation of microleakage by a three-dimensional analysis of dye penetration.

METHODS

Coronal cavities were prepared on buccal, palatal or lingual surfaces in extracted human molars. The cavities were then filled with resin composites and were subjected to 10,000 load cycles (425g). Before cavity preparation and after load cycling, physiological saline was applied and wiped off, and the change in conductance was measured across the margin of the restoration in each specimen. After dye penetration, the specimens were reduced by 100 microm in a direction parallel to the cavity floor, from the surface of the restoration to the cavity floor. The sequence of reducing the sections by 100 microm and image taking was repeated. Three-dimensional images of dye penetration were made and the proportions of the interface showing penetration were calculated.

RESULTS

Pearson's correlation coefficients between changes in conductance and the surface area of dye penetration, between these and the rate of dye penetration, and between these and the depth of dye penetration were 0.932, 0.920 and 0.732, respectively. The correlations were significant (p<0.05).

CONCLUSIONS

The results of this electrical method for microleakage evaluation showed stronger correlations with the three-dimensional amount of marginal leakage (surface area of dye penetration and rate of dye penetration) than the two-dimensional amount (depth of dye penetration).

Reproducibility of Electrical Caries Measurements: A Technical Problem?

The currently available instrument for electrical detection of occlusal caries lesions [Electronic Caries Monitor (ECM)] uses a site-specific measurement with co-axial air drying. The reproducibility of this method has been reported to be fair to good. It was noticed that the measurement variation of this technique appeared to be non-random. It was the aim of this study to analyse how such a non-random reproducibility pattern arises and whether it could be observed for other operators and ECM models. Analysis of hypothetical measurement pairs showed that the pattern was related to measurements at the high and low end of the measurement range for the instrument. Data sets supplied by other researchers to a varying degree showed signs of a similar non-random pattern. These data sets were acquired at different locations, by different operators and using 3 different ECM models. The frequency distribution of measurements in all cases showed a single or double end-peaked distribution shape. It was concluded that the pattern was a general feature of the measurement method. It was tentatively attributed to several characteristics such as a high value censoring, insufficient probe contact and unpredictable probe contact. A different measurement technique, with an improved probe contact, appears to be advisable.

Remineralisation study of artificial root caries lesions after fluoride treatment. An in vitro study using Electric Caries Monitor and Transversal Micro-Radiography

AIMS

To evaluate and compare remineralisation of root caries lesions after in vitro treatment with various fluoride (F) agents using an Electric Caries Monitor (ECM) and Transversal Micro-Radiography (TMR).

MATERIALS

Permanent human teeth were extracted and root surface specimens were sectioned, prepared (n = 35), and randomly allocated into seven different experimental groups (groups 1-7).

METHODS

Root surfaces were demineralised in an acidified gel (pH = 5.0) for 3 weeks followed by various F treatments and stored in a standardised remineralising solution at 37 degrees C for 6 weeks. The root surfaces were treated twice daily with different dentifrice slurries for 2 min, either with a neutral placebo dentifrice without F (group 5); or a neutral sodium fluoride (NaF) 1400 p.p.m. F dentifrice (group 1); or a neutral 1250 p.p.m. F dentifrice (group 6); or an acid dentifrice (pH 4.7) with 1400 p.p.m. F containing amine fluoride (AmF) (groups 3 and 4) or a 1250 p.p.m. (pH 4.7) AmF dentifrice (group 6). In groups 1, 2, 5, 6, and 7, the root surfaces were additionally rinsed for 2 min with a neutral non-F placebo solution. In groups 3 and 4, rinsing were performed for 2 min with an acid (pH 4.7) 250 p.p.m. F solution, containing 125 p.p.m. F as AmF and 125 p.p.m. F as potassium fluoride (KF), once or twice per day respectively. ECM was used to measure electrical resistance on root surfaces at baseline and after 3 and 6 weeks respectively. TMR technique was used to measure and compare root surface lesion depths and mineral loss.

RESULTS

Six weeks daily treatment with a dentifrice slurry containing AmF followed by rinsing with a combination of equal amounts of AmF and KF solution twice a day showed a statistical significant higher ECM values compared with the other groups. TMR data measuring lesion depths and mineral loss reduction supported the results of the ECM findings.

CONCLUSIONS

Daily application of a dentifrice slurry containing 1400 p.p.m. F as AmF combined with twice daily rinsing with a 250 p.p.m. F solution containing equal amount of AmF and KF significantly remineralise primary root caries lesions in vitro. ECM and TMR are valuable complementary methods in order to analyse the remineralisation processes.

Modeling AC current conduction through a human tooth

Impedance between the electrode inserted in a root canal of a human tooth and the outer electrode placed on the oral mucosa serves as a measure of the root canal length, a vital parameter necessary for efficient endodontic procedure in dentistry. For better understanding of current conduction through the tooth, the impedance has been measured on extracted teeth (in vitro) and further used to develop corresponding electrical lumped element models. For modeling the metal/solution interface and complex structure of the tooth, Fricke's constant phase elements are employed. More detailed insight into current conduction is given by numerical simulation. Numerical simulation demonstrates the influence on the impedance of several important parameters, such as dentin conductance, canal preparation, and solution conductance.

Effect of contact media on the diagnostic quality of electrical resistance measurements for occlusal caries

BACKGROUND

Electrical resistance measurements have been used for the diagnosis of occlusal caries. Both site and surface-specific techniques have been described, the latter more suited to clinical trials or epidemiological surveys. For surface-specific measurements the tooth is dried and a contact medium drawn along the fissure pattern to provide an electrical contact between a probe tip and the tooth surface.

OBJECTIVES

Different contact media have been used and it was the aim of this study to investigate whether different contact media could influence the diagnostic accuracy and repeatability of surface-specific electrical resistance measurements.

METHODS

Electrical resistance readings were taken on 99 molar teeth using saline, KY jelly, toothpaste or dental prophylaxis paste. Readings were repeated on 44 randomly selected teeth. The teeth were serially sectioned and visually examined to establish the deepest lesion if present.

RESULTS

The Student t-test showed that there were statistically significant differences between readings taken with different contact media, with the exception of toothpaste and prophylaxis paste, where no difference was found. The strongest relationship between histology and resistance reading was achieved with KY jelly (r = 0.559). The optimum sensitivity and specificity achieved was 0.59 and 0.86, respectively (resistance cut-off 0.1 M(Omega)). ROC analysis showed that the diagnostic performance of saline was significantly inferior to the other contact media (P < 0.05). Limits of agreement were used to assess repeatability which were acceptable for all media except toothpaste.

CONCLUSIONS

Differences were found between electronic resistance readings taken with different contact media. KY jelly was found to produce the best overall diagnostic performance and should be the standard material used for surface-specific measurements.

Time-dependent decrease and seasonal variation of the porosity of recently erupted sound dental enamel in vivo

Recently erupted teeth are more sensitive to dental caries than teeth that have remained free from caries lesions for a few years after eruption. It has been hypothesized that this may be ascribed to differences in enamel porosity. The objective of the present work was to assess the time-dependence of electrical conductance, as an indication of porosity, of occlusal enamel in recently erupted permanent molar teeth. Fifty children aged 5-15 years of age, receiving regular dental care at six-month intervals, participated in the study when their first molar teeth (in 5- to 6-year-olds) or their second molar teeth (in 11- to 15-year-olds) had not been exposed to the oral environment for more than six months. On the first semi-annual check-up after eruption of a first or second molar, baseline diagnostic measurements, i.e., visual inspection and electrical conductance measurements (ECMs), were made at three or four pre-defined sites in the fissures. Subsequently, data collection was repeated every six months for three years. Sites were excluded from ECMs when a caries lesion was observed at a site by visual inspection. After 36 months, there were 257 sites in teeth considered sound upon visual examination. The ECM values of these sound sites showed a clear decrease with time after the first examination. The conductance decreased on average from 0.13 (Momega)(-1) to 0.059 (Momega)(-1). Since the conductance is assumed to be proportional to the porosity of the enamel, the latter decreased by a factor of 2.2 over the 36-month period. The results furthermore indicated a higher conductance for maxillary than for mandibular enamel. Almost all sites in that sample appeared to be in teeth that were observed for the first time during the months September to December. Electrical conductance, and therefore enamel porosity, of the sites showed a periodic variation with season of observation: In the fall, the conductance was higher than in the spring. This implies that a dentist should be more prudent in the fall than in the spring when indicating restorative treatment of an incipient caries lesion.

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.

A new electrical method for detecting marginal leakage of in vitro resin restorations

OBJECTIVES

Ingress of bacteria at sites of marginal leakage has been suggested to cause pulpal inflammation. The purpose of this in vitro study was to evaluate the validity of a new electrical method to detect marginal leakage of restoratives by comparing the results obtained with those of a dye penetration test.

METHODS

After cavities were prepared on the buccal coronal surfaces and root surfaces of 16 extracted non-carious human molar teeth, eight specimens were treated with a dentin bonding system (bonding group) and the other eight specimens were not treated (non-bonding group). Resin composites were filled in the cavities of all specimens, and physiological saline was applied to the margin of the restorative. Any excess saline was wiped off, leaving only the electrolyte, which had penetrated into the marginal gap. The change in conductance was measured continuously across the margin of each specimen during this process. The marginal leakage of specimens was confirmed using the dye penetration test, and the results were evaluated by the microleakage score.

RESULTS

In both coronal and root surface cavities, the changes in conductance in the non-bonding group after filling were significantly larger than those of the bonding group (p<0.05). The change in conductance of each specimen correlated with the microleakage score (p<0.05).

CONCLUSIONS

It was concluded that the relative electrical method could detect marginal leakage in both coronal and root surface cavities.

Performance of some diagnostic systems in the prediction of occlusal caries in permanent molars in 6- and 11-year-old children

OBJECTIVES

Attempts have been made to develop diagnostic methods which enable an early diagnosis of occlusal lesions which are not detectable by visual inspection. The aim of this study was to compare the performance of visual inspection focused on finding signs of fissure decalcification and discoloration, visual inspection upon fibre-optic transillumination (FOTI), and electrical conductance measurements (ECMs) in predicting the onset of occlusal caries in 6- and 11-year-old children.

METHODS

Fifty children aged 5-7 and 11-15 years, having first or second permanent molar teeth that were not exposed to the oral environment for more than half a year, participated in the study. Following baseline data recording, the diagnostic measurements were repeated six times at 6-month intervals over a period of 2.5 years.

RESULTS

Data were collected at predefined sites in the fissures. During the study, 220 of the 652 sites, i.e. 75 of 197 molars in 31 of the 50 children were judged to require a sealant or a sealant restoration. Two examiners jointly decided on the decay status at the sites. Survival plots showed that ECMs were superior to FOTI and fissure discoloration in predicting the onset of occlusal caries, although the differences were small.

CONCLUSION

ECM is a better predictor of occlusal caries than fissure discoloration and FOTI, although the differences among the performance of the three methods in this study were very small. A cost-effective analysis is envisaged to obtain insight into the practical value of ECMs in the prediction of occlusal caries and, thus, into the effectiveness of sealant application.

The electrical resistance of enamel-dentine cylinders. Influence of NaCl content in storage solutions

OBJECTIVES

To investigate the influence of different electrolyte concentrations on the electrical resistance of sound human enamel-dentine cylinders in vitro.

METHODS

Forty cylinders of 3-mm diameter and 2-mm length were drilled from 40 extracted caries-free third molar teeth. For ease of handling the samples were fixed in Perspex discs by means of a cyanoacrylate-adhesive. An a.c. source (frequency 500 Hz, amplitude 1 microA) with a high internal resistance was applied. Only Ohm's resistance was measured. The resistance measurements on the samples were made after storage in distilled water, 0.16 mM NaCl, 1.6 mM NaCl and 16 mM NaCl and 160 mM NaCl for 24 h.

RESULTS

The mean resistance values were 2026 +/- 152, 1835 +/- 178, 1605 +/- 364, 483 +/- 265 and 60 +/- 33 k omega, respectively. All values were statistically significantly different (Wilcoxon test; P < 0.0001).

CONCLUSION

It is concluded that the choice of electrolyte solution influences the resistance values of the enamel-dentine samples. This effect should be taken into account when measuring electrical resistances in vivo and in vitro.

Electronic diagnosis of occlusal caries in vitro: adaptation of the technique for epidemiological purposes

Most studies on electronic diagnosis of occlusal caries have involved taking site-specific conductance measurements. Airflow around the electronic caries monitor probe removes superficial moisture and the conductance measurement reflects the caries status of that part of the fissure beneath the probe tip. This is an appropriate technique for a clinician to use to monitor caries status, and it could be adapted for use in epidemiological studies and clinical trials. The present work investigated an alternative technique using a jelly as a contact medium over the entire fissure system so that the probe might record the overall caries status of the tooth reflecting the worst affected site. Readings were taken on 96 extracted teeth with dye-coloured jelly acting as a contact medium. Readings were repeated on 32 teeth. Histological validation of caries status was carried out by visual examination of serial sections through each tooth to note the deepest lesion. The sensitivity and specificity of the overall electronic caries monitor readings were calculated for all lesions and dentine lesions only using selected resistance cut-off points and presented as a series of Receiver Operating Characteristic (ROC) curves. The optimum sensitivity and specificity values were, for all lesions: 61% and 86%, and for dentine lesions: 76% and 76% respectively. The reproducibility of the readings was acceptable (Kappa values for all lesions = 0.76, for dentine lesions = 0.55). The technique warrants further study as an overall reading may be more appropriate for epidemiological and clinical trial use.