Monitoring acid-demineralization of human dentine by electrochemical impedance spectroscopy (EIS)

A novel mussel-inspired desensitizer based on radial mesoporous bioactive nanoglass for the treatment of dentin exposure: An in vitro study

OBJECTIVES

The dentin exposure always leads to dentin hypersensitivity and the acid-resistant/abrasion-resistant stability of current therapeutic approaches remain unsatisfatory. Inspired by the excellent self-polymerization/adherence activity of mussels and the superior mineralization ability of bioactive glass, a novel radial mesoporous bioactive nanoglass coated with polydopamine (RMBG@PDA) was developed for prevention and management of dentin hypersensitivity.

METHODS

Radial mesoporous bioactive nanoglass (RMBG) was synthesized by the sol-gel process combined with the cetylpyridine bromide template self-assembly technique. RMBG@PDA was synthesized by a self-polymerization process involving dopamine and RMBG in an alkaline environment. Then, the nanoscale morphology, chemical structure, crystalline phase and Zeta potential of RMBG and RMBG@PDA were characterized. Subsequently, the ion release ability, bioactivity, and cytotoxicity of RMBG and RMBG@PDA in vitro were investigated. Moreover, an in vitro experimental model of dentin hypersensitivity was constructed to evaluate the effectiveness of RMBG@PDA on dentinal tubule occlusion, including resistances against acid and abrasion. Finally, the Young's modulus and nanohardness of acid-etched dentin were also detected after RMBG@PDA treatment.

RESULTS

RMBG@PDA showed a typical nanoscale morphology and noncrystalline structure. The use of RMBG@PDA on the dentin surface could effectively occlude dentinal tubules, reduce dentin permeability and achieve excellent acid- and abrasion-resistant stability. Furthermore, RMBG@PDA with excellent cytocompatibility held the capability to recover the Young's modulus and nanohardness of acid-etched dentin.

CONCLUSION

The application of RMBG@PDA with superior dentin tubule occlusion ability and acid/abrasion-resistant stability can provide a therapeutic strategy for the prevention and the management of dentin hypersensitivity.

Dentin extracellular matrix loaded bioactive glass/GelMA support rapid bone mineralization for potential pulp regeneration

The study aims to develop a novel dentin extracellular matrix (dECM) loaded gelatin methacrylate (GelMA)-5 wt% bioactive glass (BG) (Gel-BG) hydrogel for dental pulp regeneration. We investigate the role of dECM content (2.5, 5, and 10 wt%) on the physicochemical characteristics and biological responses of Gel-BG hydrogel in contact with stem cells isolated from human exfoliated deciduous teeth (SHED). Results showed that the compressive strength of Gel-BG/dECM hydrogel significantly enhanced from 18.9 ± 0.5 kPa (at Gel-BG) to 79.8 ± 3.0 kPa after incorporation of 10 wt% dECM. Moreover, we found that in vitro bioactivity of Gel-BG improved and the degradation rate and swelling ratio reduced with increasing dECM content. The hybrid hydrogels also revealed effectual biocompatibility, >138 % cell viability after 7 days of culture; where Gel-BG/5%dECM was most suitable. In addition, the incorporation of 5 wt% dECM within Gel-BG considerably improved alkaline phosphatase (ALP) activity and osteogenic differentiation of SHED cells. Taken together, the novel bioengineered Gel-BG/dECM hydrogels having appropriate bioactivity, degradation rate, osteoconductive and mechanical properties represent the potential applications for clinical practice in the future.

4D microstructural changes in dentinal tubules during acid demineralisation

OBJECTIVE

Dental erosion is a common oral condition caused by chronic exposure to acids from intrinsic/extrinsic sources. Repeated acid exposure can lead to the irreversible loss of dental hard tissues (enamel, dentine, cementum). Dentine can become exposed to acid following severe enamel erosion, crown fracture, or gingival recession. Causing hypersensitivity, poor aesthetics, and potential pulp involvement. Improving treatments that can restore the structural integrity and aesthetics are therefore highly desirable. Such developments require a good understanding of how acid demineralisation progresses where relatively little is known in terms of intertubular dentine (ITD) and peritubular dentine (PTD) microstructure. To obtain further insight, this study proposes a new in vitro method for performing demineralisation studies of dentine.

METHODS

Advanced high-speed synchrotron X-ray microtomography (SXM), with high spatial (0.325 μm) and temporal (15 min) resolution, was used to conduct the first in vitro, time-resolved 3D (4D) study of the microstructural changes in the ITD and PTD phases of human dentine samples (∼0.8 × 0.8 × 5 mm) during 6 h of continuous acid exposure.

RESULTS

Different demineralisation rates of ITD (1.79 μm/min) and PTD (1.94 μm/min) and their progressive width-depth profiles were quantified, which provide insight for understanding the mechanisms of dentine demineralisation.

SIGNIFICANCE

Insights obtained from morphological characterisations and the demineralisation process of ITD and PTD during acid demineralisation would help understand the demineralisation process and potentially aid in developing new therapeutic dentine treatments. This method enables continuous examination of relatively large volumes of dentine during demineralisation and also demonstrates the potential for studying the remineralisation process of proposed therapeutic dentine treatments.

Dentin sealing and antibacterial effects of silver-doped bioactive glass/mesoporous silica nanocomposite: an in vitro study

OBJECTIVES

To synthesize a silver-doped bioactive glass/mesoporous silica nanoparticle (Ag-BGN@MSN), as well as to investigate its effects on dentinal tubule occlusion, microtensile bond strength (MTBS), and antibacterial activity.

MATERIALS AND METHODS

Ag-BGN@MSN was synthesized using a modified "quick alkali-mediated sol-gel" method. Demineralized tooth disc models were made and divided into four groups; the following treatments were then applied: group 1-no treatment, group 2-bioglass, group 3-MSN, group 4-Ag-BGN@MSN. Next, four discs were selected from each group and soaked into 6 wt% citric acid to test acid-resistant stability. Dentinal tubule occlusion, as well as the occlusion ratio, was observed using field-emission scanning electron microscopy. The MTBS was also measured to evaluate the desensitizing effect of the treatments. Cytotoxicity was examined using the MTT assay. Antibacterial activity was detected against Lactobacillus casei, and ion dissolution was evaluated using inductively coupled plasma optical emission spectrometry.

RESULTS

Ag-BGN@MSN effectively occluded the dentinal tubule and formed a membrane-like layer. After the acid challenge, Ag-BGN@MSN had the highest rate of dentinal tubule occlusion. There were no significant differences in MTBS among the four groups (P > 0.05). All concentrations of Ag-BGN@MSN used had a relative cell viability above 72%.

CONCLUSIONS

Ag-BGN@MSN was successfully fabricated using a modified sol-gel method. The Ag-BGN@MSN biocomposite effectively occluded dentinal with acid-resistant stability, did not decrease bond strength in self-etch adhesive system, had low cytotoxicity, and antibacterial effect.

CLININAL RELEVANCE

Dentinal tubule sealing induced by Ag-BGN@MSN biocomposite with antibacterial effect is likely to increase long-term stability in DH.

Influence of sodium chloride content in electrolyte solution on electrochemical impedance measurements of human dentin

Background:

The aim of this study was to investigate the influence of sodium chloride (NaCl) content in electrolyte solution on electrochemical impedance measurements of human dentin by employing electrochemical impedance spectroscopy.

Materials and Methods:

Dentin samples were prepared from extracted molars. Electrochemical impedance measurements were carried out over a wide frequency range (0.01Hz-10MHz). After measurements, samples were characterized using scanning electron microscopy.

Results:

Electrochemical impedance measurements showed that the mean values of dentin electrical resistance were 4284, 2062, 1336, 53 and 48kΩ at different NaCl contents in electrolyte solution. One-way ANOVA test of mean values of dentin electrical resistance revealed a significant difference (P < 0.0001) as a function of NaCl content in electrolyte solution. Comparing electrical resistance values of dentin samples at 0.05% w/v and 0.9% w/v concentrations were found to be significantly different (P < 0.05 at 95% confidence level). Scanning electron microscopy revealed structure of dentin sample with intertubular dentin matrix and distribution of patent dentinal tubules.

Conclusion:

This in vitro study indicated, through electrochemical impedance spectroscopy measurements, that electrical resistance of dentin was affected by the concentration of NaCl in electrolyte solution. It is clear from the current study that NaCl concentration in electrolyte solution has a marked influence on dentin electrical resistance. Therefore, this baseline data need to be considered in any future study on dental samples.

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.

Electrochemical impedance spectroscopy in understanding the influence of ultrasonic dental scaling on the dental structure-dental filling interface

The purpose of this study was to investigate the effect of ultrasonic scaling on teeth restored with a light-cured resin. Ultrasonic scaling is a very popular periodontal therapy among dentists, and used for the removal of dental plaque and calculus in order to reduce and eliminate inflammation. Given the fact that most ultrasonic devices are used at high frequencies to perform scaling, undesirable consequences, such as loss of adhesion and increase in surface roughness, may occur in teeth that have been restored with light-cured resins. Electrochemical impedance spectroscopy (EIS) and scanning electron microscopy were used to investigate the effects of ultrasonic treatments at the dental material-hard dental tissue interface. After ultrasonic scaling, EIS measurements were performed on a human tooth that had been restored with a light-cured resin filling. The data were analyzed and the influence of ultrasound was shown after visualization of the hard dental tissues and the dental material as equivalent electrical circuits. The study revealed, through EIS measurements, that ultrasonic scaling affected the resistance of the light-cured resin filling and dentin, whereas the enamel was affected only slightly. Scanning electron microscopy revealed an increase in roughness of the dental material.

Remineralization of partially demineralized dentine substrate based on a biomimetic strategy

Dentine remineralization is clinically significant for prevention and treatment of dentine caries, root caries, and dentine hypersensitivity. However, dentine remineralization is more difficult than enamel remineralization due to the abundant presence of organic matrix in dentine. The objective of this study was to develop a biomimetic method to facilitate remineralization of demineralized dentine through phosphorylation of type I collagen in demineralized dentine using sodium trimetaphosphate. The experimental results indicated that the effect of fluoride on remineralizing dentine was limited when residual mineral crystals were lacking on the surface of demineralized dentine, whereas the phosphorylation and Ca(OH)(2) pretreatment enhanced surface remineralization of the partially demineralized dentine. This biomimetic methodology resulted in favorable surface properties (i.e. highly negative charge and low interfacial free energy between substrate and aqueous medium) for crystal nucleation, and thus could be a promising method to remineralize superficially demineralized dentine lesions.

Scanning Electrochemical Microscopy as a Tool for the Characterization of Dental Erosion

When the tooth is exposed to acidic environments, an irreversible loss of dental hard tissue occurs in a process called dental erosion. In this work, the scanning electrochemical microscopy (SECM) was used to probe the consumption of protons at the vicinity of a tooth surface with a platinum microelectrode fixed at −0.5 (V) versus Ag/AgCl/KCl(sat). SECM approach curves were recorded to assess the extent of diffusion in the solution close to the tooth substrate. SECM images clearly demonstrated that the acid erosion process is very fast at solution pH values in the range between 3 and 4.

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.