H2O2 gel bleaching induces cytotoxicity and pain conduction in dental pulp stem cells via intracellular reactive oxygen species on enamel/dentin disc

TRPA1 up-regulation mediates oxidative stress in a pulpitis model in vitro

BACKGROUND AND PURPOSE

Pulpitis is associated with tooth hypersensitivity and results in pulpal damage. Thermosensitive transient receptor potential (TRP) ion channels expressed in the dental pulp may be key transducers of inflammation and nociception. We aimed at investigating the expression and role of thermo-TRPs in primary human dental pulp cells (hDPCs) in normal and inflammatory conditions.

EXPERIMENTAL APPROACH

Inflammatory conditions were induced in hDPC cultures by applying polyinosinic:polycytidylic acid (poly(I:C)). Gene expression and pro-inflammatory cytokine release were measured by RT-qPCR and ELISA. Functions of TRPA1 channels were investigated by monitoring changes in intracellular Ca2+ concentration. Mitochondrial superoxide production was measured using a fluorescent substrate. Cellular viability was assessed by measuring the activity of mitochondrial dehydrogenases and cytoplasmic esterases. TRPA1 activity was modified by agonists, antagonists, and gene silencing.

KEY RESULTS

Transcripts of TRPV1, TRPV2, TRPV4, TRPC5, and TRPA1 were highly expressed in control hDPCs, whereas TRPV3, TRPM2, and TRPM3 expressions were much lower, and TRPM8 was not detected. Poly(I:C) markedly up-regulated TRPA1 but not other thermo-TRPs. TRPA1 agonist-induced Ca2+ signals were highly potentiated in inflammatory conditions. Poly(I:C)-treated cells displayed increased Ca2+ responses to H2O2, which was abolished by TRPA1 antagonists. Inflammatory conditions induced oxidative stress, stimulated mitochondrial superoxide production, resulted in mitochondrial damage, and decreased cellular viability of hDPCs. This inflammatory cellular damage was partly prevented by the co-application of TRPA1 antagonist or TRPA1 silencing.

CONCLUSION AND IMPLICATIONS

Pharmacological blockade of TRPA1 channels may be a promising therapeutic approach to alleviate pulpitis and inflammation-associated pulpal damage.

Can carbamide peroxide be as effective as hydrogen peroxide for in-office tooth bleaching and cause less sensitivity? A systematic review

This study aimed to answer the question through a systematic review: Can carbamide peroxide be as effective as hydrogen peroxide and cause less in-office bleaching sensitivity? A literature survey was performed in PubMed/MEDLINE, Embase, Scopus, ISI Web of Science, and gray literature. Primary clinical trials that compared the efficacy or the in-office bleaching sensitivity between carbamide and hydrogen peroxides were included. The risk of bias was evaluated using the RoB2. The certainty of the evidence was assessed using the GRADE approach. DPI training significantly improved the mean scores of the dental undergraduates from 7.53 in the pre-DPI-training test to 9.01 in the post-DPI-training test (p < 0.001). After 6 weeks, the mean scores decreased marginally to 8.87 in the retention test (p = 0.563). DPI training increased their confidence level from 5.68 pre-DPI training to 7.09 post-DPI training. The limited evidence suggests that the 37% carbamide peroxide may be similarly effective to the 35% hydrogen peroxide for bleaching teeth in-office and causes less bleaching sensitivity. However, more well-designed split-mouth clinical trials are necessary to strengthen the evidence.

Chemical painful post-traumatic trigeminal neuropathy induced by dental bleaching: A case report

Background

Teeth whitening is a frequent request in clinical practice. The most widely used whitening agent on vital teeth is carbamide peroxide. This article reports a rare adverse effect following a whitening procedure.

Case description

A 29-year-old patient was referred to the dental emergency department for severe pain that exhibited the characteristics of neuropathic pain. In the absence of any visible lesion or traumatic event, this pain was linked to the recent application of carbamide peroxide (10%) during a bleaching procedure. The diagnosis of painful post-traumatic trigeminal neuropathy (PTTN) of chemical origin was made. Treatment with the anticonvulsant gabapentin (900mg per day) gradually reduced the pain until its complete disappearance. After presenting the clinical characteristics of the case, the pathophysiological hypotheses are discussed.

Practical implications

Carbamide peroxide application may elicit nerve damage through a cascade of cellular and biological reactions, resulting in neuropathic pain. The successful management of this clinical case may provide useful information for similar situations. Key words:Case report, carbamide peroxide, painful neuropathy, pain, gingiva.

Novel Experimental In-Office Bleaching Gels Containing Co-Doped Titanium Dioxide Nanoparticles

The present study reports on the development and testing of novel bleaching agents containing co-doped metaloxide nanoparticles (NP; 0%, 5%, 10% v/w) and hydrogen peroxide (HP, 0%, 6%, 15%, and 35%). Bovine blocks (n = 200, A = 36 mm2) were obtained and randomly distributed into experimental groups (n = 10/group). NPs were incorporated into gels before bleaching (3 sessions, 7 days apart, 30 min/session, irradiated with violet light-LT). Color changes (ΔE00, ΔWID), mineral content (CO32−, PO43−), and topography were assessed (spectrophotometer, ATR-FTIR, and AFM) before and after bleaching procedures (14 days). Metabolic status and three-dimensional components of non-disrupted Streptococcus mutans biofilms were investigated using a multimode reader and confocal microscopy. The results indicate that ΔE00 and ΔWID significantly increased with NPs’ concentrations and LT. The enamel’s mineral ratio was adversely impacted by HP, but alterations were less pronounced when using NP-containing gels. The enamel’s topography was not damaged by the bleaching protocols tested. The bioluminescence results show that bleaching protocols do not render latent antibacterial properties to enamel, and the confocal microscopy results demonstrate that the 3-dimensional distribution of the components was affected by the protocols. The proposed nanotechnology improved the bleaching efficacy of experimental materials independent of hydrogen peroxide or irradiation and did not adversely impact the enamel’s surface properties or its chemical content.

2-hydroxyethyl methacrylate-derived reactive oxygen species stimulate ATP release via TRPA1 in human dental pulp cells

Extracellular ATP (adenosine triphosphate) and transient receptor potential ankyrin 1 (TRPA1) channels are involved in calcium signaling in odontoblasts and dental pain. The resin monomer 2-hydroxyethyl methacrylate (HEMA), used in dental restorative procedures, is related to apoptotic cell death via oxidative stress. Although the TRPA1 channel is highly sensitive to reactive oxygen species (ROS), the effect of HEMA-induced ROS on ATP release to the extracellular space and the TRPA1 channel has not been clarified in human dental pulp. In this study, we investigated the extracellular ATP signaling and TRPA1 activation by HEMA-derived ROS in immortalized human dental pulp cells (hDPSC-K4DT). Among the ROS-sensitive TRP channels, TRPA1 expression was highest in undifferentiated hDPSC-K4DT cells, and its expression levels were further enhanced by osteogenic differentiation. In differentiated hDPSC-K4DT cells, 30 mM HEMA increased intracellular ROS production and ATP release, although 3 mM HEMA had no effect. Pretreatment with the free radical scavenger PBN (N-tert-butyl-α-phenylnitrone) or TRPA1 antagonist HC-030031 suppressed HEMA-induced responses. These results suggest that ROS production induced by a higher dose of HEMA activates the TRPA1 channel in human dental pulp cells, leading to ATP release. These findings may contribute to the understanding of the molecular and cellular pathogenesis of tertiary dentin formation and pain in response to dental biomaterials.

New Insights into TRP Ion Channels in Stem Cells

Transient receptor potential (TRP) ion channels are cationic permeable proteins located on the plasma membrane. TRPs are cellular sensors for perceiving diverse physical and/or chemical stimuli; thus, serving various critical physiological functions, including chemo-sensation, hearing, homeostasis, mechano-sensation, pain, taste, thermoregulation, vision, and even carcinogenesis. Dysregulated TRPs are found to be linked to many human hereditary diseases. Recent studies indicate that TRP ion channels are not only involved in sensory functions but are also implicated in regulating the biological characteristics of stem cells. In the present review, we summarize the expressions and functions of TRP ion channels in stem cells, including cancer stem cells. It offers an overview of the current understanding of TRP ion channels in stem cells.

Copper Doped Carbon Dots for Addressing Bacterial Biofilm Formation, Wound Infection, and Tooth Staining

Oral infectious diseases and tooth staining, the main challenges of dental healthcare, are inextricably linked to microbial colonization and the formation of pathogenic biofilms. However, dentistry has so far still lacked simple, safe, and universal prophylactic options and therapy. Here, we report copper-doped carbon dots (Cu-CDs) that display enhanced catalytic (catalase-like, peroxidase-like) activity in the oral environment for inhibiting initial bacteria (Streptococcus mutans) adhesion and for subsequent biofilm eradication without impacting the surrounding oral tissues via oxygen (O₂) and reactive oxygen species (ROS) generation. Especially, Cu-CDs exhibit strong affinity for lipopolysaccharides (LPS) and peptidoglycans (PGN), thus conferring them with excellent antibacterial ability against Gram-positive bacteria (Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli), such that they can prevent wound purulent infection and promoting rapid wound healing. Additionally, the Cu-CDs/H₂O₂ system shows a better performance in tooth whitening, compared with results obtained with other alternatives, e.g., CDs and clinically used H₂O₂, particularly its negligible enamel and dentin destruction. It is anticipated that the biocompatible Cu-CDs presented in this work are a promising nano-mouthwash for eliminating oral pathogenic biofilms, prompting wound healing as well as tooth whitening, highlighting their significance in oral health management.

Pilot study on the applicability of boron-doped diamond electrodes for tooth whitening

Objectives

While various approaches are available for tooth whitening, the basic concept employs the use of peroxides in the form of gels, which are applied to tooth surfaces. Previous studies have shown that reactive oxygen species acting as potent disinfectants can be produced using boron‐doped diamond (BDD) electrodes for the electrolysis of water. With these electrodes being applicable, for example, for endodontic treatment, it was the goal of this pilot study to use such electrodes for tooth whitening.

Material and Methods

Two groups (n = 10) of intact clinical crowns were obtained by horizontally cutting off roots of extracted human teeth. The crowns were either bleached by applying a commercially available agent based on 40% hydrogen peroxide or were immersed in saline undergoing electrolysis with BDD electrodes. Whitening of specimens was judged on standardized photographs by examiners with three different levels of experience. Statistical analysis was based on Gwet's AC2 coefficient with quadratic weights, Shapiro–Wilk tests, and two‐way analysis of variance of aligned rank transformed data (level of significance set at α = .05).

Results

Levels of reliability ranging from fair to substantial were recorded for single persons while the level of reliability ranged between fair and moderate for groups of raters. The level of experience had no significant effect on the ratings (p = .2500). The bleaching method had a significant effect on ratings (p = .0005) with BDD electrodes showing less effect.

Conclusions

Bleaching by applying BDD electrodes was possible, but was not as effective as the use of commercially available in‐office whitening gel. A potential explanation may be seen in different concentrations of reactive oxygen species.