Fully Automated Bioreactor-Based pH-Cycling System for Demineralization: A Comparative Study with a Conventional Method.

This study aimed to develop an automated pH-cycling system using inexpensive commercial components that can replicate pH fluctuations in the oral cavity and salivary clearance to compare demineralization characteristics with the conventional method. The study found that the newly developed cycle-1 group showed improved demineralization properties, including apparent lesion depth, surface roughness, Vickers hardness, mineral loss, and depth of demineralization, compared to the control group. Additionally, the cycle-2 group, which had a longer cycle interval, showed further improvements in the demineralization properties. This system can replicate the differences in dental damage caused by differences in meals, snacking frequencies, and lifestyle rhythms, making it useful in cariology, preventive dentistry research, and oral care product development. It can be constructed using inexpensive commercial products, significantly reducing research costs and improving reproducibility and fairness between different experimental facilities. The system can replicate lifestyle rhythms, such as meals, sleep, and oral clearance by saliva, making it an in vitro pseudo-oral cavity.

Development of Root Caries Prevention by Nano-Hydroxyapatite Coating and Improvement of Dentin Acid Resistance.

There is no established method for optimizing the use of dentin to prevent root caries, which are increasing in the elderly population. This study aimed to develop a new approach for root caries prevention by focusing on bioapatite (BioHap), a new biomaterial, combined with fluoride. Bovine dentin was used as a sample, and an acid challenge was performed in three groups: no fluoride (control group), acidulated phosphate fluoride treatment (APF group), and BioHap + APF treatment (BioHap group). After applying the new compound, the acid resistance of dentin was compared with that of APF alone. The BioHap group had fewer defects and an increased surface hardness than the APF group. The BioHap group had the smallest lesion depth and least mineral loss among all groups. Using a scanning electron microscope in the BioHap group showed the closure of dentinal tubules and a coating on the surface. The BioHap group maintained a coating and had higher acid resistance than the APF group. The coating prevents acid penetration, and the small particle size of BioHap and its excellent reactivity with fluoride are thought to have contributed to the improvement of acid resistance in dentin. Topical fluoride application using BioHap protects against root caries.

Improved Enamel Acid Resistance Using Biocompatible Nano-Hydroxyapatite Coating Method.

In this study, we attempted to develop a dental caries prevention method using a bioapatite (BioHap), an eggshell-derived apatite with nanoparticle size and biocompatibility, with a high-concentration fluoride tooth surface application method. The enamel acid resistance after the application of the proposed method was compared with that of a conventional topical application of fluoride using bovine tooth enamel as an example. The tooth samples were divided into three groups based on the preventive treatment applied, and an acid challenge was performed. The samples were evaluated for acid resistance using qualitative and quantitative analytical methods. The BioHap group demonstrated reduced enamel loss and improved micro-Vickers hardness, along with a thick coating layer, decreased reaction area depth, and decreased mineral loss value and lesion depth. The combination of BioHap with high-concentration fluoride led to the formation of a thick coating layer on the enamel surface and better suppression of demineralization than the conventional method, both qualitatively and quantitatively. The proposed biocompatible nano-hydroxyapatite coating method is expected to become a new standard for providing professional care to prevent dental caries.

Improved Enamel Acid Resistance by Highly Concentrated Acidulated Phosphate Sodium Monofluorophosphate Solution.

Sodium monofluorophosphate (MFP) is a component of fluoride-containing dentifrices and is more biosafe than the conventional sodium fluoride (NaF). MFP can respond not only on the tooth surface layer but also deep into the enamel. We aim to confirm that high concentrations of acid phosphate MFP (AP-MFP, 9000 ppmF), used in professional care, could lead to a highly biosafe fluoride application method that acts through the deep enamel layers. Sample groups were respectively treated in vitro with NaF, acidulated phosphate fluoride (APF), MFP, and AP-MFP, and the samples were compared against an untreated group. Characterizations after fluoride application confirmed that MFP and AP-MFP treatments improved the acid resistance of enamel compared to that of conventional methods. Furthermore, the acid resistance of highly concentrated MFPs improved by using phosphoric acid. Although the acid resistance from the AP-MFP method is not as good as that using APF, AP-MFP can act both on the surface layer and deep into the enamel. Moreover, AP-MFP retains fluoride ions as much as APF does on the tooth surface. The proposed fluoride application method using AP-MFP introduces a dental treatment for acid resistance that is highly biosafe and penetrates deep layers of the enamel.

Plasma Membrane Ca2+-ATPase in Rat and Human Odontoblasts Mediates Dentin Mineralization.

Intracellular Ca2+ signaling engendered by Ca2+ influx and mobilization in odontoblasts is critical for dentinogenesis induced by multiple stimuli at the dentin surface. Increased Ca2+ is exported by the Na+-Ca2+ exchanger (NCX) and plasma membrane Ca2+-ATPase (PMCA) to maintain Ca2+ homeostasis. We previously demonstrated a functional coupling between Ca2+ extrusion by NCX and its influx through transient receptor potential channels in odontoblasts. Although the presence of PMCA in odontoblasts has been previously described, steady-state levels of mRNA-encoding PMCA subtypes, pharmacological properties, and other cellular functions remain unclear. Thus, we investigated PMCA mRNA levels and their contribution to mineralization under physiological conditions. We also examined the role of PMCA in the Ca2+ extrusion pathway during hypotonic and alkaline stimulation-induced increases in intracellular free Ca2+ concentration ([Ca2+]i). We performed RT-PCR and mineralization assays in human odontoblasts. [Ca2+]i was measured using fura-2 fluorescence measurements in odontoblasts isolated from newborn Wistar rat incisor teeth and human odontoblasts. We detected mRNA encoding PMCA1-4 in human odontoblasts. The application of hypotonic or alkaline solutions transiently increased [Ca2+]i in odontoblasts in both rat and human odontoblasts. The Ca2+ extrusion efficiency during the hypotonic or alkaline solution-induced [Ca2+]i increase was decreased by PMCA inhibitors in both cell types. Alizarin red and von Kossa staining showed that PMCA inhibition suppressed mineralization. In addition, alkaline stimulation (not hypotonic stimulation) to human odontoblasts upregulated the mRNA levels of dentin matrix protein-1 (DMP-1) and dentin sialophosphoprotein (DSPP). The PMCA inhibitor did not affect DMP-1 or DSPP mRNA levels at pH 7.4-8.8 and under isotonic and hypotonic conditions, respectively. We also observed PMCA1 immunoreactivity using immunofluorescence analysis. These findings indicate that PMCA participates in maintaining [Ca2+]i homeostasis in odontoblasts by Ca2+ extrusion following [Ca2+]i elevation. In addition, PMCA participates in dentinogenesis by transporting Ca2+ to the mineralizing front (which is independent of non-collagenous dentin matrix protein secretion) under physiological and pathological conditions following mechanical stimulation by hydrodynamic force inside dentinal tubules, or direct alkaline stimulation by the application of high-pH dental materials.

Physiologically Based Pharmacokinetic Models Predicting Renal and Hepatic Concentrations of Industrial Chemicals after Virtual Oral Doses in Rats.

Recently developed high-throughput in vitro assays in combination with computational models could provide alternatives to animal testing. The purpose of the present study was to model the plasma, hepatic, and renal pharmacokinetics of approximately 150 structurally varied types of drugs, food components, and industrial chemicals after virtual external oral dosing in rats and to determine the relationship between the simulated internal concentrations in tissue/plasma and their lowest-observed-effect levels. The model parameters were based on rat plasma data from the literature and empirically determined pharmacokinetics measured after oral administrations to rats carried out to evaluate hepatotoxic or nephrotic potentials. To ensure that the analyzed substances exhibited a broad diversity of chemical structures, their structure-based location in the chemical space underwent projection onto a two-dimensional plane, as reported previously, using generative topographic mapping. A high-throughput in silico one-compartment model and a physiologically based pharmacokinetic (PBPK) model consisting of chemical receptor (gut), metabolizing (liver), central (main), and excreting (kidney) compartments were developed in parallel. For 159 disparate chemicals, the maximum plasma concentrations and the areas under the concentration-time curves obtained by one-compartment models and modified simple PBPK models were closely correlated. However, there were differences between the PBPK modeled and empirically obtained hepatic/renal concentrations and plasma maximal concentrations/areas under the concentration-time curves of the 159 chemicals. For a few compounds, the lowest-observed-effect levels were available for hepatotoxicity and nephrotoxicity in the Hazard Evaluation Support System Integrated Platform in Japan. The areas under the renal or hepatic concentration-time curves estimated using PBPK modeling were inversely associated with these lowest-observed-effect levels. Using PBPK forward dosimetry could provide the plasma/tissue concentrations of drugs and chemicals after oral dosing, thereby facilitating estimates of nephrotoxic or hepatotoxic potential as a part of the risk assessment.