Yasuhisa Tsujimoto

Effects of the Hydroxyl Radical and Hydrogen Peroxide on Tooth Bleaching

The mechanisms of bleaching of discolored coronal teeth using hydrogen peroxide (H2O2) were investigated. In a scanning-electron-microscopy study, the intertubular dentin and peritubular dentin were dissolved by high concentrations of H2O2, which is used for bleaching. The X-ray diffraction study showed that hydroxyapatite was not influenced by H2O2. In an electron-spin-resonance study, more hydroxyl radical (* OH) was detected as the H2O2 concentration was increased. When amino acids that are core components of dentin proteins, such as proline and alanine, were added to H2O2, the generation of * OH decreased, but there was no change when glycine was added. A nuclear-magnetic-resonance study showed that proline was degraded completely by H2O2, the structure of alanine changed slightly, and glycine was not affected by H2O2. It is suggested that H2O2 and * OH do not influence the inorganic tissue of dentin but attack the organic component of dentin. These facts suggest that * OH has the main role in tooth bleaching with H2O2.

Generation of Free Radicals and/or Active Oxygen by Light or Laser Irradiation of Hydrogen Peroxide or Sodium Hypochlorite

Generation of free radical and/or active oxygen by light or laser irradiation of hydrogen peroxide (H2O2) or sodium hypochlorite (NaClO), which have been used for tooth whitening or root canal irrigation, was investigated using electron spin resonance spectroscopy combined with a spin-trapping technique. When H2O2 was exposed to light or laser radiation, the amount of hydroxyl radical generated changed according to the concentration of H2O2 and irradiation time. The amount of 5,5-dimethyl-1-pyrrolidone-(2)-oxyl-(1) (DMPO-X) also changed in accordance with irradiation time. The amounts of hydroxyl radical generated from H2O2 after irradiation were in the order: plasma lamp > halogen lamp > He-Ne laser > Yellow He-Ne laser. On the other hand, the amounts of DMPO-X generated from NaClO after irradiation were in the order: plasma lamp > Yellow He-Ne laser > halogen lamp > He-Ne laser.

Lipid Peroxidation as a Possible Cause of Benzoyl Peroxide Toxicity in Rabbit Dental Pulp—A Microsomal Lipid Peroxidation in vitro

The toxicity of composite resin on rabbit dental pulp was investigated biochemically. A microsomal fraction of rabbit dental pulp was incubated with each of the components of composite resins, and the formation of peroxide was determined by the thiobarbituric acid reaction. Benzoyl peroxide (BPO), the most widely used catalyst, was the most effective on peroxidation, but monomers were not. Cations such as Cu2+ or Fe2+ were required for acceleration of this reaction. Authentic polyunsaturated fatty acids and phospholipids were extensively converted into their peroxides by BPO, but amino acids and carbohydrates were not. Among the active oxygens, hydroxyl radicals were thought to be responsible for BPO-dependent peroxidation. The results presented in this paper indicate that the lipid portion of the cells may be attacked by hydroxyl radicals produced by BPO and copper or iron. Therefore, BPO is considered to be the major factor responsible for the toxicity of composite resins.

A small amount of singlet oxygen generated via excited methylene blue by photodynamic therapy induces the sterilization of Enterococcus faecalis.

INTRODUCTION The present study aimed to clarify the relationship between the amount of singlet oxygen ((1)O(2)) generated from excited methylene blue (MB) and the bactericidal effects on Enterococcus faecalis. METHODS A diode laser was used as the laser irradiation source (λ = 660 nm, 200 mW). The laser irradiation time periods were 300, 600, and 900 seconds. In experiment 1, the amount of (1)O(2) generated from each concentration (0.0001%-1.0%) of excited MB was examined by using electron spin resonance to determine the optimal concentration of MB. In experiment 2, the bactericidal effects of (1)O(2) on E. faecalis were examined. Experimental groups were with laser irradiation, L(+); without laser irradiation, L(-); including MB, M(+); and not including MB, M(-). These were combined to form 4 groups: L(+)M(+), L(+)M(-), L(-)M(+), and L(-)M(-). After treatment, E. faecalis was incubated for 48 hours at 37°C, and the bactericidal effects of (1)O(2) on E. faecalis were determined on the basis of the number of colony-forming units per milliliter. RESULTS The largest amount of (1)O(2) was generated from 0.01% excited MB. After 300, 600, and 900 seconds of irradiation, 35.2, 87.2, and 117.1 μmol/L (1)O(2) were detected, respectively. In group L(+)M(+),colony-forming units per milliliter of E. faecalis dramatically decreased depending on the amount of (1)O(2) generated. No other groups showed any bactericidal effects. CONCLUSIONS Our findings suggest that 0.001%-0.01% of MB is the most effective range for generating (1)O(2) during the application of antimicrobial photodynamic therapy. At least 35.2 μmol/L generated (1)O(2) was necessary to achieve the sterilization of E. faecalis.

Stimulatory Effects of Low-concentration Reactive Oxygen Species on Calcification Ability of Human Dental Pulp Cells

The present study was conducted to investigate the effects of reactive oxygen species (ROS) on the calcification ability of human dental pulp (HDP) cells. HDP cells were treated with 100 mumol/L hydrogen peroxide (H(2)O(2)) for 5 or 10 minutes (5-min ROS group and 10-min ROS group) to investigate the mechanism of transmission to cells. Untreated cells were used as controls. Generation of free radicals was quantified by the electron spin resonance spin-trapping method and found to be increased by treatment with ROS. Formation of calcified nodules was also investigated by von Kossa staining and alizarin red S staining. Twenty-eight days after exposure, calcified nodules were present in cell cultures that had been treated with ROS for 5 or 10 minutes. Expression of mRNAs for osteopontin (OPN) and osteocalcin (OCN) was significantly greater in 10-min ROS group 6 and 9 days, respectively, after exposure than in controls. Production of OPN and OCN by 10-min ROS group was also greater 12 and 18 days, respectively, after exposure than in controls. These results suggested that calcification of HDP cells was stimulated by H(2)O(2) and by the ROS it generated.

Analysis of Arsenic in Gray and White Mineral Trioxide Aggregates by Using Atomic Absorption Spectrometry

INTRODUCTION The aim of the present study was to investigate whether the concentration of arsenic (As) released from gray or white mineral trioxide aggregates (MTAs) met the requirement of the International Standards Organization (ISO) for dental cements. METHODS Sample preparations were carried out according to the ISO methods. After centrifugation of dissolved samples, As (III) concentration in the final supernatant was analyzed by a high-performance atomic absorption spectrophotometer. RESULTS As (III) concentration from both MTAs was much less than the required value (2 ppm) for dental cements regulated by the ISO. An experiment simulating pulp capping by using MTA revealed that As concentration was also below the standard value of the ISO. The As concentration in white MTA was lower than the value (10 ppb) recommended for tap water and environmental standards. CONCLUSIONS The present in vitro studies demonstrated that there is no threat to patient health in using commercially available brands of MTA for endodontic practices.

Effect of nonsteroidal anti-inflammatory drugs on lipid peroxidation by hydroxyl radical

1. Effects of acetaminophen and sodium salicylate on hydoxyl radical elimination were studied using an electron-spin-resonance spin-trapping method. The effects of these agents on lipid peroxidation of the human erythrocyte membrane were also investigated by the thiobarbituric acid method. 2. Acetaminophen and sodium salicylate depressed hydroxyl radical generated by Cu2+/H2O2. 3. Acetaminophen inhibited Cu2+/H2O2-dependent lipid peroxidation; however, sodium salicylate enhanced Cu2+/H2O2-dependent lipid peroxidation.

Comparison of Conventional and New-generation Nickel-Titanium Files in Regard to Their Physical Properties

INTRODUCTION This study investigated the surface, fractured structure, and physicochemical properties related to cyclic fatigue in various nickel-titanium (NiTi) files. METHODS Among a total of 10 groups of NiTi files, conventional NiTi files (ProFile [Dentsply Maillefer, Ballaigues, Switzerland] and K3 [SybronEndo, Orange, CA]) and new-generation NiTi files (ProFile Vortex [PV; Tulsa Dental Specialties, Tulsa, OK], Vortex Blue [VB; Tulsa Dental Specialties], and K3 XF [XF; SybronEndo, Orange, CA]) with the same tip diameter (ISO size 25) and 2 types of taper (0.04 and 0.06) were used in this study. Scanning electron microscopy of the file surface structure, differential scanning calorimetry, and cyclic fatigue resistance tests were conducted. RESULTS Many mechanical grooves were recognized on the file surface. The surface in the ProFile group was extremely smooth compared with that observed for the other files. Many shallow hollows besides mechanical grooves were noted on the surface in the XF group. A smooth curve was observed in the ProFile, K3, and PV groups. Defined peaks in differential scanning calorimetry were observed in the VB and XF groups. The 0.04 taper files exhibited a statistically higher number of cycles to fracture than the 0.06 taper files in all groups (P < .05). Cracks along the mechanical grooves were observed in the NiTi files, with the exception of the XF group. The start of cracking was detected at U-shape sites in the ProFile group, the cutting edge in the PV and VB groups, and radial islands in the K3 and XF groups. CONCLUSIONS The present findings suggest that new-generation NiTi files are not necessarily improved compared with conventional files.

Surface Changes of Mineral Trioxide Aggregate after the Application of Bleaching Agents: Electron Microscopy and an Energy-dispersive X-Ray Microanalysis

INTRODUCTION The aim of this study was to investigate the changes in the surface structure and chemical composition after applying bleaching agents to completely hardened mineral trioxide aggregate. METHODS A total of 12 samples of MTA blocks were divided into three groups, two different bleaching agents, and a control group. The surface structure was observed using a scanning electron microscope. The changes in elemental composition were analyzed by an energy-dispersive x-ray microanalysis (EDX) system. RESULTS The surface of the MTA covered with each bleaching agent changed in terms of both color and structure compared with the control. EDX showed that both bleaching agents affected the elemental distribution. A decrease in Ca and an increase in Si were shown, and this tendency was especially pronounced in the higher hydrogen peroxide concentration group. CONCLUSIONS The acidic conditions induced by bleaching agents brought about the deterioration of the MTA surface. These findings suggest that MTA is an insufficient barrier against tooth bleaching.

Antioxidant effects of antioxidant biofactor on reactive oxygen species in human gingival fibroblasts.

The purpose of this study was to investigate the effects of antioxidant biofactor (AOB) on reactive oxygen species (ROS). Generation of superoxide radical (O2•−) and hydroxyl radical (•OH) was determined using an electron spin resonance (ESR) spin-trapping method. AOB was added at different concentrations to these free radical generating systems. The generation of both O2•− and •OH was scavenged by the addition of AOB in a dose-dependent manner. These results indicate that AOB has strong antioxidant properties against these radicals. We further investigated the anti-oxidative effect of AOB on human gingival fibroblasts (HGFs). HGFs were treated for 3 h with α-MEM containing a combination of AOB and H2O2 (AOB + H2O2 group), containing H2O2 (H2O2 group), or containing AOB alone (AOB group). Non-stimulated HGFs were used as a control group. The number of surviving cells was in the order of the AOB group > control group > AOB + H2O2 group > H2O2 group. The level of expression of type I collagen mRNA and production of collagen were also in the order of the AOB group > control group > AOB + H2O2 group > H2O2 group. In conclusion, our results suggest that AOB may protect HGFs against oxidative stress by reducing stress-induced ROS.