Kouji Araki

Effect of calcium hydroxide on the dissolution of soft tissue on the root canal wall

Calcium hydroxide [Ca(OH)2] paste can aid in the cleaning of a root canal because of its soft tissue-dissolving potential. In this study, we examined with a scanning electron microscope the dissolution by Ca(OH)2 paste of pulpal tissue attached to uninstrumented bovine root canal walls. Extracted bovine anterior teeth were divided into small specimens at the middle portion of the roots. The experimental groups were treated with sodium hypochlorite (NaOCl), Ca(OH)2, or a combination of Ca(OH)2 + NaOCl. The control group was given no treatment. The root canal walls were observed with a scanning electron microscope, and the amount of remaining pulp tissue was compared. The amount of debris was reduced remarkably in the groups treated with NaOCl for > 30 s, or Ca(OH)2 for 7 days. The combination of Ca(OH)2 + NaOCl was more effective than the separate treatments. The results suggest that Ca(OH)2 as a root canal medicine serves as an effective agent in removing tissue debris remaining on the root canal walls.

Indirect longitudinal cytotoxicity of root canal sealers on L929 cells and human periodontal ligament fibroblasts

The cytotoxicity of two root canal sealers was evaluated in vitro. The powder components of both sealers, mainly zinc, were the same. The liquid for one sealer, Canals, was clove oil (included eugenol in more than 80%) and other materials. For the other, Canals-N, the liquid was composed of higher fatty acids and glycol. The experiments included two cell lines, heteroploid L929 mouse fibroblasts and diploid human periodontal ligament fibroblasts. Cytotoxicity was assessed using the radiochromium release method with 4-h exposure time. The assay involved using insert chambers in multiwell arrays to produce indirect contact of materials with the cell monolayer at a controlled distance of approximately 1 mm. This model also allowed for the longitudinal study of the same material sample to assess time-dependent changes in toxicity. Freshly mixed Canals was highly toxic (p < 0.01) to both cell lines. On and after 24 h of setting no toxicity was detected. At no time could cytotoxicity be observed when experimenting with Canals-N. These results indicate that both materials have a low content of water diffusible toxic components. Substituting eugenol can further decrease the toxicity of the sealer.

Reduced cytotoxicity of a root canal sealer through eugenol substitution

The cytotoxicity of two zinc oxide root canal sealers was investigated in vitro. The sealers were freshly mixed and set for 24 and 168 h. The sealers had identical powders but different liquid components. One (Canals) used eugenol, while the other (Canals-N) used fatty acids. L929 cells were incubated for 4 and 24 h in direct contact with the materials or with an eluate of the materials. The toxicity was evaluated using the radiochromium release assay. In the direct exposure assay, both sealers were cytotoxic when freshly prepared or after 24 h of setting. After 1 wk of setting, Canals was still toxic, while Canals-N was not significantly different from the control in the 4-h assay. In the elution assay the materials showed very low cytotoxicity. Only the eluate from freshly prepared Canals was clearly cytotoxic after 24 h. The liquid of Canals-N was clearly less cytotoxic than liquid from Canals. The results showed that the cytotoxicity of a root canal sealer can be reduced by replacing eugenol with fatty acids.

Biochemical Gas Sensors (Biosniffers) Using Forward and Reverse Reactions of Secondary Alcohol Dehydrogenase for Breath Isopropanol and Acetone as Potential Volatile Biomarkers of Diabetes Mellitus

This study describes two biosniffers to determine breath acetone and isopropanol (IPA) levels and applies them for breath measurement in healthy subjects and diabetic patients. Secondary alcohol dehydrogenase (S-ADH) can reduce acetone and oxidize nicotinamide adenine dinucleotide (NADH to NAD+) in a weak acid environment. NADH can be excited by 340 nm excitation lights and subsequently emit 490 nm fluorescence. Therefore, acetone can be measured by the decrease in NADH fluorescence intensity. S-ADH can also oxidize IPA and reduce NAD+ to NADH when it is in an alkaline environment. Thus, IPA can be detected by the increase of fluorescence. The developed biosniffers show rapid response, high sensitivity and high selectivity. The breath acetone and IPA analysis in healthy subjects shows that the mean values were 750.0 ± 434.4 ppb and 15.4 ± 11.3 ppb. Both acetone and IPA did not show a statistical difference among different genders and ages. The breath acetone analysis for diabetic patients shows a mean value of 1207.7 ± 689.5 ppb, which was higher than that of healthy subjects (p < 1 × 10-6). In particularly, type-1 diabetic (T1D) patients exhaled a much higher concentration of acetone than type-2 diabetic (T2D) patients (p < 0.01). The breath IPA also had a higher concentration in diabetic patients (23.1 ± 20.1 ppb, p < 0.01), but only T2D patients presented a statistical difference (23.9 ± 21.3 ppb, p < 0.01). These findings are worthwhile in the study of breath biomarkers for diabetes mellitus diagnosis. Additionally, the developed biosniffers provide a new technique for volatolomics research.

Resin–Dentin Bonding Interface After Photochemical Surface Treatment

OBJECTIVE The aim of this study is to elucidate the structure of the resin-dentin interface formed by photochemical dentin treatment using an argon fluoride (ArF) excimer laser. BACKGROUND DATA The ArF excimer laser processes material by photochemical reaction without generating heat, while also providing surface conditioning that enhances material adhesion. In the case of bonding between resin and dentin, we demonstrated in a previous study that laser etching using an ArF excimer laser produced bonding strength comparable to that of the traditional bonding process; however, conditions of the bonding interface have not been fully investigated. METHODS A dentin surface was irradiated in air with an ArF excimer laser followed by bonding treatment. Cross sections were observed under light microscope, transmission electron microscope (TEM), and scanning electron microscope, then analyzed using an energy dispersive X-ray spectroscope (EDS): EDS line profiles of the elements C, O, Si, Cl, P, and Ca at the resin-dentin interface were obtained. RESULTS The density of C in resin decreased as it approached the interface, reaching its lowest level within the dentin at a depth of 2 μm from the resin-dentin interface on EDS. There was no hybrid layer observed at the interface on TEM. Therefore, it was suggested that the resin monomer infiltrated into the microspaces produced on the dentin surface by laser abrasion. CONCLUSIONS The monomer infiltration without hybrid layer is thought to be the adhesion mechanism after laser etching. Therefore, the photochemical processes at the bonding interface achieved using the ArF excimer laser has great potential to be developed into a new bonding system in dentistry.

Effects of ArF Excimer Laser Irradiation of Dentin on the Tensile Bonding Strength to Composite Resin

OBJECTIVE The purpose of the study was to evaluate the effects of argon fluoride (ArF) excimer laser irradiation on the tensile bonding strength (TBS) of dentin to composite resin. BACKGROUND DATA Dental lasers use a photothermal process, which potentially entails risk of tissue damage caused by heat affecting the bond strength of resins. The ArF excimer laser functions by a photochemical process in which the energy of photons directly cuts covalent bonds in molecules without generating heat. METHODS Twenty extracted human molars were sectioned perpendicularly to the tooth axis to expose a flat dentin surface. The surfaces were treated with various combinations of ArF excimer laser irradiation, primer treatment, and bonding treatment. After composite resin was built up on the treated dentin surface, specimens with a 1×1 mm bonding interface were prepared and subjected to TBS tests. Treated dentin surfaces were also observed using transmission electron microscopy (TEM). RESULTS Specimens that underwent laser irradiation followed by bonding treatment had a TBS that did not differ significantly from that of specimens that received conventional treatment, with or without priming. TEM observations showed sectioned and dispersed collagen matrix in the hybrid layer after laser irradiation, priming, and bonding, but no hybrid layer after laser irradiation and bonding at the treated dentin surface. CONCLUSIONS The TBS of conditioning with ArF excimer laser irradiation was identical to that with conventional treatment when bonding was used. The bonding mechanism with the ArF irradiation differed from that of conventional bonding depending upon dentin hybridization.