Noriko Hiraishi

Water Concentration in Self-etching Primers Affects their Aggressiveness and Bonding Efficacy to Dentin

Water is required to ionize acid resin monomers for demineralization of tooth substrates. We tested the null hypothesis that altering the water concentration in two-step self-etching primers has no effect on their aggressiveness and bonding efficacy to dentin. Five experimental self-etching primers were prepared with resin-water-ethanol volume ratios of 9-0-1, 8-1-1, 7-2-1, 5-4-1, and 3-6-1. They were applied to smear-layer-covered dentin, followed by a bonding resin and composite build-ups for microtensile bond testing and TEM examination of tracer penetration. Increasing water concentration from 0–60 vol% improved acidic monomer ionization that was manifested as increasing hybrid layer thickness. However, significantly higher bond strength was observed in the 7-2-1 group, with minimal nanoleakage in the corresponding hybrid layer. When self-etching primers are formulated, a balance must be achieved to provide sufficient water for adequate ionization of the acidic monomers, without lowering the resin concentration too much, to optimize their bonding efficacy to dentin.

Effect of 2% chlorhexidine on dentin microtensile bond strengths and nanoleakage of luting cements.

OBJECTIVES The aim of this study was to investigate the effect of pre-treatment by chlorhexidine on the microtensile bond strength (mTBS) of resin cements and nanoleakage at the resin-dentine interfaces. METHODS Cylindrical composite blocks were luted to human dentine using resin cements (RelyX ARC, 3M ESPE: ARC; Panavia F, Kuraray Medical Inc.: PF; RelyX Unicem, 3M ESPE: UN) with/without pre-treatment by 2% chlorhexidine digluconate (CAVITY CLEANSER, Bisco, Inc., Schaumburg, IL, USA). CAVITY CLEANSER was applied on the acid etched dentine for 60s in the ARC group, and on smear layer-covered dentine in the PF and UN groups. After storage in water for 24h, the bonded teeth were sectioned into 1mm thick slabs and further into 0.9mm x 0.9mm beams. After immersion in water or ammoniacal silver nitrate for 24h, the beams were stressed to failure in tension. The fractured surfaces were examined by field-emission scanning electron microscopy (FE-SEM) using backscattered electron mode. The silver-stained slabs were used to examine nanoleakage within the bonded interface by FE-SEM. RESULTS The resin cement and chlorhexidine treatment had significant effects (p<0.0001) on mTBS; while the storage media had no significant effect (p=0.435). The mTBS of ARC was significantly higher than the other cements. Chlorhexidine reduced mTBS and produced pronounced nanoleakage when PF and UC were luted to dentine. CONCLUSIONS Pre-treatment with chlorhexidine affected the integrity of dentine bonding with PF and UC, while there was no adverse effect on coupling of ARC.

Chlorhexidine release and water sorption characteristics of chlorhexidine-incorporated hydrophobic/hydrophilic resins.

OBJECTIVES The aim of this study was to evaluate chlorhexidine release from unfilled non-solvated methacrylate-based resins of increasing hydrophilicity and to examine relationships among Hoys solubility parameters, water sorption, solubility and the rate of chlorhexidine release. METHODS Resin discs were prepared from light-cured, experimental resin blends (R1, R2, R3, R4 and R5) containing 0.0, 0.2, 1.0 and 2.0 wt.% chlorhexidine diacetate (CDA). Discs were immersed in distilled water at 37 degrees C, and mass changes were recorded at different periods. Spectral measurements were made to follow change in optical densities of storage solution to examine chlorhexidine release kinetics. After a 28-day period, water sorption, solubility, and the cumulative chlorhexidine release were obtained. Additionally, antibacterial study was performed by observing the presence of inhibition zone against Streptococcus mutans. RESULTS The most hydrophilic resin (R5) exhibited the highest chlorhexidine release rate. The most hydrophobic resin (R1) exhibited the lowest rate. However, no inhibition zone was produced by any specimens stored in water for 2 weeks. The addition of CDA increased solubility significantly but had no effect on water sorption. Significant positive correlations were seen between water sorption and the cumulative chlorhexidine release. SIGNIFICANCE Chlorhexidine release from resins may be related to water-induced swelling, which in turn is enhanced by the hydrophilicity of cured polymer matrix.

Tubular Occlusion Prevents Water-treeing and Through-and-Through Fluid Movement in a Single-bottle, One-step Self-etch Adhesive Model

Water entrapment occurs at resin-dentin interfaces of one-step self-etch adhesives. We hypothesized that by preventing water fluxes from dentin, any water entrapment would be attributed to incomplete removal of adhesive solvents. We tested this hypothesis by bonding to transparent carious dentin containing occluded dentinal tubules. An experimental single-bottle, one-step self-etch adhesive was applied to flat surfaces of caries-affected dentin surrounded by sound dentin, with or without pulpal pressure. Resin-dentin interfaces were examined with TEM after silver-impregnation. Although caries-affected dentin was highly porous, adhesive layers were devoid of silver deposits when tubules were occluded. Conversely, variable extents of water-treeing and water-droplets were identified from adhesive layers in bonded sound dentin. Water-treeing and water-droplet formation, being manifestations of evaporative and convective water fluxes, can be eliminated during bonding to occluded transparent carious dentin. However, the highly porous nature of this clinically relevant substrate after bonding may lead to potentially undesirable consequences.

Effect of temperature on water sorption and solubility of dental adhesive resins

OBJECTIVE This study examined the effect of temperature on water sorption and solubility characteristics of four commercial dental adhesives. The null hypothesis tested was that temperature has no effect on the water sorption and solubility characteristics of these adhesives. METHODS The tested materials were: three-step etch-and-rinse (All-Bond 2, AB), two-step etch-and-rinse (One-Step, OS), two-step self-etch (Clearfil SE Bond, SE) and one-step self-etch (Clearfil S3 Bond, S3) adhesives. Seven resin disks (6mm in diameterx1mm in thickness) were prepared from each tested material and were stored in deionized water at 23 degrees C, 37 degrees C and 55 degrees C. Water sorption and solubility of the resin disks were measured before and after water immersion and desiccation following two consecutive sorption and desorption cycles. The water sorption and solubility values obtained were analyzed using two-way ANOVA and Tukeys multiple comparison tests. The relationships between maximum water sorption, solubility and kinetics of water diffusion with temperature were evaluated by means of Pearson correlation statistic. RESULTS OS exhibited the highest water sorption and solubility values in the second sorption-desorption cycle at 55 degrees C (p<0.001). This is followed by S3, SE and AB with no significant difference between SE and AB. Significant positive correlations were observed between maximum water sorption (r=0.307, p<0.01), solubility (r=0.244, p<0.05), water sorption (r=0.651, p<0.001) and desorption (r=0.733, p<0.001) diffusion coefficients (obtained using Ficks law of diffusion) with temperature in the second cycle. SIGNIFICANCE High temperatures increased water sorption of simplified adhesives. Such water sorption may contribute to the failure of resin-dentin bonds.

Effect of pulpal pressure on the microtensile bond strength of luting resin cements to human dentin

OBJECTIVES The objectives of this study were to examine the effect of pulpal pressure on the microtensile bond strength (mTBS) of luting resin cements to human dentin and the permeability of dentin surfaces pre-treated with an adhesive and a self-etching primer. METHODS Cylindrical composite blocks were luted with resin cements (RelyX ARC, 3M ESPE: ARC; Panavia F, Kuraray Medical Inc.: PF; RelyX Unicem, 3M ESPE: UN) in the absence or presence of simulated pulpal pressure. The application of Adper Single Bond 2 (3M ESPE) and ED primer 2.0 (Kuraray) was performed under 0 cm H(2)O. After each resin cement was applied, the pulpal pressure group was subjected to 20 cm H(2)O of hydrostatic pressure for 10 min during the initial setting period. Testing for mTBS was performed on 0.9 mm x 0.9 mm sectioned beams after 24h water-storage. Scanning electron microscopy was performed to investigate the fractured surfaces after mTBS testing and additional dentin surfaces that were treated by an etchant, ED primer 2.0 and UN. Fluid permeability was measured on dentin surfaces that were applied with Adper Single Bond 2 and ED primer 2.0. RESULTS Application of pulpal pressure reduced mTBS significantly in groups ARC and PF. Porous bonding interfaces due to water permeability through the cured adhesive were observed on fractured surfaces. Dentin surfaces that were applied with the adhesive and the primer were more permeable than smear layer-covered dentin. The mTBS of UN was significantly lower than ARC and PF regardless of the absence/presence of pulpal pressure. SIGNIFICANCE Fluid permeation during the initial setting period deteriorated the bonding quality of resin cements.

Effect of artificial saliva contamination on pH value change and dentin bond strength

OBJECTIVE This study was to examine the effect of artificial saliva contamination on pH change of the dentin surface and the micro-shear bond strength (MSBS) of the two bonding systems to contaminated dentin. METHODS Fifty-six human dentin disks were tested with two resin bonding systems: a self-etching primer system, Clearfil SE Bond (Kuraray Medical Inc., Tokyo, Japan), and a one-bottle adhesive system, Single Bond (3M-ESPE, St. Paul, MN). Dentin surfaces were conditioned with the self-etching primer (primer) or phosphoric acid (etchant) and divided into four groups: conditioning without contamination (conditioning), contamination with artificial saliva (contamination), re-conditioning the contaminated dentin (re-conditioning), water-rinsing the contaminated dentin and re-conditioning (rinsing and re-conditioning). The pH change on the dentin surface was measured using a pH-imaging microscope (SCHEM-100, Horiba Ltd, Kyoto, Japan) to estimate the acid-base characteristics of the conditioned and contaminated dentin surface. The MSBS to the dentin was examined after storage in distilled water at 37 degrees C for 1 week. RESULTS The pH of intact dentin surfaces was 6.9. Conditioning with the primer and etchant decreased the pH to 5.4 and 5.9, respectively. Saliva contamination increased the pH slightly, and re-conditioning decreased the pH again. The MSBS of the two bonding systems decreased after contamination. Re-priming restored the MSBS to control values, while re-etching did not. Rinsing and re-priming produced a reduction in MSBS, and rinsing and re-etching did not increase the MSBS. SIGNIFICANCE The conditioning and saliva contamination changed the pH value of dentin surface. The MSBS decreased after contamination; however, re-priming with SE Bond primer was an adequate treatment to restore the bond strength.

The inhibitory effect of proanthocyanidin on soluble and collagen-bound proteases.

OBJECTIVE This study evaluated the inhibitory effect of proanthocyanidin (PA), a natural collagen cross-linker, on soluble and matrix-bound proteases, which are responsible for progressive degradation of exposed collagen fibrils within the hybrid layer and resin-dentine bond failure over time. METHODS The inhibitory effects of PA (1%, 2%, 3%, 4.5% and 6%) on soluble recombinant matrix metalloproteinases (MMP-2, -8 and -9) and cysteine cathepsins (cathepsin B and K) were evaluated using MMP and cysteine cathepsins fluorometric assay kits. Chlorhexidine (CHX) was used as an inhibitor control. The effect of PA on endogenous matrix-bound proteases was examined by determining the change in dry mass of demineralized dentine beams and solubilized collagen peptides over 30 days. Two-way ANOVA and Tukey multiple comparison tests were used to analyze the effect of PA and proteases on the percentage inhibition of soluble proteases (α=0.05). Kruskal-Wallis one-way ANOVA and Dunns multiple comparison tests were used to analyse the effect of PA on loss of dry mass and hydroxyproline content over time (α=0.05). RESULTS Proanthocyanidin inactivated more than 90% of soluble recombinant MMP-2, -8 and -9 and around 75-90% of cysteine cathepsin B and K, which was significantly higher than CHX (P<0.05). The inhibition of endogenous proteases by PA increased in a dose-dependent manner. The loss of dry mass and hydroxyproline release in the medium over time was the lowest in dentine beams pretreated with PA

Clinical Trials of Silver Diamine Fluoride in Arresting Caries among Children A Systematic Review

This review aims to investigate the clinical effectiveness of silver diamine fluoride (SDF) in arresting dental caries among children. A systematic search of publications was conducted with the key words “silver diamine fluoride,” “silver diammine fluoride,” “silver fluoride,” “diamine silver fluoride,” or “diammine silver fluoride” as well as their translation in Chinese, Japanese, Portuguese, and Spanish in 7 databases: PubMed (English), Embase (English), Scopus (English), China National Knowledge Infrastructure (Chinese), Ichushi-web (Japanese), Biblioteca Virtual em Saude (Portuguese), and Biblioteca Virtual en Salud Espana (Spanish). Duplicated publications were deleted. The title and abstract were screened and irrelevant publications were excluded. The full text of the remaining publications was retrieved. Prospective clinical studies of SDF that reported a caries-arresting effect among children were included. Meta-analysis was performed for quantitative analysis. A total of 1,123 publications were found, including 19 publications of clinical trials. Sixteen clinical trials studied the caries-arresting effect on primary teeth, and 3 clinical trials were on permanent teeth. Fourteen studies used 38% SDF, 3 used 30% SDF, and 2 used 10% SDF. Meta-analysis was performed on extracted data from 8 studies using 38% SDF to arrest caries in primary teeth. The overall percentage of active caries that became arrested was 81% (95% confidence interval, 68% to 89%; P < 0.001). Apart from staining the arrested lesion black, no significant complication of SDF use among children was reported. SDF was commonly used at 38%. It was effective in arresting dentine caries in primary teeth among children. Knowledge Transfer Statement: This systematic review found that 38% silver diamine fluoride (SDF) can effectively arrest caries among children. SDF treatment is noninvasive and easily operated. It can be a promising strategy to manage dental caries in young children or those who have special needs.

In vitro evaluation of plant-derived agents to preserve dentin collagen.

OBJECTIVE Biomodification of dentin by a natural crosslinker has been recommended to improve a mechanical property of demineralized dentin. This study investigated the effect of various plant-derived agents (hesperidin, proanthocyanidin, epigallocatechin gallate and genipin) on the stability of dentin collagen matrix to resist collagenase degradation. METHODS The dentin specimens were treated with glutaraldehyde (0.5% and 5.0%) and each plant-derived test solution (0.5%). They were subjected to ultimate tensile strength (UTS) and swelling ratio measurements. Demineralized human dentin powder was incubated with 0.02%, 0.1% and 0.5% of each test agent and followed by bacterial collagenase digestion. The extent of collagen degradation was investigated using hydroxyproline assay. RESULTS The UTS and swelling ratio measurements revealed that the mechanical property of dentin was improved by the use of these natural agents. The greatest reduction in collagen degradation was shown following the use of hesperidin, proanthocyanidin, and epigallocatechin gallate at 0.5%. SIGNIFICANCE The use of hesperidin, proanthocyanidin, and epigallocatechin gallate could improve the mechanical properties of collagen and resist enzymatic degradation, leading to functional repair of pathological dentin lesion.