Effect of the application of dentin primers and a dentin bonding agent on the adhesion between the resin-modified glass-ionomer cement and dentin.

OBJECTIVES: This study was designed to evaluate the influence of the application of dentin primer and/or dentin bonding agent on the adhesion of a resin-modified glass-ionomer cement to dentin. METHODS: Bovine dentin was pretreated with Dentin Conditioner or EDTA 3-2 solution, primed by an experimental dentin primer, and applied with a dentin bonding agent. A resin-modified glass-ionomer cement, Fuji II LC, was then adhered to the dentin. The tensile bond strength between the light-cured glass-ionomer cement and the pretreated dentin was measured. The components of the experimental dentin primers were 2-hydroxyethyl methacrylate (HEMA), glyceryl methacrylate (GM) and a water-soluble photo-polymerization initiator, 2-hydroxy-3-(3,4-dimethyl-9-oxo-9H-thioxanthen-2-yloxy)-N,N, N-trimethyl-1- propanaminium chloride (OTX). Significant differences in the data were examined by an analysis of variance and Scheffe's test for multiple comparisons between the means at p = 0.05. RESULTS: A significantly higher mean bond strength between the Fuji II LC and dentin was obtained by EDTA 3-2 pretreatment, QTX/GM priming, and LB Bond application. This value was comparable with that obtained with the resin composite system. Scanning electron microscopy observation showed the formation of a hybrid layer with a thickness of 1-1.5 microns. SIGNIFICANCE: The data obtained in this investigation suggest that the adhesion of Fuji II LC to dentin is closer to that provided by a resin composite system than to that of conventional glass-ionomer cements.     

Improved adhesion of a glass ionomer cement to dentin and enamel

A study has been made on improving the adhesion of a glass ionomer cement by the chemical treatment of dentin and enamel surfaces. The most effective surface conditioners were high molecular weight substances containing a multiplicity of functional groups capable of hydrogen bonding. Low molecular weight chelating agents which dissolve calciferous material and dramatically alter the surfaces of enamel and dentin are less effective.     

An in vitro study of dentin hypersensitivity using calcium phosphate cement

Calcium phosphate remineralizing slurry (CPRS), consisting of an equimolar mixture of tetracalcium phosphate (TTCP) and dicalcium phosphate dihydrate (DCPD), has previously been shown to form hydroxyapatite (HAp) spontaneously at physiological pH. Since considerable amounts of HAp may be formed in situ by CPRS, it may be effective for desensitizing hypersensitive dentin by obturating exposed dentinal tubule openings. In the present study, the effects of topically applied CPRS to etched dentin surfaces were investigated. The samples were randomly divided into 3 groups: (1) the control specimens were soaked in a saliva-like (SL) solution (2) the specimens received either 10-minute or 1-hour treatment with CPRS and (3) the specimens were treated with viscous CPRS, containing carboxymethyl cellulose (CMC) gel, for 8 hours. The SEM observations revealed that the control specimens were covered with a thin layer of plate-like crystals indicative of octacalcium phosphate (OCP). No significant penetration of the crystals into the dentinal tubules was detected. In CPRS group, the 10-minute treatment produced a 10 to 15 microns thick dense layer of precipitation consisting of needle-, rod-, and plate-like crystals. The 1-hour treatment produced a similar precipitation except that the crystals were mostly needle-like. A cross section view of the samples indicated remarkable penetration of the crystals into the tubules, thus providing significant obturation of tubule openings. Samples in the CMC-gel group were covered with an even more impervious layer of precipitation consisting of crystals of a variety of morphologies.(ABSTRACT TRUNCATED AT 250 WORDS)     

The use of acoustic microscopy to study the mechanical properties of glass-ionomer cement.

OBJECTIVES: The aim of the study was to investigate the relationship between microstructure, acoustic and mechanical properties of hardened dental cement samples, prepared with different powder/water ratios. METHODS: Glass-ionomer dental cement samples, prepared with a standard amount of cement powder and different amounts of water have been examined after being hardened. Surface microstructure and ultrasound, longitudinal and shear velocities were obtained with a scanning acoustic microscope. Conditional effective elastic modulus and Poisson's ratio have been calculated using longitudinal and shear sound velocity values. Then on the same samples elastic modulus and microhardness have been determined by standard tests. Additional samples have been used to determine compressive strength. RESULTS: Density; conditionally instantaneous elastic modulus; high-elasticity modulus and compression strength of the samples decrease when large amounts of water were used for their preparation. At the same time porosity and microhardness of the cement matrix increase. Acoustic parameters and parameters of elasticity, calculated on the basis of sound velocity, demonstrated changes, similar to those obtained in standard mechanical tests. SIGNIFICANCE: The established relation between microstructure, acoustic and mechanical parameters demonstrated a high capacity of acoustic microscopy application for non-destructive characterization of dental materials. A particular advantage of the acoustic microscopy is the opportunity to evaluate microstructure and mechanical properties on the same sample.     

Scanning electron microscopy study of the adhesion of Prevotella nigrescens to the dentin of prepared root canals

The purpose of this study was to evaluate the effect of the presence or absence of amorphous, irregular smear layers on the adhesion of Prevotella nigrescens, to the dentin of the root canal by using scanning electron microscopy (SEM). Human incisors extracted within 7 days, with no cavities, no fractures, and no evidence of calcification of the canal, were selected. After cutting the crown portion at the CEJ, root canal preparation was undertaken by using a modified crown-down technique with Profile and Gates Glidden drills. Ten milliliters of physiologic saline solution (groups 1 and 4), 10 ml of 3.5% NaOCl (groups 2 and 5), or 10 ml of NaOCl and 10 ml of 0.5 M EDTA (groups 3 and 6) were used as irrigation solution while preparing the canal. After vertical sectioning and ethylene oxide gas sterilization, samples (groups 1, 2, and 3) were immersed in brain-heart infusion broth with yeast extract, hemin, and menadione, inoculated with P. nigrescens (ATCC 33563), and incubated for 3 h at 37 degrees C. All samples were prepared for and observed with SEM. The data were analyzed by using t test and one-way ANOVA. Smear layer was observed to cover the entire root canal surface after root canal preparation. Smear layer was removed and the entrances of dentinal tubules opened widely after applying 3.5% NaOCl and 0.5 M EDTA. A significantly greater number of bacteria were found to adhere to those teeth in which a smear layer was present (p < 0.05). Given that the smear layer produced during root canal preparation promoted adhesion and colonization of P. nigrescens to the dentin matrix, it might also increase the likelihood of canal reinfection.     

Preservation of microelastic properties of dentin and tooth enamel in vitro--a scanning acoustic microscopy study.

OBJECTIVES: The aim of this study was to examine the influence of storage media on the elastic properties of dentin and tooth enamel with respect to the storage period. Several reports suggest that saline and other aqueous solutions may induce chemical reactions and the dissolution of minerals, which in turn may cause alterations of elastic tissue properties. METHODS: Three non-erupted human wisdom teeth were extracted and divided in three slices. Sections were stored in three different media for a maximum period of 21 days. During this time all sections were inspected by time-resolved 50-MHz scanning acoustic microscopy. RESULTS: Storage in saline solution resulted in a progressive decrease of the acoustic impedance up to 70% in dentin but not in enamel tissue. Hank's balanced salts solution and artificial saliva appeared to maintain the elastic properties of dentin and enamel during the entire time of storage. The measurements of surface wave velocities did not show significant differences. High resolution (900 MHz) inspection of sections cut perpendicular to the surface exposed to the storage media for 21 days revealed a progressive increase of impedance in dentin up to the initial values at a depth of approximately 300 microm. SIGNIFICANCE: These findings suggest that quantitative SAM is a suitable tool for assessing surface and sub-superficial elastic properties of tooth tissue.     

A new noninvasive model to study the effectiveness of dentin disinfection by using confocal laser scanning microscopy

Introduction

The present study was designed to develop a standardized model for quantification of the effectiveness of dentin disinfection by different antibacterial solutions including a new root canal irrigant, Qmix.

Methods

Dentinal tubules from the root canal side in semicylindrical dentin specimens were infected with Enterococcus faecalis by centrifugation of the bacterial suspension into the tubules. Scanning electron microscopy (SEM) was used to verify the presence of bacteria in dentin. The outer side of dentin pieces was closed, and the specimens were subjected to 1-minute and 3-minute exposure to sterile water, 1%, 2%, 6% sodium hypochlorite (NaOCl), 2% chlorhexidine (CHX), and Qmix. Confocal laser scanning microscopy (CLSM) and viability staining were used to quantitatively analyze the proportions of dead and live bacteria inside dentin.

Results

A heavy invasion by E. faecalis was detected by both SEM and CLSM throughout the dentinal tubules. The amount of dead cells in dentin increased with increasing NaOCl concentration and time of exposure (P < .05). Qmix was equally effective in killing bacteria in dentin as 6% NaOCl; more than 40% and 60% of the bacteria were killed by both at 1 minute and 3 minutes, respectively. One percent and 2% NaOCl and 2% CHX killed 20%–30% and 30%–40% bacteria after 1 and 3 minutes of exposure, respectively, with no statistically significant differences among the 3 agents (P > .05). In the control group, which was treated with sterile water, only 4%–6% of the bacteria were dead.

Conclusions

Centrifugation helped to create a heavy, evenly distributed infection deep into the dentinal tubules. The new model made it possible to compare the effectiveness of several disinfecting solutions in killing bacteria inside dentin by a noninvasive CLSM method.     

Study on adhesion mechanism of MMA-TBBO resin to dentin. A model experiment using decalcified dentin

As a model experiment to understand the mechanism of adhesion of the MMA-TBBO resin to dentin, MMA-TBBO was polymerized using a decalcified dentin sheet treated with aqueous citric acid (CA) solutions of copper fluoride (CF), ferric fluoride (FF), or ferric chloride (FC), which are usually used as treating agents in the bonding of the resin to dentin. The curing time for MMA-TBBO resin was considerably reduced on the decalcified dentin sheet treated with FC-CA, CF-CA or FF-CA at an appropriate concentration. Polymerization of MMA-TBBO resin was accelerated in the presence of a fluoride ion. Molecular weight of PMMA depended on the site of polymerization; PMMA polymerization inside the decalcified dentin sheet gave the highest and that outside gave the lowest molecular weight in the presence of an appropriate amount of ferric or cupric ion. These results suggested that ferric compounds adsorbed to decalcified dentin are involved in the polymerization of MMA and thus will influence the bond strength of the MMA-TBBO resin to dentin.     

Bond strength of a resin cement to dentin using the resin coating technique

The aim of this study was to evaluate the bond strength of a resin cement to dentin using different adhesive systems (AS) in the presence or absence of a low-viscosity composite liner (Protect Liner F - PLF) applied over the bonded dentin. The adhesive systems selected were: AdheSE/Vivadent (AD); Clearfil Protect Bond/Kuraray (CP); One-Up Bond F/Tokuyama (OU); Single Bond/3M ESPE (SB); Tyrian SPE/One-Step Plus/Bisco (TY); Xeno III/Dentsply (XE) and Unifil Bond/GC (UN). After removing the labial and lingual enamel surfaces of bovine incisors, dentin fragments were prepared and randomly divided into 15 groups (n = 8). The dentin substrates were bonded with the AS and the PLF was applied or not before application of the resin cement (Panavia F, Kuraray). In the control group, the ED Primer (ED) and the resin cement without PLF were used. The AS, PLF and resin cement tested were used according to the manufacturers' instructions, and all treated dentin surfaces were temporized. After water storage for one week, three cylinders of resin cement were applied to each bonded dentin surface, using tygon tubing molds. The specimens were subjected to micro-shear testing and the data were statistically analyzed (two-way ANOVA, Tukey and Dunnett tests, p < 0.05). The observed mean shear bond strengths in MPa were: ED: 20.2 +/- 2.3; AD: 30.3 +/- 6.5; CP: 25.3 +/- 4.4; OU: 28.3 +/- 6.6; SB: 25.6 +/- 6.9; TY: 24.5 +/- 2.5; XE: 17.3 +/- 3.4; UN: 28.4 +/- 6.2; AD+PLF: 32.8 +/- 4.1; CP+PLF: 29.9 +/- 3.9; OU+PLF: 34.1 +/- 4.1; SB+PLF: 29.5 +/- 8.2; TY+PLF: 29.2 +/- 3.9; XE+PLF: 32.8 +/- 6.7; UN+PLF: 32.2 +/- 4.5. The bond strength of the resin cement to dentin using the tested AS was increased when the low-viscosity composite liner was applied.     

A study of glass-ionomer cement and its interface with enamel and dentin using a low-temperature, high-resolution scanning electron microscopic technique.

This report describes a method of immobilizing the water contained in glass-ionomer cement and dental hard tissues and stabilizing the delicate organic component of dentin. With this method, the intact interface between glass-ionomer and dental hard tissues can be observed under scanning electron microscope with few of the artifacts that are caused by the desiccation associated with conventional scanning electron microscopic studies. There was a distinct zone of interaction between the glass-ionomer cement and enamel and dentin. Under severe thermal stress, glass-ionomer cement failed cohesively, leaving an intact interface with enamel and dentin. Machine-mixed glass-ionomer cements displayed a high level of porosity. Some glass particles were separated from the matrix, and there was evidence that some are dislodged from the matrix during specimen preparation.     

Effect of polyacrylic acid treatment of dentin on adhesion of glass ionomer cement

This investigation measured the effect of polyacrylic acid treatment of dentin on adhesion of glass ionomer cement. The dentin was ground on paper no. 220 or no. 500 and treated with a polyacrylic acid solution of 10% or 25% for either 10 or 30 sec. The differences observed in the scanning electron microscope between the differently treated dentin surfaces were not reflected in the bond strength results. Only variations in surface texture due to different coarseness of grinding influenced the adhesion. For specimens ground on paper no. 220, pretreatment with polyacrylic acid enhanced adhesion of glass ionomer cement. Polyacrylic acid had no effect on bonding between glass ionomer cement and dentin ground on paper no. 500.     

The effect of thermocycling on the adhesion of self-etching adhesives on dental enamel and dentin

AIM: The aim of the present study was to investigate the effectiveness of one total-etch self-priming adhesive and two one-step self-etching adhesive systems on the adhesion of a resin composite to both dentin and enamel. The effect of thermocycling on the adhesion was also investigated. The null hypothesis tested was thermocycling would not affect bond strengths to enamel and dentin treated with self-etching adhesives or a total-etch adhesive. METHODS AND MATERIALS: Two single-step self-etching adhesives [Xeno III (XE3) and Prompt L-Pop (PP)] and one two-step total-etch adhesive system (Prime & Bond NT) (P&B NT) were used in this study. Thirty caries-free unrestored human third molars were used to make specimens of enamel and dentin. Different adhesives were applied on enamel and dentin surfaces according to the manufacturer's instructions then hybrid composite restorative material was condensed on the surface using a mold. The bonded specimens were stored in distilled water at 37 masculineC for 24 hours before being tested. Half of the bonded specimens were tested for shear bond strength without thermocycling. The other half of the test specimens were thermocycled using a thermocycling apparatus in water baths held at 5 masculineC and 55 masculineC with a dwell time of one minute each for 10,000 cycles prior to shear testing. The mean shear bond strength before and after thermocycling was calculated, and the results were subjected to two-way analysis of variance (ANOVA) and repeated measure design to show the interaction between different materials and different times. RESULTS: The results showed shear bond strength on both enamel and dentin of the total-etch adhesive and the self-etching adhesives decreased after the specimens were subjected to thermocycling. CONCLUSIONS: The null hypothesis tested "thermocycling would not affect bond strengths treated with self-etching adhesives" was rejected. Furthermore, the study revealed the following: 1. The shear bond strength to both enamel and dentin of the total-etch adhesive and the self-etching adhesives decreased after the specimens were subjected to thermocycling. 2. XE3 achieved the highest bond strength to both enamel and dentin (26.994+/-1.17 and 25.22+/-1.26, respectively). 3. XE3 showed even better bonding after thermocycling to enamel and dentin than the total-etching system or PP. 4. Although PP bonded to enamel showed lower shear bond strength value than XE3, it has durable bond strength even after thermocycling.     

Effects of CO2 laser irradiation on microstructure of dentin, dentin adhesion of resin composites and dental pulp

This study was designed to investigate the effects of CO2 laser irradiation on the dentin microstructure, dentin adhesion of resin composites and dental pulp. An artificial caries lesion was produced on the bovine dentin, immersing in 0.4 mol/l acetic acid. Three kinds of dentin (sound dentin, outer or inner caries dentin) surfaces were pretreated by the laser irradiation, acid etching or no-treatment. The tensile adhesion-test of these pretreated dentin surfaces was performed. The changes in these dentin surfaces by the various treatments including the laser irradiation and the resin-dentin interfaces were examined by the SEM. Furthermore, histopathological study using monkey teeth was conducted to examine the effect of the laser irradiation on the dental pulp. Histopathological changes in the pulp were found at 3 and 90 days after the operation. The findings were as follows: 1. The outer highly and inner partially decalcified layers produced in the bovine dentin were each approximately 200 microns in thickness. 2. The bond strength of the resin composites to the laser pretreated sound dentin was approximately 40 kgf/cm2. Those of the laser pretreated outer and inner decalcified dentins were about 60 kgf/cm2. 3. At the initial stage, the laser irradiation (output power 3W : irradiation period 0.5 second) exhibited a slight pulpal response, producing irritation dentin formation in the latter stage without any severe histopathological change.