Chitosan: effect of a new chelating agent on the microhardness of root dentin

The effect of solutions of 0.2% chitosan, 15% EDTA and 10% citric acid on the microhardness of root dentin was evaluated comparatively in this study. Thirteen sound human maxillary central incisors were selected and decoronated at the cementoenamel junction. Ten roots were set into rapid polymerization acrylic resin and the root/resin block was fitted to the cutting machine to obtain slices from the cervical third. The first slice was discarded and the second slice was divided into four quadrants. Each quadrant was used to construct a sample, so that 4 specimens were obtained from each root slice, being one for each chelating solution to be tested: 15% EDTA, 10% citric acid, 0.2% chitosan and distilled water (control). The specimens were exposed to 50 μL of the solution for 5 min, and then washed in distilled water. A microhardness tester (Knoop hardness) with a 10 g load was used for 15 s. Data were analyzed statistically by one-way ANOVA and Tukey-Kramer test (α=0.05). The other 3 roots had the canals instrumented and irrigated at the end of the biomechanical preparation with the test solutions, and then examined by scanning electron microscopy (SEM) for qualitative analysis. All solutions reduced the microhardness of root dentin in a way that was statistically similar to each other (p>0.05) but significantly different from the control (p>0.05). The SEM micrographs showed that the three solutions removed smear layer from the middle third of the root canal. In conclusion, 0.2% chitosan, 15% EDTA and 10% citric acid showed similar effects in reducing dentin microhardness.

Time-dependent effects of chitosan on dentin structures

Complete debridement with smear layer removal are essential measures for achieving a successful outcome of root canal treatment. The aim of this study was to evaluate the effects of chitosan at different concentrations on the removal of the smear layer and on dentin structure after 3 and 5 min of application. Twelve recently extracted maxillary canine teeth were instrumented using the crown-down technique and irrigated with 1% sodium hypochlorite. The specimens were distributed according to the time and concentration of the final irrigating solution: G1: 0.1% chitosan for 3 min; G2: 0.2% chitosan for 3 min; G3: 0.37% chitosan for 3 min; G4: 0.1% chitosan for 5 min; G5: 0.2% chitosan for 5 min; G6: 0.37% chitosan for 5 min. All samples were prepared for SEM analysis. G1 exhibited removal of the smear layer, but not the smear plugs. G2 showed visible and open tubules with slight erosion of the peritubular dentin. Cleaning in G3 was similar to that in G2, however, the erosive effect was greater. There was expansion of the diameter of the tubules in G4; and in G5 and G6, there was severe erosion with deterioration of dentin surface. In conclusion, 0.2% chitosan for 3 min appeared to be efficient for removing the smear layer, causing little erosion of dentin.

Chlorhexidine does not increase immediate bond strength of etch-and-rinse adhesive to caries-affected dentin of primary and permanent teeth

The aim of this study was to evaluate the effect of 2% chlorhexidine digluconate (CHX) on immediate bond strength of etch-and-rinse adhesive to sound (SD) and caries-affected (CAD) primary dentin compared with permanent dentin. Flat dentin surfaces from 20 primary molars (Pri) and 20 permanent molars (Perm) were assigned to 8 experimental groups (n=5) according to tooth type (Pri or Perm), dentin condition (SD or CAD - pH-cycling for 14 days) and treatment (control - C or 60 s application of 2% CHX solution after acid etching - CHX). The bonding system (Adper Single Bond 2) was applied according to manufacturer's instructions followed by resin composite application (Filtek Z250). After 24 h water storage, specimens with cross-section area of 0.8 mm² were prepared for being tested under microtensile test (1 mm/min). Data were submitted to ANOVA and Tukey's post hoc test (α=0.05). Failure mode was evaluated using a stereomicroscope at ×400. Treatment with CHX did not result in higher bond strength values than no pre-treatment (C groups), independently of tooth type. Primary teeth and caries-affected dentin showed significantly lower (p<0.05) bond strength means compared with permanent teeth and sound dentin, respectively. Predominance of adhesive/mixed failure was observed for all groups. CHX did not influence the immediate bond strength to sound or caries-affected dentin of primary and permanent teeth.

Effect of sodium hypochlorite and edta irrigation, individually and in alternation, on dentin microhardness at the furcation area of mandibular molars

The aim of this study was to evaluate the effect of irrigation regimens on dentin microhardness at the furcation area of mandibular molars, using sodium hypochlorite and ethylenediaminetetraacetic acid (EDTA), individually and in alternation. The occlusal surface and the roots of 20 non-carious extracted human permanent mandibular molars were cut transversally and discarded. The tooth blocks were embedded in acrylic resin and randomly assigned to 4 groups (n=5) according to the irrigating regimens: 1% NaOCl solution, 17% EDTA solution, 1% NaOCl and 17% EDTA and distilled water (control). Knoop microhardness of dentin at the furcation area was evaluated. Data were analyzed using one-way ANOVA and Tukey's multiple comparison tests (α=0.05). The results of this study indicated that all irrigation solutions, except for distilled water (control), decreased dentin microhardness. EDTA did not show a significant difference with NaOCl/EDTA (p>0.05), but showed a significant difference with NaOCl (p<0.01). EDTA and NaOCl/EDTA showed a maximum decrease in microhardness. The 17% EDTA solution, either alone or in combination with 1% NaOCl reduced significantly dentin microhardness at the furcation area of mandibular molars.

Scherhaftuntersuchung zu selbstkonditionierenden Adhäsiven an Schmelz und Dentin im Vergleich zu klassischen Adhäsivsystemen der vierten und fünften Generation

Mit einem Abscherverfahren wurde in vitro die Scherhaftung (SBS) von 4 kommerziell erhältlichen Adhäsiven der 4., 5. und 6. Generation (Optibond FL, Excite, Gluma Comfort Bond, Prompt L-Pop) und 7 experimentellen Einflaschen- (Capo E1, Capo E2, Capo Water, ENA) oder selbstkonditionierenden Adhäsiven (AC, AC+Desensitizer, Resulcin Aqua Prime N) an Schmelz/Dentin untersucht.Alle Adhäsive wurden entsprechend Herstellerangaben auf flache Schmelz-/Dentinflächen appliziert. Auf alle Adhäsivflächen wurden 3,5x2mm große Tetric Ceram Prüfkörper aufgebracht. Die Proben wurden vor Thermocycling 24h in Kochsalzlösung gelagert. Anschließend wurden die SBS-Werte gemessen.Das Mehrflaschensystem Optibond (33.2/34.4) zeigte signifikant (p<0.05) höhere Werte an Schmelz und Dentin als alle experimentellen Einflaschen- und alle selbstkonditionierenden Adhäsive. Die kommerziell erhältlichen 5. Generation Bondings tendieren zu höheren Werten als die selbstkonditionierenden Adhäsive, liegen aber unter denen der 4. Generation. AC (28.1/27.0)

Push-out bond strength of CAD/CAM-ceramic luted to dentin with self-adhesive resin cements

OBJECTIVES: This study evaluated the initial and the artificially aged push-out bond strength between ceramic and dentin produced by one of five resin cements. METHODS: Two-hundred direct ceramic restorations (IPS Empress CAD) were luted to standardized Class I cavities in extracted human molars using one of four self-adhesive cements (SpeedCEM, RelyX Unicem Aplicap, SmartCem2 and iCEM) or a reference etch-and-rinse resin cement (Syntac/Variolink II) (n=40/cement). Push-out bond strength (PBS) was measured (1) after 24h water storage (non-aged group; n=20/cement) or (2) after artificial ageing with 5000 thermal cycles followed by 6 months humid storage (aged group; n=20/cement). Nonparametrical ANOVA and pairwise Wilcoxon rank-sum tests with Bonferroni-Holm adjustment were applied for statistical analysis. The significance level was set at alpha=0.05. In addition, failure mode and fracture pattern were analyzed by stereomicroscope and scanning electron microscopy. RESULTS: Whereas no statistically significant effect of storage condition was found (p=0.441), there was a significant effect of resin cement (p<0.0001): RelyX Unicem showed significantly higher PBS than the other cements. Syntac/Variolink II showed significantly higher PBS than SmartCEM2 (p<0.001). No significant differences were found between SpeedCEM, SmartCem2, and iCEM. The predominant failure mode was adhesive failure of cements at the dentin interface except for RelyX Unicem which in most cases showed cohesive failure in ceramic. SIGNIFICANCE: The resin cements showed marked differences in push-out bond strength when used for luting ceramic restorations to dentin. Variolink II with the etch-and-rinse adhesive Syntac did not perform better than three of the four self-adhesive resin cements tested.

Synthesis of bis(3-{[2-(allyloxy)ethoxy]methyl}-2,4,6-trimethylbenzoyl)(phenyl)phosphine oxide - a tailor-made photoinitiator for dental adhesives

Because of the poor solubility of the commercially available bisacylphosphine oxides in dental acidic aqueous primer formulations, bis(3-{[2-(allyloxy)ethoxy]methyl}-2,4,6-trimethylbenzoyl)(phenyl)phosphine oxide (WBAPO) was synthesized starting from 3-(chloromethyl)-2,4,6-trimethylbenzoic acid by the dichlorophosphine route. The substituent was introduced by etherification with 2-(allyloxy)ethanol. In the second step, 3-{[2-(allyloxy)ethoxy]methyl}-2,4,6-trimethylbenzoic acid was chlorinated. The formed acid chloride showed an unexpected low thermal stability. Its thermal rearrangement at 180 ° C resulted in a fast formation of 3-(chloromethyl)-2,4,6-trimethylbenzoic acid 2-(allyloxy)ethyl ester. In the third step, the acid chloride was reacted with phenylphosphine dilithium with the formation of bis(3-{[2-(allyloxy)ethoxy]methyl}-2,4,6-trimethylbenzoyl)(phenyl)phosphine, which was oxidized to WBAPO. The structure of WBAPO was confirmed by ¹H NMR, ¹³C NMR, ³¹P NMR, and IR spectroscopy, as well as elemental analysis. WBAPO, a yellow liquid, possesses improved solubility in polar solvents and shows UV-vis absorption, and a high photoreactivity comparable with the commercially available bisacylphosphine oxides. A sufficient storage stability was found in dental acidic aqueous primer formulations.

Bonding of restorative materials to dentin with various luting agents

The aim was to compare eight types of luting agents when used to bond six indirect, laboratory restorative materials to dentin. Cylinders of the six restorative materials (Esteticor Avenir [gold alloy], Tritan [titanium], NobelRondo [feldspathic porcelain], Finesse All-Ceramic [leucite-glass ceramic], Lava [zirconia], and Sinfony [resin composite]) were ground and air-abraded. Cylinders of feldspathic porcelain and glass ceramic were additionally etched with hydrofluoric acid and were silane-treated. The cylinders were luted to ground human dentin with eight luting agents (DeTrey Zinc [zinc phosphate cement], Fuji I [conventional glass ionomer cement], Fuji Plus [resin-modified glass ionomer cement], Variolink II [conventional etch-and-rinse resin cement], Panavia F2.0 and Multilink [self-etch resin cements], and RelyX Unicem Aplicap and Maxcem [self-adhesive resin cements]). After water storage at 37°C for one week, the shear bond strength of the specimens (n=8/group) was measured, and the fracture mode was stereomicroscopically examined. Bond strength data were analyzed with two-factorial analysis of variance (ANOVA) followed by Newman-Keuls' Multiple Range Test (?=0.05). Both the restorative material and the luting agent had a significant effect on bond strength, and significant interaction was noted between the two variables. Zinc phosphate cement and glass ionomer cements produced the lowest bond strengths, whereas the highest bond strengths were found with the two self-etch and one of the self-adhesive resin cements. Generally, the fracture mode varied markedly with the restorative material. The luting agents had a bigger influence on bond strength between restorative materials and dentin than was seen with the restorative material.

Micromorphology and adhesive performance of Er:YAG laser-treated dentin of primary teeth

This study evaluated (1) the micromorphology by scanning electron microscopy (SEM) and (2) the adhesive performance by microtensile bond strength (μTBS) of diamond bur-treated dentin compared to Er:YAG laser-treated dentin of human primary teeth. (1) For qualitative SEM evaluation, dentin of 18 second primary molars (n = 3/method) was treated with either diamond bur as a control (group 1a: 40 μm diamond bur only (clinical situation); group 1b: grinding + 40 μm diamond bur) or with Er:YAG laser (group 2a (clinical situation, manufacturer's settings): 200 mJ/25 Hz (5 W) + 100 mJ/35 Hz (3.5 W) laser only; group 2b (experimental setting "high"): grinding + 400 mJ/20 Hz (8 W); group 2c (manufacturer's setting "finishing"): grinding + 100 mJ/35 Hz (3.5 W); group 2d (experimental setting "low"): grinding + 50 mJ/35 Hz (1.75 W)). (2) For evaluation of adhesive performance, 64 second primary molars were divided into four groups and treated as described for group 1b and groups 2b/c/d (n = 16/method), and μTBS of Clearfil SE/Clearfil Majesty Esthetic to dentin was measured. The SEM micrographs were qualitatively analyzed. The μTBS values were compared with a Kruskal-Wallis test. The significance level was set at α = 0.05. SEM micrographs showed the typical micromorphologies with a smear layer for the diamond bur groups and open dentin tubules for all laser-treated groups. However, in group 2d, the laser beam had insufficiently irradiated the dentin area, rendering the underlying ground surface partly visible. There were no statistically significant differences between μTBS values of the four groups (p = 0.394). This suggests that Er:YAG laser treatment of dentin of primary molars provides bond strengths similar to those obtained following diamond bur treatment.

Irregularities below the Enamel-Dentin Junction May Predispose for Fissure Caries

This study investigated the structure of the fissure fundus on occlusal surfaces with respect to the detection of possible irregularities below the enamel-dentin junction (EDJ). Occlusal surfaces were examined by micro-computed tomography (µCT). In total, 203 third molars with clinically sound occlusal fissures or non-cavitated lesions were selected. All specimens were scanned with µCT. Subsequently, each tooth was sectioned, and each slice was investigated by stereomicroscopy. In 7 of 203 molars (3.4%), demarcated radiolucencies below the EDJ were detected by µCT. These defects were obviously of non-carious origin, because the µCT images revealed no gradient of demineralization in the dentin. In all cases, a direct pathway between the oral cavity and the dentin was evident. The comparison of the µCT sites with conventional histological images also revealed defects in the dentin. These results demonstrate that demarcated radiolucencies below the EDJ may not necessarily be caries lesions according to µCT images and may be classified as possible developmental irregularities. To avoid misinterpreting µCT data, dental researchers should carefully consider this condition when analyzing µCT images. The clinical significance of this finding is that these defects may predispose molar teeth to early-onset caries in occlusal pits and fissures.

Long-term bonding to eroded dentin requires superficial bur preparation

This study aims to evaluate the influence of different surface preparation techniques on long-term bonding effectiveness to eroded dentin.

Shear bond strength of resin cements to human dentin

OBJECTIVES: The objectives of this in vitro study were (1) to assess the bond strength of the universal cement RelyX Unicem to dentin and to compare it with three conventional resin cements, (2) to test the influence of aging on their bonding capacity and (3) to test the influence of the operator on bonding quality by performing the same test in two different centers. METHODS: 160 third molars, divided into 80 for tests at the University of Zurich (Z) and 80 for tests at the University of Berne (B), were assigned to 2 x 8 subgroups of 10 teeth each. The specimens were prepared with the corresponding bonding agents and acrylic rods were luted either with RelyX Unicem (U), RelyX ARC (A), Multilink (M) or Panavia 21 (P). All specimens were stored in water for 24h (W) and half of the specimens were subjected to 1500 cycles of thermocycling (5 degrees C and 55 degrees C) (T). Bond strength was measured by means of a shear test. RESULTS: After water storage RelyX Unicem exhibited lowest bond strength (UWZ: 9.2+/-1.6 MPa, UWB: 9.9+/-1.2 MPa, AWZ: 15.3+/-6.0 MPa, AWB: 12.2+/-4.3 MPa, MWZ: 15.6+/-3.3 MPa, MWB: 12.4 MPa+/-2.4, PWZ: 13.4+/-2.9 MPa, PWB: 14.9+/-2.6 MPa). Thermocycling affected the bonding performance of all four cements. However, bond strength of RelyX Unicem was least influenced by thermocycling (UTZ: 9.4+/-2.9 MPa, UTB: 8.6+/-1.3 MPa, ATZ: 11.4+/-6.3 MPa, ATB: 13.3+/-3.7 MPa, MTZ: 15.4+/-3.1 MPa, MTB: 10.3+/-2.4 MPa, PTZ: 11.1+/-2.8 MPa, PTB: 11.3+/-2.8 MPa). SIGNIFICANCE: Although the bond strength of RelyX Unicem to dentin was lower in comparison to RelyX ARC, Multilink and Panavia 21, its bond strength was less sensitive to variations in handling and aging.

Temporary zinc oxide-eugenol cement: eugenol quantity in dentin and bond strength of resin composite

Uptake of eugenol from eugenol-containing temporary materials may reduce the adhesion of subsequent resin-based restorations. This study investigated the effect of duration of exposure to zinc oxide–eugenol (ZOE) cement on the quantity of eugenol retained in dentin and on the microtensile bond strength (μTBS) of the resin composite. The ZOE cement (IRM Caps) was applied onto the dentin of human molars (21 per group) for 1, 7, or 28 d. One half of each molar was used to determine the quantity of eugenol (by spectrofluorimetry) and the other half was used for μTBS testing. The ZOE-exposed dentin was treated with either OptiBond FL using phosphoric acid (H3PO4) or with Gluma Classic using ethylenediaminetetraacetic acid (EDTA) conditioning. One group without conditioning (for eugenol quantity) and two groups not exposed to ZOE (for eugenol quantity and μTBS testing) served as controls. The quantity of eugenol ranged between 0.33 and 2.9 nmol mg−1 of dentin (median values). No effect of the duration of exposure to ZOE was found. Conditioning with H3PO4 or EDTA significantly reduced the quantity of eugenol in dentin. Nevertheless, for OptiBond FL, exposure to ZOE significantly decreased the μTBS, regardless of the duration of exposure. For Gluma Classic, the μTBS decreased after exposure to ZOE for 7 and 28 d. OptiBond FL yielded a significantly higher μTBS than did Gluma Classic. Thus, ZOE should be avoided in cavities later to be restored with resin-based materials.

Effect of tin-chloride pretreatment on bond strength of two adhesive systems to dentin

OBJECTIVES: To determine the effect on resin composite-to-dentin bond strength of incorporation of an acidic tin-chloride pretreatment in two adhesive systems. MATERIALS AND METHODS: Human molars were ground to expose mid-coronal dentin. For microtensile bond strength (μTBS) testing, dentin was treated with Optibond FL or Clearfil SE according to one of six protocols (n = 22/group). Group 1: Phosphoric acid etching, Optibond FL Prime, Optibond FL Adhesive (manufacturer's instructions; control); Group 2: Tin-chloride pretreatment, Optibond FL Prime, Optibond FL Adhesive; Group 3: Phosphoric acid etching, tin-chloride pretreatment, Optibond FL Prime, Optibond FL Adhesive; Group 4: Clearfil SE Primer, Clearfil SE Bond (manufacturer's instructions; control); Group 5: Phosphoric acid etching, Clearfil SE Primer, Clearfil SE Bond; and Group 6: Tin-chloride pretreatment, Clearfil SE Primer, Clearfil SE Bond. The molars were then built up with resin composite (Clearfil Majesty Esthetic). After storage (1 week, 100  % humidity, 37 °C) the μTBS was measured and failure mode was determined. Additionally, pretreated dentin surfaces were evaluated using SEM and EDX. The μTBS results were analyzed statistically by a Welch Two Sample t-test and a Kruskal-Wallis test followed by exact Wilcoxon rank sum tests with Bonferroni-Holm adjustment for multiple testing (α = 0.05). RESULTS: When Optibond FL was used, partial or total replacement of phosphoric acid with tin-chloride decreased μTBS significantly. In contrast, when Clearfil SE was used, inclusion of a tin-chloride pretreatment in the adhesive procedure increased μTBS significantly. CONCLUSIONS: Tin-chloride pretreatment had a beneficial influence on the bond promoting capacity of the MDP-containing adhesive system Clearfil SE.