Effect of a sodium hypochlorite gel on dentin bonding.

It has been suggested that the hybrid layer (HL) does not play any important role in the mechanism of adhesion to dentin. To substantiate this hypothetical insignificance of the HL, sodium hypochlorite (NaOCl) has been used to remove collagen from etched dentin prior to bonding. OBJECTIVES: The present study was conducted to determine the effect of a commercial 10% NaOCl gel on the dentin shear bond strengths and HL ultra-morphology of two simplified dentin adhesives. The null hypothesis tested was that treatment of etched dentin collagen with NaOCl would not compromise dentin bonding. METHODS: The labial surface of eighty bovine incisors was polished to expose middle dentin. The specimens were randomly assigned to two total-etch adhesive systems (N = 40): Prime&Bond NT (Dentsply Caulk); and Single Bond (3M Dental Products Division). After rinsing off the etchant, one drop of 10% NaOCl (AD Gel, Kuraray Ltd.) was applied to the etched dentin surface and left for 0 (control), 15, 30, or 60 s. The gel was rinsed off with water and the dentin surface kept visibly moist prior to the application of the adhesive as per manufacturer's instructions. The respective composite resin was subsequently applied and light-cured. After 24 h in water at 37 degrees C, the specimens were thermocycled for 500 cycles in baths kept at 5 and 55 degrees C and the shear bond strengths measured. The data were analyzed with two-way ANOVA. For TEM, sixteen dentin disks were taken from middle dentin of extracted human third molars, assigned to the eight treatment sequences, and observed. RESULTS: The increase in the NaOCl application time resulted in a progressive decrease in shear bond strengths for both dentin adhesives. For Single Bond, the application of AD Gel for 60 s resulted in a reduction of bond strengths to 38% of that obtained for the control. For Prime&Bond NT, the mean bond strength obtained when AD Gel was applied for 60 s was 31% of that obtained for the control. The application of AD Gel resulted in distinct morphology for each one of the two adhesives tested. For Single Bond, the general morphology of the collagen network was maintained, regardless of the deproteinization time. The interfibrillar space within the collagen network increased with increasing deproteinization times. For Prime&Bond NT, the general appearance of the HL was maintained for deproteinization times of 15 and 30 s. When the NaOCl gel was applied for 60 s, the morphological appearance of the HL lost its fibrillar arrangement. While remnants of the collagen fibers were observed in one of the dentin disks, the other specimen showed an amorphous structure without any discernible HL morphological features. SIGNIFICANCE: The integrity of the collagen fibrils left exposed upon acid-etching plays a major role in the mechanism of adhesion of the specific adhesive systems tested in this study. The intermingling of the adhesive monomers with the filigree of collagen fibers or HL should still be considered the paramount dentin bonding mechanism.     

NaOCl effects on primary and permanent pulp chamber dentin

OBJECTIVES: The dentin quality of primary and permanent pulp chamber was inspected by Fourier-transformed Raman spectroscopy (FT-Raman) and scanning electron microscopy (SEM). Fragments of pulp chamber dentin were obtained from 20 human molar crowns (primary and permanent). METHODS: The fragments were assigned to 8 groups (n=5)-Primary teeth: G1, pulp chamber dentin; G2, pulp chamber dentin irrigated with NaOCl 1% (30min); G3, pulp chamber dentin irrigated with NaOCl 1% (30min) and etched by 35% phosphoric acid; G4, pulp chamber dentin etched by 35% phosphoric acid. Permanent teeth: G5, pulp chamber dentin; G6, pulp chamber dentin irrigated with NaOCl 1% (30min); G7, pulp chamber dentin irrigated with NaOCl 1% (30min) and etched by 35% phosphoric acid; G8, pulp chamber dentin etched by 35% phosphoric acid. The spectra were subjected to the Cluster analysis. The SEM images were scored. RESULTS: Inorganic content: There was a difference between primary and permanent dentin. The groups treated with NaOCl were statistically similar between them, but differed from the groups not treated. Organic content: There was no difference between primary and permanent dentin. The groups became similar after NaOCl and phosphoric acid treatments. The microscopic images showed the presence of calcospherites on permanent dentin and their absence on primary dentin. CONCLUSIONS: The NaOCl changed the inorganic content in both dentitions; regardless of the following phosphoric acid etching. However, the chemical changes caused by NaOCl were not detected by SEM when it was followed by etching.     

Effect of removal of surface collagen fibrils on resin-dentin bonding.

OBJECTIVES: The aim of this study was to evaluate the effects of NaOCl at removing the demineralized layer by examining the morphology of the hybrid layer and measuring shear bond strengths after different dentin treatments. METHODS: Dentin disks were treated with: (1) 35% phosphoric acid (PA) 20 s; (2) PA treatment followed by 1.5% NaOCl, 2 min; (3) PA treatment, followed by a 10% NaOCl immersion for 120 h. SEM was used to analyze the morphology of dentin and its interface with dentin bonding agents (DBAs), while shear bond strength tests were used to measure adhesion. All specimens were then fractured into two halves: One half was inspected under SEM; the other half was sequentially placed in 10% PA followed by 12.5% NaOCl for 70 h, to remove all dentin from the resin replica of the original bonded interface. RESULTS: SEM observations showed that collagen fibrils were completely removed from the acid-etched surface by NaOCl treatment. The diameter and the size of dentinal tubules and the number of lateral branches of the tubules were increased following NaOCl treatment. NaOCl applied on dentin smear layers did not significantly modify their SEM morphology. Resin tags were larger in diameter after phosphoric acid/NaOCl treatment than after only phosphoric acid treatment. Resin-infiltrated dentin-layers were only observed after the single phosphoric acid (i.e. conventional etching) procedure, and were not observed after combined phosphoric acid/NaOCl treatment. Etched/NaOCl samples showed a lower bond strength using Scotchbond MP and 3M Single Bond, but were higher in Optibond FL and unmodified in Prime & Bond 2.0 groups when compared with acid-etched controls. Treatment of etched dentin with NaOCl for 120 h produced an unusual type of resin infiltration of mineralized dentin that could be called a "reverse hybrid layer" which may explain the mechanism of resin bonding to NaOCl treated dentin. SIGNIFICANCE: The use of acidic conditioners for exposure of the collagen matrix exposes a soft delicate mesh that can collapse, thereby interfering with resin infiltration. If acid-etching is followed by NaOCl treatment, high bond strengths can be achieved via "reverse hybrid layer" formation, a proposed new mechanism of micromechanical resin retention. This mechanism is not yet recommended for clinical use but demonstrates a new type of resin retention.     

In vitro study of endodontic post cementation protocols that use resin cements

STATEMENT OF PROBLEM: Sodium hypochlorite (NaOCl) may alter resin bond strength by deproteination of demineralized dentin collagen. PURPOSE: To analyze the effect of NaOCl treatment on bond adhesion and tensile strength of different post cementation protocols in vitro. MATERIAL AND METHODS: The periconductual dentin of 120 single-rooted, caries-free, unrestored human teeth was etched with 37% orthophosphoric acid. The teeth in Group I (60) were left untreated, and the teeth in Group II (60) were treated with 10% NaOCl. Four post-cementation protocols were examined (15 teeth in each) for Groups I and II: ED Primer dentin adhesive + Panavia 21 Ex; ED Primer dentin adhesive + Dual Cement; Panavia 21 Ex; and Dual Cement. For each condition, resin tags, hybrid layers over the periconductual dentin and post surface, were analyzed by scanning electron microscopy (SEM). Specimens were loaded with a uniaxial tensile force using an electromechanical testing machine until cement failure. Bond adhesion and tensile strength with different protocols were examined statistically using multiple analysis of variance at a significance level of alpha<.05. RESULTS: SEM revealed morphologic differences; Group II exhibited cylindrical, solid tags and Group I, tapered, hollow tags. Uniaxial tensile strength tests showed that in Group I, Panavia 21 Ex cement was strongest, whereas in Group II, this protocol was the weakest and Dual Cement with adhesive was the strongest. In Group II, Panavia 21 Ex diminished the tensile bond strength; however, combination with dentin adhesive increased it. CONCLUSION: Within the limitations of this study, NaOCl treatment did not significantly alter tensile bond strength, but when combined with the dentin adhesive ED Primer, a significant rise in strength resulted. A positive relationship existed between increased tag numbers and higher tensile bond strength.     

Smear layer and surface state affect dentin fluoride uptake

OBJECTIVES: Polishing generates a smear layer (SL) on in vitro dentin samples that may influence fluoride uptake. We tested two hypotheses: SL increases fluoride uptake in superficial dentin (H1) and decreases fluoride uptake in deeper layers (H2) irrespectively of the amount of fluoride administered. METHODS: Polished bovine dentin with SL present and removed by four methods (5% tannic acid, 20s [TA]; 17% EDTA, 120 s; 38% phosphoric acid, 60s [PA]; and 10s air polishing) was fluoridated with 1200 or 12000 ppm F (NaF) solution (pH 4.0). RESULTS: Scanning electron microscopy (SEM) revealed that aggressiveness of SL removal varied by method from leaving SL patches behind (TA) to collagen exposure (PA). SL increased KOH-soluble and structurally bound fluoride uptake into superficial and deeper layers compared to SL free surfaces (except PA) following 1200 ppm, but not 12000 ppm fluoridation. CONCLUSION: Presence of SL and surface conditions influence dentin fluoride uptake depending on fluoride concentration administered.     

酸蚀时间对牙本质Ⅰ型胶原降解的影响

目的 评价37%磷酸处理牙本质不同时间对牙本质Ⅰ型胶原降解的影响,以期为临床牙本质粘接操作提供实验依据.方法 37%磷酸酸蚀处理牙本质片0(空白对照组)、10、15、30、60 s,酶联免疫吸附法定量测定Ⅰ型胶原的降解量,场发射扫描电镜(field emission in-lens scanning electron microscope,FEISEM)观察胶原纤维的形态学变化.结果 酸蚀处理60 s时Ⅰ型胶原的降解量最多,为4.86(1.55)mg/g;其次为30 s组,为2.76(0.87)mg/g;再次为15 s组,为1.93(0.88)mg/g;10 s组胶原降解量较少,为0.95(0.38)mg/g;空白对照组胶原的降解量最少,为0.06(0.03)mg/g.两两比较显示,各组间差异均有统计学意义(P＜0.005).FEISEM显示,37%磷酸处理牙本质表面10 s,尽管已清除了玷污层,但牙本质小管口以及胶原纤维仍覆盖颗粒样物质.酸蚀15 s牙本质小管口开放,暴露清晰.酸蚀30 s暴露的胶原纤维表面比15 s组光滑,球状附着物减少;酸蚀60 s牙本质小管内主纤维数最减少,管内结构塌陷,次级纤维数量增加,存在纤维断裂的征象.结论 在实验时间0～60 s内,酸蚀15 s即可达到酸蚀目的 ,延长酸蚀时间,可引起更多的胶原纤维变性降解.

Abstract：

Objective To evaluate the effects of acid etching time on the degradation of type Ⅰcollagen in dentin. Methods Dentin was conditioned with 37% phosphoric acid for 10, 15, 30 and 60 s.There was no treatment for the control group. Quantity of collagen degradation in each group was determined by enzyme linked immunosorbent assay. Observations were carried out by means of a field emission in-lens scanning electron microscope (FEISEM). Results Samples conditioned with 37% phosphoric acid for 60 s showed the most degradation of collagen, which was 4. 86 (1.55) mg/g, followed by 30 s group and 15 s group, which were 2.76(0.87) mg/g and 1.93(0.88) mg/g, respectively. Group of 10 s was 0.95(0. 38) mg/g. The control group showed the least degradation of 0. 06(0. 03) mg/g. Significant differences in collagen degradation were found among groupo (P ＜ 0. 005). Smear layer were removed well but tubular orifices and collagen fibrils were covered by particles after dentin being etched with 37% phosphoric acid for 10 s, while open and clear tubular orifices were observed for 15 s group. Smoother surfaces of exposed collagen fibrils and fewer globular particles were found in 30 s group than in 15 s group. In the 60 s group,the number of major fibrils decreased while minor branching fibrils increased, which indicate that the intratubular structure collapsed and fibrils fractured. Conclusions Dentin conditioned with 37% phosphoric acid for 15 s can result in mineral dissolution without collagen structure damage. However, longer applications of 37% phosphoric acid within 60 s may increase collagen degradation.     

Effect of sodium hypochlorite treatment on the molecular composition and morphology of human coronal dentin

PURPOSE: The aim of the present study was to evaluate the deproteination potential of 5% aqueous NaOCl solution applied by rubbing action on the molecular composition and morphology of smear-layer covered and acid-etched human coronal dentin surfaces. MATERIALS AND METHODS: Paired specimens (n = 4 x 2 per group) of acid-etched (Group A) and smear-layer covered (Group B) human coronal dentin surfaces were sequentially treated with the NaOCl solution for time intervals ranging from 5 s to 120 s and analyzed by reflectance FTIR microspectroscopy and tapping mode atomic force microscopy. The changes in the mineral (v4 P-O stretching vibrations) to matrix (C = O stretching vibrations of amide I) peak area ratios and in the Ra roughness parameter were used to quantify the effect of treatment. Two-way ANOVA and Dunn's tests were used to assess the differences within each group and between groups (a = 0.05). RESULTS: In both groups, NaOCl treatment reduced organic matrix (amide I, II, III peaks), but did not affect carbonates and phosphates. In group A, the rate of deproteination was slow, and reached a peak value after 120 s. Tubule orifices became visible after 40 s of treatment; after 120 s, excessive porosity was detected, with Ra values presenting no statistically significant difference from group B. In group B after 10 s, the extent of deproteination was enhanced, reaching a plateau between 30 s and 60 s, and attaining a maximum after 120 s. Tubule diameter, intertubular porosity, and Ra were increased; intertubular dentin area was reduced. For both groups after 40 s of treatment, the mineral to matrix ratio recorded was similar to smear-layer-free sectioned dentin. CONCLUSION: The results of the present study imply that deproteination of mineralized or acid-etched dentin surfaces within a clinically relevant time frame may provide methods for bonding to dentin alternative to conventional technique-sensitive dentin hybridization.     

Do intact collagen fibers increase dentin bond strength?

The purpose of the present study was to evaluate surface morphology and shear bond strength of All Bond 2 bonded to dentin surfaces, that were treated progressively to remove collagen fibers. For the study of surface morphology, fifteen teeth were divided in to five groups. Dentin surfaces in groups 1-4 were etched either with 24% EDTA for 30 seconds or 32% phosphoric acid for 15 seconds with and without subsequent treatment with 10% NaOCl for 60 seconds. Group 5 received no treatment and served as control. Evaluation was performed using scanning electron microscopy. Thirty teeth were used for the shear bond strength test. Two experimental surfaces were prepared on each tooth and cylindrical copper matrixes were attached to the surfaces. Experimental surfaces were divided into four groups and treated in the same way as group 1-4 in the morphology part of the study. Dentin was bonded with All Bond 2, after which a flowable composite was inserted and light cured. Shear strength test was performed at a crosshead speed of 1 mm/minute until the composite debonded. Results showed that etching followed by treatment with NaOCl removed all collagen fibers from the dentin surfaces, while treatment with EDTA alone denuded the fiber structures. Shear strength was significantly decreased when surfaces were treated with NaOCl. The highest shear strength values were obtained in the EDTA etched group. The results from the present study indicate that exposed dentin associated collagen fibers increases adhesion of All Bond 2 to dentin.     

次氯酸钠配合SmearClear清除根管玷污层的研究

目的:比较4种根管冲洗方法清除根管玷污层的效果,研究出有效去除根管玷污层的方法。方法:20个无龋单根前牙随机分为4组,A组:60℃30 g/L次氯酸钠液加170 g/L EDTA,#15K锉提拉冲洗;B组:60℃30 g/L次氯酸钠液加SmearClear,#15K锉提拉冲洗;C组:60℃30 g/L次氯酸钠液加170 g/LEDTA液超声荡洗;D组:60℃30 g/L次氯酸钠液加SmearClear超声荡洗。扫描电镜下放大2 500倍和4 000倍观察根尖1/3、根中1/3和根上1/3玷污层清除情况。按照根管壁玷污层清除情况和根管壁腐蚀程度的分级标准进行统计学分析。结果:①根管壁玷污层清除情况:4组在根上2/3区玷污层均有效去除,各组间差异无统计学意义(P>0.05),B组根尖1/3基本无玷污层,A、C、D组仅见少部分玷污层被去除,B组与A、C、D组差异有统计学意义(P<0.05);②根管壁腐蚀性比较:C、D组根上2/3区腐蚀度较大,而A、B组未见明显腐蚀。C、D组与A、B组相比差异有统计学意义(P<0.05),各组根尖1/3根管壁腐蚀度差异无统计学意义(P>0.05)。结论:SmearClear与60℃30 g/L次氯酸钠液联合应用能更有效的去除根管玷污层,且对根管壁表面结构无明显破坏。     

Effect of sodium hypochlorite on dentin bonding in primary teeth

PURPOSE: The aim of this study was to evaluate the effect of sodium hypochlorite (NaOCl) on the shear bond strength (SBS) using three bonding systems in primary dentin. MATERIALS AND METHODS: Forty-five sound extracted primary molars were selected. The crowns were longitudinally sectioned, embedded in polystyrene resin, and flattened until a dentin surface was reached. The samples were assigned to 6 groups (n = 15): G1, Single Bond (SB); G2, NaOCl + SB; G3, Prime & Bond 2.1 (PB); G4, NaOCl + PB; G5, Clearfil SE Bond (CSE); G6, NaOCl + CSE. All the adhesive systems were applied according to the manufacturers' instructions, except for the application of 10% NaOCl solution for 60 s in groups 2, 4 (after acid etching), and 6 (before applying adhesive system). The composite resin was placed in increments in a mold and light cured for 20 s. The samples were stored in distilled water at 37 degrees C for 24 h and submitted to SBS testing with a crosshead speed of 0.5 mm/min. The failure sites were observed with SEM. The data were treated with ANOVA and Tukey's tests (p < 0.05). RESULTS: There was no statistically significant difference between the groups with or without treatment of the substrate with NaOCl, regardless the material used. The SBS averages in MPa (+/-SD) were: G1: 15.8(1.9)a; G2: 14.6(1.3)a; G3: 10.2(0.7)a; G4: 9.9(0.2)a; G5: 13.3(1.2)a; and G6: 10.7(1.0)a. There was a statistically significant difference between the materials (SB > or = CSE > or = PB). Mixed failure was the failure type most frequently observed for all groups. CONCLUSION: Dentin surface treatment with NaOCl did not affect the resin-dentin bonding strength in primary teeth.     

Effect of dentin deproteinization on microleakage of Class V composite restorations

The role of the collagen fibers in dentin adhesion has not clearly been established. Therefore, this laboratory study evaluated the microleakage at resin-dentin and resin-enamel interfaces of Class V composite restorations after etching enamel and dentin with phosphoric acid (H3PO4) or after etching with H3PO4 followed by deproteinization with 5% sodium hypochlorite (NaOCl) to prevent the formation of a hybrid layer. Ten extracted human molars were used to prepare standardized Class V cavities on both buccal and lingual surfaces. The teeth were randomly divided in two groups: 1) Class V cavities that were etched with H3PO4 for 15 seconds; b) Class V cavities that were etched with H3PO4 for 15 seconds followed by collagen removal with 5% NaOCl for two minutes. The cavities were restored using the Prime & Bond 2.1 bonding system and TPH resin composite. The specimens were stored in water for 24 hours at 37 degrees C and thermocycled 500 times between water baths kept at 5 degrees C and 55 degrees C. After thermocycling, specimens were immersed in a 0.5% aqueous solution of basic fuchsin for 24 hours. Three longitudinal sections of each restoration were obtained and examined with a stereomicroscope for qualitative evaluation of microleakage. The data were statistically analyzed by Mann-Whitney U and Wilcoxon matched pairs signed ranked tests. Extra specimens were analyzed with the scanning electron microscope (SEM). Occlusal margins (enamel margins) resulted in statistical lower degree of leakage than gingival margins (dentin/cementum margins) in both treatment groups. For each type of margin, there were no statistically significant differences between the etched and the etched and deproteinized groups. Under the SEM, occlusal surfaces showed no detachment between enamel and dentin, while dentin/cementum resulted in gap formation.     

Effect of chemical irrigants on the bond strength of a self-etching adhesive to pulp chamber dentin

The aim of this study was to evaluate the influence of endodontic irrigants on adhesion to pulp chamber dentin. Seventy crowns of bovine incisors were cut to expose the pulp chamber. Specimens were divided into seven groups, according to the irrigant solution used: G1, 0.9% sodium chlorite (control); G2, 5.25% NaOCl; G3, 5.25% NaOCl + 17% EDTA; G4, 2% chlorhexidine solution; G5, 2% CHX solution + 17% EDTA; G6, 2% chlorhexidine in a gel base; and G7, 2% CHX gel + 17% EDTA. After irrigation, Clearfil SE Bond was applied to pulp chamber dentin, followed by Filtek Z250 composite. Six rectangular sticks were obtained from each specimen and dentin/resin interface was tested in tension. Bond strength means were analyzed by ANOVA and Tukey test. There was a significant decrease in bond strength associated to NaOCl, whereas chlorhexidine irrigation showed no effects on adhesion. It was concluded that endodontic irrigants affected differently bond strength to pulp chamber dentin.     

Effect of primers containing N-methylolacrylamide or N-methylolmethacrylamide on dentin bond durability of a resin composite after 5 years

OBJECTIVES: The effect of experimental dentin primers containing N-methylolacrylamide (MEAA) or N-methylolmethacrylamide (MEMA) on bond durability of a resin composite (Photo Clearfil A) with a bonding agent (Clearfil Photo Bond) to bovine dentin was investigated. METHODS: The etching agents were 10% maleic acid (10% MA), 10% phosphoric acid (10% PA) and 10% citric acid-3% ferric chloride (10-3 solution). Water solutions of 35% hydroxyethyl methacrylate (HEMA), 50% MEAA or 30% MEMA were used as dentin primers. The etched dentin was pre-treated with the dentin primers for 30s. The resin composite systems were applied in a Teflon tube positioned onto pre-treated dentin surfaces. After water immersion for 1 day and 5 years, the shear bond strengths were measured. The amounts of calcium dissolved with etching agents were measured using atomic absorption spectrometry. The thicknesses of hybrid layers at the dentin-resin interfaces treated with 6 mol/l HCl and 1% NaOCl were measured using scanning electron microscopy. RESULTS: The bond strengths of the specimens (Controls) without primers to dentin etched with 10% MA and 10-3 solution significantly decreased after immersion in water for 5 years (p<0.05) while other bond strengths did not decrease. The bond strengths of the composites to MEMA- and MEAA-primed dentin were significantly higher than that of the control after 1 day, regardless of the types of etching agents (p<0.05). The 5 year bond strengths of the composites to HEMA-, MEMA- and MEAA-primed dentin were significantly higher than that of the control, regardless of the types of etching agents (p<0.05). The 1 day and 5 year bond strengths of the composite to MEAA-primed dentin were significantly higher than those of the composites to HEMA-primed dentin, regardless of the types of etching agents (p<0.05). The highest amount (182.3+/-8.0 microg/cm(2)) of dissolved calcium was determined for the pre-treatment with 10% PA, followed by that (152.0+/-6.9 microg/cm(2)) with 10% MA and that (140.1+/-2.8 microg/cm(2)) with 10-3 solution (p<0.05). The hybrid layer thicknesses (approximately 1 microm) for 10-3 solution were thinner than those (approximately 2 microm) for others after HCl immersion. For the controls, the hybrid layers after NaOCl immersion become narrower or disappeared. The main fracture pattern of specimens was a mixture of resin-dentin interface failure and dentin cohesive fracture after the bond test. CONCLUSIONS: MEAA solution was more effective in improving the bond strength of the controls to etched dentin than was HEMA after 1 day and 5 years. Clearfil Photo Bond created good hybrid dentin layers which could resist NaOCl-attack and showed good dentin bond durability when dentin primers were used, regardless of the type of etching agent.     

Effect of dentin primers containing N-methylolacrylamide or N-methylolmethacrylamide on dentin pretreatment.

The effect of experimental dentin primers containing N-methylolacrylamide (MEAA) or N-methylolmethacrylamide (MEMA) on the bonding of three commercial light-cured resin composite systems [Restorative Z 100 (Scotchbond), Palfique Estelite (Macbond) and Photo Clearfil A (Clearfil Photobond)] to etched dentin was investigated. Water solutions of 35% hydroxyethyl methacrylate (HEMA). 50% MEAA or 30% MEMA were used as dentin primers. The dentin etched with 10% phosphoric acid solution was pretreated with dentin primers for 30 s. The resin composite systems were applied in a Teflon tube positioned onto pretreated dentin surfaces. After water immersion for 1 day, the shear bond strengths were measured. The thicknesses of hybrid layers at dentin-resin interfaces treated with 6 mol/l HCl and 1% NaOCl were measured by scanning electron microscopy. The dentin primer pretreatment increased the bond strengths of all resin composite systems. For Macbond and Clearfil Photobond, the bond strengths (14.2-26.5 MPa) with MEAA and MEMA were higher than those (10.5 and 17.8 MPa) with HEMA. All hybrid layer thicknesses were 1-1.5 microns after HCl immersion. The hybrid layers after NaOCl immersion become narrower. The main fracture pattern of specimens exhibiting high bond strengths (more than 14.2 MPa) was dentin cohesive fracture after bond test. For Macbond and Clearfil Photobond, the layers of specimens pretreated with MEAA and MEMA were clearly thicker than those pretreated with HEMA after NaOCl immersion. MEAA and MEMA solutions were more effective in improving the bond strength of Macbond and Clearfil Photobond to etched dentin than was HEMA. Macbond and Clearfil Photobond created good hybrid dentin layers which could resist NaOCl-attack when MEAA and MEMA solutions were used as dentin primers.     

The influence of the modification of etched bovine dentin on bond strengths.

OBJECTIVE: The aim of this study was to modify demineralized bovine dentin surfaces by application of either 12.5% sodium hypochlorite (NaOCl), or 0.1% (w/w) Type I collagenase, after conditioning with phosphoric acid, to observe the demineralized surface and to investigate the effect on tensile bond strength. METHODS: The NaOCl was applied to etched dentin for 30 s, 1 or 2 min and the collagenase for 1, 3 or 6 h. A control group was used without NaOCl or collagenase treatment. Prior to bonding, treated surfaces were examined using an Atomic Force Microscope (AFM). A 2.3 mm diameter area of dentin was conditioned, treated and bonded with either One Coat Bond or Single Bond following each manufacturer's instructions, and a resin composite rod attached. Bonds were stressed in tension at a rate of 1 mm/min until failure. Mean bond strengths were calculated (MPa) and mode of failure was determined by observation at 20x magnification. Results were analyzed using multiple regression analysis and LSD test at the 95% level of confidence (n = 12). RESULTS: AFM results showed progressive changes of the surface collagen as the treatment time of NaOCl or collagenase increased. For both bonding systems, the bond strengths of 1 min NaOCl and 3 h collagenase treatments were significantly higher than the control or other treatment groups (p < 0.05). Bond failure consisted of mostly adhesive failure between dentin and resin combined with small regions exhibiting cohesive failure of resin. SIGNIFICANCE: Bond strengths were not dependent on the thickness of the hybrid layer, but rather quality of the hybrid layer.     

The role of Carisolv and different auxiliary chemical substances in the removal of bovine root canal smear layer

To evaluate the effectiveness of Carisolv and different auxiliary chemical substances in root canal smear layer (SL) removal. SL was produced in the centre of 40 hemi-disks of bovine root dentine. The samples were divided into four irrigation groups (G): GI (control) - 0.9% NaCl; GII - 1% NaOCl + 0.9% NaCl; GIII - Carisolv + 0.9% NaCl; GIV - 1% NaOCl + 10% citric acid solution + 0.9% NaCl. The photomicrographs (SEM analysis) were coded (0 - absence of SL; 1 - moderate SL; 2 - dense SL with visible tubules; 3 - dense SL with no visible tubules). GIV was more effective in SL removal (P < 0.01). It should be noted that GI and GIII obtained score 3 in 100% of the samples (P > 0.01). Conclusion: NaOHCl, citric acid and NaCl solutions, when used together, presented a better performance in the removal of SL when compared to the other solutions.     

Effect of dentinal pretreatments on coronal dentin primary carious lesions: a field emission SEM study

The aim of the study was the morphological analysis of coronal dentin caries and the modifications induced by different pretreatments with phosphoric acid or sodium hypochlorite. Carious dentin specimens were obtained from human molars affected by carious lesions. Specimens were divided in four groups and submitted to: (1) untreated; (2) 35% phosphoric acid for 15 s; (3) 35% phosphoric acid for 15 s and 5% sodium hypochlorite for 2 min; (4) sodium hypochlorite for 5 min. Specimens were observed under high-resolution SEM. Different areas were identified within the carious lesion: a deeper, inner region revealing closed highly mineralized tubules, and a more superficial outer layer showing an increasing demineralization rate toward the surface of the lesion. Phosphoric acid followed by NaOCl treatment removed all collagen fibrils from greatly altered carious outer-dentin layer. The 5-min treatment with sodium hypochlorite affected both inner and outer dentin, removing all collagen fibrils and increasing the porosities of deeper intertubular hypermineralized dentin. FEISEM analysis confirmed that only inner carious dentin after phosphoric acid treatment may be considered a suitable substrate for dentinal bonding system. On the contrary, the outer dentin is an unstable substrate for any type of bonding systems and must be avoided/removed from any surface before conditioner application.     

Structural Analysis of Bovine Root Dentin after Use of Different Endodontics Auxiliary Chemical Substances

IntroductionThe use of chemical substances in endodontics during chemical-mechanical preparation may alter the structure of dentin, mainly collagen, which contributes considerably to the mechanical properties of this structure. This study evaluated the effect of different auxiliary chemical substances during endodontic treatment in root canal walls by implementing polarized light microscopy (PLM) and scanning electron microscopy (SEM).MethodsSixty bovine incisors were randomly divided into six groups (n = 10): G1, 5.25% NaOCl + 17% EDTA; G2, 2% chlorhexidine (CHX) gel; G3, 5.25% NaOCl; G4, 17% EDTA; G5, 2% CHX + 17% EDTA; and G6, 0.9% sodium chloride solution (control). Teeth were chemomechanically prepared and fractured into two fragments. One fragment was used for PLM, and the other was used for SEM analysis.ResultsGroups treated with 5.25% NaOCl, whether associated or not associated to 17% EDTA, presented a significantly different birefringence pattern compared with the control group. The results revealed that groups irrigated with 2% CHX and EDTA, independently or combined, did not present any significant differences compared with the control group. SEM analysis showed structural alterations of the root canal inorganic matrix for all groups that used 17% EDTA.ConclusionsIt is possible to conclude that 5.25% NaOCl, whether associated or not associated with 17% EDTA, causes alterations in the dentin collagen. The obtained SEM images revealed demineralization areas for groups that used 17% EDTA alone or associated with other substances.     

2-year Clinical evaluation of sodium hypochlorite treatment in the restoration of non-carious cervical lesions: a pilot study

This pilot study evaluated the effect of removing acid-etch-exposed dentin collagen on the clinical performance of composite restorations of noncarious cervical lesions placed using 2 different adhesive systems. Fifty-six restorations were placed in 14 subjects, each subject receiving at least 4 restorations. No cavity preparation or mechanical retention form was used. The variables tested were: 1) dentin treatment prior to application of the adhesive (acid-etch only vs acid-etch and collagen removal) and 2) type of adhesive (acetone- vs ethanol-based). For the acid-etch only groups, enamel and dentin were etched with 37% phosphoric acid for 15 seconds, rinsed and blot dried. Prime & Bond 2.1 (Dentsply Caulk) or Single Bond (3M ESPE) was applied and light-cured according to the manufacturer's instructions. For the acid-etch and collagen removal groups, the enamel and dentin were etched and rinsed in the same manner and a 10% sodium hypochlorite (NaOCl) solution was applied for 60 seconds and rinsed before adhesive application. Filtek Z-250 (3M ESPE) was applied to all specimens and light-cured according to the manufacturer's instructions, and the restorations were finished and polished immediately. The restorations were evaluated for pre- and post-operative sensitivity, retention, marginal staining and secondary caries at baseline, 12 and 24 months after placement, using modified USPHS criteria. Data were analyzed using the Kruskal-Wallis and Wilcoxon statistical tests (p=0.05). At 24 months, the retention rates for Prime & Bond 2.1 with and without NaOCl pretreatment were 80% and 63%, respectively. The corresponding retention rates for Single Bond were 70% and 90%. Marginal staining was minimal. Statistical analyses revealed no significant differences at any time interval between groups for retention or marginal staining. No post-operative sensitivity or secondary caries was detected during the study.