Efficacy of sodium hypochlorite activated with laser in intracanal smear layer removal: an SEM study

Introduction: The purpose of the present study was to evaluate the different concentrations of sodium hypochlorite activated with laser in removing of the smear layer in the apical, middle, and coronal segments of root canal walls by scanning electron microscopy analysis

Methods: Sixty single-rooted human mandibular teeth were decoronated to a standardized length. The samples were prepared by using Race rotary system to size 40, 0.04 taper and divided into 4 equal groups [n = 15]. Group 1, irrigated with EDTA 17% and 5.25% NaOCl, groups 2, 3 and 4, 1%, 2.5%, and 5% NaOCl activated with Nd:YAG laser, respectively. Teeth were split longitudinally and subjected to scanning electron microscope [SEM]. Data were analyzed by Kruskal-Wallis, Mann-Whitney tests. P value of <0.05 was considered statistically significant

Results: Five percent NaOCl LAI [laser-activated irrigation] showed best smear layer removal in test groups and the difference was statistically significant [P < 0.001]. Control group [EDTA 17% and 5.25% NaOCl irrigation] showed significantly better outcomes in comparative with test groups [P < 0.001]. In the apical third, compared to coronal and middle third, the canal walls were often contaminated by inorganic debris and smear layer

Conclusion: All different concentrations of sodium hypochlorite activated with laser have a positive effect on removing of smear layer. Sodium hypochlorite activated with laser removed smear layer more effectively at the coronal and middle third compared to the apical third

Effect of surface treatment with carbon dioxide [CO[2]] laser on bond strength between cement resin and zirconia

Since it is not possible to form an adequate micromechanical bond between resin cement and zirconia ceramics using common surface treatment techniques, laser pretreatment has been suggested for zirconia ceramic surfaces. The aim of this study was to evaluate the effect of Carbon Dioxide [CO[2]] Laser treatment on shear bond strength [SBS] of resin cement to zirconia ceramic. In this in vitro study thirty discs of zirconia with a diameter of 6 mm and a thickness of 2 mm were randomly divided into two groups of 15. In the test group the zirconia disc surfaces were irradiated by CO[2] laser with an output power of 3 W and energy density of 265.39 j/cm[2]. Composite resin discs were fabricated by plastic molds, measuring 3 mm in diameter and 2 mm in thickness and were cemented on zirconia disk surfaces with Panavia F2.0 resin cement [Kuraray Co. Ltd, Osaka, Japan]. Shear bond strength was measured by a universal testing machine at a crosshead speed of 0.5 mm/min. The fracture type was assessed under a stereomicroscope at ×40. Surface morphologies of two specimens of the test group were evaluated under SEM before and after laser pretreatment. Data was analyzed by paired t-test [p value < 0.05]. The mean SBS values of the laser and control groups were 12.12 +/- 3.02 and 5.97 +/- 1.14 Mpa, respectively. Surface treatment with CO[2] laser significantly increased SBS between resin cement and zirconia ceramic [p value = 0.001]. Under the limitations of this study, surface treatment with CO[2] laser increased the SBS between resin cement and the zirconia ceramic

Antibacterial properties of composite resins incorporating silver and zinc oxide nanoparticles on Streptococcus mutans and Lactobacillus

OBJECTIVES: Recurrent caries was partly ascribed to lack of antibacterial properties in composite resin. Silver and zinc nanoparticles are considered to be broad-spectrum antibacterial agents. The aim of the present study was to evaluate the antibacterial properties of composite resins containing 1% silver and zinc-oxide nanoparticles on Streptococcus mutans and Lactobacillus. MATERIALS AND METHODS: Ninety discoid tablets containing 0%, 1% nano-silver and 1% nano zinc-oxide particles were prepared from flowable composite resin (n = 30). The antibacterial properties of composite resin discs were evaluated by direct contact test. Diluted solutions of Streptococcus mutans (PTCC 1683) and Lactobacillus (PTCC 1643) were prepared. 0.01 mL of each bacterial species was separately placed on the discs. The discs were transferred to liquid culture media and were incubated at 37degrees C for 8 hr. 0.01 mL of each solution was cultured on blood agar and the colonies were counted. Data was analyzed with Kruskall-Wallis and Mann-Whitney U tests. RESULTS: Composites containing nano zinc-oxide particles or silver nanoparticles exhibited higher antibacterial activity against Streptococcus mutans and Lactobacillus compared to the control group (p < 0.05). The effect of zinc-oxide on Streptococcus mutans was significantly higher than that of silver (p < 0.05). There were no significant differences in the antibacterial activity against Lactobacillus between composites containing silver nanoparticles and those containing zinc-oxide nanoparticles. CONCLUSIONS: Composite resins containing silver or zinc-oxide nanoparticles exhibited antibacterial activity against Streptococcus mutans and Lactobacillus.

Bond strength of resin cement to CO2 and Er:YAG laser-treated zirconia ceramic

OBJECTIVES: It is difficult to achieve adhesion between resin cement and zirconia ceramics using routine surface preparation methods. The aim of this study was to evaluate the effects of CO2 and Er:YAG laser treatment on the bond strength of resin cement to zirconia ceramics. MATERIALS AND METHODS: In this in-vitro study 45 zirconia disks (6 mm in diameter and 2 mm in thickness) were assigned to 3 groups (n = 15). In control group (CNT) no laser treatment was used. In groups COL and EYL, CO2 and Er:YAG lasers were used for pretreatment of zirconia surface, respectively. Composite resin disks were cemented on zirconia disk using dual-curing resin cement. Shear bond strength tests were performed at a crosshead speed of 0.5 mm/min after 24 hr distilled water storage. Data were analyzed by one-way ANOVA and post hoc Tukey's HSD tests. RESULTS: The means and standard deviations of shear bond strength values in the EYL, COL and CNT groups were 8.65 +/- 1.75, 12.12 +/- 3.02, and 5.97 +/- 1.14 MPa, respectively. Data showed that application of CO2 and Er:YAG lasers resulted in a significant higher shear bond strength of resin cement to zirconia ceramics (p < 0.0001). The highest bond strength was recorded in the COL group (p < 0.0001). In the CNT group all the failures were adhesive. However, in the laser groups, 80% of the failures were of the adhesive type. CONCLUSIONS: Pretreatment of zirconia ceramic via CO2 and Er:YAG laser improves the bond strength of resin cement to zirconia ceramic, with higher bond strength values in the CO2 laser treated samples.

[Comparison of the anti-caries effect of polyphenol extract of green tea with 0.05% fluoride, 0.2% chlorhexidine and fluoride-chlorhexidine, an in vitro study]

Mouth rinses beside the other methods have an important role in reducing dental caries. The aim of this study was in-vitro comparison of the anti-caries effect of polyphenol extract of green tea with 0.05% fluoride, 0.2% cholorhexidine and fluoridecholorhexidine. In this laboratory experimental study, 50 maxillary premolars were placed separately in tubes which contained cariogenic solution [streptococcus mutans, lactobacillus and 3 ml sucrose solution of 20%]. Each tube regarding the rinse solution was placed in 5 experimental groups [n=10] as follows: 1] normal saline, 2] 10% solution of green tea polyphenol extract, 3] 0.05% fluoride, 4] 0.2% cholorhexidine and 5] fluoride_cholorhexidine. Every 24 hours, the teeth were rinsed with 5 mL of the rinse. After 21 hours, the depth of decay was measured by polarized light microscope. Data were analyzed by SPSS V 13.0 software using Colmogrove Smirnove, One way ANOVA and Tukey tests. The mean and standard deviation of the depth of the caries in group 1 to 5 were 194 +/- 16.43, 175 +/- 17.94, 142 +/- 9.34, 155 +/- 13.27, and 144 +/- 8.57, respectively. One way ANOVA showed that there were significant differences between the groups [P<0.001]. Tukey test showed that although there was no significant difference in the depth of the caries between groups 1 and 2 [P=0.205], it was significantly less than groups 3 to 5 [P<0.001]. There were no significant differences between the depth of the caries in group 3, 4 and 5. According to the results of the current study, the anti-caries effect of flouride_cholorhexidine was the greatest between the groups. As the anti cariogenic effect of green tea was similar to that of normal saline and significantly less than fluoride or chlorhexidine, its use as a common mouth rinse needs more research

Effect of Epigallocatechin Gallate on shear bond strength of composite resin to bleached enamel: an in vitro study

OBJECTIVES: The aim of this study was to determine the effect of epigallocatechin gallate (EGCG) on the shear bond strength of composite resin to bleached enamel. MATERIALS AND METHODS: Ninety enamel surfaces of maxillary incisors were randomly divided into 9 groups as follows: G1: control (no bleaching); G2: bleaching; G3: bleaching and storage for seven days; G4 - 6: bleaching and application of 600, 800 and 1,000 micromol of EGCG-containing solution for 10 minutes, respectively; G7 - 9: bleaching and application of 600, 800 and 1,000 micromol of EGCG-containing solution for 20 minutes, respectively. The specimens were bleached with 30% hydrogen peroxide gel and a composite resin cylinder was bonded on each specimen using a bonding agent. Shear bond strength of the samples were measured in MPa. Data was analyzed using the two-way ANOVA and Tukey HSD tests (alpha = 0.05). RESULTS: The maximum and minimum mean shear bond strength values were observed in G1 and G2, respectively. Time and concentration of EGCG showed no significant effects on bond strength of the groups (p > 0.05). Multiple comparison of groups did not reveal any significant differences between the groups except for G2 and all the other groups (p < 0.05). CONCLUSIONS: There is a significant decrease in bond strength of composite resin to enamel immediately after bleaching. A delay of one week before bonding and the use of EGCG increased bond strength of composite resin to bleached enamel.