Microshear Bond Strength of OptiBond All-In-One Self-adhesive Agent to Er:YAG Laser Treated Enamel After Thermocycling and Water Storage

Introduction: This study aimed to compare the microshear bond strength of composite to enamel treated with Erbium-Doped Yttrium Aluminum Garnet (Er:YAG) laser using a self-etch one step bonding agent.Methods: Seventy-six enamel surfaces were prepared from 38 sound human third molar teeth. Specimens were randomly divided into four groups of 18. The enamel surface in half the specimens was irradiated with Er:YAG laser. One extra specimen from each group was evaluated under a scanning electron microscope (SEM). Composite micro-cylinders were bonded to the specimen surfaces using OptiBond All-In-One (OB) adhesive agent and stored in distilled water for 24 hours. Half the specimens were thermocycled (2000 cycles) and stored in distilled water at 37°C for three months (TW). The microshear bond strength of composite to enamel was measured using a universal testing machine at a crosshead speed of 1 mm/min. The fractured surfaces were evaluated under a stereomicroscope at ×40 magnification to determine the mode of failure. Data were analyzed using repeated measures analysis of variance (ANOVA) and t test.Results: The mean values (±standard deviation) were 17.96 ± 2.92 MPa in OB group, 22.29 ± 4.25 MPa in laser + OB group, 18.11 ± 3.52 MPa in laser + OB + TW group and 9.42 ± 2.47 MPa in OB + TW group. Repeated measures ANOVA showed that laser irradiation increased the microshear bond strength (P < 0.001). Bond strength decreased when the samples were thermocycled and stored for three months (P < 0.001). The interaction effect of water storage and laser treatment on bond strength was significant (P < 0.05).Conclusion: Enamel surface preparation with Er:YAG laser is recommended to enhance the durability of the bond of self-etch bonding systems to enamel

Perception of Undergraduate Dental Students About the Advantages and Disadvantages of Distance Education During the COVID-19 Pandemic

Objectives The present study aimed to assess the dental students' perception about distance education during the coronavirus disease-2019 (COVID-19) pandemic. Methods An analytical cross-sectional study was done on 288 dental students from Shahid Beheshti and Mashhad Universities of Medical sciences in February 2022. A standardized, electronic questionnaire was used for data collection. The questionnaire included a comparison of pros and cons of distance and in-person education and the NAVID system with online video lectures. The content validity of the questionnaire was assessed by qualitative and quantitative validation tools. The Chi-square test was used to compare the advantages and disadvantages of distance learning. Online video lectures and the NAVID system were compared by the Wilcoxon signed rank test. Results Totally, 288 students (141 females and 147 males) completed the online questionnaire. Instant access to online sources was the most essential advantage of e-learning (74.7%), and the most critical disadvantages were lack of student-tutor (50.5%) and student-student interactions (50%). The NAVID system was easier to use than the online video lectures. The online classes were less successful in building student-tutor interactions compared with in-person classes. The NAVID system received more scores in fulfilling the students' expectations about the quality of conveying the concepts and learning. Conclusion The sudden shift from in-person to distance learning has caused some educational problems and lowered the student-student and student-tutor interaction quality. However, optimizing the infrastructure and necessary facilities for online education would help obviate the students' academic needs

Influence of CO2 Laser Irradiation and CPP-ACP Paste Application on Demineralized Enamel Microhardness

Introduction: It has been suggested that the application of casein phosphopeptide-amorphous calcium phosphate paste (CPP-ACP) and CO2 laser irradiation on enamel could increase the resistance of enamel to caries and acid attacks. The aim of the current study was to compare the influence of CPP-ACP paste application and irradiation of CO2 laser on microhardness of demineralized enamel.Methods: Thirty sound maxillary extracted premolars were selected. The crowns were cut at the cervical line and were split into facial and palatal halves. Specimens were mounted in self-cure acrylic blocks in such way that the enamel surface was exposed to 4×4 mm. After a pH cycling of the specimens, they were randomly divided into 4 groups (n = 15), as follows: CG: Control group, LAS: CO2 laser, CP: CPP-ACP and LASCP: laser combined CPP-ACP treatment. The Vickers microhardness of the specimens was measured (500 g load, 5 seconds, 3 points). Data were analyzed using one-way ANOVA and post hoc Tukey tests (α = 0.05).Results: The lowest mean Vickers microhardness value was observed in CG group (192.57±50.87 kg/mm2) and the highest in LASCP group (361.86±22.22 kg/mm2). There were significant differences between groups (P < 0.001). The pairwise comparison of the groups revealed that there were significant differences between these groups: CG versus LAS, CP, LASCP (P < 0.05) and LASCP versus LAS and CP (P < 0.05). No significant difference between LAS group versus CP group (P > 0.05) was observed.Conclusion: The results of the current study revealed that CO2 laser and CCP-ACP were effective for improvement of enamel hardness value after demineralization. Incorporation of CO2 laser irradiation and CCP-ACP paste application provides additional remineralizing potential for demineralized enamel

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 Diode Laser (810 nm) Irradiation on Marginal Microleakage of Multi-mode Adhesive Resins in Class V Composite Restorations

Introduction: Some studies have shown that laser irradiation on unpolymerized adhesives can improve composite-dentin adhesion. The aim of the present study was to evaluate the effect of the Diode laser (810 nm) on the microleakage of multi-mode adhesive systems at enamel and dentin margins of composite restorations.Methods: Classic Class V boxes were prepared on 48 sound premolar teeth and randomly divided into six groups (n=16). In the control groups, Scotch bond U(SBC), G-Premio (GBC), and Ambar U (AMC) were used by a self-etch mode. In the test groups (SBL, GBL, ABL), the 810 nm Diode laser was irradiated (1 Watt) for 10 seconds before the polymerization of the adhesive. The Boxes were restored by the resin composite. After finishing and polishing, the samples were thermocycled (5℃ to55℃) for 1000 cycles and then immersed in 0.1% Methylene blue dye (48 hours). Dye penetration through the gingival and occlusal margins was measured by Stereomicroscope. The data were analyzed at the 5% significance level using Kruskal-Wallis and Mann-Whitney U tests.Results: Significant differences were found between the control and test groups (p<0.05). The occlusal margins of the SBL and GBL groups and the cervical margin of the SBL group exhibited the lowest microleakage (p<0.05). The AM control group showed maximum microleakage at cervical and occlusal margins.Conclusions: The irradiation of the 810 nm Diode laser on the unpolymerized universal adhesive systems in a self-etch mode caused a significant reduction in enamel and dentin marginal microleakage of composite restorations.

Effect of Tubular Orientation on the Microtensile Bond Strength of Composite-dentin using Universal Bonding Agents

The aim of this study was to evaluate the effect of dentinal tubules orientation on the composite-dentin microtensile bond strength using universal adhesives. A total of 36 caries-free third molars were selected. The teeth were allocated to (axial, wall) and (occlusal, floor) groups and each group was divided into three subgroups based on the type of bonding used. The specimens were then sectioned to obtain dentin-composite sticks with a binding area of approximately 1 mm2. Then sticks were mounted in the universal testing machine (UTM) at a crosshead speed of 0.5mm/min. Data collection was carried out using two-way ANOVA and T-test. Then, the failure mode of the specimens was observed using a stereomicroscope, and one specimen from each group was evaluated under a scanning electron microscope (SEM). The results of two-way ANOVA showed that the highest and lowest mean microtensile bond strength (μTBS) were observed in the group of Adper Single Bond 2 adhesive (axial, wall) (28.92±8.75) and Single Bond Universal adhesive (occlusal, floor) (12.83±7.90), respectively. On the other hand, there was no significant difference between the three adhesives in the mean of μTBS in the (occlusal, floor)orientation, but the mean μTBS of Adper Single Bond 2 adhisive was significantly higher than that of G-premio and Single Bond Universal adhesives in the (axial, wall) orientation (P=0.05). There was no significant difference in two universal adhesives (P= 0.994). The stereomicroscopic analysis showed that the highest adhesive failure was related to Adper Single Bond 2 in (axial, wall) orientation. However, the failure mode results were nearly identical in both adhesives in the (axial, wall) orientation. The failure mode results were also similar in all three adhesives in the (occlusal, floor) orientation. The dentinal tubules orientation showed no significant effect on the microtensile bond strength of the Gpremio, Single Bond Universal adhesives. Adper Single Bond 2 had a significantly higher μTBS rate in the (axial, wall) orientation, but its μTBS was similar to that of the universal adhesives in the (occlusal, floor) orientation, which was not statistically significant

Total antioxidant capacity of saliva and dental caries

Objective: Dental caries is one of the most common infectious diseases worldwide. Saliva has many functions in the oral cavity and is the first line defense against dental caries. Oxidative stress can affect initiation and progression of many inflammatory and infectious diseases such as dental caries. Thus the aim of this study was to evaluate the relationship between total antioxidant capacity (TAC) of saliva and dental caries. Study D esign: 100 healthy high school students (50 female and 50 male) with age range of 15 -17 years were randomly selected, divided to four groups. Unstimulated whole saliva specimens were collected at the morning. TAC of saliva was evaluated by spectrophotometric assay. Statistical comparisons were performed using Student's t-test, by SPSS 13. Results: The level of TAC was significantly higher in the saliva of caries active group relative to the caries free subjects. Statistical analysis for male and female groups showed a statistically significant reduction of TAC level in female group. Conclusion: TAC was higher in caries active group. Thus this result showed that total antioxidant capacity may influence in dental caries and activity can be measured by salivary factors and this may be helpful in preventive dentistry

Effect of Surface Treatment with Carbon Dioxide (CO2) Laser on Bond Strength between Cement Resin and Zirconia

Introduction: 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 (CO2) Laser treatment on shear bond strength (SBS) of resin cement to zirconia ceramic.Methods: 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 CO2 laser with an output power of 3 W and energy density of 265.39j/cm2. 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).Results: 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 CO2 laser significantly increased SBS between resin cement and zirconia ceramic (p value = 0.001).Conclusion: Under the limitations of this study, surface treatment with CO2 laser increased the SBS between resin cement and the zirconia ceramic

Effect of 940nm Diode Laser Irradiation on Microtensile Bond Strength of an Etch and Rinse Adhesive (Single Bond 2) to Dentin

Statement of the Problem: Laser can influence bonding mechanism by increasing the penetration depth of adhesive in smear layer. The effect of 940 nm diode laser on microtensile bond strength of adhesive to dentin has not been investigated in previous studies. Purpose: The aim of this study was to evaluate the effect of 940 nm diode laser irradiation on microtensile bond strength of Single Bond 2 to dentin. Materials and Method: Thirty sound premolars extracted for orthodontic reasons were randomly divided into five groups as follows: G1 or control: etching+ Single Bond2 (SB); G2: diode laser (940 nm wavelength, 1W power, continuous mode)+ etching+ SB; G3: etching+ laser irradiation+ SB; G4: etching+ SB+ laser irradiation+ adhesive curing; G5: etching+ laser irradiation+ SB +laser irradiation +adhesive curing. After the bonding procedure, Z250 composite resin was applied on the dentin surface in three layers of 2 mm thickness. After 24 hours of immersion in distilled water at 37°C and thermocycling for 1000 thermal cycles, the teeth were sectioned into 1mm2 sticks. The microtensile bond strength was measured using a universal testing machine. Bond strength (MPs) was analyzed by one-way ANOVA followed by HSD post hoc Tukey’s test (α=0.05). Results: G4 (38.35±8.99) showed the significant highest bond strength compared to other groups (p= 0.000). G5 (25.16±6.14) showed significantly higher bondstrength than the control group (18.85±4.79) (p= 0.032).Bond strength of G2 (23.39±6.07) and G3 (22.85±5.11) groups was the same and similar to that in the control group (p> 0.05). Conclusion: Based on the results of this study, it may be concluded that dentin surface irradiation with 940 nm diode laser after adhesive application and prior to curing can significantly increase the bond strength of composite to dentin