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

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 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

Global, regional, and national burden of disorders affecting the nervous system, 1990–2021: a systematic analysis for the Global Burden of Disease Study 2021

BackgroundDisorders affecting the nervous system are diverse and include neurodevelopmental disorders, late-life neurodegeneration, and newly emergent conditions, such as cognitive impairment following COVID-19. Previous publications from the Global Burden of Disease, Injuries, and Risk Factor Study estimated the burden of 15 neurological conditions in 2015 and 2016, but these analyses did not include neurodevelopmental disorders, as defined by the International Classification of Diseases (ICD)-11, or a subset of cases of congenital, neonatal, and infectious conditions that cause neurological damage. Here, we estimate nervous system health loss caused by 37 unique conditions and their associated risk factors globally, regionally, and nationally from 1990 to 2021.MethodsWe estimated mortality, prevalence, years lived with disability (YLDs), years of life lost (YLLs), and disability-adjusted life-years (DALYs), with corresponding 95% uncertainty intervals (UIs), by age and sex in 204 countries and territories, from 1990 to 2021. We included morbidity and deaths due to neurological conditions, for which health loss is directly due to damage to the CNS or peripheral nervous system. We also isolated neurological health loss from conditions for which nervous system morbidity is a consequence, but not the primary feature, including a subset of congenital conditions (ie, chromosomal anomalies and congenital birth defects), neonatal conditions (ie, jaundice, preterm birth, and sepsis), infectious diseases (ie, COVID-19, cystic echinococcosis, malaria, syphilis, and Zika virus disease), and diabetic neuropathy. By conducting a sequela-level analysis of the health outcomes for these conditions, only cases where nervous system damage occurred were included, and YLDs were recalculated to isolate the non-fatal burden directly attributable to nervous system health loss. A comorbidity correction was used to calculate total prevalence of all conditions that affect the nervous system combined.FindingsGlobally, the 37 conditions affecting the nervous system were collectively ranked as the leading group cause of DALYs in 2021 (443 million, 95% UI 378–521), affecting 3·40 billion (3·20–3·62) individuals (43·1%, 40·5–45·9 of the global population); global DALY counts attributed to these conditions increased by 18·2% (8·7–26·7) between 1990 and 2021. Age-standardised rates of deaths per 100 000 people attributed to these conditions decreased from 1990 to 2021 by 33·6% (27·6–38·8), and age-standardised rates of DALYs attributed to these conditions decreased by 27·0% (21·5–32·4). Age-standardised prevalence was almost stable, with a change of 1·5% (0·7–2·4). The ten conditions with the highest age-standardised DALYs in 2021 were stroke, neonatal encephalopathy, migraine, Alzheimer's disease and other dementias, diabetic neuropathy, meningitis, epilepsy, neurological complications due to preterm birth, autism spectrum disorder, and nervous system cancer.InterpretationAs the leading cause of overall disease burden in the world, with increasing global DALY counts, effective prevention, treatment, and rehabilitation strategies for disorders affecting the nervous system are needed

Global burden of 288 causes of death and life expectancy decomposition in 204 countries and territories and 811 subnational locations, 1990–2021: a systematic analysis for the Global Burden of Disease Study 2021

BACKGROUND Regular, detailed reporting on population health by underlying cause of death is fundamental for public health decision making. Cause-specific estimates of mortality and the subsequent effects on life expectancy worldwide are valuable metrics to gauge progress in reducing mortality rates. These estimates are particularly important following large-scale mortality spikes, such as the COVID-19 pandemic. When systematically analysed, mortality rates and life expectancy allow comparisons of the consequences of causes of death globally and over time, providing a nuanced understanding of the effect of these causes on global populations. METHODS The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2021 cause-of-death analysis estimated mortality and years of life lost (YLLs) from 288 causes of death by age-sex-location-year in 204 countries and territories and 811 subnational locations for each year from 1990 until 2021. The analysis used 56 604 data sources, including data from vital registration and verbal autopsy as well as surveys, censuses, surveillance systems, and cancer registries, among others. As with previous GBD rounds, cause-specific death rates for most causes were estimated using the Cause of Death Ensemble model-a modelling tool developed for GBD to assess the out-of-sample predictive validity of different statistical models and covariate permutations and combine those results to produce cause-specific mortality estimates-with alternative strategies adapted to model causes with insufficient data, substantial changes in reporting over the study period, or unusual epidemiology. YLLs were computed as the product of the number of deaths for each cause-age-sex-location-year and the standard life expectancy at each age. As part of the modelling process, uncertainty intervals (UIs) were generated using the 2·5th and 97·5th percentiles from a 1000-draw distribution for each metric. We decomposed life expectancy by cause of death, location, and year to show cause-specific effects on life expectancy from 1990 to 2021. We also used the coefficient of variation and the fraction of population affected by 90% of deaths to highlight concentrations of mortality. Findings are reported in counts and age-standardised rates. Methodological improvements for cause-of-death estimates in GBD 2021 include the expansion of under-5-years age group to include four new age groups, enhanced methods to account for stochastic variation of sparse data, and the inclusion of COVID-19 and other pandemic-related mortality-which includes excess mortality associated with the pandemic, excluding COVID-19, lower respiratory infections, measles, malaria, and pertussis. For this analysis, 199 new country-years of vital registration cause-of-death data, 5 country-years of surveillance data, 21 country-years of verbal autopsy data, and 94 country-years of other data types were added to those used in previous GBD rounds. FINDINGS The leading causes of age-standardised deaths globally were the same in 2019 as they were in 1990; in descending order, these were, ischaemic heart disease, stroke, chronic obstructive pulmonary disease, and lower respiratory infections. In 2021, however, COVID-19 replaced stroke as the second-leading age-standardised cause of death, with 94·0 deaths (95% UI 89·2-100·0) per 100 000 population. The COVID-19 pandemic shifted the rankings of the leading five causes, lowering stroke to the third-leading and chronic obstructive pulmonary disease to the fourth-leading position. In 2021, the highest age-standardised death rates from COVID-19 occurred in sub-Saharan Africa (271·0 deaths [250·1-290·7] per 100 000 population) and Latin America and the Caribbean (195·4 deaths [182·1-211·4] per 100 000 population). The lowest age-standardised death rates from COVID-19 were in the high-income super-region (48·1 deaths [47·4-48·8] per 100 000 population) and southeast Asia, east Asia, and Oceania (23·2 deaths [16·3-37·2] per 100 000 population). Globally, life expectancy steadily improved between 1990 and 2019 for 18 of the 22 investigated causes. Decomposition of global and regional life expectancy showed the positive effect that reductions in deaths from enteric infections, lower respiratory infections, stroke, and neonatal deaths, among others have contributed to improved survival over the study period. However, a net reduction of 1·6 years occurred in global life expectancy between 2019 and 2021, primarily due to increased death rates from COVID-19 and other pandemic-related mortality. Life expectancy was highly variable between super-regions over the study period, with southeast Asia, east Asia, and Oceania gaining 8·3 years (6·7-9·9) overall, while having the smallest reduction in life expectancy due to COVID-19 (0·4 years). The largest reduction in life expectancy due to COVID-19 occurred in Latin America and the Caribbean (3·6 years). Additionally, 53 of the 288 causes of death were highly concentrated in locations with less than 50% of the global population as of 2021, and these causes of death became progressively more concentrated since 1990, when only 44 causes showed this pattern. The concentration phenomenon is discussed heuristically with respect to enteric and lower respiratory infections, malaria, HIV/AIDS, neonatal disorders, tuberculosis, and measles. INTERPRETATION Long-standing gains in life expectancy and reductions in many of the leading causes of death have been disrupted by the COVID-19 pandemic, the adverse effects of which were spread unevenly among populations. Despite the pandemic, there has been continued progress in combatting several notable causes of death, leading to improved global life expectancy over the study period. Each of the seven GBD super-regions showed an overall improvement from 1990 and 2021, obscuring the negative effect in the years of the pandemic. Additionally, our findings regarding regional variation in causes of death driving increases in life expectancy hold clear policy utility. Analyses of shifting mortality trends reveal that several causes, once widespread globally, are now increasingly concentrated geographically. These changes in mortality concentration, alongside further investigation of changing risks, interventions, and relevant policy, present an important opportunity to deepen our understanding of mortality-reduction strategies. Examining patterns in mortality concentration might reveal areas where successful public health interventions have been implemented. Translating these successes to locations where certain causes of death remain entrenched can inform policies that work to improve life expectancy for people everywhere. FUNDING Bill & Melinda Gates Foundation