The influence of mesiodistal dimension of abutment preparation design on stress distribution in fiber-reinforced composite inlay fixed partial dentures: a finite element study

Introduction: Fiber-reinforced composites (FRCs) arecomprised of fiber and composite resin. Use of this materialin conservative dentistry for fabricating fixed partialdentures is growing. Although different studies have investigatedFRC inlay fixed partial dentures, the reportedresults have been controversial. Due to the limitations ofexperimental studies for assessment of masticatory forcesin the oral cavity, computer software was used in thepresent study to simulate oral environment. The aim ofthis study was to compare stress distribution in FRC inlaybridges with two abutment preparation designs with differentmesiodistal (MD) dimensions using a 3-dimensionalfinite element analysis.Method: ABAQUS software version 6.3-1 (HKS Inc.) wasused to create a 3D design. Two 3-unit inlay bridges weredesigned with two different abutment preparations inthe anterior teeth with different MD dimensions: dovetailpreparation with larger MD dimension and box preparationwith smaller MD dimension. Next, 50 N load was appliedwithin one second to the cingulum.Results: The maximum stress in the two bridges was concentratedat the connector areas between the abutmentsand the pontic. The difference in this respect was statisticallysignificant. The stress was approximately 10 timeshigher in the box preparation with smaller MD dimensionthan dovetail preparation.Conclusion: The stress distribution was more uniform indovetail preparation with greater mesiodistal dimensionthan in the smaller box design

Effect of different treatment on Surface Morphology of laser bleached teeth: SEM Evaluation

Objective: The aim of this study was to evaluate and compare the effect of dental surface treatment with Er:YAG , Nd:YAG ,CO2 lasers and sodium ascorbate to recently laser bleached enamel by scanning electron microscope (SEM).Methods: 15caries-free extracted human third molars were selected for this study. The samples were bleached by Heydent JW power activated by diode laser 810 nm. After 7 day, the bleaching procedure was repeated as same as first time. Then, the samples were divided to five groups randomly as follow: Group 1: treated using Nd:YAG laser with output power of 1 W, Group 2: treated using Er:YAG laser with output power of 0.5 W, Group 3: treated using CO2 laser with output power of 0.5 W, Group 4: sodium ascorbate 10%, Group 5: no surface treatment. After treatments, the surfaces were evaluated using Scanning Electron Microscope (SEM) analysis.Results: The surfaces treated by Nd:YAG laser showed some melting area but the surface treated by Er:YAG laser showed irregular and micro porous surface. CO2 laser treatment of surfaces resulted in melting of superficial layer of dental substrate and micro cracks. Sodium ascorbate did not change the surface except changes raised from bleaching.Conclusion: Laser conditioning of laser-bleached teeth can be beneficial for enhancing bond  strength of resin material to recently bleached enamel

In Vitro Evaluation of the Effect of Different Laser Irradiations on the Enamel Surfaces of Teeth Treated with Home Bleach Procedure

Introduction:The aim of this study was to evaluate the effect of dental surface treatment with Erbium-Doped Yttrium Aluminum Garnet(Er: YAG), Neodymium-Doped Yttrium Aluminium Garnet(Nd: YAG) and Carbon Dioxide Laser  (CO2) lasers and sodium ascorbate to recently home bleached enamel by scanning electron microscope (SEM).Methods: Thirty extracted human third molars were selected for this in vitro study. The teeth were randomly divided in two groups including home bleached group and control group (non-bleached). In group 1, the samples were bleached by home bleach technique. No bleaching procedure was done in second the group which served as control group. Then, the samples of two groups were divided to five subgroups as follow:  Subgroup 1: treated using Nd:YAG laser with output power of 1 W, Subgroup 2: treated using Er:YAG laser with output power of 0.5 W, Subgroup 3: treated using CO2 laser with output power of 0.5 W, Subgroup 4: sodium ascorbate 10%, Subgroup 5: no treatment. After treatments, the surfaces were evaluated using Scanning Electron Microscope (SEM) analysis.Results:The surfaces treated by Nd:YAG laser showed some melting and recrystallized areas and in some area droplet pattern was observed. But the surface treated by Er:YAG laser showed irregular and micro porous surface with flake pattern. CO2 laser treatment of home-bleached surfaces resulted in melting area and cracks. Sodium ascorbate did not change the home-bleached surface.Conclusion:Among different surface treatments used in this study, it seems that Er:YAG laser can best interact with home-bleached teeth

Effect of different conditioning methods on the surface roughness of dental amalgam: SEM analysis

The purpose of this study was incorporation of SEM micrographs for evaluating the effect of different mechanical and chemical treatments on surface roughness of dental amalgam. Amalgam was condensed in 18 plastic molds and the following modification methods were accomplished on samples surface: 1) Chemical solutions (5 groups) on fresh amalgam 2) Chemical solutions (5 groups) on aged amalgam 3) Sandblast on aged amalgam 4) Sandblast on fresh amalgam (2 groups) before & after primary setting. 5) Use of diamond bur (0.10 coarse) on aged amalgam. 6) Acid etch (37% phosphoric acid) on fresh amalgam. 7) Metal etch on fresh amalgam. 8) Varnish solvent in amalgam capsule, trituration &condensation (fresh). 9) Standard sample without any treatment. All groups were analyzed by SEM (×l00, ×500 magnifications were used for roughness quantification and chemical analysis respectively). The numbers of surface peaks were counted in 5 area of each micrograph and consequently the data were assessed by K-S & student T- tests. All groups have statistically significant difference with control except three ones (incorporation of phosphoric acid, EDTA+NH3, and NaOH+I2 on fresh amalgam). Sandblast, diamond bur & metal etch reduced surface roughness and use of chemical solutions showed different reactions

Effect of different conditioning methods on the surface roughness of dental amalgam: SEM analysis

The purpose of this study was incorporation of SEM micrographs for evaluating the effect of different mechanical and chemical treatments on surface roughness of dental amalgam. Amalgam was condensed in 18 plastic molds and the following modification methods were accomplished on samples surface: 1) Chemical solutions (5 groups) on fresh amalgam 2) Chemical solutions (5 groups) on aged amalgam 3) Sandblast on aged amalgam 4) Sandblast on fresh amalgam (2 groups) before & after primary setting. 5) Use of diamond bur (0.10 coarse) on aged amalgam. 6) Acid etch (37% phosphoric acid) on fresh amalgam. 7) Metal etch on fresh amalgam. 8) Varnish solvent in amalgam capsule, trituration &condensation (fresh). 9) Standard sample without any treatment. All groups were analyzed by SEM (×l00, ×500 magnifications were used for roughness quantification and chemical analysis respectively). The numbers of surface peaks were counted in 5 area of each micrograph and consequently the data were assessed by K-S & student T- tests. All groups have statistically significant difference with control except three ones (incorporation of phosphoric acid, EDTA+NH3, and NaOH+I2 on fresh amalgam). Sandblast, diamond bur & metal etch reduced surface roughness and use of chemical solutions showed different reactions

Effect of Er: YAG Laser on Microtensile Bond Strength of Bleached Dentin to Composite

Introduction: In non-vital tooth bleaching, dentin is in direct contact with the bleaching agent, 1 to 3-week delay is needed to eliminate free radicals from tooth structure. The present study aimed to evaluate the effect of irradiation of Er: YAG laser on immediate microtensile bond strength of bleached dentin to composite.Methods: Sixty sounds human teeth were collected and randomly divided into 4 groups (n = 15): no bleaching (NB), opalescence endo hydrogen peroxide (HP) gel bleaching, sodium perborate (SP) bleaching and laser bleaching with heydent gel (LB). The groups were divided into 3 subgroups (n = 5): no surface treatment, Er: YAG laser irradiation and 10% sodium ascorbate (SA). All samples were restored and underwent microtensile bond strength testing. Statistical analysis was carried out using one-way and two-way ANOVA.Results: Bond strength in NB-SA group had a significant difference with the NB group (P < 0.05) while no significant difference was noted between NB and NB-Er groups (P = 0.55). Application of SA and Er: YAG laser after bleaching with SP did not enhance the bond strength (P = 0.07).Conclusion: Application of SA and Er: YAG laser after HP gel bleaching significantly enhanced the bond strength. Application of Er: YAG laser after internal bleaching with HP gel could enhance the bond strength

Microtensile Bond Strength of Three Restorative Core Materials with IPS E.max Press Ceramic by Two Resin Cements

Objectives: The aim of this study was to compare the microtensile bond strengths (µ TBS) of three core materials with one lithium disilicate reinforced ceramic using two resin cements.Methods: Three core materials (Nulite F® (Biodental Technologies), Filtek Z250® (3M-ESPE), Prettau-Anterior® (Zirkonzhan, Germany)) were prepared as blocks (10×10×4 mm3) according to the manufacturer’s instructions. Lithium disilicate ceramic blocks were also constructed and bonded to core specimens with two dual curing luting resin cements (Duo-Link® (Schaumburg, IL), Bifix QM® (VOCO, Cuxhaven, Germany)). Micro-bar specimens were prepared and loaded in tension to determine the µ TBS Failure modes were classified by scanning electron microscope (SEM). Data were analysed using two-way ANOVA and Tukey HSD test.Results: The µ TBS varied significantly depending on the core materials and resin cements used (P< 0.05). The µ TBS of Bifix QM was significantly higher than of Duo-Link in all core materials. The µ TBS of zirconia core was significantly higher than of both composite cores with both resin cements. There were no statistically significant differences among Nulite F and Filtek Z250 (P> 0.05). The highest bond strength was obtained between zirconia core and Bifix QM (45.3 ± 6.7 MPa).Conclusion: In vitro µ TBS of glass ceramic blocks bonded to zirconia core material showed higher bond strength values than resin-based core material, regardless of the resin cement type used

Cytotoxicity of Silver Nanoparticles on Human Gingival Epithelial Cells: An In Vitro Study

Objective: Nanosilver has numerous applications in medicine due to its potent antibacterial activity. However, data regarding the bio-safety of its effective concentrations is scarce. This study aims to assess the toxicity of silver nanoparticles on human gingival epithelial cells under in-vitro  conditions.Methods: This in vitro study evaluated the toxic effects of filtered and unfiltered nanosilver solution on human gingival epithelial cells obtained from the Pasteur Institute of Iran using the methylthiazol tetrazolium bromide (MTT) assay (mitochondrial function)and membrane leakage of lactate dehydrogenase (LDH) at 24, 48 and 72h time points. The concentrations of silver nanoparticle solution used were 0.05, 0.1, 0.2, 0.5, 1, 2, 5, 10, 20 and 50µg/ml.Results: The MTT assay showed that nanosilver solution at high concentrations (20 and 50µg/ml) significantly decreased the viability of cells at all time points. The lower non-fatal concentrations at 24 and 48h were capable of causing cell death or significantly inhibit cell growth at 72h. The LDH assay demonstrated that death of epithelial cells only occurs at high concentrations of nanosilver (20 and 50µg) and no significant toxicity was seen at lower concentrations.Conclusion: Based on the results, silver nanoparticles have toxic effects on human gingival epithelial cells and this effect is time and dose-dependent

Sesame extraction gel as an agent for prevention of dental caries: An in-vitro study

BACKGROUND AND AIM: Sesame has a high content of calcium. Regarding to the lack of adequate data about its remineralizing potential, we conducted this study to evaluate the surface hardness of enamel exposed to sesame extraction gel in comparison to artificial saliva and fluoride. METHODS: After mounting and polishing twenty-four caries-free human premolars, the baseline microhardness was recorded. Subsequently, decalcification was accomplished by immersing into cola, after which the surface hardness was recorded again. Ultimately, the samples were divided into three groups, which were treated by either the sesame gel (SG), artificial saliva (AS) or the fluoride gel (FG). The final microhardness was assessed again. The repeated measure analysis of variance (ANOVA) was employed for comparison of baseline (B), decalcified (R) and remineralized (R) hardness while the one-way ANOVA followed by least significant difference test was used for comparison of different remineralizing agents. RESULTS: There was significant difference among the teeth at baseline, after decalcification and after treatment by experimental solutions (P < 0.001 and P = 0.002 for pair wise comparison of B/D and D/R, respectively). Moreover, after remineralizing treatment, there was no significance difference between the solutions (P = 0.350, P = 0.150 and P = 0.610 for pair-wise comparisons of SG-FG, SG-AS, FG-AS, respectively). However, the mean microhardness value was increasing in that order. CONCLUSION: Although treating the decalcified enamel by sesame extraction enhanced its microhardness, there was no significant difference between sesame, fluoride and artificial saliva when they were applied for just 15 min. KEYWORDS: Sesame; Dental Enamel; Hardnes

The Effect of Incorporation of 0.5 %wt. Silica Nanoparticles on the Micro Shear Bond Strength of a Resin Modified Glass Ionomer Cement

Statement of the Problem: The clinical success of glass ionomer restorations depends on the strength of resin-modified glass ionomer (RMGI) cement bonding to dentin and there is limited information available regarding the bond strength of resin modified glass ionomers containing silica nanoparticles to dental structures. Purpose: The aim of this study was to compare the microshear bond strength (µSBS) of RMGI with and without silica (SiO2) nanoparticles to dentin of permanent teeth. Materials and Method: in this experimental study, the occlusal surfaces of 30 freshly extracted intact third molars were ground to expose the flat dentin and after conditioning with 20% poly acrylic acid, were randomly assigned to two main groups (n=15). The first group was filled with RMGI (Fuji II LC, GC) and the second group was filled with RMGI plus 0.5%wt. silica nanoparticles. Then, each main group was divided into three subgroups, and then stored in an incubator at 37 oC with 100% humidity for 1, 7, and 30 days. The µSBS test was performed using a universal testing machine (1 mm/min). The data were analyzed by t-test, repeated measures ANOVA and Tukey test (p< 0.05). Results: There were no statistically significant differences between the mean µSBS of the groups with and without nanoparticles along the different storage periods (p> 0.05). There was significant difference in µSBS values among the three different storage periods in all the tested materials (p< 0.05). Conclusion: Incorporation of 0.5 %wt. silica nanoparticles did not compromise the µSBS of Fuji II LC RMGI to dentin