Mean Microhardness Values Research Articles

An In-Vitro Comparative Evaluation of Pre-treatment With Nano-Silver Fluoride on Inhibiting Secondary Caries at Tooth Restoration Interface.

Introduction and aimDental caries is the global burden worldwide and has a negative effect on the quality of life. Restorative materials in pediatric dentistry have shown satisfactory properties; however, the highest failures are still reported due to the occurrence of secondary caries. The article aims to assess the effectiveness of pre-treatment with nano-silver fluoride (NSF) in inhibiting secondary caries at the tooth restoration interface.Materials and methodsForty tooth specimens were prepared from 20 newly extracted human premolar teeth by sectioning the tooth mesiodistally. Class V cavities were prepared on each specimen at enamel dentin junction. Specimens were randomly distributed into four groups (n=10): 1) glass ionomer cement (GIC) restoration, 2) composite restoration 3) NSF pre-treatment + GIC restoration, 4) NSF pre-treatment + composite restoration. After sterilization, specimens were subjected to artificial caries formation by pH cycling method for 14 days. Specimens were sectioned and mounted to evaluate the demineralization by using the Vickers microhardness test. Outer lesion depth was measured at the tooth restoration interface on digital radiographs. Data was analyzed using Student unpaired t-test, one-way ANOVA, and Tukey honestly significant difference (HSD) post hoc test.ResultsThe mean microhardness value of pre-treated GIC and composite group with NSF was more than the non-treated NSF group, with a significant difference at the enamel, indicating lesser demineralization. Outer lesion depth was lesser in the pre-treated group showing better tooth restoration integrity with a statistically significant difference between the groups.ConclusionPre-treatment with NSF is beneficial in increasing the resistance of GIC and composite resin restoration to secondary caries formation.

In Vitro Evaluation of Physical and Mechanical Properties of Light-Curing Resin Cement: A Comparative Study.

Objective The aim of study was to evaluate in vitro the surface hardness, sorption, solubility, and color stability of three light-cured resin cements, namely RelyX Veneer (RLX), Variolink Veneer (VLK), and All Cem Veneer (ACV). Materials and Methods Cylindrical samples (15 × 1 mm) were made for each group using a metallic mold ( n = 10). Vickers microhardness test was performed, and average hardness was calculated from three indentations (300 gf/15s) per sample. The sorption and solubility of the materials were evaluated according to ISO 4049:2009 based on three samples weighing: initial ( m 1 ), after immersion in distilled water for 7 days ( m 2 ), and final (after removal of all moisture [ m 3 ]). The color change was observed using a digital spectrophotometer, at three different time points, baseline, 1 day, and 1 week of immersion in coffee and distilled water (control). Statistical Analysis Shapiro–Wilk test was used to analyze the normality of the data, and groups were compared using Kruskal–Wallis and Mann–Whitney tests. A significance level of 5% was used. Results RLX showed the highest microhardness mean values (36.96 VHN), but higher sorption (23.2 µg/mm 3 ) and solubility (2.40 µg/mm 3 ), with statistically significant differences with the other groups. For color stability, higher ∆E was observed for the samples immersed in coffee ( p = 0.009). The VLK resin cement presented statistically significant differences from the other groups, with higher color changes in coffee at 1 day (15.14) and after 1 week (23.65). Conclusion RLX resin cement showed better hardness results. All materials tested performed satisfactorily for sorption and solubility according to ISO 4049:2009. All materials showed high-staining values after 1 week of immersion in coffee.

Influence of ultrasonic excitation on microhardness of glass ionomer cement.

Numerous researchers have attempted to improve the mechanical properties of glass ionomer cement since 1972. In this study, ultrasonic curing treatment was introduced during the mixing of glass ionomer cement (GC Fuji IX) to facilitate intimate mixing, compaction and adaptation of residual glass particle which consequently improves densification of the material. To assess the influence of ultrasonic treatment on the microhardness of glass ionomer cement (GC Fuji IX) and compare it with the conventionally cured method. A total of 40 specimens (2 × 2 mm) were fabricated and equally divided into two groups: Group I (conventional curing method) and Group II (ultrasonically cured). For Group II, an ultrasonic scaler was used which provides energy to ensure proper mixing of material without leaving any air bubbles or unmixed particles. Vicker's hardness test was employed to generate the average microhardness values by making three indentations at different points on each specimen. Statistical Package for Social Sciences (SPSS) Version 17 was used, employing independent samples T test to compare the difference in microhardness values between two curing groups. The average surface hardness value for conventional cured GIC was 62.21 ± 13.61 while ultrasonically cured GIC exhibited a higher mean microhardness value of 66.37 ± 12.83. Additionally, the average microhardness values produced by the two groups showed statistically significant differences (p value < 0.035). Ultrasonic excitation treatment leads to intimate mixing and accelerated hardening of glass ionomer cement thereby enhancing its microhardness and reducing early weakness.

Synergistic Effect of Arginine on Remineralization Potential of Fluoride Varnish and Nanohydroxyapatite on Artificial Caries Lesions: An In Vitro Study

To evaluate the synergistic effect of arginine on the remineralizing potential of fluoride varnish and nanohydroxyapatite. A total of 100 teeth were taken; of them, 50 teeth were allotted for microhardness test and 50 teeth for scanning-electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX) analysis. Fifty teeth used for hardness testing were sectioned to obtain 100 samples, and the baseline hardness values were measured. Samples were allotted into five groups (n = 20): group I: arginine; group II: fluoride varnish; group III: nanohydroxyapatite; group IV: arginine + fluoride varnish; group V: arginine + nanohydroxyapatite. Microhardness values were measured after 96 hours of demineralization and then again after application of remineralizing agents (pH cycling) for 10 days to check for gain in microhardness. The other 50 samples were subjected to SEM-EDX analysis for evaluating gain in the mineral content after demineralization and after application of the remineralizing agents. The collected data were subjected to statistical analysis using SPSS software version 22.0. The maximum mean microhardness values were observed in group IV and group V. There was no statistical significance between them. Similarly, maximum mineral gain was seen in groups IV and V. A significant increase in fluoride gain was seen in group IV. Arginine has a synergistic effect on remineralization potential of fluoride varnish and nanohydroxyapatite. The incorporation of arginine into fluoride varnishes and nanohydroxyapatite significantly increased their remineralization potential.

Evaluation of diode laser application on chemical analysis and surface microhardness of white spots enamel lesions with two remineralizing agents.

BackgroundTo investigate the effect of diode laser application and two commercial remineralizing agents on the remineralization and surface microhardness of white spot enamel lesions. Material and MethodsSixty specimens were prepared then equally divided into six groups (n=10/group), according to the diode laser and the two commercial remineralizing agents applied to demineralized enamel surfaces (APF gel and sodium fluoride NaF mousse) with or without diode Laser application as follows; Group A; control, Group B; diode Laser application, Group C; APF gel application, Group D; NaF mousse application, Group E; APF gel application + diode Laser, Group F; NaF mousse application+ diode Laser. Then the teeth were investigated for their Ca, P & F ions content and surface microhardness. One-way ANOVA followed by Tukey’s (HSD) post hoc test were used for statistical analysis. ResultsCa ion wt% showed no statistically significant difference between tested groups, with the highest mean value recorded with Group C. P ion wt%, showed a statistically significant difference between Groups A and C, and the highest mean value was recorded for Group A. The highest F ion wt% was recorded for Group C, while the lowest was recorded for both A and B groups. The highest significant microhardness mean values was recorded for Group E, while the lowest was recorded for Group A. ConclusionsDiode Laser treatment of the demineralized enamel surface had a positive influence on the chemistry and surface microhardness and it may represent a promising adjunct for enamel surface remineralization. Key words:Diode Laser application, chemical analysis, surface microhardness, remineralizing agents, white spot lesions.

In situ fabrication of TiC-NiCr cermets by selective laser melting

In situ synthesis of TiC-NiCr cermets during selective laser melting (SLM) was investigated. Powder mixture consisting Ti, C and Ni80Cr20 solid solution was prepared by milling process to attain the nominal composition of TiC-40 wt% NiCr. Feedstock powder was milled for 7 h by a high energy ball mill. SLM process was applied at three scanning speeds and the effect of input energy density on phase formation, microstructure and hardness of resultant samples was evaluated. Morphology of the powders and microstructure of in situ fabricated cermets were investigated by field emission electron microscopy (FESEM), and structural evolution during SLM was studied by X-ray diffractometery (XRD). The results showed that TiC can be synthesized during SLM process even at relatively low energy densities and the formation mechanism of TiC phase is affected by the input energy density. Relative density of the samples increased from 88.24% to 98.53% with increasing the energy density from 138.7 to 346.7 Jmm−3. The sample fabricated by SLM process using the maximum energy density of 346.7 Jmm−3showed the highest mean microhardness value of 1289 HV.

Effect of curing time on top to bottom microhardness of bulk-fill composite

Objectives: The aim of this study was to determine the effect of light curing time on top to bottom microhardness of bulk-fill resin composites. Materials and Method: Three bulk-fill resin composites were used Admira fusion x-tra (voco), Tetric Evoceram bulk-fill (Ivoclar vivadent) and Filtek bulk-fill (3M ESPE). Sixty composite specimens were prepared in cylindrical shape. Teflon molds (4mm×4mm) diameter that are open at the top and the bottom sides were used to prepare the specimens. Thirty specimens were cured according to manufacturers’ instructions and the other thirty were cured for 40 seconds using EliparTM light curing unit. All the specimens were cured at 0 mm distance. After curing process, the specimens were stored at 37˚C at 100% humidity for 24 hours. Surface microhardness was measured and data presented as means and standard deviations (SD). Multivariant ANOVA was used to study the effect of different curing time on top and bottom values of microhardness. One-way ANOVA was also used to study the effect of different curing time on top/bottom ratio of microhardness. Results: Curing time showed a non-statistically significant effect on top and bottom mean values of microhardness of bulk-fill composite at P > 0.05. However, curing time showed a statistically significant increase on top to bottom microhardness mean ratio of all the materials P ≤0.05. Conclusion: Under the limitations of this study, it can be concluded that, the increase in the light curing time increased the top to bottom microhardness of bulk-fill materials.

The effect of two different toothpastes and tooth brushing timing on enamel surface microhardness after an erosive challenge – Ex vivo study

Introduction: Excessive consumption of carbonated beverages, fruit juices, high-energy drinks, and candies are the main causes of erosive dental lesions. Several studies have shown that phosphoric, citric acids and other substances present on these products have an erosive action on enamel surface [1]. The aim of this study is to compare the effect of two different toothpastes, with fluoride or chlorhexidine, and toothbrush timing on enamel surface microhardness after an erosive challenge with Redbull®. Materials and methods: Sample was obtained from 10 human molars (intact, caries/fracture-free). This study was approved by Egas Moniz Ethics Committee. Each tooth was sectioned in four enamel specimens (4x3mm) giving rise to 40 enamel specimens, randomly assigned in 4 different groups (n = 10): Group A - specimens were subjected to an erosive challenge (EC) with Redbull® 3 minutes, 4 times a day, 5 days and brushed with a fluoride based toothpaste immediately after (Oral B® pro-expert); Group B - EC, and brushed with a chlorhexidine based toothpaste immediately after (CHX - Elgydium® gum protection); Group C – EC, specimens were submersed two hours in artificial saliva, at 37ºC, and then tooth brushed with the same fluoride based toothpaste of group A; Group D – EC specimens were submersed two hours in artificial saliva, at 37ºC and then tooth brushed with the same chlorhexidine based toothpaste of group B. Enamel surface microhardness values were obtained with a Vickers Microhardness tester. One-way ANOVA was used for the comparison of group microhardness means and post hoc tests (Bonferroni test) for pairwise comparison of groups. Statistical significance was accepted at p < 0.05. Results: Enamel surface microhardness mean values were: Group A – 275.36 ± 50.10 HV; Group B – 304.60 ± 36.15 HV; Group C – 361.78 ± 36.17 HV; Group D – 387.16 ± 39.01 HV. Statistical analysis of data has shown no significant differences between the means of groups A and B (p = 0.117), and between the means of groups C and D (p = 0.172). However, there is statistical evidence that means of groups A and B are significantly different than means of groups C and D (p < 0.001). Discussion and conclusions: Our results suggest the best timing for tooth brushing after the extrinsic erosion of enamel with a high-energy drink should be two hours, rather than immediately after the erosive challenge. No significant differences were found in enamel surface microhardness mean values when brushing with the fluoride based compared with the chlorhexidine-based toothpaste, considering the same brushing time.

The effects of sodium hexametaphosphate combined with other remineralizing agents on the staining and microhardness of early enamel caries: An in vitro modified pH-cycling model

This study was conducted to determine the effects of sodium hexametaphosphate (SHMP) combined with other remineralizing agents on the staining and microhardness of early enamel caries. in This in vitro study The enamel buccal surfaces of 70 bovine incisors were classified into seven study groups (n = 10). Remineralizing agents were employed alone and in combination with SHMP in different groups, including: (1) 8% SHMP, (2) 2% sodium fluoride, (3) 2% sodium fluoride + SHMP, (4) Remin Pro®, (5) Remin Pro®+SHMP, (6) MI Paste Plus, and (7) MI Paste Plus + SHMP. A modified pH-cycling technique was used to reconstruct the dynamics of caries. Colorimetric and microhardness analyses were conducted before demineralization (T1), after caries formation (T2), and after the remineralizing treatment (T3). The data were analyzed by the one-way analysis of variance and the repeated measurement analysis (P > 0.05). After remineralizing cycles, the experimental groups treated with either SHMP alone or in combination with other materials showed less significant changes in the three variables of color (Δa, Δb, and ΔL) and the overall color change (ΔE). The enamel caries treated with Remin Pro® presented the highest color change, while Remin Pro®+ SHMP resulted in the least changes. The mean value of microhardness after remineralization improved significantly in all groups, except in the MI Paste Plus + SHMP group that showed the lowest value. In contrast, the highest microhardness value was recorded for Remin Pro®, being comparable to that of the sound teeth (P > 0.05). SHMP, either alone or combined with remineralizing agents, created the least staining. Remineralizing materials alone showed higher surface hardness, while sodium fluoride alone showed higher surface hardness when combined with SHMP.

Microhardness testing of resin cement versus sonic bulk fill resin composite material for cementation of CAD/CAM composite block with different thickness

Objective: evaluate the microhardness and depth of cure of sonic bulk fill resin composite material for cementation of CAD/CAM composite block with different thicknesses versus the traditionally used dual cured resin cement by assessing microhardness at the top and bottom and calculating bottom/top ratio to determine the depth of cure.Materials and methods: CAD/CAM resin composite blocks (Grandio) restorative materials were used in the present study. For cementation options, two resin materials were selected: SonicFill 2 bulk fill resin composite (Kerr) and Dual-link universal Resin cement (Bisco). Four sections were prepared from each CAD/CAM blocks thickness of 1 mm, 1.5 mm, 2 mm and 3 mm respectively. Sectioned specimens of each CAD/CAM blocks were then divided according to their thickness into three groups (n=5).Portions of each composite cement were placed on a 1-mm thick transparent glass slide and squeezed to a 100µm film thickness Each specimen was covered with one of the CAD–CAM composite block slabs or left uncovered (control) and then light-cured for 40 sec that was positioned perpendicularly on top and in direct contact with the CAD–CAM slabs or the top glass (control).Micro-hardness was obtained for the top and bottom surface of specimens. The mean microhardness values and hardness ratio % of the specimens were calculated and tabulated. Microhardness measurements were performed twice; one immediately and after 24 hours. Statistical analysis was performed. Significance of the difference within the same group was evaluated using one way analysis of variance (ANOVA) test, followed by Tukey’s post hoc test when ANOVA indicated a significant difference. T test was used to compare between both groups. The level of significance was set at P < 0.05. Results: Immediately, in control, a higher mean value was recorded in Sonicfill group, with a statistically significant difference (p=0.011). In 1 mm, 1.5 mm, 2mm, a higher mean value was recorded in SonicFill 2 group, with a statistically significant difference (p=0.003, p=0.00, p=0.00 respectively). In 3 mm resin cement recorded a mean value of 0.495±0.012.After 24 hours, in control, a higher mean value was recorded in resin cement group, with no statistically significant difference (p=0.44). In 1 mm, 1.5 mm, a higher mean value was recorded in SonicFill 2 group, with no statistically significant difference (p=0.55, p=0.356 respectively). In 2 mm, resin cement recorded a significantly higher mean value (p=0.00). In 3 mm, resin cement recorded a mean value of 0.876±0.008Conclusions: Under the limitation of the current study it could be concluded that bulk fill light cured resin composite as new trend in cementation procedure can be efficiently cured through CAD/CAM composite blocks with thickness not more than 1.5mm. Indeed, dual curable resin cement remains convenient for cementation of thicker indirect esthetic restoration.

An in vitro study to compare the influence of different all-ceramic systems on the polymerization of dual-cure resin cement.

Aim:The aim of the study is to compare the effect of composition of three different all-ceramic systems on the polymerization of dual-cure resin cement, using different curing cycles and evaluated immediately within 15 min and after 24 h.Materials and Methods:Resin cement disc samples were fabricated by polymerization through three different all-ceramic disc, namely: lithium disilicate discs – IPS e.max (Group B), leucitereinforced discs – IPS Empress (Group C), zirconia discs – Cercon (Group D), and without an intervening ceramic disc, as control (Group A). A total of 80 resin cement disc samples were fabricated for fur groups (n = 20). Each group further consisted of two subgroups (n = 10), t10 and t20 according to two different exposure times of 10 and 20 s, respectively. Each of the 80 resin disc samples was evaluated for their degree of polymerization achieved, by measuring the microhardness(Vickers hardness number) of the samples immediately within 15 min and after 24 h, giving us a total of 160 readings. Oneway analysis of variance test, ttest, and paired ttest were used for multiple group comparisons followed by Tukey's post hoc for groupwise comparison.Results:Direct activation of the resin cement samples of control (Group A) showed statistically significant higher mean microhardness values followed by Groups C then B and D, both immediately and after 24 h. The mean microhardness for immediate post-activation was always inferior to the 24 h post-activation test. For both 10 and 20 s curing cycle, there was a significant increase in the microhardness of the resin cement discs cured for 20 s through the different ceramics.Conclusion:Ceramic composition affected the polymerization of dual cured resin cement. Doubling the light irradiation time or curing cycle significantly increased mean microhardness value. Greater degree of conversion leading to an increase in hardness was observed when the resin cement discs were evaluated after 24 h.

Remineralization potential of grape seed extract hydrogels on bleached enamel compared to fluoride gel: An in vitro study.

BackgroundRemineralizing of bleached enamel is a common procedure that aims to compensate enamel mineral lose. This study aimed to evaluate the remineralization effectiveness of experimentally prepared grape seed extract hydrogels (GSE) compared to fluoride gel on bleached enamel.Material and MethodsThirty extracted maxillary incisor were bleached using white smile bleaching agent. Bleached specimens were divided into three groups (10/group) according to the remineralizing agents tested: [GSE 6%, GSE 10%, or fluoride gel]. After bleaching and remineralization procedure, the specimens were stored in artificial saliva at 37°C. Micro-hardness and Energy-Dispersive X-ray and ultra-morphological evaluation were tested at baseline, after bleaching and after remineralization.ResultsStatistical significant decrease on mean micro-hardness values had resulted after bleaching procedure compared to baseline, followed by a significant increase in GSE (10%) and fluoride groups. GSE (6%) application showed the least statistical significant mean micro-hardness, which was statistically insignificant different compared to bleaching procedure. Elemental analysis results revealed a statistical significant decrease on Ca, and Ca/P ratios (At%) values after bleaching compared to baseline, followed by a significant increase after treatment with all tested remineralizing gels. SEM photomicrograph of sound enamel shows smooth uniform appearance with few pores. Bleached enamel showed irregular pitted disorganized enamel surface. Bleached enamel exposed to GSE and fluoride gel showed occlusion of enamel surface porosities and precipitates of different sizes.ConclusionsThe specially prepared GSE hydrogels has positive effects on the remineralization process of bleached enamel making it an effective natural agent with remineralizing potential. Key words:Remineralization, bleaching, grape seed extract, fluoride, enamel.

Effect of Erbium, Chromium-Doped: Yttrium, Scandium, Gallium, and Garnet and Erbium: Yttrium-Aluminum-Garnet Laser Etching on Enamel Demineralization and Shear Bond Strength of Orthodontic Brackets.

Objective:The objective of this study was to compare the effect of two types of laser irradiation (erbium, chromium-doped: yttrium, scandium, gallium, and garnet [Er,Cr:YSGG] and erbium: yttrium-aluminum-garnet [Er:YAG]) and acid etching on enamel demineralization and shear bond strength (SBS) of orthodontic bracketsastry.Materials and Methods:Ninety premolars were selected, scaled, and polished with no fluoridated pumice, and metal brackets were bonded to them. Then, they were randomly allocated to three groups based on the etching procedure: phosphoric acid etching, Er:YAG (100 mJ, 10 Hz) laser etching, and Er,Cr:YSGG (600 mJ, 20 Hz) laser etching. Teeth to be evaluated for demineralization and SBS were exposed to pH and thermal cycling, respectively. For SBS test, a universal testing machine was used, and adhesive remnant was index scored after debonding. Microhardness of enamel was evaluated with Vickers test. Data were analyzed statistically (α = 0.05).Results:The acid-etched group exhibited significantly higher SBS values compared to the laser groups (P < 0.05); however, the difference between the Er:YAG and Er,Cr:YSGG laser groups was not significant. Microhardness mean values in descending order were as follows: Er,Cr:YSGG, Er:YAG, and acid etched. There were significant differences between the laser and control groups (P < 0.001); however, the difference between the two laser groups was not significant (P = 0.320). There were no significant differences between the three groups in adhesive remnant index scores.Conclusion:Er:YAG and Er,Cr:YSGG laser etching resulted in clinically acceptable SBS; therefore, apart from its other advantages over acid etching, it can be a good appropriate alternative for bonding of orthodontic brackets.

Effect of Wet and Dry Finishing and Polishing on Surface Roughness and Miarohardness of Bulkfill Resin Composites

Objective: The aim of this in vitro study was to evaluate surface roughness and microhardness of two bulkfill resin composites after wet and dry finishing. Materials and methods: Two Types of resin composite materials SonicFill (Sonic-activated bulk-fill Nanohybrid resin composite) and X-tra fil (Bulk-fill micro- hybrid light-cured posterior resin composite) were used. Thirty samples were fabricated of each resin composite using a metal mold measuring (6mm x 4mm). Composites were applied to molds and placed between two transparent Mylar strips and pressed flat with a microscopic glass slide. A glass slab was placed on top of the upper Mylar strip and a constant pressure was applied. The samples were cured according to manufacturers’ instructions. The samples were divided into three groups (n=10). Group A: No finishing (control group), Group B: wet finishing under water coolant, and group C dry finishing. Surface roughness was evaluated using a stereomicroscope and microhardness was measured by Vicker’s hardness tester. Data were analyzed using one-way ANOVA (P 0.05. The control group showed the lowest microhardness mean values in both materials. Dry finishing showed the highest microhardness mean values among the groups (P<0.05). Conclusion: Dry finishing and polishing increased the surface roughness and microhardness of X-tra fil (microhybrid) and (nanohybrid sonic activated) Sonicfill resin composites.

Microstructural Evolution and Mechanical Properties in Superlight Mg-Li Alloy Processed by High-Pressure Torsion.

Microstructural evolution and mechanical properties of LZ91 Mg-Li alloy processed by high-pressure torsion (HPT) at an ambient temperature were researched in this paper. The microstructure analysis demonstrated that significant grain refinement was achieved after HPT processing with an average grain size reducing from 30 μm (the as-received condition) to approximately 230 nm through 10 turns. X-ray diffraction analysis revealed LZ91 alloy was consisted of α phase (hexagonal close-packed structure, hcp) and β phase (body-centered cubic structure, bcc) before and after HPT processing. The mean value of microhardness increased with the increasing number of HPT turns. This significantly increased hardness of specimens can be explained by Hall-Petch strengthening. Simultaneously, the distribution of microhardness along the specimens was different from other materials after HPT processing due to the different mechanical properties of two different phases. The mechanical properties of LZ91 alloy processed by HPT were assessed by the micro-tensile testing at 298, 373, 423, and 473 K. The results demonstrate that the ultra-fine grain LZ91 Mg-Li alloy exhibits excellent mechanical properties: tensile elongation is approximately 400% at 473 K with an initial strain rate of 1 × 10−2 s−1.

The effect of transtooth curing technique using different LED light intensities on microhardness and depth of cure of nanofilled resin composite restorations

Aim: To evaluate the effect of different LED light intensities on microharness and depth of cure of nanofilled resin composite restorations using transtooth illumination technique with different thickness of buccal wall.Materials and methods: The materials used for this study was nanofilled resin composite material (Filtex Z350XT, 3M, ESPE) shade A3with its corresponding bonding system (single bond universal, 3M, ESPE). A total of 10 sound extracted human maxillary premolar teeth were used in this study. The teeth were divided into 2 main groups of 5 teeth each according to curing light intensities; either standard LED curing mode (800 mW/cm2) for 30 sec or high intensity LED curing mode (1400 mW/cm2) for 10 sec. In each tooth, 2 cavity preparations were performed; moderate cavity preparation width (1/3 intercuspal distance) in the mesial aspect of each tooth and wide cavity preparation (1/2 intercuspal distance) in the distal aspect. All specimens were light cured using transtooth curing technique from the buccal and lingual surfaces. Each tooth was sectioned in a mesio-distal direction into 2 equal halves. Surface Micro-hardness of the specimens was determined. The mean microhardness values and hardness ratio % of the specimens were calculated. One way analysis of variance ANOVA, Tukey’s post hoc and independent t tests were used to compare between more than 2 groups. The significance level was set at p ≤ 0.05.Results: The highest mean value for B/T ratio was recorded in Post. High I/3 ICD, whereas the lowest mean was recorded in Post.conv. I/3 ICD. ANOVA test revealed a significance difference between all groups (p<0.0001). Tukey’s post hoc test revealed no significant difference between the post high ½ ICD group and the post conv. 1/3 ICD group. Comparisons within the same groups revealed a significance difference within the post high groups, and within the post Conv. Groups (p= 0.0007, p=0.012 respectively. Moreover, there was a significant difference between the 1/3 subgroups (p<0.0001). However, the difference between the ½ ICD subgroups was not statistically significant (p=0.1174).Conclusions: Transtooth curing techniques is greatly affected by cavity width. Light intensity is critical factor that should be considered when performing transtooth curing techniques. High LED light intensity successfully able to perform optimum polymerization for resin composite in both cavity width (moderate and wide).

The Effects of Tricalcium Phosphate and Novamin Remineralizing Agents on Microhardness of Bleached Enamel with 35% Hydrogen Peroxide-An In vitro Study

Objectives: The aim of the present study was to evaluated the effects of remineralizing agents (Tricalcium phosphate and Novamin) on microhardness of bleached enamel surface with 35% hydrogen peroxide (in office).Materials and Methods: Forty human permanent maxillary premolars free from caries or enamel malformation were used. The teeth were sectioned transversally across the cemento-enamel junction, and specimens were embedded in self-cure acrylic. The labial enamel surface faced upward and then they were ground flat and polished with silicon carbide abrasive papers. A total specimen were prepared and kept in deionized water. Then the specimens were drying subjecting them for baseline microhardness testing (control). The dental bleaching treatment was performed just on the labial enamel surface of the specimens using a commercial 35% hydrogen peroxide Whitness HP bleaching gel (in-office ).It was used according to the manufacture instruction. Microhardness was tested for all specimens after bleaching. Specimens were divided into two groups according to remineralizing agent n=20, Group I: Treated by NUPRO Sensodyne with NovaMin, Group II: Treated by Clinpro™ White Varnish Tri-Calcium Phosphate. The remineralizing agent was applied for three minutes per day. Two remineralizing agents were applied for fourteen consecutive days. After each application procedure, the specimens were washed with deionized water and then kept in artificial saliva. At the end of the fourteen days the remineralized specimens were subjected to microhardness testing and values were recorded. All the data were analyzed by ANOVA and Tukey’s post hoc test. Results: Results revealed that a statistically significant decrease on mean microhardness values after enamel bleaching compared to control, followed by a significant increase on mean microhardness after the application of the both remineralizing agents. One way-ANOVA showed a statistically insignificant difference between NUPRO Sensodyne with NovaMin and Clinpro™ White Varnish at p≥0.05.Conclusions: Based on the results of this in vitro study both Tricalcium phosphate and Novamin are effective in remineralization of bleached enamel surface and no significant difference was detected in their efficacy.

The effect of different biomimetic materials as a remineralization protocol on microhardness and ultramorphology of bleached enamel

Aim: To compare the effect of Nano-HA and Nano-BG as remineralizing protocol on the microhardness and structural morphology of bleached enamel.Materials and methods: Two different biomimetic materials were used; Nano-bioactive glass powder and Nanohyroxyapatite powder. Five extracted sound human central incisors were selected. The labial of each tooth was divided longitudinal into two equal halves. The mesial half was assigned for BG group and the distal half was assigned for HA group. A total number of 20 Specimens were randomly divided into 4 groups (5specimens each). Group1 represent sound unbleached enamel, group2 represent bleaching enamel surface, and group3 represents remineralization by BG and group4 represents remineralization by HA. The specimens in group2 were bleached using 40% Hydrogen Peroxide following the manufacturers’ instructions. For Nano-BG group: a mixture of bioactive glass 45S5 powder with particle size (25-120 um) with poly-acrylic acid powder was done (PAA –BAG). Then, one milliliter of the artificial saliva was added then was applied on the bleached enamel surface followed by rinsing for one minute.For Nano-HA group: HA mixed with distilled water then was applied to bleached enamel surface followed by rinsing. All specimens were subjected to de and remineralization cycles. Surface Micro-hardness of the specimens (before bleaching after bleaching and after remineralization protocol) was determined and the mean microhardness values of the specimens were calculated, tabulated and statistically analyzed using one way analysis of variance (ANOVA) and Tukey post hoc tests were used to study the significance. The surface morphology of two representative sample of each tested group were examined using scanning electron microscope attached with energy dispersive X-ray analyzer. Results: Microhardness results revealed that the greatest mean value was recorded in unbleached enamel, followed by remineralized enamel with Nano- BG, then remineralized enamel with Nano- HA, with the least value in bleached enamel. ANOVA test revealed that the difference was extremely statistically significant (p<0.0001). Tukey’s post hoc test revealed no significant difference between unbleached enamel and remineralized enamel with Nano- BG. Moreover, there was no significant remineralized enamel with Nano- HA and remineralized enamel with Nano- BG. This was associated with some morphological changes in the enamel surfaces between different tested groups. Conclusions: The use of bleaching agents greatly affects the structural integrity of enamel surface and resulted in great mineral loss. It is strongly recommended to perform remineralization protocol after any bleaching procedure. The biomimetic materials are very promising due to their ability to perfectly reconstruct partially damaged bleached enamel surface. Bioactive glass material was able to perform almost complete recovery of the structural integrity of bleached enamel. Also, Nanohydroxyapatite successfully restore the damaged bleached enamel surface but to less extend compared to bioactive glass.

Characterization Investigations of a Al-5 wt.% Si/2 wt% (NbB&lt;sub&gt;2&lt;/sub&gt;, NbC) Hybrid Composite Fabricated via Mechanically Alloying and Sequentially Milling (Mechanical Alloying + Cryomilling)

In this study, microstructural and mechanical properties of a Al-5 wt.% Si/2 wt% (NbB2, NbC) composite synthesized by sequentially milling (mechanical alloying (MA) and/or cryogenic milling (CM)) were investigated. Nb2O5, B2O3 and C powder blends were milled using high energy milling for 5 h and annealed at 1400 oC for 12 h to produce NbB2-NbC hybrid powders. The NbB2-NbC hybrid powders were mixed with the matrix Al-5 wt.% Si powders to constitute the Al-5 wt.% Si/2 wt.% (NbB2-NbC) powders blends which were mechanically alloyed (MA'd) for 4 h using SpexTM Mixer/Mill, cryo-milled for 10 min in a SpexTM 6870 Freezer/Mill and finally MA’d for 1h in SpexTM Mixer/Mill again. As-blended, MA’d and cryomilled powders were compacted in a hydraulic press with a uniaxial pressure of 450 MPa. Compacted samples were sintered at 570°C for 2 h under Ar gas atmosphere. Microstructural characterizations of the as-blended/MA'd powders and the sintered composites were performed using X-ray diffractometry (XRD) and scanning electron microscopy (SEM) techniques. Density and microhardness measurements and sliding wear tests were performed on the sintered composite samples. Sequentially milled and sintered Al-5 wt.% Si-2 wt.% (NbB2-NbC) samples had the highest mean microhardness value (2.29 ± 24.98 GPa) and the lowest wear volume loss (0.038 mm3).

Effect of CO2 Laser and Fluoride Varnish Application on Microhardness of Enamel Surface Around Orthodontic Brackets.

Introduction: Orthodontic treatment has many advantages such as esthetic improvement and self-esteem enhancement; yet it has some disadvantages such as increasing the risk of formation of white spot lesions, because it makes oral hygiene more difficult. It is rational to implement procedures to prevent these lesions. The present study was aimed to assess the effect of CO2 laser and fluoride varnish on the surface of the enamel surface microhardness around the orthodontic braces. Methods: Eighty extracted premolar teeth were selected, scaled, polished with nonfluoridated pumic and metal brackets were bonded to them. Then, they were randomly allocated to 5 groups: control (neither fluoride nor laser is used on enamel surfaces), fluoride (4 minutes fluoride varnish treatment of the enamel surfaces), CO2 laser (10.6 µm CO2 laser irradiation of the teeth), laserfluoride (fluoride application after laser irradiation) and fluoride-laser (fluoride was applied and then teeth were irradiated with laser). After surface treatment around brackets on enamel, the samples were stored in 0.1% thymol for less than 5 days and then they were exposed to a 10-day microbiological caries model. Microhardness values of enamel were evaluated with Vickers test. One sample of each group (5 teeth from 80 samples) was prepared for SEM (scanning electron microscopy) and the data from 75 remaining teeth were analyzed with analysis of variance (ANOVA) and chi-square tests (α =0.05). Results: Microhardness mean values from high to low were as follow: fluoride-laser, laser-fluoride, laser, fluoride and control. Microhardness in fluoride-laser group was significantly higher compared with that of the control group. Distribution adhesive remnant index (ARI) scores were significantly different between groups and most of bond failures occurred at the enamel-adhesive interface in groups 2 to 5 and at the adhesive-bracket interface in the control group. Conclusion: Combination of fluoride varnish and CO2 laser irradiation can reduce enamel demineralization around orthodontic brackets.