جستجوی مقالات مرتبط با کلیدواژه « hardness » در نشریات گروه « پزشکی »

This study aimed to measure light transmittance (LT) through various thicknesses of computer‑aided design/computer‑aided manufacturing bleach shade ceramics and to assess the Vickers microhardness (VMH) of underlying light‑cured resin cement.

In this in vitro study, a total of 90 ceramic discs (VITA Mark II [VM], VITA Suprinity, and CELTRA Duo) were prepared in 0.5, 1, and 1.5 mm thicknesses. To measure LT, the Valo light‑curing unit was placed in direct contact with the ceramics on the radiometer. The average LT was recorded after three measurements. In addition, 90 specimens of light‑cured resin cement (Allcem Veneer) were cured in Teflon molds (0.5 mm in depth) beneath ceramic pieces. Ten specimens of resin cement were also cured without the presence of ceramic as a control group. VMH of the cement specimens was reported. The data were analyzed by one‑way analysis of variance and multiple comparison tests (α =0.05) in SPSS version 17.

In each ceramic group, LT was negatively related to ceramic thickness (P < 0.05). At a thickness of 1.5 mm among all ceramic types, the VMH of resin cement was significantly decreased (P < 0.05). In all thicknesses, theVMH of resin cement was lower significantly than the control group, except for the thickness of 0.5 mm of VM.

According to the results of this study, light‑cured cement is not a suitable option for cementing the studied bleach shade ceramics. Furthermore, the thickness of the ceramic has a significant effect on LT (P < 0.05), unlike VMH.

This study aimed to compare the precision of a temporomandibular joint (TMJ)-related bite-registration technique with the occlusion-related registration technique using various polyvinyl siloxane materials.  The interocclusal relation of 40 patients was transferred to stone casts by bite registrations using polyvinyl siloxane materials with different Shore harnesses (SH) values including Registrado clear (SH=70 A), Registrado xtra (SH=51 D) and Registrado scan (SH=90A). A joint-related registration technique (called the Gerber technique or gothic arch tracing) was also applied in all patents. The clinical contact situation and the contacts on stone casts were marked and transferred to a 3D-measuring software. The deviation of the occlusal contacts on the stone casts to the clinical reference was measured and compared between the registration methods.   There was no statistically significant difference in contact deviation values between different types of registration methods (P=0.093). However, the frequency of missing contacts was significantly greater in the Gerber technique compared to the occlusion-related bite registrations (P<0.001). Gerber technique revealed greater deviations of the contact points in subjects with pain in TMJ and masticatory muscles. Irrespective of the registration technique, the patient-related factors including orthodontic pretreatment, treatment of TMD with occlusal splints, pain on palpation, joint noises, and restricted mandibular movement did not significantly affect the degree of occlusal contact deviation (P>0.05). The hardness of the polyvinyl siloxane materials for occlusion-related bite registration did not affect the precision of the registration techniques in dentulous patients. Polyvinyl siloxane materials should be preferred for joint-related registration in TMD patients

Some endodontic procedures require using intracanal medicament between treatment sessions. The effectiveness of these agents on dentin microhardness is crucial for deciding whether to use them or not. This study aimed to compare the effectiveness of three intracanal medicaments including Triphala, calcium hydroxide (Ca(OH)2) paste, and chlorhexidine (CHX) gel on the root dentin microhardness. Forty-eight single canal mature permanent teeth were selected. Mechanical preparation was done using RaCe rotary files. The samples were randomly allocated to four equal groups (n=12), according to the applied intracanal medicament. Group 1 received no medicament, whereas the root canals in groups 2, 3, and 4 were filled with Triphala, Ca(OH)2, and CHX, respectively. Specimens were stored for one week.  Then, the roots were sectioned and the Vickers microhardness value was recorded at 0.5 mm from the pulp–dentin interface. Data were analyzed by one-way ANOVA and Tukey test and a P-value < 0.05 was considered statistically significant. The mean microhardness values in the Triphala and calcium hydroxide groups were comparable to each other (P>0.05) and significantly lower compared to the control and CHX groups (P<0.05). No significant difference in microhardness was found between the CHX and control groups (P>0.05). Triphala and Ca(OH)2 had similar effects on root dentin microhardness. Given the favorable characteristics of Triphala medicament, it can be considered a suitable alternative to Ca(OH)2 for intracanal application.

Due to the importance of using more effective varnishes to prevent dental caries, this study aimed to compare the effect of conventional casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) and CPP-ACP with 1 and 2 w% nanosilver particles on microhardness of enamel of primary canines.

  The initial surface micro-hardness of 36 intact human deciduous canines were measured by a Vickers hardness tester, then samples were immersed in demineralization solution for 24 hours, and then the microhardness of samples was re-measured. All samples were randomly divided into 4 groups (n=9): (A) control group(without therapy), (B) conventional CPP-ACP, (C) CPP-ACP  with  1% nano silver, and (D) CPP-ACP  with  2% nanosilver. Then samples were entered into pH cycles for 7 days. At the end of pH cycling, the surface microhardness of samples was measured, and the mean for each group was calculated. Data analysis was performed using one-way ANOVA and Tukey analysis.

The mean enamel micro-hardness in all groups after demineralization decreased significantly (P<0.05), but this reduction was significantly less in all three experimental groups compared to the control group (P<0.05). There was no significant difference in the rate of surface microhardness changes between the three experimental groups (P>0.05).

Conventional CPP-ACP and CPP-ACP with 1 and 2 w% Nanosilver particles were equally effective on the enamel surface microhardness of human deciduous teeth. Silver Nanoparticles have no negative effect on enamel microhardness.

This study assessed the effects of blue and Er:YAG lasers, fluoride varnish, and their combination on microhardness, and calcium and phosphorus content of demineralized enamel.

The primary Vickers microhardness of 28 third molars was measured and their enamel calcium and phosphorous content was quantified by energy-dispersive X-ray spectroscopy. They were then randomly assigned to five groups of 5% sodium fluoride (NaF) varnish, 445nm blue laser, Er:YAG laser, 5% NaF + 445nm blue laser, and 5% NaF + Er:YAG laser. The teeth then underwent pH-cycling to induce caries-like lesions. The surface microhardness of the teeth and the calcium and phosphorous content of demineralized enamel were measured again. Data were analyzed by one-way ANOVA and Tukey’s test (alpha=0.05).

NaF, NaF-diode laser, and NaF-Er:YAG laser groups experienced a significant increase in microhardness of demineralized enamel close to the baseline value (P<0.05). The efficacy of NaF-blue laser and NaF-Er:YAG laser was higher than NaF . In blue and Er:YAG laser groups, the mean final microhardness was significantly lower than the baseline microhardness. The percentage of phosphorus in all groups was similar to that of sound enamel. The percentage of calcium in NaF group was significantly lower than that of sound enamel and all other groups. The calcium content in other groups was similar to that of sound enamel.

Fluoride varnish had a synergistic effect with Er:YAG and blue lasers to increase the demineralized enamel microhardness; blue and Er:YAG lasers alone were less effective.

Due to the poor mechanical properties of Glass Ionomer Cement (GICs), their use is limited to low stress-bearing areas. This study aimed to assess the effect of the addition of Titanium Dioxide (TiO2) nanoparticles on the flexural strength and surface hardness of GIC.  In this in vitro study, 3, 5, and 10 wt.% TiO2 nanoparticles were added to Fuji II conventional GIC powder. The purity and composition of the as-synthesized titania were investigated by using XRD and FT-IR tools. The homogeneity of powder particles within the used matrix was evaluated under a Scanning Electron Microscope (SEM). The SEM micrographs confirmed the homogenous mixing of TiO2 nanoparticles with GIC powder. Nevertheless, the flexural strength of experimental groups was not significantly different from that of the control group (p=0.384). However, the surface hardness of experimental groups was decreased in comparison with that of the control group (p<0.001).

Statement of the Problem: 

The prevalence of non-carious dentin lesions is on the rise mainly due to improved life expectancy. Successful management of these lesions is often challenging, and given that dentin can be remineralized, adverse consequences due to progression of these lesions can be prevented or minimized as such.

This study aimed to assess the effect of casein phosphopeptide amorphous calcium phosphate (CPP-ACP) and Remin-Pro remineralizing agents on dentin microhardness of non-carious dentin lesions.

This in vitro, experimental study evaluated 36 extracted sound human premolars. The teeth were decoronated at the cementoenamel junction. Enamel was removed, and dentin was exposed at the cervical third of the buccal surface. The primary microhardness of dentin was then measured. The teeth, standardized in terms of dentin microhardness, then underwent demineralization by acid etching and were subjected to microhardness test again. They were then randomized into three groups for treatment with CPP-ACP, Remin-Pro, and artificial saliva (control), and dentin microhardness was measured for the third time after treatment. Data were analyzed using ANOVA.

Within group comparisons showed a significant difference in microhardness at the three time points in all three groups (p< 0.005). Between-group comparisons revealed that the microhardness of the three groups was not significantly different at baseline or after demineralization. However, the microhardness of the three groups was significantly different after the intervention (p= 0.000). Pairwise comparisons revealed significantly higher microhardness in the CPP-ACP group than the other two groups (p= 0.003). Remin-Pro and the control groups were not significantly different in this respect (p= 0.340).

CPP-ACP can be used for remineralization of non-caries dentin lesions; however, Remin-Pro does not appear to be effective for this purpose.

Zinc oxide (ZnO) and graphene oxide (GO) nanoparticles (NPs) have antimicrobial properties. The present study was undertaken to evaluate the effects of incorporating these NPs and their chemical and physical blends on abrasion, translucency, and microhardness of flowable composite resin.

In the present in vitro study, flowable composite resin samples (Grandio Flow, VOCO, Germany) were evaluated in 5 groups and the sample size was 10 for each group of each experiment (n = 10) as follows: Group 1, without NPs; Group 2, with ZnO NPs; Group 3, with GO NPs; Group 4, containing a physical mixture of GO and ZnO; and Group 5, containing a chemical mixture of GO and ZnO NPs. In all the groups, 1 wt% of the NPs were incorporate into flowable composite resin. Abrasion, translucency, and microhardness of the samples were evaluated. Data were analyzed with analysis of variance, followed by post hoc Tukey’s tests at the level of significance of P < 0.05.

In Groups 2, 4, and 5 (all the groups containing ZnO), a significant decrease in abrasion and microhardness of flowable composite resin was observed compared to the control group. Incorporation of NPs in all the groups resulted in a significant decrease in translucency compared to the control group.

Incorporation of NPs into flowable composite resin resulted in a decrease in translucency. The microhardness was reduced in groups containing ZnO, but the abrasion was also reduced in these groups. The incorporation of GO did not significantly alter the abrasion and microhardness of the composite resin.

The durability of composite restorations is directly affected by the mechanical properties of the composite. The aim of this study was to evaluate the hardness and wear resistance of self-adhesive flowable composite (SAF) in comparison with conventional flowable composites.

In this in vitro study, 50 composite specimens were prepared in brass molds with 10mm ×10mm ×2mm and divided into five groups (n=10). Specimens included three conventional flowable composites (Grandio flow, Filtek flow and Admira fusion flow), one self-adhering flowable composite (SAF, Vertise flow) and a microhybrid composite (filtek z250). After polishing, the micro-hardness of the specimens was measured in a Vickers hardness device, and the specimens were then subjected to 5000, 10000, 20000, 40000, 80000 and 120000 wear cycles in a wear tester. One-way ANOVA/Games-Howell, Kruskal Wallis, and Friedman tests were used for statistical analysis. The significance level was set at P<0.05.

The surface micro-hardness of the SAF was significantly lower than that of the microhybrid composite (P=0.01). There was no significant difference between the surface hardness of the different tested flowable composites (P>0.05). Also, the wear resistance of the studied composites was not significantly different in various cycles (P>0.05).

Based on our results, SAF would not be an ideal substitute for conventional flowable composites in high-stress areas.

Recalcitrant organics remediation from water resources continues to be a significant environmental problem and there is a continued effort to demonstrate practicable and economical treatment options for pollution removal.

In this study, the efficiency of the permeable reactive barrier (PRB) in a column reactor using zero-valent iron (ZVI) particles and sand mixture in the removal of methyl tert-butyl ether (MTBE) from aquatic phases was investigated. The system performance was MTBE removal while initial pH,reaction time, pollutant content, catalyst load, hydraulic loading rate (HLR), and the reaction rate constant were independent variables.

The results showed that the process efficiency decreased by increasing pH, HLR, and pollutant concentration. In this case, the optimal conditions were obtained at pH = 7, HLR = 0.23 m3/m2·d, and C0 = 1 mg/L, which achieved a remarkable removal efficiency up to 90.32%. The high nitrate concentrations and hardness as intervening factors reduced process efficiency to less than 44.61 and 51.4%, respectively. The lack of interfering factors had a considerable effect on the reaction rate of MTBE reduction, which is approximately 2.65 and 4.11 times higher than that in the presence of calcium hardness and nitrate, respectively.

The PRB technology can be suggested as a reliable and robust system to remediate groundwater containing hydrocarbons based on filling media and hydraulic conditions.

White spot formation is one of the common side effects in orthodontic treatments and multiple enamel conditioning might happen even during on session of fixed orthodontic treatments. The aim of the present study was to evaluate the impact of multiple enamel conditioning with different methods on enamel micro‑hardness (MH).

In this In vitro experimental study, the buccal surfaces of 105 extracted premolars were evaluated in seven groups: One control and six experimental groups. The enamel conditioning was performed in three ways: Etching with phosphoric acid 37%, etching with phosphoric acid 37% followed by primer application and conditioning with self‑etch primer. The conditioning process in each way was also performed twice consecutively. The specimens were submitted in pH cycling model with demineralization and re‑mineralization solutions for 14 days. Afterward Vickers MH test was applied with 0.981N force on the teeth for 10 s indentation time. Data were analyzed using One‑Way ANOVA and Tukey HSD (honestly significant difference) test for multiple comparisons. A value of P < 0.05 was considered statistically significant.

MH analysis showed statistically significant differences between the control group and the other conditioned groups (P < 0.05). The groups conditioned with acid‑etch and primer, particularly twice, showed the lowest amount of MH in comparison to other groups. Self‑etch primer had the least effect on MH of the enamel. Single time etching without using primer, made no considerable difference when compared to multiple etching.

Etching process and covering the enamel with primer decrease enamel MH. Using self‑etch primer is a more conservative method of enamel conditioning

Considering the studies on the effects of bleaching materials on properties of dental materials, The aims of this in vitro study were to evaluate the effects of two different concentrations of bleaching agents on flexural strength and microhardness of VITA ENAMIC.

In this experimental in vitro study, 30 rectangular‑shaped specimens(2 mm width × 2 mm height × 12 mm length) for flexural strength and 30 specimens (5 mm width × 5 mm length × 2 mm height) for microhardness tests were prepared from VITA ENAMIC blocks 12 × 14 × 18 mm. The specimens were polished using silicon‑carbide sandpapers 400, 600, 800, 1200, 2000 under flow of water for 60 s each. The prepared samples for flexural strength and microhardness were divided into 3 subgroups (n = 10): control group (C), samples bleached using Opalescence PF 15% (B15), and samples bleached with Opalescence Xtra Boost 40% (B40). Flexural strength measurement was done using a universal testing machine, and microhardness test was done using Vickers. Data were analyzed using analysis of variance and post hoc tests and P < 0.05 was considered significant.

The mean microhardness values of C, B15, and B40 groups were 255.46 ± 3.02, 249.86 ± 4.18, and 235.53 ± 4.61 kgf/mm2 . Opalescence PF 15% and Opalescence Xtra Boost 40% affected microhardness of ENAMIC significantly (P < 0.05). The mean flexural strength values of C, B15, and B40 groups were 155.26 ± 16.13, 142.14 ± 11.52, and 133.39 ± 16.13 MPa. A significant decrease in flexural strength was found between the C and B40 groups (P = 0.007). However, the difference between flexural strength of the C and B15 groups was not significant (P > 0.05).

Our study showed that both concentrations of bleaching agents can affect microhardness of ENAMIC. Moreover, hydrogen peroxide 40% has a negative effect on the flexural strength of ENAMIC

Methocarbamol is a skeletal muscle relaxant drug. In this study, we investigated the potential of developing methocarbamol effervescent tablets to facilitate drug administration. Effervescent tablets containing 1000 mg methocarbamol were prepared using direct compression method. The effect of various formulations parameters such as citric acid, sodium bi-carbonate, PEG 6000, PVP k30 on different physicochemical properties of tablets were evaluated at two levels. Different formulations with various amounts of mentioned excipients along with constant amount of methocarbamol, sucralose, mannitol and different flavoring agents were prepared and their properties including hardness, friability, pH, effervescent time, CO2 content and taste were studied. Optimized formulation was B8 which contained 400 mg of citric acid, 525 mg of sodium bicarbonate, 226.5 mg of PVP k30, 113.2 mg of PEG 6000, 100 mg of mannitol and 30 mg of sucralose. This formulation had effervescent time of 112.67± 2.05 seconds, hardness of 71.10± 2.51 N and pH of 6.01±0.02. Statistical analysis by Design Expert software showed that the hardness of tablets is mostly affected by the amount of PEG 6000. Volunteers reported that sour cherry had the most pleasant taste to them. In summary, current effervescent tablets are shown to be suitable vehicles for methocarbamol with potential for use in patients with swallowing problems and will enhance patience compliance.

Considering the high prevalence of consumption of iron drops, and the resultant reduction in microhardness of primary enamel, this in vitro study aimed to assess the effects of Sucrosomial® iron and iron drop diluted with natural fruit juice on microhardness of primary enamel.

This in vitro, experimental study evaluated 45 extracted sound primary anterior teeth, that were randomly assigned to three groups (n=15) of Sideral, Irofant, and Irofant + natural apple juice. The titratable acidity and pH of solutions were measured. After measuring the baseline microhardness by a Vickers hardness tester, the teeth in the three groups were exposed to the respective iron drop solutions at 37°C for 5 minutes. They were then rinsed with distilled water, and their secondary microhardness was measured. Data were analyzed using the dependent Student t-test, ANOVA, and ANCOVA (alpha=0.05).

Irofant had the lowest pH and the highest titratable acidity among the tested solutions. A reduction in enamel microhardness occurred in all groups after exposure to iron drops (P=0.0001). The reduction in microhardness was significantly greater in Irofant group compared with Irofant + natural apple juice (P=0.0001). Also, the reduction in microhardness was significantly greater in Irofant + natural apple juice compared with Sideral iron drop group (P=0.0001).

Sideral iron drop with Sucrosomial iron has minimal adverse effect on microhardness of primary enamel. Also, dilution of iron drops with natural apple juice can be suggested as an effective strategy to decrease their adverse effects on microhardness of primary enamel.

Continuous development of denture base materials has led to the introduction of innovative alternatives to polymethyl methacrylate. The present study aimed to evaluate the mechanical properties, adaptation, and retention of alumina nanoparticles (Al2 O3 NPs) modified polyamide resin versus BioHPP (high-performance polymer) denture base materials.

Four groups of specimens, one control (group I) (unmodified polyamide) and two groups (groups II and III) (2.5 and 5 wt% Al2 O3 NP-modified polyamide, respectively) versus BioHPP specimen group (group IV), were tested for surface microhardness and flexural strength. Complete dentures fabricated from 5 wt% Al2 O3 NP-modified polyamide resin and BioHPP were used to evaluate denture base adaptation and retention.

The higher concentration in the alumina NP-modified polyamide group (5 wt%) demonstrated significantly higher flexural strength values and insignificantly higher hardness values than the lower concentration (2.5 wt%). There was a significant increase in the BioHPP group in both flexural strength and surface hardness compared to all polyamide groups. A statistically insignificant difference was observed between the two denture base materials regarding mean misfit values of the calculated total tissue surface area and four of the total seven evaluated areas. Satisfactory and comparable retention values were observed for both denture base materials.

BioHPP and Al2 O3 NP-modified polyamide resin could be used as a promising alternative denture base material with good adaptation, retention, and mechanical properties.

Cention N has been introduced as an alternative material for amalgam. The purpose was to investigate the flexural strength and microhardness of this material in self‑cure and dual‑cure modes before and after thermocycling.

In this experimental study, 40 samples of Cention N were prepared in order to determine and compare the microhardness. Half of the samples were set by self‑cure method and the other half with dual‑cure method. The Vickers microhardness test was performed once after 24 h and again after 10000 thermocyclings. Three‑point flexural test was used to determine and compare the flexural strength of 52 rod‑shaped samples. Half of the samples were set by self‑cure method and the other half with dual‑cure method. Among 26 samples in each group, 13 samples were randomly selected and three‑point flexural test was performed after 24 h and for another 13 samples after 10,000 thermocyclings. Data were analyzed using two‑way ANOVA and paired samples t‑test (P < 0.05).

There was a statistically significant difference between the mean of microhardness values in two curing methods (P < 0.001) and in two storage conditions (P < 0.001). The mean of dual‑cure microhardness (100.99 ± 7.22) was higher than that of self‑cure (64.61 ± 12.51) and the mean value associated with pre‑thermocycling (89.75 ± 15.84) was higher than that of the post‑thermocycling (76.44 ± 23.56). There was no statistically significant difference between the mean flexural strength in the two curing methods (self‑cure [72.85 ± 16.26], dual cure [79.87 ± 23.07]; [P > 0.05]). However, the mean flexural strength without thermocycling (85.98±21.74) was higher than that of the thermocycled group (64.24±6.40)(P<0.001).

The microhardness of Cention N in dual‑cure mode was higher than that of self‑cure mode, but the flexural strength of dual‑cure was not significantly different from that of self‑cure. Thermocycling had a significant effect on the microhardness and flexural strength.

The purpose of this study was to compare the Vickers hardness number (VHN) and depth of cure of two types of bulk fill composites in high, low and soft light curing modes.

In this experimental study, 60 cylindrical samples were fabricated from two types of bulk fill composites (Tetric N-Ceram and X-tra fil) in a Teflon mold with one semi-circular notch. Then, the samples were randomly divided into the following three subgroups based on the curing modes (high, low and soft) and were light-cured. The samples were removed from the molds, and their VHN and depth of cure were measured. Data were analyzed using One-way ANOVA and Tukey’s post hoc test at the significance level of P<0.05.

The mean VHN of the X-tra fil composite was significantly higher than that of Tetric N-Ceram composite (P<0.001). The depth of cure of X-tra fil composite was also significantly higher than that of Tetric N-Ceram composite in high and soft curing modes (P<0.001).

According to the current results, X-tra fil composite is a convenient material for the restoration of deep cavity in posterior teeth compared with Tetric N-Ceram.

Interim restorations play a critical role in success of restorative treatments. However, they need to preserve their integrity in the oral environment. Microhardness is an important factor in preservation of the integrity of restorations. This study aimed to compare the microhardness of three interim restorative materials namely polyether ether ketone (PEEK), an indirect composite, and polymethyl methacrylate (PMMA).

This in vitro, experimental study evaluated 10 disc-shaped specimens, measuring 15 mm in diameter and 1 mm in thickness, fabricated from PEEK, an indirect composite, and PMMA. The microhardness of the specimens was measured at three points of each specimen using the Vickers’ hardness test before and after water storage for 30 days. Data were analyzed using repeated measure ANOVA, one-way ANOVA and Tukey’s test.

Indirect composite showed maximum microhardness, which was significantly higher than that of the other two materials (P=0.001). However, no significant difference was noted in microhardness of PEEK and PMMA (P=0.33). The microhardness of the materials did not significantly change after 30 days of water storage (P=0.06). Conclusion The microhardness of indirect composite was higher than that of PEEK and PMMA. Also, 30 days of water storage had no significant effect on microhardness of the materials.