جستجوی مقالات مرتبط با کلیدواژه "hardness" در نشریات گروه "پزشکی"

This study aimed to assess the alterations in microhardness of Clearfil Universal Bond Quick (CUBQ), G-Premio Bond (GPB), and Scotchbond Universal (SBU) immediately, 24 hours, and 6 months after curing.  

In this in vitro study, a composite disc was fabricated. A putty/wash impression was made from the disc to serve as a mold. CUBQ, GPB, and SBU adhesives were applied in the mold, and after allowing 3 hours for the solvent to evaporate, they were cured by a LED curing unit for 20 seconds. Ten specimens were fabricated from each adhesive. The microhardness of the specimens was measured by a microhardness tester immediately, 24 hours, and 6 months after curing. Data were analyzed by repeated measures ANOVA (alpha=0.05). 

The mean microhardness of the three adhesives was significantly different immediately after curing (P<0.001), and CUBQ showed significantly higher microhardness than GPB (P<0.001) and SBU (P=0.004). The difference in microhardness of the three adhesives was not significant after 24 hours and 6 months (P>0.05).

The present results showed that the microhardness of all three tested universal adhesives increased with time.

The aim of this study was to compare the mechanical properties of the polymer brackets with metal and ceramic brackets and verify if the polymer brackets could be used clinically.

A thorough search was conducted in four electronic databases, including Scopus, PubMed, Cochrane, Ovid, and Lilacs, with article selection based on Preferred Reporting Items for Systematic Reviews and Meta‑Analysis standards. A computerized search of the database was done from January 1990 to June 2024. Two independent reviewers were involved in study selection, data extraction, and synthesis. Disagreements were resolved by discussion with a third reviewer. The risk of bias was assessed by the quality assessment tool for in vitro studies (QUIN tool). The outcomes measured included permanent deformation, hardness, and torquing capacity.

Ten studies were selected after excluding duplicates, screening, and complete text reading to identify the articles that met the eligibility criteria. All ten studies showed medium risk based on the quality assessment tool for in vitro studies (QUIN Tool).

The following findings were obtained: Polymer brackets have lower mechanical properties in terms of torque loss, fracture resistance, hardness, and torsional creep compared to metal brackets. Among the polymers listed in the studies, it was found that polyamide exhibited low hardness and polyoxymethylene exhibited the highest torque loss. Torque deformation was highest with a ceramic‑reinforced polymer bracket, followed by pure polymer. Torque deformation was minimal with metal slot‑ and ceramic‑reinforced polymers, followed by metal slot‑reinforced polymers.

The aims of study to investigate physico-chemical properties do a proximate analysis of black cumin seeds (Nigella sativa L.) of AN-1 variety and development of value-added products by incorporating black cumin paste and powder in various proportions.

The sensory evaluation of incorporating black cumin to have value-added products was performed using hedonic scale method. Physico-chemical properties of black cumin seeds were determined in the initial stage of study. Then, the proximate analysis was performed. In the second phase, Total Soluble Solids (TSS), pH, acidity, and antioxidant activity of the developed products were determined. The antioxidant activity of prepared products was determined by 2,2-diphenyl-1-picrylhydrazyl (DPPH) method. The antioxidant activity of coriander chutney was increased from 55.75 to 57.07 by increasing the fortification of black cumin paste, and in bottle gourd, Ready To Serve (RTS) was increased from 40.73 to 42.08 as by increasing the fortification of black cumin powder.

It was observed that level 1% incorporation of black cumin paste and RTS was found best by judges after sensory evaluation of chutney when compared to level 2 and 3% black cumin fortified paste. However, in biscuits, black cumin powder supplemented level up to 2% was found acceptable on the basis of spread factor and hardness as compared to 3 and 4% fortification powder. It was concluded that 1% black cumin paste supplemented in coriander chutney, 1% black cumin powder supplemented in bottle gourd RTS and 2% black cumin powder supplemented in biscuits, were the best selected value- added products.

This study revealed that black cumin seeds are a potentially rich source of phytochemicals, and regular consumption of black cumin incorporated products with added value may reduce the risk of numerous diseases.

This study evaluated the effects of incorporating 1% and 2% cinnamon oil into a soft liner on the growth of Candida albicans colonies and the material's hardness. Thirty soft liner specimens were prepared for the disk diffusion and thirty for the hardness test.  In each test, the specimens were divided into three subgroups based on the concentration of cinnamon oil: A) 0% (control), B) 1%, and C) 2% by weight. Cinnamon oil was added to the monomer of a heat-polymerized soft liner. C. albicans was cultured on Mueller-Hinton agar, and the diameters of the inhibition zones around the specimens were measured. The Shore A hardness test was conducted using the Shore durometer. Statistical analysis was performed by the independent t-test, one-way ANOVA, and Tukey post-hoc test (α=0.05). The control group showed no inhibition zone. The specimens in Group C exhibited a significantly larger inhibition zone (16.72 ± 0.82 mm) than Group B (12.56 ± 0.82 mm; P < 0.001). The hardness values differed significantly among groups (P < 0.001). Group C demonstrated the highest hardness (48.54 ± 0.95), significantly greater than both Groups B (47.13 ± 0.72; P < 0.05) and A (45.23 ± 0.73; P < 0.05). Adding cinnamon oil improved the antifungal activity and hardness of the soft denture liner. Adding 2% cinnamon oil increased the hardness values to the upper limit of clinical acceptability. Therefore, the 1% concentration is recommended to balance antimicrobial efficacy and maintain optimal mechanical properties of the soft liner.

Bulk-fill composites are a new class of materials introduced to speed up the clinical process of posterior restorations. This study compared the curing quality of bulk-fill and conventional composites at different irradiation times and depths. In this in-vitro study, 40 specimens from a bulk-fill composite, Tetric N-Ceram bulk-fill (TNB), and a conventional composite, Tetric N-Ceram (TN), were fabricated using a metal mold (6 mm × 4 mm) (n = 10). The composites were placed and cured in bulk for each composite. For each composite, half of the samples were cured for 20 seconds (s) using a light-emitting diode (LED) curing unit, and the irradiation time for the other half was 40. After 24 hours of storage in distilled water, the hardness of the samples was measured using a microhardness tester at different depths (0.1, 1, 2, 3, and 4 mm). Statistical analysis was done using multivariate ANOVA and independent t test (P ˂ 0.05). Both composites presented a significant reduction in hardness value with increasing depth. TNB showed significantly higher hardness values at all depths in both irradiation times than conventional composite. TNB composite did not achieve a depth of cure (DOC) of 4 mm at any of the two curing times. Irradiation time significantly affects hardness values in both composites. Given that neither bulk-fill nor conventional composite was cured at depths greater than 3 mm, it is suggested that prolonged curing cycles be used to improve the DOC of composites.

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 aimed to compare the effect of human blood and platelet-rich fibrin (PRF) on the surface microhardness of hydraulic calcium silicate-based cements (OrthoMTA and RetroMTA).

Two types of mineral trioxide aggregate, OrthoMTA and RetroMTA, were mixed and placed into cylindrical molds. The lower surfaces of all cements were exposed to saline. The upper surfaces of cements were exposed to human blood, PRF, or phosphate buffer saline (PBS). After storage for 7 days in fully saturated humidity at 37°C, the microhardness of cement surface exposed to blood, PRF, or PBS was measured using the Vickers microhardness test. The data were analyzed using two-way analysis of variance and post hoc Tamhane’s T2 test. The significance level was set at P<0.05.

Exposure to blood and PRF significantly decreased the surface microhardness of OrthoMTA and RetroMTA. The microhardness of PBS-contacted cements was significantly higher than that of blood or PRF groups (P<0.001). The microhardness values for OrthoMTA exposed to PRF were significantly higher than the blood group (P=0.020). There were no significant differences between RetroMTA contacted with blood or PRF groups (P=0.985). When exposed to blood or PBS, RetroMTA had a significantly higher microhardness than OrthoMTA (P<0.001 for blood, P=0.002 for PBS).

Exposure to blood or PRF decreased the surface microhardness of both cements. Blood-contaminated RetroMTA showed significantly higher surface microhardness than OrthoMTA contacted with blood. No significant difference was found between PRF-contacted OrthoMTA and RetroMTA

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