| کلیدواژههای انگلیسی مقاله |
Compressive strength, Hydroxyapatite, Mineral trioxide aggregate, Zinc oxide, Nanoparticles, IntroductionMineral trioxide aggregate (MTA) is hydrophilic cement with calcium silicate base, which is widely used in endodontics to repair perforations, in vital pulp therapy and as a surgical retrograde material due to several favorable properties, including biocompatibility and the ability to induce osteogenesis and cementogenesis [ 1, - 3, ]. One of the disadvantages of MTA is its long setting time and difficult handling [ 4, - 5, ]. Various methods have been proposed to improve the MTA properties, including adding materials such as sodium hydrogen phospha-te (Na2HPO4), calcium chloride, and nanoparticles [ 6, - 9, ].The physical properties of an endodontic biomaterial, such as compressive strength, are important in cases where this material is subjected to occlusal forces [ 10, ]. The similar clinical conditions of this case are the application of MTA as a pulp capping material, in apexogenesis and in perforation repair [ 11, ], where the material is subjected to the force of restorative materials as well as to occlusal forces [ 12, ]. According to previous studies, the compressive strength for MTA immediately after setting is 40 MPa (Mega Pascal), which increases to 67 MPa within 21 days [ 13, - 14, ]. Several factors affect the compressive strength, including the type of MTA, condensation pressure, the acid etching process, the mixing technique, and the liquid mixed with MTA [ 12, - 13, ]. Over time, various materials have been added to improve the properties of MTA. One of the materials that have been considered in this regard in various studies is nanoparticles, including silica, silver, and silver zeolite [ 9, , 15, - 17, ]. In one study, the incorporation of silica nanoparticles reduced the setting time and increased the compressive and flexural strengths of MTA [ 16, ].Hydroxyapatite (HA) is an important biological material and is the main component of the mineral bone and teeth [ 18, ]. It is widely used in medicine and dentistry [ 18, - 19, ]. HA is used to improve the setting time of MTA [ 20, ] and to improve the osteogenic properties because of its biocompatibility [ 21, ].Zinc oxide (ZnO) particles are antimicrobial substances, which have been used for many years in various dental compositions due to biological adaptation [ 17, ]. Zinc activates enzymes, which are toxic to bacteria at low concentrations, and inhibits plaque growth at higher concentrations [ 22, ].The effect of adding new agents to MTA mixture on its properties should be assessed and so far there is no published study on the compressive strength of MTA mixed with ZnO and HA nanoparticles. This study was designed to evaluate the properties of this substance after 4 and 21 days.Materials and MethodDetermination of the sample sizeThe study was approved by the Research and Ethics Committee of Tabriz University of Medical Sciences. A sample size of 64 was considered based on the results of a pilot study, the materials used and the evaluation time of the compressive strength (8 groups, n=8). The study groups mentioned in Table 1, was based on the type of the material in the cylinder and the evaluation time of the compressive strength test.Study groupsType of material inside cylinderEvaluation time1MTA42MTA21310% Nano ZnO+MTA4410% Nano ZnO+MTA21510% Nano HA+MTA4610% Nano HA+MTA2175% Nano HA+5% Nano ZnO+MTA485% Nano HA+5% Nano ZnO+MTA21Table 1. Study groupsIn this study, we considered that all the cylinders were filled with the material and that the upper surface of the material was leveled with the edges of the cylinder. The cylinders that did not have this feature were excluded from the study.Confounding variablesSince the setting condition of the material affects the compressive strength, the conditions for mixing and placing the materials and the test time were considered the same for all the specimens. In addition, the materials were placed inside the cylinders and mixed by one operator. The condenser size used to pack the material inside the cylinder was also the same for all the specimens. The powder-to-liquid ratio of 3,1 was the same in all the samples. The whole stages of the work were based on the ISO standard, which minimizes the probability of error.Procedural stepsThe HA powder was purchased from SIGMA-ALDRICH Co. (USA). ZnO nanoparticles were synthesized by a nano-technologist colleague in Tehran University of Medical Sciences using Zn(CH3COO)2.2H2O and NaOH with methanol solvent. The resultant mixture was transferred to an autoclave and kept at 120&,deg C for 6 hours. The solid and white product was then isolated by filtering. The crystal structure of nanoparticles was examined by x-ray diffraction (XRD) and the morphology of nanoparticle was examined under a scanning electron microscope (SEM). The amount of surface hydrophilic rate was examined by contact angle test and particle size was examined by dynamic light scattering (DLS). In groups 1 and 2, white ProRoot MTA powder (Dentsply, Tulsa, USA) was mixed with physiologic serum at a powder-to-liquid ratio of 3,1 according to the manufacturer&apos,s instructions and was placed within the molds within thirty seconds after mixing. According to the standard, the selected stainless steel molds had a height of 6 mm and a diameter of 3 mm, the internal surface of which was lubricated with paraffin. In groups 3 and 4, 10% Nano ZnO+MTA powder was used. First, MTA powder weight (wt) was measured using a digital weighing machine and ZnO was added at 10 wt% of it. In the remaining groups, the weight of the nanoparticles was calculated with this method and added to MTA groups 5 and 6, 10% Nano HA+MTA and in groups 7 and 8, 5% Nano HA+5% Nano ZnO+MTA were mixed. The powders of the above groups were mixed with a ratio of 3,1 with the serum, transferred to the molds using a MTA carrier and packed into the selected molds with a dental plugger. The samples were then welded in distilled water gas and stored in a container at 37&,deg C until the compressive strength measurement.The compressive strength was measured accordance to ISO 6876. The device used for this purpose was a universal testing machine (Hounsfield Test Equipment, model, H5K-S, Perrywood Business Park, Honey Corckland, Salfords, Redhill, Surrey, UK).The samples in groups 1, 3, 5 and 7 were evaluated on the 4th day, and the samples in groups 2, 4, 6 and 8 were evaluated on the 21st day. The samples were retrieved from the molds and the machine head applied a force at a speed of 1 mm/min on the longitudinal axis until the material was crushed or broken. This force was registered in Newton and converted to MPa with the formula of CS = 4p/&,mu d, where p is the maximum force applied in Newton, and d is the actual diameter of the samples in mm.Statistical analysisStatistical analysis was performed using SPSS (Statistical Package for Social Science, SPSS, version 20.0, SPSS, Chicago, IL, USA).The Kolmogorov-Smirnov test was used to check the normal distribution of the data. After calculating the mean &,plusmn standard deviation of compressive strength, two-way ANOVA test was used to compare the groups and determine the significance of the effect of time and material on the compressive strength. In the current study, p&,lt 0.05 was considered statistically significant.ResultsThe results of the descriptive statistics, i.e. means and standard deviations of the data (Table 2,) showed the highest compressive strength at 4-day interval after mixing for the MTA+Nano HA group (38.5&,plusmn 9.24) and the lowest compressive strength at this time interval for MTA+Nano ZnO group (26.5&,plusmn 9.42).GroupsCompressive strength 4 days after mixing (MPa)Compressive strength 21 days after mixing (MPa)p ValueMTA31.12&,plusmn 6.1941.12&,plusmn 6.530.007*,MTA+Nano ZnO26.5&,plusmn 9.4233.5&,plusmn 10.40.180MTA+Nano HA38.5&,plusmn 9.2440&,plusmn 12.660.882MTA+Nano ZnO+ Nano HA26.87&,plusmn 6.4930.75&,plusmn 6.540.254*rence between the two groups is significant. |
| نویسندگان مقاله |
Mahsa Eskandarinezhad |
Dept. of Endodontics, Dental and Periodontal Research Center, Dental School, Tabriz University of Medical Sciences, Tabriz, Iran.
Mostafa Ghodrati |
Dept. of Endodontics, Dental and Periodontal Research Center, Dental School, Tabriz University of Medical Sciences, Tabriz, Iran.
Fateme Pournaghi Azar |
Dental and Periodontal Research Center, Dept. of Operative Dentistry, Faculty of Dentistry, Tabriz University of Medical Sciences, Tabriz, Iran.
Farnaz Jafari |
Dept. of Endodontics, Dental and Periodontal Research Center, Dental School, Tabriz University of Medical Sciences, Tabriz, Iran.
Parvin Samadi Pakchin |
Research Center for Pharmaceutical Nanotechnology, Tabriz University of Medical Sciences, Tabriz, Iran.
Amir Ardalan Abdollahi |
Dept. of Endodontics, Dental School, Urmia University of Medical Sciences, Urmia, Iran.
Amirhouman Sadrhaghighi |
Dept. of Orthodontics, Faculty of Dentistry, Tabriz University of Medical Science, Tabriz, Iran.
Forouzan Reazvan |
Private Practice, Tabriz, Iran.
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