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Showing 5 results for Microhardness
Effect of three different calcium hydroxide mixtures (calcium hydroxide with glycerine, normal saline and distilled water) on root dentin microhardness
Sm. Hasheminia , S. Norouzynasab ,
Volume 20, Issue 2 (5-2007)
Abstract

Background and Aim: During root canal therapy, it is necessary to remove as many bacteria as possible from the root canal. The use of medicaments is recommended to reduce the microbial population prior to root filling. Calcium hydroxide pastes have been used because of their antibacterial effects and the ability of tissue dissolving. The aim of this study was to evaluate the effect of calcium hydroxide/glycerine mixture, calcium hydroxide/normal saline mixture and calcium hydroxide/distilled water mixture on root dentin microhardness in storage times of 7 and 14 days.

Materials and Methods: In this in vitro study, fifteen extracted maxillary canines and central incisors were selected. The crowns of the teeth were removed and the canals were prepared. Teeth were sectioned transversally to produce a total of 30 dentin discs from the middle third of the roots. Specimens were divided into three groups of 10 discs each. Dentin samples were subjected to calcium hydroxide/glycerine, calcium hydroxide/normal saline and calcium hydroxide/distilled water mixtures for 7 and 14 days. Dentin microhardness was measured by a Vickers indenter with a load of 200 g for 15 seconds. Data were analyzed using ANOVA, Paired t-test and LSD with p<0.05 as the level of significance.

Results: Statistical analysis showed that all three mixtures decreased dentin microhardness. After 7 days, reduction in dentin microhardness by calcium hydroxide/glycerine combination was significantly higher than calcium hydroxide/normal saline and calcium hydroxide/distilled water combinations. After 14 days, reduction in dentin microhardness by calcium hydroxide/distilled water combination was significantly higher than the other two groups.

Conclusion: Based on the results of this study, the use of calcium hydroxide combinations for intracanal dressing reduces dentin microhardness. After 7 days calcium hydroxide/glycerine combination and after 14 days calcium hydroxide/distilled water combination are the most effective combinations.


Comparative evaluation of the microhardness of White and Gray MTA after contamination with blood
Ms. Sheikhrezaie, Mh. Nekoofar, K. Oloomi,
Volume 21, Issue 4 (1-2009)
Abstract

Background and Aim: One of the unique properties of MTA is its setting ability in presence of moisture. The sealing ability of MTA used as a root-end filling was shown to be unaffected by the presence of blood, in vitro. It has been recommended that, because of MTA ability to set in the presence of blood, there is no need to dry the perforation site before MTA placement. On the other hand, based on an in vitro study, it is recommended that hemorrhage be controlled at the perforation site and blood be removed from the perforation walls before placement of tooth-colored MTA. Blood contamination may also affect the crystalline structure of MTA. The microhardness of a material is influenced substantially by some fundamental properties of the material such as crystal structure stability. Thus, it can be used as an indicator of the setting process. It can also indicate the effect of various setting conditions on the overall strength of a material. The aim of this study was to evaluate the effect of blood contamination on microhardness of white and gray MTA as an indicator of their setting process.

Materials and Methods: In groups 1 and 2 each material has been mixed with distilled water according to manufacturer,s instruction (No contamination groups). In groups 3 and 4 samples were prepared like groups 1 and 2 but the surface of material placed in contact with blood (Surface blood contamination groups). Samples of groups 5 and 6 were mixed with blood instead of distilled water and also the surfaces of the materials were placed in contact with blood (Mixed with blood groups). All samples were stored in 370C and 100% humidity for 96 hours. The microhardness of the samples was measured with Vickers test.

Results: White MTA samples which have not contaminated with blood had the highest microharness (59.9±11.4 N/mm2) while gray MTA mixed with blood had the lowest hardness (18.45±7.8 N/mm2). One-way ANOVA test showed that contamination with blood significantly reduces the microhardness of both white and gray MTA (p<0.001). The difference between white MTA and gray MTA was significant in groups of no contamination (p<0.001), surface blood contamination (p=0.043), and mixed with blood (p<0.001) according to T-Test analysis. In all of them white MTA had higher hardness than gray MTA.

Conclusion: According to results of our study we recommend that hemorrhage should be controlled and any blood contamination should be removed before placement of both white and gray MTA.


Effect of type of cavity preparation (bur,Er:YAG laser) and restorative materials on prevention of caries lesion
Masumeh Hasani Tabatabaei, Sakineh Arami, Fatemeh Khajavi, Zohreh Moradi,
Volume 29, Issue 4 (1-2017)
Abstract

Background and Aims: Despite the reduction of incidence of dental caries in recent years, this disease is common and many efforts were conducted to decrease the prevalence of dental caries. On the other hand secondary caries lesions are the main reason for replacement of direct restorations. Therefore, the aim of the current study was to evaluate suitable methods of preparation and restorative materials to reduce caries recurrence.

Materials and Methods: In this experimental study, eighty human teeth were collected and stored in normal saline. The teeth were soft-tissue debrided and cleaned with water/pumice slurry and rubber cups in a low-speed handpiece. Speciments were randomly divided in two main groups. Cavities were prepared with diamond burs or Er:YAG laser (10 Hz, 300 mJ, 3W). Each group was divided into 4 sub-groups, and restored with a glass-ionomer cement (Fuji IX), resin modified glass-ionomer (Fuji II LC), total etch bonding + composite resin or self-etch bonding + composite resin. The specimens were submitted to pH cycling. Speciments were then sectioned, polished and Vickers microhardness measurements were performed on each specimen. Differences among the medians were analyzed using two way ANOVA test at a 95% confidence level and Tukey test.

Results: Statistical analysis showed significant difference in the type of substrate (enamel, dentin) in both main groups (P<0.0001) but no differences in the caries lesion development between the cavities restored with the same material and prepared with diamond burs or Er:YAG laser.

Conclusion: The Er:YAG laser used for cavity preparation and different types of restorative materials used did not show the ability to guarantee significantly more acid-resistance tooth structure against demineralization.


The effect of resin infiltrant (Icon), MI paste plus and Nd:YAG laser on enamel microhardness
Alireza Daneshkazemi, Abdolrahim Davari, Motahareh Amiri, Fatemeh Mirhosseini,
Volume 33, Issue 1 (7-2020)
Abstract
Background and Aims: Erosion is the chemical dissolution of a tooth by acid without bacterial involvement. The purpose of the current study was to investigate the effect of resin infiltration (Icon), MI paste plus, and Nd:YAG laser on the enamel microhardness.
Materials and Methods: 40 enamel samples were obtained from the third molar tooth. Primary microhardness was measured in all specimens. Then, erosion was created using hydrochloride acid on the surfaces of enamel and the microhardness values were measured. The samples were randomly divided into four groups. G1: MI paste plus, G2: MI paste plus+ Nd:YA laser, G3: ICON without etching, G4: ICON with etching. Erosion was induced again by hydrochloric acid and then subjected to thermocycling. Finally, the microhardness of the samples was measured. Statistical analysis was performed using SPSS23 software, one-way ANOVA, multiple Tukey and T-test comparisons. P<0.05 was considered as a significant level.
Results: The microhardness increased in the third stage compared to the second stage in all groups, which was statistically significant (P<0.000). Also, the comparison of the increase of microhardness among groups, except second group with the fourth group, was statistically significant.
Conclusion: All the materials used in this study significantly increased the microhardness of the eroded enamel.

Evaluation of the effect of nanohydroxyapatite-containing toothpaste and mouthwash on remineralization of early enamel caries and occluding of dentinal tubules
Abdolrahim Davari, Farnaz Farahat, Sepideh Abbasi,
Volume 35, Issue 0 (5-2022)
Abstract
Background and Aims: Different factors play a role in causing tooth decay. Modern dentistry is looking for a way to prevent tooth decay and suggests different ways to increase remineralization. The aim of this study was to evaluate the effect of nanohydroxyapatite toothpaste and mouthwash on remineralization of primary enamel lesions and obstruction of tubules.
Materials and Methods: In this study, 90 human extracted central teeth were used. Artificial decay was induced by placing the specimens for 72 hrs in a demineralization solution in an incubator at 37 °C. Hardness of the specimens was determined by a microhardness test before any surface treatment. The specimens were then divided randomly into 6 groups of 15. For 1-6 groups, the specimens were subjected to a pH cycling for 14 days, which included 3 hrs of demineralization and 21 hrs of remineralization. At the same time, 1-3 groups were in contact with diluted toothpaste in a ratio of 1:3 with deionized water at a rate of 5 ml twice a day for two min. Eac specimen of 4-6 groups was exposed to 5 ml of three types of mouthwashes for one min. Then, the specimens were cut in the buccolingual direction in order to simultaneously evaluate the dentinal tubules and Vickers microhardness test was performed again and the before and after microhardness values were compared. Then, the percentage of deposition on the surface and tubule obstruction were analyzed using SEM (Scanning electron microscope) (P=0.006). Data were analyzed using SPSS24 software bu the descriptive statistics, ANOVA analysis of variance, and multiple Tukey comparisons.
Results: The results of analysis of variance test showed that there was a statistically significant difference in the microhardness changes between study groups (P=0.006). Also, in-group analysis of microhardness changes, there was a significant difference (P<0.0001). Besides, only in the group containing 0.5% nanohydroxyapatite toothpaste, more than 50% tubule deposition and obstraction was observed (P<0.05).
Conclusion: According to the present study, nanohydroxyapatite can be one of the treatment strategies to repair incipient lesions of teeth and the addition of nanohydroxyapatite, preferably to toothpaste, increases the dental microhardness.

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