Effect of sodium hypochlorite on dentin microhardness

This study was designed to evaluate the effect on root dentin microhardness of 2.5% and 6% sodium hypochlorite solutions for various irrigation periods. Forty-two bovine roots were divided into seven groups. The control group was irrigated with saline. The experimental samples were continuously irrigated with 2.5% or 6% NaOCl for 5, 10, or 20 min. Microhardness was measured at depths of 500 mum, 1000 mum, and 1500 mum from the lumen. A decrease in microhardness was found at 500 mum between the control and samples irrigated with 6% NaOCl and 2.5% NaOCl (p = 0.352, p = 0.084 respectively) at all irrigation periods. There also was a significant difference in groups irrigated for 10 or 20 min (p = 0.001, p < 0.001 respectively). At all distances, the decrease in microhardness was more marked after irrigation with 6% NaOCl than 2.5% NaOCl.     

Effect of intracoronal bleaching agents on dentin microhardness

The purpose of this in vitro study was to compare the effect of intracoronal bleaching agents associated or unassociated with chlorhexidine gel on dentin microhardness. Sixty human maxillary incisor crowns were divided into six groups, and bleaching agents were sealed into the pulp chambers as follows: sodium perborate + water (SPW), sodium perborate + 2% chlorhexidine gel (SP + CHX), sodium perborate + 30% hydrogen peroxide solution (SP + HP), 37% carbamide peroxide gel (CP), 37% carbamide peroxide gel + 2% chlorhexidine gel (CP+CHX), and water (W). After the bleaching procedure, microhardness testing was carried out on the dentin surface at three different levels: inner, middle, and outer dentin. The greatest reduction in microhardness was observed for the SP + HP group. No differences were observed between the SPW and SP + CHX group. The 2% chlorhexidine gel did not adversely affect dentin microhardness when associated with the tested bleaching agents. CHX might be considered as an antimicrobial vehicle during intracoronal bleaching.     

Effect of different EGTA concentrations on dentin microhardness

The effect of 1%, 3% and 5% EGTA (ethylene glycol-bis-(beta-amino-ethyl ether) N,N,N',N'-tetra-acetic acid) on the microhardness of root dentin of the cervical third of human teeth was studied. Five newly extracted maxillary incisors were sectioned transversely at the cementoenamel junction, and the crowns were discarded. The roots were embedded in blocks of high-speed polymerized acrylic resin and cut transversely into 1-mm sections. The second section of the cervical third of the root of each tooth was sectioned and divided into four parts. Each part was placed on an acrylic disc that was used as a base for microhardness measurement. Fifty microliters of 1% EGTA, 3% EGTA, or 5% EGTA were applied to the dentin surface. Deionized and distilled water was used as control. Dentin microhardness was then measured with a load of 50 g for 15 s. Statistical analysis showed that the three concentrations of the chelating solution EGTA significantly reduced dentin microhardness when compared with water (ANOVA, p < 0.01), and that there was a statistically significant difference among the three solutions (Tukey test, p < 0.05).     

Effect of demineralization and remineralization on microhardness of irradiated dentin

The aim of this in vitro study was to evaluate the effects of irradiation and fluoridation on the demineralization and remineralization patterns of root dentin. From the cervical regions of 84 bovine incisors, each of four dentinal blocks were prepared and randomly assigned to four groups: 1) no irradiation; 2) irradiation of specimens up to 60 Gy (2 Gy/d, 5 d/w); 3) no irradiation, but fluoridation of specimens for 5 min/d with Elmex Gelée; and 4) irradiation and daily fluoridation of specimens for 5 min/d. Subsequently, the specimens were demineralized for 2, 4, 6 or 8 days with acidulated hydroxyethylcellulose (n = 21), and Knoop hardness numbers (KHN) were determined before, as well as after the demineralization period. Then seven specimens from each group were fluoridated with one of three fluoride gels (Elmex Gelée [1.25%], STOP [0.4%], Fluoridgel [1.25%]; 2 x 15 min/d, 10 d), and immersed in synthetic saliva at a temperature of 37 degrees C. Finally, KHN for all specimens were determined. Irradiation resulted in a significant decrease in microhardness. There was a reduction in microhardness with increasing demineralization time in all groups. The highest percentage decrease in microhardness could be observed with group 1. Due to the preceding decrease of KHN in the irradiated specimens (group 2), these samples showed less percentage reduction in microhardness during demineralization when compared to group 1 (ANOVA; p < 0.001). The decrease in microhardness was significantly hampered by fluoridation in the non-irradiated, as well as in the irradiated samples (groups 3 and 4; p < 0.001). The remineralization with Fluoridgel resulted in the greatest increase in microhardness. It is concluded that demineralization can be hampered by regular fluoride application in irradiated dentin. However, due to the considerable irradiation effect, this benefit might be negligible.     

Effect of chelating solutions on the microhardness of root canal lumen dentin

Introduction

The greatest reduction in microhardness of the most superficial layer of dentin of the root canal lumen is desired. The use of chelating agents during biomechanical preparation of root canals removes smear layer, increasing the access of the irrigant into the dentin tubules to allow adequate disinfection, and also reduces dentin microhardness, facilitating the action of endodontic instruments. This study evaluated the effect of different chelating solutions on the microhardness of the most superficial dentin layer from the root canal lumen.

Methods

Thirty-five recently extracted single-rooted maxillary central incisors were instrumented, and the roots were longitudinally sectioned in a mesiodistal direction to expose the entire canal extension. The specimens were distributed in seven groups according to the final irrigation: 15% EDTA, 10% citric acid, 5% malic acid, 5% acetic acid, apple vinegar, 10% sodium citrate, and control (no irrigation). A standardized volume of 50 μL of each chelating solution was used for 5 minutes. Dentin microhardness was measured with a Knoop indenter under a 10-g load and a 15-second dwell time. Data were analyzed statistically by one-way analysis of variance and Tukey-Kramer multiple-comparison test at 5% significance level.

Results

EDTA and citric acid had the greatest overall effect, causing a sharp decrease in dentin microhardness without a significant difference (p > .05) from each other. However, both chelators differed significantly from the other solutions (p < .001). Sodium citrate and deionized water were similar to each other (p > .05) and did not affect dentin microhardness. Apple vinegar, acetic acid, and malic acid were similar to each other (p > .05) and presented intermediate results.

Conclusion

Except for sodium citrate, all tested chelating solutions reduced microhardness of the most superficial root canal dentin layer. EDTA and citric acid were the most efficient.     

Effect of different laser devices on the composition and microhardness of dentin

This study determined the compositional changes and microhardness of the cavity floor prepared by Er,Cr:YSGG and Er:YAG lasers and compared the results with the conventional method of bur preparation. Fifteen non-carious human molars were used in this study. On the buccal and lingual surfaces of each tooth, two cavities (mesio-distal 3 mm, inciso-gingival 3 mm, depth 2 mm) were prepared with two different laser devices (Er,Cr:YSGG laser; Waterlase MD and Er:YAG laser; KaVo Key Laser 3) and a high-speed turbine. The teeth were embedded into polyester resin and cross-sectioned. The microhardness measurements from the floor of each half cavity were recorded with the Vickers surface hardness tester. The remaining halves of the cavities were subjected to SEM-EDS atomic analysis. The results were statistically evaluated by one-way ANOVA and Kruskal Wallis tests (p = 0.05). No significant differences were observed among the microhardness values, quantities of Ca (Ca weight %), P (P weight %) and Ca/P ratio of the lased and conventionally prepared cavities (p > 0.05). The cavity preparation techniques and differences in laser devices did not significantly alter the composition and microhardness of dentin tissue. Both laser devices used in this study were observed to lead to minimal thermal damage in the dentin tissue and minimal thermally-induced changes in dentinal compositions.     

根管冲洗液对牙本质、牙釉质微硬度的影响

目的 评价根管冲洗液对牙本质、牙釉质微硬度的影响。方法 收集团正畸拨除的新鲜前磨牙44颗,将牙冠沿牙长轴剖开,用3％双氧水,5％次氯酸钠,17％EDTA及氯仿分别处理5、15min,采用微硬度测定仪测定不同处理时间前后的牙本质、牙翻质微硬度。结果 处理后的牙本质、牙翻质微硬度均显著降低,且与处理时间相关。结论 不同化学冲洗液对牙本质、牙釉质微硬度均产生一定的影响。     

Effect of home bleaching agents on the microhardness of human enamel and dentin

In this study, the effects of home bleaching agents that contains carbamide peroxide (in different concentrations such as 10 and 15%) on the surface hardness of human enamel and dentine were evaluated. The buccal surfaces of 90 recently extracted human mandibular anterior teeth were used. The specimens in the dentine group were ground to expose of dentine surface. Then, samples in both enamel and dentine group were randomly divided into six main groups with 15 in each group. In the group 1 and 4, 15% carbamide peroxide was applied to the enamel and dentine surfaces and then the teeth were left in an incubator at 37 degrees C and 100% humidity for 4 h first, then left 28 h after repeating the same procedures seven times. The teeth were treated with 10% carbamide peroxide in groups 2 and 5 and distilled water in groups 3 and 6 (control groups), using the same procedures. Vicker's microhardness of enamel and dentine were assessed on each tooth before and after each treatment period (4 and 28 h). The hardness of control group specimens was also obtained after 4 h in distilled water and then after 28 h. For statistical analysis one-way ANOVA and post-hoc Tukey tests were used. For both 10 and 15%, there were no statistically significant differences between the untreated control specimens and the specimens treated with the bleaching materials for enamel and dentine at any given measurement time (P > 0.05). Nevertheless, in vivo use of bleaching agents on tooth hard tissues requires further analysis.     

Fluoride treatment and microhardness of dentin.

Effects of various fluoride treatments on the microhardness of human dentin were determined. Treatment with acidulated phosphate-fluoride at pH 3.0 induced a significant (p less than .05) softening when compared to treatment with water. APF at pH 4.0 did not bring about a significant change. Response to treatment with 0.4% SnF2 did not differ significantly from water treatment. Sequential treatment with APF (pH 4.0) followed by SnF2 produced significant (p less than .05) hardening of dentin. This hardening with APF-SnF2 differed at a high level of significance (p less than .001) from the softening produced by the pH 3.0 APF. A similarly significant difference was found between this single APF treatment and the single SnF2 treatment. When hardening of exposed dentin surfaces is desired, the sequential treatment method should be employed.     

Effect of smear layer removal agents on the microhardness and roughness of radicular dentin

PurposeTo evaluate the effect of phytic acid (IP6) on the surface roughness and microhardness of human root canal dentin and compare it to other smear layer removal agents.Materials and methodsFifty extracted human maxillary incisors were sectioned longitudinally into a total of 100 specimens followed by embedding in auto-polymerizing acrylic resin. The specimens were polished and then randomly divided into five groups (n = 20) according to the test solution used to condition root canal dentin: 17% ethylenediaminetetraacetic acid (EDTA); 10% citric acid (CA); 1% IP6; 37% phosphoric acid (PA); or distilled water (control group). Each specimen was treated with a total volume of 1 ml of each solution for 1 min with agitation. Each group was then divided into two subgroups of 10 specimens each. The specimens of the first subgroup were used to determine microhardness, using Vickers hardness tester, and the specimens of the second subgroup were used to measure surface roughness, using a confocal laser scanning microscope. The results were analyzed statistically using one-way ANOVA and Tukey tests, α = 0.05.ResultsAll the tested groups exhibited microhardness and surface roughness values that were statistically significantly different when compared with the control group (P < 0.05). The microhardness value obtained with IP6 was significantly lower when compared to EDTA, CA, and the control group, whereas its roughness value was significantly higher compared to the aforementioned groups. However, there was no significant difference between IP6 and PA (P > 0.05).ConclusionsIP6 and PA showed the lowest microhardness and the highest surface roughness values.     

Effect of trichloracetic acid on the microhardness and surface morphology of human dentin and enamel

Abstract Trichloracetic acid is recommended For the treatment of external cervical root resorption. The present study examined the effect of 90% trichloracetic acid on the microhardness and surface morphology of human dentin and enamel. Intact extracted human teeth were sectioned and embedded in acrylic resin. Each tooth was grinded and highly polished exposing a flat surface of den Lin and enamel. The teeth were treated with 90% trichloracelic acid for 30, 60 and 90 s. Vicker's microhardness of the dentin and enamel was assessed for each tooth before and after each treatment. In addition the surface morphology of a trichloracetic add treated tooth was examined via SEM. The results showed that 90% trichloracelic acid caused a second order type reduction of the microhardness, as well as structural changes in both dentin and enamel.     

Effect of trichloracetic acid on the microhardness and surface morphology of human dentin and enamel.

Trichloracetic acid is recommended for the treatment of external cervical root resorption. The present study examined the effect of 90% trichloracetic acid on the microhardness and surface morphology of human dentin and enamel. Intact extracted human teeth were sectioned and embedded in acrylic resin. Each tooth was grinded and highly polished exposing a flat surface of dentin and enamel. The teeth were treated with 90% trichloracetic acid for 30, 60 and 90 s. Vicker's microhardness of the dentin and enamel was assessed for each tooth before and after each treatment. In addition the surface morphology of a trichloracetic acid treated tooth was examined via SEM. The results showed that 90% trichloracetic acid caused a second order type reduction of the microhardness, as well as structural changes in both dentin and enamel.     

Effect of chloroform, xylene, and halothane on enamel and dentin microhardness of human teeth

OBJECTIVE: The purpose of this study was to assess in vitro the effect of commonly used gutta-percha solvents on the microhardness of human enamel and dentin. STUDY DESIGN: Crowns of human teeth were cut and treated with chloroform, xylene, and halothane. Treatment consisted of exposing the specimens for 5 or 15 minutes to the test solvents. Acid-treated and saline-treated specimens served as controls. After each treatment period, the specimens were rinsed, dried, and prepared for Vicker's microhardness analysis. Vicker's microhardness values for each specimen were recorded before and after treatment, and the differences were statistically compared. RESULTS: A statistically significant decrease in enamel and dentin microhardness was found in most solvent-treated groups; the amount of the decrease was directly related to the exposure time. CONCLUSIONS: Chloroform, xylene, and halothane may cause a significant softening effect on both enamel and dentin. This softening is already apparent after 5 minutes of treatment.     

Monitoring of demineralized dentin microhardness throughout and after bleaching

PURPOSE: To evaluate the effect of six bleaching agents: Nite White [NW] 10% and 22% Excel 2Z (Discus Dental), Rembrandt (REM) 10% and 22% (DenMat), Opalescence (OPA) 10% and 20% (Ultradent) and a placebo agent on demineralized dentin microhardness at different time intervals. METHODS: 105 human dentin slabs (3 x 3 mm) were embedded, planed and submitted to cariogenic challenges, composed of de- and remineralization cycles. For 42 days, specimens were exposed to bleaching agents, consisting of applying them daily for 8 hours, removing and storing the specimens in artificial saliva for 16 hours. At the end of the bleaching treatment, specimens were kept in artificial saliva for 14 days. Knoop Microhardness tests were performed on specimens' surface before (baseline), during (8 hours, 7, 14, 21, 28, 35 and 42 days) and after bleaching procedures (7 and 14 days). RESULTS: The ANOVA for split-plot showed significant effect on the interaction between bleaching agent and time (alpha =0.05). Tukey's test revealed no significant differences on demineralized dentin microhardness exposed to bleaching agents until Day 7. Regression analyses demonstrated that NW 10% and 22% and OPA 10% and 20% increased dentin microhardness in different magnitudes, whereas REM 10% and 22% induced mineral loss during bleaching agent application, followed by microhardness recovery in the post-treatment period.     

The relationship between dentin microhardness and tubule density

Abstract The purpose of this study was to determine the possible correlation between dentin microhardness and dentin tubule density in normal human permanent teeth. A new technique was developed which permitted serial determinations of the micro-hardness and tubule density of the same group of tubules, beginning near to the dentino-enamel junction and progressing to the pulp chamber. The results show that there is a highly statistically significant inverse correlation between dentin micro-hardness and tubular density. Tubular density increased as the pulp chamber was approached. This was associated with a decrease in dentin microhardness, presumably due to a decrease in the amount of intertubular dentin and an increase in individual tubular diameter.