Surface Microhardness Test Research Articles

Anticariogenic potencial of acidulate solutions with low fluoride concentration

Objectives:The aim of this study was to verify the anticariogenic effect of acidulate solutions with low NaF concentration, using pH-cycling model and bovine enamel.Material and methods:Enamel blocks were submitted to the surface microhardness (SMH) test and randomly divided in 12 experimental and one placebo groups. The blocks were submitted to pH cycling for 7 days, with daily applications once/day of 0.05% NaF and 0.1% NaF and twice/day of 0.02% NaF solutions. Four different pH: 4.0, 5.0, 6.0 and 7.0 were used. Next, SMH test was again used to determine the surface microhardness percentage change (%SMH). Data obtained for %SMH were homogeneous and passed through variance analyses and Tukey's test (5%) as far as fluoride concentrations and pH.Results:The results showed that pH influenced %SMH in 0.02% NaF and 0.05% NaF solutions with pH 4.0, which had less mineral loss compared to pH 7.0 (p<0.05). The 0.02% NaF - pH 4.0, and 0.05% NaF – pH 7.0 groups showed similar results (p>0.05). A dose-response relationship was observed among the tested solutions, with better anticariogenic effect for the 0.1% NaF solution.Conclusion:The results suggest that the addition of citric acid to acidulate mouth rinses reduce mineral loss.

Qualitative and quantitative evaluation of enamel after various stripping methods

In this study, we investigated ultramorphology, surface roughness, and microhardness of permanent and deciduous tooth enamel after various stripping methods. One hundred twenty deciduous and permanent teeth (n = 60 each) were used. Qualitative (scanning electron microscopy) and quantitative (surface roughness and microhardness tests) experiments were carried out in the following experimental groups: group 1, stripping disk; group 2, diamond-coated metal strip; group 3, stripping disk and Sof-Lex discs (3M-ESPE, Seefeld, Germany); group 4, diamond-coated metal strip and Sof-Lex discs; group 5 (chemical stripping), 37% orthophosphoric acid in conjunction with diamond-coated metal strip; group 6 (control), no stripping. Surface roughness values (Ra) for permanent and deciduous enamel were evaluated with Welch analysis of variance (ANOVA) and Tamhane tests, and Kruskal-Wallis and Mann-Whitney tests, respectively. Microhardness values were evaluated statistically with Kruskal-Wallis, 1-way ANOVA, and Duncan tests. Deciduous and permanent teeth showed similar results in terms of surface roughness and surface morphology. Groups 3 and 4 had the smoothest deciduous and permanent enamel surfaces, whereas chemical stripping (group 5) produced the roughest surfaces in both enamel types. Stripping did not lead to a significant change in the microhardness of permanent enamel. All stripping methods significantly roughened the enamel surfaces. Polishing the stripped surface with Sof-Lex discs decreased the roughness.

The influence of dietary simulating solvents on a recent composite topography (in vitro study )

Objective: study the influence of dietary simulating liquids on the micro hardness ,surface roughness, and color stability of polished and non-polished organically modifiedceramic, at different storage time .Methods: 240 samples were prepared and then stored in a dark phial containingdistilled water (D.W) at 37C for 7 days before conditioning then the samples divided into3 groups, 80 samples in each, and stared in the conditioning liquids at 40 C for 1, 7 and41 days At the end of each conditioning time the specimens were subjected to colorcomparison test, surface roughness test (RA) and microhardness test Vickers hardnessnumber (VHN .)Results &amp; conclusion Increase aging time will increase the VHN value anddecrease the Ra value of ormocer specially for the control group (aged in D.W). Aging in( food stimulated liquids) F SLs produced an increase in VHN value but to a degree lessthan that of D.W. which in turn produced significant effect of these liquids on Ormocerhardness with time in comparison to the control group Most effect will be seen with 50%Ethanol VHN and color stability. The effect of FSLs on Ormocer VHN were on longterm duration (ll days) while for color change ;(7 days) is the critical time and after thefirst week no additional color will take place. Surface roughness of polished and non -polished Ormocer was not affected by any FSLs and at any aging time. Polishing ofOrmocer will increase the VHN value and Ra value for all FSLs and for all timeintervals .Change in organic base matrix of composite resins is of great value for improvingcmposite properties and durability .

Dry drilling of alloy Ti–6Al–4V

This work is focused on the combined study of the evolution of tool wear, quality of machined holes and surface integrity of work-piece, in the dry drilling of alloy Ti–6Al–4V. Tool wear was studied with optical microscope and SEM–EDS techniques. The quality of machined holes was estimated in terms of geometrical accuracy and burr formation. Surface integrity involves the study of surface roughness, metallurgical alterations and microhardness tests. The end of tool life was reached because of catastrophic failure of the drill, but no significant progressive wear in cutting zone was observed previously. High hole quality was observed even near tool catastrophic failure, evaluated from the point of view of dimensions, surface roughness and burr height. However, microhardness measurements and SEM–EDS analysis of work-piece showed important microstructural changes related with a loss of mechanical properties. Depending on the application of the machined component, the state of the work-piece could be more restrictive than the tool wear, and the end of tool life should be established from the point of view of controlled damage in a work-piece.

Microhardness of Composites in Simulated Root Canals Cured with Light Transmitting Posts and Glass-Fiber Reinforced Composite Posts

The aim of this study was to evaluate the depth of cure of composite resin cured within simulated root canals by means of light-transmitting plastic posts, glass-fiber–reinforced composite posts, and conventional light curing method. Thirty black plastic cylinders measuring 15 mm in length and 4 mm in internal diameter were divided into three groups. The composite resin was packed into simulated canals. The light-transmitting plastic posts and glass-fiber–reinforced composite posts were inserted into simulated canals and light cured for 90 seconds. The control group was light cured directly. To ensure continual change of material properties by increasing the length of material, a surface microhardness test was done 2 mm, 4 mm, 6 mm, 8 mm, 10 mm, 12 mm, and 14 mm from the light exposure surface. The results showed a significant increase in microhardness of composite resin (depth of cure) for both light-transmitting plastic posts and glass-fiber–reinforced composite posts compared with the control group. The microhardness of composite resin was also significantly higher with light-transmitting plastic posts than glass-fiber–reinforced composite posts after 8 mm.

Selected characteristics of an Ormocer and a conventional hybrid resin composite

Objectives. The objective of this in vitro study was to evaluate surface roughness, hardness and wear resistance of an Ormocer (Admira), polymerized by a plasma arc system. A secondary objective was to investigate two placement technique bulk or incremental layers. Methods. Blocks from Admira and Amelogen (a microhybrid composite) were prepared in cylinders, 3 mm in diameter, and 2 and 5 mm in thickness (bulk or incrementally placed) and polymerized by a plasma arc and a conventional light system. Surface roughness measurements were taken by a Surface Profilometer on the top of the specimens. Vickers hardness measurements, with a load of 600 mN were taken on the top and bottom of 2 mm and top, intermediate and bottom of 5 mm thick specimens. For the wear test, specimes (8 mm in diameter and 2 mm in thickness) of Admira, Amelogen and amalgam were tested in a ball-on design, by circular movements of the antagonist (alumina ball; diameter 10 mm) under 10 N load. For the statistical evaluation of the results of surface roughness, microhardness and wear test; a paired samples t-test and Kruskal-Wallis analysis of variance test, were performed. Results. Admira showed highest hardness values in all polymerization types at the top surface and this was statistically significant ( p<0.05). These highest hardness values were obtained with conventional polymerization (81.84±1.167 VHN). Meanwhile, the wear resistance of Admira was found to be higher than Amelogen (Wd admira=0.024±0.00149 mm 3; Wd amelogen=0.032±0.00075 mm 3). However, Admira demonstrated the highest surface roughness value compared to Amelogen, with plasma arc 5 s (0.65±0.023 μm). Amelogen was found to have the lowest surface roughness value with conventional 40 s (0.45±0.012 μm). Significance. The results indicated that Ormocer, which was developed by Ormocer technology, demonstrated higher microhardness and wear resistance when compared to a hybrid composite; however, the polishability of Ormocer needs further investigation. Also the selection of visible light activated composite resins exhibited higher surface microhardness values when polymerized with conventional rather than with plasma arc.

Aluminium nitrides growth film in a triode plasma system over a varying cathode current density scale

Intensified plasma assisted processing is a novel method that uses a triode discharge system to intensify the glow discharge. In this project, this system was investigated across a range of variables to confirm the optimum operating parameters. The aluminium nitride coatings produced by this method were characterized using scanning electron microscopy (SEM), electron dispersion spectroscopy (EDS) and surface micro-hardness tests. The result obtained showed that at the optimum level the aluminium nitride films had a grain size of 8 nm. The hardness in comparison with similar films produced by other traditional plasma processes showed a superior quality. The current results will be directed to establishing ideal parameters for operation.

The effects of plasma nitriding process parameters on the wear characteristics of AISI M2 tool steel

The main aim of this work is to evaluate the effects of the plasma nitriding process on AISI M2 tool steel. In previous work, treatment time and temperature were varied to identify the treatment conditions for good wear behaviour. In the present work, the treatment time was fixed while temperature and gas pressure were varied. Samples were characterised by glow discharge optical spectroscopy, scanning electron microscopy, X‐ray diffraction, surface microhardness and wear test. The specimens nitrided at 400 and 900 Pa showed the best wear performance, which is possibly due to reduction of the friction coefficient and the low adhesive wear observed. Samples processed at 200 Pa showed spalling during the wear test, indicating a brittle surface.

In vitro Quantitative Microhardness Assessment of Enamel with Early Salivary Pellicles after Exposure to an Eroding Cola Drink

To assess the erosive effect of a cola drink on enamel incorporating early salivary pellicles, 72 groups of human enamel slabs were immersed in fresh cola, with groups differing in that slabs were (1) incubated in whole or in clarified saliva, (2) under three regimes of frequency intake (1, 5 and 10 times/day); (3) immersed with or without agitation, and (4) the pellicle was incubated for 20 min, 6 or 24 h. Quantitative assessments were done over an 8–day interval using surface microhardness testing. Results for primary enamel showed a sharp decrease from baseline (344.2±32.4 Vickers Units; mean ±SD) to day 1 (268.9±36.8), and reached 155.2±68.6 on day 8. Results for permanent enamel were 350.8±42.2, 315.9±39.2, and 149.8±85.2. Microhardness was affected by agitation, level of intake and type of saliva, but not by the pellicle incubation interval nor the type of enamel. The joint effect of static baths and higher immersion frequency was the most important factor in decreasing hardness.

A method to measure clinical erosion: the effect of orange juice consumption on erosion of enamel

Objective: Acidic soft drinks are frequently implicated in dental erosion, but there are limited supporting data. Research is problematic due to the insidious nature of erosion and accuracy in assessing tissue loss. The aim of this study was to develop and validate, using a negative control, a model to accurately measure erosion in situ due to a single aetiological agent over a relatively short time period. Methods: An intra-oral appliance capable of retaining an enamel sample was designed in order to assess the effect of orange juice consumption on enamel. The study was a single centre, randomized, placebo controlled, blind, crossover design. Results: Ten subjects, each consuming 11 of orange juice per day for 15 days, showed significantly more erosion on the enamel specimens than the same subjects consuming 11 of water per day over the same time period, measurements undertaken with surfometry. The same investigation was performed in vitro. Again, orange juice was significantly more erosive; indeed, it was in the order of 10 times that produced in situ. Surface microhardness testing in situ and in vitro demonstrated statistically significant differences between exposed and unexposed areas after orange juice treatment. Conclusions: Changes produced by water either in situ or in vitro were always well within the baseline measurement parameters (± 0.3μm) set down for the method and hence validated the clinical model in terms of reproducibility and accuracy in measurement. It is concluded that this method has confirmed the erosive potential of orange juice in situ. The method could have many applications to study dental erosion under highly controlled conditions and over realistic time periods.

In vitro Quantitative Assessment of Enamel Microhardness after Exposure to Eroding Immersion in a Cola Drink

Studies assessing the erosive potential of soft drinks have employed long time intervals of immersion that may not accurately depict the impact of frequent soft drink consumption on enamel. This in vitro study assessed the effect of a cola drink on enamel, replicating an actual drinking pattern. Six groups of 4 human enamel slabs were immersed (5 min each bath) in fresh cola drink, with immersions taking place with or without agitation, and under 3 regimes of frequency intake (low intake, 1 immersion/day; medium, 5/day; high, 10/day). Quantitative assessments of surface erosion were done over an 8-day interval using surface microhardness testing (Vickers). Results showed a sharp decrease from baseline (mean value 352.1 Vickers Hardness Number, SD 32.5) to day 1 (269.3, SD 41.0) and then continued decreasing throughout the assay, although less markedly, to reach 204.5, SD 45.4 on day 8. Microhardness decreased regardless of frequency regime, except on day 8, on which slabs from the low intake group were harder (233.2, SD 25.0) than slabs from the high intake group (169.8, SD 49.5; p < 0.05). Results from the ANOVA on the factorial experiment indicated that the role of agitation was statistically significant (d.f. = 1, F = 7.2, p = 0.020) while the level of intake was of borderline significance (d.f. = 2, F = 3.2, p = 0.075). The main effect resulting from the joint roles of agitation and intake indicated that there was an important interaction between the two variables (d.f. = 3, F = 4.5, p = 0.023).

The optimum curing cycle for a light‐ and heat‐cured composite inlay material

summary The transverse bend test and surface microhardness test were used to determine the optimum curing cycle for a light‐ and heat‐cured composite inlay material. Specimens were light‐cured (control) and light‐ and heat‐cured using the following temperatures: 50°C for 5 min; 50°C for 10 min; 100°C for 1 min; 100°C for 5 min; 100°C for 10 min; and l00°C for 15 min. Heat‐curing in boiling water at 100°C for at least 1 min significantly improved the transverse strength, modulus of elasticity and surface microhardness compared to light‐curing only or at 50°C. The curing cycle of 100°C for 5 min is considered the most appropriate.

Relationship between microhardness and fluorine contents on tooth enamel determined by PIGE analysis

The remineralization effect of fluoride has been measured by surface microhardness on tooth enamel. The purpose of this study was to investigate the relationship between microhardness and fluorine concentration on tooth enamel. Twelve sound bovine enamel specimens were prepared and immersed in 0.05% NaF solution for 1, 3, 6, 24 and 36 hours, respectively. The concentration of fluorine in specimens were measured by PIGE analysis and surface microhardness of each specimen was measured by surface microhardness tester. Fluorine concentration was increased by immersing time. There was no change in microhardness of each specimen by fluorine content. The results of this study suggest that there was no relationship between the fluorine concentration and surface microhardness in sound tooth enamel. PIGE analysis can be used effectively to assess the remineralization effect of fluorine content in tooth enamel.

The influence of different factors on in vitro enamel erosion.

The aim of this study was to use two demineralization test methods to analyze the erosive potential of beverages and foodstuffs. In addition, the surface microhardness test and the iodide permeability test were compared. Surface microhardness and iodide permeability were measured before and after exposure. To characterize the beverages and foodstuffs the content of phosphate, calcium and fluoride, pH, the titrable amount of base to pH 5.5 and 7.0 as well as the buffer capacity at pH 5.5 were determined. Sprite light showed the highest significant decrease in surface microhardness (p < or = 0.05) followed by grapefruit juice, apple juice and salad dressing. The highest significant increase in iodide permeability (p < or = 0.05) was caused by exposure to grapefruit juice followed by apple juice (Sprite light was not tested). Multiple linear regression analyses revealed that the erosive capacity of different drinks, juices and foodstuffs are statistically significantly associated with their acidity, pH values, phosphate and fluoride contents as well as the baseline surface microhardness or iodide permeability values of the exposed enamel.

Comparison of the Iodide Permeability Test, the Surface Microhardness Test, and Mineral Dissolution of Bovine Enamel following Acid Challenge

The relationship among the iodide permeability (Ip) test, the surface microhardness (SMH) test, and enamel demineralization chemically analyzed as mineral loss was investigated using bovine enamel blocks. Demineralization periods of 0 (control) and 5, 15, 30, and 45 min using 0.05 mol/l lactate (pH 4.75) were chosen to approximate the acid challenge occurring during the intraoral enamel demineralization test. Mineral loss (Ca and PO4) was found to be directly proportional to dissolution time (r = 0.95). Changes (delta) in Ip and SMH each increased linearly over time (r = 0.58 and 0.64, respectively) and were similarly related to mineral loss (r = 0.60 and 0.65, respectively). The correlation between delta Ip and delta SMH was 0.55. When longer demineralization periods (60, 120, and 240 min) were included, the correlation between delta Ip and delta SMH was 0.68. We conclude that both the Ip test and the SMH test can be used as measures of the early stages of enamel dissolution.

Transmission electron microscopy in lubricant evaluation

A pilot study has been made using transmission electron microscopy to determine how well this technique reveals the microstructure of wear-damaged surface layers in a metal alloy (type 304 stainless steel) and whether the results correlated with lubricants chosen over a wide performance range. It has been shown that very thin specimens (2 × 10 −5 cm) of wear surface layers can, in fact, be prepared by electrochemical methods and their structures evaluated with transmission electron microscopy. It was found that lubricant grade, based upon 4-ball wear tests and surface microhardness tests, can be related to the severity of mechanical damage in the metal surface layer. The best lubricants, the ones containing sulfur and chlorine, appear to produce lightly worked surfaces, whereas a poorer lubricant, one containing only a lubricity agent, leads to extremely heavily worked surface layers. In this latter case, sub-surface damage was associated with very fine crystalline precipitate particles in the 304 stainless steel. It is thought that these particles are carbides formed as a consequence of high local surface temperatures, approaching 1000°C, and the very severe working associated with poor lubricants.