Changes In Surface Microhardness Research Articles

Microhardness of glass carbomer and high-viscous glass Ionomer cement in different thickness and thermo-light curing durations after thermocycling aging

BackgroundThe objective of our study was to compare the upper and lower surface microhardness and surface changes of Glass Carbomer Cement (GCP) and EQUIA Forte (EF) in different thickness after thermo-light curing durations and aging.MethodsA total of 504 samples (5 mm-diameter) were prepared by using GCP-252 (GCP Dental, and Vianen, Netherlands) and EF-252 (EQUIA Forte, GC, Tokyo, Japan). Three different thickness samples (2, 4, and 6 mm) were prepared with 84 samples in each subgroup. The samples were prepared by three curing procedures (Non-exposed, 60s, 90s). Their varnishes were applied to the upper surfaces of half of each subgroup (n = 7). The upper microhardness measurements were evaluated before and after aging. To compare the effect of different thicknesses, the bottom surfaces of the samples were evaluated before aging in terms of microhardness measurements. Also, the upper surfaces were analyzed in the SEM before and after aging.ResultsThe upper surface values of all the samples were higher than the bottom values (p < 0.05). There were no significant differences between the varnished and non-varnished samples in both materials (p > 0.05). Although this increase was not significant in some groups, temperature variations increased the surface microhardness values of both materials except for the non-exposed-varnished EF samples. The highest microhardnesses values were recorded in the non-exposed-varnished EF (125.6 ± 6.79) and unvarnished GCP (88.1 ± 7.59) samples which were thermo-light cured for 90 s before aging. The bottom hardness values were affected by thickness variations in both GCP and EF materials (p < 0.05). The sample deformations and microcracks after aging were greater than before in all the materials. Thermo-light curing in 90 s to the samples reduced the cracks in both the materials before and after aging.ConclusionsThermal aging adversely affected the microhardness of the materials, which is important for clinical success. The thermo-light curing process improved the microhardness of the GCP group without varnish application. Varnish application increased the microhardness of the EF group without applying thermo-light curing. The microhardness of the bottom surfaces decreased with increasing thickness. The thermo-light curing did not increase the bottom surface microhardness of all the samples.

Influence of structure and properties of surface layer on fatigue durability of hardened steels strengthened by combined electromechanical treatment

Using the example of hardened carbon steels (steel 45, U8), the effect of combination of various surface hardening technologies is considered (using electromechanical processing, surface plastic deformation, non-abrasive ultrasonic finishing and their combination) on changes in structural state and surface microhardness, cyclic durability of hardened specimens and fatigue failure mechanisms. The studies were carried out by the methods of optical and scanning electron microscopy and by microhardness and fatigue tests. It is shown that for the investigated steels in quenched state, a high-speed pulsed thermo-deformation effect during electromechanical processing is accompanied by an increase in the surface microhardness (by more than 50 %) and decrease in the fatigue limit (by 20 – 30 %). Such a change in properties is associated with formation in the surface layer of substantially non-equilibrium, inhomogeneous in chemical composition, ultradispersed phases with increased hardness. At the same time, in the near-surface metal volumes tempering processes of the hardened structure proceed with the formation of softening zones and tensile residual stresses, accompanied by a decrease in the microhardness in these zones and the fatigue limit of the specimens. Such effects reduce some of the materials performance characteristics during surface hardening. The ways to improve the properties of such products due to additional technological operations require further studies. Combined surface hardening (based on electromechanical processing, surface plastic deformation and non-abrasive ultrasonic finishing) of carbon steels allows, due to variations in the intensity of temperature and deformation effects, to purposefully change the structural-phase composition and stress-strain state of the surface and near-surface metal layers. As a result, it becomes possible to form a balanced complex of strength and fatigue characteristics of the samples, depending on the preliminary heat treatment of steel. The operations of surface plastic deformation and non-abrasive ultrasonic finishing after electromechanical hardening, due to intensive plastic deformation provide smoothing of the surface and healing of near-surface defects and allow correction of stress-strain state of the processed metal. It provides an increase in microhardness in the tempering zone by 20 – 25 % and the fatigue limit of the samples by 25 – 30 %.

An In Vitro Investigation of Anticaries Efficacy of Fluoride Varnishes.

Most currently marketed fluoride varnishes (FVs) have not been evaluated for their effectiveness in preventing dental caries. The objective of this study was to investigate the anticaries efficacy, measured as fluoride release into artificial saliva (AS); change in surface microhardness of early enamel caries lesions; and enamel fluoride uptake (EFU) of 14 commercially available FVs and two control groups. Bovine enamel specimens (5×5 mm) were prepared and assigned to 18 groups (n=12). Early caries lesions were created in the specimens and characterized using Vickers microhardness (VHNlesion). FV was applied to each group of specimens. Immediately afterward, specimens were incubated in 4 mL of AS for 18 hours, which were collected and renewed every hour for the first six hours. AS samples were analyzed for fluoride using an ion-specific electrode. Specimens were then brushed for 20 seconds with toothpaste slurry and subjected to pH cycling consisting of a four-hour/day acid challenge and one-minute treatments with 1100 ppm F dentifrice for five days. Microhardness was measured following pH cycling (VHNpost). EFU was determined using microbiopsy. Acid resistance (eight-hour demin challenge) was performed after pH cycling, and microhardness was measured (VHNart) and compared with baseline values to test the FV impact after pH cycling. One-way analysis of variance was used for data analysis (α=0.05). FVs differed in their release characteristics (mean ± SD ranged from 14.97 ± 2.38 μg/mL to 0.50 ± 0.15 μg/mL), rehardening capability (mean ± SD ranged from 24.3 ± 15.1 to 11.7 ± 12.7), and ability to deliver fluoride to demineralized lesions (mean ± SD ranged from 3303 ± 789 μg/cm3 to 707 ± 238 μg/cm3). Statistically significant but weak linear associations were found between ΔVHN(post - lesion), EFU, and fluoride release (correlations 0.21-0.36). The results of this study demonstrated that differences in FV composition can affect their efficacy in in vitro conditions.

Effect of air-abrasion pre-treatment with bioactive glass 45S5 on enamel surface loss after erosion/abrasion challenge

ObjectivesThe aim of this in vitro study was to evaluate the effect of air-abrasion surface pre-treatment with bioactive glass (BAG) 45S5 on enamel surface loss after erosion/abrasion challenge. MethodsTwenty-four sound bovine incisors were used for this study. Four experimental groups (n=12) were assigned as follows: Group 1 was the negative control group, Group 2 specimens were treated with a SnF2 gel (positive control group), Group 3 specimens were air-abraded with BAG 45S5 (ProSylc) and Group 4 received both treatments. The specimens were submitted to erosion/abrasion challenge using a common soft drink. Enamel surface loss was evaluated using an optical profilometer. Additionally, surface roughness (VSI method) and surface microhardness (Vickers method) changes were evaluated, as well as SEM and EDS analyses were performed on enamel surface. The data were statistically analyzed using one-way ANOVA and Tukey’s post-hoc test at a level of significance a=0.05. ResultsSurface pre-treatment with BAG 45S5 reduced surface loss in comparison with negative control group (p<0.001), which exhibited the highest surface loss of the experimental groups (p<0.05). The positive control group (SnF2 treatment) and Group 4 specimens, which received both air-abrasion pre-treatment and SnF2 treatment, presented the lowest surface loss (p<0.05), but did not show significant differences to each other (p=0.65). SignificanceAir-abrasion pre-treatment with BAG 45S5 may be beneficial as an in-office preventive method for the limitation of enamel erosive wear induced by excessive consumption of soft drinks. The clinical significance of the results regarding this preventive method should be confirmed by clinical studies.

Effect of Thermo-mechanical Aging on the Surface Roughness and Micro-hardness of Four CAD/CAM Materials

Aim of the study: The aim of this study was to evaluate the changes in surface roughness and micro-hardness of four CAD/CAM materials after thermo-mechanical aging.Materials and methods: Four commercially available CAD/CAM materials were investigated in this study; two ceramic materials; CEREC Blocs, Celtra Duo, and two hybrid ceramics; CERASMART and VITA ENAMIC. The materials’ blocks were cut into 5 disks each and were subjected to thermo-mechanical aging through 250,000 thermocycles in a mechanical chewing simulator. Surface roughness and micro-hardness were evaluated for each material pre and post thermo-mechanical aging using digital image processing technology and Vickers hardness testing machine, respectively. Results were statistically analyzed using one way analysis of variance (ANOVA), Bonferroni Post Hoc test and paired t test (P≤0.05).Results: Regarding surface roughness; there was no significant difference between all investigated materials before thermo-mechanical aging. After aging, all materials showed insignificant difference between them and insignificant change between pre and post aging with exception of CERASMART that showed significant increase in surface roughness. Regarding surface micro-hardness, the tested materials showed significant difference pre aging in the ascending order of Cerasmart < Enamic < Cerec Blocks < Celtra Duo. But after aging, all materials showed insignificant difference in surface micro-hardness between them and insignificant change between before and after the test.Conclusions: Within the limitations of the current study, it can be concluded that although within the clinical acceptable range, the surface roughness of Cerasmart was significantly affected by the thermo-mechanical aging. The composition is still the most important parameter affecting the surface roughness and micro-hardness of CAD/CAM ceramic and hybrid ceramic materials

Carious lesion remineralizing potential of fluoride- and calcium-containing toothpastes: A laboratory study

BackgroundThe authors conducted a laboratory study to determine the carious lesion remineralization and fluoridation potential of fluoride (F)- and calcium-containing toothpastes. MethodsThe authors created early carious lesions in bovine enamel specimens and assigned them to 7 treatment groups on the basis of their surface Vickers microhardness: Clinpro Tooth Crème (Clinpro) (3M ESPE), CTx4 Gel 1100 (CTx4) (Oral Biotech), Enamelon Fluoride Toothpaste (Enamelon) (Premier Dental), MI Paste ONE (MI-One) (GC America), Crest Cavity Protection Toothpaste (Crest) (Procter & Gamble), and 2 F-dose controls (low F, high F). The authors pH cycled the specimens for 10 days by using an established model, determined changes in surface microhardness, calculated percentage of surface microhardness recovery (%SMHr; primary outcome variable), and measured enamel F uptake (EFU). The authors used a 1-way analysis of variance for data analysis. ResultsStudy results showed an F-dose response for both %SMHr (low-F control: mean, 9.8; 95% confidence interval [CI], 5.7 to 13.8); Crest: mean, 26.2; CI, 21.8 to 30.6; high-F control: mean, 33.5; CI, 29.4 to 37.5) and EFU (low-F control: mean, 47; CI, 12 to 83; Crest: mean, 225; CI, 189 to 260; high-F control: mean, 307; CI, 271 to 342; all micrograms of F per cubic centimeter). For %SMHr, Clinpro (mean, 26.5; CI, 22.5 to 30.6) and CTx4 (mean, 27.3; CI, 23.1 to 31.5) were similar to Crest, all being superior to Enamelon (mean, 15.6; CI, 11.6 to 19.7), which was superior to MI-One (mean, 4.3; CI, 0.3 to 8.3). For EFU, there were no differences between Clinpro (mean, 189; CI, 153 to 224), CTx4 (mean, 177; CI, 142 to 213), Enamelon (mean, 196; CI, 161 to 232), and Crest, all being superior to MI-One (mean, 66; CI, 30 to 102). ConclusionsThis study’s results failed to show superior remineralizing efficacy of any of the toothpastes compared with those of a calcium-free F toothpaste, with 2 of the 4 toothpastes being inferior. Clinical testing will be required to establish conclusive evidence. Practical ImplicationsClinicians should be aware of the remineralizing potential of new anticaries products.

Surface microhardness of different restorative materials exposed to candida albicans biofilm isolated from the oral cavity of hiv-infected children

Introduction: Candida albicans is one of the microrganisms that most often colonizes the oral cavity of HIV-infected children. This fungus secretes organic acids, which decrease the pH of the oral cavity; an environment that is already particularly acidic in HIV-Infected children because of their hypercaloric diets, use of sugary medicines, and poor oral hygiene. Considering the large number of dental restorations and the high prevalence of caries in this population, these conditions, including the metabolism of C. albicans, can potentially cause problems in terms of the surface of restorative materials. Objective: Therefore, the aim of this study was to evaluate, in vitro, the potential of C. albicans isolated from the dental biofilm of HIV-infected children to cause surface demineralization of the restorative materials used in pediatric dentistry. Material and method: Forty-four blocks of four different materials (2 resins, 1 compomer, and 1 glass ionomer cement) were made and separated into four groups (n = 11). All blocks were submitted to initial surface microhardness (ISM) analysis. Subsequently, each block was exposed to C. albicans biofilm, formed from a 1 mL standard suspension containing 105 yeasts/mL, over seven days. The blocks were then cleaned and kept at 4 °C until being submitted for measurement of the final surface microhardness (FSM). The Mann-Whitney test was used for intragroup comparisons between ISM and FSM values. Results: The percentage of microhardness loss (% MHL) values between the four groups were compared using the Kruskall- Wallis test (95% CI). The ISM values ranged from 63.54 ± 11.41 to 77.92 ± 10.91, with no statistical differences being found (p = 0.76). After exposure to biofilm, no significant changes in surface microhardness were observed when comparing the values of ISM and FSM, except for group 3 (compomer VitremerTM), which had an FSM value of 40.45 ± 7.57 (p = 0.001). The % MHL of the compomer (group 3) was significantly higher (41.16%) than the other groups (5.35% group 1; 7.02% group 2; and 9.57% group 3) (p = 0.036). Conclusion: It can be concluded that, in vitro, C. albicans isolated from the dental biofilms of HIV-infected children can cause significant reduction in the surface microhardness of compomer compared with other materials.

Influence of Light-curing Units on Surface Microhardness and Color Change of Composite Resins after Challenge

The aim of this study was to evaluate microhardness and color change (ΔE) of composite resins, light cured with different light emission diodes (LEDs) and submitted to artificial accelerated aging (AAA). Two composite resins with lucirin- TPO photoinitiator were selected: Tetric N-Ceram (Ivoclar Vivadent, A1) and Vit-l-escence (Ultradent, WO).A resin with the only camphorquinone photoinitiat or was chosen as a negative control: Filtek Z350XT (3M ESPE, WD). Disc-shaped specimens were prepared (5 mm diameter; 1.5 mm thick) and photopolymerized with an LED with one wavelength (Radii-Cal, SDI) or multiple wavelengths (Valo, Ultradent), for each composite resin (n = 10). Surface microhardness and color evaluations were performed immediately after specimen preparation and after AAA. Microhardness results were analyzed using Kruskal-Wallis and Mann-Whitney tests for multiple comparisons. To compare the evaluation of microhardness at different times, the Wilcoxon test was used. Mean values of ΔE, ΔL, Δa, and Δb were evaluated using two-way analysis of variance (ANOVA), and Tukey test for multiple comparisons (a = 0.05). Regarding microhardness, a statistically significant difference between the two LEDs was observed for Vit-lescence after AAA. When comparing composite resins that were light-cured with the same device, FiltekZ350XT obtained the greatest microhardness. All groups presented a statistically significant decrease in microhardness from the initial time to the AAA. Regarding ΔE, no statistically significant difference between the two LEDs was observed. When comparing composite resins, FiltekZ350XT showed the highest ΔE values. In general, an LED with multiple wavelengths influenced the microhardness of only one resin containing lucirin-TPO after AAA. The ΔE was more influenced by the composite resin than the LED device. The knowledge of composite resin with deficiencies in the polymerization mechanism could contribute to preventing restorations to become more susceptible to color change and reduction of the mechanical strength.

The Effect of Oral Rinsing Solution on the Color Stability, Surface Microhardness and Surface Roughness Change of Composite Resin

The Effect of Oral Rinsing Solution on the Color Stability, Surface Microhardness and Surface Roughness Change of Composite Resin

Role of Candida albicans on enamel demineralization and on acidogenic potential of Streptococcus mutans in vitro biofilms.

There is growing evidence that C. albicans is associated with dental caries, but its role on caries development needs to be better clarified. Label="OBJECTIVE">To evaluate at the hard tissue level the effect of C. albicans on the cariogenic potential of S. mutans biofilms focusing on the mineral profile of induced carious lesions. This study also aimed to evaluate the effect of C. albicans on the acidogenic potential of S. mutans biofilms. METHODOLOGY Dual-species (CA+SM) and single-species biofilms (CA or SM) were grown on the surface of enamel slabs in the presence of glucose/sucrose supplemented culture medium for 24, 48 and 72 hours. Demineralization was evaluated through percentage of surface microhardness change (%SMC) and transversal microradiography analysis (ILM and LD) and pH of the spent medium was recorded daily. Data were analyzed by two-way ANOVA followed by Bonferroni correction. RESULTS%SMC was statistically different among the biofilms at each time point being the highest for SM biofilms and the lowest for CA biofilms which also differed from CA+SM biofilms [SM (24 h: 47.0±7.3; 48 h: 66.3±8.3; 72 h: 75.4±3.9); CA (24 h: 7.3±3.3; 48 h: 7.1±6.4; 72 h: 6.6±3.6); CA+SM (24 h: 35.9±7.39.1; 48 h: 47.2±9.5; 72 h: 47.6±9.5)]. pH of spent medium was statistically lower for SM biofilms compared to the other biofilms at each time point and remained constant over time while pH values increased from 24 to 72 h for both CA and CA+SM biofilms [SM (24 h: 4.4±0.1; 48 h: 4.4±0.1; 72 h: 4.5±0.1); CA (24 h: 6.9±0.3; 48 h: 7.2±0.2; 72 h: 7.5±0.2); CA+MS (24 h: 4.7±0.2; 48 h: 5.1±0.1; 72 h: 6.1±0.6)]. IML and LD for SM biofilms increased over time while no difference was observed from 24 to 72 h for the other biofilms. CONCLUSIONS The present data suggest that C. albicans has low enamel demineralization potential and the presence of C. albicans can reduce both the cariogenic and acidogenic potentials of S. mutans biofilms.

Effect of CPP-ACPF and Nano-hydroxyapatite Preventive Treatments on the Susceptibility of Enamel to Erosive Challenge.

The purpose of this in vitro study was to evaluate the effect of two preventive clinical treatments on bovine enamel susceptibility after erosive challenge induced by a soft drink. Eighteen sound bovine incisors were used for this study. Three experimental groups were assigned as follows: Group 1 was the control group; Group 2 specimens received a CPP-ACPF paste treatment; and Group 3 specimens received a treatment with a product containing 1% nano-hydroxyapatite and 455 ppmF-. The specimens were submitted to erosive challenge using a common soft drink (Coca Cola). The erosive activity on the enamel was evaluated by measuring surface microhardness change (Vickers method), surface roughness alterations and surface loss (vertical scanning interferometry (VSI) method). The data were statistically analysed using one-way analysis of variance (ANOVA) and Tukey's post-hoc test at a level of statistical significance a = 0.05. The tested treatments exhibited significantly lower decreases in surface microhardness compared to the control group after the erosive challenge (p < 0.05). The tested treatment groups did not show statistically significant lower increases in surface roughness compared to the control group (p > 0.05). In addition, the treatment groups exhibited statistically significant lower surface loss than the control group (p < 0.05). Although the tested treatments reduced erosive activity, none of them provided complete protection against the development of enamel erosion, which means that they should be only used as a part of an individually tailored preventive programme.

Imaging of demineralized enamel in intact tooth by epidetected stimulated Raman scattering microscopy.

Stimulated Raman scattering microscopy (SRS) was deployed to quantify enamel demineralization in intact teeth. The surfaces of 15 bovine-enamel blocks were divided into four equal-areas, and chemically demineralized for 0, 8, 16, or 24h, respectively. SRS images (spectral coverage from ∼850 to 1150 cm - 1) were obtained at 10-μm increments up to 90 μm from the surface to the dentin-enamel junction. SRS intensities of phosphate (peak: 959 cm - 1), carbonate (1070 cm - 1), and water (3250 cm - 1) were measured. The phosphate peak height was divided by the carbonate peak height to calculate the SRS-P/C-ratio, which was normalized relative to 90 μm (SRS-P/C-ratio-normalized). The water intensity against depth decay curve was fitted with exponential decay. A decay constant (SRS-water-content) was obtained. Knoop-hardness values were obtained before (SMHS) and after demineralization (SMHD). Surface microhardness-change (SMH-change) [ ( SMHD - SMHS ) / SMHS] was calculated. Depth and integrated mineral loss (ΔZ) were determined by transverse microradiography. Comparisons were made using repeated-measures of analysis of variance. For SRS-P/C-ratio-normalized, at 0-μm (surface), sound (0-h demineralization) was significantly higher than 8-h demineralization and 24-h demineralization; 16-h demineralization was significantly higher than 24-h demineralization. For SRS-water-content, 24-h demineralization was significantly higher than all other demineralization-groups; 8-h demineralization and 16-h demineralization were significantly higher than 0-h demineralization. SRS-water-content presented moderate-to-strong correlation with SMH-change and weak-to-moderate correlation with depth. These results collectively demonstrate the potential of using SRS microscopy for in-situ chemical analysis of dental caries.

Economic analysis of remanufacturing of engine valves - a case study

With the fast development and frequent changes of the engineering products, natural resources are arbitrary exploited and the environment is used without repayment, which causes many problems of great magnitude such as zoology damaged all over the globe, resource waste and depletion, environmental pollution and so on. Therefore, remanufacturing engineering is the necessity of the current scenario to solve the ambivalence of economic development and resource shortcoming. This article provides an insight on the economic analysis of remanufacturing engineering using a comparative analysis of upgraded part with the new part. Interestingly, hybrid electrochemical abrasive finishing (ECAF) have a unique capability to finish the 3d part in a single setup which majorly help to minimize the operation time. It is found that the remanufactured part cost only 42.12% of new part with 94% savings of material. No significant changes in realistic surface micro-structure and micro-hardness have been observed after ECAF process. SEM micrograph depicts the no presence of micro-cracks, craters, voids, scars and peeling on the rebuild surface. It means that the remanufactured part is able to perform like a new performer.

Influence of Titanium Dioxide Nanoparticles on the Sulfate Attack upon Ordinary Portland Cement and Slag-Blended Mortars.

In this study, the effects of titanium dioxide (TiO2) nanoparticles on the sulfate attack resistance of ordinary Portland cement (OPC) and slag-blended mortars were investigated. OPC and slag-blended mortars (OPC:Slag = 50:50) were made with water to binder ratio of 0.4 and a binder to sand ratio of 1:3. TiO2 was added as an admixture as 0%, 3%, 6%, 9% and 12% of the binder weight. Mortar specimens were exposed to an accelerated sulfate attack environment. Expansion, changes in mass and surface microhardness were measured. Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-ray Diffraction (XRD), Thermogravimetry Analysis (TGA) and Differential Scanning Calorimetry (DSC) tests were conducted. The formation of ettringite and gypsum crystals after the sulfate attack were detected. Both these products had caused crystallization pressure in the microstructure of mortars and deteriorated the mortars. Our results show that the addition of nano-TiO2 accelerated expansion, variation in mass, loss of surface microhardness and widened cracks in OPC and slag-blended mortars. Nano-TiO2 containing slag-blended mortars were more resistant to sulfate attack than nano-TiO2 containing OPC mortars. Because nano-TiO2 reduced the size of coarse pores, so it increased crystallization pressure due to the formation of ettringite and gypsum thus led to more damage under sulfate attack.

Red fluorescence of dental biofilm as an indicator for assessing the efficacy of antimicrobials.

The study aimed to determine whether the red fluorescence (RF) of a dental microcosm biofilm as measured with quantitative light-induced fluorescence (QLF) technology is useful for assessing the efficacy of antimicrobials. Dental microcosm biofilms were formed on bovine enamel discs and grown under 0.3% sucrose challenge and treated with chlorhexidine (CHX) solutions at different concentrations (0.05%, 0.1%, and 0.5%) plus a negative control [sterile distilled water (DW)] twice daily for 7days. The biofilms were photographed using a QLF-digital system to evaluate the RF by calculating the red/green ratio, and pH values of the medium were measured daily. After 7days, the bacterial viability of the biofilm was assessed by measuring the counts of viable total bacteria and aciduric bacteria, and the percentage surface microhardness changes (%SHC) was evaluated. The RF and cariogenic properties were compared for the different concentrations of CHX, and their correlations were examined. The RF and its increase rate were much lower for CHX-treated biofilms than for DW-treated biofilms. The RF after 7days of maturation decreased significantly with increasing CHX concentrations (p<0.001) and was from 31% (for 0.05% CHX) to 46% (for 0.5% CHX) lower than that of the DW group. Strong correlations were reported between the RF of the 7-day-maturation biofilms and cariogenic properties, such as the number of total bacteria (r=0.93), number of aciduric bacteria (r=0.97), supernatant pH (r=0.43), and %SHC (r=0.98). In conclusion, the RF of dental biofilms as measured with QLF technology can be used to nondestructively assess and monitor the effect of antimicrobials against biofilm.

The presence of acquired enamel pellicle changes acid-induced erosion from dissolution to a softening process

Erosive wear undermines the structural properties of enamel resulting in irreversible enamel loss. A thin protein layer formed from natural saliva on tooth surfaces, acquired enamel pellicle (AEP), protects against erosive wear. The exact components in saliva responsible for such protection are not yet known. We prepared three solutions containing different components: proteins and ions [natural saliva (NS)], minerals with no proteins [artificial saliva (AS)] and neither proteins nor ions [deionised water (DW)]. To assess the protection of the three solutions against citric acid enamel erosion, enamel specimens were immersed in the corresponding solution for 24 h. All specimens were then exposed to five erosion cycles, each consisted of a further 30 min immersion in the same solution followed by 10-min erosion. Mean step height using a non-contacting profilometer, mean surface microhardness (SMH) using Knoop microhardness tester (final SMH), and roughness and 2D profiles using atomic force microscopy were measured after five cycles. The final SMH values were compared to the starting values (after 24 hr). NS group had significantly less tissue loss but greater SMH change (P < 0.0001) than AS and DW groups. Specimens in NS were softer and rougher (P < 0.001) but less eroded than specimens in AS and DW.

Effect of a Bioactive Glass Ceramic on the Control of Enamel and Dentin Erosion Lesions.

This study evaluated the effect of a bioactive glass ceramic for the control of erosion and caries lesions. Fragments (n=10) of bovine enamel and root dentin received daily application of different treatments (Biosilicate; Acidulated Phosphate Fluoride- APF; Untreated - control) during the performance of erosive cycles. Surfaces were analyzed with 3D optical profilometry to quantify the superficial loss in four periods (1, 7, 14 and 21 days), as well as the lesion depth with confocal laser scanning microscopy. For caries progression assessment, initial Knoop microhardness was measured on enamel bovine fragments. Initial carious lesions were developed and specimens were divided into three groups (n=10), according to the daily topical application (Biosilicate; APF; no application - control), during the de-remineralization cycles for 14 days. Final microhardness was obtained to calculate the change of surface microhardness. Subsurface demineralization was analyzed using cross-sectional microhardness (depths 10, 30, 50, 70, 90, 110 and 220 µm). Data were tested using ANOVA and Tukey's test (a=5%). Results of erosive evaluation showed that Biosilicate promoted the lowest (p<0.05) values of surface loss, regardless of time, for both enamel and dentin; APF promoted lower (p<0.05) surface loss than control; analyzing different periods of time, APF did not show difference (p>0.05) between 14 and 21 days of demineralization. Results of enamel caries assessment showed that Biosilicate resulted in higher (p<0.05) surface and subsurface microhardness than both APF and control-applications. It may be concluded that Biosilicate application showed a higher potential to reduce surface loss and development of erosion and caries lesions.

Gładkościowe nagniatanie ślizgowe stopów metali i kompozytów na osnowie metalowej

Results of the research performed at the Institute of Advanced Manufacturing Technology (IAMT) regarding the possibility of slide burnishing of metal alloys and metal matrix composites are presented. Results include among others, analysis of surface geometry, microstructure and microhardness changes of the surface layer for selected materials.

Food acid content and erosive potential of sugar-free confections.

Dental erosion is an increasingly prevalent problem associated with frequent consumption of acidic foods and beverages. The aim of this study was to measure the food acid content and the erosive potential of a variety of sugar-free confections. Thirty sugar-free confections were selected and extracts analysed to determine pH, titratable acidity, chemical composition and apparent degree of saturation with respect to apatite. The effect of the sugar-free confections in artificial saliva on human enamel was determined in an in vitro dental erosion assay using change in surface microhardness. The change in surface microhardness was used to categorize the confections as high, moderate or low erosive potential. Seventeen of the 30 sugar-free confections were found to contain high concentrations of food acids, exhibit low pH and high titratable acidity and have high erosive potential. Significant correlations were found between the dental erosive potential (change in enamel surface microhardness) and pH and titratable acidity of the confections. Ten of these high erosive potential confections displayed dental messages on the packaging suggesting they were safe for teeth. Many sugar-free confections, even some with 'Toothfriendly' messages on the product label, contain high contents of food acids and have erosive potential.

Effect of fluoride varnish with added casein phosphopeptide-amorphous calcium phosphate on the acid resistance of the primary enamel.

BackgroundThis study aimed to investigate the effects of a fluoride varnish with added Casein Phosphopeptide-Amorphous Calcium Phosphate (CPP-ACP) treatments on acid resistance of primary teeth enamel.MethodsEnamel specimens obtained from 40 primary incisors (for surface microhardness testing) and 40 primary molars (for demineralization depth measurement) were randomly divided into four groups (n = 10 incisors and 10 molars) each according to surface treatment: no treatment (control), MI varnish (1–8 % sodium fluoride and 1–5 % CPP-ACP), Clinpro White (1–5 % sodium fluoride and <5 % modified tricalcium phosphate), Duraphat (<5 % sodium fluoride). Specimens were stored for 24 h in a moist environment. After varnish residues were removed, specimens were subjected to pH cycling. The effects of fluoride varnishes were evaluated according to surface microhardness, lesion depth and structural changes. Results were analyzed by ANOVA and Tukey’s tests.ResultsThe lowest changes in surface microhardness and lesion depth occurred in MI varnish group, followed by the Clinpro White, Duraphat and no treatment (control) group (for percentage of loss surface microhardness −20.80, −34.60, −57.80 and −73.40; for lesion depth values 23.60 μm ± 3.36, 29.85 μm ± 3.27, 40.37 μm ± 3.41 and 54.56 μm ± 4.16, respectively). Statistically significant differences in both surface microhardness and lesion depth were observed among all groups (P < 0.05).ConclusionsWithin the limitations of this in vitro study, fluoride varnish containing CPP-ACP was more effective in increasing the acid resistance of primary enamel than other fluoride varnishes. However, further clinical research is needed to confirm these in vitro results.