Influence of a glycolic acid-based final irrigant for photosensitizer removal of photodynamic therapy on the microhardness and colour change of the dentin structure

IntroductionThis study aimed to evaluate the influence of glycolic acid-based final irrigant for photosensitizer removal of photodynamic therapy on the microhardness and colour change of the dentin structure.MethodsEighty extracted single-rooted human incisors were used. Sample preparation and root split resulted in 160 samples, 80 samples being used for microhardness and 80 samples for colour change evaluation. In the first, PDT protocol was performed and 80 samples were randomly divided into 4 groups (n = 20), according to the final irrigation protocol: distilled water (DW); 17 % ethylenediaminetetraacetic acid (EDTA); QMix; 17 % glycolic acid (GA). Microhardness was evaluated using the Vicker tester, before and after, PDT and final irrigation protocols, calculating the percentage of microhardness reduction. In the second evaluation, PDT and final irrigation protocols were performed in the same way. Colour change was evaluated using digital spectrophotometer before and after these protocols, calculating the ΔE colour change using the CIELAB system (L*a*b* values). Specific statistical analysis was performed for both evaluations (α = 5%).ResultsThe highest percentage of microhardness reduction was observed in 17 % EDTA, QMix and 17 % GA groups, with no significant difference among them (p > 0.05). Furthermore, none of these protocols was effective in photosensitizer removal, and all final irrigation protocols were statically similar to control group (p > 0.05).ConclusionsGA promotes microhardness reduction and also contributes to the colourization of dentin structure during the photosensitizer removal process, followingPDT .     

Effect of exposure time and moving the curing light on the degree of conversion and Knoop microhardness of light-cured resin cements

ObjectiveTo evaluate the effect of exposure time and moving the light-curing unit (LCU) on the degree of conversion (DC) and Knoop microhardness (KH) of two resin cements that were light-cured through ceramic.MethodsTwo resin cements: AllCem Veneer APS (FGM) and Variolink Esthetic LC (Ivoclar Vivadent) were placed into a 0.3 mm thick matrix in 6 locations representing the canine to canine. The resins were covered with 0.5 mm thick lithium disilicate glass-ceramic (IPS e.max CAD, Ivoclar Vivadent). A motorized device moved the LCUs over the ceramic when the LCU was on. Two single-peak LCUs: Elipar DeepCure-L (3M Oral Care) and Emitter C (Schuster), and one multi-peak: Bluephase G2 (Ivoclar Vivadent) were used with 3 different exposure protocols: a localized exposure centered over each tooth for 10 or 40 s; moving the tip across the 6 teeth for a total exposure time of 10 or 40 s; and moving the tip across the 6 teeth resins for a total exposure time of 60 or 240 s. After 24 h, the DC and KH were measured on the top surfaces and the data was analyzed using three-way ANOVA and Tukey’s tests (α = 0.05).ResultsInterposition of 0.5 mm of ceramic reduced the irradiance received by the resin by approximately 50%. The 40 s localized exposure over each tooth always produced significantly higher DC and KH values. Moving the LCUs with a total exposure time of 10 s resulted in the lowest DC and KH. There was no beneficial effect on the DC or KH when the multi-peak (violet-blue) LCU (Elipar DeepCure-L or Bluephase G2), but the lower light output from a small tip LCU reduced the DC and KH values (Emitter C).SignificanceMoving the LCUs when photo-curing light-cured resin cements is not recommended. This study showed that a single-peak LCU could activate a resin cement that uses Ivocerin™ as well as the multi-peak LCU.     

Remineralization effects of conventional and experimental ion-releasing materials in chemically or bacterially-induced dentin caries lesions

Objectives

The aim of this study was to evaluate the remineralization effects of conventional and experimental ion-releasing materials on different artificial dentin carious lesions.

Inhibitory properties of Coffea canephora extract against oral bacteria and its effect on demineralisation of deciduous teeth

Objectives

The antibacterial activity of Coffea canephora extract was evaluated in vitro against Streptococcus mutans and Streptococcus sobrinus. The viability of planktonic cells was analysed by susceptibility tests (MIC and MBC) and time-kill assays. The effect of the extract on dental demineralisation was also investigated.

Methods

Primary 1st molar fragments (n = 24) were inoculated with a saliva pool and sustained in a multiple plaque growth system for 10 days to form biofilm. The biofilm was treated with light roasted C. canephora extract at 20%, Milli-Q water (negative control) and chlorhexidine (positive control) once a day, during a week. Blank controls comprised fragments without treatment. Biofilm pH was monitored in the last day of treatment. Changes in tooth mineralisation were assessed by cross-sectional microhardness (CSMH) test.

Results

MIC and MBC for S. mutans were 7 ± 2 mg/mL and 160 ± 0 mg/mL, respectively, showing no activity for S. sobrinus. The extract produced a 4-log reduction in the number of colonies of S. mutans after 3-h treatment (p < 0.05) with undiluted extract (20%) and MBC concentration (16%). There was no difference among negative/blank controls and coffee plaque pH. Differences between CSMH values of dental fragments subjected to the coffee extract and to chlorhexidine were not significant. At depths up to 30 μm from the enamel surface, coffee extract and chlorhexidine promoted higher CSMH values when compared to blank/negative controls (p < 0.05).

Conclusion

Our data suggest that light roasted C. canephora extract is beneficial as an anticariogenic substance.     

Chitosan effect on dental enamel de-remineralization: An in vitro evaluation

Objectives

The aim of this work was to evaluate the in vitro effect of chitosan (concentration and time of action) treatment on enamel de-remineralization behavior upon a pH cycling assay.

Methods

Different group of human tooth samples were exposed to de-remineralizing solutions of controlled pH using a random experimental design. Microhardness and phosphorus chemical analysis were employed to evaluate the loss of phosphorus from the samples. Optical coherence tomography (OCT) images were obtained for selected specimens in order to evaluate the degree of penetration of chitosan into enamel.

Results

Vickers microhardness results were higher for samples treated with chitosan for concentration between 2.5 mg/mL and 5.0 mg/mL and time of action between 60 s and 90 s. A maximum inhibition of mineral loss of 81% was obtained. Chemical analysis indicated lower net pohosphorus loss (net P loss) for samples treated with chitosan. Best results were obtained in the same conditions found out with microhardness measurements. Chitosan had little effect on the remineralization process. OCT results indicated a correlation of chitosan penetration with chitosan concentration. For chitosan concentrations of 2.5 g/mL and 5.0 g/mL the penetration was up to the dentin–enamel junction.

Conclusions

Chitosan interferes with the process of demineralization of the tooth enamel inhibiting the release of phosphorus in this laboratory study. Demineralization is influenced by the concentration and exposure time of the biopolymer to the enamel. Microhardness measurements may be used as an indication of mineral loss from tooth enamel. Additionally, OCT images support the idea that chitosan may act as a barrier against acid penetration, contributing to its demineralization inhibition.     

表面氮化处理对钴铬合金机械性能影响的研究

目的：探讨氮化钛镀膜对钴铬合金表面机械性能的影响,为临床上氮化钛镀膜技术应用于钴铬合金支架修复体提供实验基础。方法对钴铬合金试件进行等离子渗氮后,应用磁控溅射沉积方法在其表面沉积TiN薄膜,测量其表面显微硬度、耐磨性能和膜基结合强度。结果钴铬合金表面经过渗镀复合处理后,其表面显微硬度显著性提高,在不同载荷下钴铬合金的平均摩擦系数和磨损质量明显减少,膜基结合力较大。结论渗镀复合表面处理技术可以显著改善并提高钴铬合金的机械性能。     

Effects of temperature and in-office bleaching agents on surface and subsurface properties of aesthetic restorative materials

Objectives

To investigate the effects of in-office bleaching agents on surface and subsurface properties of dental materials at different environmental temperatures.

Methods

Four composite resins, a compomer, a conventional glass-ionomer cement (CGIC), and an industrially sintered ceramic material were evaluated in the present study. Four groups of each material (n = 10) were treated: bleaching with 40% hydrogen peroxide at 25 °C and 37 °C, stored in artificial saliva at 25 °C and 37 °C. The specimens from bleaching groups were bleached for two sessions, each of two 20 min application, at respective temperatures. After bleaching, the surface and subsurface (0.1–0.5 mm) microhardness were evaluated using a Vickers microhardness tester. The substance loss was determined by surface profilometry. The data were statistically analyzed with ANOVA and the Tukey's post hoc test.

Results

All materials were found to have surface softening after bleaching, and bleaching effects on surface micorhardness increased at 37 °C compared with 25 °C, except for the ceramic. After being bleached at 37 °C, the microhardness values of flowable composite resin significantly reduced at a depth of 0.1 mm compared with control specimen stored at 37 °C. No significant difference was found between the control and bleached specimens with respect to substance loss for any of the materials.

Conclusion

The influence of environmental temperature on the in-office bleaching effects on surface and subsurface microhardness of dental materials was material-dependent. However, no substance loss was detected due to the tested bleaching regimen.

Clinical significance

Environmental temperature should be considered when evaluating the possible bleaching effects on restorative materials. Moreover, dentists should be aware that there might be a need for polishing of restorative materials in clinical situations in which restorations are accidentally exposed to bleaching gels.     

纳米复合树脂牙与普通树脂牙显微硬度的对比研究

目的目前临床上常用的普通树脂牙、纳米树脂牙和自研纳米人工牙显微硬度的对比分析研究。方法用动态超显微硬度仪对试件进行显微硬度测试。结果经动态超显微硬度仪测试，目前临床常用的几种复合树脂牙的雏氏硬度分别是：427．67Mpa、469．67Mpa、706．33Mpa、666．33Mpa（P〈0．05），我们研制的纳米树脂牙硬度为577．67Mpa。结论研制的人工牙显微硬度优于普通树脂牙，但与塑钢牙、纳米牙相比，还存在一定差距。     

Properties of dental resins submitted to pH catalysed hydrolysis

Objectives

This study evaluated the surface microhardness (SM) and roughness (SR) alterations of dental resins submitted to pH catalysed degradation regimens.

Methods

Thirty discs of each TPH Spectrum (Dentsply), Z100 (3M-ESPE), or an unfilled experimental bis-GMA/TEGDMA resin were fabricated, totaling 90 specimens. Each specimen was polymerized for 40 s, finished, polished, and individually stored in deionized water at 37 °C for 7 days. Specimens were randomly assigned to the following pH solutions: 1.0, 6.9 or 13, and for SM or SR evaluations (n = 5). Baseline Knoop-hardness of each specimen was obtained by the arithmetic mean of five random micro-indentations. For SR, mean baseline values were obtained by five random surface tracings (R_a). Specimens were then soaked in one of the following storage media at 37 °C: (1) 0.1 M, pH 1.0 HCl, (2) 0.1 N, pH 13.0 NaOCl, and (3) deionized water (pH 6.9). Solutions were replaced daily. Repeated SM and SR measurements were performed at the 3-, 7- and 14-day storage time intervals. For each test and resin, data were analysed by two-way ANOVA followed by Tukey's test (α = 0.05).

Results

There was significant decrease in SM and increase in SR values of composites after storage in alkaline medium. TPH and Z100 presented similar behaviour for SM and SR after immersion in the different media, whereas unfilled resin values showed no significant change.

Conclusion

Hydrolytic degradation of resin composites seems to begin with the silanized inorganic particles and therefore depend on their composition.

Significance

To accelerate composite hydrolysis and produce quick in vitro microstructural damage, alkaline medium appears to be more suitable than acidic medium. Contemporary resin composite properties seem to withstand neutral and acidic oral environments tolerably well.