Zinc reduces collagen degradation in demineralized human dentin explants

Objectives

Dentin matrix metalloproteinases are implicated in the pathogenesis of caries and contribute to collagen degradation in resin-dentin interfaces. The objective was to determine if collagen degradation may be modulated by an excess of zinc or zinc chelators.

Methods

Mineralized and phosphoric acid demineralized human dentin specimens were tested. Chlorhexidine digluconate, doxycycline or ZnCl₂ were added to the media. In half of the groups, active exogenous metalloproteinase-2 was incorporated into the solution. C-terminal telopeptide determinations (radioimmunoassay) were performed after 24 h, 1 and 3 weeks.

Results

Collagen degradation was prominent in demineralized dentin. Doxycycline fully blocked dentin proteolysis. Chlorhexidine digluconate reduced the degradation at the 24-h period. Zinc in excess strongly inhibits hydrolysis of collagen and its effect was maintained for 3 weeks.

Conclusions

Zinc in excess reduces MMP-mediated collagen degradation. The hypothesis that binding of zinc to collagen results in protection of sensitive cleavage sites of metalloproteinases requires further validation.     

Effect of low level fluoride on demineralization kinetics of human dental enamel

The purpose of this study was to examine the effect of fluoride levels similar to those reported for saliva from low fluoridated and high fluoridated water areas on the demineralization of human permanent enamel. An adaptation of the method described by Robinson et al. was used. Sections of sound enamel were immersed in a vial containing demineralizing solution [2.0 mM Ca(NO₃)₂, 1.2 mM KHPO₄ in 50 mM acetic acid, pH 4.8] for 1 hour. The demineralizing solution contained 0, 0.02 or 0.05 ppm fluoride, added as NaF was prepared. Twenty microliters aliquots were taken from the demineralizing solution at the time point up to 1 hour, with a sampling frequency bias towards the early time point. The phosphate content of the removed sample was determined by colorimetry. When the mineral loss curves for fluoridated and non-fluoridated demineralizing solutions were compared, there were significant differences between both groups. There was a decrease in the net mineral loss when fluoride was used. This result suggested that salivary fluoride levels of 0.02 ppm and 0.05 ppm had a protective effect against demineralization.     

Compressive mechanical properties of demineralized and deproteinized cancellous bone

A method to completely demineralize and deproteinize bone was used to investigate the mechanical properties of either the mineral or protein phase in cancellous bone and compared to an untreated one. Compression tests on cancellous bovine femur and elk antler (Cervus elaphus canadensis) were performed on demineralized, deproteinized, and untreated samples in an air-dry condition. Results showed that the elastic modulus and compressive strength of the demineralized (protein only) and deproteinized (mineral only) samples were far lower than that of the untreated ones, indicating a strong synergetic effect between the two phases. Experimental data showed that the demineralized, deproteinized, and untreated samples can be modeled as cellular solids, with the strong dependence of mechanical properties on the relative density. Deformed samples were examined under SEM and different failure mechanisms were observed. Plastic buckling was observed in demineralized samples while brittle crushing was found in deproteinized ones.     

In vitro demineralization of human enamel natural and abraded surfaces: A micromechanical and SEM investigation

Objectives

To compare the demineralization pattern that occurs in abraded samples and unabraded ones quantitatively and microscopically using nanoindentation and SEM.

Methods

Using 12 human third molars, one half of each tooth was abraded to a depth approximately 200 μm below the outer surface enamel, and the other half was left untreated. All specimens were demineralized for 3 d, 5 d, 7 d and 14 d respectively. The cross sections of all lesions were evaluated with nanoindentation and SEM.

Results

Unabraded samples had least loss of mechanical properties and lesion depth compared to abraded samples, with most mechanical property loss occurring within a shallower layer of the lesion. The variation of mechanical properties in unabraded samples was wider than abraded samples. SEM images showed a characteristic “keyhole” structure for both samples after demineralization, with the rod core extensively demineralized while the interrod remained intact. Acid attack initiated at the rod sheath space then penetrated into the rod core before extending into neighbouring rods through the rod tail.

Conclusion

Abraded samples exposed to in vitro demineralization form deeper lesion depths and greater loss of mechanical properties than unabraded samples subjected to the same demineralization. Unabraded samples manifested characteristic subsurface demineralization with a shallow surface layer that remained intact, whereas no intact surface was found in abraded samples. The demineralization pattern of unabraded samples more closely resembled the pattern of natural white spot lesions and displayed wide inter-sample variation. Consideration should be given to experimental design with unabraded teeth specimens for future demineralization studies.     

Effect of fluoridated bleaching gels on the remineralization of predemineralized bovine enamel in vitro

Objectives

This study evaluated possible differences regarding the remineralization of predemineralized enamel after exposure to fluoridated or non-fluoridated bleaching gels.

Methods

120 enamel specimens were prepared from sixty bovine incisors; before and after demineralization (37 °C; pH 4.95; 10 d), one-quarter of each specimen's surface was covered with nail varnish (control sound/demineralized). Subsequently, the specimens were stored for 16 h daily in a remineralizing solution (pH 7.0; 14 d), while for the remaining time (8 h) various bleaching gels were applied: (1) no treatment (control), (2) Opalescence regular (O, Ultradent), (3) Opalescence PF (O-PF), (4) Nite White ACP (NW-ACP, Discus Dental) and (5) Nite White ACPF (NW-ACPF). Following, half of the bleached parts were nail-varnished and stored for another 3-weeks period in a remineralizing solution. Differences in mineral losses (ΔΔZ) and lesion depths (ΔLD) before and after treatment/remineralization period were evaluated from microradiographs. ΔΔZ_surface values (mineral loss of the outer 18 μm of the lesion) were calculated.

Results

After 2 and 5 weeks ΔΔZ/ΔLD values of the bleaching groups did not differ significantly from the controls. Treatment with NW-ACPF for 2 weeks resulted in significantly lower ΔΔZ values compared to NW-ACP (p = 0.032) and NW-ACPF in higher values than Opalescence regular (p = 0.006). Two weeks treatment with O and O-PF resulted in decreased ΔΔZ_surface values compared to control (p < 0.0005), whereas with NW-ACPF no significant differences could be observed (p = 0.062). Application of NW-ACP induced significantly increased ΔΔZ_surface values compared to control (p = 0.001).

Conclusions

No supporting influence of fluoride-containing bleaching gels on remineralization could be observed.     

不同浓度氟保护漆抑制人牙釉质脱矿能力的体外研究

目的:观察和比较两种浓度氟保护漆在体外抑制人牙釉质脱矿的能力.方法:将预备好的40个无龋的牙釉质块随机分为4组,每组10个标本,5个用作实验,5个备用;0.5%氟保护漆组、0.1%氟保护漆组为实验组,0.02%氟化钠为阳性对照组,去离子水为空白对照组,经过人工酸蚀48h后,分别采用原子吸收分光光度计和紫外分光光度计测量酸蚀液中的钙、磷溶出量.结果:实验组抑制钙、磷溶出效果明显好于对照组.实验组和对照组之间有高度的显著性差异(P＜0.0001);实验组之间没有显著性差异(P＞0.05);对照组之间有显著性差异(P＜0.05).结论:两种浓度的氟保护漆都能够有效的抑制离体人牙釉质的脱矿反应;两者之间抑制牙釉质脱矿能力没有显著性差异.     

茶多酚致釉质脱矿与再矿化的初步研究

目的　研究茶多酚对釉质脱矿和再矿化的影响。方法　脱矿实验将完整牛切牙釉质分为 5组、再矿化实验将经酸脱矿牛切牙釉质分为 4组 ,经实验溶液、酸性缓冲液、中性缓冲液处理进行 p H循环。原子吸收光谱测定酸性缓冲液钙离子浓度 ,计算机辅助图象分析系统测定采釉质块脱矿面积 ,显微硬度仪测定釉质块的平均硬度(KHV)。结果　在脱矿实验中 ,钙释出率 (CDR)分别为 (0 .4 3± 0 .0 5 ) ,(0 .4 9± 0 .0 0 6 ) ,(0 .2 1± 0 .0 2 ) ,(0 .2 1±0 .0 3)和 (0 .5 0± 0 .11) μg/ (mm2· h) ,% KHV减少分别为 94 .19± 3.5 0 ,96 .6 2± 0 .6 3,74 .74± 4 .0 9,77.79±3.11,97.32± 4 .0 3。两茶多酚组 ,两氟化纳组比较 ,CDR、% KHV减少均无显著性差异 (P>0 .0 5 ) ,茶多酚组和氟化纳组比较 ,差异具有显著性 (P<0 .0 5 )。在再矿化实验中 ,% KHV增加分别为 - 11.96± 10 .1,- 2 1.32± 11.3,- 4 9.5 2± 2 4 .6 ,- 4 .2 4± 8.5 1,茶多酚组同去离子水组 ,两氟化纳组比较 ,无显著性差异 (P>0 .0 5 ) ,茶多酚组和氟化纳组比较 ,差异具有显著性 (P<0 .0 5 )。结论　在体外条件下 ,茶多酚对釉质脱矿和再矿化没有明显的抑制或促进作用 ,同氟没有协同作用。提示茶多酚的抗龋作用是通过抗菌和抗菌斑作用实现的。     

Effect of sodium fluoride on oral biofilm microbiota and enamel demineralization

ObjectiveFluoride is widely used as an anti-caries agent, e.g. in toothpastes and mouth rinses. However, the nature of the anti-caries action is not entirely clear. Mechanisms suspected to explain the cariostatic effect include inhibitory effects on acid formation by bacteria, inhibition of extracellular polysaccharide (EPS) production, inhibition of enamel demineralization and enhancement of remineralizaton or combination thereof. The aim of this study was to examine with the supragingival Zurich in vitro biofilm model the effect of fluoride in NaF formulation, on the microbiota and on demineralization.MethodsBiofilms consisting of Actinomyces oris, Candida albicans, Fusobacterium nucleatum, Streptococcus oralis, Veillonella dispar and Streptococcus sobrinus, were grown anaerobically on sintered hydroxyapatite or bovine enamel disks, exposed to 200, 400, and 1400 ppm of NaF, or 0.1% chlorhexidine (positive control). The biofilms were harvested after 64 h and CFUs were assessed for total bacteria. Demineralization of enamel disks was measured by quantitative light-induced fluorescence.ResultsNaF did not affect the bacterial numbers. No enamel mineral loss was observed at 1400 and 400 ppm of fluoride, whereas the pH of the surrounding medium was increased to 5.5 and 5.0, respectively, compared to the untreated control (pH 4.5 and mineral loss ΔF of −32%). At 1400 ppm NaF the biofilm’s EPS volume was also significantly reduced.ConclusionsAdministration of NaF completely prevented demineralization without affecting biofilm composition and growth. This protective effect may be attributed to the observed decrease in acid production or EPS volume, or to a shift in the de/remineralization balance.     

Ultrasound Characterization of Bone Demineralization Using a Support Vector Machine

We propose an ultrasound-guided remote measurement technique, utilizing an acoustic radiation force beam as our excitation source and a receiving hydrophone, to assess non-invasively a bone's mechanical properties. Features, such as velocity, were extracted from the acoustic pressure received from the bone surface. The typical velocity of an intact bone (3540?m/s) was higher in comparison to that of a demineralized bone (2231?m/s). According to the receiver operating characteristic curve, the optimal velocity cutoff value of ≥3096?m/s yields 80% sensitivity and 82.61% specificity between intact and demineralized bone. Utilizing a support vector machine, the hours of bone demineralization were successfully classified with maximum accuracy >80% using 18% training data. The results indicate the potential application of our proposed technique and support vector machine for monitoring bone mechanical properties.     

蛋白水解酶在牙釉质脱矿中的作用

本文报道用木瓜蛋白酶、胶原酶和胰蛋白酶,处理活体人牙,用木瓜蛋白酶和胰蛋白酶处理离体人牙,结果这些酶对有机酸对牙釉质的脱矿作用无明显的影响,但木瓜蛋白酶和胰蛋白酶对人牙釉质内的蛋白质有溶解作用。作者认为,即使牙菌斑内有溶解牙釉质内蛋白质的物质存在,但对牙釉质的脱矿却无明显影响。