Erosive cola-based drinks affect the bonding to enamel surface: an in vitro study

Objective

This study aimed to assess the impact of in vitro erosion provoked by different cola-based drinks (Coke types), associated or not with toothbrushing, to bonding to enamel.

Material and Methods

Fifty-six bovine enamel specimens were prepared and randomly assigned into seven groups (N=8): C- Control (neither eroded nor abraded), ERO-RC: 3x/1-minute immersion in Regular Coke (RC), ERO-LC: 3x/1-minute immersion in Light Coke (LC), ERO-ZC: 3x/1-minute immersion in Zero Coke (ZC) and three other eroded groups, subsequently abraded for 1-minute toothbrushing (EROAB-RC, EROAB-LC and EROAB-ZC, respectively). After challenges, they were stored overnight in artificial saliva for a total of 24 hours and restored with Adper Single Bond 2/Filtek Z350. Buildup coronal surfaces were cut in 1 mm² -specimens and subjected to a microtensile test. Data were statistically analyzed by two-way ANOVA/Bonferroni tests (α=0.05). Failure modes were assessed by optical microscopy (X40). The interface of the restorations were observed using Confocal Laser Scanning Microscopy (CLSM).

Results

All tested cola-based drinks significantly reduced the bond strength, which was also observed in the analyses of interfaces. Toothbrushing did not have any impact on the bond strength. CLSM showed that except for Zero Coke, all eroded specimens resulted in irregular hybrid layer formation.

Conclusions

All cola-based drinks reduced the bond strength. Different patterns of hybrid layers were obtained revealing their impact, except for ZC.     

Enamel white spot lesions can remineralise using bio-active glass and polyacrylic acid-modified bio-active glass powders

Objective

To evaluate the potential of bio-active glass (BAG) powder and BAG containing polyacrylic acid (PAA-BAG) to remineralise enamel white spot lesions (WSL).

Methods

32 human enamel samples with artificial WSLs were assigned to 4 experimental groups (n = 8); (a) BAG slurry, (b) PAA-BAG slurry, (c) “standardised” remineralisation solution (positive control) and (d) de-ionised water (negative control). Mechanical properties of enamel were assessed using surface and cross-section Knoop microhardness. Micro-Raman spectroscopy in StreamLine™ scan mode was used to scan lesion cross-sections. The intensity of the Raman phosphate peak at 959 cm⁻¹ was fitted and measured producing depth profiles analysed using a double-step fitting function. A further 20 samples (n = 5) were used to obtain 3D images of surfaces using non-contact white light profilometry permitting measurement of lesion step height in relation to the sound enamel reference level, and to scan the lesion surface using scanning electron microscopy (SEM). Data were analysed statistically using one-way ANOVA with Tukey's HSD post-hoc tests.

Results

BAG, PAA-BAG and the remineralisation solution exhibited statistically significantly higher surface and cross-section Knoop microhardness compared to the negative control. Micro-Raman spectroscopy detected significantly higher phosphate content within the treated groups compared to the negative control group. Lesions’ depth was not significantly reduced. SEM images revealed mineral depositions, with different sizes and shapes, within BAG, PAA-BAG and the positive control groups.

Conclusion

BAG and PAA-BAG surface treatments enhance enamel WSL remineralisation, assessed by the resultant improved mechanical properties, higher phosphate content and morphological changes within the artificial lesions.     

釉质基质蛋白对乳牙牙髓干细胞体外增殖、分化能力的影响

目的：研究釉质基质蛋白（enamel matrix proteins,EMPs）对人脱落乳牙牙髓干细胞（stem cells from hu—man exfoliated dediduous teeth,SHED）体外增殖分化能力的影响。方法：利用酶消化法联合组织块法获得脱落乳牙牙髓干细胞,并进行形态学观察。三氯乙酸法制备EMPs,用不同浓度的EMPs对SHED进行诱导,利用四唑盐比色法（MTT）检测并分析诱导后的SHED增殖活性的变化,检测经诱导后的培养液中碱性磷酸酶（ALP）。RT—PCR检测牙本质涎磷蛋白（dentin sialophosphoprotein,DSPP）及牙本质基质蛋白1（dentin matrix protein1,DMP-1）的mRNA表达。结果：人脱落乳牙牙髓干细胞呈集落生长,并且在体外具有一定的自我增殖能力。EMPs对乳牙牙髓干细胞的增殖无明显影响,而能够显著提高ALP的活性,并呈现一定的剂量依赖性。经EMPs诱导后,细胞相对高表达DSPP、DMP-1mRNA。结论：EMPs对于SHED向成牙本质样分化具有积极作用。     

电子探针分析乳牙釉质和牙本质钙含量的研究

目的研究乳牙釉质和牙本质中钙含量及分布,探讨其与龋患状况之间的关系。方法运用电子探针显微分析仪测定40颗离体下颌乳中切牙纵剖面上不同深度的钙含量,并以标本所在个体的龋患状况分组,分别进行统计学分析。结果 40例下颌乳中切牙标本的总计钙含量均值为37.13±1.10（wt%）。其中,牙釉质钙含量均值为38.31±0.94（wt%）,牙本质钙含量均值为36.66±1.38（wt%）;牙釉质表层下50μm、100μm处钙含量高于250μm处钙含量;牙本质釉牙本质界下50μm、100μm处钙含量分别低于450μm、500μm、550μm、600μm处钙含量。正常乳牙钙含量在无龋组、龋病低危组、龋病高危组间未见统计学差异。正常乳牙钙含量与龋补牙数、龋补牙面、龋蚀指数之间均无相关关系。结论正常乳牙中钙元素分布呈非均质状态。牙釉质钙含量从表层向釉牙本质界方向呈逐渐下降趋势;牙本质钙含量从釉牙本质界向髓腔侧呈逐渐上升趋势。发育正常的乳牙钙含量不能作为反映个体龋患状况的单一指标。     

Effects of periodic fluoride treatment on fluoride ion release from fresh orthodontic adhesives

Objective

Periodic fluoride treatment may contribute to the ability of fresh orthodontic adhesives to provide long-term F⁻ release. The effects of periodic fluoride treatment on the amount of F⁻ release from fresh orthodontic adhesives was investigated.

Methods

F⁻ release was measured from a nonfluoride-releasing composite, a fluoride-releasing composite, a polyacid-modified composite (compomer), and two resin-modified glass-ionomer cements (RMGICs) at 1, 2, and 5 days after one of the following treatments: 225 ppm F⁻ solution, 900 ppm F⁻ solution, acidulated phosphate fluoride gel (APF), fluoridated dentifrice, and deionised water (control). F⁻ release was measured in a 5-day cycle, which was repeated 9 consecutive times. The amount of F⁻ release for each group was analysed using the repeated measures analysis of variance. Statistical significance was set at a level of α = 0.05.

Results

Periodic fluoride treatment temporarily increased F⁻ release in fresh fluoride-releasing orthodontic adhesives, but not in fresh nonfluoride-releasing composite. The order of effective fluoride-release was RMGICs > compomer > fluoride-releasing composite > nonfluoride-releasing composite. The application of APF or 900 ppm F⁻ solution was the most effective way to maintain F⁻ release from fresh orthodontic adhesives. However, the amount of F⁻ release gradually decreased with increasing specimen age.

Conclusion

Given the difficulty of routine use of APF at home, the results of this study show that a combination of RMGICs and high-dose fluoride mouth rinse is the most effective protocol to maintain F⁻ release from fresh orthodontic adhesives.

Clinical significance

Most studies have investigated fluoride-uptake abilities using aged materials in which fluoride had been lost for at least 1 month. This study has found that periodic fluoride treatment altered the conventional F⁻ release pattern of fresh fluoride-releasing materials and type of fluoride-containing medium plays a more critical role in fluoride recharging of the materials than fluoride concentration. This study will help clinicians to find the most effective fluoride treatment protocol of fresh materials.     

正畸固定矫治后牙釉质脱矿及其危险因素分析

目的：调查正畸固定矫治后牙釉质脱矿的流行情况及其危险因素。方法：采用单纯随机抽样的方法,随机抽取武汉大学口腔医院正畸科2008年6~8月3个月内结束正畸固定矫治的202例患者,进行釉质脱矿检查和问卷调查,脱矿检查由一名检查者完成,将检查和问卷的相关结果进行分析比较。结果：202例正畸固定矫治结束的患者中釉质脱矿者117例,患病率为57.9%,性别上无显著性差异;每人平均有4.81颗牙齿发生釉质脱矿。下颌尖牙、上颌侧切牙、上颌尖牙釉质脱矿患病率高。根据问卷调查结果,Logistic回归分析,控制混杂因素后,年龄、正畸治疗中不良习惯的改变、正畸疗程、甜食的摄入频率引起牙釉质的脱矿OR分别为0.40、0.27、3.22、2.91（P〈0.05）。结论：正畸固定矫治后牙釉质脱矿是一个不容忽视的问题,应对正畸固定矫治患者尽早开展釉质脱矿的防治工作。     

The carbohydrate moiety of mineral-bound proteins from fetal enamel: A basis for enamelins heterogeneity

Summary Enamelins were prepared from the soft enamel of bovine fetuses. They were purified on synthetic hydroxyapatite and separated in two fractions by affinity chromatography on a ConA-ultrogel column. The two fractions were different with respect to their electrophoretic behavior, stainability, amino acid composition, phosphorylation, and glycosylation. The ConA-binding fraction, consisting of three molecular species with apparent molecular weights of 33, 37, and 45 kD, contained organic phosphorus and high levels of sugars. The Gal/Man ratio suggested a biantennary structure. The ConA-unbound fraction contained two major molecular species with molecular weights of 70 and 56 kD, and represented 70% of the total enamelin preparation. The amino acid composition of this fraction showed a higher level of alanine and a lower level of proline when compared with that of total enamelins. Its sugar composition was unusual, being principally constituted of N-acetyl galactosamine and N-acetyl glucosamine.     

Analysis of Hydroxyapatite Surface Coverage by Amelogenin Nanospheres Following the Langmuir Model for Protein Adsorption

The assembly of amelogenin protein into nanospheres is postulated to be a key factor in the stability of enamel extracellular matrix framework, which provides the scaffolding for the initial enamel apatite crystals to nucleate and grow. Adsorption isotherms were evaluated in order to investigate the nature of interactions of amelogenin nanospheres with hydroxyapaite crystals in solution, where their assembly status and particle size distribution are defined. We report that the adsorption isotherm of a recombinant mouse amelogenin (rM179) on synthetic hydroxyapatite crystals can be described using a Langmuir model indicating that amelogenin nanospheres adsorb onto the surface of apatite crystals as binding units with defined adsorption sites. The adsorption affinity and the maximum adsorption sites were 19.7 × 10⁵ L/mol and 6.09 × 10^–7 mol/m², respectively, with an r² value of 0.99. Knowing the composition and particle size distribution of amelogenin nanospheres under the condition of adsorption experiments, we have calculated the number of nanospheres and the crystal surface area covered by each population of nanospheres at their maximum adsorption. It was found that total maximum binding covers 64% of the area unit. This observation supports the speculation that amelogenin binding onto apatite surface is selective and occurs only at certain sites. Present address for N.B.: Department of Material Science, University of Patras, GR-26500 Patras, Greece