IN VITRO INDUCTION OF ENAMEL SUBSURFACE DEMINERALIZATION FOR EVALUATION OF DIAGNOSTIC IMAGING METHODS

The aim of this study was to investigate a model of inducing enamel subsurface demineralization for evaluating diagnostic imaging methods. Fifty sound teeth had their crowns coated with acid-resistant varnish, leaving a 7 mm² circular window of exposed enamel in one of the proximal surfaces. The specimens were assigned to 5 groups (4 experimental and the control) and were kept immersed in a buffer solution at pH 4.8, 50% saturated in relation to enamel, for 60, 75, 90 and 120 days, or were not exposed to the solution. Digital radiographs were taken, prior to and after each immersion period, and interpreted by a radiologist. For validation, the enamel was submitted to microhardness profiling. In addition, the solutions were analyzed for phosphorus (P_i) and calcium (Ca) concentrations. Microhardness data were evaluated using two-way ANOVA (p<0.05) and Tukey''s test. P_i and Ca concentrations were compared using one-way ANOVA (α = 0.05). The performance of radiography was assessed by ROC analysis. The microhardness values for the control group ranged from 405 to 432 KHN. Of the 4 experimental groups, the 60-day group demonstrated the highest values (179-379 KHN) and the 120-day group, the lowest values (103-277 KHN). The lowest total concentrations of P_i and Ca (1.74 mM and 2.63 mM, respectively) were found in the solutions of the 60- day group, indicating the lowest rate of mineral loss, however, there was no significant difference among the other experimental groups. The performance for detecting images consistent with caries lesions was high (A_z = 0.89). Therefore, this in vitro model of inducing demineralization may be considered suitable for research intended to evaluate imaging methods for the diagnosis of proximal caries lesions.     

不同表面处理方法对牙本质表面形貌及粗糙度影响的原子力显微镜研究

目的采用原子力显微镜(atomic force microscopy AFM)研究不同处理方法对牙本质表面形貌及粗糙度的影响,为牙本质表面处理方式的临床应用提供理论依据。方法将离体前磨牙牙本质表面分为三组,分别采用磷酸处理,磷酸/次氯酸钠处理,未做任何处理的表面作为空白对照组,在接触模式下(contact mode),采用原子力显微镜观察表面形貌,应用AFM的自带软件测量其表面粗糙度,粗糙度结果经t检验对各组进行统计学分析。结果牙本质表面经过磷酸处理后,牙本质小管变大,粗糙度增加,经过磷酸/次氯酸钠处理后,牙本质表面呈现均一的微观表面,粗糙度显著增加,各组之间均存在统计学差异。结论磷酸处理后能通过牙本质小管的脱矿来增加牙本质表面的粗糙度,而磷酸/次氯酸钠处理后,能在牙本质表面形成均匀的孔隙,极大地增加了表面粗糙度,后者为指导临床中的牙本质表面处理方式提供了新思路。     

Inhibition of dentine demineralization by zinc oxide: In vitro and in situ studies

OBJECTIVE: The objective of this study was to evaluate the inhibitory effect of zinc oxide on dentine demineralization in vitro and in situ. METHODS: In the in vitro study, dentine specimens treated with a zinc oxide suspension were demineralized in a pH 5 solution. In the in situ study, subjects wore dentine specimens on their teeth and instructed to rinse with zinc-containing toothpaste slurry three times a day for 14 days. The design of study was a crossover one. RESULTS: Microradiography employed in the in vitro study revealed the dentine surfaces treated with distilled water had a lower mineral content than those treated by zinc. Toothpaste with zinc had a statistically significant, 49% greater inhibitory efficacy on dentine demineralization over the control. In the in situ study, zinc-containing toothpaste was also confirmed to have an inhibitory effect on dentine demineralization when compared to the zinc-free toothpaste. These in vitro and in situ studies revealed that zinc oxide can have a significant effect on the inhibition of dentine demineralization, even when the zinc oxide is blended into toothpaste. SIGNIFICANCE: This suggests that zinc oxide may be effective in the prevention of root caries.     

三种氟素制剂对离体乳牙牙釉质抗酸性影响的比较研究

目的 比较三种常用氟素制剂对离体乳牙牙釉质抗酸性的影响。方法 40个离体乳前牙，随机分为4组。开窗，酸蚀，1、2、3组分别涂布10%（NH4）2MoO2F4溶液，38%Ag(NH3)2F溶液，APF-LaCl3溶液联用3min,第4组涂去离子水3min，将经上述处理的牙齿标本分别浸泡于8ml0.1mol/L乳酸中，开始记时，于1、3、6、12、24、48、72、144h各取出1ml液体，检测其Ca^2 浓度的A值，计算各处理组各时间点釉4质钙溶出总量，统计分析。结果 同对照组相比，3种氟素制剂处理组牙釉质脱矿总量显著降低。其中APF-LaCl3溶液联用处理组最低，10%（NH4）2MoO2F4溶液与38%Ag(NH3)2F溶液处理组牙釉质脱矿总量无差别。结论 3种氟素制剂均可有效地抑制牙釉质脱矿。其中APF-LaCl3溶液联用作用最强，10%（NH4）2M煤F4溶液与38%Ag(NH3)2F溶液抑制牙釉质脱矿作用的能力相当。     

Physical chemical effects of zinc on in vitro enamel demineralization

Objectives

Zinc salts are formulated into oral health products as antibacterial agents, yet their interaction with enamel is not clearly understood. The aim was to investigate the effect of zinc concentration [Zn²⁺] on the in vitro demineralization of enamel during exposure to caries-simulating conditions. Furthermore, the possible mechanism of zinc's action for reducing demineralization was determined.

Methods

Enamel blocks and synthetic hydroxyapatite (HAp) were demineralized in a range of zinc-containing acidic solutions (0–3565 ppm [Zn²⁺]) at pH 4.0 and 37 °C. Inductively coupled-plasma optical emission spectroscopy (ICP-OES) was used to measure ion release into solution. Enamel blocks were analysed by Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR), and HAp by X-ray diffraction (XRD) and neutron diffraction (ND).

Results

ICP-OES analysis of the acidic solutions showed a decrease in [Ca²⁺] and [PO₄³⁻] release with increasing [Zn²⁺]. FTIR revealed a α-hopeite (α-Zn₃(PO₄)₂.4H₂O)-like phase on the enamel surfaces at >107 ppm [Zn²⁺]. XRD and ND analysis confirmed a zinc-phosphate phase present alongside the HAp.

Conclusions

This study confirms that zinc reduces enamel demineralization. Under the conditions studied, zinc acts predominantly on enamel surfaces at PO₄³⁻ sites in the HAp lattice to possibly form an α-hopeite-like phase.

Clinical significance

These results have a significant implication on the understanding of the fundamental chemistry of zinc in toothpastes and demonstrate its therapeutic potential in preventing tooth mineral loss.     

不同种类饮料对牙釉质脱矿作用的研究

目的 探讨饮料酸性程度与其引起牙釉质脱矿程度的关系,验证脱矿牙釉质在模拟唾液中自我矿化修复能力以及脱矿后马上刷牙对牙釉质影响.方法 ①在36.5℃条件下,将牛牙分别浸泡于可乐、橙汁和冰红茶中10 min、30 min和60 min,然后,置于模拟唾液中浸泡60 min;测量唾液浸泡前后的牙釉质表面硬度.另仅选可乐,在相同条件下进行人牙实验.②将牛牙置于可乐中浸泡60 min后即刻刷牙1 min、再置于模拟唾液中10 min和30 min后分别刷牙1 min,并另选人牙做验证实验,最后,对所有样本观察牙釉质表面形貌改变.结果 ①牛牙在饮料中浸泡不同时间后,硬度均有不同程度降低,其中可乐组牛牙硬度降低最显著.而在模拟唾液中浸泡60 min后,硬度值有一定程度的提高.②可乐浸泡的牙齿立即进行刷牙会在牙齿表面留下明显的排状划痕,如果再在模拟唾液中浸泡一定时间后刷牙,则未见留下划痕.人牙结果与牛牙类似.结论 酸性饮料会使牙釉质脱矿;模拟唾液可恢复已脱矿牙釉质的硬度,恢复程度与其脱矿程度以及在唾液中浸泡的时间相关;即刻刷牙会进一步损伤已被酸性饮料脱矿的牙釉质,而在模拟唾液中一段时间后使牙釉质硬度有所恢复.     

不同粒径和形貌的羟基磷灰石对牙本质小管的堵塞作用及耐磨性研究

目的 从定性和定量两方面研究不同粒径和形貌的羟基磷灰石(Hydroxyapatite,HA)对牙本质小管的堵塞作用及其耐磨性.方法 选择人前磨牙40颗,以高速手机制取牙本质片并抛光,酸蚀后随机均分为4组:20 nm HA组;30 nm HA组;12μm HA组;空白对照组(不使用任何实验品).各组分别用对应的材料刷洗牙本质片表面7d.将牙本质片一分为二,一半扫描电镜观察;另一半进行刷牙磨耗实验后扫描电镜观察,应用Image-Pro Plus 6.0图像分析软件计算牙体质小管堵塞率.结果 扫描电镜下见牙本质小管被颗粒状物堵塞,堵塞率达82%~96%,平均堵塞率为30 nm HA组(短棒状)>20 nm HA组(针状)>12μm HA组(球形).牙刷磨耗实验后,扫描电镜下见牙本质表面沉积层光滑致密,仍有63%以上的小管被封闭.结论 30 nm短棒状HA、20 nm针状HA及12μm球形HA对牙本质小管均具有良好的堵塞作用及耐磨性.     

绿茶对唾液流速及pH值的影响

目的 探讨饮用清水及不同浓度绿茶对唾液流速及pH值的影响.方法 纳入18~25岁全身健康状况良好的在校大学生20人为研究对象,受试者于晚上9:00-10:00分别饮用清水和低、中、高浓度绿茶后,测定一定时间段内唾液流速和pH值.结果 饮用中、低浓度绿茶水后,女性口腔健康者中唾液流速高于高浓度茶水组和清水组(F=5.20,P<0.01);男性口腔健康者各组别差异无统计学意义(F=1.81,P=0.14).饮用低、中和高浓度茶水后的唾液pH值要低于清水组(F=3.50,P=0.02),各浓度茶水组的差异无统计学意义.结论 中、低浓度绿茶水可预防女性口腔健康者唾液流速降低,而对男性无明显作用.饮用各浓度绿茶水后,唾液pH值降低.     

Comparison of in vitro techniques to controllably decrease bone mineral density of cancellous bone for biomechanical compressive testing

It is not surprising that an orthopedic device used with poorly mineralized bone can have lower mechanical fixation strength than the same device with well-mineralized bone. As new devices are being designed and tested, it is important to develop a controllable technique to decrease the bone mineral density of bone in vitro, so the fixation strength of the devices can be better modeled. Several different bone demineralization techniques have been established, but some use caustic chemicals and comparisons of their rates of demineralization have not been performed. In this study, a total of 120 cancellous bone cores were excised from ovine vertebra, scanned using a pico dual energy X-ray absorptiometry system to determine bone mineral density, then placed into one of five solutions (0.9% saline, 0.5 M hydrochloric acid, 0.5 M ethylenediaminetetraacetic acid, 0.5 M formic acid, and 5% acetic acid). For each solution, 12 time periods ranging from 0 to 144 h were investigated. After demineralization, all cores were rescanned and biomechanically loaded in compression to failure. Based on the rate of demineralization, the ease of use, the availability, and the correlation with the compressive bone strength, it was determined that the 5% acetic acid was the optimal demineralization solution to controllably decrease the bone mineral density of cancellous bone.