预加热对两种复合树脂机械性能的影响

目的：探讨预加热对两种光固化复合树脂机械性能的影响。方法：采用混合填料树脂Z250和纳米树脂Z350分别制作40个树脂试件并分为两组,分别进行常温23℃和加热40℃处理,使用发光二极管（LED）光固化灯固化40 s,测定表面显微硬度和抗压强度,并进行对比分析研究。结果：两种材料加热40℃处理后其表面显微硬度和抗压强度均高于常温23℃处理组,有统计学意义（t＝-5.189,P＜0.01）。结论：预加热可以提高光固化复合树脂机械性能,推荐临床使用。     

缓释氟粘贴片体内防治龋齿效果的评价

目的评价缓释氟粘贴片体内防治龋齿的作用。方法受试者7例,无氟期(唾液单独作用)和有氟期(唾液与氟片共同作用)戴右侧上颌舌侧和左侧下颌颊侧装置各一,每装置有正常和4小时人工龋釉质标本各1块。有氟期氟片置于上颌中切牙前庭沟处的粘膜表面,每天一次,一次一片。实验后将正常釉质块放入37℃酸胶中48小时。观察两期人工龋表面硬度值的改变、表面沉积物的情况和实验后釉质抗酸能力的变化。结果有氟期人工龋表面硬度值增加量(上下颌分别为73.9±6.3kg/mm2和35.1±8.9kg/mm2,P<0.5)高于无氟期(上下颌分别为55.9±8.3kg/mm2和31.1±14.5kg/mm2,P>0.5),上颌硬度值增加最多,P<0.5。有氟期人工龋釉质表面有小而致密的矿物盐沉积,无氟期的沉积物大而疏松。有氟期正常釉质经酸处理后脱矿程度低于无氟期。结论缓释氟粘贴片能提高唾液对早期龋的再矿化作用,增进正常釉质的抗酸能力。     

离体人氟斑牙脱矿与再矿化的研究

通过研究不同严重程度人氟斑牙在体外经人工龋脱矿实验及再矿化处理前后,釉质表面显微硬度值的变化,探讨氟斑牙的严重程度与脱矿再矿化的关系。结果发现:脱矿后氟斑牙的表面显微硬度损失百分比(%SMHD)为TFI4(18.92±1.31)TFI3(20.50±1.32)TFI2(25.08±1.69)TFI1(27.77±1.79)TFI0(30.70±1.35),(P0.05),轻度氟斑牙TFI1(27.77±1.79)与对照组正常牙TFI0(30.70±1.35)没有显著统计学差异。再矿化处理后氟斑牙的表面显微硬度恢复的百分比(%SMHR)为TFI1(55.17±4.03)TFI0(53.97±4.96)TFI2(49.17±3.11)TFI3(44.85±3.21)TFI4(36.51±2.95)(P0.05);中重度氟斑牙的抗龋性显著高于轻度氟斑牙及正常牙,轻度氟斑牙再矿化的效果明显好于中重度氟斑牙,同时也比正常牙稍好。值得临床注意。     

EFFECTIVENESS OF HOME BLEACHING AGENTS IN DISCOLORED TEETH AND INFLUENCE ON ENAMEL MICROHARDNESS

Objectives:

This study evaluated the effectiveness of different home bleaching agents on color alteration and their influence on surface and subsurface microhardness of discolored bovine enamel.

Material and Methods:

Forty-five fragments of bovine incisors were randomly allocated into 3 groups (n=15) according to the bleaching agent: 10% carbamide peroxide gel (CP10), 16% carbamide peroxide gel (CP16) and 6.5%-hydrogen-peroxide-based strip (HP6.5). Before bleaching treatment, initial values of Knoop surface microhardness and color (CIEL*a*b*) were obtained and the fragments were artificially stained in hemolyzed rat blood. Then, bleaching treatments were performed over a 21-day period. Color changes (ΔE) were assessed at 7, 14 and 21 days, and final surface microhardness reading was done after 21 days. Thereafter, the fragments were bisected to obtain subsurface microhardness. Data were subjected to ANOVA and Tukey''s tests (α=5%).

Results:

Color changes produced by CP16 were similar to those of CP10, and the color changes produced by these materials were significantly superior to those produced by HP6.5. Color changes at 21 days were superior to 7 days and similar to 14 days. The time did not influence color changes for CP16, which showed similarity between the 14- and 21-day results. No statistically significant differences were found among the home bleaching agents for surface and subsurface microhardness.

Conclusions:

Microhardness of bovine enamel was not affected by the bleaching agents. The 16% carbamide peroxide gel was the most effective for bleaching the stained substrate.     

Artificial methods of dentine caries induction: A hardness and morphological comparative study

Objective

To assess the ability of two chemical and a microbiological methods to produce dentine caries lesions resembling naturally developed dentine caries lesions.

Design

Forty sound second primary molars were divided into four experimental groups according to the method to produce artificial caries lesions: (1) sound (negative control); (2) acidified gel; (3) pH-cycling; and (4) microbiological, all for 14 days. Ten second primary molars presenting natural dentine caries lesions comprised the (5) positive control group. After the artificial caries induction, all samples were longitudinally sectioned and polished in order to obtain Knoop microhardness values from 10 to 500 μm depth from the bottom of the cavities. Morphological analysis of the surfaces was carried out by SEM. Hardness data were compared among the five experimental groups using One-Way ANOVA and post hoc SNK's test.

Results

The hardness values of chemically created caries-like lesions did not differ from that of natural caries lesions on shallower depths. The results indicated that chemical caries induction methods promote a superficial demineralization and that pH-cycling is more effective than acidified gel. The former, produced a thicker layer of demineralization, with similar hardness values than natural lesions. Despite the microbiological method provided an excessive softness of the primary dentine, this method presented morphology more comparable to natural lesions.

Conclusions

pH-cycling is more appropriated to simulate a substrate that resembles affected caries dentine layer, after caries removal. The microbiological method seems more indicated to simulate a dentine caries lesion with an infected layer, previously to caries removal.     

Effects of tooth whitening and orange juice on surface properties of dental enamel

Objective

To study the effects of 6% H₂O₂ activated with LED light on surface enamel as compared to orange juice challenges in vitro.

Methods

A total of 40 human enamel discs were incubated in saliva overnight to allow pellicle formation and then divided into three groups: 15 for whitening treatments, 15 for orange juice immersions and 10 for normal saline controls. Baseline microhardness was measured with a microhardness Knoop indenter (50 g, 10 s) and surface topography was evaluated with a focus-variation 3D scanning microscopy. Enamel discs were treated with H₂O₂ or orange juice for 20 min each cycle for five cycles to simulate daily treatment with the products for 5 days. The discs were stored in saliva between treatment cycles. Microhardness and surface topography were evaluated again after treatments. Changes in microhardness and in surface area roughness (Sa), mean maximum peak-to-valley distance (Sz) and the developed surface area ratio (Sdr) were compared before and after treatments (t-test) and among groups (ANOVA).

Results

Enamel surface hardness decreased by 84% after orange juice immersion but no statistically significant changes were observed in the whitening and control groups. Surface topography changed significantly only in the orange juice group as shown by increased Sa (1.2 μm vs. 2.0 μm), Sz (7.7 μm vs. 10.2 μm) and Sdr (2.8% vs. 6.0%). No such changes were observed in the whitening and control groups.

Conclusion

In comparison to orange juice challenges, the effects of 6% H₂O₂ on surface enamel are insignificant. Orange juice erosion markedly decreased hardness and increased roughness of enamel.     

In vitro action of Bordeaux red wine on the microhardness of human dental enamel

Several studies have demonstrated that the regular and large consumption of wine is associated with increased risk of tooth erosion. Here, the effect of Bordeaux red wine on enamel was estimated by measuring changes in its Vickers microhardness. Thirty premolars were used; microhardness tests were performed on buccal areas before and after 10, 30, 90 and 120 s immersion in the wine (pH=3.9). Enamel surfaces were also observed by scanning electron microscopy. No statistically significant difference was found between the mean Vickers microhardness obtained at t=0 and 90 s, but slight signs of enamel demineralisation were observed with the scanning electron microscope. It appears that wine has no disastrous effect on the microhardness of dental enamel when the two are in contact for less than 90 s. When the exposure is for at least 120 s, it may become harmful, as the decrease in the microhardness of enamel was then significant (P<0.05).     

Mineralization of the enamel of ovine permanent central incisor teeth using microhardness and histological techniques

Summary In this study, microhardness testing showed that enamel development was more closely related to the length of the developing incisor than to the age of the animal. Increase in hardness values was seen initially at the tip of the tooth and gradually progressed towards the apex. The development of the thinner lingual enamel was always in advance of that of the labial enamel. The appearance of the ameloblasts was related to the hardness pattern. Long secretory ameloblasts were seen in relation to labial enamel still increasing in thickness, i.e., in developing teeth of <12 mm or in longer teeth 5–6 mm from the growing end. The enamel at this stage was very soft [<50 Knoop hardness value (KHN)]. Ameloblasts related to the maturation or secondary mineralization phase (13 mm in extent) showed considerable variation in cell length. This produced a scalloped appearance of the basal border with at times marked cellular spaces. Enamel hardness increased during this phase attaining that of the mature tissue (250–350 KHN), just as the ameloblasts became short and regular with centrally placed nuclei (1.5 mm in extent). The enamel epithelium then disintegrated allowing the formation of cementum on the outer surface of the enamel, prior to the eruption of the tooth. This study was undertaken as a prerequisite for the production of developmental defects of enamel and for the identification of the pattern of mineralization at the time of experimental trauma.     

氯化镧对脱矿釉质再矿化的影响

为了了解镧对脱矿釉质矿化的影响，以基础矿化液及含１０ｐｐｍｌａ＾３＋或氟的矿化液分别处理脱矿后人牙釉质，再作实验开窗区剖面表及里的显微硬度测定，结果显示各试验组表层硬度明显低于内层硬度，但１００μｍ以内各点之硬度值比较差异均无显著性，以各实验组相比较，表层硬度值之间差异有显著性，其他层次相应点之间硬度值无无显著性。     

Protective effect of the in situ formed short-term salivary pellicle

Salivary pellicle, as previously investigated, protects the enamel surface after certain processes of maturation against the influence of acidic agents. The aim of the present study was to investigate the protective effect of the short-term salivary pellicle formed in situ over periods of 3, 60 and 120 min. Six human volunteers used intraoral acrylic splints with bovine enamel samples fixed at the buccal and palatal sites of the maxillary first molars and second premolars. Enamel specimens (n = 252) with and without pellicle were immersed for 60 s in 1.0% citric acid solution under agitation. Knoop surface hardness (KHN) of uneroded polished enamel was measured as a baseline and estimated immediately after erosive treatment reflecting the microhardness loss (DeltaKHN). The amounts of calcium dissolved from the eroded enamel surface were analysed by atomic absorption spectroscopy and scored in mg/l per 10 mm2 of enamel surface area. In addition, the scanning electron microscope was used for the micromorphological examination of the erosive alterations of the enamel surface. The average microhardness loss values after erosion of the enamel samples with buccally/palatally formed pellicle layers were measured as 139.1/144.9 DeltaKHN for 3 min pellicle, 145.9/146.9 DeltaKHN for 60 min pellicle and 141.7/138.6 DeltaKHN for 120 min pellicle. Calcium release values from the specimens with buccal/palatal pellicles were amounted to 15.0/14.9, 16.5/15.9 and 15.3/17.4 mg/l per 10 mm2 for 3, 60 and 120 min-old pellicles, respectively. No significant differences were related to the pellicle formation time and intraoral site (buccal or palatal) in all tested series (ANOVA, P < 0.05). However, significant protection of the enamel surface provided by the pellicle layer was observed on all pellicle-covered surfaces if compared to the non-covered enamel samples (calcium release: 25.6 mg/l per 10 mm2; microhardness loss 187.0 DeltaKHN). These data were in accordance with the morphologic alterations caused by citric acid on the pellicle-covered and pellicle non-covered specimens. It could be concluded that salivary pellicle formed in situ within a period of 3 min offers protection of enamel against citric acid. However, pellicle does not completely inhibit the erosive action of citric acid under the conditions of the present study.