Surface alteration of human tooth enamel subjected to acidic and neutral 30% hydrogen peroxide

Objectives

To investigate the effects of acidic and neutral 30% hydrogen peroxide (HP) on human tooth enamel in terms of chemical structure, mechanical property, surface morphology and tooth colour.

Methods

Twenty-seven human dental blocks were obtained from premolars and randomly divided into three groups (n = 9): Group acidic HP (30% HP, pH ≈ 3.6), Group neutral HP (30% HP, pH ≈ 7.0) and Group DW (distilled water, pH ≈ 6.8). Attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), Raman spectroscopy, atomic force microscopy (AFM) investigation, microhardness test and colour measurements were carried out before and after treatments. ATR-FTIR and Raman spectroscopy were analysed and then the carbonate:mineral ratio (C:M), Raman absolute intensity (RAI), Raman relative intensity (RRI), and laser-induced fluorescence intensity (FI) were obtained for evaluation.

Results

The C:M, percentage microhardness and percentage RRI of group acidic HP decreased more significantly than those of group neutral HP (P = 0.02, P = 0.001, P < 0.001, respectively) and group DW (P = 0.01, P = 0.008, P < 0.001, respectively). Whilst group neutral HP and group DW had no statistical difference in above terms (P = 0.818, P = 0.528, P = 0.158, respectively). Significant morphological alterations were observed in group acidic HP. Group acidic HP and neutral HP had no significant difference in percentage FI (P = 0.652) and ΔE (P = 0.906).

Conclusions

This study suggested that neutral 30% HP had the same efficiency in tooth bleaching and it caused less deleterious effects on enamel than acidic 30% HP.     

明朝金属全冠及其粘接剂之成分分析

目的考察我国明朝（公元１３６８～１６４４年）的口腔修复技术，并为我国口腔医学史提供一些细节资料。方法借助目测及扫描电镜能谱分析，对江苏武进博物馆编号为０７５４／００４６的二颗馆藏明朝人类牙齿冠部的金属全冠及其粘接剂作了初步成分分析。结果考古分析表明，二牙系明朝嘉靖至万历年间（公元１５００～１６００年）遗物，均为上前牙且无牙体制备痕迹，金属全冠系锤造后焊接而成。能谱分析显示二金属冠分别含金７９３３％及８５８６％，含铜２０６７％及１４１４％，粘接剂内含锌元素。结论我国明朝已能利用高硬度铜金合金及粘接材料修复牙体缺损，表明我国明朝已有较成熟的口腔修复技术。     

用傅立叶变换红外光谱仪研究复合树脂的双键转化度

为了研究牙科复合树脂的聚合，采用傅立叶变换红外（Ｆｏｕｒｉｅｒｔｒａｎｓｆｏｒｍｉｎｆｒａｒｅｄ，ＦＴＩＲ）光谱仪测定８种牙科复合树脂的双键转化度并比较了压片制样法和薄膜制样法对转化度的影响。结果发现，树脂的双键转化度在４５％～７４％之间；可见光固化树脂的转化度高于化学固化树脂者。在光固化树脂中，混合填料树脂的转化度高于超微填料树脂者，粘接辅助剂的转化度最高。对光固化树脂而言，压片制样法所测得的转化度值高于用薄膜制样法；而在化学固化树脂，用二种制样方法所测得的转化度值相同。本研究结果可供临床应用复合树脂参考。     

Effect of a dentifrice containing the peptide of streptococcal antigen I/II on the adherence of mutans streptococcus

Objective

Antigen I/II of mutans streptococcus (MS) is a surface protein, which binds to salivary receptors. The objective of this study was to study the effect of a peptide corresponding to residues 1025-1044 of antigen I/II and a dentifrice containing peptide on the adherence of MS.

Methods

The peptide was synthesized and included into dentifrice. Anti-adherence experiments of the peptide and a dentifrice containing it were processed in vitro and in vivo.

Results

The results showed that the adherence of MS to hydroxyapatite was inhibited by synthetic antigen I/II peptide and also by a dentifrice containing the peptide in vitro. The numbers of MS in plaque from subjects treated with dentifrices containing the peptide for 1 month was significantly reduced compared to baseline (log 3.11 ± 0.80 vs log 4.09 ± 0.90, P < 0.01), whereas the control group showed no reduction.

Conclusion

The adherence of MS to hydroxyapatite was inhibited by both a synthetic peptide and a dentifrice containing the peptide. The peptide dentifrice produced a significant reduction of MS in dental plaque in vivo.     

Effect of stimulus parameters and contraction level on inhibitory responses in human jaw-closing muscles: Implications for contingent stimulation

Objective

Examine the effect of stimulus duration, intensity and level of muscle contraction on the inhibitory responses evoked by electrical stimuli in human jaw-closing muscles applied to the right mental nerve.

Design

The inhibitory jaw-reflexes, short-latency (ES1) and long-latency (ES2), were recorded in the surface electromyogram (EMG) of masseter and temporalis muscles in 16 healthy subjects. Three stimulus durations (1 ms single square-wave pulse, 10 and 450 ms square-wave pulse train), two stimulus intensities adjusted to perceived intensity of 3 (non-painful) and 7 (distinct painful) on a 0–10 verbal rating scale were applied to the right mental nerve while the subject was biting at 25% and 50% of the maximal voluntary contraction (MVC).

Results

The magnitude of suppression in the ES2 evoked by 1 and 10 ms stimuli was dependent on stimulus intensity (P < 0.002 and P < 0.001, respectively) but not contraction level. However, ES1 could not be observed in most of the recordings. There were significant decreases evoked by the 450 ms stimuli in RMS–EMG values in the 400–500 ms compared with the pre-stimulus interval (P < 0.001) which was dependent on contraction level (P < 0.01) but not on stimulus intensity (P = 0.486).

Conclusions

The present results suggest that the ES2 reflex response is associated with the duration of the electrical stimuli, the intensity level but not the contraction level. In contrast, the inhibitory effects of ultra-long stimuli (450 ms) are not specifically related to the intensity level suggesting that this is a non-nociceptive response.     

A custom mandibular distraction device for the rat

In the last several years, the rat model has been used as a reliable means of studying distraction osteogenesis (DO). This model has several benefits, including lower cost, the availability of molecular reagents for the rat, and the ability to perform a large number of operations in a short time. We have recently developed an external device that is custom-made for the rat mandible and secured at the mandibular ramus. The device consists of a Leone (Florence, Italy) jackscrew distraction assembly (0.2 mm per one-quarter turn), 2 Luhr L-shaped 0.8-mm five-hole microplates, and four 0.8-mm x 3-mm microscrews (Stryker-Leibinger Corp., Kalamazoo, MI) for fixation. Additionally, there is a methylmethacrylate block that is placed on the lingual surface of the angle of the mandible to support the posterior screws. Sterile surgical technique was used, and the same two surgeons performed all operations. To date, we have operated on 153 Sprague-Dawley rats. The procedure has been well tolerated by the animals. We had 17 postoperative deaths (11% mortality), largely as a result of anesthetic complications. There were no wound infections or dehiscence. A mandible fracture was noted in 6 rats (4%), which occurred at the time of device placement. There were no device dislodgments. Postmortem examination showed the device to be well positioned in all rats, with good callous formation at the distraction site. The rats surpassed their preoperative weight after an average of 9.2 days. These results compare favorably with those of other models currently in use. We have developed a device that is currently being used in the study of DO in the rat mandible. Our device is small in size, does not require wide undermining for its placement, and has had a low incidence of device dislodgment or infection. This model has shown great reproducibility and thus should be effective in its application for the histologic and biochemical investigation of DO in the rat.     

反复玻璃渗透对In-Ceram氧化铝基底微观结构的观察

目的 :研究In Ceram氧化铝基底在玻璃料渗透前及反复多次玻璃料渗透后样本的微观结构 ,探讨渗透次数对微观结构的影响。方法 :分别观察玻璃料渗透前、玻璃料渗透 1～ 5次的样本的SEM断面。结果 :In Ceram氧化铝烧结后 ,形成了连续开放的多孔网状结构。玻璃料渗透后 ,氧化铝颗粒之间的孔隙被渗透玻璃充盈、占据 ,二相互相锁结。结论 :In Ceram氧化铝基底在渗透前后 ,微观形貌发生明显改变 ;随着渗透次数的增加 ,渗透深度逐渐加深 ,微观结构也更为致密