Shaping ability of progressive versus constant taper instruments in curved root canals of extracted teeth

AIM: To compare the shaping ability of progressive versus constant taper shaft instruments in curved root canals of extracted human teeth. METHODOLOGY: A total of 40 root canals of mandibular molars with curvatures ranging between 20 degrees and 40 degrees were divided into two groups of 20 canals each and embedded in a muffle system. The root canals sectioned horizontally at three levels before preparation and then remounted into the mould. All root canals were prepared with ProTaper (progressive taper) or Hero Shaper (constant taper) instruments. Pre- and post-instrumentation radiographs and cross-sectional images were obtained. The parameters evaluated were: working safety (instrument failure, apical blockage and loss of working length) and shaping ability (straightening, cross-sectional area, transportation and centring ability). The data were analysed statistically using Student's t-test. RESULTS: No instrument fractured during preparation. One Hero Shaper instrument permanently deformed. Both instrument systems maintained working length well. The canals prepared with Hero Shaper instruments were straightened to a lesser degree (P < 0.05). ProTaper instruments removed more dentine in the coronal and the middle sections of the canals. Canals prepared with Hero Shaper instruments had less transportation (P < 0.01) and better centring ability (P < 0.05) in the apical section. CONCLUSIONS: Both instrument systems were safe to use and maintained working length well. The canals prepared with Hero Shaper had less transportation and were better centred in the apical region, possibly because their smaller taper reduced instrument stiffness.     

骨性Ⅲ类错He畸形对语音功能的影响

为了探讨骨性Ⅲ类错Ｈｅ畸形对语音功能的是否有影响，我们以２０名骨性Ⅲ类错Ｈｅ畸形的成年患者为研究对象，由语音专家对其语音进行判听，同是应用计算机语音工作站（ｃｏｍｐｕｔｅｒｉｚｅｄｓｐｅｅｃｈｌａｂ）进行了语音声学分析，结果表明：（１）多数此类错Ｈｅ患者存在的语音功能异常，在ｚｈ，ｃｈ，ｓｈ，ｚ诸输音上最常见出现发音错误，错误类型为发音失真（ｄｉｓｔｏｒｔｉｏｎ）和发音替代（ｓｕｂｓｔｉｔｕｔｉｏ     

Mechanical behavior of ProTaper universal F2 finishing file under various curvature conditions: a finite element analysis study

Introduction

The purpose of this study was to visualize the stresses and strain distribution patterns in ProTaper Universal F2 files (Dentsply Maillefer, Ballaigues, Switzerland) and to establish the stress- and strain-curvature relationship for this instrument under various conditions by using a dynamic, three-dimensional finite-element model.

Methods

An accurate geometric model of a ProTaper Universal F2 instrument was created. Two short, straight tubes were also modeled to represent the parts of root canal apical and coronal to the curvature. Then, the file was constrained to a curve of varying degree, curve length, and position. The maximum von Mises stress and strain on the tension side of the instrument was measured at 5-degree intervals in a numerical simulation package (LS-DYNA; Livermore Software Technology, Livermore, CA).

Results

The mechanical performance of the ProTaper F2 file under various conditions was simulated. A long curvature length produced lower values of stress and strain under the same angle of curvature. An increase in the curvature angle generally induces higher stress and strain. For the same degree and curve length, the stress and strain increased if the curved portion was situated further up the shaft of the instrument (ie, with a larger diameter).

Conclusions

The dynamic, numerical model may be used to evaluate and compare the effect of various root canal curvatures on the behavior of different designs of root canal instrument. The magnitude of stress and strain imposed on the instrument is influenced by the abruptness and degree of curvature as well as the location of the curved portion.     

表皮生长因子受体在颊粘膜鳞状细胞癌中的表达及其临床病理学意义

表皮生长因于受体（EGFR）是一单跨膜糖蛋白，与细胞的增殖、转化有关。本文采用免疫组化ABC法检测8例正常颊粘膜上皮及40例颊粘膜鳞癌中EGFR的表达状况，结果显示：EGFR在颊癌组织中呈异质性表达，其阳性率明显高于正常颊粘膜组织（P＜0．05）；EGFR表达状况与颈淋巴结转移及预后间存在相关关系（P＜0．05）。EGFR（＋）表达者多数伴有颈淋巴结转移，预后差。以上结果说明，EGFR在颊癌组织中的表达水平，可作为评估颊癌细胞增殖状态，颈淋巴结转移情况及患者预后的一项参考指标。     

The current for a two-electron reaction is not necessarily twice that of a one-electron reaction

Two-setp oxidation or reduction of a molecule is considered for the case where removal (or addition) of the second electron is more difficult than that of the first. In such cases, the comproportionation reaction between the final product and the original reactant to give two molecules of the one-electron intermediate is favored and can occur in the diffusion-reaction layer. When the diffusion coefficients of the three species differ, the current seen at potentials where the two-electron reaction occurs will not be twice that seen at potentials where the one-electron reaction occurs, i.e. n_app does not equal 2. For chronoamperometry, digital simulations have been employed to predict the dependence of n_app on the relative diffusion coefficients. It has been shown that equality of the diffusion coefficients of the reactant and the one-electron product is sufficient to guarantee that n_app will be 2. Diffusion coefficients of neutral tetracyanoquinodimethane (TCNQ), its radical anion and the dianion have been meaured in acetonitrile. It is predicted that n_app will be 1.98 for reduction of neutral TCNQ and 2.18 for oxidation of TCNQ^2?. Within experimental error, these values were found experimentally using normal pulse voltammetry. The effect of unequal diffusion coefficients was also observed in cyclic voltammetry and confirmed by simulation.     

Effect of compounds of Galla chinensis on remineralisation of initial enamel carious lesions in vitro

OBJECTIVE: To evaluate the effect of compounds of Galla chinensis on the remineralisation of initial enamel carious lesions in vitro. METHODS: Sixty bovine enamel blocks with early lesions were prepared and randomly divided into six treatment groups. The lesions were subjected to a pH-cycling regime for 12 days. Each daily cycle included 4x1min applications with one of six treatments; 1000ppm F aq. (as NaF, positive control); deionized water (negative control); or 4000ppm aqueous solutions of four G. chinensis extracts (GCEs); GCE, GCE-B, GCE-B1, or GCE-B2. Surface enamel microhardness was measured on the enamel blocks before and after demineralisation, and after pH-cycling, and percentage surface microhardness recovery (%SMHR) was calculated. The enamel specimens were then sectioned (thickness ca. 80microm) and examined by polarized light microscopy. RESULTS: All samples rehardened significantly compared to baseline. Fluoride had a significantly greater effect than all other treatments. In the GCEs groups, %SMHR was significantly greater than DDW for the GCE, GCE-B and GCE-B1 groups. There was no significant difference between the GCE-B2 group and DDW. Polarized light microscopy showed that the thickness of the surface layer increased obviously in all specimens including NaF group, GCE group, GCE-B group and GCE-B1 group. Negative birefringent band appeared in the lesions body and the depth of the lesions was obviously reduced. CONCLUSION: The present study has demonstrated the potential of three GCEs (GCE, GCE-B and GCE-B1) to effect net rehardening of artificial carious lesions under dynamic pH-cyclic conditions.     

Evaluation of formocresol versus ferric sulphate primary molar pulpotomy: a systematic review and meta-analysis

AIM: To present a systematic review of the effects of formocresol and ferric sulphate when used as medicaments in pulpotomized primary molar teeth. METHODOLOGY: The study list was obtained by using MEDLINE, the Cochrane Library, EMBASE and SCI search. Only those papers which met the inclusion criteria were accepted. The quality of studies used for meta-analysis was assessed by a series of validity criteria according to Jadad's scale. A systematic review and meta-analysis were performed. RESULTS: Eleven clinical studies comprising four randomized-clinical trials (RCTs), four controlled clinical trials (CCTs) and three retrospective studies were included. The results of the meta-analysis of six prospective clinical trials suggested that the two popular pulpotomy medicaments were not significantly different in terms of clinical outcomes, radiographic findings, prevalence of apical and furcal destruction, internal root resorption or pulp canal obliteration. The relative risk (RR) value and 95% CI for those parameters were 0.72 (0.43-1.23), 0.87 (0.59-1.30), 0.67 (0.27-1.66), 1.77 (0.56-5.58) and 1.41 (0.63-3.15), respectively. The overall clinical and radiographic success rates based on the data of treatments with ferric sulphate from the 11 studies included ranged from 78% to 100% (mean 91.6 +/- 8.15%) and from 42% to 97% (mean 73.5 +/- 18.40%), respectively. CONCLUSIONS: In primary molar teeth with exposure of vital pulps by caries or trauma, pulpotomies performed with either formocresol or ferric sulphate have similar clinical and radiographic success. Ferric sulphate may be recommended as a suitable replacement for formocresol.