Development of cranial flexure and Rathke's pouch in the chick embryo

Experiments were done to investigate the cause of the cranial (mesencephalic) flexure of the chick brain during stages 10 to 14. Measurements of the length and thickness of the roof and floor of the mesencephalon gave values similar to the values obtained previously by others. The labeling index was determined in the roof and floor of the prosencephalon, mesencephalon, and rhombencephalon as a preliminary measure of cell division. The labeling index was about the same in all regions, and was high enough to suggest that most of the cells were dividing. The labeling indices did not suggest that differential growth was caused by differential rates of cell division in the roof and floor of the mesencephalon. It was found through time lapse photography that the foregut and heart remained stationary along the rostrocaudal axis, whereas the prosencephalon moved rostrally and the mesencephalon underwent flexure. Measurements suggested that the neural tube cranial to the otic primordium grew in volume exponentially at a rate consistent with the labeling index. The rostral tip of the neural tube was observed to be linked to the rostral tip of the foregut by the ectoderm that formed Rathke's pouch at the neural tube and the pharyngeal membrane (prospective stomodeum) at the foregut. As the neural tube grew in length, the link between the neural tube and the foregut did not. We suggest that because of this link, the growing neural tube had to bend around the foregut, forming the cranial flexure, and the ectoderm folded where it attached to the prosencephalon, forming Rathke's pouch. © 1994 Wiley-Liss, Inc.     

腰大肌作用力与脊柱伸展应力关系的生物力学实验研究

目的:探讨腰大肌作用力带动脊柱伸展应力的生物力学关系。方法:取家兔12只,分3组,每组4只,解剖后保留枢椎以下完整之脊柱及骨盆、髋关节、上段股骨,不损伤脊柱前、后纵韧带、椎间盘及所附着之腰大肌,保留脊柱背侧的竖脊肌、棘上韧带,置于生物力学拉伸测试仪(日本岛津制作所产AGS-J系列)。上端十字头分别夹枢椎(颈胸腰段)、第1胸椎(胸腰段)和第12胸椎(腰段),下端十字头夹股骨上部;分别作有腰大肌状态下和切断腰大肌状态下,股髋自屈曲位到过伸带动脊柱自屈曲位到过伸位拉伸试验,测定两种不同状态下脊柱各节段的伸展应力(N/mm2)。结果:有腰大肌状态和切断腰大肌状态下,股-髋-脊柱拉伸后脊柱伸展应力分别为:颈胸腰全段平均为306.6675N/mm2:78.7167N/mm2;胸腰段为680.8417N/mm2:373.0375N/mm2;腰段为1990.7944N/mm2:523.0608N/mm2;经统计学分析,具显著性差异,P<0.01。结论:腰大肌作用力对脊柱伸展应力影响显著,颈胸腰段占74.33%、胸腰段占45.21%,腰段占73.73%的伸展应力源自腰大肌。脊柱在腰大肌作用下产生腰椎向腹部的弯曲。     

Surgical Treatment and Subsequent Outcome of Patients with Carcinoma of the Splenic Flexure

Extended resection, comprising extended right hemicolectomy, splenectomy, and distal pancreatectomy, has been advocated for carcinoma of the splenic flexure because the lymphatic drainage at this site is variable. The present study addresses the problems associated with selecting the most appropriate operative procedure to achieve cure of splenic flexure cancers. We conducted a retrospective review of 27 patients with splenic flexure cancer who under-went curative resection. Left partial colectomy was performed in 20 patients and partial resection of the transverse/descending colon was performed in 7 patients. The combined resection of adjacent organs due to tumor adherence was performed in three patients. The spleen and distal pancreas were the organs most frequently resected among a collective total of six adjacent organs. The median duration of follow-up was 60.9 months after resection for splenic flexure cancer. No patient developed local recurrence. There was no significant difference in 5-year survival between patients with splenic flexure cancers and those with colon cancers at other sites. In conclusion, splenic flexure cancer resected by left partial colectomy or partial resection of the transverse/descending colon without routine extended resection was not associated with a worse prognosis than colon cancers at other sites. Received: February 17, 2000 / Accepted: September 26, 2000     

Short-chain fatty acids do not alter jejunal motility in man

Short-chain fatty acids (SCFAs) alter ileal and colonic motility, but their effects on duodenojejunal motility are unknown. Simultaneous jejunal manometric recordings and hydrogen breath tests after lactulose were performed in eight healthy subjects during continuous duodenal infusion of either saline or SCFAs. These experiments were conducted in the fasting state and postprandially. The effects of various boluses of SCFAs on duodenojejunal motility were also determined in six subjects. During the fasting period, the number and characteristics of migrating motor complex, prolonged propagated contractions, discrete clustered contractions, motility indes, and orocecal transit time were similar during saline and SCFAs. Similarly, the motility index and the duration of the postprandial period were not different between SCFAs and saline after the meal. The motility index was significantly increased after each of the 100-ml boluses (saline or SCFAs), but was not altered after the 12.5-ml boluses, suggesting a volume-related effect. Thus, SCFAs do not seem to affect proximal small bowel motility in healthy humans.This work was supported in part by a research grant from Institut National de la Santé et de la Recherche Médicale (INSERM) (CRE 887009), and by Smith Kline and French (Paris, France).     

Survival probability of zirconia-reinforced lithium silicate ceramic: Effect of surface condition and fatigue test load profile

ObjectivesThe present investigation evaluated the step stress accelerated test (SSALT) load profiles on the survival probability of a glass ceramic under two surface conditions (polished or roughened).MethodsSuprinity–ZLS blocks (Vita Zhanfabrik) were shaped into cylinders, cut in a sawing machine, and crystalized according to the manufacturer's instructions. 60 discs were obtained (Ø = 12 mm, thickness = 1.2 mm) and randomly assigned into two surface conditions: “p” polished surface (400–1200-grit SiC papers), and “r” roughened surface (200-grit SiC papers). Profilometry was performed in all discs to evaluate average surface roughness prior to flexural fatigue strength testing. 3 discs of each group were submitted to biaxial flexural strength in an universal testing machine (0.5 mm/min) and the mean load to failure (N) was calculated to determine SSALT profiles. 27 specimens per surface condition were assigned into three profiles – Mild (n = 9), Moderate (n = 9), and Aggressive (n = 9), and submitted to the fatigue test (60–320 N, 140,000 cycles at 1.4 Hz). The results were analyzed using the Kaplan-Meier and Wilcoxon tests (5%), 2-way ANOVA and Tukey test (α = 5%).ResultsKaplan-Meier and generalized Wilcoxon showed (P = 0.002) that polished groups showed higher survival probability than roughened condition (P < 0.05). A rough internal surface impacted deleteriously on the fatigue strength and reliability of ZLS ceramic. Both surface conditions were more sensitive to the aggressive profile than the other profiles, even worst for the roughened group. Regardless the load profile, 0% survival probability was observed at 384 MPa for polished condition. While for roughened, aggressive tested specimens did not survived 147 MPa followed by moderate at 312 MPa and mild at 384 MPa. The failure modes showed fracture marks originating from superficial grooves for both surface conditions.SignificancePolished specimens are sensitive to the load profile variation, confirming the effect of surface morphology on the fatigue results.     

Probing the interfacial strength of novel multi-layer zirconias

ObjectivesThe rapidly increasing use of zirconia-based CAD/CAM multi-layer structures in dentistry calls for a thorough evaluation of their mechanical integrity. This work examines the effect of the multi-layering architecture as well as variations in composition and inclusion of pigments among the layers on the flexural strength of multi-layer zirconias.MethodsA modified 4-point bending test, aided by a Finite Element Analysis (FEA), was used to probe the interfacial strength of 3 classes of yttria-partially-stabilized zirconia: Ultra Translucent Multi-Layer (UTML—5Y-PSZ), Super Translucent Multi-Layer (STML—4Y-PSZ), Multi-Layer (ML—3Y-PSZ). In accord with the size limitation (22-mm height) of CAD/CAM pucks, test samples were prepared in the form of “long” (25 × 2 × 3 mm) and “short” (17.8 × 1.5 × 2 mm) beams. Homogeneous beams (both long and short) were produced from either the Enamel (the lightest shade) or Dentin (the darkest shade) layer, whereas multi-layer beams (short beam only) were obtained by cutting the pucks along their thickness direction, where the material components of various shades were stacked.ResultsThe Enamel and Dentin layers exhibited similar flexural strength for a given material class, with ML amassing the highest strength (800–900 MPa) followed by STML (560–650 MPa) and UTML (470–500 MPa). The 3 classes of multi-layer zirconia showed a trade-off between strength and translucency, reflecting different yttria contents in these materials. The failure stress of the cross-sectional multi-layer beams was, however, ∼30% lower than that of their Enamel or Dentin layer counterparts, regardless of material tested.SignificanceThe weakness of interfaces is a drawback in these materials. Additionally, when measuring strength using short beam flexure, friction between the specimen and supporting pins and accuracy in determining loading span distances may lead to major errors.     

上消化道造影检出儿童无症状肠旋转不良作用研究

[目的]探讨上消化道造影（upper gastrointestinal imaging,UGI）常规检查十二指肠空肠曲（duodenojejunal flexure,DJF）位置的意义.[方法]回顾性分析350例行UGI患儿的影像学资料,56例临床怀疑肠旋转不良的患儿,其余患儿根据是否检查DJF位置分为2组：A组198例检查了DJF位置,B组96例未检查DJF位置.记录患儿的年龄、性别、UGI的检查时间和DJF位置.[结果]56例临床怀疑肠旋转不良的患儿有24例有DJF位置的异常（42.8％）,A组198例患儿仅有1例发现DJF位置异常（0.5％）.B组患儿的年龄和性别与A组比较差异无统计学意义（P＞0.05）.2组患儿UGI的检查时间比较差异有统计学意义（P＜0.01）.A组的检查时间显著大于B组.[结论]本研究发现对临床没有怀疑肠旋转不良的患儿,UGI发现DJF位置异常的概率非常小,故儿童UGI可不常规检查DJF位置以降低辐射剂量.     

The reliability in flexural strength testing of a novel dental composite

Objectives. To investigate the reliability of bi-axial flexure and three-point flexure testing of an experimental, low-shrink oxirane-based dental composite, EXL596 compared with two conventional methacrylate based restoratives, Z250 and Z100.

Methods. Specimens (n=20) of a novel oxirane-based composite and two commercially available methacrylate based composites were fabricated for flexural testing to evaluate mean bi-axial flexure strengths, three-point flexure strengths and the associated Weibull moduli (m) following 24 h immersion in a lightproof waterbath maintained at 37±1 °C.

Results. Mean bi-axial flexure strengths and the associated m of EXL596, Z250 and Z100 were 168±11 MPa (m=16.2±4), 140±12 MPa (m=11.9±3) and 126±13 MPa (m=10.2±2), respectively. Three-point flexure strengths and the associated m of EXL596, Z250 and Z100 were 113±15 MPa (m=9.2±2), 92±10 MPa (m=8.5±2) and 79±16 MPa (m=6.3±1), respectively.

Conclusions. The present investigation suggests that bi-axial flexure strength testing of dental resin-based composites provides a more reliable testing method than three-point flexure. The increased reliability was considered in terms of the associated Weibull moduli following bi-axial flexure testing as a result of the elimination of the additional induced variability introduced during the curing regime of three-point flexure specimens.