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。     

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.     

便携式灭菌器内筒结构强度与稳定性分析

目的:便携式灭菌器的内筒作为持续承受外压的薄壁构件,在虚拟设计同期完成性能评估,以保证设计的安全性。方法:应用大型分析软件Pro/Engineer的Mechanica模块对内筒结构进行屈曲分析。结果:分析结果表明,内筒的强度与稳定性设计满足工程要求。结论:装备研发过程中,同期开展的虚拟性能评估,可以检验设计数据的安全性,降低设计成本,缩短设计周期。     

Routine Mobilization of the Splenic Flexure is not Necessary During Anterior Resection for Rectal Cancer

Purpose Splenic flexure mobilization is widely considered to be an essential component of anterior resection for rectal cancer. It was our hypothesis that selective splenic flexure mobilization would reduce operative times without increasing morbidity or affecting cure. Methods A total of 100 consecutive patients with rectal cancer (mean 8 (range, 4–15) cm from anal verge) who underwent anterior resection for cure between 1996 and 2002 had splenic flexure mobilization only as required to achieve a tension-free anastomosis. Operative time, postoperative morbidity, pathologic findings, and recurrence rates were recorded. Results There were no clinicopathologic differences between those who had splenic flexure mobilization (n = 26) and those who did not (n = 74). Mean operative time in the splenic flexure mobilization group was longer, 167 (range, 130–200) minutes vs. 120 (range, 95–180) minutes in the nonmobilized group (P = 0.023). Mean length of specimen resected was longer in the splenic flexure mobilization group: 36 vs. 18 cm (P = 0.008). Anastomotic complications (4 percent), local recurrence (7 percent, median follow-up, 38 months), perioperative morbidity (32 percent) and mortality (2 percent), and survival did not differ between the two groups. Conclusions Routine splenic flexure mobilization is not required for safe anterior resection in patients with rectal cancer. Avoiding splenic flexure mobilization results in shorter operative times and does not increase postoperative morbidity, anastomotic leakage, or local recurrence. Presented at the Freyer Surgical Meeting, Galway, Ireland, September 2 to 3, 2005.     

The oncologic safety of left colectomy with modified complete mesocolic excision for distal transverse colon cancer: Comparison with descending colon cancer

BackgroundThe optimal surgical approach for distal transverse colon cancer has not been well established. This study aimed to evaluate the oncologic safety of left colectomy with a modified complete mesocolic excision for distal transverse colon cancer as compared with descending colon cancer.Material and methodsThis study involved 383 patients who underwent left colectomy with modified complete mesocolic excision for non-metastatic distal transverse and splenic flexure colon (transverse group, N = 110) and descending colon cancer (descending group, N = 237) from 3 institutions. Recurrence-free survival (RFS) and overall survival (OS) were compared between the two groups.ResultsBaseline characteristics between the two groups were similar except for the length of the distal margin (transverse group = 11.0 cm vs descending group = 9.0 cm, p = 0.004). During a median follow-up of 47.0 months, RFS and OS were not different between the transverse and descending groups (5-year RFS: 82% vs 71%, p = 0.139; 5-year OS: 83% vs 79%, p = 0.416, respectively). In multivariable analysis, RFS and OS were not different between the two groups (transverse group vs. descending group: adjusted hazard ratio [aHR] = 1.557, 95% CI = 0.786–3.084, p = 0.204; aHR = 1.251, 95% CI = 0.530–2.952, p = 0.609).ConclusionThe oncologic outcomes of left colectomy with a modified complete mesocolic excision of distal transverse colon cancer were comparable to those of descending colon cancer. Left colectomy with a modified complete mesocolic excision can be an acceptable surgical treatment for distal transverse colon cancer.