Stress analysis of endodontically treated teeth restored with post-retained crowns: A finite element analysis study

BackgroundThe authors conducted a study to analyze the stress concentration areas in a tooth restored with a post-retained crown under various conditions.Materials and MethodsThe authors constructed a three-dimensional finite element model describing a maxillary second premolar restored with an all-ceramic crown supported by a titanium post and a resin-based composite core. They applied static vertical and horizontal loads of 100 newton to the cusp tip of the crown and recorded Von Mises and tensile stress values. The variables investigated were the presence of the post, coronal and apical post extensions, post diameter, post shape, and post and core material.ResultsThe study results showed that horizontal loading generated higher levels of stress than did vertical loading. The greatest stress levels were concentrated at the cervical region and at the post-dentin interface in all models. Under both loads, a higher modulus of elasticity of the post material and a wider post diameter were associated with increased stress values at the post-dentin interface. Reduction of the post extension above the level of bone was associated with increased dentinal stresses near the apex of the post.ConclusionsAlthough endodontic posts provide retention for coronal restorations, they result in dentinal stress values higher than those of crowns without posts. Posts that had a similar modulus of elasticity to dentin and smaller diameters were associated with better stress distribution. Resting coronal restorations on sound dental tissues affected stress distribution more than did the core material or the length of the coronal post extension.Clinical ImplicationsMany factors influence the distribution of stress within dentin and, consequently, the fracture resistance of teeth restored with post-retained crowns. Clinicians need to keep these factors in mind when performing endodontic procedures that involve placement of post-retained crowns to ensure optimal success.     

咀嚼肌表面电极肌电图重复性检验和参考值的建立

目的:对成年人咀嚼肌表面电极采集的肌电信号加以分析,研究下颌在6种不同运动状态下咀嚼肌肌电信号的可重复性,并取得正常参考值。方法:30名22-44岁受试者进行咀嚼肌表面电极肌电图检查,记录下颌姿势位、牙尖交错位和扣齿运动时双侧咬肌、颞肌前束和二腹肌前腹的肌电活动,每个受试者在3个不同时段各测试一次。结果:3次测试的咀嚼肌峰值电位之间无统计学差异(P>0.05)。下颌姿势位时,右侧咬肌峰值电位95%正常参考值为0-0.1,左侧为0-0.13,右侧颞肌前束为0-0.67,左侧颞肌前束为0-0.1,右侧二腹肌前腹为0-0.13,左侧二腹肌前腹为0-0.1;牙尖交错位时,右侧咬肌峰值电位95%正常参考值为0.33-2.53,左侧为0.47-2.5,右侧颞肌前束为0.23-2.23,左侧颞肌前束为0.2-3.67,右侧二腹肌前腹为0.13-1.07,左侧二腹肌前腹为0.1-0.87;扣齿运动时右侧咬肌峰值电位95%正常参考值为0.5-2.5,左侧为0.73-2.3,右侧颞肌前束为0.4-3.47,左侧颞肌前束为0.3-3.63,右侧二腹肌前腹为0.2-1.07,左侧二腹肌前腹为0.13-0.97。结论:表面电极采集的双侧咬肌、颞肌前束和二腹肌前腹的肌电活动具有一定的可重复性。     

三种常用比色板色度值的比较研究

目的:比较研究3种常用比色板的色度值差别,以指导临床及技工室制作瓷修复体。方法:将比色板每一色片分成上中下、左中右9个象限,分别测试每1象限的Lab值,并对不同比色板相同编号色片进行两两比较。结果:3种常用比色板同一编号色片在同一部位的色度差值(△Eab)范围是:1.67～22.83NBS,超出肉眼可分辨的范围1.5NBS。结论:不同比色板同一色片之间存在肉眼可分辨的色度差,建议医师在登记比色结果时,应注明所用比色板的厂家名称,技工应采用相应比色板厂家的瓷粉完成瓷修复体。     

β-内酰胺酶抑制剂复方制剂非临床研究技术指南

β-内酰胺酶抑制剂复方制剂在临床上被广泛应用于治疗耐药菌所致感染,由于早期β-内酰胺酶抑制剂的抑酶谱较 窄,抑酶谱更广泛的酶抑制剂在不断研发之中。与一般抗菌药物临床前研究不同,β-内酰胺酶抑制剂复方制剂的临床前研究需 明确β-内酰胺类药物或酶抑制剂本身的抗菌谱与抗菌活性,尤其是明确酶抑制剂是否具有抗菌活性。需要确定合适的β-内酰胺 类药物与酶抑制剂复方制剂,以及适用的不同酶型的目标病原菌。本文主要介绍新型β-内酰胺酶抑制剂复方制剂临床前研究方 法。临床前研究阶段的β-内酰胺酶抑制剂复方制剂研究包括体外研究和体内研究两部分,前者主要为体外药效学研究和体外药 动学/药效学(pharmacokinetic/pharmacodynamic, PK/PD)研究,常用研究方法包括β-内酰胺类药物和β-内酰胺酶抑制剂复方制剂最 低抑菌浓度测定、最低杀菌浓度测定、抗生素后效应测定及时间杀菌曲线。后者主要为动物药动学研究、感染动物药效学研究 和感染动物药动学/药效学研究。在动物药动学/药效学研究中,需考虑β-内酰胺类药物与酶抑制剂的相互影响。这些研究方法的 应用旨在阐明β-内酰胺酶抑制剂复方制剂两组分药效学特点、药动学相似与否、PK/PD指数及其临床前PK/PD靶值,为进入临 床试验阶段目标适应症及剂量选择提供依据。     

1-甲基-4-亚硝基哌嗪国家标准物质的研制及其核磁定量考察

目的 以1-甲基-4-亚硝基哌嗪为例,介绍亚硝胺类化合物标准物质研制过程,并讨论采用核磁定量方法分析时需注意的问题。方法 采用气质联用、红外光谱和核磁共振法对该原料进行结构确证,定量考察方面进行HPLC纯度分析及水分测定;采用质量平衡法计算1-甲基-4-亚硝基哌嗪的含量,同时辅以定量核磁共振法验证本批原料的含量。结果 本批1-甲基-4-亚硝基哌嗪原料结构准确,在定量核磁考察中发现采用不同内标物对核磁定值结果影响较大。结论 由于1-甲基-4-亚硝基哌嗪本身具有碱性,使得其在核磁定量分析中采用酸性内标物测定易降低含量数值,因此提示对于该类样品在核磁定量过程中应选择适宜的内标物。     

新疆维吾尔药材质量标准研究现状与建议

制定和完善新疆维吾尔药材质量标准是维吾尔医药临床用药的安全性和有效性的重要保障,也是积极推进维吾尔医药产业传承与创新的重要内容。对国家药品标准和新疆地方药品标准所收载维吾尔药材质量标准研究现状进行系统综述,并对维吾尔药材质量标准修订给出相关建议。进一步加强维吾尔药材真伪鉴别、安全性和有效性评价研究,建议引入民族药对照药材作为重要质量控制技术策略,有利于控制维吾尔药材内在质量,健全完善新疆维吾尔药材标准体系,推动维吾尔医药产业迈向现代化和国际化,更好地保障公众用药安全有效。     

速释口服固体制剂人体生物等效性试验豁免药学研究的要求

随着科学认知的不断深入,为缩短药品的批准上市时间,不同药品监管机构相继出台了人体生物等效性豁免的相关法规及技术文件,旨在通过体外研究来替代体内试验。总结和比较国内外相关指导原则对速释口服固体剂型的仿制药药学研究的要求,重点关注存在的差异之处,探讨背后的科学原因,并在最终经国际人用药品注册技术协调委员会协调一致的过程中得到思考和启示,以期增加仿制药被豁免体内试验的成功率、进而降低仿制药的开发成本,但同时亦能保证其质量和疗效与参比制剂一致,真正实现其临床可替代性。     

不同年龄段健康人群骨代谢指标Ⅰ型前胶原N末端前肽的特点分析

目的确定健康中国人群中Ⅰ型前胶原N末端前肽(type Ⅰ procollagen propeptide,PⅠNP)的年龄和性别特异性参考区间。方法采用骨密度测定法测定骨密度正常的中国人群599份血清,建立参考区间。年龄组分为20～29岁、30～39岁、40～49岁、50～59岁、≥60岁。结果在划分中国男性和女性人群的年龄组时,不同年龄组的总PINP存在显著差异。在男性人群中,PⅠNP水平随着年龄的增长而降低,然后在中年后保持稳定。在女性人群中,与男性人群相似的下降趋势与50～59岁年龄组的急剧增加相似。结论本研究初步建立了具有正常骨密度的中国男性和女性人群与年龄相关的PⅠNP参考区间。     

Cartilage assessment using preoperative planning MRI for femoral component rotational alignment

BackgroundSurgical planning of posterior referencing total knee arthroplasty (TKA) using computed tomography (CT) might lead to over-rotation of the femoral component because CT could not detect cartilage thickness of the posterior femoral condyle. The purpose of this study was to examine the rotational alignment difference of the femoral component between magnetic resonance imaging (MRI) and CT.MethodsFor elderly varus osteoarthritic patients, 66 varus osteoarthritic knee patients that underwent primary TKA were selected. Twenty-seven young patients who underwent primary anterior cruciate ligament reconstruction were selected as control. After the transepicondylar axis (CEA), the surgical epicondylar axis (SEA) and the posterior femoral condylar line (PCL) were drawn on CT and on MRI at the same angles as CT. Then, the practical PCL was drawn on MRI considering the cartilage thickness (the cartilage PCL). The angle between the SEA and the cartilage PCL (the cartilage posterior condylar angle (PCA)) was measured as preoperative planning. To investigate the accuracy of preoperative MRI measurement, the cartilage thickness on posterior femoral condyles was directly measured during TKA.ResultsThe cartilage PCA for varus osteoarthritic patients averaged 1.3 ± 1.3°. The cartilage PCA was 1.8 ± 1.0° significantly smaller than the bone PCA (the PCA measured on CT). Meanwhile, the cartilage PCA was 0.2 ± 0.4° significantly larger than the bone PCA in young people. The preoperative angle measurement on MRI strongly correlated with the direct measurement of cartilage thickness during TKA.ConclusionThere was 1.8° of divergence between MRI and CT in varus osteoarthritic patients due to cartilage degeneration of the medial femoral condyle. Cartilage assessment using MRI was useful for femoral component rotational alignment.