Bussiness ManagementMBAstrategyHuman ResourceMarketingHospitalityE-commerceInternational Tradingproject managementmedia managementLogisticsFinanceAccountingadvertisingLawBusiness LawEducationEconomicsBusiness Reportbusiness planresearch proposal
英语论文题目英语教学英语论文商务英语英语论文格式商务英语翻译广告英语商务英语商务英语教学英语翻译论文英美文学英语语言学文化交流中西方文化差异英语论文范文英语论文开题报告初中英语教学英语论文文献综述英语论文参考文献
ResumeRecommendation LetterMotivation LetterPSapplication letterMBA essayBusiness Letteradmission letter Offer letter
澳大利亚论文英国论文加拿大论文芬兰论文瑞典论文澳洲论文新西兰论文法国论文香港论文挪威论文美国论文泰国论文马来西亚论文台湾论文新加坡论文荷兰论文南非论文西班牙论文爱尔兰论文
小学英语教学初中英语教学英语语法高中英语教学大学英语教学听力口语英语阅读英语词汇学英语素质教育英语教育毕业英语教学法
英语论文开题报告英语毕业论文写作指导英语论文写作笔记handbook英语论文提纲英语论文参考文献英语论文文献综述Research Proposal代写留学论文代写留学作业代写Essay论文英语摘要英语论文任务书英语论文格式专业名词turnitin抄袭检查
temcet听力雅思考试托福考试GMATGRE职称英语理工卫生职称英语综合职称英语职称英语
经贸英语论文题目旅游英语论文题目大学英语论文题目中学英语论文题目小学英语论文题目英语文学论文题目英语教学论文题目英语语言学论文题目委婉语论文题目商务英语论文题目最新英语论文题目英语翻译论文题目英语跨文化论文题目
日本文学日本语言学商务日语日本历史日本经济怎样写日语论文日语论文写作格式日语教学日本社会文化日语开题报告日语论文选题
职称英语理工完形填空历年试题模拟试题补全短文概括大意词汇指导阅读理解例题习题卫生职称英语词汇指导完形填空概括大意历年试题阅读理解补全短文模拟试题例题习题综合职称英语完形填空历年试题模拟试题例题习题词汇指导阅读理解补全短文概括大意
论文作者:佚名论文属性:短文 essay登出时间:2009-12-01编辑:lisa点击率:3721
论文字数:500论文编号:org200912011103394775语种:英语 English地区:中国价格:免费论文
关键词:DEVELOPMENT BIOLOGY OF ENAMEL
To understand how molecular biologists are attacking the problem of inherited disorders of enamel, a brief review of dental embryology is needed, The early stages of tooth development are characterized by a budding off of epithelium from the oral epithelium itself into the area of the future alveolar bone. This tooth precursor will give rise to both primary and permanent dentitions in the area (incisor, premolar, etc.). Only the inner layer of the double layer of cells (the inner enamel epithelium) has a functional tooth fate-it gives rise to the enamel. The sequence in which this occurs is now well documented and provides an excellent example of how embryonic tissues differentiate under the influence of adjacent but developmentally different cells. In this case, neural crest cells migrating into the dental lamina area from around the developing neural tube came to lie in an intimate but not touching relationship next to the inner enamel epithelium. The two developmentally different cell layers (inner enamel epithelium [enamel] and the neural crest [dentin]) are separated by an extracellular matrix, the ECM. The sequence of molecular events leading to enamel formation may be summarized as follows:
l. Neural crest cells secrete an enamel-inducing substance that migrates across the intervening matrix (ECM) as a matrix vesicle and makes contact with the inner enamel epithelium (IEE).
2. This enamel-inducing substance penetrates the IEE cell and activates that cell to begin producing its organic enamel matrix.
3. The future enamel cell (preamloblast) in turn sends a different organic molecule (message) back across the matrix to the neural crest cells (preodontoblasts) where it signals these cells to initiate the full scale production of dentin.
4. The matrices of both cell types (ameloblast and odontoblast) consist of specific proteins that will ultimately calcify into enamel, which is much harder than dentin. Molecular biologists working in this area recognize two proteins in enamel (amelogenin and enamelin) and a phosphoprotein in dentin.
To be consistent with current genetic concepts, we presume that all the inherited defects of enamel can be traced to DNA alterations (mutations) that will result in errors in either one or both of these proteins. The most intriguing dental research today is l) the attempt to localize the genes for these proteins to a given chromosome and 2) the biochemical identification of specific defect in the protein that prevents it form functioning normally. The following is a discussion of genetic principles best exemplified by the heritable disorders of enamel.
Based upon the clinical appearance, radiographic characteristics and microscopic features, oral pathologists have recognized three major types of inherited enamel defects: hypoplasia, hypocalcification and hypomaturation. These terms also provide us with the general description of the disease phenotypes. For example, in type l, enamel hypoplasia, the enamel is hard, well calcified but defective in amount. Two types of deficient enamel phenotypes are seen: generalized (all the enamel) and localized (pits and grooves in specific areas). Type 2, hypocalcification. Disorders are those in which the enamel matrix is so drastically altered, that normal calcificatio本论文由英语论文网提供整理,提供论文代写,英语论文代写,代写论文,代写英语论文,代写留学生论文,代写英文论文,留学生论文代写相关核心关键词搜索。