跟读练习: Pascal Magne Part #2 - 通过视频学习英语口语
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Music And
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if you take these basic material properties of enamel, like the elastic modulus, the thermal extension,
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expansion coefficient, the ultimate tensile strength, first you will see that enamel is very stiff,
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about 80 gigapascal of stiffness.
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Compared to dentin, it is much more.
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It is almost five times.
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Enamel is very brittle and very low resistance in tensile strength.
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And this is very important.
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It's a major difference between enamel and dentin.
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Dentin is much tougher and can resist more in tensile stress in crack propagation.
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For enamel, what is the closest substitute?
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What do you think is the closest substitute?
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There are not many possibilities.
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We have a material that is a similar elastic modulus.
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We have a material that has almost the exact same thermal expansion.
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And in this class of material, the weakest that we found is still two to four times stronger than enamel.
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And what is this material?
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Of course it is porcelain.
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And what porcelain?
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The weakest porcelain we have on the market.
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It is feldspatic porcelain.
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Still I told you two to four times stronger than enamel in tensile strength.
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For dentin, as you guessed, dentin is flexible, is bendable.
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What do we have that is five times less rigid than enamel, that is in the same range of elastic modulus.
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Unfortunately, there is no material in that range that has really a good thermal expansion.
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It is composite resins.
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As you see, composite resins are also a little less tough than dentin.
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And that's not a big problem in that case because as you can see,
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feldspatic porcelain have like a reserve of strength that we can spend to compensate on the weakness of the composite resin.
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So now we just need a dentine enamel substitute and what is the dentine enamel junction substitute, excuse me, it is dentine bonding.
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And I must tell you I am very confident in the way we bond to dentin today.
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Because, unlike the dentin enamel junction, current dentin bonding agent, especially fourth generation,
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not the sixth, not the fifth, the sixth and the seventh,
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the fourth generation dentin bonding agent act very much as an interphase,
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exactly like the dentin enamel junction we have inter diffusion between
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two materials on one side the collagen fibers of dentin on the other side the resin component
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and this is not a simple interface it is an interface
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I hope you see the difference in the pronunciation the S versus the C it's an interface
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and I have to tell you I could spend an hour on dentin bonding.
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I'm not going to do that of course, but I want to tell you that for good dentin bonding there are four steps required.
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And these four steps you cannot go around.
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These are separate, let's call them bottles or products and separate steps that must be applied to dentin.
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And the first one is etching, deneralizing the collagen surface to obtain this porous layer.
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The second step is using a primer, a hydrophilic resin that is able to penetrate the the deminolized collagen.
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It has to be hydrophilic and you cannot mix too much the hydrophilic and the hydrophobic.
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The hydrophobic is going to be the next layer which is the bonding resin.
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Now you can't mix these three in the same bottle.
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Of course you can, But what you will get is kind of a salad dressing
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that is not going to work as well as if you use each of these products independently and separately.
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And there is a fourth step, I told you fourth step.
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What is the fourth step to bonding to successful bonding it
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is the use of light pre-curing the adhesive before you apply the restorative material
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when we do direct restorations we always do
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that we we pre-cure the adhesive before we actually place the restoration for indirect techniques it is not popular yet
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but I I will show you, we have now a number of works showing that the adhesive should be placed and pre-cured and before you take your impression,
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which is the only way to solve the problematic that is specific to indirect restoration.
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I will share that with you later.
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So, can we do dentin bonded veneers?
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The answer is yes.
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and I will not say three times, yes, yes, yes, we can do dentin bonded veneer, but we need to know how to bond to dentin.
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And this requires the technique I mentioned just before.
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You see a case here, I will show you more details just after, but with a large exposure of dentin,
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we have actually enamel only remaining at the margins in the interproximal and the incisal.
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If you note carefully, what you will see is that dentin has been sealed immediately and before taking the impression.
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It is the technique called immediate dentin sealing.
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And it is absolutely fundamental when you are doing indirect bonded restoration.
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I will talk to you about that a little more extensively later.
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So you see the same case.
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You see the picture taken just before taking the impression, before making the impression.
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And you see that dentin is sealed already before that, and I will show you the step by step.
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This case was also using a very nice layering technique with the simulation of the root portion of the tooth to simulate,
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to maintain the good width by length ratio in that case.
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It was a a case of severe erosion of the dentine, of enamel, excuse me, that led to major dentine exposures.
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You see the case five years later.
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So I will talk more about this problem of dentine
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and let's go now in a general description of what can be done with bonded porcelain restoration.
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I like to call them bonded porcelain restoration instead of veneers
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because you will see you can do much more than a simple fingernail type restoration on an incisor.
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It is much more comprehensive than that.
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As I said,
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bonded porcelain restorations by definition allow you to be biomimetic allows you to let's say abandon the principles of prosthodontics
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that we've all learned at dental school stabilization
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and retention this is now replaced by adhesion
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and it is kind of a i don't want to say a leap of faith
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but once once you see what you can do with
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that you will do fantastic and and you have to believe first
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and i'm here today making maybe and hopefully to make you believe even more in
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that approach so we need dentin-like and enamel-like materials now we understand
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that and what are these materials we know they are simple traditional materials
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that we are going to use in an advanced way
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but the technique themselves itself is not very advanced
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because the composites we need are micro hybrids
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and the ceramics we need are simple feldspatic How long have we had these materials on the market?
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Micro hybrids for 15 years, feldspatic, porcelain now for even more than that.
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And so these are very traditional materials.
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But together, together with dentin bonding, which is maybe the only thing that was really refined recently,
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then we can have a fantastic approach to biomimetics.
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And dentin boning, I tell you, is maybe the only thing I changed in the technique recently.
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The rest was available to us and has been available to us for almost 20 years now.
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So composites will give us adhesion and economy of tooth substrate.
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Adhesion will allow us to forget about stabilization and retention.
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Porcelain will give us durability and aesthetics.
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This is very important.
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We know that composite materials for this type of restoration are not able to fulfill these criteria of durability
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and aesthetics in the long term.
背景与上下文
在这段视频中，Pascal Magne深入探讨了牙釉质和牙本质的物理特性。讲者详细描述了牙釉质的弹性模量、热膨胀系数和抗拉强度等关键数据，这些信息不仅对于牙科领域的专业人士至关重要，也对那些想通过看YouTube学英语的学生提供了科学背景。掌握这些术语能够帮助学习者在专业对话中更加自信，并提升他们的英语听说能力。
日常交流中的五个重要短语
- 弹性模量 (elastic modulus): 指材料在应力下变形的能力。
- 热膨胀系数 (thermal expansion coefficient): 描述材料随着温度变化而变化的尺寸。
- 抗拉强度 (tensile strength): 材料在受拉时承受力的能力。
- 界面 (interface): 不同材料之间的接触区域。
- 去矿化 (demineralization): 去除材料中的矿物质，形成多孔层。
逐步影子跟读指南
对于初学者来说，掌握视频中的技术和术语可能会有一定难度。以下是一些建议，帮助你通过英语影子跟读不断提升自己的听说能力：
- 观看视频：首先，观看视频并注意讲者的发音和语调。试着理解每个短语背后的意思，尤其是那些与牙科相关的术语。
- 分段练习：将视频分成小段，重复每段以便更好地理解。在发音的时候，尽量模仿讲者的语调和节奏。
- 使用本地化术语：在影子跟读时，尝试将与牙釉质和牙本质相关的术语融入你的练习中，这样能增加你在专业交流中的自信。
- 记录自己的声音：录下你的影子跟读练习，之后与原视频对比，找出发音上的不足。
- 重复与巩固：定期复习这些重要短语，确保它们在你的日常对话中变得自然。可以通过使用影子跟读网站来找到更多练习材料。
通过以上方法，学习者可以在日常生活中更加自如地使用英语，同时也能深入理解材料科学的相关理论，帮助他们在未来的专业领域中脱颖而出。
什么是跟读法？
跟读法 (Shadowing) 是一种有科学依据的语言学习技巧，最初开发用于专业口译员的培训，并由多语言者Alexander Arguelles博士普及。这个方法简单而强大：您在听英语母语原声的同时立即大声重复——就像是一个延迟1-2秒紧跟说话者的影子。与被动听力或语法练习不同，跟读法强迫您的大脑和口腔肌肉同时处理并模仿真实的讲话模式。研究表明它能显着提高发音准确性，语调，节奏，连读，听力理解和口语流利度——使其成为雅思口语备考和真实英语交流最有效的方法之一。