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健康:了解“智齿”

kira86 于2009-01-24发布 l 已有人浏览
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Wising Up About Wisdom Teeth迅雷专用 This is the VOA Special English Health Report.Wisdom teeth are normally t
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Wising Up About Wisdom Teeth


迅雷专用

This is the VOA Special English Health Report.

Wisdom teeth are normally the last teeth to appear in the mouth. It usually happens when people are older and wiser. That is, when they are in their late teenage years or early twenties.

Wisdom teeth are molars, or chewing teeth at the back of the mouth. The third set of molars, if you have them, are your wisdom teeth. 

TeethThey can grow into place normally and never cause a problem. But often there is not enough room for them in the mouth. They might crowd the other teeth. Sometimes they even push through the gums sideways.

An impacted wisdom tooth is one that fails to completely rise through the gums -- the term is erupt. Wisdom teeth that only partly erupt can leave space for bacteria to enter around the tooth.  Infection is a risk in these cases.

Experts say people should have their mouths examined between the ages of sixteen and twenty for placement of their wisdom teeth. X-rays can show wisdom teeth below the gums. Those that are not well aligned and become impacted are often removed.

The American Dental Association says removal is generally advised when wisdom teeth only partly break through the gums. Removal is also advised if there is a chance that poorly aligned wisdom teeth will damage other teeth. And removal is called for in cases where fluid collects around a wisdom tooth that is partly or fully below the gum.

But why do we have wisdom teeth if we often need to get them removed? One theory has to do with our diets. Scientists say the diet of prehistoric humans probably required more chewing teeth. Life was probably a little rougher on the teeth back then, too. So it was good to have extras.

The removal of wisdom teeth is performed by oral surgeons. They say if removal is advised, the best time to do it is before the teeth cause any problems or pain.

The American Association of Oral and Maxillofacial Surgeons says young adults are the best candidates for wisdom teeth removal. The group says older patients may be at greater risk for disease in the tissue surrounding the molars.

Patients can have general anesthesia during the operation. Or they might choose to have a local painkiller and remain awake. It may depend on the condition of the wisdom teeth and the number to be removed.

After surgery, there can be swelling of the gums and face and some pain. Both can be treated with cold wraps and medication.

And that's the VOA Special English Health Report, written by Caty Weaver. I'm Faith Lapidus.

智齿的由来
  
智齿是指人类口腔内,牙槽骨上最里面的上下左右各一的四颗第三磨牙。因为这四颗第三磨牙正好在 20岁左右时开始萌出,此时人的生理、心理发育接近成熟,于是被看做是“智慧到来”的象征,故称它为“智齿”——智慧之齿。其实,从现代医学的观点看,智齿是人类进化的必然。众所周知,“用进废退”是生物进化论中的一个普遍规律。智齿就是极好的例证。
  
智齿,学名第三大臼齿,俗称智慧齿,立事牙,尽头牙,是口腔最靠近喉咙的牙齿,如果全部生长出来一共4颗,上下颚各两颗,一般是于16岁或之后才生长出来。相较于幼儿时期长出的乳齿与儿童时期更换的恒齿,智齿通常是在人类心智已经趋于成熟时才长出,因而得名。在智齿的生长方面,个体差异很大,有的人20岁之前,有的人40、50岁才长,有的人终生不长,这都是正常的。而且四颗智齿也不是都必然会长全,某些人的智齿可能只长1至2颗,有的智齿甚至长到一半就不再生长,这种情况称为智齿阻生。智齿的位置从门牙牙缝开始,由一侧门牙向里数牙齿数目,如果有第八颗牙,它就是智齿。
  
智齿是如何生长的?
  
在青春后期,颌骨发育到接近成人大小。但有些人颌骨还不够大,没有足够位置供智齿萌出。智齿就会阻生在颌骨内,向其他方向生长。可能只有部分牙冠露出牙龈,或完全埋在颌骨里。牙根可能变形或向上颌窦或下颌骨神经所在部位生长,这很危险。

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