经济学人下载:牙科X光 请不要太频繁

Science and technology
科学技术

Dental X-rays
牙科X光

Little and not often, please
请不要太频繁,一点就好

Confirmation that dental X-rays can be bad for you
已证实牙科X光对你是有危害的

If you are a suspicious type you may be disturbed by the fact that, despite reassurances of the safety of the procedure, dentists and their technicians, when administering X-rays, usually step out of the room while the deed is done.
尽管牙科X光实施程序的安全已得到了证实，牙医和技工们还是会在拍X光时离开房间。如果你是一个多疑的人，这样的事实可能会困扰你。

Not only that, they often drape a lead-lined apron over your body to protect your vital organs. Well, all but one: your brain.
不但如此，在拍X光时他们还经常用铅衬的围裙盖住你的身体以保护重要器官—但是是除了大脑以外的所有器官。

A study by Elizabeth Claus, of Yale University, just published in Cancer, suggests your suspicions might be justified.
耶鲁大学的伊丽莎白. 克劳斯医生的一项研究结果刚在癌症杂志上发表。此项研究表明你的怀疑可能并非杞人忧天。

Dr Claus thinks she has identified, in those who have had dental X-rays often, a significant rise in the admittedly small risk of developing a brain tumour.
克劳斯医认为她已发现那些经常拍牙科X光的病人得脑瘤的风险确实有显著升高。

In rich countries, five men in every 200,000, and twice as many women, develop tumours called meningiomas that affect the membranes surrounding the brain.
在富裕的国家里，每200，000人中就有5名男性得一种叫脑脊膜瘤的脑瘤，此瘤破坏脑膜，而且发病的女性人数是男性的两倍。

Meningiomas account for a third of primary brain tumours.
脑脊膜瘤的患者占原发性脑瘤患者的三分之一。

Only about 2% of them are malignant, but non-malignant does not mean non-dangerous.
只有2%的脑脊膜瘤是恶性的，但是非恶性并不代表没有危险。

Even a benign meningioma can kill.
即使是良性的脑脊膜瘤也会至死。

Around 30% do so within five years of diagnosis. Symptoms can include seizures and blindness, and treatment may involve surgery, chemotherapy or, ironically, radiotherapy.
大约30%的至死病例是发生在确诊后5年。这种脑瘤的症状包括:痉挛和失明，可以通过手术，化疗，或者用放射疗法来进行治疗。

Ironically, because past research studying the after-effects of exposure to things like atom bombs and radiation treatments for cancer suggests the most important environmental risk factor for meningiomas is ionising radiation.
讽刺的是，对人体暴露于类似原子弹辐射和癌症放射疗法的后果的研究显示，产生脑脊膜瘤的最主要的环境风险因素是离子辐射。

These days, however, the main source of ionising radiation for most people is neither fallout from bombs nor radiotherapy; it is dental X-rays.
然而，现今影响大多数人的离子辐射的主要源头既不是原子弹的辐射尘埃也不是放射疗法，而是牙科X光。

Despite that, surprisingly little research has been done on those X-rays' effects.
尽管如此，令人惊讶的是几乎没有牙科X光对人类影响的研究。

Dr Claus and her colleagues have tried to plug the gap.
克劳斯医生和她的同事们已在努力填补这一空白。

They studied 1,433 Americans who have had meningiomas and compared them with 1,350 others who have not.
他们研究了1433名美国的脑脊膜瘤患者，并把他们与1350名非患者进行对比。

These others were chosen to match the study group's age profile, sex ratio and dwelling place.
这些被选择的非患者构成符合研究所需的年龄组成，性别比例和所在居住地。

The researchers then inquired about both groups' family, medical and dental histories.
研究人员获取了这两组研究对象的家庭，病史，和牙病史的数据。

In the case of their dental histories, participants were asked whether they generally had standard X-rays, known as bitewings, every year, or never had them, or fell somewhere in between.
对于牙病史，参与者被问及他们是否通常每年接受常规的牙医X光，或是从没拍过，或是介于以上两者之间。

They were also asked how often they had had panoramic X-rays—so-called panorexes—taken of their entire mouths, and whether they had ever had braces, the fitting of which often involves a panoramic X-ray.
他们还被问及拍全颌x光—对整个口腔拍摄X光的经常性，以及是否做过牙齿整形—通常是会要求拍全颌x光。

The researchers found that people who had had a meningioma were more than twice as likely as those who had not to have had at least one bitewing X-ray.
研究发现患脑脊膜瘤的病人发病的可能性是那些没拍过咬翼片的人的两倍以上。

And the more bitewings they had been given, the greater that likelihood was.
拍咬翼片次数越多的人，可能性越大。

Even more troubling was the finding that people who had been given a panorex when they were under ten had 4.9 times the normal risk of developing a meningioma.
更让人担忧的发现是十岁以下拍过全颌x光的人患脑脊膜瘤的概率是正常风险值的4.9倍。

To be fair, only 22 participants in the study had both had a panorex and developed such a tumour.
公平地说，只有22名研究参与者拍过全颌x光并患有脑脊膜瘤。

But according to Dr Claus, the panorex was not common when most of the people in the study had been children.
但据克劳斯医生说，以前研究对象大部分是儿童，拍全颌x光的现象并不普遍。

Nowadays, she says, before getting braces all the kids have it.
如今，她说，在牙齿整形之前所有儿童都拍过全颌x光了。

What these results mean in practice is debatable.
以上研究发现的实际意义还是有争议的。

The radiation dose from an individual dental X-ray, Dr Claus points out, has gone down by about half over the past 30 years or so.
克劳斯医生指出，单次牙医X光的辐射剂量已在过去的30年降低到原来的一半左右。

In addition, some dentists and orthodontists—though far from the majority—have turned to digital methods that expose patients to even lower levels. But others are using fancy new techniques like cone-beam computerised tomography which actually expose people to much higher levels of radiation.
另外，一些牙科医生和整牙医师—虽然并不占多数，已转用电子手段，这就更大程度的降低了病人所受的辐射程度。

Moreover, guidelines from the American Dental Association state that healthy adults should have a bitewing X-ray no more than once every two or three years, and that there is little reason to X-ray patients who do not have symptoms.
此外，美国牙科协会的指南规定健康成年人每两到三年不应拍超过一次的咬翼片，并且没有理由给无病症的病人拍X光。

These are policies which Dr Claus describes as quite reasonable.
克劳斯医生认为这些政策是很合理的。

But if what her participants told her is true, not all dentists are heeding their own professional body's advice.
如果研究参与者所告知的都是事实的话，可见并不是所有牙科医生都留心自身的建议。

Most of those who took part in the study reported having at least one X-ray a year.
大多数参与研究的人表示一年至少拍了一次x 光。

Dr Claus's work, then, is a timely reminder that X-rays are dangerous, that dentists should use them sparingly and that patients who have suspicions about their use are not necessarily paranoid.
克劳斯医生的工作及时地提醒了我们，拍x光是有危险的，牙医应该保守地使用它们，这样看来病人们对x光的疑虑并不是所谓的妄想。