为什么尸体的牙齿那么坚固，活人却会蛀牙？

 

为什么人死了，几百年后尸体都腐烂了，牙齿还好好的，不会蛀了，可是活人却偏偏会蛀牙呢？

Why do people die, the corpse will rot after hundreds of years, and the teeth are good and will not decay, but the living people will have tooth decay?

平时看到的几百年的尸体的骨骼、牙齿都不会腐烂，而我们平常看到的“骷髅头”标本都是骨头和牙齿。而牙齿在法医中甚至发展成了法医口腔学，变成了人的“身份认证”。第一个法医口腔学家为美国的 Paul Revere，其为美国独立战争中死去的士兵确定身份。那么为什么软组织会腐烂、硬组织如骨头、牙齿不会腐烂呢？

The bones and teeth of hundreds of years of corpses that we usually see will not rot, but the "skeleton" specimens we usually see are bones and teeth. In forensic medicine, teeth have even developed into forensic stomatology, becoming a person's "identity authentication". The first forensic dentist was Paul Revere of the United States, who identified the soldiers who died in the American Revolutionary War. So why do soft tissues decay, hard tissues such as bones, and teeth not decay?

除了细胞内的酶以外，其实是因为微生物的作用，软组织开始腐烂。人的肠道里有很多微生物，平时因为有免疫系统的存在，所以才能与之抗衡。当人生命停止之后，免疫系统也停止了工作，这些微生物就开始大放厥词，开始“吃”我们的肠道，然后穿破肠道，蔓延到全身其他的部分。这些微生物将人体组织为养料，慢慢“吃”身体的软组织，先从肝脾开始，之后到心脏和大脑。到了后期，软组织腐烂差不多了，里面的骨头露出来，就是“白骨化”尸体了。地下尸体形成的白骨化所需时间约需 5 年以上，土中尸体白骨化所需时间大约为 2-10 年， 有的 10-30 年^[1]。

In addition to the enzymes in the cells, it is actually because of the action of microorganisms that the soft tissues have begun to decay. There are many microorganisms in the human intestines, and they can compete with them because of the existence of the immune system. When a person's life ceases, the immune system also stops working, and these microorganisms begin to speak out, start to "eat" our intestines, then pierce the intestines and spread to other parts of the body. These microorganisms use human tissues as nourishment and slowly "eat" the soft tissues of the body, starting from the liver and spleen, and then to the heart and brain. In the later stage, the soft tissues are almost decomposed, and the bones inside are exposed, which is a "white bone" corpse. The ossification of underground corpses takes more than 5 years, and the ossification of corpses in the soil takes about 2-10 years, and some 10-30 years ^[1].

骨头和牙齿是由什么组成的？的确有有机物，但是大部分组成为无机物。骨骼和牙齿的主要无机成分构成都是羟基磷灰石（骨骼约 2/3，牙釉质约 97%，牙本质约 70%）。

What are bones and teeth made of? There are indeed organics, but most of the composition is inorganic. The main inorganic components of bones and teeth are hydroxyapatite (about 2/3 of bones, about 97% of enamel, and about 70% of dentin).

在骨骼中，羟基磷灰石在胶原纤维内间隙有序排列^[2]。

In bones, hydroxyapatite is arranged in an orderly manner in the interstices of collagen fibers [2].

在牙齿中，主要 97%组成成分也是羟基磷灰石，而牙本质是由 70%的羟基磷灰石组成，因为有无机物的组成，牙齿和骨骼不会“腐烂”掉啦～但是由于里面有机物和水分的丢失，随着时间的推移骨骼牙齿会“风干”，变得脆脆地～

In teeth, 97% of the main component is also hydroxyapatite, and dentin is composed of 70% of hydroxyapatite. Because of the composition of inorganic substances, the teeth and bones will not “rot” out~ but because of the inside With the loss of organic matter and water, bones and teeth will "air dry" and become brittle over time~

Why do living people’s teeth consist of 97% hydroxyapatite (inorganic), and they still "eaten"?

答案是因为酸！虽然牙齿上的细菌不吃羟基磷灰石，但是他们吃我们的食物（比如碳水化合物）会产生酸腐蚀我们的牙齿。牙面上的牙菌斑代谢碳水化合物产生各种有机酸（乳酸、乙酸、丙酸）。酸慢慢地到达牙釉质羟基磷灰石晶体表面，并与蛋白质和脂质竞争晶体表面的活性部位，然后使晶体脱矿、形成蛀牙。

The answer is because of acid! Although the bacteria on the teeth do not eat hydroxyapatite, they eat our food (such as carbohydrates) will produce acid corrosion of our teeth. The plaque on the tooth surface metabolizes carbohydrates to produce various organic acids (lactic acid, acetic acid, propionic acid). Acid slowly reaches the surface of enamel hydroxyapatite crystals and competes with proteins and lipids for active sites on the crystal surface, and then demineralizes the crystals and forms tooth decay.

通过这个我们发现，蛀牙需要存在细菌、食物、宿主、时间（也就是龋病病因四因素），一个一个来分析。

Through this we found that tooth decay needs to have bacteria, food, host, and time (that is, the four factors of the cause of dental caries), and analyze them one by one.

1. The first is bacteria: Are the bacteria that decompose a corpse the same as the bacteria that cause tooth decay?

2016 年，有学者在 science 上发表了文章^[3],无论你死在哪里，分解你尸体的那群细菌都是相似的……环境不同的土壤中储存有类似的尸体微生物库，最后使得分解尸体的微生物类似。Javan 等学者^[4]分析了刑事案件中的 27 具尸体，死亡时间在 3.5-270 小时之间，其中以专性厌氧的梭状芽胞杆菌为主。虽然牙菌斑的致病菌也有很多，研究较多的是变异链球菌、放线菌、乳杆菌等，看起和分解尸体的丰度不同。

In 2016, a scholar published an article in science[3], no matter where you die, the bacteria that decompose your corpse are similar...Similar corpse microbial pools are stored in soils with different environments, and finally make decomposition The microbes of the corpse are similar. Scholars such as Javan [4] analyzed 27 corpses in criminal cases, the death time was between 3.5-270 hours, among which obligate anaerobic Clostridium spp. Although there are many pathogenic bacteria of dental plaque, the most studied are Streptococcus mutans, Actinomycetes, Lactobacillus, etc., which seem to have different abundances from the decomposed corpse.

人死了以后就没有食物吃进口腔啦！我们常常说小朋友不能多吃糖，因为一多吃口腔里的牙菌斑就越高兴，那就可以分解碳水化合物腐蚀我们的羟基磷灰石牙齿啦！

After a person dies, there is no food to eat! We often say that children should not eat more sugar, because the more plaque in the mouth, the happier it will decompose carbohydrates and corrode our hydroxyapatite teeth!

然而，人死了之后，口腔里面的微生物没有“食物原料”了，所以也就不能形成蛀牙。

However, after a person dies, the microorganisms in the oral cavity have no "food ingredients", so tooth decay cannot be formed.

可能有的人说，人自体的腐烂的软组织也可以给口腔细菌提供原料呀？的确哈，大部分研究认为蛀牙的食物是蔗糖，蛀牙细菌的确也可以利用葡萄糖的，但是蛀牙细菌利用葡萄糖的效率比较慢，所以还是蔗糖更高。

Some people may say that the decaying soft tissues of the human body can also provide raw materials for oral bacteria? Indeed, most studies believe that the food for tooth decay is sucrose. Tooth decay bacteria can indeed use glucose, but the efficiency of the use of glucose by tooth decay bacteria is slower, so sucrose is still higher.

虽然每个人死了之后都一样，但是细菌的附着是需要活人的唾液中的酸性唾液蛋白还有黏蛋白的！人死了之后口腔内的环境改变，细菌也无法附着上去。

Although everyone is the same after death, the attachment of bacteria requires the acidic salivary protein and mucin in the saliva of living people! After a person dies, the environment in the oral cavity changes, and bacteria cannot attach to it.

蛀牙不是一两天形成的！要经常吃糖（有了食物）、而且经常不好好刷牙（有了牙菌斑），而且上面的前提是经常（时间）才能得了蛀牙。那么在尸体上，如果有正正好，就是有了那波细菌！就是有了那波可以供细菌分解的食物！环境也得当！那么这个“正正好”的条件也存在不了多久，可能细菌刚开始要作妖产酸，它们的原材料就没有了。

Tooth decay does not form in one or two days! You have to eat sugar often (with food), and often do not brush your teeth well (with plaque), and the premise above is that you can get tooth decay often (time). Then on the corpse, if it happens to be, there is that wave of bacteria! There is that wave of food that can be broken down by bacteria! The environment is also right! Then this "just right" condition won't exist for long. Maybe the bacteria just started to demonize and produce acid, and their raw materials will be gone.

From website: https://daily.zhihu.com/