為什么人死了，幾百年后尸體都腐爛了，牙齒還好好的，不會蛀了，可是活人卻偏偏會蛀牙呢？

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?

平時看到的幾百年的尸體的骨骼、牙齒都不會腐爛，而我們平?？吹降?ldquo;骷髏頭”標(biāo)本都是骨頭和牙齒。而牙齒在法醫(yī)中甚至發(fā)展成了法醫(yī)口腔學(xué)，變成了人的“身份認(rèn)證”。第一個法醫(yī)口腔學(xué)家為美國的 Paul Revere，其為美國獨(dú)立戰(zhàn)爭中死去的士兵確定身份。那么為什么軟組織會腐爛、硬組織如骨頭、牙齒不會腐爛呢？

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?

除了細(xì)胞內(nèi)的酶以外，其實(shí)是因?yàn)?b>微生物的作用，軟組織開始腐爛。人的腸道里有很多微生物，平時因?yàn)橛忻庖呦到y(tǒng)的存在，所以才能與之抗衡。當(dāng)人生命停止之后，免疫系統(tǒng)也停止了工作，這些微生物就開始大放厥詞，開始“吃”我們的腸道，然后穿破腸道，蔓延到全身其他的部分。這些微生物將人體組織為養(yǎng)料，慢慢“吃”身體的軟組織，先從肝脾開始，之后到心臟和大腦。到了后期，軟組織腐爛差不多了，里面的骨頭露出來，就是“白骨化”尸體了。地下尸體形成的白骨化所需時間約需 5 年以上，土中尸體白骨化所需時間大約為 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].

骨頭和牙齒是由什么組成的？的確有有機(jī)物，但是大部分組成為無機(jī)物。骨骼和牙齒的主要無機(jī)成分構(gòu)成都是羥基磷灰石（骨骼約 2/3，牙釉質(zhì)約 97%，牙本質(zhì)約 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，羥基磷灰石在膠原纖維內(nèi)間隙有序排列^[2]。

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

在牙齒中，主要 97%組成成分也是羥基磷灰石，而牙本質(zhì)是由 70%的羥基磷灰石組成，因?yàn)橛袩o機(jī)物的組成，牙齒和骨骼不會“腐爛”掉啦～但是由于里面有機(jī)物和水分的丟失，隨著時間的推移骨骼牙齒會“風(fēng)干”，變得脆脆地～

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?yàn)?b>酸！雖然牙齒上的細(xì)菌不吃羥基磷灰石，但是他們吃我們的食物（比如碳水化合物）會產(chǎn)生酸腐蝕我們的牙齒。牙面上的牙菌斑代謝碳水化合物產(chǎn)生各種有機(jī)酸（乳酸、乙酸、丙酸）。酸慢慢地到達(dá)牙釉質(zhì)羥基磷灰石晶體表面，并與蛋白質(zhì)和脂質(zhì)競爭晶體表面的活性部位，然后使晶體脫礦、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.

通過這個我們發(fā)現(xiàn)，蛀牙需要存在細(xì)菌、食物、宿主、時間（也就是齲病病因四因素），一個一個來分析。

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，有學(xué)者在 science 上發(fā)表了文章^[3],無論你死在哪里，分解你尸體的那群細(xì)菌都是相似的……環(huán)境不同的土壤中儲存有類似的尸體微生物庫，最后使得分解尸體的微生物類似。Javan 等學(xué)者^[4]分析了刑事案件中的 27 具尸體，死亡時間在 3.5-270 小時之間，其中以專性厭氧的梭狀芽胞桿菌為主。雖然牙菌斑的致病菌也有很多，研究較多的是變異鏈球菌、放線菌、乳桿菌等，看起和分解尸體的豐度不同。

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.

人死了以后就沒有食物吃進(jìn)口腔啦！我們常常說小朋友不能多吃糖，因?yàn)橐欢喑钥谇焕锏难谰呔驮礁吲d，那就可以分解碳水化合物腐蝕我們的羥基磷灰石牙齒啦！

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，口腔里面的微生物沒有“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.

可能有的人說，人自體的腐爛的軟組織也可以給口腔細(xì)菌提供原料呀？的確哈，大部分研究認(rèn)為蛀牙的食物是蔗糖，蛀牙細(xì)菌的確也可以利用葡萄糖的，但是蛀牙細(xì)菌利用葡萄糖的效率比較慢，所以還是蔗糖更高。

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.

雖然每個人死了之后都一樣，但是細(xì)菌的附著是需要活人的唾液中的酸性唾液蛋白還有黏蛋白的！人死了之后口腔內(nèi)的環(huán)境改變，細(xì)菌也無法附著上去。

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.

蛀牙不是一兩天形成的！要經(jīng)常吃糖（有了食物）、而且經(jīng)常不好好刷牙（有了牙菌斑），而且上面的前提是經(jīng)常（時間）才能得了蛀牙。那么在尸體上，如果有正正好，就是有了那波細(xì)菌！就是有了那波可以供細(xì)菌分解的食物！環(huán)境也得當(dāng)！那么這個“正正好”的條件也存在不了多久，可能細(xì)菌剛開始要作妖產(chǎn)酸，它們的原材料就沒有了。

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/