sorry can't type Chinese.

A. based on what you said, I guess the decay you had now was caused by the wisdom tooth which might not erupt in the right place and the decay has been progressed for more than 2 years. Now it's too deep to keep the pulp (basiclly the nerve) intact.

exactly, 昨天那医生就是这么和我说的~ 不过我觉得就算早发现也没有办法补牙阿，因为decay在牙龈以下，对吗？

Even though the decay is subgingival, it can be restored only after the wisdom tooth is extracted. But now since you already have the symptoms of pulpitis and usually it's irereversible, the root canal is the best option.

B. the decay is below the gum margin which will cause any treatment difficult. The small surgery your dentist talked about is not to extend the gum, but it's called crown lengthening--cut off some gum tissue to make the defect area exposed better. This is not for the root canal therapy but for the crown after the therapy.

所以我应该先做根管，再做这个“crown lengthening”,如果它的目的是为了重建crown,那么每个根管术之后都需要它了? 除非不加冠？那么我们学校的dentist就需要refer我两次，一次是去做根管，一次是去做crown lengthening,他好像和我说牙冠重建学校自己能做。

I'm not 100% sure about the order of these procedures, but root canal might be the first. The crown lengthening is to remove some gum and bone tissue to make the decay area at least at the gum margin level so that the decay can be completely removed and later the margin of the crown will be at the same level (even above) of the gum margin which causes less irritation and makes the cleaning much more efficient. The crown lengthening can be done by a general dentist or a periodontal specialist.

有没有可能做普通的补牙呢？还是因为decay在牙龈以下根本没办法补？所以必须得做根管？

See the answer for the first question.  The crown is necessary because the tooth becomes brittle after the root canal therapy since the pulp is dead and a big portion of the tooth is missing.

C. If you are not sure about it, get a consultation from an endodontic specialist. You may ask your dentist to refer you one. This is somewhat a complicated case and specialists are better for handling it.

D. personally I don't suggest you go back to do it. I'm not implying anything. You now have a pulpitis and it's better to get treated asap. Second, the quality of RCT and the crown here can be guaranteed if you find a good specialist or even general dentist.

这个根管和crown lengthening都算常规项目么？

我的意思是，听上去满恐怖的，在国内还可以挂挂专家门诊什么的，在这里我也不知道医生水平怎么样呀~

我们学校的牙医说会把我refer到specialist那里去，

那么这样我就不用担心治疗质量了？我为什么觉得中国医生老做这些，会手法比较熟练~汗。。。

As I mentioned before, the endodontic specialists here are particularly trained for the root canal therapy and they are very good at it. Also the standards and criteria here are pretty high and this should not be a worry for you. If you are still worried, when you go to the specialist, ask as much questions as you want, such as how many canals I have for this tooth, is any of them blocked? You can ask to see the x-ray after the therapy to make sure all the canals are filled with opaque materials all the way to the tip of the canals.

Hope this helps. Let me know if you have more questions.