Post History

I can't provide a specific answer, but I'll try a general one based on evolutionary theory and (refuted) teleology.

The body is indeed equipped to fight infections. I believe the human immune system is particularly strong, compared to other animals.

However, it is incorrect to think of "immunity" to infections. There is an [ongoing arms race](https://en.wikipedia.org/wiki/Red_Queen_hypothesis) between infectious agents and hosts where one evolves defenses and the other evolves countermeasures. At any given point in evolutionary history, it is not unexpected to find that certain microorganisms are able to overcome defenses of their chosen host and cause problems. This defeats one premise in the question, that of surprise at a healthy body not being able to drain the abscess.

Moreover, not all potential evolutionary improvements are instantly realized. Evolution happens in steps of a generation, which for humans is a few decades. Many changes require multiple steps. If the selective pressure is weak, it can take even longer. Considering that humans arose on the order of 1 million years ago, that's 10-100k generations, not really a huge amount of space to optimize things. We are very much a "WIP" species, many bugs and serious breakage should be expected. Of course, evolution was acting for much longer on our primate and therapsid ancestors, but then non-human tooth diseases are a whole other can of worms.

Lastly, tooth diseases have greatly changed in modern industrial society. The modern diet, which came to be in the last few centuries, is vastly different from what our ancestors experienced for 99% of our evolutionary history. Refined sugar, for example, was not readily available until a few centuries ago, and life histories of humans were much different prior to the advent of modern healthcare and nutrition. Thus, perhaps we should not expect thousands of rounds of selection but merely tens or hundreds in the case of dental disease.

This doesn't really answer the question, but I think it's a sufficient argument for why we shouldn't be **surprised** that nature has endowed us with bodies which cannot drain tooth abscesses. Aside from the answer of *should the abscesses drain on their own*, there is still the question of what prevents them from draining, anatomically speaking. My answer is already long so I will leave the anatomy to a different answer.