Once upon a time, I had a tooth that had a cavity. It bothered me, and even hurt quite a bit occasionally, so on at least three separate occasions I specifically pointed it out to my dentist. Each time, he looked at it for about five seconds and said, "It's fine."
Fast forward to about six months after the last time he said that - this would be the end of spring break 2005 - and it was starting to bother me. I took some tylenol and it was fine. Then I ended up on a train for 24 hours, and at this point the tylenol had completely stopped working. When I got back to school, I immediately had to make a dentist's appointment. By the time I got there, I hadn't slept or eaten for three days.
An X-ray revealed an infection about the size of a nickel in the root of my tooth. Turns out there was a small cavity near the gumline, which had gone untreated so long that I now needed a root canal. The swelling was bad enough that they couldn't even give me a topical painkiller, so I got the distinct pleasure of having a dentist drill through an unanesthetized nerve. (The drilling hurt way less than the toothache, at this point.) The oral surgeon remarked it was the worst she'd ever seen. They had to do it in two parts, basically drilling a hole in my tooth and letting the infection drain for a few days before sending me back so they could fill it. (They also gave me some Vicodin, which was completely ineffective until several hours later when the swelling finally went down a bit.)
Fast forward to now, and I need to visit an endodontist because by the time a non-incompetent dentist took a look at the tooth it was essentially dead. I now get to decide between a thousand dollar repair job on the root canal (with anesthetic this time), or a two thousand dollar extraction and a titanium replacement. Chances are I get the more expensive option. (At least I don't have an unbelievable toothache... yet.)
I will never again be able to pass through a metal detector without setting it off, nor will I be able to get an NMRI without liquefying my brain.
I am going to use my new titanium tooth to kill my old dentist.