Many can recall a time when a tooth started hurting, then getting to another level entirely... And then really starting to kick. Gack! The pulp, or living tissue inside of each of our teeth, is usually the culprit. It's a very small bit of tissue, so it seems positively unfair to me as a dentist (and to you, if you've been through it), that such a small thing could cause such outrageous pain. There are good reasons, though. The nerves that give sensation to the face and jaw are short and carry a lot of impulses- right to the brain, being in the same zip code and all. Also, since the pulp resides inside a hard tooth, it's effectively in a sealed case, like champagne in a bottle. But not as much fun when the pressure builds up...
(These images are from microcomputed tomography- microCT scans. Can't you just imagine a line of avant-garde barstools for English pubs with quirky names, like the "Moon Under Water", based on this design? They'd make a great way to limit each patron to two beers or less...) (See May 28 for more on English pubs. Oh, and teeth.)
Sometimes, though, the pulp of a tooth will die off and get infected without ever really hurting along the way. We always look hard for a reason for this- deep decay, gum disease, trauma. Sometimes a tooth just seems to have nothing wrong with it at all, nothing that could lead to an infection inside. The main culprits in those cases are trauma, perhaps even in the distant past, or small developmental weaknesses in teeth that break away with age and allow bacteria to work their way in and cause their mayhem.
The main "radiographic sign" of infection in a tooth is a dark area at the tip or side of the root. This comes from the damage to the bone caused by the immune system fighting off the germs. They usually stay somewhat self-contained, but the dangerous part of dental infections is if they ever break out and start causing major swellings.
While X-rays are very helpful in diagnosing dental infections, we never treat X-rays, we treat people. We have to watch that we don't mistakenly treat one of the innocuous conditions that mimic root canal infections. So we test other factors before making a definitive diagnosis and starting treatment.
Here's a case of root canal infection that was silent- painless. Due to the lack of symptoms and "life got in the way", treatment was delayed from the time of diagnosis for about a year. The dark area got larger but remained symptom-free. We opened this tooth and found infection; once it was treated it started healing nicely. In a few months the dark area will diminish and come back to looking normal. This is because once the germs are removed from the root canal system, the body sends immune cells into the area to clean up the mess. (My personal favorite immune cells are "macrophages", which means "big eaters" in Latin. They're great scavengers.)
(The hyper-modern filler for root canals that I use, Resilon, is made to show up light on X-rays so that we know where it is.)
So, much like high blood pressure, glaucoma, and early coronary artery disease, some root canal infections are painless and do not warn us of the danger to our bodies. More and more research demonstrates that these kinds of quiet infections can increase the chances of events such as heart attacks and strokes, since the bacteria and their toxins cause inflammation inside the bloodstream. Regular exams and X-rays at appropriate intervals are the gold standard of care for the human mouth.
And if you fall off one of those quirky barstools in a pub with a quirky name, definitely get your teeth checked for the effects of trauma. Or wear a sports mouthguard to the bar...