A student asked me recently how long it takes for caries to progress from enamel to dentine. Just in case anyone else was wondering, I thought I'd pop up my response. It's not profound but may help...
We're taught that there are four variables in the caries process: tooth surface, cariogenic bacteria, substrate and time.
So, increase the resistance of the tooth to caries and time goes down.
Decrease number of bacteria and time goes down.
Decrease frequency of substrate and time goes down.
And vice versa.
It's one of those how-long-is-a-piece-of-string-questions. Progress in rampant caries (i.e. when substrate and bacteria are high and resistance low) may be a couple of months. Reduce either the substrate frequency or the number of bacteria and we may be talking months to a couple of years. Whack in some Sodium Fluoride 5000ppm toothpaste, cut sugar to minimum and turn your patient into a TePe hugger and the process may stop entirely.
Predicting caries is a difficult issue. We try to assess the risk of caries but even then we can't say with any confidence if someone has a 20%, 50% or 90% risk of caries in the next year / two years / 10 years. But the risk probably goes up if the substrate frequency goes up, the bacteria go up and the resistance goes down.