The time it takes for caries to go from one stage to another is very hard to say, but your teeth are in-built with mechanisms to slow the progress of the decay, in order to protect your nerve and keep it alive.
Your teeth are protected by:
(i) The remineralising effects of saliva
(ii) The Amelo-Dentinal Junction or ADJ for short (the border between enamel and dentine in a tooth)
(iii) Secondary dentine being laid down
Once into dentine, the rate of progression will speed up, exactly just how much we don't know. This is partly due to dentine's weaker tubular structure and partly becasue the plaque is now sheltered and less affected by fluoride and saliva.
The rate of caries will depend on your caries risk- the more high risks items you say 'yes' to, the faster it is likely to progress.
The most influential of these risk factors are:
- The frequency, type and time sugar is being consumed
- The resistance of the tooth- amount of fluoride, quality saliva and the maturity of your enamel
- The amount of plaque allowed to collect there- position of the caries, quality of your oral hygiene and cleaning.
Let's quickly highlight this with a couple of examples:
(i) Consider a young boy age 7, who sneaks out to drink coca cola at night, while his parents are asleep and buys a packet of hard toffees every day- he picks at them throughout the school day. He only brushes his teeth in the morning and takes about 20 seconds to do it- sometimes eating an apple instead because he thinks this will do the job. You can imagine just how fast the dental caries would progress in this boy's teeth.
(ii) Contrast that to a middle aged woman with a good diet, but who is a big coffee drinker- having 2-3 cups a day (always with one heaped teaspoon of sugar). She brushes twice a day but rarely flosses. The rate of progression would most likely be quite slow and early problems if spotted, could potentially be reversed.
The site of the caries is also important and where it is hidden from view, eg. In-between the teeth (and detected in its early stages only by X-rays), it is likely to decay further before it gets noticed.
Dental caries itself progresses slowly most of the time and that is why it is important to see your dentist regularly. If you go every 6 months and the dentist discovers you have some very early caries, it may possible to reverse the situation or solve it by placing a small simple filling.
The longer you leave it, the greater the chance of the nerve being affected and all sorts of future problems can arise. A big visible hole in your tooth (that hasn't been previously filled) is likely to have been going on for at least a couple of years.
As I have mentioned, since fluoride resurfaces the overlying enamel, huge holes can occasionally go undetected and for this reason, screening X-rays
are important so don't avoid them. If it is time you had them (your dentist will advise you), try to think of it as saving yourself money down the track not what you are spending on the X-rays.
The rate at which this type of decay progresses has slowed in recent decades and a study showed that about 50% progress to dentine after 2 years and 75% after 4 years. Lots of dentists report that not all caries follow this pattern and a number actually arrest before reaching dentine.
Fissure caries in children can be very rapid and regular visits are needed to pick this up. Children are more vulnerable to caries because the enamel of their permanent teeth is less mature (weaker) when they first erupt. Couple this with frequent snacking and sugar cravings and you have a recipe for a quick cavity.
Caries in this situation can progress deep into dentine within 1-2 years compromising the nerve. Unfortunately it is a sight I see more often than I would like, where the whole tooth has been eaten out by decay, leaving a thin and vulnerable tooth that may, or may not need root canal treatment. Often this is called 'egg shell caries' for obvious reasons. The chances of keeping this tooth for a life time is unfortunately, quite small.
It takes an average of about 4 years for interproximal caries to reach dentine and again, not all will progress, particularly if you change the conditions in favour of remineralisation. That's why an 'early nick' in the enamel should be given a chance to become arrested caries with preventative measures.
Smooth surface caries
There is a lot of evidence to suggest that caries on smooth surfaces takes even longer to progress to dentine- because this area is the most accessible to the tooth brush, it is the most easily stopped.
As you can see caries actually progresses pretty slowly (most of the time) and because of this, we can sometimes adopt a 'watch and wait' approach meaning we simply monitor how things go. This is only sensible if you regularly see your dentist and it is always a good idea when doing this to take a good look at your oral hygiene and all the other preventative measures to give you a helping hand.
If the dentist for one reason or another, believes it is likely to progress- perhaps you are 'high risk' and they've seen other similar problems progress before-maybe the area is particularly difficult to clean, then it may be best not to 'watch and wait' but to step in and sort it out there and then.
One final point, if you regularly change your dentist, it is not possible to 'watch' things in the same way and a new dentist is much more likely to tell you that the questionable things they are seeing for the first time need a filling