Ideally you should be getting an oral health check at least annually, if for no other reason than to check the lining of your mouth for unhealthy or abnormal pathology, which is largely a check for Oral Cancer and its cousins.
Gums recede with age naturally, this is so that humans "in the wild" would still have some tooth left sticking out to chew with when they had worn down what they started with, giving them a few years more before they starved to death. Most herbivores ( homo sapiens is most closely descended from herbivores than carnivores: though of course, with the notable exception of MTQGraham, we are now omnivores) lifespans are largely dictated by the lifespan of their dentition, foremost amongst other things.
If you don't have alot of wear, and as a result vertical loss of tooth length, this gum recession occurs anyway, making you literally "long in the tooth".
You won't normally notice this that much as its so gradual, ( like the gradual expansion of that bald spot on the back of your head until it suddenly crests the horizon of your crown when you look in the mirror one day and.......but enough about...... errr..... my friend), unless that is there is a visible fixed reference point, like the point where a crown finishes and the rest/root of the tooth begins. If it has "died" and been "root filled" , quite often the root would go quite dark, and almost black with some of the older style root filling materials/techniques, making the contrast between the crown and root very striking and unaesthetic. On occasions this can be improved by using a white filling at the joint to improve the appearance, but the improvement will usually be very limited at best and not worth it. Alternately you can replace the crown, extending the joint point to where the tooth emerges from the gum, the gingival crevice....... hang on a mo.........YOU AT THE BACK.......YES YOU.......YES, I used the word "CREVICE" .......now calm down and stop sniggering.......
sorry about that.... where were we.... yes you can replace the crown.
But basically, dark borders beyond the edge of a crown, whilst unaesthetic, don't necessarily mean your crowns are on the way out. Get yourself a check up though. Could save you alot of grief long term, and it sounds like you've already had your fair share in the past. Perhaps best to keep ahead of probs while you're still having a good run?
This certainly doesn't mean that you are looking at problems with your crowned teeth, but you should really get them checked at least annually, assuming the rest of your oral health is tickety boo, which of course if you haven't had it check, you kinda don't know.
For those folks searching for a new dentist by the way, I'm often asked if I can recommend an NHS dentist, sadly not in my area, and there are precious few private ones fo rthat matter that I'd happily see a friend attend, but a good tip is to look at teh reviews recieved on NHS Choices for any practice you are looking at attending. Though the mumbers of reviews is often quite low, for the practices in my area they seem to be a pretty accurate refelection of the type of experience you might expect. See NHS Choices and use teh postcode search for practices near you. Also tells you who is accepting NHS patients
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