Easy Rests The Crown

 
Kind of reminds one of those ancient kings with the silly sceptres, doesn't it?

Yet our question for today is: What is a dental crown?  And why would we need one?  Well, a crown is a dental restoration that covers the top of a tooth and all of its sides, all the way to the gumline.  We don't do these procedures lightly- many teeth will never need a crown.  But if enough of a tooth is missing, crowns are the best way to make it beautiful and functional again.  Damage to teeth comes from many sources- cavities, old fillings, fractures of parts of the tooth around the cavity or fililing, hockey pucks... (Go Flyers!)  The best way to visualize anything is to go to the furthest extreme.  So imagine a hockey player who gets a tooth not knocked out entirely, but broken off at the gumline, so that everything from the gums up is missing.  If the root isn't fractured vertically, we can fix even such a tooth as this. 

Here is a stylized representation of what a crown looks like as it hovers over the tooth that it is so eager to protect:

 

Crowns can be made of all porcelain, porcelain with a metal (hidden) substructure, porcelain with a zirconia substructure (which is white, not clear), or all metal.  Porcelain, while possessing incredible compressive strength, can fracture under the repetitive stresses in the human mouth.  The metal crowns are made of precious metal alloys and are essentally unbreakable.  Yet they are often objectionable to patients on grounds of appearance these days, unless they are far in the back or you're going for some extreme bling in your look.

Let's examine just a few situations where a crown is essential to saving the health of an individual tooth that has been compromised in some way.

 

A tooth such as the one pictured above with its fracturing, corroded old amalgam filling would greatly benefit from a modern bonded composite resin restoration.  However the science does not support placing a crown on a tooth with this sort of moderate sized existing restoration.  That simply involves removing too much tooth structure, it's not justified.  Unless- if one of those four cusps or corners breaks away (see Repetitive Stress, 5/21/10), then we prefer to do a crown before the entire tooth crumbles further and makes our job more difficult, and the outcome more uncertain.  You see, the more tooth that we have to start with, the longer these devices tend to last.  The hockey-puck-injured tooth that is all artifical from the gums up is much more likely to eventually fracture deep inside and fail than a tooth where there was something more to build on to start with.

Then we have:

 

This view is the one that I always call in my mind "The Smiling Monkey".  Doesn't it look like one?  If I ever was to find myself owning an English pub, I'd call it "The Smiling Monkey".  Google a search of English pub names and you'll see that mine isn't even quirky, by Brit standards of quirkiness.  "Bag O'Nails", "Snig's Foot", "The Quiet Woman"(?) and my personal favourite "The Frog and Radiator" in Greenwich are remarkable flights of nomenclatural fancy.  (A visit to The Frog and Radiator is on my official Bucket List, by the way.)

Apologies for the digression.  This is a view of a root canal treated tooth, a lower molar, with the larger back canal still unfilled.  Hey, it made for a better picture this way.  Molars see extremely heavy use in grinding our foods, and are located right within the muscle sling that closes our jaws, so that these teeth normally require a crown after root canal treatment in order to keep them from breaking catastrophically.  The thin walls that are left after removing old restorations and all decay are often just not strong enough to hold up for years and years, even with bonded composite resins. 

There are exceptions to all rules, of course. Sometimes teeth need root canal treatment (which is done to cure internal infections in the pulp, or soft tissue inside) for reasons of trauma or developmental defects, and the opening needed to treat is so small, and nothing else is damaged in the tooth, that a crown is not necessary.  We also have front teeth that have needed root canal treatment because of trauma that shocked the tooth but did not break it.  These often are best restored with small bonded restorations, not crowns.   So only teeth which have had root canal treatment and are moderately or heavily damaged by prior decay and large fillings will need crowns in this era of strongly bonded restorations.

For a look at the ultimate save, a tooth with a developing vertical fracture, have a look at "Molar With Thin Walls And Fracture", next post.  It's brevity in bytes.

http://rickwilsondmd.typepad.com/rick_wilson_dmds_blog/2010/05/molar-withthin-walls-and-fracture.html

And then come by and meet me at The Smiling Monkey- first pint is on me!

Comments

[Annemcx]

Thanks Rick, and the first drink at The Frog and Radiator is on me!

That was a very entertaining post!

I now understand more about why I've had trouble with two bottom molars in the last year, and I now understand a lot more about teeth.

And let me buy you another at The Crooked Billet, which is our new hangout, just off Wimbledon Common. I'll send you a picture.

[Tom Bentley]

Rick, thanks for your passionately dispassionate exegesis on crowns, and their royal ways. Unfortunately, I have a legacy (in my case, maybe 40 years) filling in a lower molar that's leaking or some such, noted because it's sending a regular signal of displeasure around my mouth.

So I'm having it replaced next week. I'm fearing though that when my dentist drills it out (it's a big one), that he's going to conclude that the tooth needs a crown. Probably to match all the other heads of state that crowd my mouth.

And if I have to get another root canal, I'll be drinking what's IN the radiator, frogs and all.

[Jenna Schrock]

So that's why they had me a dental implant when they did a root canal in my molars. Crown's steely look doesn't bother me that much so I'm okay - besides, the bad tooth is way beyond the back of my teeth LOL! Good thing my dentist in Los Angeles is good.

[Jeff]

I like this post ... It's better than most because you use humor and great analogies to explain what is going on.

Not sure I'd go to your pub though ;) j/k

[Rick Wilson DMD]

Thanks, Jeff, for your kind words.
Oh, and not to worry- there won't be ANY stray dental instruments in The Smiling Monkey!

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