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CROWNS
(Caps)
There is much more to this topic than the steps actually
taken to perform this procedure. The TYPE of crown selected is much more a concern for me
when I am making a diagnosis and this decision makes a huge difference when it comes to
longevity and esthetics. The terms “crown” and “cap” describe the very
same thing. A crown is a metal (usually gold) or porcelain "helmet" that
covers and protects a tooth.
The procedure
consists of:
- Reshaping the tooth.
- Making an impression of the tooth and surrounding teeth.
- Making a temporary crown to fit on the tooth for several
weeks.
- The impression is sent to a lab where the dental laboratory
technician makes the actual crown. The crown that fits over the stone model is made to
very precise tolerances.
- At the second appointment, the temporary crown is easily
lifted off, the final crown is tried into position, adjusted and final cemented to place.
Both gold and porcelain crowns have their place in dentistry. There are advances being made
continually in this area of dentistry. The ability to bond crowns and especially all
porcelain crowns to the tooth structure itself is one such improvement. New porcelains
that are less abrasive to opposing teeth is another such improvement.
Variations and
descriptions of crowns available are;
a. Gold crowns -
- Full gold crowns - cover the entire tooth to the gum line.
- Gold onlays - equal strength as full crown BUT less
tooth reduction and edges that do not go all the way to the gum line.
- Gold inlays - gold castings that replace
only the areas where a typical filling would be placed.
b.
All porcelain crowns -
- No metal under porcelain. These
are most often used for front teeth. These can be placed on molars as well but personally I am suspect of their
longevity and a porcelain fused to metal crown can be done very
esthetically.
c.
Porcelain/gold combination crowns -
- Porcelain fused to metal crowns - thin metal
casting is first made, porcelain applied over the entire surface. No metal
is placed at the gumline where the teeth are viewed - this is referred to as
a porcelain margin.
- These are extremely esthetic when
prepared and made correctly.
Gold
Crowns versus Porcelain crowns -
This
an area that you won't find discussed by many dentists nor at many places on the web yet I
find it the cornerstone to the restorative part of my practice. "Restorative"
refers to primarily placing crowns as required on weak and broken teeth. Naturally most
people have negative thoughts about "gold" in their teeth. They think of it as
old technology and very unaccepable in appearance. As far as technology goes, there have
been advances in the metals combined with gold to improve its properties and dental
cements have made huge progress in helping gold (and all crowns) stay in place much
better. When it comes to the appearance of gold I would NEVER place a crown in an
unacceptable visual area. I would never try to "talk" a 24 year old woman into
gold in areas that would show in a smile. Yet I WOULD try to convince this same attractive
woman into have gold placed on very back molars where it would out last porcelain and NO
ONE could ever see it.
WHY GOLD ???
What a good question. Even within this website there is a
"cosmetic dentistry" area. I even show cases that have all porcelain and
porcelain-to-metal crowns. So what gives? Well, first off we're speaking about gold on
back teeth and most specifically, the molars. Second, taking off perfectly good
enamel just to cover it back with something that looks like enamel stopped making sense to
me. Third, where necessary, tooth colored materials can be used on the front side of
crowns so that metal won't appear in the smile line. Fourth, experience is a great
teacher, it takes time to really develop a philosophy of practice. There are many
philosophies to choose from, one famous philosopher - Hippocrates - cautioned physicians
that their main goal was to "do no harm". Seeing failures and finding incredible
mentors I got to the point where I knew I would only have gold restorations in my mouth
and in the mouths of my family, I could then do no different for my patients. Fifth, (and
VERY important) I always educate the patient to the benefits before proceeding with this
or any other therapy, ultimately, it is the patient's decision as to how to restore their
teeth.. Read on and I think you'll begin to see why I feel the way that I do.
When polled on the subject, dentists overwhelmingly respond that if their own teeth
are being restored with crowns, they want restorations that include the least tooth
preparations along with the most forgiving restorative materials (gold), yet statistics
show that more than 90% of crowns placed in America today are porcelain-to-metal. How is
it then that dentists routinely place in their patients mouths that which they would not
accept in their own mouths?
The average crown placed today has an expected life span of
less than 5 years. Five years! How can this be? The answer, in a nutshell is that partial
coverage tooth preparation procedures have been abandoned in favor of more aggressive
procedures using unacceptable materials because it is easier to teach, easier to do,
and in the minds of the dentists doing this work, more acceptable to patients.
There are two basic premises that hold true for restorative
dentistry: (1) be as conservative as possible in removing tooth structure, and (2) use
biologically acceptable materials. Crown and bridge dentistry is yielding to the demands
of esthetics. There is much damage being done by the overuse of porcelain coverage on back
teeth. This is a problem that is created by dentists who, for the most part, are trying to
do something good for their patients.
Why is it that I and others say gold on back teeth is more
acceptable than porcelain? This question has many answers.
- When an excellent gold restoration is done it is most often
performed as a partial coverage restoration, what this means is that the tooth is not
reduced nearly as much as for placing porcelain. Instead, anywhere possible, good enamel
and tooth structure is left. (Image 1 and 2 below)
- Reduction of a tooth for a porcelain-to-metal crown is much
more severe than for metal alone. This also tends to produce more nerve problems than
partial coverage crowns. When asked in 1970 what the major cause of root canal therapy
was, Dr. Maury Massler, one of the fathers of modern root canal therapy, responded without
hesitation, "the porcelain-to-metal crown!"
- Partial coverage also stays away from the gums and therefore
less irritation is present. Many times around porcelain crowns, there are bleeding gums
that stay continuously irritated and can eventually lead to periodontal (gum) disease
problems.
- Porcelain (no matter how polished it seems) is 16 times more
abrasive than enamel! This is because porcelain (glass) is an inherently fragile material,
so alumina has been added to the ceramic for increased strength. This is essentially the
same material we use in the laboratory for sand blasting. If a single porcelain crown
opposes a natural tooth, a gold crowns or filling material, it will immediately begin to
destroy that surface. (Image 3 below)
- Gold castings are more accurate in their fit to the prepared
tooth. Conversely, porcelains shrink as much as 20% during application.
- Longevity - gold restorations will be in service much longer
than most porcelain-to-metal crowns. (Image 4 below)
As a footnote, there is not a significant fee difference
between the porcelain-to-metal and partial coverage gold crowns.
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IMAGE 1
Gold castings cemented to place. Note that the enamel is left intact wherever possible.
The molars to the left have onlays placed on them and the bicuspids have inlays. |
IMAGE 2
This photo from the front is the same as seen in image 1. Note how there is very nice
esthetics. Excellent enamel and tooth structure was not removed. |
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| IMAGE 3 This upper gold crown is opposing a porcelain crown. Note the destruction
and holes "patched" with fillings on the top surface. |
IMAGE 4 These gold castings were placed in 1947 and photographed in 1996 (50 years
of service) Note the health of the gums and amount of enamel preserved. From a front view
this metal would not be seen. |
Photos courtesy Tom Colquitt, DDS and William McHorris, DDS
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