Yes- I'll certainly agree that mastication of food alone does not
cause the type of wear seen when a porcelain restoration has worn away
the opposing occlusal material.
That's because during normal chewing, food contacts the teeth, and the
opposing occlusion really doesn't contact very much.
Instead, wear requires the contact of the hard porcelain against the
softer material. Crushing food between the teeth during mastication
does not produce significant contacts between the tooth surfaces. So
we can't blame eating for that TYPE of observed wear.
Because teeth do indeed contact (but not much during chewing), the
relative hardness of the opposing materials has some consequences.
I have never seen a gold crown wear down an opposing porcelain
occlusal, even in patients who are hard bruxers.
Neither have I seen natural tooth enamel wear down any opposing
porcelain restoration's cusp tips.
However, I have seen plenty of porcelain crowns wear down opposing
gold and natural enamel, time and time again.
Parafunction vastly increases the opposing wear patterns, and makes
them starkly obvious. One of the best services we can render to such
patients is to find a way (often spelled "NTI") to halt the
destruction of bruxism and clenching. But no amount of parafunction
will make a gold crown wear a hole through an opposing porcelain
crown. In fact, the worse the parafunction, the greater the wear in
the gold.
Actually, most of the time that teeth are in occlusal contact, there
is no mastication taking place. It is well established that the teeth
often contact during swallowing. It is also established that the vast
majority of the saliva that is produced every day is swallowed (unless
there are a lot of people running around with little tin spit cups
dangling below their chins, as in the old Saturday Night Live skits).
So just considering the all-day, every day swallowing of normal saliva
production, the teeth may contact hundreds of times a day without
mastication. Some slight wear takes place during these contacts, as
microscopic as it may be.
Ultimately, if people live long enough, their enamel is subject to the
same fate as their original mamelons. Those mamelons didn't just
vaporize one day -- they were worn down.
- dentaldoc
On Jul 1, 11:37 am, "Amatus Cremona" <Nic...@sottovocce.com> wrote:
> I will respectfully disagree and say that chewing does not contribute to
> tooth wear.
>
> --
> /
>
> Amatus
>
> /"Bill" <dental...@hotmail.com> wrote in message
>
> news:cd314675-c83b-43a8-b28f-ffefb8b729ce@l28g2000prd.googlegroups.com...
> On Jul 1, 12:38 pm, churin <krone8...@mypacks.net> wrote:
>
>
>
>
>
> > Mark & Steven Bornfeld wrote:
>
> > > churin wrote:
> > >> Bill wrote:
> > >>> On Jun 27, 9:58 am, churin <krone8...@mypacks.net> wrote:
> > >>>> I had metal crown on molar(#31)but it lasted about ten years. A part
> > >>>> of
> > >>>> the top surface area was removed and cement underneath was exposed.
> > >>>> The
> > >>>> broken crown was replaced with again a metal crown. This time it
> > >>>> lasted
> > >>>> only one year. The damage was done in the same way as the previous
> > >>>> one.
> > >>>> I chose metal crown because the both dentists who did the first one
> > >>>> and
> > >>>> second one recommended metal crowns.
>
> > >>>> I still keep the removed crown which lasted 10 years. It really looks
> > >>>> "worn out" and appears badly deformed from the original shape. It
> > >>>> looks
> > >>>> as though the opposing porcelain bridge struck hard on the metal
> > >>>> crown
> > >>>> which appears softer than porcelain so that it yielded to the impact
> > >>>> by
> > >>>> deforming itself.
>
> > >>>> Now I have to decide for a new replacement crown whether to go for
> > >>>> metal
> > >>>> crown again or switch to porcelain.
>
>
> > >>>> What is typical life of a metal crown on molar?
> > >>>> What is a downside(s) of porcelain(PFM), cosmetic aspect aside?
> > >>>> Any suggestion for choosing type of crown?
>
> > >>> It sounds as though it might have been a cheap stainless steel crown.
> > >>> We call those "temporary."
>
> > >>> But even a cast metal crown (much better than stainless steel pre-
> > >>> formed) can eventually be worn through by harsh contact from an
> > >>> opposing porcelain bridge.
>
> > >>> Generally I like to make a crown of a material similar to that which
> > >>> it's going to occlude against (bite against).
>
> > >>> So if there are no other confounding factors, generally if the tooth
> > >>> is going to bite against a porcelain bridge, I like to place a
> > >>> porcelain crown to match.
>
>
> > >> How can I make sure that I get a quality crown whether it is metalic
> > >> or porcelain? Does it entirely depended upon a dentist I go to? Is
> > >> there anything I can do to help getting better crown?
>
> > > Not easy. Amatus can place a crown or inlay in a day (one long visit
> > > with a break) but most of us send impressions to a lab, so it will
> > > require multiple visits. Of course, even here the quality is dependent
> > > on both the dentist and the lab. The dentist should be able to discuss
> > > the materials to be used. You should be able to discuss this problem of
> > > chewing through the crowns, and formulate with your dentist a plan to
> > > minimize having this happen again. For me, unwillingness to discuss
> > > these issues in a respectful and comprehensible manner should be an
> > > automatic disqualifier to using the dentist for your treatment.
>
>
> > Thanks for your suggestion.
>
> > churin- Hide quoted text -
>
> > - Show quoted text -
>
> Please do remember that when you place a crown into occlusion (bite)
> against an opposing crown that is made of a DIFFERENT material,
> eventually the harder material will grind down the softer material.
>
> That's why dentists frequently see porcelain bridges wearing away the
> opposing teeth and opposing gold crowns.
>
> If you grind your teeth, the wear is even faster.
>
> My advice is to make sure that the opposite crowns match each other.
>
> - dentaldoc- Hide quoted text -
>
> - Show quoted text -
Steven Fawks
Amatus Cremona
