Quote:
> Hi Frank,
> Can you cite a study relating the expansion of amalgam beyond the initial
> oxidation layer formation???
I have read a few, but so long ago, I'll have to do research to find them
again.
So many people like to talk about amalgam
Quote:
> expanding until it cracks the tooth in half. I have never seen a study
> correlating amalgam and expansion beyond an oxidation layer of specific
> engineered thickness.
We are talking apples and oranges. Each amalgam has an initial setting
expansion, as you know, and this actually can help the seal. It is very
much affected by if the alloy got wet or even high humidity during setting.
Setting expansion is more if wet (but you already knew that)
This has a little effect because of the number of walls that receive the
stress. (Have you heard of the "C" factor ?) it is used to explain why
class I resins are usually more sensitive than class II (another topic we
can discuss later)
essentially, it states that the more walls for the resin to pull against in
different planes, the more setting shrinkage.
This works the same for amalgam. First, anecdotally, I have noticed many
more vertical fractures on teeth with old class I amalgams than Class II.
When I was listening to a guy describe this "c" factor regarding resin
sensitivity, it made sense. Just now, I realized it also fits the expansion
stresses on a tooth that is worse on a class one simply because there is
only one direction to go-- occlusally and what is in the way? The opposing
teeth (wow we are onto something here, this could explain a lot of other
issues!)
Anyway, I believe this internal strain in a non flexible internal of a
crystalline tooth has potential energy that is not released. ON a class II,
however, the proximal spaces allow a relief of this "tension" or PE.
All the points you made are valid and become factors as time goes on.
NOW the real aging amalgam expansion issue is really metal fatigue "CREEP".
this is a time dependent factor as any metalurgist will tell you and affects
steel construction and it is why they alloy their metals the way they do.
Now bear with me...
So, as WEAKENED TEETH (due to the factors you mentioned such as size,
unsupported enamel, etc and I'll add these white lesions we were so keen on
not restoring due to one study that shows they can recalcify, which I am not
denying, it can happen) BUT, guess what? The cracks are only present in
the situations you state, but my argument is that the conditions you
describe lessen the strength of the enamel (and I say, "white lesions" may
not be decayed, but the enamel is weaker), and this pent up early expansion
and late metal fatigue now goes to the path of least resistance (the weak
parts of the tooth you describe well ) and are expressed in a "give" of the
the crystalline enamel that we call incomplete fractures. They only ,in my
opinion, become fractures as the metal alloy fatigue sets in and expansion
increases in the filling's later years. If this is not true, why does the
documented and rarely discussed creep occur in older amalgams (buccal
filling sticking out 1/2 mm from {*filter*}l surface but otherwise intact,
obviously at one point in time it was flush.
The Class I vs Class II issue I just heard about (the C factor when
referring to resins--perhaps we could patent the term C-Am factor:-) and get
rich like Boyd!)
Quote:
> After being out of school for 17 years and the two years in the school
> clinic, I have never seen amalgam failure expect when the tooth failed, or
> the material was asked to do more than it is capable of doing.
Examine these limited statements carefully. Both are true, but don't
address creep as we don't label it as failure.
My personal empirical observation over the years is that almost all
fractures I drill into have thin, unsupported enamel and or decalcification
(often a white "recalcified" lesion) as you stated well, BUT why would it
happen so late in the life of the restoration and why more on class I's???
(Look for that in your patients and see if it isn't true.
Restorations
Quote:
> greater than half the width of the tooth fail from horizontal fractures at
> the base of the dentin/enamel cusp due to insufficient bulk of tooth
> material. I see this with any dental material--not just amalgam.
> Restorations placed over a flexible base cement crack and leak regardless
of
> the material chosen. Restorations with an abrupt change in width or depth
> (leaving a sharp internal corner) typically crack, also regardless of the
> material chosen.
> I don't believe age of the amalgam is nearly as important as:
> 1) removing unsupported enamel at the margins, (remember margin trimmers?)
> 2) having adequate bulk of amalgam (depth and width),
> 3) maintaining adequate bulk of remaining tooth structure,
> 4) keeping occlusal contacts off the restoration margins,
> 5) condensing the amalgam against solid tooth structure rather than softer
> cement bases, 6) rounded and flowing internal line angles,
> 7) not "patching" new amalgam against old amalgam--the entire restoration
> needs to be one piece
> 8) condensing adequately (no thumb-prints) in a clean field
and I would add low humidity and dry to clean
Quote:
> 9) carving the occlusal anatomy properly with "sluice-ways" for the cusps
to
> pass through in excursions--no flat fillings
> 90% of the failed amalgams are from unsupported enamel or amalgam chipping
> off at the margins and allowing recurrent caries to begin.
I notice that most of the fractured teeth I restore, DO NOT have a "failed"
or cracked amalgam, but indeed an intact amalgam that has creeped if class
II. Other observations I'll cover later to stay on track
I am saying tooth failure (cracking) not filling cracking.
Also, how many amalgams older than 20-30 years old have you taken out and
NOT found a fracture somewhere in the pulpal or axial walls?
The exceptions I see are ones that followed the rules you stated and were
burnished or polished properly!
Quote:
> I have no problems with choosing any dental material to restore teeth
> with--if used properly. I have not seen studies correlating older
amalgams
> with continuous expansion of the metal. Surface oxidation will only occur
> if the surface is exposed. Once the oxidation seals the cavity, what
> further expansion can you be referring to.
> If I have missed an important study,,,, I apologize and promise to read it
> right away.
> BTW, don't bother flaming me with mercury arguments. I have an active
> filter going and don't mind increasing the list. This debate is about
> expansion, not toxicity.
> Respectfully, just trying to debate an issue, not trying to stretch
> friendships.
> Steverino
Good point to debate. I bet we all can learn. (especially as we challenge
our long held beliefs and evaluate how many we really see and how many we
were "taught" to follow )
Quote:
> --
> =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
> Stephen Mancuso, D.D.S.
> +_+_+_+_+_+_+_+_+_+_+_+_+_+_+_+
> This posting is intended for informational or conversational purposes
only.
> Always seek the opinion of a licensed dental professional before acting on
> the advice or opinion expressed here. Only a dentist who has examined you
> in person can diagnose your problems and make decisions which will effect
> your health.
> ......................
> > 1. highest level of mercury vapor release is when they are removed
unless
> > under {*filter*} dam and high voluum suction and it never touches your
tissue
> or
> > you don't breath it.
> > 2. Plausable. As amalgams get past a certain age (10-20 years depending
> on
> > how carefully placed and if they got wet or not after placed), the metal
> > starts to fatigue and change physical properties and can expand and
> contract
> > more than it it's earlier years often leading to premature fracture of
the
> > crystalline enamel.
> > I'd have to see your mouth for a proper opinion.
> > fmn
> > --
> > Practice win-win or no deal. (Stephen R. Covey)
> > > I just discovered this newgroup and have been snooping around quite a
> bit.
> > > Wish I would have found it sooner.
> > > Over the last year and a half my dentist has been on a mission to
remove
> > all
> > > my amalgam. Initially she wanted to replace it with composites, but is
> now
> > > pushing for inlays (onlays?). She has done several replacements, two
of
> > them
> > > ended up requiring root canals. Prior to this I did not have any
> problems
> > at
> > > all with the amalgams. However, she cited mercury risk, plus she
stated
> > that
> > > some of my amalgam fillings were expanding - leading to cracks in my
> > teeth -
> > > or contracting and allowing decay to form around them.
> > > I read in another thread that there were risks associated with amalgam
> > > removal, but the risk was not described. What are the risks?
> > > Are her reasons for replacing the amalgam fillings plausible? Is it
> > possible
> > > for them to meaningfully expand/contract?
> > > Thank you in advance!
What are risks of amalgam removal?