|
Adhesive Newsletter #36
by Nelson Gendusa, DDS
In the last issue, I modestly suggested that
bond-strength tests have virtually no direct clinical value. You
can’t use bond-strength numbers to predict in-the-mouth success.
Well - Now that I’ve irritated all the researchers - Let’s
take a few wacks at the lecture circuit.
I don’t know Dr. X (he is a real guy, but I caved in to our
lawyer and left out his name). I’ve never heard him lecture,
but I understand he’s a dynamic speaker on subjects cosmetic.
However, in a recent editorial he wrote one of the flat-out dumbest
comments I’ve read in recent years.
“Please don’t tell me that you bond amalgam to teeth.
Test after test has proved that this doesn’t happen.”
Now you may not like amalgam. You may feel that it offends your
esthetic sensibilities, that it’s killing your patients, depleting
the ozone layer and poisoning the environment.
I don’t know if any of that’s true or not, but I do know
one thing: you most definitely can bond amalgam to teeth.
The overwhelming preponderance of the studies suggests that it DOES
happen ... provided, of course, you use Amalgambond.*
So here’s an instance of someone writing as an authority concerning
something he knows nothing about. Obviously, he hasn’t read
the research. And (I’m just guessing now) I suspect he’s
never attempted to bond amalgam himself. I sent him an e-mail offering
to show him my research if he’d show me his. No response.
My point is that once an expert steps outside his narrow area of
expertise, he’s as stupid as the rest of us. And unfortunately,
when they’re basking in the glow of adoration before an admiring
audience, experts rarely remain within their area of expertise.
I don’t mean to pick on Dr. X. He’s not alone. I’ve
heard other experts suggest to audiences ...
- “You can save significant money by substituting Jet®
or Snap™ powder for the C&B-Metabond powder.”
Wrong. Or rather you CAN save some money. You can save even more
if you substitute self-rising flour. But the quality of the bond
will plummet.
- “C&B-Metabond won’t bond to dentin.”
C&B-Metabond bonds to dentin better than anything in this
area of the cosmos.
- “It’s been ‘proven’ that the hybrid
layer theory of bonding is nonsense.” It later became
the dominant theory of bonding.
- “C&B-Metabond’s thick film makes it hard
to work with.”
- “C&B-Metabond’s thin film makes it hard
to work with.” In fact the film thickness is controlled
by the amount of powder you add.
By the way, these pearls weren’t offered by no-name lecturers
at a county dental society meeting. They fell from the lips of some
of the most respected icons in the dental world.**
“Who you gonna believe? ... Me? ... Or your lyin’
eyes.”
I’ve heard speakers dis’ audience members who had the
temerity to report clinical success with a product the speaker had
ignored ... or even savaged.
Fact is, you know more about your dental practice than anyone in
the world. And there’s a very good chance you know more about
the products you use daily than the person behind the podium. (No,
really, it’s true!) That’s because you actually use
them. You’ve actually walked the walk. Quite often the person
with the microphone hasn’t even clinically tried the product
he’s talking about.
Bottom line: Don’t automatically believe everything you hear
or read. (Including this.)
Bugs on the prep. Do you need to disinfect the
tooth before bonding?
“In our practice we use Peridex® to disinfect
preparations before bonding. I notice that it contains glycerine.
Now we use glycerine to prevent the oxygen-inhibited layer from forming
when we cement bonded indirect restorations, so I’m concerned
about the affect it might have on the bond.”
Dave Vocal
New Albany, OH
Unless it’s completely removed, glycerine will almost certainly
affect the quality of the bond. Some studies suggest that disinfecting
agents will reduce the bond. Others studies don’t.
But why take the chance? Especially since disinfection may be a waste
of time. At the latest IADR meeting, a team from the Tokyo Dental
College provided evidence that 4-META adhesives are “self-disinfecting.”1
Class V preparations were cut in dog teeth and the surfaces were intentionally
contaminated with bacteria from saliva and plaque. Three minutes after
prepping, one group of restorations was bonded with C&B-Metabond.
The other group was left unbonded.
After three months, the teeth were extracted and microscopically examined.
The second group (the one with no treatment) had bacteria partying
everywhere. Not just on the surface where the contamination was originally
placed, but deep down the tubules.
On the other hand, the C&B-Metabond teeth had no bacteria anywhere.
Not on the surface. Not in the tubules.
When they looked verrrry carefully, however, the researchers could
make out a layer of tiny “particles” embedded at the top
of the hybrid layer. Presumably these were the remains of bacteria
that died a horrible death, screaming and frantically waving their
flagelli as they were entombed alive in the 4-META resin.
Okay, I made up the screaming part.
The four habits of highly effective bonding
agents.
New product development invariably involves compromises. Lots of
compromises. Precisely which features a manufacturer emphasizes
during development and which it sacrifices depends largely on its
philosophy of bonding.
So I thought I’d devote a page or two to our philosophy of
bonding. Here are what we and our Comrades-in-Adhesion at Sun Medical
consider the 4 characteristics of all highly effective bonds.
1.) They retain the restoration. (Duh.)
2.) They prevent post-op sensitivity.
3.) They are not technique-sensitive. That is, small variations
in procedure should not produce significant variations in results.
4.) They protect the dentin surface with a dense hybrid layer
that penetrates through the decalcified zone and encapsulates the
exposed hydroxyapatite crystals on the surface of the sound dentin.
(This is stolen directly from Dr. Nobuo Nakabayashi’s seminal
research into hybridization.)
In our judgement, any adhesive that delivers these 4 things provides
an “excellent bond.” I occasionally hear someone say “I’m
getting excellent bonds, but some post-op sensitivity.” That’s
an oxymoron. If you’re getting sensitivity, you are NOT getting
excellent bonds.
Notice that none of these characteristics includes anything about
“bond strength.” In our view, most of the shear or tensile
data you read are artifacts synthesized in a laboratory. No one
has ever demonstrated that they have any meaningful relationship
to clinical performance.2,3,4,5
Long-time readers of this newsletter know I don’t care much
for 5th generation bonding agents (One-Step®,
Prime&Bond®, Easy-Bond™.) A quick comparison
against those 4 criteria above, shows why. Gen5 agents can produce
impressive bond-strength numbers, but they can also be quite technique-sensitive.
Variation from the ideal technique can produce wicked post-op sensitivity.
In other words, the 5th generation flunks 2 out of our 4 criteria.
Here’s how those 4 criteria influence our adhesive strategy:
- We have a bias AGAINST strong acids on dentin. Strong
acids tend to denature the dentinal collagen. If the tooth surface
gets too dry it forms a gooey mess on the surface that adhesive
monomers have trouble penetrating. That’s why the green dentin
activator that comes with most of our adhesives (10% citric acid,
3% ferric chloride) is the least aggressive acid used in resin
bonding. And so far as I know, Touch&Bond®
has the highest pH of all the “no-etch” materials.
- We have a bias AGAINST mandatory wet-bonding. It’s
difficult to communicate the precise degree of dampness that “wet-bonding
agents” require.
So we attempt to offer adhesives that bond to both wet
and dry surfaces. That way, the condition of the tooth is irrelevant,
and the technique much less demanding.
- We have a bias TOWARD molecular penetration into the tooth
surface - If the decalcified zone you create when you etch
isn’t completely filled with the adhesive, the exposed collagen
may degrade with time. We feel that an adhesive’s ability
to penetrate into the intertubular dentin is strongly related
to its long-term success.
That’s why all Parkell adhesives contain 4-META.
It’s the smallest of the adhesive molecules ... roughly half
the size of the adhesive molecule in All-Bond® and
One-Step®. The smaller the molecule, the more easily
it penetrates into the tooth without the need to soften the surface
using strong acids.
And for the same reason, we avoid reinforcing the 4-META adhesive
with a stiff back-bone like BisGMA. Incidentally, this is a perfect
example of how a manufacturer’s bonding philosophy affects
the kind of materials he offers. Adding BisGMA generally enhances
a material’s laboratory bond strength. If we were shear bond
fans, we’d probably jump at the opportunity to stick in some
BisGMA.
But BisGMA’s large benzene rings reduce its ability to penetrate.
Think of BisGMA as a dumbbell. Actually, that’s what a BisGMA
molecule looks like. Like a dumbbell, it’s strong. But did
you ever try to jam a dumbbell down a rat hole? Me neither. But
I imagine it might be difficult.
Our bonding agents are far more likely to rely on narrow flexible
aliphatic or alicyclic molecules (such as UDMA or MMA), because
they slide Slinky®-like into porosities. That is,
they are better penetrators. And they also create a more flexible
adhesive layer ... which leads to our next bias ...
- We have a bias TOWARD resilience instead of rigidity -
A resilient bonding agent tends to dissipate stress and create
a more fracture-resistant bond.
When researchers have to explain why Amalgambond and Touch&Bond
preserve margins and resist gapping better than materials with
much higher “Bond Strength”, they often speculate that
it’s due to the resiliency of the adhesive film. When researchers
had to explain why C&B-Metabond resisted peel-failure almost
100 times (Yes, 100 times!) better than Panavia, again they pointed
to Metabond’s resilience.
- We have a bias toward Clinical vs Laboratory Testing
- To us, laboratory data is what a manufacturer uses when
he doesn’t yet have clinical data. Lab studies can be useful
when you’re developing new products - or when scientists
are trying to figure out why a product performs as it does.
But the simple truth is this: It is impossible to accurately predict
clinical performance from laboratory studies. Most bond-strength
research is conducted primarily for propaganda purposes ... and
to keep researchers off the streets.
So we spend considerable time and money collecting in-the-mouth
information. The nicest thing about clinical data is that it remains
valid even if all our assumptions about bonding are wrong!
For example, suppose we’re dead wrong about the importance
of molecular penetration. Suppose it has no affect at all on the
longevity of the bond.
If that’s the case, then any spectroscopic analysis we showed
you to prove that the 4-META molecule penetrates better than other
molecules might be true ... but it would be clinically irrelevant.
However, the C&B-Metabond cases in the mouth for 20 years
wouldn’t be irrelevant, because they don’t depend
on any shared philosophical belief.
Or suppose my bias against wet-bonding is completely unfounded,
and in fact agents that require wet-bonding are no more sensitivity-prone
than other materials. That wouldn’t change the fact that 93%
of the dentists who compared One-Step and Touch&Bond say that
T&B is “Better” or even “Wonderful” in terms
of post-op complaints.
I suggest you find a manufacturer whose bonding philosophy makes
sense to you. Because if we’re faced with a trade-off between
improving penetration and sacrificing a little shear-bond strength,
you KNOW what we’re going to do. If you share our philosophy,
you’ll approve. But if shear bond data is the one thing you
look for in a bonding agent ... you might be uncomfortable with
our choice.
One more comment about the difference between
“bond strength” and “clinical bond”
I ran across two new studies out of Europe
that throw some further doubt on the clinical significance of bond
numbers. Interestingly, both studies involved Touch&Bond.
Touch&Bond provides a good reliable bond to dentin. I can say
that with great confidence because we’ve done extensive clinical
reviews of the results. However, in terms of “shear bond”
numbers in the laboratory, Touch&Bond ranks about the middle of
the pack, down there with Prime&Bond® NT and (in
at least one study) All-Bond®.
If you ask researchers why bond strength numbers are so important,
they usually say that “obviously” you need a certain bond
strength to avoid gaps at the margins and to prevent gapping at the
interior interface due to composite shrinkage.
Seems to makes sense, I guess. But is it true?
Several researchers at the University of Berlin studied how margins
of composite restorations degrade over time. After a year in water,
they stressed the restorations by thermocycling the restored teeth
2000 times. Restorations bonded with Touch&Bond showed the greatest
percentage of continuous margin. Better than the 10 other bonding
agents studied. (Reminder: That’s “middle-of-the-bond-strength-pack”
Touch&Bond.)6
Researchers at the University of Cologne compared bond strength with
resistance to gapping between tooth and restoration. They could find
“no relationship” between gapping and bond strength. By
the way, once again, Touch&Bond came out on top. It showed the
least gapping of all the commercial bonding agents tested.7
Don’t misunderstand me. I’m not arguing that Touch&Bond
is better than everything else out there. I’m arguing that those
bond strength numbers we manufacturers cite to “prove” our
stuff is the best are (at best!) of marginal importance ... and at
worst, downright deceptive.
Putting our ad money where our mouth is
When I first entered the
field of adhesive dentistry I believed bond-strength data with all
my heart and soul. Everybody did back then ... except my good friend
Nobuo Nakabayashi, PhD (father of the 4-META molecule.) When I’d
rave to Nobuo about the astronomical bond numbers his C&B-Metabond
generated, he’d shake his head and tell me that the “quality”
of a bond was much, much more important than the strength.
Back then I thought he was just being modest ... or inscrutable.
My disillusionment was gradual. To my surprise, competitive adhesives
with relatively low bond strength didn’t suffer the dire consequences
I’d predicted. When I looked for research into the relevance
of traditional bond tests, I discovered there wasn’t much.
In fact, what research there was couldn’t find any relationship
at all between bond strength and clinical performance.
When I tried to discuss this curiosity with a researcher at an IADR
meeting, he gave me one of the most astonishing responses I ever
heard.
“Yes? Well - personally, I don’t put much stock
in that clinical stuff.”
Until 5-6 years ago, our advertising featured a lot of graphs emphasizing
in vitro bond strength. This reached a peak in 1994, with a C&B-Metabond
ad that included a mind-numbing 15 different graphs. Today, Parkell
advertising is much more likely to emphasize clinical cases or feedback
from actual users than laboratory data.
To misquote Vince Lombardi, “Clinical success isn’t
the most important thing ... It’s the ONLY important thing.
“It’s not the stuff
we don’t know that’s the problem ...
It’s the stuff we know, that ain’t so.”
Will Rogers
The bewildering messages about bonded cores
There are several rules of thumb going around the circuit right
now concerning the proper kind of bonding agent to use with self-cure
core materials.
Rule of thumb #1: Light-cure bonding agents are a no-no.
Rule of thumb #2: 5th Generation bonding agents are a no-no.
Rule of thumb #3: Self-etchers are a no-no.
I’ll grant you that bonding self-cure core materials can be
a challenge. Light-cure composites are more chemically active than
self-cures, so they bond better to virtually all bonding agents.
At the latest IADR meeting, a team of researchers from Creighton
University measured shear bond strength of two core materials to
dual-cured and chemically-cured adhesives(below).8 If
this study is clinically relevant (a valid question concerning all
bond tests), the message is pretty clear -
“All chemically-cured adhesives are not universally
compatible with all chemically-cured resin systems.”
In a similar study9 (below), researchers from
the University of the Pacific used the original hand-mixed version
of Core Paste™ instead of the automix version. And what a difference
it made!
Multipurpose™, the standout winner in the first study, came
in dead last in the second with no detectable bond at all!
To those of you who’ve been told that light-cure bonding
agents won’t bond to self-cure resins: Notice that
the highest bonds were created with Optibond® FL
... a light-cure.
To those of you who’ve been told that 5th generation
bonding agents won’t bond to self-cure resins: Notice
that there are Gen5 materials near the top of the graph (One-Step®)
AND the bottom (Optibond Solo®).
And to those of you who’ve heard that self-etchers won’t
bond self-cure resins: Notice that the self-etcher in this study
(Clearfil SE) performed just fine. Though Touch&Bond wasn’t
included in the study, it also bonds nicely both to our Absolute
Dentin (dual-cure) and to the original Core-Paste (self-cure).
These studies suggest that compatibility is very much a case-by-case
issue, and those rules-of-thumb may be “all thumbs and little
rule.” Fortunately, creating the mother-of-all-bonds to an
endo core may not be as important as some think. The forces on a
core are distributed through the crown, so stress on the tooth/resin
interface should be substantially less than on a direct class 5
or class 2.
How often have you had a core debond after the crown is cemented?
If your crown margins sit on tooth structure, I bet it’s been
pretty rare. (And if your margins don’t sit on the tooth? Well,
I’m afraid your bonding agent won’t help the poor prognosis
much.)
My suggestion? Don’t get your shorts in a bunch about the relative
bond strength of your adhesive agent. There may be a lot less to
all this than meets the eye.
If you’re still skeptical about “self-etch”
or “no-etch” systems ...
Get your hands on Gordon Christensen’s new video #C-901A. You
can get the general idea of the message from the video’s title
“YOU NEED SELF-ETCHING PRIMERS.”
He doesn’t
give preference to any particular self-etcher. In fact, he says
this is the first time he’s ever evaluated a product category
this large and liked every brand in it.
* If you doubt my
assertion, drop me a note and I’ll send you an annotated bibliography.
** I apologize that all my examples involve Parkell products, but
that’s MY narrow area of expertise.
1 Miyakoshi S, et al. 4-META resin inhibits the proliferation
of oral bacteria, Jour Dent Res. 81:Spec, Abstr #1791, Mar 02
2 Sudsangiam S, van Noort. Do dentin bond strength tests serve a
useful purpose. Jour of Adhsv Dent. 1:1, p57-67, 99
3 DeHoff PH, et al. Three-dimensional finite element analysis of
the shear bond test. Dent Mater. 11:2, p 126-31, 95
4 Platt JA, et al. Correlation of dentin adhesive laboratory and
clinical performance at one-year. Jour Dent Res, 75:Spec, Abstr
#1282, p178, Mar 96
5 Platt JA, et al. Correlation of dentin adhesive laboratory and
clinical performance at 2 years. Jour Dent Res. Abstr #1368, p184,
Mar 97
6 Blunk U, Roulet JF. Effect of one-year waterstorage on the effectiveness
of dentin adhesives in Class V composite restorations. Jour Dent
Res. 81:Spec, Abstr #946, Mar 02
7 Finger WJ, Balkenhol M. Comparative in vitro evaluation of self-etching
primer adhesives. Jour Dent Res. 81:Spec, Abstr #2403, Mar 02
8 Latta MA, et al. Dentin bond strength of resin core pastes using
auto-cured adhesives. Jour Dent Res. 81:Spec, Abstr #1153, Mar 02
9 Hagge MS, Lindemuth JS. Shear bond strength of an autopolymerizing
core buildup composite bonded to dentin with 9 dentin adhesive systems.
Jour Prosthet Dent. 86:6, p620-623, Dec 01
©2002 Parkell, Inc. Notice
|
