Resin  has used acid-etching as far back as the mid 1950s
(Buonocore)--a decade before the first commercially available composite
resin (I believe that was Adaptic, made by J&J).  Bonding agents I think
came in maybe in the 1970s--back when the only photoactivated resin was
the Nuva system--and that used UV rather than visible light.
    Parkell at one point claimed you can bond amalgam, but I don't think
I've ever heard anyone else make that claim.  When I was in dental
school (1973-76) we did NOT bond our composites.  Unbonded composites,
and esp. those self-cure resins generally available back then leaked
very badly--far worse than amalgam.  However, I would guess that modern
composite resins properly bonded probably leak less than do amalgams for
the most part.
    I don't have the confidence that Dartos does about very large resins,
because I have had some problems with them.  That may well be me rather
than a failure of the material.  There is no doubt that as a restorative
material, amalgam is closer to being idiot proof.  What that means about
me I'll leave to others to speculate.

Steve

First, ALL restorative materials leak to a certain extent.  Amalgam
leaks like a sieve.  After the gap between the amalgam and the tooth
fill with corrosion products, it leaks less than when it was first
placed.

Composite actually bonds to tooth structure.  Amalgam does not.
Properly placed composites absolutely leak less than amalgam.

Claims of superior longevity for any restorative material are
often judgement calls.  It also matters who did the work, and
with what materials/technique.

It is a little more work, and a little more demanding to place a
good posterior composite.  However, most of the important issues
are also important for a well done amalgam (i.e.-adequate decay
removal, uncontaminated tooth surfaces, and quality materials used
according to directions).

Cutting corners compromises quality of any dental work.  Amalgam
can be more forgiving for sloppy technique, but that is really no
excuse to not be just as particular with amalgam as with composite.

I've been placing posterior composites since 1984.  I have had excellent
retention and longevity with the material.  I would place my restoration
success against their amalgams any day of the week.

As far as stampeding away from amalgam, I admit to being an early
convert to composites, but it was mainly from patient preference.
I would spend 10 minutes explaining the *honest* differences between
the materials, and then the patient would say, "I want the one that
looks like my tooth".

Sure, there were a few who said, "I don't care", but not many.  I just
decided to quit wasting an hour a day when patients either preferred
composite, or didn't care either way.

Then it's just a matter of being good at what you do.

JMO,
D

Paging Hans Blix!