... after I wrote:

...As Eddy Murphy said, in Beverly Hills Cop (#1), as he was wished to
"Have a nice day, Mr. Foley....", as he was getting the guts punched out
of him:

.... Ah'll try....
SP

Stovamatic,

If you did a CEREC for every case you did a "core" on, how many would you do
a month?

... Can you <dong> a three unit bridge yet with the CEREC yet?
SP

George,

I will refer to this different paradigm of thinking as the "CEREC Concept".
In reality, it is the technique used by most of the more experienced CEREC
dentists who have participated in an on-line discussion forum.

This is a different way to approach dentistry.  You have to be able to
change your fundamental way of thinking.  In school we were brain-washed
into thinking separate core first, then full crown on everything which
looked weak.  Then, we got to do bridges and implants as a lot of these
teeth broke off at the CEJ.

The CEREC concept is to use the inner surface for retention, NOT the outer
surface.  Usually, there already is caries and/or existing restorations
inside the tooth.  Tradition says, we cleanout the inside, fill it, then
grind down the outer surface 0.5-2.0 mm circumferentially (depending on gold
or PFM).  What we just did, is we made the cervical portion of the tooth
paper thin.  If you would cut the crown prep first, then clean out the
inside of the tooth, you would be scared in most cases.  What tooth
structure we leave behind is pitifully thin.  Since we were taught to take
care of the inside first, then prep the tooth, we never look to see how thin
the dentin is at the cervical aspect.  Yet, every time a PFM snaps off the
root, you look inside and see how very thin we left the residual dentin that
we asked to support this entire tooth.  Vertical height of the crown prep
means nothing if the walls are 0.5 mm thick.

With CEREC (assuming you can look beyond DS), you do mostly modified Onlays
instead of full crowns.  You clean out the tooth as you would for the core.
You study the inner surface of the prep for fracture lines, (especially at
the base of the cusps).  Any thin cusps or cracked cusps, you reduce in
height 1/3 to 1/2 the height of the tooth.  Round the inner line angles to
remove sharp edges and smoothen the floor.  Make sure you do not have
undercuts at the cavosurface line angles of the proximal areas.  Powder,
scan, design, mill and bond.  NEVER prep the cervical third enamel unless it
is carious or you are trying to cover dark tetracycline staining.  You now
are leaving the tooth 4 mm --> 6 mm thick in the cervical region instead of
0.2 mm --> 2.0 mm.  I have not had a single tooth, I restored, snap off at
the CEJ since I started prepping this way.

For the RCT molar, I take a diamond disk in the HS handpiece and drop the
occlusal reduction 1/2 the vertical height of the tooth.  I remove all
existing internal restorations.  I use my straight diamond to prepare the
inner surfaces of the pulp chamber to get my retention and resistance form.
IF the pulp chamber is very short (vertically), I prep down into the root
2-4 mm to get extra length to these internal walls.  The final restoration
looks like a porcelain "mushroom".  The center of the restoration is 8-14 mm
thick.  The cusps are covered in 4 mm of porcelain.  The thickness of the
residual tooth at the CEJ is 6 mm, or so.  No metal or fiber posts in
molars.  In non-emergency cases, I cut this prep, powder, scan, design, and
start the milling process, then do the RCT.  The crown is milled about a few
minutes before the RCT is done.  Cleanout the pulp chamber with solvents,
and bond the crown in place.  RCT & Crown/Post done in just over two hours.

For the RCT pre-molar with a wide (M-D) root, I treat it like I would a
molar.  If the root is narrow in a M-D direction, I will bond in a
fibre-post (I happen to like the Whaledent ones with the bulbous top).  Once
the post is set, powder, scan, design, mill and bond.  The camera will not
see the undercut around the bulbous post-head and mill the crown with space
here.  I bond the crown in place with heated 3M Z-100 and Scotchbond.  The
"core" is created by the adhesive in this case.

For anterior RCT, the treatment is much like the pre-molar except  that the
preparation is different.  For anteriors, the facial is usually bad and I
prep the facial as you would for a labial veneer, but about 0.75 --> 1.0 mm
reduction.  Lingually, I prep down to the incisal aspect of the cingulum.  I
do not cut away healthy tooth in the cingulum area.  The final crown looks
like a thick veneer with a large incisal wrap.

Pins?  I only use those if I am trying to put back a PFM which snapped off
and I want to do a "reverse composite core" under the PFM, and the tooth is
vital.  I warn the patient that this is not very ideal, and the tooth will
probably fail and need extraction eventually.

Some CEREC users refer to the full cuspal coverage Onlay design as being a
"V-Prep".  That is because if you look at the prep from the mesial, it has a
flattened obtuse "V" shape, rather than the conventional 3-box shape.  The
outer cavosurface margin (at the enamel) is the highest point.  The dentinal
surface of the cusp tip, then slopes towards the center of the prep at about
a 30 degree angle.  The occluso-axial line-angle at this point is very
rounded.  The floor is often curved down to the center so that it is rather
like a "moon crater".  These sound drastic, but they actually sacrifice the
very thin parts of the prep, and leave the residual tooth structure very
thick and strong.

Failures only occur if you have a parafunctional clencher.  Give them and
NTI to wear at night, the failures stop.  I routinely place these
restorations on second molars.

Make sense????

W_B has sat in with me and assisted while I did some of these on a patient.
You can ask him how it comes out.