Here’s an everyday CEREC partial coverage case. The large failing amalgam on the first molar is an indication for an indirect restoration, but that big fat palatal cusp looks rock solid. In my opinion, if I can maintain the palatal cusp 3 mm wide at its base, I will go with partial rather than full coverage. Why 3 mm? There is no scientific reason behind this number; it just feels right to me. I feel very confident that if I have a solid 3 mm thick cusp it will hold up just fine, assuming no parafunction. The beauty of CEREC is that I can prep these teeth very conservatively. I removed only the dentin and enamel I absolutely needed to ensure a clean bonding surface.
I usually don’t like Empress in the posterior, but I’ll make an exception for partial coverage. Again, I don’t have any science to back this up, but I figure that with this prep design the bond will fail before the material will fracture, so I can get away with a “weaker” porcelain. In fact, while I’ve had some partial coverage restorations debond, I have yet to have one fail due to material fracture. Empress is a great choice for partial coverage because it mills quickly and looks beautiful with amazing margins. This is Empress A2 Multi bonded with Interface, Surpass, and Anchor A2.
CEREC parameters…. often mysterious and misunderstood, although the latest versions of the software do a great job showing exactly what each parameter does. If you are ever in doubt, go into your parameters, move the sliders around, and watch what happens on the screen.
CEREC docs often want to compare each other’s parameters, so here are mine:
Occlusal milling offset -175
Proximal contact strength 0
Occlusal contact strength -25
Dynamic contact strength 0
Minimal thickness (occlusal) 700
Minimal thickness (radial) 500
Margin thickness 120
Marginal adhesive gape (onlays only) 80
So there they are. Now before you run off to your machine to change your parameters to EXACTLY the same as mine 😉 keep in mind that my parameters are not based on any science or research. I’ve set them there because that’s what they teach in Scottsdale and they seem to work for me. And if your parameters are working for you, then don’t change them! The only time I might suggest that a CEREC user adjust their parameters is if they are consistently having the same problems like high (or low) occlusion, binding, open margins, etc. But if you’ve got your workflow dialled in and are in tune with your machine, don’t mess with success! Changing the parameters might throw everything off.
My parameters are generally “set it and forget it”. In fact I had to open my machine and check what my parameters were for this post, since I usually don’t even give them a second thought. I rarely change my parameters (except when restoring implants which is a completely different story). But here are two situations where I might consider adjusting my parameters for a case.
Situation 1 – Changing parameters to check minimal thickness
The occlusal minimal thickness parameter can be used to check the material thickness of your proposal before sending it to the mill. This is a very fast and easy way of checking for thin spots in your ceramic that might cause increased risk of fracture.
When you are finished your design and ready to check material thickness, click on the Restoration Parameters at the bottom of the screen. These are your Local Parameters and will only affect this case (as opposed to the Global Parameters accessed via the top of the screen that will affect ALL cases).
My Minimal Thickness (Occlusal) parameter was originally set at 700 microns. Move the slider from 700 to 1500, which is the recommended minimal thickness for most materials. Note how the light blue bubble over the prep gets a little bit thicker when you move the slider to the right.
Now when I go back to my proposal, the light blue minimal thickness bubble is showing through the proposal in all the areas that are less than 1500 microns thick. I can then adjust my proposal to make sure my ceramic is at least 1.5 mm.
Pretty neat trick, right? A beginner CEREC user might wonder why we don’t just set the Minimal Thickness parameter to 1500 microns in the first place? Why set it at 700 microns and then change it to 1500 microns to check the thickness? The answer is that if you set the Minimal Thickness parameter too high, you can get crazy proposals as the software tries to design without violating the Minimal Thickness parameter. Which of these two initial proposals would you rather work with?
I would much rather deal with some minor minimal thickness issues in the second proposal than try to fix the occlusion in the first one. So this one situation where I might consider changing my parameters – to check for minimal thickness. Now on to Situation 2.
Situation 2 – Changing parameters to correct binding or seating issues
CEREC likes super smooth preps. If you have some rough or sharp spots on your prep, the software does a very good job overmilling these areas, but every once in a while you will have a bump in your prep that interferes with seating. If this happens, the ceramic will bind and not seat all the way, leading to an open margin. This is much more common in partial coverage than full coverage restorations, so I routinely check for binding every time I do partial coverage. Here’s how I do it.
This is what the Mill Preview screen usually looks like when you are ready to mill.
To check for spots that might be binding and therefore interfere with seating, first turn on the rest of the model by selecting Display Options, and then turning the Upper (or Lower) Jaw on.
Now take the model and flip it over. Imagine if you were working on a stone model and you flipped it over to look at the base of the stone. This is the view you will see. It’s a little tough to wrap your head around it from looking at a static image, but you are actually looking at the underside of the prep. The important thing to note is the light grey speck. This speck is an are of binding, where the ceramic will not seat all the way.
At this point you have 4 options:
Go ahead and try to seat it anyways and risk an open margin.
Go back and smooth out the prep, and the re-do the imaging and design.
Mill the ceramic, remember the binding spot, and then adjust the corresponding spot on the ceramic.
Change the parameters.
Guess which option I chose for this case! Go to the Local Parameters again, and this time change the Spacer from 120 to 150 microns.
Now when you go back to the Mill Preview screen the grey speck is gone! By increasing the spacer, you have eliminated the binding spot and everything will seat perfectly.
Here is the final case fully seated. Emax A2 HT.
So that is the second type of case where I might consider changing parameters – to correct binding and seating issues.
There are so many options for CEREC materials these days that it is easy to get stuck in a rut of using the same block for every single case. But if you are looking to take your CEREC experience from GOOD to GREAT, keeping different materials on hand and understanding when to use each one is a great place to start. These days my go-to block is Emax. It’s a beautiful block with a long history, but don’t forget about other blocks too – in this case, Dentsply’s Celtra Duo.
This is a very straightforward everyday molar case. Conservative prep with high and dry margins wherever possible. I am relying on the bond, not the prep, for retention, especially the bond to that big fat 360-degree band of enamel.
And here is the finished case in Celtra Duo, hand polished, A1 HT, bonded with Surpass and Anchor. Nothing fancy or special about this case, which is exactly the point. This is an everyday molar crown situation – one that I’m sure we all see many times a day.
But let’s talk materials, which is the whole point of this post. 6 years ago when I first started my CEREC journey, I would have done this case in Vita Mark II. I’ve had to replace a bunch of those due to fracture. Ever since I got my Programat CS oven a few years ago, these cases would be 100% Emax with an extremely high success rate. But these days I like to keep an open mind to alternative materials, in this case Celtra Duo. I am not ready to replace Emax as my workhorse, but Celtra Duo does have a couple of advantages over Emax, namely speed and simplicity.
Celtra Duo, as the name implies, can be finished in two ways. It can be glazed in the oven like Emax, or hand polished right out of the mill. This case is hand polished. There is no characterization or glaze. We dentists will nitpick about the lack of stain and characterization, but to the patient this is a perfectly acceptable and beautiful result, completed in half the time it takes to fabricate an Emax crown. I also love the fact that if you do choose to bake it, you can place it directly on the firing tray without the messy putty. And by the way, the cost per Celtra Duo block is about half the cost of an Emax block!
It’s not a perfect material, however, and the compromise comes in its lower flexural strength vs emax. Out of the oven, Celtra and Emax have similar flexural strengths of about 360 MPa. But hand polished Celtra is lower at about 210 MPa (compared to 160 MPa for Vita Mark II). The question though, is how strong of a material do you really need? In other words, if flexural strength was so important to CEREC success, why don’t we all use full contour zirconia crowns (1200 MPa)?
In my hands, assuming proper prep design, material thickness, and bonding protocol – any of these materials is appropriate for premolars and anteriors. However, I no longer use traditional glass ceramics like Vita Mark II or Empress CAD for full coverage on molars due to my personal experience with fractures. For full coverage molars, I am using mostly Emax, with some Enamic and some Celtra Duo for certain situations. I am loving Celtra Duo for these cases where I can take advantage of its simplicity and time savings versus Emax. So keep an open mind to different materials. Use some common sense, do your homework, and consult with some mentors that you trust. Having more tools in the toolbox and understanding when to use them can help take your CEREC experience from GOOD to GREAT!
As much as I love the technology, CEREC is NOT a miracle machine. Let me explain what I mean by showing you this everyday CEREC case.
This patient had old PFM’s on his premolars with recurrent decay, and a broken second molar. He was treatment planned for three CEREC crowns.
Sounds simple enough, until the PFM’s were removed and the extent of recurrent decay was clearly visible. Yuck!
No matter how confident you are in your CEREC skills, this is not a CEREC problem, it is a fundamental fixed prostho problem. You can’t expect the CEREC machine to do all the work for you! I don’t care if you reach for the CEREC or the PVS, if you can’t clean up the decay, place a pristinely bonded composite core, get excellent isolation, and clearly expose the margins, you might as well reach for the forceps.
So don’t expect your CEREC to be a miracle machine. If you can’t get a clean prep and image, you are likely going to fail no matter what technology you choose. These were restored with Emax LT A2 on the premolars, and Enamic HT 1M2 on the second molar.
This is one of my favourite CEREC cases ever. Non-CEREC docs just don’t understand the gratification that comes from treating an emergency single central case like this same day. Here’s what happened:
I was having dinner with my aunt when she bit down on a crab leg and heard “CRACK!”. Uh oh. She spit the crab shells out and along with it about two-thirds of her upper left central. Since she wasn’t in pain and we were really enjoying the crab, we finished up dinner and then headed into the office. I guess it pays to have a dentist in the family!
She saved the broken piece and it was a pretty clean break. Good thing too, because by now it’s 9 pm and I can use one of my favourite time-saving CEREC tools – it’s biocopy time! This is a perfect biocopy situation; I’ll get a perfect proposal with minimal software design time, and I don’t even need to scan a lower arch or take a buccal bite.
Not my greatest prep. But cut me some slack – it was past 9:30 pm now and I was alone at the office with my aunt.
Here it is right out of the milling unit. Biocopy is awesome – a perfect copy of the shape and contours of the pre-op condition. This is emax HTA2. Now time to make it pretty.
Here’s my stain and glaze plan. I used three shades of the standard emax stains – sunset, blue, and white.
The final CEREC crown immediately post-op.
And here she is at recall. Not bad for a Saturday night emergency!
Quite a few people have emailed me asking me about my go-to prep design: occlusal reduction and minimal football bur bevel margin on the facial. It seems docs out there are worried about debonds with such a minimally retentive prep design.
The short answer: NO – I am not worried about debonds with a very conservative and minimally retentive CEREC prep.
The long answer: Well…. of course I always try to minimize the chance of failures, including debonds, with every restoration I place, CEREC or not. Read on for more of my thoughts…..
As a refresher, here is the prep design in question:
This is my typical CEREC prep:
Remove existing restorative material
Get occlusal reduction
Flat top the lingual margin (sometimes I’ll drop a 1-2 mm chamfer)
Football bur esthetic bevel as coronal as possible on the facial
Smooth everything off
The end result is a very conservative, minimally prepped tooth. I am relying a great deal on bonding and very little on conventional retention form.
Let me start by saying I have only had a single debond out of probably 1,000 units prepped exactly like this. That single debond was two days after the crown was cemented, and the adhesive failure was at the crown-cement interface; all of the cement was still on the tooth and none was in the crown. I suspect that this failure was due to a mistake in how the crown was treated during the bonding steps. So chalk it up to user error.
Now having said that, I know we all realize that the key to an astronomical 999/1000 success rate is simple: case selection.
I don’t use this prep design all of the time. I use it when I feel like I can get 99.9% success. A simpler way to look at it is to break down the situations where I don’t feel comfortable with such a non-retentive prep design:
Too much of the margin on old, dirty, sclerotic, amalgam-stained dentin
Too much of the margin that is subgingival, i.e. you may need to cement the crown with RMGI vs bond due to lack of isolation
Signs of heavy side to side bruxing that will put excessive lateral forces on the crown
I believe that with today’s bonding agents, it is not always necessary to prep conventional 6 degree tapers with 3 mm ferrule like we were taught in school. As long as you have a big fat band of clean enamel and excellent isolation, trust your bonding agent. As a result, a conservative CEREC prep will:
Save as much natural tooth structure as possible
Be very easy to image and marginate in the software
Offer great isolation and predictable bonding
Be very cleansable for the patient
Be very easy to monitor for leaking margins at recalls
Endo, core, and CEREC crown is a very common procedure in my practice. Traditionally, the endo is completed first, then the core built up, and then the crown prepped. While that is a perfectly acceptable treatment sequence, we CEREC docs are always looking for any tiny little edge we can gain in terms of efficiency and simplicity. So think outside the box – why not prep the crown first, fabricate the CEREC crown while you complete the endo, and then cement?
First, here are some reasons WHY you might want to use this workflow:
Leverage CEREC fabrication time so that the patient’s total appointment length is shorter. The CEREC crown will be made while you do the endo. For molar endo, core, and CEREC crown I book a total of 90 minutes.
One consistent and smooth workflow for the doctor. During this procedure I don’t stop working except for PA’s. With the traditional method, I would do the endo, prep the crown, take a long break while the CEREC crown is fabricated (which usually takes about 45 minutes in my office), and then come back to the patient to cement.
The core build up is super easy. I use a resin cement that also acts as a core material (continue reading below for more details). When I am ready to cement, I fill the endo access with cement, fill my CEREC crown with the same cement, seat the crown, and cure everything at the same time.
Let’s look at an everyday endo/core/CEREC case that demonstrates some tips, indications, and contraindications for one of my favourite (and most productive!) CEREC appointments.
This patient’s upper left first molar was diagnosed with irreversible pulpitis and treatment planned for endo, core, and CEREC crown. Right away I start thinking about my prep design. Since this will be a RCT-treated tooth, partial coverage is out of the question. This looks like a great case for my go-to prep design – reduce the occlusal, football bur esthetic bevel on facial to blend in the margin, and maybe drop a small margin on the lingual. As I hope you’ve noticed before, I have a lot of faith in bonding versus traditional mechanical retention form, especially when bonding to high and dry margins with a thick band of enamel.
But WAIT!!! Don’t prep that CEREC crown yet! These days I always do my endo access first before prepping the crown. I have found that if I do it the other way around (prep the crown first and then do the access), I lose my orientation and anatomical landmarks, and my endo access ends up too large or in the wrong part of the tooth.
Do the CEREC scan once the prep is complete. After acquiring prep, opposing arch, and buccal bite images, you are brought to this screen:
Normally you would stitch the upper and lower models together using buccal bite, and then proceed with the right arrow to the rest of the design. But in this case, don’t forget that the tooth was scanned with an occlusal endo access. If we were to proceed as normal, the software would try to design a crown with a post in the middle going down into the endo access. This will result in a crown with a funny proposal, or it won’t seat, or it will seat but may have higher risk of tooth fracture. Instead, we need to trick the software into “forgetting” that there is an occlusal endo access so that it can design a “normal” crown. We will deal with the endo access later.
So when you get to the Buccal Bite Registration bite registration step, go back (left arrow) to the Edit Model phase:
Now you can see the image of the prep with the occlusal endo access. On the right side of the screen, click on “Tools”, and then “Replace”.
To use the Replace tool, draw a line around the occlusal access. It doesn’t need to be super precise, just whip it around the neighbourhood of the access like a lasso.
Drawing the line for the Replace tool is similar to drawing the margin. Double click to end the lasso, and then click “Apply”.
The software will “replace” everything inside the lasso with smooth, average data – virtually filling your occlusal endo access! Now you can proceed with the design and fabrication of the CEREC crown as normal.
Here’s an angled shot of the prep with the “virtual core” made with the Replace tool. Note my preferred prep design for almost all of my CEREC crowns – reduce occlusally, football bur esthetic bevel on the facial to blend in the mid-facial margin, and then either flat top the lingual or drop a very small margin (as I did in this case).
Another angle showing the esthetic bevel, made with a football-shaped diamond bur. I find this to be the best design for blending in a mid-facial margin.
Software design is complete, shown below with and without the crown.
On most cases, the CEREC crown is out of the oven right around the time I am finishing up the endo. Ideally the timing works so that I can obturate, clean up the access and prep, and go right into bonding the crown without stopping, all under rubber dam for the most ideal isolation. One of the keys for this workflow is to use a cement that can act both as a cement for the crown as well as a core. I use products from Apex Dental Materials: Interface to etch and silanate the emax crown, Surpass (3 bottle etch/prime/bond), and Anchor dual cure cement and core material.
This is a video of the bonding step. Surpass bonding agent is applied. Anchor is injected into the access to act as a core, and then also to seat the crown, and the whole complex is cured as one monolithic piece.
And here’s the final result. Emax A1HT, lightly stained and glazed. The whole thing completed in 90 minutes with no interruptions other than stopping to take PA’s required for the RCT.
This is my preferred workflow for endo, core, and CEREC crown. However, there are certain situations where I end up doing the traditional workflow (complete the endo, prep the crown, place the core, take CEREC images, then place the crown):
Sometimes I don’t think I could get a rubber dam clamp on if I prepped the crown before doing the endo. There are certain situations (usually buccal or lingual subgingival margins) where doing the axial reduction required for the crown prep would make isolating the tooth for endo with rubber dam very difficult.
Premolars. I tend to save this workflow for molars. The difference with premolars is that if I do the endo access first, and then prep axially for the crown, I worry that the walls of the prep will get very thin and the unsupported pieces may break off during the course of treatment. Also, I am more likely to use Empress vs Emax on a premolar than a molar, so the time savings of fabricating the crown during the endo are not as great on a premolar case.
The case above was an ideal situation for this workflow, resulting in a very smooth, stress-free, predictable, and productive appointment.
Here’s an everyday CEREC case. First molar with pre-existing MOD composite resin and recurrent decay. Don’t prep and pray – start thinking prep design right away before even touching the tooth. Because of the wide MOD filling, the buccal wall is fairly thin. There appears to be recurrent decay around the DL cusp. But the MB cusp looks big, fat, and beautiful. For this case, I’m thinking conservative CEREC partial coverage crown (or “onlay” if you prefer).
Existing restorative and recurrent decay has been removed. My indications for when to save a cusp and go partial coverage with CEREC:
I want a nice thick cusp, at least 3mm wide at the base.
The cusp can not undermined or undercut.
Restorative margin not in occlusion with the opposing tooth.
I have enough remaining sound tooth structure to bond, so that I don’t need the retention of a conventional 360-degree crown prep.
Worst case scenario, if the preserved cusp fractures, the tooth will still be restorable.
CEREC partial coverage preps need to be super smooth, with flowing line angles and margins. I dropped my favourite margin on the facial – an esthetic bevel using a football-shaped diamond bur, held at approximately 30 degrees.
These screenshots (Omnicam, SW 4.3) show another view of the shape of the esthetic bevel margin on the facial, made with the diamond-shaped football bur. This type of margin is critical for blending in the margin, especially when left mid-facial for the purposes of conserving tooth structure. There’s no point trying to be conservative and preserving a cusp, yet dropping the facial margin all the way down to the gingiva. So I like to keep my margins high and dry, and this margin design makes it easy.
The final result is a very nice looking CEREC partial coverage crown. This is Emax A2HT, bonded with Interface, Surpass, and Anchor A2. The margins are nearly imperceptible!
This patient presented with a broken premolar. The buccal cusp was intact, as was the pre-existing MOD restorative. The palatal cusp was fractured near the gingiva. Treatment plan is to restore with full coverage CEREC restoration. A conservative CEREC prep is what I would want in my own mouth, preserving as much of the buccal wall as possible.
Once the pre-existing restorative was removed, the palatal portion of the tooth was smoothed and a light finish line placed. The buccal cusp was reduced occlusally by 1.5mm, and then a long esthetic bevel placed in the mid-facial using a football-shaped diamond.
This is my preferred CEREC margin and prep design in a case like this because:
It is ultra-conservative. I’ve only reduce enough occlusally for the thickness of the material, and then a facial bevel for esthetic purposes. I am relying on bonding for the bulk of my retention.
It is FAST. A prep like this takes 5 minutes max.
The esthetic bevel results in a very smooth, gradual, and nearly invisible margin, even though it is placed mid-facial.
This is Empress A1HT, bonded with Interface, Surpass, and A2 Anchor. The conservative CEREC prep design is the key. Conservative, beautiful, and predictable CEREC dentistry – just the way it should be!
Endo treated premolar from today. These can be tricky preps. Prep a conventional 360 degree crown and all of a sudden you have zero tooth structure left. Often times aggressively-prepped premolars will come back fractured at the gingiva.
In these cases, my prep design is determined by the desire to be conservative balanced with esthetic needs. I would rather maintain the buccal and lingual walls as much as possible. However, in this case I decided to drop the buccal margin right to the gingiva in order to cover the greying endo-treated tooth. The lingual margin, however, was kept high and dry.
Emax A2LT, stained and glazed, bonded with Interface, Surpass, and Anchor. While the final result is not esthetically perfect (slight grey showing through, surface texture is a little pitted, and I don’t like the distal line angle), it certainly is very clinically acceptable and should serve this patient a very long time.