By Dr. Amarjit Rihal
Dr. Amarjit Rihal graduated in 1995 from the University of Manitoba and is a partner in a large group practice. Currently, he is the President of the Manitoba Dental Association and serves on the boards of the National Dental Examination Board (NDEB) and the Commission on Dental Accreditation of Canada (CDAC). Dr. Rihal’s interests include CAD/CAM and implant dentistry and he currently is a mentor for CERECDOCTORS.com
What would you do in this situation? A long standing patient came in and informed me that his insurance is running out and would like to upgrade an endodontically treated tooth I restored 10 years ago with a full coverage restoration. When you look at the pre-op photo of #21 you can see that it is going to be a challenge.
Here is the bad news when I look at the contralateral tooth in comparison:
- High smile line
- #11 is a thin tooth buccal-lingually. Thin biotype with evidence of recession
- High degree of incisal translucency (3mm band) where you can see the outline of a peio-probe through the incisal edge
- High degree of surface texture with anatomic lobes (tough to replicate)
- Lots of variation in color, definitely will require a custom shade staining.
Here is the good news:
1. Open bite with minimal functional wear on adjacent teeth. This gives us some leeway with material selection.
Some practitioners that I know use their CAD/CAM systems for posterior teeth only and feel that it is not suited for anterior aesthetically demanding cases. I feel that you have greater control and more predictable outcomes in tough clinical situations with CAD/CAM materials and technologies.
First things first, what material would you use? Would you do a conventional PBM restoration? The crown definitely would be thicker than the #11 and the degree of natural translucency would be tough to match. How about a zirconia based restoration? It would still be too thick although the translucency would be a bit better with a shaded zirconia. How about a Captek crown? This is probably the best choice for a metal based restoration but the masking of the metal will reduce the natural look of the tooth. How about a monolithic EMAX crown? The crown would now be the right dimension but even a high translucency EMAX block won’t be translucent enough at the incisal edge.
The solution? I chose a multilayer feltspathic monolithic CAD block, Empress Multi-CAD. Just as a skilled ceramist would cut back this case and layer different porcelains to mimic #11 this CAD block has 3 layers of porcelain built into it. On my CEREC inLab software I can visualize the dentinal, enamel and incisal porcelain and I am able to position my crown in the block to achieve what ever desired visual effect. Another CAD advantage is the ability to modify the parameters of the mill to change the virtual die spacer… as a result I can vary the color of my cements to achieve a true life like aesthetic. Lets look at how the process works….
Open the software and tell the computer that you are going to do a crown on #21. It doesn’t stop there, I’m going to tell CEREC’s inLab software that I want to copy the surface texture of the #11. Remember I said that #11 had a thin but accentuated anatomy, CEREC will mirror the contour of that tooth exactly. This is called ‘ Biogeneric Reference’ design and is one of the biggest advantages of CEREC’s CAD dentistry. It is easy to match contralateral teeth perfectly. Here is what the administration window looks like in the software, all you have to do point and click.
Next you have to select your material. As you can see by the following slide CEREC offers you the greatest selection when it comes to material choices. This is one of the most important factors when choosing a CAD system for your office. Greater materials offer greater applications. In this case I chose Ivoclar’s Empress Multi-CAD.
Here is the actual block… if you look close you can see the different layers. They come in a variety of sizes and all the Vita colors.
Prep and scan your tooth. I did a standard CEREC crown prep and marginated the tooth supra gingivally on enamel. Since there is no metal substructure with this restoration, the preparation gets easier and you can capitalize on the bond strength of enamel. You can see the shape of the #11… tough!
The InLab software asks you what tooth you would like to reference in your design. I choose #11 and verified that I would like to mirror this tooth.
The software lets you highlight the exact areas you would like to copy as seen by the white line on tooth #11. I reference or copy the full facial surface and the incisal edge on the lingual aspect.
This is the magic moment when the computer renders your proposal. Look at how it is a perfect replication of #11.
We spend a couple of minutes adjusting a bit of the contour to make sure that the crown looks perfect before we send it to the mill.
Adjust parameters. As you can see you can specify exactly how much interproximal contact force you would like or how much die space you would like. I change the virtual die space to 100 microns to allow more room for my cement in order to intrinsically alter the final shade of the crown if needed.
Adjust incisal translucency by moving the prep in the block. You can see the different layers of porcelain by the colours, there is even a millimeter scale lower left of the screen. I make sure I have the incisal edge 3mm in the blue ‘translucent’ stratification.
After milling the restoration we do a simple custom stain/glaze. We use try-in pastes to see what colour of resin cement gives us the best result. I used Ivoclar’s Vario-link cement. Here it is immediately after cementation. One of the interesting principles behind CAD blocks is that when you bond them the fracture resistance can go from 160 MPa to close to 1000 MPa. For this particular block you would like a thickness of material to be around 1.5-2.0mm which we managed to achieve. The translucent incisal band was the result of the positioning of the prep in the CAD block and not so much by stain.
Here is the crown recalled after a few months… Notice the great gingival adaptation and natural appearance. As you can see CAD/CAM can be a true advantage when it comes to anterior aesthetic cases.
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