How to Fix a Tooth With CAD/CAM (CEREC)

This instructable is about CEREC, a powerful CAD/CAM technology designed to fix teeth.
This is important because this technology is increasingly being used nation wide.

Why this matters:

1. It's here to stay.
   • Corporate mills, private practices, and national dental labs are adopting this because it's faster and cheaper--frankly insurance doesn't pay like it used to.
   • Patients love one visit crowns.
2. New possibilities for patient treatment.
   • If you can do something faster, cheaper, arguably better--why not?
   • Less sensitivity--Milled restorations have much less shrinkage than composites and less thermal conductivity than silver.
   • Quickly replaceable--break it? No problem. Mill a new one from a saved file.
3. CAD/CAM is cool

Note: Gold is the very best restoration in existence.

• It lasts longer than a ceramic crown.
• It spares the enamel from the opposing tooth
• It will not fracture catostrophically
• But it costs over $1700 an oz. 

Note:
At the time of writing, the author has no financial connections to Ivoclar, 3M, Patterson, or Sirona.

Note 2:
Sorry for taking so long! 
The community has been doing such a great job, that I couldn't think of anything of worth contributing until recently.
Feel free to PM me with any ideas you'd like covered.

Step 1: Capture a Reference

To make a restoration, the CEREC needs a 3-D model.
This model is made by taking an optical scan.

In the case of the BlueCAM (formerly state of the art), it involves stitching multiple images together.
For the OptiCAM (released late last year), the scanner creates a 3-D image by compiling from a video feed in live time.

1. Start one tooth distal (to the back) to the main tooth to one tooth mesial (to the front of the prepared tooth).
2. Have a steady hand.
3. Capture the smallest area required.  For the bluecam, try to have no more than 3 images to the model.
4. Less data-> faster processing.

Step 2: Cut the Tooth. Scan.

1. Cut the tooth.
   • CEREC needs at least 2 mm of occlusal clearance (2 mm cut off the top) for the porcelain to stay strong.
   • 1 mm axial reduction.
   • Try to have a clean preparation--preferably above the gumline
2. Scan prepared tooth.
   1. Dry.
   2. Powder (if bluecam or earlier)
   3. Scan 

Follow the same guidelines as before.

Again, try to minimize the number of scans to speed up processing power.

Step 3: Design Restoration

Good design respects the harmony of the mouth.

My observations:

• Interproximal (side to side) contacts are important.
  • A poor contact results in good getting jammed into the gums.
  • Often Food gets stuck. Gums get damaged. I recommend beefing the contacts to yellow. 2.
• CEREC tends to make a light occlusion  (a light "bite").
  • This minimizes occlusal adjustments, but is based on the assumption that teeth will supraerupt into position.  There will be a slight shifting of other teeth.
• Most patients don't care about tooth anatomy (the valleys and ridges on the top of the tooth).
  • However a good dentist tends to pay particular attention to having

For anterior cases, you *will* need to tweak things by hand. CEREC tends to create an adequate margin, contacts and occlusion. Heights of contour tend to be oversimplified and "fake" looking.

Note: There is a very well done CEREC anterior case on Youtube. 
However, it doesn't mentiont that a master ceramicist did a final cutback, build up, and glaze prior to placement. 
Of course it should look good!

Step 4: Mill

Choose the shade, material, and size.

• Dilithium silicate (e-max) is chosen for crowns and posterior onlays due to it's great toughness.
• Empress is chosen for inlays and anterior onlays due to it's easy machinability and esthetics.

Translucency

• HT- high translucency; for relatively esthetic looking restorations.  Tend to mimic enamel.
• LT- low translucency; for teeth that have been heavily stained.  Tends to block out dark spots.

Mill.

Step 5: Try In.

• Check margins and contacts.
• Grind off sprue (the thin rod that sticks out after milling).

Don't check occlusion until the restoration is cemented.

• This is because the cement film may slightly change the height of the restoration.

Step 6: Stain. Glaze. Bake

1. For the most lifelike restoration, stain it:
   • Most teeth aren't one color.
   • Darker stains in groove.
   • Increased chroma at neck of the tooth.
2. Glaze.
3. Bake.
   • Most porcelains are fairly weak until baked.
   • The baking initiates cross-linkages in the material that greatly prevent against fracture.

Step 7: Cement. Adjust Occlusion

Cement the restoration.

Adjust the occlusion:

• If the bite is too high, it will hurt to bite on the tooth.
  • If the contact point is too large, additional stress is placed on the periodontal ligament.
  • This results in great pain that is usually triggered on biting.
  • Additionally, the tooth will be increasingly sensitive to cold.
  • Generally, this can be diagnosed because the pain is quick onset, quick offset--seconds, not minutes.
• CEREC and many labs default to a crown slightly out of occlusion.
  • The theory is that a tooth will supraerupt and the crown will raise to the right place
  • Unfortunately, this doesn't work for implant crowns (which won't erupt)
  • Personally, I feel that this is mainly a matter of laziness and I like my crowns to perfectly occlude.
• For an ideal contact, aim for point contacts in harmony with the original occlusion.

Occlusion is pretty complicated.
Frankly, it is one of the most important things that a dentist should know.
Personally, I recommend Kois, Dawson or Pankey to have a good grasp of it.

Strangely, occlusion (how teeth come together) is one of the most controversial topics in dentistry.

Step 8: Strengths and Weaknesses

CEREC is a powerful technology that offers some strengths, but has serious flaws.

Strength:

• Convenient.
  • Immediate results.
  • No temporaries to break or fall out.
  • Less gas for patient.
• Cheaper
  • Less visits--less overhead: sterilization, drapes, sleeves, staff time,
  • A block of Ceramic is far cheaper than a ceramic crown.
• Quality control
  • Many labs are "off-shoring" work to Asia.
  • While some labs are great, many labs use mystery metals and techniques with no oversight.
  • Many domestic labs are also dropping in skill as experienced lab men are leaving.
  • Lastly, most domestic labs are making CAD/CAM milled crowns as their standard restoration

. Cons:

• More tooth has to be cut.
  • More tooth cut--> tooth more prone to failure.
• Inferior fit and durability to a good lab crown.
  • A good crown is built to the tooth.
    • Margins will stay intact indefinitely if hygiene is maintained and be *much* more resistance to breaking.
    • There is less space for washout.
  • The milling bur of a CEREC unit is fairly large, and will create various gaps in the restoration unless the tooth is prepared into a formless blob with minimal line angles.
    • *However,* a CEREC can be remade the same day, same hour. No problem.
    • With newer resin-modified cements, it is impossible to clinically see the difference in the short-term.
• Inferior long-term esthetics CEREC stains wash out easily. However, most people don't care.

Step 9: Final Thoughts.

Final note: what would you choose?

1. Faster, cheaper, replaceable, one visit?
2. Longer lasting, better looking, more time, more expensive?

Please tell me what you think!

Note: this porcelain-fused-to gold crown will last forever, saves more enamel, and look great for decades.
However, it takes a lot more time to make, and at least 2 visits from patients:

1. Numbing Shot.  Prep. Impress. Make temp crown. Cement temp crown
2. Wax coping. Invest.  Bake for 2 hours
3. Cast gold coping. Polish
4. Hand stack porcelain base shade.
5. Bake.
6. Cut back
7. Repeat steps 4-6 until happy. Most good labs will have 1-3 cycles. World class ceramicists may do up to 20 cycles.
8. Final contour
9. Glaze.
10. Bake
11. Seat patient in chair. Cement.  Polish