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So imagine you've spent so much time and efforts adjusting the temporary restorations (or mockups if you preferred so) and told your dental technician to make the final restorations according to that. How disappointing it is when you have to adjust the definitive restoration clinically and send it back to the laboratory for additional glazing? This isn't the fault of your the dental technician, but rather the inaccuracy of the analog process. There are just too many steps that can affect the final restoration. Furthermore, your dental technician doesn't use the mockup index directly, but rather manually adjusting the restoration after layering the ceramics by hands.
In the blog post, I will talk about accurately copying the temporary restoration into the final restoration by applying digital dentistry into your practice. Please note that each dental suppliers have different names for this feature: CEREC calls this feature Biogenerics copy and 3Shape calls this feature Pre-preparation. The idea is that you would scan both the temporary restorations and the prepared teeth, the software would superimpose these two models. With this information, the CAD dental software can accurately copying the mockup for you.
The diagram below provides an overview of the process using an intral-oral scanner:
Step 1: Scan everything
I prefer scanning everything at the beginning of an appointment. This includes scanning the working jaw (with mockup if available), the opposite jaw and occlusion. There are 2 reasons for doing this:
- Easier to retract patient's tongue and cheek.
- More accurate occlusion scan.
The longer you work on the patient, the longer the patient have to open their mouth. This leads to various problems that can affect the accuracy of the scan like tongue and cheek get in the way or the patient can't bite correctly due to muscle fatigue.
Step 2: Marking or cutting the teeth in working area
Instead of re-scanning the entire quadrant or jaw for the final impression, you can just cut out the area that you're going to prepare and re-scan that area afterward.
CEREC Primescan's clinical manual said that I can rescan the working area after preparation without cutting it but it doesn't work in some cases and often leads to a "heavy" scan file. I would advise against this for now.
Step by step guide on how to do this for each scanner:
- 3Shape TRIOS 3/4
TRIOS Training material on "How to Add Pre-Prepation Scan to the workflow" - CEREC Primescan/Omnicam
How to image for Biogeneric Copy with CEREC Primescan/Omnicam
Step 3: Prepare the teeth in working area
This step requires no further discussions, prepare the teeth like you normally would.
Step 4: Scanning final situation (Taking final impression digtally)
Now it's time to pack some cords and rescan the final impression with your intra-oral scanner. Like I've said in step 2, this time it would be really quick since you're only rescan the working area.
Below is what the result looks like in CEREC SW when entering Design mode. Notice the transparent contour in the four upper incisors. That's the mockup scan superimposed onto the final scan.
Have fun practicing dentistry!
