More and more dental clinics send digital dental cases, because it greatly decreases the turnaround time. Meanwhile, many dentists ask if we can make single full zirconia crowns without 3D models. In this way, they can reduce treatment cost for their patients.
Theoretically, full zirconia crowns are computer-aid-designed and computer-aid-milled. Therefore, the margin, contact and occlusion for single crowns can be very precise. As a result, there is no need to produce 3D models. Actually, we can do that, but on condition that all digital cases come with correct bite relationship, clear margins and more importantly, doctors are willing to spend time on chairside adjustments. In reality, however, most cases don’t come to us ideally.
1. Correct bite relationship
Ideally, your scans should come to our dental lab like this. There is a correct bite relationship between the upper scan and lower scan: the upper teeth can slightly touch the lower teeth. The measurement also shows that the gap between upper and lower is 0.000 mm. With such bite, we can always make a crown with perfect occlusion.
2. Problematic bite relationship
In most cases, however, we cannot find correct bite, or even cannot find any bite relationship. Under those circumstance, we will have to print 3D models, and articulate the upper and lower models by hand.
In this case, the bite is open. Our 3Shape measurement shows that the gap between upper and lower is 0.670 mm. If we make a crown with this bite, doctors will find the crown is with high occlusion.
With this case, the upper bites into the lower.
In this case, the upper front teet can touch the lower front teeth. However, the upper back teeth cannot touch the lower back teeth.
In this case, there is no bite relationship at all.
In this case, there is no occlusal clearance. Also, the upper is a crown. So we will have to trim the abutment, and make a reduction coping for our dentist.
3. Clear margins and unclear margins
Usually, your digital dental cases should come to us with clear margins and clear shoulders. In this case, we can see the margin is above the gum. The margin and shoulder is very clear to identify. Therefore, our technicians can make crowns with great fitting.
However, on many scans, we find margins are covered with blood, saliva or gum tissue. In this case, the gum is swelling, and the blood is not cleaned. If so, Robust technicians will have to print models, and extend margins a bit by hand.
3. Need adjustments in lab
A single full zirconia crown can be precisely milled from a machine. After that, we need fine tunes for details. Also, a crown requires in-lab adjustments for proper interproximal contacts, because a full zirconia usually has thicker contacts after glaze is applied on it. Suppose we don’t print models, dentists will have a difficult time on chairside adjustments.
In conclusion, we need to print 3D models for your single zirconia crowns. Actually, we not only print high quality models, but also print 2 checing models to minimize man-made errors. A high quality 3D model should be precise and should stay in shape for at least 10 days. When we print models and make crowns without the need for chairside adjustments, our dentists and patients are always very happy.