When an orthodontist selects an appliance for treatment, we often face a method that has slop in the system. For fixed appliances, for example, the “ideal” placement of the bracket may not lead to complete correction of the problem. For example, an incisor’s severe mesial rotation may lead the experienced provider to place the bracket more mesial than the tooth’s normal position. Hence, the tooth is not only fully rotated but overcorrected. A deep bite case may need leveling of the curve of Spee, and we add an archwire that doesn’t just finish the ideal correction but overtreats to compensate for the lag in the appliance.
Using clear aligner therapy does not avoid these same principles that orthodontists have become accustomed to implementing. The challenge in a digital system is that the CAD software shows a nice image of a simulated result. This displayed outcome can mislead many to approve cases based on how well they look on the computer screen without considering doctoring these results. We should be adding overtreatments and overcorrections to reach the desired results. Let’s review the top 3 overcorrections and overtreatments I suggest you implement into your CAD workflow:
Intrusive movements
The intrusion of L3-3 in deep bites depending on severity, finish the setup with 0 mm of overbite or even open the anterior more in severe cases.
The intrusion of maxillary molars in open bite cases is another common intrusive force that needs overtreatment. Finish your CAD setup with a posterior open bite, even if you perform a vertical bite jump.
Anterior rotations
Watch the final positions as they are often under-treated and should be over-treated. Most severe movements need greater correction since the lag in the system will leave the results lacking. Add 20% more rotation in the setup, or better yet, ask for overcorrection in your prescription notes. Your lab technician can then help you address these over treatments.
Add space for overcrowding
When addressing dental crowding, we need to ensure proper forces, adequate time, and plenty of space. There is a greater potential for collisions from overcrowding in a closed system, such as clear aligner therapy. The software often manages collisions with IPR, but in orthodontic treatment, we traditionally address crowding by expansion, proclination, or distalization. Instead of IPR, I encourage adding spaces with significant overlap to remove the unpredictability of IPR and the negative effects when the treatment does not have enough space to resolve dental arch discrepancies.
When crowding leads to greater than 50% overlap of adjacent teeth, I overcorrect the crowding adding spaces M-D to the crowding. I often add 0.2 mm of room in these contacts. When the overlap is 100% or greater, I will add 0.4 mm of interdental space. Adding this space increases the predictability of complex movements and removes factors that can cause failure. In additional aligners, excess space can be easily closed in a few aligners, while insufficient correction of complex issues can take months to correct.
