# Evaluation of Tooth Movement Accuracy with the F22 Aligner System: A Retrospective Study
## 4 Discussion
In this regard, our data are perfectly in line with those reported by other authors with the Invisalign system, with a rotation accuracy that ranged from 49.59% \(\pm\) 29.43% (n = 128) for maxillary canines to 62.86% \(\pm\) 35.03% (n = 152) for maxillary premolars, and 57.70% \(\pm\) 29.90% (n = 143) for mandibular canines and 54.19% \(\pm\) 35.79% (n = 174) for mandibular premolars. On the whole, the imprecision of the rotation of the rounded teeth was between 2.57\({}^{\circ}\)\(\pm\) 2.16\({}^{\circ}\) and 4.38\({}^{\circ}\)\(\pm\) 3.23\({}^{\circ}\), in line with results reported byCharalampakis et al., who recorded a 3.05\({}^{\circ}\) discrepancy between the planned and achieved rotation of the mandibular canines [23]. [PERSON] et al. found that neither the use of ellipsoidal brackets nor IPR can increase the rotation accuracy substantially in the Invisalign system, although a slight improvement was noted [8]. The same authors highlighted that the accuracy of maxillary canine rotation decreased considerably if \(>\)15\({}^{\circ}\) was planned, falling from 35.8% to 18.8%. They suggest overcorrections be incorporated in the attempt to overcome this problem [7]. Similarly, [PERSON] et al. reported a decrease in accuracy from 43.3% to 23.6% when programming derotations \(>\) 15\({}^{\circ}\) for premolars, and recommended reducing the derotation speed by \(<\)1.5\({}^{\circ}\) per step to increase predictability [14]. Overall, however, it is evident that generally CAT struggles to effectively rotate the rounded teeth, and despite the introduction of purportedly more effective clinical protocols and new materials, the situation has not improved much over time. The teeth that F22 Aligner system derotated with greatest efficiency were the mandibular incisors (72.64% \(\pm\) 32.06%, n = 307), especially when compared to the mandibular canines, mandibular premolars, maxillary canines and maxillary incisors. This could be explained by the \"paddle-shaped\" coronal morphology of the mandibular incisors [40] and the smaller root surface to be moved. Analysis of the variable amounts of prescribed movement, tooth type and presence or absence of grip points revealed that these only have an effect on angulation and rotation movements. As for the former, it seems that mesial coronal tipping (accuracy from 59.4% to 67.9%, n = 297) is less predictable than the distal coronal tipping (from 67.9% to 76.3%, n = 422); this could be due to the distal thrust surface generally being smaller than the mesial one [41]. The effectiveness of distal tipping also appears to depend on the different crown heights of the various tooth types, as reflected by the different accuracy figures for the various tooth groups, with the lowest being recorded for the mandibular premolars (from 51% to 59.4%, n = 42), intermediate for the maxillary incisors and mandibular canines (from 59.4% to 67.9%, n = 179), and highest for the maxillary canines, mandibular premolars and mandibular incisors (from 84.8% to 93.2%, n = 201). However, this pattern was not repeated when mesial tipping was planned, perhaps because the distal coronal thrust surface is more homogeneous across the various tooth types [41]. It was also interesting to note that the presence of grip points tends to lower the percentage movement obtained through mesial tipping (from 59.4 to 67.9%, n = 245 to 42.5 to 51%, n = 52). Although grip points were not positioned to increase the angulation accuracy, but rather to facilitate rotation (for rotations \(>\) 10\({}^{\circ}\) of rounded teeth, and rotations \(>\) 20\({}^{\circ}\) of maxillary and mandibular lateral incisors), it can be assumed that major derotation reduces the predictability of tipping angulation movement prescribed for the same teeth. Alternatively, if CAs fit poorly in the later stages of CAT, grip points may even generate opposing forces, as previously reported by [PERSON] et al. [14].