# Anchorage Loss Evaluation during Maximillary Molars
## 4 Discussion
In fact, when programming the distalization movements, it is possible to associate an intrusive force vector able to control any extrusion, simultaneously improving the fitting of the aligner and promoting the bodily movement of the dental elements. Some authors [35; 36] suggested that it could even be the structure of the aligner that promotes an intrusive movement. The results obtained indicate that the occlusal force applied in association with the thickness of the aligners promotes intrusion force and, therefore, controls the clockwise rotation of the occlusal plane during distalization. [PERSON] et al. [37] found that CAT could prevent the expression of an undesired vertical movement thanks to its structure, which covers the occlusal surface. The extrusive force vector resulting from using Class II elastics is opposed by the biting force and, therefore, keeps the vertical dimension unchanged. The limitation of these previous studies is that they measured the accuracy of the tooth movements at the final stage and not after achieving distal molar movement, so the final planning movement of the anterior teeth could influence their results. Therefore, the purpose of our study was to investigate the immediate effect of completed maxillary molar distalization on premolar and canine anchorage loss using 3D digital dental casts, and to our knowledge, only [PERSON] et al. [24] evaluated a similar clinical condition. Our chosen measurements were defined by landmarks located on palatal anatomical structures represented by the palatal rugae area, so they were not influenced by the anterior tooth movement [38; 39]. The decision to use the palatal rugae area in our study was based on the ability to evaluate the precision position of all dental elements at any given moment of the therapy, without the need to submit the patients to X-ray exposure and the possibility to use invariable landmarks for the entire treatment time. Moreover, the possibility of obtaining digital models of the patient during each orthodontic check-up allows for an accurate and rapid collection of records during treatment, without the need to request additional, more invasive, and expensive examinations. Regarding the CAT efficacy in achieving the distalization movement, our results agreed with those of previous studies [1; 17; 18; 24; 34; 40; 41], showing a significant improvement in the sagittal position of first molars, with an average distalization movement of 2.5 mm. On the contrary, a significant anchorage loss was detected at the level of both upper canines with an average of 1.3 mm of mesialization movement, while no statistically significant differences for the first and second premolars were observed. This result was also found by [PERSON] et al. [24], reporting that the anchorage loss involved the central incisors (39.9%), the lateral incisors (37.4%), and canines (22.7%) during molar distalization movement. According to the other studies presented in the literature [1; 17; 18; 24; 34; 40; 41], also in our research, no statistically significant movements were detected at the premolar level. Slight differences were found at the level of the second premolars, attributable to the start of distal movements, as required by the protocol, but nonetheless not significant. In our study as well as in the study by [PERSON] et al. [24], the major loss of anchorage was detected in patients who had poor compliance with the use of Class II elastics. This indicates that the use of Class 2 full-time elastics was able to generate an equal and opposite force to the reaction force in the anterior sector, supporting the distalization movement, strengthening the anterior anchorage, and counteracting the unwanted side effects. The significant mesial movement of upper canines could also be due to the mechanics of the device. In fact, CA is a closed system of forces, and the applied distalization movement could produce a plastic deformation of its structure, which \"stretches\" distally and produces a reaction force in the anterior part of the arch [42].