# Evaluation of Tooth Movement Accuracy with the F22 Aligner System: A Retrospective Study
## 1 Introduction  
The undisputed global trend that orthodontics is experiencing today is the growing use of clear aligners (CAs) for the resolution of malocclusions of various types and severity, not only in adults, but also in growing patients [1]. This is due to the fact that CAs are aesthetically inobtrusive [2], facilitate daily oral hygiene procedures [3], do not require urgent intervention, and offer both considerable comfort for the patient and convenience for the clinician [4]. The remarkable initial success of the clear aligner treatment (CAT) has led manufacturers to develop increasingly sophisticated operating protocols [5], with the latest generation materials that, according to the manufacturers, provide superior performance [6]. This has purportedly made it possible to extend the indications for CAT to even the most severe malocclusions. However, these improvements were not validated by scientific research before they were put on the market; in fact, the most famous study to exhaustively investigate the effectiveness of CAs was conducted about 11 years after their launch, by Align Technology in 1998 (Santa Clara, CA, USA) [7]. In that study, [PERSON] et al. showed that the mean accuracy was 41%, with the most accurate movement being lingual crown tipping (47.1%), and the least accurate movements both derotation of the mandibular canines (28%) and extrusion of the maxillary incisors (18%) [7]. Recently, the same authors replicated their initial study, given that in the interim improvements had been introduced regarding aligner materials (introduction of the Smart Track(r) material, Align Technology Santa Clara, CA, USA), clinical protocols (G protocols) and digital planning [8]. However, they found only a minimal improvement in Invisalign aligner accuracy, which they calculated as at around 50% on average, with the weaknesses of the system remaining the same. In light of these results, they therefore confirmed that generally CAT should preferably be used to treat cases of mild-to-moderate difficulty, in which they were even more effective than fixed appliances (FAs) [8; 9; 10]. As for complex treatments involving extraction, ref. [11], root torque, ref. [12], overbite modifications \(>\) 1.5 mm [13] or severe rotations of the rounded teeth [14], these would be difficult to resolve satisfactorily with CAT; in such cases, it would be appropriate to opt for FAs [15; 16; 17]. Another alternative is the so-called hybrid approach, which involves combining CAs with both other orthodontic appliances (rapid palatal expander, intraoral distalizers, etc. ), with or without the use of skeletal anchorage [18], auxiliaries such as fixed vestibular or lingual sectional appliances and derotation or extrusion chains [19]. As a matter of fact, [PERSON] et al. reported that about 80% of patients treated only with the Invisalign system usually need mid-course corrections or at least one (and often multiple) additional finishing clear aligner phase, which increases both costs and treatment time [20]. In fact, the recourse to additional CAs is so common that [PERSON] et al. consider refinement/additional aligner stage as a normal phase of CAT, comparing it to the finishing phase with FAs. They reported a high percentage of accuracy of the movements investigated when additional CAs are taken into account, but acknowledged that this causes treatment times to increase significantly, with an average of 21.2 additional aligners required for each treated arch [21]. Despite the evidence in the literature, complex treatments are still undertaken with CAT and, for this reason, the results may differ greatly from those provided for in the virtual setup [7; 8; 22; 23], leading to an increase in treatment time, and in the need for multiple refinements and mid-course corrections [20]. However, the intrinsic efficacy of CAT is further hampered by other factors, such as fitting [24; 25] and patient compliance, and these factors should also be taken into account.