## 1 Introduction  
With the advent of digital dentistry, orthodontics has ushered in a more diverse patient population seeking more esthetic treatment options. More specifically, clear aligner therapy (CAT) has sparked the interest of patients pursuing the correction of their smiles without the use of brackets and wires [1, 2]. Clear aligner therapy has been shown to be an effective treatment modality in the correction of malocclusion. Through advancements in technology and materials, CAT has expanded its application from its initial stages of only the correction of simple anterior crowding to comprehensive orthodontic treatment [3, 4, 5]. These advancements have enabled possible tooth movements of nearly any desired vector and has established an esthetic and effective treatment option. Through its increased use in orthodontics, limitations have been noted in CAT's ability to correct malocclusions. These limitations have been brought to light through recent comparisons in the literature of ClinCheck predictions and expressed post-treatment tooth movement [6; 7; 8]. [PERSON] et al. demonstrated that Align ClinCheck software greatly overpredicts its ability to correct an anterior deep bite. This finding shows that ClinCheck software cannot accurately predict the clinical expression of intrusive movements with clear aligners. The deficiency in clinical expression was seen in 95.3% of the cases evaluated [6]. This finding comes with great clinical relevance as more and more patients are requesting this treatment modality. The issues with predicted tooth movement in CAT was even further highlighted in research by [PERSON] et al., where anterior intrusive movements were specifically evaluated [7]. Again, the predictability of CAT was questioned as it was found to have significant insufficiencies in its ability to intrude the dentition. One must question how and why these large discrepancies exist so that more accurate treatment planning and increased efficiency in tooth movement can take place. In mandibular anterior intrusion, the inaccuracy of ClinCheck's predictions in the vertical dimension should also prompt the questioning of its accuracy in a horizontal plane as well. Intrusive movements of lower incisors have historically been accompanied by the tipping or flaring of the lower incisors, also known as relative intrusion, as demonstrated by [PERSON] in the 1970s [8]. The intrusion accomplished with Invisalign CAT should be investigated for the presence of relative intrusion and an increased incisor mandibular plane angle (IMPA). This holds great clinical importance as incisor position can have a significant impact on facial esthetics and profile [9]. There has also been evidence to suggest that IMPA can play a crucial role in long-term post-orthodontic treatment stability; thus, controlling such proclination can improve the predictability of treatment [10]. Furthermore, all existing studies evaluating ClinCheck prediction have only evaluated orthodontic movements in non-growing adult patients. As CAT is being used more frequently in growing patients, it is imperative that an evaluation of efficacy in this patient population be completed. One might assume that a closer adherence to ClinCheck prediction would be observed based on the increased velocity of orthodontic tooth movement seen in younger subjects [11]. However, that has yet to be demonstrated in clinical studies related to CAT. Thus, further investigation of the efficacy of CAT in children must be conducted. The aim of this current study is to evaluate the predictability of mandibular incisor bodily intrusion in both growing and non-growing patients using CAT and ClinCheck software and evaluating the angular control of mandibular incisors during intrusive movements.