## 1 Introduction  
Bimaxillary protrusion is prevalent among individuals of African and Asian descent, prompting them to seek orthodontic treatment [1, 2]. The introduction of orthodontic temporary anchorage devices (TADs) has broadened the scope of non-extraction tooth alignment by improving anchorage. However, these orthodontic treatment methods may have limitations in terms of enhancing facial esthetics due to risks of root resorption, excessive posterior inclination of the anterior teeth, and reduction in the alveolar bone in the palatal region [3].  
Anterior segmental osteotomy (ASO) with premolar extraction was developed to effectively address these adverse effects while efficiently correcting protrusions [4]. However, despite its ability to overcome several limitations of orthodontic treatment, ASO may lead to various postoperative complications and impose economic and psychological burdenson patients. According to a comparative study conducted by [PERSON] et al. [5] on ASO versus nonsurgical extraction orthodontics (NASO), the ASO group exhibited a lower Orthodontic Discrepancy Index than the NASO group did. Additionally, the ASO group showed posterior movement of the anterior maxilla [sella-nasion-point A (SNA), point A to nasion (N)-perpendicular] and a more significant reduction in the point A-nasion-point B (ANB) angle. Regarding the dentition, previous research has indicated that the changes in the angle of the maxillary anterior teeth were less pronounced in the ASO group compared to those in the NASO group [5]. Moreover, [PERSON] et al. [6] reported significant differences in incisal angle changes between the ASO and NASO groups, with values of 7.18\({}^{\circ}\) and 11.93\({}^{\circ}\), respectively. Furthermore, a recent comparative study by [PERSON] et al. [7] demonstrated that patients who underwent ASO were more likely to achieve an interincisal angle of 135 \(\pm\) 5\({}^{\circ}\) after treatment compared to those who underwent NASO, and long-term follow-up of patients who underwent ASO revealed that adverse effects were rare. However, so far, no studies have comprehensively compared the treatment outcomes between Class II ASO and NASO employing TADs. While previous studies have compared these modalities, most have focused only on ASO cases or lacked consistent adjunctive anchorage protocols. This study was distinguished by its focus on skeletal Class II patients treated with ASO or NASO while incorporating TADs in the NASO. In addition, a subgroup analysis was performed for patients with comparable baseline ANB values, allowing for a more refined comparison of treatment effects under similar skeletal conditions in borderline cases.  
Therefore, this study aimed to analyze and compare the skeletal and dental changes resulting from ASO with those of treatment with TADs in NASO. The clinical significance of this research was hypothesized to lie in its potential to assist in determining the most effective treatment outcome based on the patient's initial characteristics and concerns, thereby aiding in the formulation of an appropriate treatment plan.  
In this study, particular attention was given to the incisor mandibular plane angle (IMPA) due to its diagnostic and therapeutic significance in cases of bimaxillary protrusion, considering treatment stability or esthetic outcomes [8]. When the posterior movement of the lower incisors can be achieved by changing the IMPA--primarily through crown retraction--NASO may be sufficient to obtain the desired outcome. However, when the bodily movement of the entire tooth, including root apex retraction, is required, ASO becomes essential. Therefore, IMPA may serve as a key decision-making parameter in evaluating the appropriateness and limits of each treatment modality in this cohort.