# Factors Associated with the Proximity of the Incisive Canal to the Maximally Central Incisor
## 1 Introduction  
Maxillary incisors contribute to esthetics and physiological functions such as speech and mastication [1; 2; 3]. Thus, the position of the maxillary incisors is crucial in orthodontic diagnosis and treatment planning. The anterior portion of the maxilla, also known as the incisor alveolar bone, may present abnormal growth with various malformations, such as prognathism and deep bite [4]; proclined maxillary incisors are considered the most frequent type of malocclusion [5]. The ideal position of the maxillary incisors is determined based on various soft and hard tissue criteria, and patients with maxillary pragnathism typically undergo maximum anterior retraction for improving their facial and esthetic profile [6; 7; 8; 9]. Meanwhile, the clinical guideline based on the \"enlargement of discrepancy\" recommends that the maximum amount of maxillary incisor retraction by orthodontic intervention alone should be 7 mm [10; 11]. Orthodontic tooth movement within the biological limits is desirable for successful treatment results with long-term stability as excessive movement can cause fenestration and root resorption from the alveolar bone [12; 13]. One of the anatomically limiting factors in maxillary incisor retraction is the palatal cortical plate [14; 15; 16; 17; 18; 19; 20]. Moreover, the incisive canal (IC) should be considered for interventions that involve retraction of the maxillary central incisor (MCI). The IC is an anatomical structure located in the median plane of the maxillary processus gelatinus, posterior to the root of the MCI, surrounded by thick cortical bone [21]. It is an elongated structure connecting the oral and nasal cavities through the incisive and nasopalatine fornain, encompassing the nasopalatine vessels and maxillary branch of the trigeminal nerve andmaximally artery [22; 23; 24; 25; 26; 27; 28]. Because the IC is located between the palatine cortical plate and MCI, the presence and morphometric properties of the IC should also be included as essential components of the treatment planning procedure [29; 30]. Maxillary incisor retraction is presumed to influence MCI invasion into the IC, and the thrust into the IC or contact between the peri-cortical bone of the IC and tooth root induces root resorption [7; 9; 20; 30; 31; 32; 33]. According to radiographic examination, the IC is surrounded by a radiopaque cortex, shown as a well-defined radiopaque area [28]. Cone-beam computed tomography (CBCT) provides more detailed information about the IC, including morphology and morphometric properties [9; 34]. Computed tomography (CT) scans [22], micro-CT images [23], or high-resolution magnetic resonance imaging [35] have been used to analyze the macro- and microanatomy of the maxillary anterior region. In this study, the anterior maxillary region was evaluated using CBCT for tomographic imaging. CBCT administers a lower radiation dose to the patient compared to conventional CT scans and has many other advantages [36]. Because avoiding contact between the MCI and IC, and even intrusion into the IC, is vital for maxillary anterior tooth movement planning, the distance assessment between the IC and MCI has received clinical attention in the planning of orthodontic treatment involving MCI retraction [6; 7; 8; 9; 20; 29; 30; 34]. Cephalometric radiographs, which are two-dimensional X-ray examinations, cannot accurately assess the relationship between the IC and MCI owing to the overlapping of the facial structures [37]. However, they can assess craniofacial morphology and anterior tooth positioning, which are most frequently requested as part of orthodontic planning and orthognathic surgery. Furthermore, as maxillofacial morphology is closely related to jaw growth and the development of malocclusion [38], assessment of the relationship to craniofacial morphology is important for orthodontic treatment planning, in addition to structural evaluation of the IC and MCI.