## 1 Introduction  
Temporary anchorage devices (TADs) are widely used in orthodontic treatment for expanding the boundaries of tooth movement. TADs are used to obtain skeletal anchorage to move teeth, and make it possible to achieve absolute anchorage, to distalize or mesialize molars, to intrude molars, or to rotate the occlusal plane without the patient's compliance. Two types of temporary anchorage devices are used in orthodontics, namely, miniplate appliances and miniscrew appliances. The miniplate appliances are more stable than the miniscrew appliances because they are supported by two or more screws, but flap surgery is required to insert and remove them, which causes swelling and discomfort in patients. Although the miniscrew appliances are less stable than the miniplates, they show clinically acceptable success rates, and can be placed without flap surgery. Thus, the miniscrew appliances are the most common temporary anchorage devices nowadays. While the insertion of miniscrews is much easier than that of miniplates, there are limitations regarding placement sites. Since the head of the miniscrew needs to pass through the attached gingiva to avoid patient discomfort, the position of the placement cannot be as deep as that of the miniplates. Thus, the miniscrews often need to be placed in the interradicular space whey they are placed in the buccal region, which may result in the proximity of miniscrews to the tooth roots. The proximity of the miniscrew to the roots of the adjacent teeth is a major cause of the failure of miniscrews [1]. Many previous studies have reported that a higher failure rate was observed when the proximity of the miniscrews occurred. It was reported that when the body of the miniscrew was overlaid onto the lamina dura, the success rate was only 35%, while the overall success rate was more than 80% [2]. A finite element analysis showed the excessive stress was caused by the occlusal force around a miniscrew when a miniscrew is too close to the adjacent root [3]. Thus, the miniscrew must be placed with high caution when it is positioned in the interradicular region. Furthermore, in the worst-case scenario, the tooth roots can be injured during the insertion of the miniscrews [4]. If a miniscrew touches the root of the adjacent tooth, it may damage the root surface. Most root injuries are resolved spontaneously with restorative cement formation after the removal of the miniscrews. However, root perforation was outlined in a previous report, and permanent changes are sometimes caused, such as nerve damage, lesions of the dentin-pul complex, or periapical periodontitis, and endodontic or surgical treatment might be required. Cone-beam computed tomography (CBCT) is useful to assess the root direction and bone quality of the placement site of the miniscrews [5]. Using CBCT, clinicians can measure the distance between the roots more accurately than using other 2D X-ray methods such as panoramic X-ray, dental X-ray, or cephalosporgrams. By viewing CBCT images, they can find the best place for miniscrew insertion, where there is enough interradicular distance and enough cortical bone thickness. However, if no surgical guides are utilized, the accuracy of the insertion depends on the clinical proficiency of a doctor. The doctor must put great effort into matching the CBCT image and the patient's mouth and estimating the position of the roots from the crown portions. Also, they must hold the screwdriver precisely during the insertion. Previous studies have reported that freehand insertion showed a large deviation in the position and direction of the miniscrews [6]. To overcome this issue, several methods to fabricate surgical guides have been proposed. [PERSON] and [PERSON] [7] used a prefabricated adjustable guide for placing miniscrews. The guide consisted of metal vertical arms of different lengths, and a Gurin lock for fixing the guide to the archive and the guide sleeve. [PERSON] et al.