###### Abstract
According to the different studies, forces on mini screws should persist at less than 200 gf [16; 17; 18; 19; 20], and more forces have not influenced any success of the orthodontic treatment [21]. Moreover, the surrounding hard tissue and soft tissue structures are playing an important role in the success rate of mini screws, which need to be evaluated thoroughly. Though the success rate of mini screws is based on many parameters, many previous studies concentrated on the stress distribution of the mini screws in the soft and hard tissue. In addition, stress distribution on the trabecular or cortical bone varies from case to case. Moreover, the outside and inside ratio of the mini screw is also accountable for the variance of the stress distribution. The 3D Finite element method commenced to identify the tooth movement, distribution of stresses, and imitating the pattern of orthodontic tooth movement [22]. The first finite element study on stress distribution on the hard bone was performed in 2004, which reported that the 50-cN applied load on a mini screw was predominantly disseminated in the cortical bone [23]. Tooth movement could be analyzed non-invasively via the finite element models. Moreover, the amount of quantitative data about the physiological interaction and reactions of the individual tissue provided through the finite element study could increase the comprehension of tooth movement and different morphology of the tooth in a wide range. Finite element studies indicate that teeth with the deviated root are more prone to developing root resorption [24]. Moreover, the usage of torque during orthodontic treatment varies based on the appliances. A finite element study could also identify the influence of different materials such as different types of brackets on tooth movement [25]. Stresses are produced around the periodontium, while the orthodontic tooth movement takes place. During the treatment planning, these stresses need to be accounted for properly; otherwise,unbalanced forces might occur, which generally cause root resorption [26; 27]. Therefore, stress evaluation while the combination of forces was applied during orthodontic tooth movement is necessary to comprehend during the tooth movement. Finite element model analysis is one of the approaches to study stresses that deliver orthodonists the quantitative data to recognize the physiological responses of the dentition during applied orthodontic forces. The biomechanical effect on the retraction of upper incisors has been previously investigated through holographic interferometry, photo-elastic technique, and magnetic sensing system [28]. However, the former model constructed could hardly simulate the whole characteristics of the retraction system. The 3D finite element method is an efficient measure to investigate orthodontic tooth movement; nevertheless, most former studies focus on the single tooth or parameter analysis. Thus, the current study aimed to evaluate the stress distribution of the maxillary anterior segment during en masse retraction by using bilateral orthodontic posterior mini screw implants with different heights of hooks placed in the mesial to the canine.