## 4 Discussion  
Many designs of temporary anchorage devices (TADs) were developed in order to provide skeletal anchorage in adult orthodontic treatment, which was first proposed in 1983 [31]. After that, TADs started to be used widely in orthodontic treatments [32]. The mini screw is one of the TADs which gradually became popular due to its advantages of using it. The mini screw is easy to insert and remove without any complicated surgery during the orthodontic treatment as per requirements. Moreover, forces could be applied immediately after inserting the orthodontic treatment. This current study was conducted on adult orthodontic patients where first premolars were extracted, and mini screws were placed between the second premolars and first molars and used for en masse retraction of the maxillary anterior teeth. Anchorage is a very perilous factor in terms of en masse retraction procedures. Orthodontists focused on maintaining anchorage during en masse retraction for the effective outcome of the treatment [3]. There are alternate approaches developed in cases of retracting the anterior teeth efficiently. Tooth-borne anchorages require additional and complicated mechanics to control the absolute anchorage. The most common method of incisor retraction is to retract the canines followed by the four incisor teeth. However, no difference was observed between two step retraction and en masse retraction. Both procedures possessed some anchorage loss [33]. Retracting all anterior teeth with the preadjusted appliances oftentimes works as a double-edged sword for orthodontists. The advantages and drawbacks compensate each other. Whereas insignificant wire bending along with sufficient spaces work advantageously over the loop mechanics, posterior tipping and extrusion are observed in the sliding mechanics during the retraction of the anterior teeth. On the other hand, stability of the anchorage might occur while the tipping action developed into the anterior brackets. Extra oral anchorage such as Headgear has been used to strengthen the anchorage earlier; nevertheless, the action of extra oral anchorage is patient dependent [34]. Moreover, any extra oral anchorage device is typically worn for less than 12 h, while orthodontic forces need to be applied continuously and steadily. Intra oral trans palatal arches appended the anchorage to the next stages. However, previous studies showed that trans palatal arches also cause anchorage loss [35; 36; 37]. Orthodontic treatment has been enhanced with the advancement of skeletal anchorage. Dental implants [37], micro screws [32; 38], mini screws [31], and mini plates [39] provide skeletal anchorage during orthodontic tooth movement without the loss of anchorage. Retraction could be performed using the elastomeric chain or nickel titanium (NiTi) coil spring. However, the current study used only the NiTi coil spring for the anterior teeth retraction. A finite element model study was conducted to determine the stress distribution of the mini screw on the soft and hard bone along with the deformation of the tooth. The finite element models were carefully created so that the models could be utilized adequately, and the general versatility of the models was preserved. In group 1, the force application was from the titanium mini screw implant at 8 mm of height (between the second premolar and first molar) to the power arm at 4 mm of height (between lateral incisor and canine). The force was applied bilaterally at the force of 250 gm/side and was delivered by a nickel titanium coil spring. When models were analyzed in group 1 for stress generation and distribution, it was observed that, amongst central incisors, lateral incisors, and canines on both sides, maximum stress was seen around canines in hard and soft bone. The concentration of stresses in soft and hard bones around the canine is due to the initial tipping of canines, which generates maximum stress in the alveolar crest present around the canine.