## 2 Materials and Methods
### Applications of the ASSD Appliance  
* The bands for upper and lower first permanent molars in both sides were fitted, then an alginate impression was taken and poured into stone plaster for fabrication of the working model.
* Fabrication of the upper and lower parts of the ASSD (Figure 1).  
Figure 1: Upper and lower parts of ASSD appliance.  
In the upper jaw, two palatal arms made from 2 mm stainless-steel wire were soldered to the expansion mini-screw, as well as two 1.2 mm stainless-steel wire teardrop loops that are used for insertion of two anterior mini implants at the level of the first premolar connecting it to the upper appliance.  
In the lower jaw, a buccal arch made of 2 mm stainless-steel wire was soldered to the first molars band on both sides. Two buccal stainless-steel hooks solder to the buccal arch at the level of the lower canines bilaterally for the attachment of the Class III intraoral elastics (Figure 2).  
Insertion of the appliance.  
Insertion of the appliance in the patient's mouth was performed by bonding it to the teeth by glass ionomer cement (RMGI Cements, 3535 TK, 3M, Monrovia, CA, USA). After cementation of the appliance, the mini-implant was inserted at the distal end of the two teardrop loops and passively fit over it, and the expansion screw was opened by 1 mm by the operator. The mini-implant was inserted according to the manufacturer's instructions using the Cope placement protocol. This protocol is considered the least invasive protocol because, in most cases, there is no need for local anesthesia or flap incision or predrilling.  
Two mini implants were inserted about 3 mm away from the mid-palatal suture. In the anterior palate bilaterally (1.8 mm width and 10 mm length) at the level of the second premolars and about 8 mm posterior to the incisive foramen, in a position that coincides with the plane of maximum resistance of the maxilla and near to the maxillary center of resistance. The length of the mini-implant was determined according to a previous study [10; 11]. The mobility of the mini-implant was checked with the application of 500 gm of force determined by force gauge (Correx, Orthocare, U.K.), where intraoral elastics (3M, Bummer (heavy) 6 oz, 3M, Monrovia, USA) were attached in a direction nearly perpendicular to the mini-implant. This test was made at the start of treatment and every month until the end of the active treatment period [12].  
After 24 h from the fixation of the ASSD in the patient mouth (Figure 3), the patient was instructed to perform the alternate rapid maxillary expansion and contraction (Alt.RAMEC) according to the schedule given starting from 4 turns/day of open and close the expansion screw, which corresponds to 1 mm until reaching 28 turn/day, which corresponds to 7 mm until end of the active treatment period [6].  
After two weeks of the start of treatment, the patient was asked to wear intraoral elastics (3M, Bummer (heavy) 6 oz, 3M, Monrovia, USA), which exerts protraction forces of about 500 gm in each side that was attached to the upper and lower part of the appliance [13]. To decrease the counterclockwise rotation of the upper occlusal plane, the elastic oriented with a 15-30 degree angle to the occlusal plane [9]. The oral hygiene of the patients was monitored throughout the treatment.  
Figure 2: Application of Class III intraoral elastics to the buccal hooks of the upper and lower appliance.