Maxillary deficiency or retrusion is generally accepted as one of the most difficult and complex orthodontic anomalies to diagnose and treat. Facemask therapy is usually preferred for the treatment of subjects with skeletal and dental Class III malocclusions with a retruded maxilla, and it is known that if the patient is sufficiently motivated to wear a facemask, this type of therapy is quite successful. patient compliance required during facemask therapy due to its poor aesthetics and intraoral appliances for Class III malocclusion treatment such as the Fränkel III , bionator III don't give treatment goals .Hybrid appliance tandem traction bow appliance (TTBA)is introduced by Chun et al. 1999 , as a more aesthetic, effective and comfortable device. Klempner, 2003 modified tandem appliance and published two case reports suggested that TTBA and modified applications have a similar treatment effect to that of an expander-facemask combination(2). A review of the literature showed that there were no statistical studies documenting the effects of modified tandem appliance comparing to traditional expander-facemask therapy and these are the investigators study purposes.

Study design: patients aged between 8-10 with anterior cross bite will be selected from orthodontic department in faculty of dentistry in Damascus university. Pretreatment cephalometric radiography will be taken. Subjects follow inclusion criteria (Skeletal Class III (ANB \< 0 degree), due to maxillary retrusion, or a combination of maxillary retrusion and mandibular protrusion, Angle Class III malocclusion with an anterior crossbite., an optimum SN/GoGn angle between 26 and 38 degrees ,fully erupted maxillary incisors,,no congenitally missing teeth or congenital syndromes such as a cleft lip/palate will be . Patient will divided to two group tandem group and face mask group depended on growth pattern. Where from patients in face mask group have normal or horizontal growth pattern,tandem group have vertical one.

Appliance Design The Tandem Appliance comprises three separate components,two fixed and one removable. The upper section is a fixed McNamara expander with buccal arms soldered for attachment of protraction elastics. The lower section is consist of two bands with buccal headgear tubes and buccolingual welded arch for support . Third one is head-gear facebow inserted into the lower tubes and the outer bows bent out for elastics attachment. At the beginning of treatment, patients or Panther are instructed to wear the appliance with light, 8oz /14-16/ hours a day training elastics from the outer face-bow to the buccal arms of the upper expander. Subsequently, heavy orthopedic traction with 14oz /14-16/ hours a day,elastics effectively delivers the protraction force to the maxilla. Lateral cephalometric radiographs without the expander will be taken after a Class I molar relationship and a minimum overjet of 2 mm is obtained. Pre-treatment and post-treatment lateral cephalmetric dentofacial , sagittal and vertical skeletal parameters will be retraced by the author . Statistical analysis will be undertaken using the Statistical Package for Social Sciences, Windows version 19.0 (SPSS Inc., Chicago, Illinois, USA) Paired t-test will be used to evaluate the treatment effects and changes in same group. In depended t-test will be used to evaluate the treatment effects I between groups. confidence level 95% (P\< 0.05).