The effectiveness of double plate system prompted the author (Osama Al-ali) to develop a fixed double-plate system, Fixed Lingual Mandibular Growth Modification Appliance (FLMGMA), that would not require patient compliance. A PhD Clinical research is now in progress to identify the effects of FLMGMA treatment. The present case report demonstrates description and use of this new Class II corrector. The hard tissue effect was three dimensionally quantified using cone beam computed tomography (CBCT) data. In addition, three dimensional (3D) superimposition was used to display of the overall treatment outcomes qualitatively. The FLMGMA consists of two separate and fixed parts. The maxillary part consists of acrylic button, two retention wires, two retention hooks, advancement loops. The Mandibular part is made in a similar manner to a standard lingual arch but It includes an inclined guiding plane. This new corrector, which represents the fixed version of the removable double-plate system, is aesthetic, cost effective and clinically easy to handle. Keywords: fixed lingual mandibular growth modification appliance (FLMGMA), class II functional appliance, cone beam computed tomography, three dimensional cephalometric analysis, three dimensional superimposition