The Tweed-Merrifield Directional Force System is a system based on sound physics and biological science and allows the orthodontist to acheive proper dental and jaw function, stability, healthy supporting tissues, and the best esthetic smile. The Tweed Study Course is given twice a year and began in 1941 Dr. Lavern Merrifield, co-inventer of the Tweed-Merrifield system, was chosen by Dr. Tweed to keep the Tweed Course and Tweed Foundation the very best in orthodontics. It is the longest running orthodontic postgraduate course in the world. Dr. Merrifield was a strong leader and a brilliant thinker who contributed a wealth of knowledge and advancement to the field of orthodontics.