The past 40 years in orthodontics have seen dramatic advances in materials and technology that have seen evolutionary advances in the orthodontic fixed appliance that include sophisticated bracket designs and wire formulations along with the development of armamentaria that include TADS and fixed orthopedic modifiers while AI, digital scanning and computerized 3D printing has revolutionized clear aligners to advance from Dr. H.D. Kesling’s Tooth Positioner to today’s versatile medical grade plastic tooth-moving, jaw- positioning appliances to often supplant braces. We have entered the Orthodontic Plastic Age from the Metal Age but In its commercial success and public’s attraction to its comfort and esthetics, underemphasized are its biomechanics, applications and limitations. Today’s Father/Son tandem generational review, contrasts the traditional and popular and reminds us that it is still the basis of diagnostics and biophysical realities that make orthodontic treatment predictable and possible within the Envelope of Discrepancy.