Twin Block

The Twin Block, developed by Dr. William Clark in 1977, is the most widely used removable functional appliance for Class II malocclusion. It consists of separate upper and lower acrylic bite blocks with 70° inclined planes that guide the mandible forward during function. Worn full-time including meals.

• Upper Acrylic Block — Full palatal coverage with 70° inclined posterior bite plane • Lower Acrylic Block — Lingual horseshoe design with anterior 70° incline • Adams Clasps — 0.8mm SS wire on upper and lower first molars and first premolars • Labial Bow — 0.7mm SS wire across maxillary anteriors (passive) • Ball Clasps — Lower anterior retention between canines and lateral incisors • Midline Expansion Screw (optional) — Dentaurum 602-810

When the patient closes, the 70° inclined planes interlock, forcing the mandible into a protracted position. This creates functional forward posturing that stimulates condylar growth and glenoid fossa remodeling. Full-time wear maximizes neuromuscular adaptation. Typical advancement: 5-7mm sagittal, 3-5mm vertical.

1. Receive intraoral scans (upper + lower) and construction bite (5-7mm advancement) 2. 3D-print upper and lower working models at 50μm resolution 3. Hand-bend Adams clasps (0.8mm) and labial bow (0.7mm) on printed models 4. Wax upper and lower bite blocks with 70° incline angles 5. Flask and process with heat-cured PMMA 6. Remount on articulator — verify incline angle and bilateral symmetry 7. Polish, disinfect, package 8. QC: Incline angle (70°±3°), clasp retention, passive fit

• Acrylic: Heat-cured PMMA (ISO 20795-1), minimum 2.0mm thickness • Wire: ASTM F899 SS — 0.8mm clasps, 0.7mm labial bow • Incline angle: 70° ± 3° • Sagittal advancement: 5-7mm per prescription • Expansion screw (if ordered): Dentaurum 602-810, 0.25mm/quarter-turn • QC: Bilateral incline symmetry, clasp retention test, passive fit on original model