Twin block has separate upper and lower appliances with occlusal bite blocks, so the appliance gives greater freedom of movement in anterior and lateral excursions and causes less interference in normal function. The patient can eat comfortably with the appliances in mouth, and the patient can learn to speak normally with twin blocks. Twin blocks can be designed with no visible anterior wires without losing its efficiency in correction of arch relationships. Twin blocks may be fixed to teeth temporarily or permanently to guarantee patient compliance. Adjustment and activation is simple and chairside time is reduced in achieving major correction.It can also be used to correct transverse discrepancy by incorporating midline jackscrew. Therefore, the twin-block appliances due to its acceptability, adaptability, versatility, efficiency, and ease of incremental mandibular advancement without changing the appliance have become one of the most widely used functional appliances in correction of class II malocclusion.Financial support and sponsorshipNil.Conflicts of interestThere are no conflicts of interest.REFERENCES1. Kelly JE, Harvey C. An assessment of the Teeth of Youths 12-17 Years. DHEW Publication No (HRA) 77-1644. Washington, DC: National Center for Health Statistics; 1977.2. McLain JB, Proffitt WR. Oral health status in the United States: Prevalence of malocclusion. J Dent Educ 1985;49:386-97.3. Proffit WR, Fields HW Jr., Moray LJ. Prevalence of malocclusion and orthodontic treatment need in the United States: Estimates from the NHANES III survey. Int J Adult Orthodon Orthognath Surg 1998;13:97-106.4. McNamara JA Jr., Components of class II malocclusion in children 8-10 years of age. Angle Orthod 1981;51:177-202.5. Chen JY, Will LA, Niederman R. Analysis of efficacy of functional appliances on mandibular growth. Am J Orthod Dentofacial Orthop 2002;122:470-6.6. Johnson LE. Orthodontics: State of the Art, Essence of the Science. St. Louis: C. V. Mosby; 1986. p. 88-99.7. Wieslander L, Lagerstrom L. The effect of activator treatment on Class II malocclusions. Am J Orthod Dentofacial Orthop 1979;75:20-6.8. Moss ML, Salentijn L. The primary role of functional matrices in facial growth. Am J Orthod 1969;55:566-77.9. Fränkel R. The treatment of class II, division 1 malocclusion with functional correctors. Am J Orthod 1969;55:265-75.10. Bishara SE, Ziaja RR. Functional appliances: A review. Am J Orthod Dentofacial Orthop 1989;95:250-8.11. Bjork A. The principles of the Andresen method of orthodontic treatment: A discussion based on cephalometric x-ray analysis of treated cases. Am J Orthod 1951;37:437-58.12. Pancherz H. A cephalometric analysis of skeletal and dental changes contributing to class II correction in activator treatment. Am J Orthod 1984;85:125-34.13. Harris JE. A cephalometric analysis of mandibular growth rate. Am J Orthod 1962;48:161-74.14. DeVincenzo JP. Changes in mandibular length before, during, and after successful orthopedic correction of class II malocclusions, using a functional appliance. Am J Orthod Dentofacial Orthop 1991;99:241-57.