1. White SC, Pharoah MJ. Oral radiology: principles and interpretation. 7th ed. St. Louis: Mosby; 2013. p. 154.
2. Whaites E, Drage N. Essentials of dental radiography and radiology. 5th ed. Philadelphia: Churchill Livingstone; 2013. p. 120.
3. Iannucci J, Howerton LJ. Dental radiography: principles and techniques. 4th ed. St. Louis: Saunders; 2011. p. 197.
4. An overview of radiographic film holders;Dixon;Dentomaxillofacial Radiol,2005
5. Thomson EM, Johnson ON. Essentials of dental radiography for dental assistants and hygienists. 10th ed. London: Pearson; 2018. p. 169.