Case Scenario: A 40-year-old female patient came to the dental clinic with complaints of a broken left upper front tooth and cavities in the left lower molar. The patient wants her teeth to be as beautiful as their original teeth. The results of the intra-oral examination showed that tooth 21 had a fracture of 1/2 crown, and tooth 36 had caries reaching the occlusal pulp extending from mesial to distal. Composite resin fillings were also seen on teeth 12 and 13, and glass ionomer cement fillings on tooth 16. After conducting other examinations and various considerations, the dentist planned root canal treatment and final restoration of teeth 21 with ceramic crowns and 36 with ceramic onlays.
Question: Explain the radiographic images of the restorative materials 21 and 36, and compare them with the radiographic images of the restorative materials of teeth 12, 13 and 16.