Fixed denture retainers are clinically common as extracoronal retainers, also known as full crowns, which means that the teeth are fully lined with porcelain, metal or all-ceramic. The types of extracoronal retainers are porcelain, metal, and all-ceramic. Metal is slightly less aesthetically pleasing, but its chewing strength is greater and it is generally placed on the back teeth; porcelain is a layer of metal base inside, and a layer of porcelain is baked on the outside, and the advantages of porcelain are more aesthetically pleasing. For some patients who have higher requirements for aesthetics, when they smile or sing, they can’t let others see that they are dentures, so they can choose a full crown of porcelain type. However, it has a disadvantage, because it contains metal, so if the patient does MRI and other examinations, the metal inside will give the examination a certain interference, so you can choose a better retainer all-ceramic. All-ceramic, as the name suggests, is porcelain inside and out, and in addition to its aesthetics, its biocompatibility is very good, and there is no irritation to the teeth at all. In addition, if an MRI examination is done later, the all-ceramic retainer will not produce magnetic interference.