One day, a frightening scene occurred in the MRI room of a hospital, where the family secretly pushed the wheelchair into the room of MRI, resulting in the wheelchair “kissing” on the MRI machine, and the net rumor is that the repair cost of the instrument will reach 3 million yuan. The netizen exclaimed: stupidity and ignorance! Don’t be so capricious, okay? It is understood that at the time of the incident, the patient had completed the examination, and the patient’s family pushed the wheelchair into the examination room because they were anxious to pick him up from the examination room. As the MRI machine was in standby mode and still magnetic, the metal wheelchair was quickly attached to the instrument. In fact, in addition to the entry of various types of large metal objects, patients must remove all metal objects from their bodies before MRI examinations. Magnetic objects such as watches, metal necklaces, dentures, metal buttons, metal contraceptive rings, etc. cannot be worn for MRI examinations. In addition, wearing a pacemaker and having paramagnetic metal implants in the body, such as metal clips, stents, plates and screws, are not allowed to undergo MRI examinations. Experts say that magnetic resonance imaging has the advantages of high contrast, no bone artifacts, arbitrary orientation tomography, etc., and plays an irreplaceable role in head and neck surgery, neurosurgery and oral and maxillofacial surgery. However, metal restorations in the oral cavity can affect areas involving the skull, neck, face, inner ear, etc. during MRI. Therefore it is necessary to understand how much the various metal restorative materials affect MRI. In recent years, all-ceramic materials have become the first choice for cosmetic restorative materials due to their excellent aesthetics, no harmful stimulation of body tissues, and no effect on MRI of the brain and neck without artifacts, but they are expensive and therefore do not affect the mainstream status of metal restorative materials. At present, the commonly used metal restorative materials include precious metal materials such as gold-platinum alloy and palladium alloy; non-precious metal materials such as soft cobalt-chromium alloy (low cobalt content), hard cobalt-chromium alloy (high cobalt content), titanium and titanium alloy. Professionally, the artifacts caused by metallic materials are divided into ferromagnetic metal artifacts and non-ferromagnetic metal artifacts, and the size of the artifacts generated is related to the magnetization rate and magnetic field strength of the metallic materials, and the larger the magnetization rate and the higher the magnetic field strength, the larger the artifacts generated. It has been shown that in the same imaging sequence, the effect of gold alloy is the smallest, followed by soft cobalt-chromium alloy, and hard cobalt-chromium alloy is the largest. The artifacts produced by the same metal also differed in different imaging sequences. It is recommended that when only metal crowns can be used for fixed oral restorations, preference should be given to precious metal crowns, and when cobalt-chromium alloy crowns must be chosen, the MRI examiner needs to select a reasonable imaging sequence (choose a spin-echo sequence and avoid using a planar echo sequence). In addition, the classic filling material, silver amalgam, is also an alloy material. Although its impact on MRI is small and within the acceptable range, patients are advised to use non-metallic materials such as composite resin fillings in order to minimize or avoid the formation of artifacts. Some people may wonder if dental implants are also metal, will they affect the MRI? The answer is, no. Most dental implants are made of pure titanium, which has good physical and chemical properties. Titanium is non-magnetic and pure titanium dentures will not be magnetized in a magnetic field, so they will not affect the cranial MRI. In summary, gold, platinum alloys, silver and silver amalgam have minimal effect on MRI; pure titanium also produces relatively small artifacts, while cobalt-chromium and nickel-chromium alloys have a greater effect on MRI. Also, the position and size of the metal restoration within the mouth has an effect on the MRI artifacts differently. The size of the artifact is twice the proximal and distal median diameter of the metal crown and bridge and four times its buccolingual diameter. Therefore, it is recommended that when the oral fixed restoration, priority should be given to all-ceramic restorations, and when metal crown and bridge have to be used, priority should be given to precious metals (gold alloy, gold-platinum alloy, etc.), followed by pure titanium metal, followed by titanium-containing alloys, and finally cobalt-chromium and nickel-chromium alloys. Even if you choose precious metals, it is still appropriate to have individual single crowns and avoid multi-unit crown and bridge restorations.