Artifacts Of Magnetic Resonance Imaging Caused By Ni-Cr Alloy And Co-Cr Alloy In Prosthodontics

Magnetic resonance imaging (MRI) is considered a powerful diagnostic method for diseases in oral maxillofacial, head and neck, because MRI is capable of producing high resolution images in any plane and blocks without biologic hazard caused by X-ray. The presence of metallic sources, such as dental amalgam fillings, orthodontic appliances, dental metal crowns, and so on, can disturb the signal of MRI and cause artifacts, resulting in the difficulty of distinguishing normal tissues and pathologic areas. The damage in image caused by metal artifacts depends on the kind of metal material, the size of metal objects, the field strength and MRI sequences. Nowadays 1.5T and 3.0T MRI are clinically most common used. Understanding the extent of artifacts caused by dental metallic materials has great instructions on the use of dental metal and the practise of MRI on oral maxillofacial area.Objective:To investigate the influence of Ni-Cr and Co-Cr alloy procelain-fused-to-metal crowns on the artifacts of magnetic resonance imaging during the examination of 1.5T MRI and 3.0T MRI.Methods:We investigated 89 metal artifacts of 1.5T MRI and 3.0T MRI caused by Ni-Cr and Co-Cr alloy procelain-fused-to-metal crowns from clinical cases. Measure the maximum area and observe adjacent anatomic tissue affected by MRI artifacts. Use T-test to compare the maximum areas and the results indicate significant difference when P<0.05.Results:With the same field strength of MRI and the same number of tooth, the artifacts caused by Co-Cr alloy are larger than Ni-Cr alloy (P<0.05). The maximum area increases with the increase of the length of pocelain-fused-to-metal crowns (P<0.05) and shows larger in 3.0T (P<0.05). Artifacts mainly affect alveolar bones, lip, tongue and buccal tissues and show no affection on pharyngonasal cavity, orbital part, brain and cervical vertebra.Conclusions:1) Both Ni-Cr and Co-Cr alloy can produce obvious artifacts in MRI and the artifacts caused by Co-Cr alloy are relatively larger. It is better to avoid the use of Ni-Cr and Co-Cr alloy in prosthodontics.2) The maximum area of artifacts increases with the increase of the length of porcelain-fused-to-metal crowns. In clinic we should avoid long bridge of base metal porcelain-fused-to-metal restorations.3) Low field strength MRI produces smaller metal artifacts, but it has no significant difference on affected anatomic structures. Therefore, the use of low field strength MRI cannot avoid the affection of metal artifacts in the MRI of oral maxillofacial area.4) When examing the area apart from porcelain-fused-to-metal restorations, we can ignore the affection of metal artifacts and do not need to remove the restorations.