Study Of The Influence Of Common Metal Restorations On Magnetic Resonance Imaging In Vitro And In Vivo

Objectives To compare in oral cavity the size of artifacts of the restorations made by the four commonly-used repair materials(cobalt chromium, nickel chromium, titanium,zirconium oxide) in the nuclear magnetic resonance imaging(MRI); to observe the specifically-affected anatomical structures in magnetic resonance examination because of different materials in different dental positions and different numbers of fixed restorations inside the mouth; and to provide experimental bases for how to select fixed dental restoration materials clinically and whether the restorations of the patients undergoing the magnetic resonance examination need to be removedMethods 1 Experimental research:In vitro experiment: in the standard model of uplink 6tooth preparation, preparation of nickel chromium alloy crown, in order to ensure the uniform of the shape and thickness of each specimen, with the production of nickel chromium alloy crown as the template, to obtain the digital information of the full crown through the scanner(3-shape); to complete the production of full crowns of cobalt chromium, pure titanium and zirconium oxide with the cutting system; and finally to fabricate the an porcelain crown. With all these finished, the specimens were grouped and put into plastic containers filled with distilled water. Inspect these specimens using the common sequence(GRET2WI) in the head and neck, measure, analyze and compare the size of the artifacts.2 Clinical analysis: The cases of the study came from the patients undergoing magnetic resonance examination with head and neck in People’s Hospital of Fengrun District in Tangshan City from July 2012 to March 2015. The basic requirements were as follows: 1.5T magnetic resonance; with the method of conventional sequence scanning in craniocerebra or in head and neck; the patients wear a unit or multi-unit metal fixed restorations, but there are no metal obturators or implants or titanium plates and other metal materials in their mouths. Through access to case materials to get the basic information of patients, there was a total of 148 cases in accordance with the inclusion criteria. First observe the range of metal artifacts involved; then make the statistical analysis of the measured data using SPSS17.0 software. Comparison among multiple groups was by means of the analysis of variance, and comparison between two groups was by means of SNK test, and the comparison of the means between two groups was by means of T test. The difference was statistically significant at P<0.05.Results Under the same field intensity, the artifact areas of full metal crown made by different materials decreased in turn. The order from large to small was: nickel chromium alloy, cobalt chromium alloy, pure titanium, zirconium oxide(P<0.05); the descending order of artifact areas of porcelain crowns made by different materials was: nickel chromium alloy, cobalt chromium alloy, pure titanium, zirconium oxide(P <0.05); but with the same material, the artifact area of the full metal crown was greater than that of the ceramic crown(P<0.05) The fixed restoration of a single tooth had little effect on the anatomical structure in MRI. The fixed restorations of multiple teeth had great effect on MRI: the front teeth involved the upper and lower lips, the tip of the tongue, the gums, the alveolar bone, the nasal fossae, and the nasal soft tissue; the premolar teeth region mainly involved the upper and lower alveolar bone, the jaw, the gums, the middle of the tongue,the anterior wall of antrum highmori, the sublingual gland; the molar region mainly involved the upper and lower alveolar bone, the jaw, the gums, the middle of the tongue,the anterior wall of antrum highmori, the sublingual gland, the salivary gland and theparotid gland.Conclusions 1 Under the condition of this experiment, the artifact produced by the nickel chromium alloy was the biggest and that of cobalt chromium alloy took the second place; pure titanium had little effect on MRI and zirconium oxide had no significant effect.2 The fixed restoration of a single tooth had little effect on MRI, therefore patients needn’t remove their restoration while undergoing the magnetic resonance examination. The fixed restorations of multiple teeth had great influence on MRI, especially those made by nickel chromium alloy and cobalt chromium alloy. Therefore, in MRI examination related to the oral and maxillofacial region, the patients need to remove their restorations. And the patients should be informed of this influence. The suggestion should also be given to them that the restorations made by pure titanium and zirconium oxide be adopted. The fixed restorations of a single tooth or multiple teeth were not affected in the cranial or cervical magnetic resonance examination.