Analysis Of Multiple Factors Of The Impact Of FPD Of Different Materials On MRI Of Head And Neck

Objectives:To investigate the influence and related factors of artifacts caused by FPD(three-unit) made of different currently used materials on MRI images of head and neck, for the reference of selection of repairing material in practice, improvement of the MRI image, and upgrading of materials. Methods:A volunteer who lost his mandibular first molar on both sides was recruited, and the left was conventionally restored using porcelain FPD of 45, 46, and 47 with an inner crown of seven different materials, i.e., Ni-Cr alloy, Co-Cr alloy, Ti, Pd-Ag alloy(9052), Pd-Au alloy(sp-78), Au-Pt alloy(DIO98-2) and Zirconia. The seven FPDs was put into the mouth one at a time, then, MRI examination was conducted by two models(SIEMENS 3.0T MAGNETOM Trio and SIEMENS 1.5T MAGNETOM Avanto) in three sequences(T1-TSE, T2-TSE, and T2-GRE). As a control, MRI without a FPD in the mouth was also conducted. Structures affected by the artifacts were observed and recorded. The maximum diameter was measured according to ASTM standard F2119-07 three times each to obtain the average figures. All data were processed by SPSS 19.0, mono factor analysis of variance, and the significant level was set as P<0.05. Results: 1. Artifact signal appearanceIn TSE sequence, expressions of artifacts have nothing to do with restoration materials, MRI equipment models or T1/T2-weighted, shows up as loss of signal, change of intensity(weaken or strengthen), image distortion and different shapes on different planes. In GRE sequence, it has nothing to do with restoration materials or MRI equipment models and shows up as a suborbicular region of lost signal without a distinct border. 2. Comparison between different materials of the inner crownEffect of restoration materials on artifacts is the most significant. Under the experimental setting conditions, difference in the maximum diameter in the artifacts of 7 different materials were statistically significant(p < 0.01). Affected by the interaction of models and sequences, artifact size of the tested materials in different scanning conditions varied. 3. Comparison between different modelsMost statistics of Trio 3.0T is larger than Avanto 1.5T(p<0.05), with the same material and sequence.4. Comparison between different sequencesIt was statistically significant that Artifacts of GRE is larger than TSE(p<0.01), with the same material and model. The quality of GRE image is worse than TSE overall. 5. Affected structuresArtifacts of the FPD were restricted to the maxillofacial without the involvement of cervical spine or brain. Artifacts in TSE image weren’t over the center line, but artifacts in some GRE image went across the septum of tongue. 6. BiosafetyDuring the experiment, the volunteer had no uncomfortable feelings such as denture displacement/ tendency, the local temperature increment or electric shock-like pain in the scanning process. Conclusion:1. The three-unit FPD had no impact on the MRI image of brain, eyeballs, cervical vertebra, cervical soft-tissue, and contralateral soft tissue, but oral and maxillofacial tissue to varying degrees.2. Under the same scanning conditions, non-precious metal alloy dentures generated larger artifacts than precious metal materials. Among non-precious metal alloy dentures, the artifacts of nickel-chromium alloy and cobalt-chromium alloy were larger than pure titanium. Among precious metal alloy dentures, the artifact of gold-platinum alloy is the smallest, and all the precious metal alloy dentures are not needed to be taken off before the examination of MRI. Under some scanning conditions(Trio 3.0T:T1-TSE-sag/T1-TSE-cor/T2-GRE-tra/T2-TSE-sag/T2-TSE-cor. Aanto 1.5T:T1-TSE-tra/T1-TSE-sag/T1-TSE-cor/T2-GRE-tra/T2-TSE-sag/ T2-TSEcor.), Zirconia FPD produces a smaller artifact(not the smallest), and its MR compatibility is equal to or better than precious metals in most cases, and not involving the maxillofacial important organizational structures.3. In general, artifact is more likely to appear in GRE sequence than TSE and is bigger in higher intensity than lower. Parameter setting may improve the quality of MRI image.4. The three-unit FPD showed good biosafety to the object who accepted MRI examination in case of good adhesion.