ABSTRACT
<p><b>OBJECTIVE</b>This study aimed to observe and evaluate six 3.0 T sequences of metallic artifacts produced by metal dental crowns.</p><p><b>METHODS</b>Dental crowns fabricated with four different materials (Co-Gr, Ni-Gr, Ti alloy and pure Ti) were evaluated. A mature crossbreed dog was used as the experimental animal, and crowns were fabricated for its upper right second premolar. Each crown was examined through head MRI (3.0 T) with six sequences, namely, T₁ weighted-imaging of spin echo (T₁W/SE), T₂ weighted-imaging of inversion recovery (T₂W/IR), T₂ star gradient echo (T₂*/GRE), T2 weighted-imaging of fast spin echo (T₂W/FSE), T₁ weighted-imaging of fluid attenuate inversion recovery (T₂W/FLAIR), and T₂ weighted-imaging of propeller (T₂W/PROP). The largest area and layers of artifacts were assessed and compared.</p><p><b>RESULTS</b>The artifact in the T₂*/GRE sequence was significantly wider than those in the other sequences (P < 0.01), whose artifact extent was not significantly different (P > 0.05).</p><p><b>CONCLUSION</b>T₂*/GRE exhibit the strongest influence on the artifact, whereas the five other sequences contribute equally to artifact generation.</p>
Subject(s)
Animals , Dogs , Alloys , Artifacts , Crowns , Magnetic Resonance Imaging , TitaniumABSTRACT
BACKGROUND: The shear bond strength between ceramic orthodontic brackets and teeth is so large that ceramic brackets are not easily eliminated safely. Whether the shear bond strength of self-etching primer/adhesive can be decreased and the injuries to enamel can be reduced has been always concerned by orthodontists. OBJECTIVE: To evaluate the bond strength between self-etching primer/adhesive system and ceramic orthodontic brackets and make a comparison with Jingjin enamel adhesive most commonly used by clinicians in China.DESIGN, TIME AND SETTING: Controlled observation, performed at Hebei University of Science and Technology in March 2006.MATERIALS: Twenty permanent premolars extracted due to orthodontic treatment were selected. The premolars were required to have excellent enamel and gloss, no cracks or carious lesions, and have not been given any chemotherapy. Ceramic orthodontic brackets were arch wire ceramic premolar brackets with 0.022-inch standard edgewide (3M company,USA). The bottom bracket area was 12.16 mm2. Self-etching sealant and TransbondTM fight-cure adhesive were purchased from 3M company, USA. Jingjin enamel adhesive, a conventional self-etching adhesive, was provided by Tianjin Institute of Synthetic Materials Industry, China.METHODS: The 20 premolars were randomly evenly divided into a self-etching primer/adhesive group, in which,self-etching sealant and TransbondTM fight-cure adhesive were applied, and a Jingiin enamel adhesive group, in which,Jingjin enamel adhesive was used.MAIN OUTCOME MEASURES: After 24 hours, shear bond strength was determined respectively in the two groups using anti-shearing testing machine. Simultaneously, residual adhesive remaining on the teeth was examined. RESULTS: The mean shear bond strength was lower in the self-etching primer/adhesive group than in the Jingjin enamel adhesive group, but there was no significant difference (P > 0.05). The mean shear bond strength in the two groups was clinically acceptable. The residual adhesive remaining on the teeth was significantly less in the self-etching prime/adhesive group than in the Jingjin enamel adhesive group (P < 0.01).CONCLUSION: Self-etching prime/adhesive system used for bonding ceramic orthodontic brackets can satisfy clinical requirements. Moreover, its bond strength can be appropriately decreased and ceramic brackets are easily removed, thereby,injuries to enamel can be reduced.