| Preformed metal post and resin core are widely applied in the restoration of residual crowns and roots, which can simplify the process of restoration, reduce the incidence of dental root fracture and ensure adequate retention for the prosthesis in dental practice.The proportion between the length of the post in the root and the root length plays an important role in the retention of post and core and in the avoidance of dental root fracture. Direct digital radiography helps ensure a perfect restoration by making the post in the optimal position of the root.However, the images may be larger or smaller than the actual objects, which disturbs the precise placement of preformed metal posts, since direct digital radiography system can be influenced by many factors. In this study, the lengths of the preformed metal posts in the digital images were measured with software. Through comparing the measured length with the actual value, the distortion rate was calculated, which can provide valuable information to improve the clinical application of driect digital radiography.The result is that the distortion rate of direct digital radiography in placement of preformed metal posts is high, and counter measures should be taken to minimize the distortion rate to reach the need for clinical applications. MRI is one of the most valuable diagnostic tools for the examination of the head and neck regions in radiology and diagnostic sciences. However, in patients with metallic dental devices, artifacts due to misregistration at MR imaging can obscure normal anatomy or pathologic conditions and degrade the assessment quality of regions of interest near the devices.The metallic materials widely used in dental practice include Nickel- chromium alloy, Cobalt-chromium alloy, Titanium, gold alloy, etc. The popular fixed prothesises consist of crown, post and core, fixed bridge and so on. This study was attempted to evaluate the artifacts caused by metallic materials of the fixed prothesis in MR imaging. Crowns and post-and-cores made of different metals, fixed prothesises with various units made of two types of metallic materials most popularly used in dental practice were imaged by means of 1.5T MRI apparatus in specific conditions.This investigation could provide valuable information which conforms to the practice more than that of the previous studies concerning the artifacts caused by metallic dental devices in current use.The main results are as follows:1. With the use of T1-WI GRE pulse sequence, the artifacts caused by metallic dental devices were dependent on the types of metals of metallic devices. High noble metal alloys produce small artifacts, however, Cobalt-chromium alloys produce large artifacts.2. With the use of T1-WI GRE pulse sequence, the artifacts caused by metallic dental devices were dependent on the size, on the shape, on the position in the oral cavity and on the amounts of the metals of metallic devices.3. In the selection of the materials of fixed prothesis, in terms of the generation of the artifacts, preformed Titanium post resin core could be chosen to restore residual roots and crowns as one of the optimal materials, however, the effect of the fixed prothesises covering the post-and-core on MRI should be taken into account in dental practice. |
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