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[Analysis of registration parameter of the dental radiographs for digital subtraction].

OBJECTIVE
To investigate the registration parameters in the dental radiographs for digital subtraction, to find out the significance of them and try to improve the quality control of the registration of the dental radiograph for the digital subtraction.


METHOD
Sixteen projections of molar and premolar of mandible of minipigs were investigated for stability of the registration system of the dental radiographs. The rotation and the movements of the bite plans were measured with different height of edge of the bite plan. The 128 radiographs with varying parameters of the projection were digital subtracted. The noise of the subtraction photograph was compared for analyses of the relationship between subtraction noise and the projection parameters.


RESULTS
The depth of the bite plan and the strength of the connect bar between the X-ray tube and the bite plans are the most significant parameters for the stability of the registration system. The thicker bar the better of the registration was. When the strength of the connected bar is increased, the depth of the bite plan is permitted not too strict. There is not significant effect for digital subtraction with other parameters in this investigation.


CONCLUSION
For the best stability of the registration of dental radiographs, the connected bar with 8 mm in diameter is strong enough and the depth of the bite plan between 2.5-4 mm are adequate.