Ikuya Watanabe, DDS, PhD(a) P. Andrew Benson, BS(b) and Khoi Nguyen, BS(b)
(a)Department of Biomaterials Science, Baylor College of Dentistry, Texas A&M University System Health Science Center, and (b)Baylor College of Dentistry, Texas A&M University System Health Science Center, Dallas, TX, USA
Purpose: The aim of this study was to examine the radiolucency of cast titanium discs having different thicknesses using radiographs taken by a dental X-ray unit under various conditions to detect internal porosity of the cast titanium metal frameworks.
Materials and Methods: Radiographs of eight cast discs (0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 4.0, and 5.0 mm thick; 8 mm diameter) were taken on dental occlusal film using a dental X-ray unit under the following conditions: tube voltage: 70 kV or 90 kV, exposure time: 0.25, 0.5, 0.75, 1.0, 1.5, 2.0, 3.0, or 4.0 s. The density levels (0, black-255, white) of the radiographs were measured using computer graphics.
Results: The mean density levels of the radiographs taken at 90 kV dramatically decreased to zero (black, X-ray 100% penetrated) with shorter exposure time and greater disc thickness. When a tube voltage of 70 kV was applied, there was a wide range of exposure times to reach a "0" density level for each disc thickness.
Conclusion: The use of lower voltage and a longer exposure time for dental X-ray unit is appropriate to clearly detect the internal porosity. (Int Chin J Dent 2004; 4: 72-77.)
Clinical Significance: Cast titanium frameworks must be examined radiographically before further steps to fabricate the prostheses in laboratory. On the basis of the results obtained in this study, the use of lower voltage and a longer exposure time for dental X-ray unit is appropriate to clearly inspect the internal porosity in cast titanium metal frameworks.
Key Words: cast defect, cast titanium, internal porosity, radiolucency.