ALUMINUM RADIOPACITY STANDARDS FOR DENTISTRY - AN INTERNATIONAL SURVEY

Objective: the aims of this study were to determine the appropriate co mposition and purity limits of aluminium alloy radiopacity standards f or dental biomaterials, taking into account the current status in repr esentative laboratories worldwide, and to formalise the calculation pr ocedure for processing radiopacity data. Methods: a series of aluminiu m step-wedges were obtained from academic and industrial research labo ratories. These were analysed by energy dispersive X-ray procedures. T he set of step-wedges were independently characterised for radiopacity at two University dental schools. Results: the percentage of aluminiu m together with the percentages of minor alloying elements (magnesium, manganese, iron and silicon) have been determined as mass percentages . For each centre, the optical density versus step-height for all wedg es was judged to fall on a common curve, with the main exception of on e step-wedge that was found to contain 4% copper, by mass. A suitable calculation procedure was described explicitly. Conclusion: of the exa mined representative step-wedges, all but the aluminium-4% copper mate rial were satisfactory and gave results comparable with wedges of high purity. Limits should therefore be revised for composition of alumini um radiopacity step-wedges or test blocks to a more realistic level of purity. Alloys with more than 0.05% copper or 1.0% iron should be exc luded and the aluminium content should be at least 98% by mass. In the calculations deployed for deriving radiopacity as 'equivalent alumini um thicknesses', an appropriate linear regression procedure should be employed and considerable care taken in the evaluation of materials of low or borderline radiopacity, relative to specification limits. The method described is principally suitable for materials with radiopacit y greater than 1 mm. For materials with radiopacity less than 1 mm alu minium, thicker specimens (2 mm) should be used. (C) 1998 Elsevier Sci ence Ltd. All rights reserved.