Effect of 10% formalin on radiographic optical density of bone specimens

Objectives: The aim of this work was to determine whether the fixation process with 10% formalin modifies the radiographic optical density of bone. Methods: Eight rabbit tibiae were placed in separate containers with one of the following fixative solutions: 10% formalin (n = 3), 10% phosphate-buffered formalin (n = 3) or 10% calcium carbonate-buffered formalin (n = 2). Radiographs were obtained at 5 different times: before fixation (time zero), then I day, 15 days, 30 days and 90 days following immersion in the fixative solution. Radiographs were scanned and optical density was determined using ImageTool software. Results: There was no significant difference in radiographic optical density among the specimens fixed in 10% formalin (146.60 +/- 32.44), 10% phosphate-buffered formalin (149.84 +/- 32.43) and 10% calcium carbonate-buffered formalin (146.61 +/- 35.92). Regardless of buffering, optical density at time zero was significantly higher than that at 15 days, 30 days and 90 days. However, while optical density at I day was significantly higher than that at 30 days and 90 days, it did not differ from that at 15 days. There was also no significant difference in density between 30 days and 90 days (ANOVA, Tukey, at 5% level of significance). Conclusion: The radiographic optical density of specimens stored in 10% formalin diminishes with time, irrespective of buffering, which suggests the occurrence of bone demineralization.