The effect of different combinations of fixatives and decalcifying agents on rat and rabbit hard tissues, a guide for histologic processing

Background and purpose: In order to acquire the best method that can simultaneously maximize tissue morphology and staining quality, we compared the effect of different fixative and decalcifying solutions on the quality of rabbit and rat bone histology. Method: Fifty-four rat hemimaxillae and 54 rabbit quarter-parietal bones were allocated into 3 fixation groups (formalin, 10 %sodium-phosphate-buffered-formalin and 10 %calcium-phosphate-buffered-formalin). Each fixative was divided into 6 groups and decalcified with 5 % and 10 % nitric acid (NA), 5 % and 10 % formic acid (FA), Gooding-Stewart liquid (GSL) and EDTA. Slide quality was evaluated on hematoxylin/eosin slides by 3 observers and mean-scores for total-cell-characteristics (TCC) and total-tissue-characteristics (TTC) were statis-tically analyzed. Result: Significant differences in decalcification-time were observed in different combinations of decalcifiers and fixatives in both animals. In rats, TCC was better preserved when using 10 %NA/calcium-phosphate-buffered-formalin compared to 10 %NA/sodium-phosphate-buffered-formalin (P = 0.03). GSL/sodium-phosphate-buffered-formalin performed better than both other fixatives (P < 0.001). TCC differed among the decalcifiers in each of the fixatives. In rabbits, there were differences in TCC among the decalcifiers when formalin (P = 0.001) and sodium-phosphate-buffered-formalin (P = 0.01) were used. TTC only showed significant difference when 10 %FA was used in rats (P = 0.044), with formalin performing better than sodium-phosphate-buffered-formalin (P = 0.01). Conclusion: Based on our results, if time is an issue, 10 %NA/calcium-phosphate-buffered-formalin could provide good cellular quality and if time is not a consideration, FA (5 % or 10 %) with sodium-phosphate-buffered-formalin followed by EDTA with formalin, would have the best performance. In rabbits, GSL provides the fastest results, regardless of the fixative and FA/sodium-phosphate-buffered-formalin gives the best cellular quality.