Effects of bleaching techniques used in osteological preparation in biological collections and their implications for dental microwear analysis

: Dental microwear analysis is the study of enamel marks produced by ingested elements, allowing dietary inference in fossil groups. To generate these extrapolations, it is necessary to study reference specimens from biological collections. Observations on teeth of specimens treated with hydrogen peroxide (H 2 O 2 ) and/or sodium hypoclorite (naClO), a preparation technique used in some institutions, reveal patterns on the enamel surface inconsistent with dietary scars. To understand how these chemicals could be affecting teeth enamel and microwear patterns we ran controlled experiments using a Hydrochoerus hydrochaeris tooth. Distal portion was treated with naClO 1.25% for 1 minute and then with H 2 O 2 10% from intervals of 30 to 120 minutes. mesial portion was submerged in naClO 1.25% during the same intervals. Casts were made for control and treatment stages and examined in scanning electron microscope (sem) at 400x magnification. H 2 O 2 progressively softens shallow traces and at longer exposure erodes deep scars. naClO deepens the scars, changing its shape. Both chemicals homogenize enamel surface at longer exposure. Based on these results we highly recommend avoiding these chemicals and emphasize the importance of reporting their use in vertebrate collections as the inclusion of treated teeth in microwear analysis could result in erroneous dietary inferences.