This project examined the effects of burning on saw mark characteristics of isolated semi-fleshed white-tailed deer (Odocoileus virginianus) long bones as a substitute for human remains. Different classes of saws were examined to determine which type of saw mark characteristics are obliterated when burned and which are not. The saw mark characteristics that were examined are superficial false start scratches, false start kerfs, and completely sectioned cuts with breakaway spurs/notches. The long bones were burned at the Boston University School of Medicine using a muffle furnace, at differing temperatures and at differing time increments. The author hypothesized that the higher the temperature and the longer the duration of bone burning, the greater will be the obliterative effect on saw mark characteristics. All samples were examined using a Motic® Digital Light Microscope 12 VDC with a Nikon® MKII Fiber Optic Light attached with accompanying Motic® imaging and measuring software. Distances were measured between striations on complete cuts, false start kerf widths, and false start scratch widths using the Motic® imaging and measuring software. Images were also taken of the cross sections of the kerf floors. The striations on the kerf walls, false start kerf widths, and false start scratch widths were compared to the control samples. Measurements taken from false start scratches, false start kerfs, and complete cuts were averaged and compared to the averages from each temperature and the control samples, to assess the degree of shrinkage from thermal alteration. The false start kerf profile shapes were blindly examined and classified into Class A, B, C, or D(following the system of Symes 1992) and compared to the control samples. Kerf flare and blade drift were examined to determine if thermal alteration obliterated those saw mark characteristics. The chainsaw false start kerfs and complete cuts were examined macroscopically to determine what effects thermal alteration had on those types of marks. All thermally altered samples were assessed for color change, heat-related fracturing, and whether or not the saw marks were still visible. The author found that all saw marks made with the mitre saw, crosscut saw, and bow saw were still visible and identifiable, even in a fractured state and, when burned up to 700°C for one hour. Most of the false start kerf samples were classified into the correct kerf profile shape as outlines in Symes (1992). False start kerfs and complete cuts made with the chainsaw were blindly examined and showed that these marks are distinct and easily identifiable when the bone is completely intact or has very minimal fracturing. The crosscut saw false start scratch and crosscut saw complete cut samples showed signs of shrinkage. The average width of the false start scratch samples burned at 700°C for one hour was about 50% smaller than the control sample's average width. The same was true for the complete cut striation widths. Shrinkage did not appear to alter the crosscut saw false start kerf widths or the bow saw false start scratch widths. For all cuts made with the mitre saw shrinkage did appear to alter the samples. Warping did occur where some of the burned averages were larger than the control sample averages. This suggests that some warping did take place by widening the kerf, thus changing the analysis of the saw mark characteristics. Blade drift and kerf flare were seen in the samples and thus were not affected by thermal alteration. The author's hypothesis was not rejected, because in some cases thermal alteration did modify the saw mark characteristic measurements and in some cases thermal alteration did not alter the measurements. Some of the saw marks were affected by shrinkage, while others were not. False start kerf profile shape classification was not affected by thermal alteration. The chainsaw samples were affected most by the thermal alteration, because of the obliterative effects of heat-related fracturing which progressed generally with the greater temperature.

Ce travail expérimental s’est intéressé aux lésions osseuses produites par des scies et par une hachette, sur des échantillons humains et animaux. En ce qui concerne les scies, 170 faux départs ont été étudiés au stéréomicroscope en utilisant cinq scies différentes. Les scies universelles se comportent comme les scies à tronçonner, du fait de l’inclinaison vers l’arrière de chaque dent. La largeur minimum du faux départ permet de classer les lésions selon les catégories de Symes. Les profils convexes indiquent l’utilisation d’une scie universelle ou d’une scie à tronçonner. Les profils concaves sont beaucoup plus variés, et indiquent l’utilisation d’une scie à refendre. La forme des murs permet de déterminer le type d’avoyage sauf quand ils sont droits ou difficiles à analyser. Parmi les critères secondaires, l’aspect des stries au fond de la lésion s’est révélé de grande importance pour identifier le type d’avoyage. En ce qui concerne la hachette, nous avons utilisé un protocole standardisé produisant des lésions osseuses de petites dimensions. Le stéréomicroscope a constaté le caractère vertical des stries, qui s’explique par le mouvement vertical effectué par l’instrument au moment de l’impact. Le microscope électronique à balayage a permis de décrire parfaitement les lésions, de comprendre la surélévation des berges (« uprising ») et l’effet exercé à distance (« lateral pushing back »). La présence du latéral pushing back et de stries verticales permet d’affirmer que les lésions osseuses ont été produites par un instrument tranchant contondant. Ces caractères se pérennisent même après carbonisation. / In this experimental work bone lesions produced by saws and a hatchet on human and animal samples were analyzed. With regard to the saws, 170 experimental false starts lesions were studied under stereomicroscope produced by five different saws. Universal saws behave like crosscut saws, because each tooth displays a tilt backwards. The minimum width of the kerf makes it possible to classify bone lesions according to Symes’ categories. Convex profiles indicate the use of a universal or crosscut saw. Concave profiles vary a great deal and indicate the use of a rip saw. The shape of the walls allows for determining the type of set except when they are straight or difficult to analyze. Among the secondary criteria, the appearance of the striae on the kerf floor is able to point the type of set. For the study of bone lesions by a hatchet a standardized device was used to produce small bone lesions. The stereomicroscope was able to observe the vertical striae explained by the vertical movement of the instrument at the time of impact. The scanning electron microscope allowed for a detailed analysis of bone lesions and made it possible to understand the uprising and the lateral pushing back. The presence of a lateral pushing back and of vertical striae is sufficient to determine that the bone lesions were achieved by a sharp blunt instrument. These characters are visible even after carbonization.