Effects of temperature on bone tissue. Histological study of the changes in the bone matrix

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Abstract

The analysis of burned human remains has given rise to many publications in the literature and has caused great interest among forensic specialists and physical anthropologists due to the difficulty in its analysis and interpretation. The main goal of this study has been to measure the changes that occur in bone matrix as a consequence of the increased temperature and establishing categories of histological morphology in relation to fire temperature. To this end, a total of 150 bone cylinders from the ilium obtained by bone biopsy. These samples have been obtained from forensic cadavers and burned at controlled temperatures between 100 and 1100 °C in an oven. The samples were fixed in methyl methacrylate and stained with hematoxylin–eosin, Goldner's trichrome and toluidine blue stains. The samples were studied using an optical microscope at 100×. Our study classifies the morphological changes that occur in bone matrix in four stages as a result of the temperature.

Introduction

The analysis of burnt human remains has been of great interest among forensic anthropologists largely due to the difficulty that their recovery, classification, reconstruction, and identification present. The main purpose of this analysis is to determine the best methodology for the preservation and interpretation of burnt bones as a consequence of thermal processes. We include analyses of the distinction between burnt bones with and without flesh, relation between the color and temperature reached by fire, contraction, and macro-microscopic structural changes [1].

In the last decade, the investigations have been focused on the bone surface color and the macroscopic and microscopic morphology of the crystalline structure in a controlled environment [2], [3], [4], [5]. However, a review of the anthropological literature reveals that the current methodologies for the burnt human bone analysis is still, at best, confusing. Presently there are no publications centered on the histological structural changes caused by fire.

At a macroscopic level we can observe that during the cremation process, the fire and heat modifies and destroys the bone structure in size, color and shape [6], [7]. Between 100 and 300 °C the bone dehydrates, causing a reduction in its size by 1–2 percent of its volume [8]. Afterward, between 300 and 600 °C, begins a phase which produces a change to the primary structural characteristics in the mineralized bone tissue. At a temperature of 600–800 °C, the organic material fully burns and bone structure contraction increases [9]. At temperatures higher than 800 °C, the crystals, generated by the increase in temperature, melt into bigger crystals and the bone structure becomes more fragile [10], [11]. The melting point is approximately at 1630 °C [12], [13], [14].

All of these microscopic changes have led to a wide variety of studies, the majority of which are contradictory, and the few studies on the histological changes have been performed with instruments that are too expensive for some laboratories.

Our research proposes an easily applied method with a simple microscope of which the main purpose is to determine the changes produced in bone matrix as a consequence of the increase in temperature. The study of these changes is necessary due to the important effects that fire and heat produce in the alteration of material evidence and human remains.

Section snippets

Methods

A total of 165 samples were obtained from forensic cadaver autopsies, with an age range of 26 to 88 years. All individuals had died from unexpected (not necessarily sudden) or violent death. Of the collected samples, 15 were discarded for one or more of the following reasons: time of death exceeded more than 24 h; insufficient quantity of collected samples; error in sample processing; and evidence of disease that could affect bone metabolism. Of the 150 studied samples, 87 were male and 63 were

Results

At 100 °C, micro-fractures appear in the matrix, but the most characteristic sign is the cord-like structure which corresponds to collagen fibers that tend to separate due to the effect of heat and bone micro-fracture (Fig. 2).

At 200 °C, the arrangement of the collagen fibers acquire a more rigid and compact tone, leaving this cord-like arrangement from the previous phase to acquire a bar arrangement, conferring a more orderly and parallel arrangement of the fibers (Fig. 3).

At 300 °C, this phase

Discussion

In this study, the ilium was chosen to represent the changes that occur in both the cortical and spongy bone of most of the skeleton [15], [16], [17]. During the burning process, fire affects all the muscles in an exposed body, causing muscle fibers to warm and reduce. The final position of remains is thus affected by muscle and ligament contraction that initiates after approximately 10 min at a temperature of 800 °C. This muscle contraction will result in greater exposure of certain anatomical

Conclusions

To conclude, we have focused on the histological changes in the collagen polymerization and hydroxyapatite crystallization processes. These temperature-related changes can be classified into four distinct stages (Table 1). This classification can be made by a simple bone biopsy and offers information about the temperatures to which human remains were exposed. Of course, in casework other factors also should be considered, such as duration of elevated temperatures and context.

Conflict of interest

None.

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