Teeth frequently remain after fires, a curious phenomenon given that most biological tissues are highly combustible. Their remarkable resilience to extreme heat contrasts with other body parts, raising questions about their unique composition and what happens to them when exposed to fire.
The Unique Composition of Teeth
Teeth do not burn like other tissues due to their distinct material makeup. They are composed of four main components: enamel, dentin, cementum, and pulp. Enamel, the outermost layer, is the hardest substance in the human body. It consists of approximately 96% inorganic mineral content, primarily hydroxyapatite, with only 1% to 4% organic material and water. Hydroxyapatite, a crystalline form of calcium phosphate, is a naturally occurring mineral also found in bones.
Beneath the enamel lies dentin, which forms the bulk of the tooth structure and is highly calcified, composed of about 70% inorganic minerals, 20% organic matrix, and 10% water by weight. Cementum, covering the tooth root, has a composition similar to bone, with roughly 45% to 50% inorganic material and 50% to 55% organic matter and water. The high percentage of these non-combustible inorganic minerals, particularly hydroxyapatite, provides teeth with their exceptional resistance to fire. In contrast, other body tissues are predominantly organic, containing much higher proportions of water, proteins, and fats, which are highly combustible.
How Teeth React to Extreme Heat
While teeth do not burn in the traditional sense, they undergo significant transformations when exposed to extreme heat. Temperatures in typical house fires, often around 1,100°F (600°C), are usually below enamel’s melting point. This heat can cause dehydration and loss of water content. The organic components, though a small percentage, will char or carbonize, leading to color changes such as yellow-orange, metallic black, or chalky white, depending on temperature and duration of exposure.
As temperatures rise, the mineral structure remains, but rapid expansion and contraction can cause enamel to crack and fracture, sometimes separating from the underlying dentin. This can result in a “popcorn” effect at very high temperatures, around 2,300°F (1260°C). Despite these alterations, the core mineral structure largely persists, albeit in a more brittle and fragmented state. Damage, including micro-cracks and changes in dentinal tubules, provides clues about the temperature and duration of fire exposure.
Beyond the Burn: Forensic and Archeological Insights
The remarkable durability of teeth makes them invaluable in forensic and archeological contexts. In forensic investigations, especially where other remains are severely damaged by fire, teeth often serve as the sole means of identification. Their resistance to environmental factors like fire, desiccation, and decomposition, combined with their unique dental records, allows forensic odontologists to establish positive identification. Even fragments of teeth can provide crucial information when other parts of the body are incinerated.
In archaeology, the robust nature of teeth provides a wealth of information about past populations. Teeth preserve exceptionally well over long periods, often centuries, making them among the most commonly found human remains at archaeological sites. Analysis of ancient teeth can reveal insights into the age, diet, health, and migration patterns of individuals and entire populations. Scientists can study wear patterns, dental calculus, and even extract DNA from teeth to reconstruct aspects of ancient life, offering a unique window into humanity’s past.