The common query about whether a tooth will float is answered by understanding the concept of density, which is the mass of an object relative to its volume. The fate of a dislodged tooth in water is determined by comparing its density to the density of the surrounding liquid. This physical property, established by the tooth’s unique composition, explains why the outcome is nearly always the same.
Understanding Tooth Density
An intact human tooth is one of the densest biological structures in the body, suggesting it will not float. The outer layer, the enamel, is the most mineralized substance, consisting of approximately 96% inorganic material by weight. This material is primarily a crystalline calcium phosphate known as hydroxyapatite.
Enamel’s high mineral content gives it a density ranging from 2.6 to 3.6 grams per cubic centimeter (g/cm³). The underlying dentin layer is less mineralized, with a density between 1.8 and 2.1 g/cm³. Since fresh water has a density of only 1.0 g/cm³, and any object denser than the fluid will sink, the tooth’s mineral structure ensures it drops straight to the bottom.
Environmental Factors and Buoyancy
While an intact tooth will always sink, environmental factors can subtly affect the sinking rate or its final resting place. One factor is the type of water, specifically its salinity. Fresh water has a density of 1.0 g/cm³, but the salt content in ocean water makes it denser, averaging about 1.025 to 1.027 g/cm³ at the surface.
This slight increase means the buoyant force is marginally greater in the ocean than in a lake, but this difference is not enough to keep the tooth suspended or floating. The tooth’s density remains too great to be overcome by the denser seawater. A tooth’s condition also plays a role, as extensive decay or fragmentation can alter the overall density.
Severe decay involves demineralization, a loss of hydroxyapatite, which slightly lowers the tooth’s average density. Conversely, the presence of dental restorations, such as amalgam fillings composed of dense metallic alloys, can increase the tooth’s overall mass and cause it to sink faster. However, the original tooth material is dense enough to ensure the object will settle rather than float.
Real World Relevance
The property that prevents a tooth from floating—its extreme density and durability—makes it invaluable in fields like forensic science and archaeology. Teeth are the most durable part of the human body, capable of resisting decomposition, fire, and environmental damage. This resilience means that in mass disasters or ancient burial sites, teeth are often the only remains preserved well enough for analysis.
In forensic odontology, teeth provide a stable record for identification because they can be compared against antemortem dental records. The dentin and enamel can trap chemical signals and ancient DNA from the individual’s diet and environment, providing archaeologists with data for genetic and dietary studies of past populations. The physical reality that teeth sink and remain intact makes them uniquely reliable markers for human identity and history.