Despite differences in material composition, human and shark teeth are remarkably equally tough.
Understanding Tooth Strength: More Than Just Hardness
It's a common belief that shark teeth, known for their sharpness and predatory use, must be inherently stronger or tougher than human teeth. While shark teeth are indeed very hard, scientific research indicates that hardness isn't the only factor determining overall tooth strength or durability. Toughness, which is the ability to resist fracture, is equally important.
According to new tests reported in the Journal of Structural Biology, despite human teeth being largely composed of a mineral softer than that found in sharks, they are just as tough. This suggests that the structural design and composition play a crucial role in achieving comparable resistance to breaking or chipping under stress.
Composition vs. Toughness
The primary difference lies in the composition of the outer layer:
- Human teeth have enamel, primarily made of hydroxyapatite.
- Shark teeth have enameloid, which contains a higher concentration of fluorapatite, making it generally harder than human enamel.
However, toughness isn't simply about how hard the material is. It's about how the material and structure work together to resist the spread of cracks. Human teeth have a complex internal structure with dentin supporting the enamel, and the enamel itself has a sophisticated rod-like structure that helps dissipate forces and prevent fractures. This intricate biological engineering helps human enamel achieve a toughness level comparable to the harder shark enameloid, as demonstrated by the research.
Key Differences and Similarities in Tooth Properties
Here's a comparison of some key features:
| Feature | Human Teeth | Shark Teeth |
|---|---|---|
| Outer Layer | Enamel (Hydroxyapatite-rich) | Enameloid (Fluorapatite-rich) |
| Hardness | High | Very High (often harder than enamel) |
| Toughness | High (Resistant to fracture) | High (Resistant to fracture) |
| Replacement | Once (Deciduous then permanent set) | Continuous (Throughout life) |
| Structure | Complex layers (enamel, dentin, pulp) | Simpler structure but outer layer optimized |
Practical Insight
The findings from studies like the one in the Journal of Structural Biology highlight the remarkable evolutionary adaptations in both species. While sharks rely on continuous replacement of their very hard teeth to maintain a functional set, humans have evolved incredibly tough teeth designed for a varied diet and meant to last a lifetime. This research also provides valuable insights for material science and engineering, showing how different material compositions and structural designs can achieve similar performance outcomes in demanding biological roles.
