The question of the “strongest” substance in the human body is not simple, as “strength” is defined by several scientific metrics. A material strongest in one sense, such as resistance to surface scratching (hardness), may be weak in another, like resistance to pulling or bending (tensile or compressive strength). To determine the strongest material, it is necessary to differentiate between these properties. The candidates for the title of strongest biological material each excel in their specialized domain, reflecting the complex engineering of the body’s tissues. Understanding these parameters is necessary to compare the unique mechanical properties of the body’s load-bearing components.
The Crown of Hardness: Tooth Enamel
Tooth enamel is the hardest substance found in the human body, a property that allows it to withstand the daily forces of chewing and grinding. This exceptional hardness stems from its highly mineralized composition, which consists of approximately 96% inorganic material by weight. The primary mineral compound is hydroxyapatite, a crystalline form of calcium phosphate that is densely packed into organized rod structures.
The enamel forms a durable outer layer, acting as a barrier to protect the softer dentin and pulp tissues beneath it. Its strength is measured by its high resistance to wear and abrasion, which prevents the surface from being easily scratched or chipped during mastication. However, this high mineral content also makes enamel brittle and susceptible to degradation from acids, which can dissolve the calcium and phosphate ions.
The Load-Bearing Framework: Cortical Bone
While enamel is the hardest, cortical bone claims the title for structural strength, exhibiting superior resistance to tension and compression. This dense tissue forms the outer layer of most bones and provides the main structural support for the skeleton. Cortical bone is a complex composite material, balancing rigidity with flexibility to prevent catastrophic failure.
Its composition blends organic and inorganic elements. The mineral component provides stiffness, and the organic protein collagen provides flexibility and tensile strength. Hydroxyapatite crystals give the bone rigidity and resistance to compression, while interwoven collagen fibers allow it to resist pulling forces and absorb impact. Cortical bone is notably stronger under compression along its long axis, a characteristic optimized for weight-bearing.
Building and Maintaining Biological Strength
The creation and maintenance of these robust materials require mineralization, where calcium and phosphate ions are deposited into an organic matrix. This process is crucial for both enamel and bone, yet the mechanisms for their upkeep are fundamentally different, reflecting their diverse functions.
In bone tissue, strength is sustained through a dynamic and continuous process called remodeling, overseen by two specialized cell types. Bone-building cells (osteoblasts) deposit new bone matrix, while osteoclasts break down and reabsorb old or damaged tissue. This cycle allows bone to repair microfractures, adapt to mechanical stress, and maintain the skeleton’s overall integrity throughout a lifetime.
Conversely, mature tooth enamel is an acellular tissue, meaning it contains no living cells and cannot undergo metabolic repair or regeneration once fully formed. While saliva can facilitate a minor process of remineralization on the surface, any significant damage to the enamel structure is permanent. This lack of self-repair capability underscores the importance of external care to protect the enamel’s biological strength.