Human teeth are the hardest substances in the body, known for their incredible strength and resilience. Their durability stems from a unique mineral composition, allowing them to withstand the rigors of daily chewing and biting.
The Primary Mineral: Hydroxyapatite
The primary mineral responsible for the exceptional hardness of teeth is hydroxyapatite. This naturally occurring compound is a crystalline form of calcium phosphate, characterized by the chemical formula Ca₅(PO₄)₃(OH). Its highly organized crystalline structure provides teeth with their rigidity and resistance to mechanical stress. Hydroxyapatite is a significant component not only of teeth but also of bone, comprising about 65% to 70% of bone mass.
This mineral’s properties directly contribute to tooth hardness and its ability to resist deformation. The tightly packed arrangement of calcium, phosphate, and hydroxyl ions forms a dense, insoluble material. The presence of hydroxyapatite allows teeth to endure the constant forces of chewing while also providing a stable mineral reservoir.
Tooth Structure and Composition
Hydroxyapatite is integrated into the distinct layers of the tooth, with varying concentrations in each to fulfill specific roles. The outermost layer, enamel, is the hardest substance in the human body, composed of approximately 96% inorganic material, primarily hydroxyapatite. This high mineral content makes enamel exceptionally resistant to physical and chemical attacks, serving as the tooth’s primary protective shield. The hydroxyapatite crystals in enamel are tightly packed and highly organized.
Beneath the enamel lies dentin, which makes up the bulk of the tooth structure. Dentin is less mineralized than enamel but more so than bone, consisting of about 70% inorganic material, largely hydroxyapatite, along with organic material and water. The hydroxyapatite crystals in dentin are smaller and more dispersed than those in enamel, contributing to dentin’s flexibility and toughness. This flexibility helps absorb and distribute forces from chewing, preventing fractures in the more brittle enamel.
Cementum covers the tooth root, providing an attachment point for the periodontal ligament that anchors the tooth to the jawbone. Its composition is similar to bone, with approximately 45% to 50% inorganic material, predominantly hydroxyapatite, and organic matter and water. The varying concentrations and arrangements of hydroxyapatite across these layers—enamel, dentin, and cementum—collectively contribute to the tooth’s overall structural integrity, function, and resilience against daily stresses.
Protecting Your Teeth’s Minerals
The mineral integrity of teeth is under constant processes of demineralization and remineralization. Demineralization occurs when acids, produced by oral bacteria metabolizing sugars or from acidic foods and drinks, dissolve calcium and phosphate ions from the hydroxyapatite crystals in tooth enamel. If demineralization outweighs remineralization, it can progress to cavities.
Remineralization is the natural repair process where minerals, primarily calcium and phosphate from saliva, are redeposited onto the tooth surface, helping to rebuild weakened enamel. Fluoride plays a significant role in this process by integrating into the enamel structure, forming fluorapatite, which is more resistant to acid attacks than original hydroxyapatite. Regular exposure to fluoride, through fluoridated toothpaste, water, or professional treatments, strengthens teeth and enhances their resistance to decay.
Maintaining good oral hygiene is essential for supporting remineralization and preventing demineralization. Brushing twice daily with fluoride toothpaste and flossing removes plaque, reducing acid production by bacteria. A balanced diet that limits sugary and acidic foods also minimizes acid exposure to teeth. Regular dental check-ups allow for early detection of demineralization and professional intervention to maintain mineral health.