People often wonder if teeth are bones or made of keratin, the protein found in hair and nails. This common misconception arises because teeth share superficial resemblances with both, such as hardness. However, teeth possess a unique biological makeup, differing significantly from bones and keratin, enabling their specialized functions.
What Are Bones and Keratin?
Bones are rigid body tissues forming the skeletal framework. They are primarily composed of collagen, a fibrous protein providing flexibility, and calcium phosphate (hydroxyapatite crystals), which hardens the structure and provides compressive strength. Bones are living tissues containing cells like osteoblasts, osteocytes, and osteoclasts. This cellular activity allows bones to constantly remodel and repair themselves. Bones also contain blood vessels and nerves, making them vascularized and sensitive.
Keratin is a fibrous structural protein found in skin, hair, and nails. Produced by keratinocytes, it provides structural support and protection. Rich in cysteine, keratin forms strong disulfide bonds, contributing to its strength and durability. Once formed, keratinized tissues like hair and nails are non-living.
The Specialized Makeup of Teeth
Teeth are complex structures comprising four distinct tissues: enamel, dentin, pulp, and cementum. Each layer has a unique composition and function, contributing to the tooth’s overall strength and vitality.
Enamel
Enamel is the outermost covering of the tooth crown and the hardest substance in the human body, surpassing bone. It consists of about 96% minerals, primarily hydroxyapatite, with small amounts of water and organic material. This mineralized composition provides exceptional durability, protecting the tooth from damage. Enamel is non-living tissue, lacking cells, blood vessels, or nerves, and cannot regenerate once fully formed.
Dentin
Beneath the enamel, dentin forms the bulk of the tooth structure. This yellowish tissue is harder than bone but softer than enamel. By weight, it consists of approximately 70% hydroxyapatite crystals, 20% organic material (mostly collagen fibers), and 10% water.
Dentin contains millions of microscopic channels called dentinal tubules, which radiate outwards from the pulp. These tubules contain extensions of odontoblasts, making dentin a living tissue that can form new dentin throughout life. Fluid and nerve fibers within these tubules contribute to tooth sensitivity.
Pulp
The innermost part of the tooth is the pulp, a soft tissue containing nerves, blood vessels, and connective tissue. The pulp provides nourishment to the dentin and transmits sensory information like pain, temperature, and pressure. It also plays a role in dentin formation and defense.
Cementum
Cementum is a bone-like tissue that covers the tooth root, interlocking firmly with the dentin. It is a mineralized connective tissue composed of hydroxyapatite crystals, collagen fibers, and water. Its function is to anchor the tooth to the jawbone through periodontal ligaments. Cementum also helps protect the sensitive dentin of the root.
Distinguishing Teeth from Bones and Keratin
While teeth and bones share mineral content, they are fundamentally different in biological properties and functions. Bones are living tissues with cells, blood vessels, and bone marrow, allowing them to constantly remodel, grow, and repair after a fracture. A broken bone initiates a healing process involving collagen formation and new bone tissue growth.
Teeth, particularly their enamel, lack this regenerative capacity. Damaged or lost enamel cannot regrow because ameloblasts, the cells that form it, are no longer present after tooth eruption. While dentin can produce secondary dentin, this is a limited repair mechanism.
Teeth also do not contain bone marrow and are not directly connected to the skeletal system. Instead, they are anchored in sockets by cementum and periodontal ligaments. Bones provide structural support and protection, whereas teeth are specialized for chewing and aiding speech.
Comparing teeth to keratin reveals distinct differences. Keratin is a protein providing structural integrity to non-mineralized tissues like hair, skin, and nails. Teeth, conversely, are highly mineralized structures, with enamel being almost entirely inorganic material. Their hardness and function in mastication are due to this mineral composition, not protein structure. Teeth are not made of keratin, and their biological roles are entirely separate.