What Holds the Crystal Lattice of Tooth Substance Together

Three Layers With Different Mineral Content

A tooth is made up of several tissues that differ markedly in the ratio of mineral to organic content. The outermost layer, enamel, consists almost entirely of crystalline material and contains very little organic substance. Beneath it lies dentin, whose crystals are embedded in a dense network of collagen fibers. The root surface, finally, carries a thin layer of cementum, whose mineral content falls between that of the other two tissues.

Tissue	Mineral Content (by Weight)	Characteristics
Enamel	about 96%	Nearly pure crystalline material, no living cells once mature
Dentin	about 70%	Crystals embedded in a network of collagen
Cementum	about 45–50%	Thin outer layer of the tooth root, anchored in the jawbone

The Hydroxyapatite Lattice in Detail

The mineral portion of all three tissues is, at its core, the same compound: hydroxyapatite, with the formula Ca₁₀(PO₄)₆(OH)₂. The numbers in this formula are not arbitrary — they are the fixed ratio in which the components come together to form a repeating unit cell: ten calcium ions, six phosphate groups, two hydroxide ions.

The crystal system is hexagonal. In cross-section, the arrangement of unit cells forms a six-sided pattern, and along the long axis the cells line up much like a column.

Two Crystallographically Distinct Calcium Sites

Within the unit cell, the ten calcium ions occupy two different positions. Four of them, designated Ca(I), form columns along the crystal’s main axis and are surrounded by nine oxygen atoms. The remaining six, designated Ca(II), sit in triangular groups around a central channel through which the hydroxide ions run in a single line. These two positions differ in their binding geometry and, as a result, respond with different sensitivity to substitution by other ions from the surroundings.

Calcium is needed for the maintenance of normal teeth. EU-authorized wording · Regulation (EU) No 432/2012.

A Lattice That Is Never Entirely Rigid

Unlike a textbook model crystal, hydroxyapatite in living tissue rarely matches the ideal formula exactly. Smaller amounts of other ions from the surroundings — carbonate in place of some of the phosphate groups, for instance — can enter the lattice and slightly alter its size and solubility. This detail belongs to the crystal chemistry of the tissue and is not the subject of the EU claim quoted above.

Ameloblasts: From Matrix to Mineralized Structure

The formation of tooth enamel begins long before a tooth reaches the mouth. Specialized cells, the ameloblasts, pass through several developmental stages, each with its own role.

Stage	Role of the Ameloblasts
Secretory stage	Depositing a protein-rich, still mineral-poor matrix at full layer thickness
Transition stage	Reshaping of the cell surface, preparing for increased ion transport
Maturation stage	Transport of large amounts of calcium through the ruffled cell surface, breakdown of organic matrix remnants

The Ruffled Surface of the Maturation Stage

In the maturation stage, the shape of the ameloblasts changes visibly: the cell membrane facing the matrix folds into numerous small ruffles, which multiplies the contact area between the cell and the tissue many times over. Across this enlarged surface, membrane-bound transport proteins carry calcium ions in a directed manner into the surrounding tissue.

At the same time, enzymes break down most of the original matrix proteins, and the breakdown products are carried back out through that same ruffled surface. At the end of this interplay between supply and breakdown stands a tissue whose mineral content is many times higher than that of the early matrix.

Why Ameloblasts Are Absent From the Finished Tooth

By the time a tooth erupts, the ameloblasts are already gone — they die off at the end of the maturation stage. As a result, finished enamel no longer has its own cell supply and, unlike dentin or bone, can no longer rebuild itself through cellular activity after this point.

Saliva as an Ion Reservoir

The finished tooth does not sit in isolation in the mouth — it is in constant contact with saliva. Saliva contains dissolved calcium and phosphate ions at a concentration that a simple aqueous solution could not ordinarily hold — a state chemistry calls supersaturation.

Small Proteins Against Premature Precipitation

The fact that the ions stay dissolved despite this high concentration, rather than spontaneously precipitating as crystals, is due in part to small, calcium-binding salivary proteins. Statherin and several proline-rich proteins bind to dissolved calcium and to existing crystal surfaces, slowing both uncontrolled precipitation in the fluid and overly rapid crystal growth at the tooth surface.

An Equilibrium With Two Directions

At the boundary between crystal and saliva, two opposing processes take place at the same time: ions detach from the lattice while other ions from the solution attach anew. Which of the two directions prevails at any given moment depends on the local pH. Acids produced by the metabolism of oral bacteria or from food temporarily lower this pH and shift the equilibrium briefly toward dissolution; once the pH rises again afterward, attachment prevails.

This ongoing back-and-forth is a purely chemical process at the crystal surface. The wording of the EU claim quoted above does not describe it in detail — it simply records the general outcome that calcium is needed for the maintenance of normal teeth.

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