Tooth enamel

Description

Enamel forms the outer, white layer of the tooth crown and is the hardest substance in the body of mammals. In humans, it is up to 2.5 mm thick, consists of approximately 96% of bioapatite and contains no living cells.

Tooth enamel mineralizes in childhood and adolescence. It does not have any active metabolism, does not undergo systematic turnover and remains unchanged throughout life. Enamel formation starts at the enamel-dentine junction of the highest point of the tooth crown and then progresses outwards and towards the root of the tooth. Enamel formation begins as an organic matrix, which mineralizes increasingly due to the incorporation of bioapatite.

Human teeth begin to form in utero and tooth formation continues throughout childhood with different formation periods according to tooth types, until adolescence. The following groups of teeth can be distinguished with regard to their mineralization periods:

• Deciduous teeth: in utero until first year of life
• First permanent molar: approx. birth until 3 years of age
• Front teeth: 1^st to 5^th year of age
• Canines: 1^st to 7^th year of age
• 2^nd permanent molar, premolars: 2^nd/3^rd – 6^th/7^th years of age
• 3^rd permanent molar (wisdom tooth): approx. 7^th – 14^th partly to 18th year of age

During these times, main and trace elements are ingested through food and drinking water and stored in the crystal structure of the bioapatite of the tooth enamel. Comparing element and isotope data from teeth with different periods of crown formation provides evidence for changing average diet compositions or mobility in childhood. The periods of crown formation should therefore be taken into account when selecting samples for bioarchaeometric analyses.

Sample properties

Complete teeth should be submitted for element and isotope analyses on enamel. The crown should be well preserved (minimum height for human teeth 2-3 mm, no severe chipping; carious lesions, use wear, and epigenetic features in the area to be sampled should be avoided).

For strontium and oxygen isotope analyses, the enamel is usually separated from one cups of a molar using a diamond-coated cutting disc mounted on a dental drill. In the case of more severe abrasion or if several kinds of analyses are combined, the sampling can also extend to a second cusp.

The surface and adhering dentine are removed by milling and the enamel pieces are then homogenized in an agate mortar.

Typical amounts of enamel powder for sample preparation for strontium and oxygen isotope analyses are 10 – 12 mg. For oxygen isotope analysis without pre-cleaning approx. 1 mg of material is sufficient.