Human teeth are composed of:
Enamel
Enamel is the hardest and most highly mineralized substance of the body. 96% of enamel consists of minerals, primarily hydroxyapatite (crystalline calcium phosphate). Enamel varies in thickness, up to 2.5mm.
Dentin
Supporting the enamel and forming the majority of the tooth, this porous, yellow-hued material is a mineralised tissue with an organic matrix of collagenous proteins. It accounts for the majority of the structure of the tooth.
Cementum
Cementum is a bony substance covering the root of a tooth. It is composed of 45% inorganic material (mainly hydroxyapatite), 33% organic material (mainly collagen) and water.
Pulp
The dental pulp occupies the central part of the tooth. It consists of blood vessels and nerves, entering the tooth at the apex of the root. Along the border between the dentin and the pulp are odontoblasts, which initiate the formation of dentin. The pulp is what most people call 'the nerve' of the tooth. And yes, it's the bit that is sensitive to pressure and temperature.
Information via Wikipedia
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