Tooth discoloration Light hitting a tooth undergoes reflection, absorption and transmission by varying degrees in each tissue layer of the tooth substance. Reflected light detected by the human eye determines the perceived appearance of a tooth. Teeth have a thin enamel layer on the outer surface. The enamel layer is whiter and semitransparent, and contributes blue, pink green tints to the tooth color. The underlying dentin layer is darker than enamel, yellow-brown in color, and less transparent. Dentin forms the bulk of the tooth substance, and contributes most to the overall tooth color. At the core of the tooth is soft connective
Human tooth mixed stage. The mixed stage lasts until the last primary tooth is lost and the remaining permanent teeth erupt into the mouth. There have been many theories about the cause of tooth eruption. One theory proposes that the developing root of a tooth pushes it into the mouth. Another, known as the cushioned hammock theory, resulted from microscopic study of teeth, which was thought to show a ligament around the root. It was later discovered that the "ligament" was merely an artifact created in the process of preparing the slide. Currently, the most widely held belief is that the periodontal