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Universal numbering system. This is a dental practitioner view, so tooth number 1, the rear upper tooth on the patient's right, appears on the left of the chart. The Universal Numbering System, sometimes called the "American System", is a dental notation system commonly used in the United States. [1] [2]
The enamel on primary teeth has a more opaque crystalline form and thus appears whiter than on permanent teeth. The large amount of mineral in enamel accounts not only for its strength but also for its brittleness. [6] Tooth enamel ranks 5 on Mohs hardness scale (between steel and titanium) and has a Young's modulus of 83 GPa. [4]
As of 2024, the prevalence of pathology reaches over 90%. In patients aged 20 years, an average of 4 intact teeth with enamel cracks are identified. Before 30 years of age, this rate increases 3 times and after 45–50 years of age it is 100%. In 60% of cases there are single fissures, multiple fissures are found in 40% of examined patients.
Produced during the second stage of enamel calcification, also known as the maturation stage, ameloblasts produce matrix and enamel at the rate of 4 micrometers per day; however every fourth day there is a change in development. Brownish lines, the striae of Retzius, develop as a result of a change in the growth process.
Amelogenesis is the formation of enamel on teeth and begins when the crown is forming during the advanced bell stage of tooth development after dentinogenesis forms a first layer of dentin. Dentin must be present for enamel to be formed. Ameloblasts must also be present for dentinogenesis to continue.
% of adults 65+ who have had all teeth extracted. CDC 2022: Image title: Map of percentage of adults age 65 and older who have had all teeth removed due to tooth decay or gum disease. Centers for Disease Control (CDC) 2022. Width: 100%: Height: 100%
Thus, the count of perikymata may be used to assess how long a tooth crown took to form. They may disappear as the enamel wears over time after the tooth erupts. Perikymata are the expression of striae of Retzius at the surface of enamel. They can be found on all teeth, but are usually the easiest to notice on anterior teeth (incisors and canines).
In about 60–65% of teeth, the cementum overlaps the enamel at the CEJ, while in about 30% of teeth, the cementum and enamel abut each other with no overlap. In only 5–10% of teeth, there is a space between the enamel and the cementum at which the underlying dentin is exposed. [3]