Take the teeth of cattle as an example:
1. Opposite teeth: the deciduous teeth of cattle (that is, the teeth that grow after birth) are small and white, with obvious neck and large tooth gap. Permanent teeth (that is, new teeth that regrow after deciduous teeth fall off) are large and thick, yellowish in color, neatly arranged and close to each other. Generally, 1 pair of deciduous incisors grow out about half a month after birth, and four pairs of deciduous incisors are flush about 4-5 months, and then gradually wear and shorten. Buffalo is about 3 years old, yellow cattle 1.5-2 years old, 1 deciduous teeth fall off. The 1 pair of permanent teeth, that is, the opposite teeth, will fall off and update 1 pair every year, gradually from 4 teeth, 6 teeth to 8 teeth (same mouth). Generally, buffaloes are about 6 years old and yellow cattle are 4.5-5 years old.
2. Tooth marks: After the teeth are arranged neatly, the permanent teeth begin to wear in turn, and the wear surface gradually changes from rectangular pattern to black ellipse or triangle, and the gap between teeth gradually expands until the root of the tooth is exposed or even the permanent teeth fall off, and the rectangular pattern is printed on the wear surface of the teeth. Buffalo is about 7 years old and cattle is 5.5-6 years old, so they wear 1 pair every year until 8 prints. Buffalo 10 years old, yellow cattle 8.5-9 years old.
3. Tooth beads: The black oval pattern on the worn surface of teeth is "beads". Buffalo is about 1 1 year-old, cattle is about 9.5-1year-old, and so on until eight pearls (full of pearls, also called Laokou), buffalo is about 14 year-old, and cattle are full of pearls. Buffalo 14 years old and cattle 13 years old have basically lost their service performance and reproductive performance.