The human milk teeth usually all erupt at the age of 2.5 years, and by the age of 5 or 6 years, the other permanent teeth have not moved at all, while the first permanent tooth quietly grows behind the upper and lower four milk molars, which is called the sixth age tooth because it occurs mostly at the age of 6 years. Because it erupts early and does not replace any teeth, many parents mistakenly think it is a milk tooth and neglect to protect it. Sixth-aged teeth are very important to human oral health, and once they erupt, they are likely to stay with us for the rest of our lives. It is the largest tooth in the occlusal surface area, bearing 40% of the pressure of chewing for the rest of one’s life. In addition, these four teeth are like the four pillars of a house, supporting the entire oral space, helping to position the erupting permanent teeth, and playing a major role in establishing the bite and maintaining the facial shape of children. The early loss of sixth-age teeth not only leads to the decrease of children’s chewing power, but also causes the neighboring teeth to shift and tilt, induces bite disorder, and hinders the normal development of children’s face. Ninety percent of children’s caries occurs on four six-age teeth On the one hand, six-age teeth are the Hercules of food grinding, but on the other hand, they suffer from caries frequently. According to the results of the third national oral epidemiological survey, the prevalence of dental caries in permanent teeth of children aged 12 is 28.9%, 90% of which occurs in the sixth age teeth. Why the caries mainly occurs in the sixth age teeth but not other 24 teeth? There are two main reasons: firstly, there are many small sockets in the sixth-aged teeth, which are easy to retain food residues. The shape of sixth-aged teeth is different from incisors, it has the largest biting area, more cusps, and more sockets between cusps and cusps, not only more but also very narrow and deep, food residues are very easy to hide in them, and over time they are decomposed into acid by bacteria, leading to enamel surface demineralization, so it is easy to lead to tooth decay. Secondly, the enamel of six-year-old teeth is thin and has poor calcification ability. Since the teeth of the sixth age erupt the earliest, the enamel is still thin when erupting, the development of the facial sulcus is not sound, and the calcification is poor, so the self-protection ability is greatly reduced. “Six-year-old teeth erupt earliest, ‘suffering’ begins early, so the chance of damage is also the greatest.” Dental experts are sweating for the six-year-old teeth.