Specifically, a polymer composite resin material is applied to the sulcus of children’s teeth, and the liquid resin cures and hardens after entering the sulcus, forming a protective barrier, just like putting a protective coat on the defective teeth to protect the teeth from food and bacteria, thus enhancing Tooth decay resistance. 1.Harm: The sulcus of each tooth has different shapes and depths, which is the suitable place for food residue retention and bacteria growth and reproduction. If the sulcus is very deep, then the bacteria will use the sugar in the residual food to reproduce and grow in these hidden narrow sulcus, and produce acid in the process of metabolism to corrode the teeth, and it is easy to occur caries, which is called sulcus caries in medicine. The data shows that more than 90% of the caries (worm teeth) of our teenagers occur in the sulcus, so the risk of caries in deep sulcus is very high. 2.The best age: The sulcus closure is mainly for the purpose of preventing caries (worm teeth), so it is mainly for the newly erupted permanent molars of children and adolescents. Sixth-aged teeth are the teeth that bear the most important function of chewing, because of early eruption, if not pay attention to protection, it is easy to suffer from caries (insect tooth), so it becomes the main target of the gully closure. Usually, six-year-old teeth are fully erupted at the age of 7-8 years old, which is the best age for closure.3 Notes: (1) Clean the tooth surface: Install a rubber cup or a small brush on the low-speed handle and dip it into the appropriate amount of abrasive to clean the tooth surface. Be careful not to use cleaners containing oil. After cleaning, rinse the tooth surface with water gun and drain the saliva. (2), acid etching dental surface: clean the dental surface that is wet with cotton rolls, blow dry the dental surface with a fine brush, small cotton ball or small sponge block dipped in acid etching agent coated on the dental surface to be closed, acid etching agent for the gel containing phosphoric acid or phosphoric acid liquid, acid etching area should be accepted to close the range, generally 2/3 of the oblique surface of the tooth tip, acid etching time for 30 seconds to 60 seconds, pay attention to the acid etching process do not wipe the tooth surface, the amount of acid etching agent to appropriate, do not spill into the oral soft tissue. (3), rinsing and drying: acid etching after thorough rinsing of the tooth surface, which is one of the keys to successful closure, usually pressure rinsing 10 seconds to 15 seconds to remove the enamel surface of the acid etchant and reaction products, rinsing immediately after the exchange of dry cotton rolls isolated wet, followed by compressed air blowing dry tooth surface for about 15 seconds, can also be used to dry with the aid of volatile solvents such as anhydrous ethanol or ether, be careful not to use the compressed air with oil and water. The acid-etched surface is dried with a white haze appearance. If the acid-etched enamel does not show this phenomenon, the acid-etching should be repeated. Make sure that the acid-etched surface is not contaminated with saliva during the procedure, and if saliva contamination occurs, the surface should be rinsed again and re-etched. During the operation, care should also be taken not to allow the enclosed person to spit out the cotton roll used for isolation of wetness or rinse the mouth by himself. (4), coated sealant: the use of self-consolidating sealant, each closed before taking equal amounts of A, B components (containing initiator and accelerator, respectively) mix and blend, mix to pay attention to the speed of mastering so as not to produce bubbles, affecting the quality of curing. Self-curing sealant curing time is generally 1 minute ~ 2 minutes, usually mixed 10 seconds ~ 15 seconds, completely mixed within 45 seconds that should be coated, because after the self-curing sealant into the initial stage of condensation, viscosity increases, liquidity decreases, so the mixing and coating to master the timing, completed before the initial stage of condensation. Light solid sealant does not need to mix, directly remove the coating on the tooth surface, such as continuous closure of multiple teeth, pay attention to the amount should not be too much, light solid sealant in natural light will also gradually solidify. Method of application: use a fine brush pen, small sponge or manufacturer’s special supply, the closure material coated on the acid-etching teeth, pay attention to make the sealant penetrate into the sulcus, squeeze out the air in the sulcus, and place an appropriate amount of closure material to cover all acid-etching teeth, without affecting the occlusion as much as possible to have a certain thickness, sometimes there may be a high point, but 2 days ~ 3 days can be naturally worn away, if the coating is too thin will lack sufficient compressive strength, easy to be bitten. (5), curing: self-setting sealant coated 1 minute ~ 2 minutes to cure on their own. Light solid sealant coating, immediately after the visible light source irradiation, irradiation distance of about 1 cm from the tip of the tooth, irradiation time is based on the type of product used and visible light source performance decision, generally 20 seconds to 40 seconds. (6), check: sealant curing, with a probe for a comprehensive inspection to understand the degree of curing and bonding, looking for missed or unsealed sockets and re-sealing, observe whether there is too much sealing material and whether it needs to be removed, find the problem in time to make the appropriate treatment. The teeth with completed sealant should be reviewed periodically (3 months, half year or one year) to observe the retention of sealant, and the sealant should be redone when it falls off, then the retention rate of sealant and caries reduction rate will be improved.