As people have become more aware of the state of oral hygiene, they have developed the habit of brushing their teeth every day. Indeed, brushing teeth using the correct method is an effective way to maintain oral hygiene. However, it is also reported that simple brushing can only remove about 50% of the plaque on the surface of teeth on average, especially it is difficult to eliminate the plaque on the adjacent surface of teeth. Older people are prone to plaque because of gum recession and increased gaps, so in addition to brushing, they need to floss regularly to help remove plaque from the adjacent surfaces of their teeth. Dental floss has been commonly used in foreign countries. Generally, dental floss can be made of nylon or tape-like material, with moderate thickness. The fibers of the floss are loose and do not need to be twisted together. In this way, the fibers can be arranged in a flattened shape when we use it, and it is easy to slowly pass through the areas of close contact between teeth. The floss sold on the market is usually waxed floss, which helps protect the gums. Depending on the level of flossing proficiency, take a piece of floss of moderate length and connect the two ends of the floss to form a coil. You can also take a piece of floss and wrap each end around the fingers of both hands. To clean the upper right back teeth, for example, use your right thumb and left index finger to tense the floss, then slowly pass the floss through the contact points, moving the floss back and forth, up and down. The thumb is on the outer side of the tooth, holding the cheek open. This can also be done with the index fingers of both hands. When the floss is passed through the contact point, the fingers should slowly increase the force so that the floss reaches the tooth surface below the contact point and enters the bottom of the gingival sulcus to clean the gingival sulcus area. Care should be taken not to use too much force to avoid damaging the periodontal tissue. If the contact point is tight and not easy to pass, pull the floss above the contact point in a horizontal pulling motion to gradually pass the contact point. Put the floss against the tooth surface of the tooth neck and wrap it around the tooth surface, so that the area of contact between the floss and the tooth surface is increased. The floss is then pulled up and down to scrape away plaque and soft scale from the adjacent surfaces. Each tooth surface should be scraped up and down 4 to 6 times until the tooth surface is clean. Sometimes a “crunching” sound can be heard. Then clean the other surface in the same way as above. Finally, remove the floss from the direction of the occlusal surface, enter the adjacent tooth space again, and scrape away the plaque from the adjacent surfaces of the whole mouth one by one. Be careful not to miss the last tooth of the upper and lower jaws on the last surface. Also, after treating each tooth in one direction, it is best to rinse your mouth with water to remove the scraped plaque. Flossing is best done once a day, especially after dinner. If it is not convenient for your fingers or if you have trouble opening your mouth, you can buy “floss sticks” from the supermarket. The back end is a very sharp, thin tip that can be used as a toothpick. Before flossing in elderly patients with periodontal disease, basic periodontal treatment such as supragingival scaling and subgingival scraping should be performed in the dentist’s office. If there is an overhang on the adjacent surface of the tooth, it should be polished first to make it consistent with the anatomical shape of the tooth so that the overhang does not hook the floss and make the floss wear out and break easily, damaging the gums.