One of the main objectives of orthodontics is to align the teeth on the dental bed in a very regular manner. Due to evolutionary reasons, most modern people’s dental bed cannot completely put their teeth down and there is more or less crowding, so almost 50% of modern orthodontic patients need to have their teeth extracted to correct the problem. The orthodontic profession generally believes that if the crowding in a single jaw is more than 3mm, it needs to be extracted. However, some patients are afraid of extraction or their parents are against it and ask the orthodontist to grind down the teeth for correction. In fact, the gap that can be obtained by grinding the teeth is very small. In the past, we thought that each tooth has two adjacent surfaces, and each adjacent surface can be ground off 0.5mm, so that each tooth can obtain 1mm gap, and there are six front teeth can obtain 6mm gap, but a lot of clinical facts prove that this amount of grinding is too much. Now in clinical practice I try not to do adjacent surface slicing, if I must do a surface is generally not more than 0.2mm. The aforementioned grinding teeth, the technical term in orthodontics is reduction or slicing, through a special cutting tool to cut or grind the adjacent surface of the teeth and the left and right sides of the adjoining. Unlike mahjong tiles, which are not square, teeth that are normally aligned are in point contact or small surface contact rather than surface contact, which facilitates the self-cleaning of the teeth. If the shape between the adjacent surfaces is not well restored after the artificial slicing, then they will form the surface contact between them, and such contact will easily cause tooth decay. The following is a case in which all the sliced teeth are severely decayed due to improper slicing