An overdenture is a full or removable partial denture in which the abutment of the denture covers and supports the roots or crowns of the teeth that have been treated, and these covered teeth or roots are called overdenture abutments. This type of denture preserves the roots of the teeth, reduces the resorption of the alveolar bone, and enhances the retention, stability and support of the denture. They can be classified as simple overdentures, double-crowned overdentures, and magnetic retention overdentures. There is an interdependent relationship between the tooth and the alveolar bone, which develops as the tooth grows, erupts, and is maintained by the health and function of the tooth. Once the tooth is extracted for some reason, the width and height of the alveolar bone changes and gradually shrinks. Although there are many factors that affect the resorption of the alveolar bone, the teeth have the greatest influence keeping the roots of the teeth is the only reliable way to prevent alveolar bone loss. Since the overdenture preserves the teeth or roots to protect the alveolar bone from resorption, the corresponding periodontal membrane proprioceptors are also preserved, reducing alveolar bone resorption while improving the support, retention and stability of the denture, and the efficiency of the function is greatly improved compared to the edentulous complete denture. After the extraction of diseased teeth, the alveolar bone is progressively resorbed, and wearing a denture can only slow down the rate of alveolar bone resorption, but cannot prevent the continuous resorption of alveolar bone. Currently, the only reliable way to prevent alveolar bone resorption is to prevent tooth loss. Preservation of the tooth or the remaining root preserves the alveolar bone at the same time. Therefore, the application of overdenture is an ideal solution to the problem of resorption of alveolar bone. Due to the rapid advancement of oral materials and equipment in recent years, some affected teeth that were considered to be extracted in the past have been preserved, providing conditions for the production of overdenture. Therefore, through reasonable treatment, preserving the real teeth and roots as much as possible and restoring overdentures on them is a treatment method that is beneficial to oral health and acceptable to patients. In general, bad teeth and roots need to be extracted for veneers, but sometimes some patients are not suitable for extraction for some reasons or have other conditions, so the doctor can retain the roots or crowns of the bad teeth in the dental bed after perfect treatment, and on the basis of this, the patient can restore a denture, which is called overdenture. The overdenture is called an overdenture because it preserves the roots of the teeth and therefore reduces the resorption of the alveolar bone, which greatly improves the chewing performance and also preserves the ability to discriminate the nature and hardness of food when eating. If further attachment devices are added to the roots or crowns, the retention capacity of the denture can be improved, making it less likely to fall out. These are the advantages and benefits of overdentures. There are some disadvantages of overdentures that cannot be overcome at present. For example, the abutment teeth covered by the denture are prone to caries, and the lip and cheek are protruding due to the presence of the roots, thus affecting the aesthetic effect of the denture. In addition, due to the complicated fabrication process, it takes more time and cost for the patient, therefore, the decision of whether a person is suitable for overdenture should be made by the doctor according to the specific situation and needs.