In recent years, the importance of deciduous teeth and the hazards of caries in deciduous teeth have gradually attracted the attention of professionals and parents of children. The dental pulp disease and periapical disease of deciduous teeth are the main and important factors that cause deciduous teeth defects, deciduous dentition and mixed dentition deletion, which have a serious impact on the physical and mental health of children from the local or systemic aspects. From the point of view of children's stomatology, according to the principle of treatment of dental caries of deciduous teeth, vital pulp preservation should be selected in patients with deep caries and reversible pulpitis; This concept has been carried forward especially after the advent of new materials with good biocompatibility and good edge sealing. After judging the existing state of the affected teeth (such as deep caries or reversible pulpitis) and removal of caries, indirect pulp capping, direct pulp capping, and vital pulpotomy can be correspondingly selected. Complete healthy pulp can be preserved in indirect pulp capping and direct pulp capping. During vital pulpotomy, coronal pulp due to infection induced by various causes is removed, and healthy root pulp is retained.

The success of the preservation of vital pulp in carious deciduous teeth depends not only on determining the health status of the pulp, but also on selecting the most suitable pulp capping agent. No matter the use of calcium hydroxide and mineral trioxide aggregate (MTA) or new biomaterials, controlling pulp inflammation and preserving healthy pulp are the keys to successful treatment. The clinical reality is that it is not easy to determine the state of the pulp accurately because of the child's feelings of pain and the unreliability of the description. Thus, the secondary treatment can be easily produced after treatment. For example, pulp re-infection requires dental pulp extraction; or severe infection results in removal of the affected teeth and space maintenance. In the face of this reality, many clinicians will advise parents to select dental pulp extraction for deciduous teeth at the first visit. If there is a reliable clinical pathway for the preservation of the vital pulp of the carious deciduous teeth, the doctor will put aside his worries. Therefore, this study is designed to find a suitable clinical pathway and to increase the success rate of the preservation of the vital pulp of carious deciduous teeth. The key to solving this problem lies in the selection of suitable pulp capping agent, as well as the repair method of the crown selection to obtain a better edge sealing. Numerous studies have confirmed that crown repair of deciduous teeth can obtain better edge sealing on the basis of obtaining the largest degree of morphological restoration. The difficulty and key point are to select the best biomaterials as the pulp capping agents for the preservation of vital pulp.

The investigators will select classical and new biomaterials for the preservation of vital pulp and compare them so as to select a pulp capping agent with high success rate. With the further research of biomedical ceramic materials, such as restorative material for pulposis Bioaggregate and restorative material to dentin Biodentine, the biocompatibility of such materials allows the destructed dental pulp tissue to be reconstructed. Shayegan et al. performed vital pulpotomy for pigs using Biodentine, white MTA and formaldehyde cresol as pulp capping agents, and using Biodentine, white MTA and calcium hydroxide as direct pulp capping, and observed the response to dental pulp tissue. They concluded that Biodentine and white MTA have the same biocompatibility, and they are suitable for the pulp capping material of porcine deciduous teeth. In recent years, TheraCal LC has emerged as a new type of pulp capping agent. Some scholars believed that both MTA and TheraCal are good indirect pulp capping materials. TheraCal has better operability and similar chemical property as MTA. In the indirect pulp capping treatment of deciduous teeth, TheraCal can be a successful alternative to MTA. Nevertheless, TheraCal is rarely used in direct pulp capping, and vital pulpotomy.

In summary, this study will select Biodentine and TheraCal, verify their efficacies, and explore their superiorities. Calcium hydroxide and MTA will be selected as controls, which will be separately used in indirect pulp capping, direct pulp capping, and vital pulpotomy to provide reliable choices for clinicians.