1. The dental pulp has been irreversibly damaged, but the deep root canal has not yet been infected/infected Mildly infected dental pulp still retains vitality and is called a non-infected root canal 2. RCT of teeth with vital pulp, also known as pulp extraction

1. Sterility: The focus of infection control is to strictly adhere to aseptic operations to avoid iatrogenic infection into the deep root canals (strict disinfection of instruments/materials, strict isolation/sterile operations during operations, etc.) 2. Shaping: The main task of root preparation is to remove the pulp tissue in the root canal and shape the root canal. Use rubber dam/sterilized instruments, pay attention to the operating techniques, remove the pulp immediately under good local anesthesia and complete the treatment in one time, which can prevent to the greatest extent spread of infection

1. Pulp necrosis/gangrene, severe root canal infection 2. In addition to the remnants of necrotic and infected dental pulp, the pulp cavity also contains a large number of bacteria and toxic products, which is called infected root canal. 3. Some bacteria in the medullary cavity may exist in the form of biofilms, with enhanced symbiosis/pathogenic capabilities

1. Strengthen debridement: In addition to strengthening root canal debridement (a combination of mechanical debridement and ultrasound), residual infection must be further removed by sealing medicine, which not only removes the tangible material in the medullary cavity, but also cleans the root canal wall. /Biofilms within complex tubule systems 2. Use medullary cavity opening with caution: Opening the medullary cavity in the oral cavity can cause changes in the bacterial flora deep in the root canal, complicating a relatively simple bacterial infection, and increasing bacterial virulence and becoming more pathogenic/drug-resistant. Medullary cavity opening should be used with caution. /So as not to increase the difficulty of treatment

1. Most of them are related to insufficient infection control. As root canals with difficult-to-control infection 2. The affected tooth may have problems such as anatomical particularities, diagnostic uncertainty, operating defects, or microleakage. 3. When the leakage from the mouth enters the root canal/periradicular tissue fluid or the inflammatory exudate flows back into the root canal space, the bacteria quickly regain control and form a new active infection state.

1. It should be treated as a root canal with difficult-to-control infection. Only by analyzing the reasons for past failures can we clearly propose effective treatment countermeasures. 2. For cases with poor infection control, the key to successful retreatment still relies on effective treatment of infection in the root canal. 3. Culture + surgery: Due to the particularity of anatomy/uncertainty of diagnosis/operational defects or micro-leakage, initial treatment can easily complicate a relatively simple bacterial infection in the root canal, making the bacteria more virulent and more pathogenic. drug resistance/drug resistance, at this time, it is necessary to conduct bacterial culture/drug sensitivity test in the root canal to determine the sensitive drug and apply it; if the effect is still not good, root canal surgery can be considered

1) Root filling is a key step directly related to the success. The ultimate goal is to seal the root canal with a material with good biocompatibility/eliminate the dead space and seal the trace residual pathogenic irritants in the root canal/ To seal the apical hole, the root filling material must have good adaptability to the root canal and irregular cavities of the root canal system. The root filling material should occupy all the space in the root canal for the purpose a. Eliminate leakage pathways in the root canal system and prevent bacteria from re-entering the prepared and cleaned root canals b. Prevent residual bacteria and their metabolites in the root canal from passing through the apical foramen and entering the periapical tissue c. Prevent tissue fluid from the periapical tissue from penetrating into the unfilled gaps in the root canal and providing nutrients for the reproduction of residual bacteria in the root canal.

2) The materials currently used for root filling are gutta-percha and sealant. Gutta-percha needs to occupy the main root canal space. The sealant filled in the root canal in the form of paste should not be too much. Its function is only to fill the gutta-percha. and the gap between gutta-percha and root canal wall. Excessive shrinkage after hardening may cause leakage After root filling, the tooth should be restored with a crown as soon as possible

After root filling, the tooth should be restored with a crown as soon as possible

1) If you design a post-core crown, pay attention to the remaining amount of root filling at the root tip after post preparation. At least 5mm should be reserved to ensure that the root tip is sealed; after the post is placed, its end should be in close contact with the remaining root filling. No space should be left to maintain the integrity of the tight seal of the root canal system

2) If the crown cannot be fixed and repaired within a few weeks, the pulp cavity should be filled transitionally or directly bonded to repair it.

3) If the crown restoration falls off/the pulp cavity is open/the root filling is exposed, but the affected tooth has no symptoms/signs/no periapical shadow on the agent or silver tip, the RCT must be redone

The observation period specified by WHO is 2 years after surgery

①Medical history/treatment history ②Pain situation: range/time/nature/degree/inducing and alleviating factors ③Swelling situation: Is there a history of swelling/suppuration? ④Functional condition: Is the chewing function good?

①Tooth condition: whether the crown restoration is suitable/complete/painful upon percussion ②Periodontal condition: soft tissue color and structure/swelling/periodontal pocket sinus tract/looseness/presence of tenderness

①Root canal: whether the filling is tight/appropriate; whether there is any bypass/instrument breakage ② Root tip: Whether there is external resorption at the root tip ③Around the apex: Periapical sparse area (size/shape/density/peripheral condition) periodontal ligament cavity/bone plate/alveolar bone

1. No symptoms/signs, normal occlusal function/complete occlusal relationship, X-ray shows tight and appropriate root filling/periapical radiolucent area disappears/ Periodontal ligament space is normal/hard plate is intact 2. Or there are no signs/symptoms, good occlusal function, and X-ray films show reduced periapical radiolucent area and increased V density.

1. No symptoms/signs, mild bite discomfort, X-ray film shows little change in periapical radiolucent area 2. Or there are obvious symptoms and signs, and the patient cannot perform normal chewing function. X-ray films show that the periapical radiolucent area has become enlarged or there was no periapical radiolucency. The abnormal person has a transmissive area