When it comes to assessing the success of endodontic therapy, the changes that occur in the periapical region are crucial indicators. A successful treatment typically results in the formation of new cementum, regeneration of the alveolar bone, and regeneration of the periodontal ligament. These processes are all part of the body's natural healing response to the removal of infection and the introduction of a biocompatible filling material in the root canal system. Thus, all of the above factors contribute to the overall success of the treatment.

Because residual H₂O₂ might react with debris and produce gas that can cause continuous pain.

Explanation: The age group of 8-12 years is commonly associated with the highest incidence of dental fractures in permanent teeth. This is often due to increased physical activity and sports participation during this developmental stage, leading to a higher risk of trauma.

Both sonic and ultrasonic instruments are used in dental procedures, particularly in endodontics and scaling. They generate vibrations that help in the removal of debris and biofilm. A key feature of these instruments is that they require the use of copious amounts of irrigating solutions to enhance their effectiveness, cool the instrument, and flush out debris. While they may also be used for flaring coronal portions of root canals and can be controlled during operation, the commonality that stands out is the need for irrigating solutions.

Vertical root fractures are often associated with a poor prognosis because they can lead to significant loss of tooth structure and are difficult to treat. They typically result in the need for extraction, especially if they extend into the periodontal ligament or if the fracture is not detected early.