Formocresol is a commonly used fixative and disinfectant in endodontic treatment. It is known to produce tissue fixation by causing coagulative necrosis. This is the process by which the proteins within the tissue are coagulated or precipitated, leading to the death of cells due to dehydration and denaturation. The necrotic tissue is then replaced by a fibrous connective tissue, which is essential for the healing process in the periapical region following root canal treatment.

The most frequent failures of root canal treated cases are often due to inadequate obturation. This can occur when the root canal filling material does not completely fill the space or when it is not properly compacted, leaving gaps where bacteria can persist and cause reinfection. Proper preparation and sterilization are also crucial, but inadequate obturation is the most common technical error leading to treatment failure.

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.

Explanation: Furcation perforations occur in the area where the roots of a multi-rooted tooth diverge. These perforations are particularly challenging to manage because they can lead to periodontal disease and loss of attachment in the furcation area. The prognosis is poor due to the difficulty in achieving adequate sealing and maintaining periodontal health in this area, making it more susceptible to infection and further complications.

In a hot bead sterilizer, the temperature is highest in the inner zone of the sterilizer. A hot bead sterilizer uses a heated metal bead to transfer heat to the instruments, which are placed around the bead in a basket. The inner zone is where the bead is located and where the temperature can reach up to 300°C, which is sufficient to kill microorganisms and sterilize the instruments. The outer zone is cooler and does not contribute significantly to the sterilization process.