Sodium hypochlorite, often recognized as a component in household bleach, is a distinct and purified solution when used in dentistry. This halogenated compound appears as a clear, pale, yellowish-green liquid with a characteristic chlorine odor. In dentistry, it is a precisely controlled and diluted substance. Its alkaline nature, typically with a pH around 11.6, contributes to its effectiveness.
Role in Endodontic Treatment
During root canal therapy, the inner nerve and pulp tissue are removed from the tooth’s internal canal system. Sodium hypochlorite serves as the primary irrigant, acting as a disinfectant rinse to cleanse this complex space. It aims to disinfect the internal canals and dissolve any remaining organic tissue. This helps ensure the root canal system is clean before it is sealed.
Mechanism of Action
Sodium hypochlorite achieves its cleaning and disinfecting actions through chemical reactions within the root canal. Its high pH and oxidative properties break down the essential components of bacteria, fungi, and viruses, effectively neutralizing these microorganisms. Specifically, it causes biosynthetic alterations in cellular metabolism, phospholipid destruction, and irreversible enzymatic inactivation in bacteria, leading to their demise.
Beyond its antimicrobial capabilities, sodium hypochlorite also excels at dissolving organic tissue. It does this by saponifying fats, converting them into fatty acid salts (soap) and glycerol (alcohol), which reduces the surface tension of the solution and aids penetration. Additionally, it denatures proteins and neutralizes amino acids, allowing it to break down and dissolve remaining pulp tissue, necrotic debris, and biofilms that instruments cannot physically reach within the root canal anatomy.
Concentration and Safety Protocols
In dentistry, sodium hypochlorite is used in specific concentrations, typically ranging from 0.5% to 6%, which are distinct from the much higher concentrations found in household bleach. Dentists employ safety protocols to ensure the solution remains confined within the tooth and does not harm the patient. One primary measure is the use of a rubber dam, a thin sheet made of latex or non-latex material, which isolates the tooth and protects the surrounding oral tissues, gums, and throat from the irrigant.
Specialized irrigation needles, often side-vented or closed-ended, are also used to prevent the forceful extrusion of the solution beyond the root’s tip into the surrounding bone. These needles allow the solution to flow out laterally rather than directly through the end, reducing pressure at the root apex. Proper technique involves gentle, passive irrigation, ensuring the needle is not bound or wedged tightly within the canal, which could otherwise lead to inadvertent extrusion of the solution.
Potential Complications and Management
Despite safety protocols, an accidental extrusion of sodium hypochlorite beyond the root apex into the surrounding bone and soft tissue can occur, commonly termed a “sodium hypochlorite accident.” When this happens, patients experience immediate, severe, burning pain, often accompanied by rapid and significant swelling of the affected area. Extensive bruising, known as ecchymosis or hematoma, can develop in the soft tissues, sometimes appearing hours or days after the incident.
Profuse bleeding from the root canal itself may also be observed. Management by the dentist begins with immediately stopping the irrigation and rinsing the root canal with saline or an anesthetic solution. Local anesthetic is administered to manage the severe pain, and cold compresses are applied to the swollen area for the first 24 hours, followed by warm compresses. Analgesics are prescribed for pain relief, and antibiotics may be given to prevent secondary infection.
Alternative Irrigating Solutions
While sodium hypochlorite is widely used, other substances can be employed for root canal irrigation, each with different properties. Chlorhexidine (CHX) is one such alternative, known for its broad-spectrum antibacterial properties and its ability to adhere to canal walls, providing a prolonged antimicrobial effect. However, chlorhexidine does not possess the tissue-dissolving capability of sodium hypochlorite, meaning it cannot break down organic debris or necrotic tissue.
Another solution, Ethylenediaminetetraacetic acid (EDTA), is primarily used as a chelating agent to remove the inorganic “smear layer” from the canal walls. This smear layer consists of mineralized debris created during instrumentation, and EDTA helps to open the dentinal tubules, allowing better penetration of other disinfectants. Unlike sodium hypochlorite, EDTA does not have significant antibacterial properties or the ability to dissolve organic tissue. Despite the potential risks, sodium hypochlorite’s unique combination of strong disinfection and unparalleled tissue dissolution remains why it is frequently the irrigant of choice in modern endodontics.