ENDO, 02/2019

Oral biofilms are complex structures formed on different surfaces of the oral cavity. They comprise a dynamic system where bacteria live within a multicellular community that protects them from external threats and allows bacteria to adapt and survive. Oral biofilms share general mechanisms of biofilm formation with other microbial communities in the rest of the human body: primary colonisers attach to a lightly coated substratum and, subsequently, these initial cells lead to the growth of microcolonies and maturation of the biofilm. The only oral environment that does not harbour a 'normal' oral biofilm is the root canal, but oral bacteria are able to enter this area in the event of a breach in the hard-tissue barriers. Current evidence shows that bacteria colonising the root canals of teeth form biofilm communities similar to their parent population (dental plaque). The presence of these biofilm communities in root canals of teeth has been related to inflammatory conditions of the dental pulp and the adjacent periapical tissues. Thus, a major goal of root canal treatment is the disinfection of infected root canals to their full extent. However, studies have proven that the disinfection of root canals is a real challenge due to it complex anatomy especially in the form of isthmuses, lateral canals and apical deltas. Keywords: biofilm, complex anatomy, disinfection, root canal bacteria

Irrigant delivery by a syringe and needle is still widely used during root canal treatment. It seems to perform similarly to other irrigation methods in the main root canal, provided that the needle is inserted close to working length, the canal is adequately enlarged and the irrigant is delivered at a sufficient flow rate. However, additional delivery and activation methods are needed to clean and disinfect areas beyond the main root canal. Neither the entrapment of air bubbles in the apical part of the root canal ('apical vapor lock') nor the surface tension of irrigants are limiting irrigant penetration during syringe irrigation. Keywords: flow, irrigation, needle, penetration, syringe

Ultrasonic irrigant activation is the most widely used supplementary irrigation method. It relies on the oscillation of an instrument at ultrasonic frequency while surrounded by irrigant, which results in heating of the irrigant, intense streaming and, under certain conditions, cavitation. A variety of ultrasonic files, tips, wires and needles have been used for this purpose. The efficacy of ultrasonic activation depends on the size of the instrument, the power setting and the direction of oscillation. Sodium hypochlorite, ethylenediaminetetraacetic acid (EDTA) and chlorhexidine are the most commonly activated irrigants and they can be delivered either simultaneously or between activation periods. This method appears very effective in the removal of pulp tissue remnants and hard tissue debris from the root canal. However, there is conflicting information regarding its antimicrobial effect and there seems to be no improvement in the treatment success rate, at least in single-rooted teeth. Instrument-to-wall contact appears inevitable under clinical conditions and may result in oscillation dampening and removal of small amounts of dentine. Ultrasonic instruments may fracture during use because of fatigue. Irrigant extrusion through the apical foramen is very limited except when the irrigant is continuously delivered and activated by an ultrasonic needle. Electromagnetic interference with pacemakers is unlikely to occur. Important knowledge gaps still exist, so ultrasonic activation is a topic of interest for future studies. Keywords: acoustic streaming, cavitation, irrigation, ultrasonic activation

The main goal of chemomechanical preparation is to remove microorganisms, pulp tissue remnants and dentine debris from the root canal system. Irrigation plays a major role in the cleaning and disinfection of the root canal. A large number of chemical compounds have been suggested over the years for use as irrigants during root canal treatment. At the moment there is no single irrigant that can satisfy all of these requirements, so a combination of irrigants is frequently used during treatment while seeking a balance between efficacy and safety. However, the need to use more than one solution also brings additional challenges because they may interact with each other inside the root canal. The aim of this article is to provide a critical review of the current evidence on the properties of the root canal irrigants, focusing particularly on those that are most widely used. Keywords: endodontics, interactions, irrigating solutions, properties, root canal irrigation

A critical narrative review focusing on studies providing insight about the potential and actual effect of lavage (irrigants and irrigation techniques) on clinical, biological, chemical and mechanical outcomes of root canal treatment, including microbial load reduction, periapical healing, postoperative pain, tooth survival and dentine changes. Keywords: biofilm, canal anatomy, irrigation, sodium hypochlorite, wound infection

Inadvertent extrusion of sodium hypochlorite toward the periapical tissues is an infrequent, yet alarming complication during root canal treatment. Such accidents seem to occur more often in female patients and during the treatment of maxillary teeth. Authors of case reports have proposed a number of possible causes for these accidents but corroborating evidence is usually lacking, so their aetiology is still a matter of debate. Various theories have been suggested to explain their occurrence and provide guidelines for clinicians in order to prevent them. Their management has been extensively discussed in the literature and appears more straightforward. This review aimed to present a critical analysis of the evidence on sodium hypochlorite accidents, highlight potential knowledge gaps and provide directions for future case reports and experimental studies. Keywords: accident, apical pressure, compliance, extrusion, sodium hypochlorite