Apical periodontitis is primarily caused by bacteria infection of the necrotic root canal system. In teeth with vital pulps there is no infection in the root canal space, thus the therapeutical approach in these cases is completely different from infected teeth. Infection is often established as a biofilm covering the walls of the main canal lumen, and can spread to other distant areas of the canal system that are difficult to reach and may require especial treatment strategies. If bacteria persist in the root canal after treatment, there is an increased risk of failure. This presentation will cover the most relevant aspects of root canal infection, including progression of necrosis/infection in the root canal space, and the diversity, location, morphology and behavior of bacterial biofilms. The limitations in eradicating infection will also be revealed, including a discussion on the implication of residual infection. What happens when bacterial load has been reduced but infection has not been completely eradicated? Does healing occur even with a reduced amount of bacteria surviving in the root canal system?

The impact of light used for bacterial biofilm eradication is know for long. Photodynamic therapy or Photo-activated disinfection (PAD) was already initiated in the beginning of the previous century. Around the 1980’s the use of dental lasers for biofilm interactions gained renewed attention. The introduction of laser cavitation induced fluid streaming (laser activated irrigation - LAI) rang in a new era at the beginning of this century.
Laser light is unilateral, meaning there is no side firing. As we rely on fibers with straight forward emission, solutions for better 3D laser-biofilm interaction are needed. Both LAI (even with the fiber outside the root canal lumen i.e. PIPS or SWEEPS) and PAD (impregnation of the biofilm with a dye before exposure to laser light) pick up on these shortcomings. Light activated nanoparticles are now investigated to overcome the shortcomings of PAD.

Instrument retrieval may sometimes be frustrating because it often implies the sacrifice of consistent amounts of sound dentin, which may lead to iatrogenic accidents such as perforation. Within this presentation, the different microbiologic conditions of the root canal system that can be present at inception of the endodontic treatment are illustrated. It is stressed how vital, although inflamed, pulp tissue does not harbor bacteria, for which reason a sterile instrument separated in a canal with previously vital pulp is unlikely to cause treatment failure. Under such circumstances, depending on the location of the separated segment, attempts to remove it may be more risky than leaving it and a “wait and see” strategy is indicated. On the contrary, when separation occurs in a canal with necrotic/infected pulp and apical radiolucency, infection control in the whole canal length is prevented. Therefore, attempts to remove the fractured instrument must be undertaken.

Coronal leakage is a critical yet often underestimated factor in endodontic failures. This lecture will examine the etiology and mechanisms by which coronal leakage compromises root canal therapy, shedding light on its role in bacterial reinfection and the breakdown of obturation materials. Strategies for prevention, including advancements in restorative techniques, material selection, and clinical protocols, will be emphasized. Attendees will gain insights into evidence-based approaches to mitigate coronal leakage, ensuring the long-term success of endodontic treatments.

Plenary discussion directed by Dr. Domenico Ricucci

The aim of this presentation is to evaluate options that the endodontic retreatment spectrum provides to retain natural dentition. Modern clinical practice requires dentists to be familiar with new developments in materials, instruments and procedures to assist their patient in electing the most beneficial long-term treatment option in terms of maintaing health and function. Endodontic Surgery has evolved tremendously in the last decade, into a microsurgical procedure. Due to advancements in dental materials and surgical techniques, surgical micro-endodontics has greater predictable outcomes. However, there are specific cases, for which surgical endodontics is not a replacement for conventional retreatment. Successful treatment requires a thorough understanding of the causes of failure, the prognosis of each approach, technologies and materials that allow for the best possible outcome. This presentation will review the relevant literature, which evaluates prognosis of microsurgical and conventional retreatment which will help the decision-making process an informed one.

Clinicians may sometimes face severely compromised teeth in which orthograde endodontic treatment or apical microsurgery are not feasible. In these situations the choice of intentional replantation (IR) can be considered, if the involved tooth has simple root form for smooth extraction. In some instances, when a donor tooth is found in the same mouth, autotransplantation (ATT) could be the more optimal option.
In this presentation, the indications, advantages of IR and ATT will be extensively discussed. The treatment of clinical cases with varying severity will be thoroughly illustrated.

A common clinical dilemma in endodontics arises when a small, asymptomatic periapical radiolucency is observed, often visible as a hypodense area on CBCT images, despite the case being clinically asymptomatic for a certain period. The decision of whether to treat or not depends on various factors, including understanding the etiology of the lesion, potential reasons for incomplete healing, and patient expectations. This presentation will review relevant literature on the topic and explore clinical cases to illustrate decision-making in such scenarios.

When a root-treated tooth with apical periodontitis shows no symptoms but fails to exhibit radiographic healing during follow-up, clinicians face uncertainty regarding the necessity of further intervention. This presentation will illustrate diverse clinical cases examined through histopathology, shedding light on the so-called non-microbial causes of failure such as "true cysts" and "foreign body reactions." The contentious topic of healing via "scar tissue" will also be critically analyzed. Concluding with an exploration of factors contributing to the loss of endodontically treated teeth, this discussion offers evidence-based insights into complex diagnostic and therapeutic dilemmas in contemporary endodontics.

Plenary discussion directed by Dr. Domenico Ricucci