This summary is based on information found in Disinfection of Root Canal Systems: The Treatment of Apical Periodontitis (Wiley Publishing, 2014)
- Six biological factors that lead to asymptomatic radiolucencies persisting after root canal treatment:
- Intraradicular infection persisting in the complex apical root canal system;
- Extraradicular infection, generally in the form of apical actinomycosis;
- Extruded root canal filling or other exogenous materials that cause a foreign body reaction;
- Accumulation of endogenous cholesterol crystals that irritate apical tissues; and
- True cystic lesions, and (vi) scar tissue (1).
- The internal anatomy can be notoriously complex, especially in molars, and includes extra canals, recesses, fins, isthmuses, and accessory canals that provide space for the biofilms to reside.
- Biofilms are a thousand times more difficult to eradicate than planktonic organisms floating in an aqueous environment (2–4).
- It is because of the combination of anatomical hiding places and the difficulty of destroying the biofilm that complete debridement of the canal space is probably impossible with our current treatment protocols.
Root canal configuration and classification
- The flatter or more ovoid the root cross-section, the greater the propensity for complexity.
- In the maxilla, the most variation will be found in the premolars, especially the second and the mesiobuccal (MB) root of the molars. In the mandible, anterior, premolar, and molar teeth are the ones that will show the greatest variation.
- The use of small field cone beam computed tomography (CBCT) scans are a valuable adjunct to help the clinician to and mentally image the canal system shape.
Root canal morphology
- Pulp space shape is conceptualized by many to be a round hole; however, they mimic the external shape of the root: if it is round, the pulp shape will be round.
- There are a family of minor complexities in anatomy that are difficult to categorize, and they include fins, niches, loops, and other oddities. They are a reflection of the unlimited variations in pulp space anatomy that exists.
- Accessory and lateral canals extend from the pulp to the periodontium. They are found in all teeth and are formed when Hertwigs’s epithelium root sheath traps the periodontal vessels during tooth formation.
- Complex multirooted teeth have more cervical lateral canals and may present patent accessory canals in the furcation region in 29.4% in mandibular molars, and 27.4% in maxillary molars (11).
Isthmuses and intracanal communications
- Any root that has more than one canal will always present some degree of communication between those canals spaces.
- This anatomical communication should be taken into consideration during endodontic treatment as well as during apical surgery (14).
- Debridement, disinfection, and obturation of these complex spaces are difficult or impossible.
- A pattern of small accessory canals at the apex of some teeth that looks like a river delta.
- The complexity and multiple portals of exit of the pulp system make these areas very hard to debride and disinfect.
- Anatomic variation to keep in mind when treating maxillary and mandibular molars with adjoining or fused roots, which results in a C-shaped configuration of the canal spaces (15).
- The canal can vary from one distinct ribbon-shaped canal from pulp chamber to apex to three distinct separate canals with interconnections between the canals.
- The C-shaped canal has been reported in mandibular premolars and molars as well as in maxillary molars and its prevalence seems to be related to the ethnicity, with higher incidence of C-shaped canals in Asian populations.
- The challenge in treating C-shaped canals lies in the thorough debridement and complete obturation because of the irregular areas of the canal house debris and necrotic tissue that is difficult to clean and fill.
- Caution should be taken when preparing the isthmus area as it is frequently very thin leading to a strip perforation.
- Disinfection is accomplished chemically delivering and activating irrigants with ultrasonic and negative pressure irrigation with the purpose of enhancing debridement and disinfection.
The source of complexity
- The anatomy complexity has its source in the development of teeth. Internal pulp anatomy is a reflection of the external anatomy of the root. This is due to the tooth formation process.
- As a general rule, any tooth with a concavity in its root form has the potential for multiple canals and aberrant internal anatomy.
- All maxillary molars and premolars and most mandibular anterior and molar teeth have root concavities.
- This complex internal anatomy has been around for eons (Figure 2.7) but has been recognized and appreciated by the dental community only slowly.
- It was not until the advent of research grade micro-CT technology that it was possible to visualize the complexity of the internal anatomy on a broader sample size.
- Micro-CT scanners have resolutions that can produce around 10 μm voxel data. This is high enough resolution to demonstrate much of the complexity of the anatomy.
- Micro-CT machines currently produce the gold standard images for visualizing the internal anatomy of teeth. As they become more common, other datasets will become available, which will lead to a better understanding. However, there is a level of anatomy that these machines do not have the ability to resolve.
The importance of understanding anatomy toward better outcomes
- Anatomical variations present significant challenges to irrigation, disinfection, and obturation of the root canal space.
- Without treatment, extra canals will lead to unresolved problems and poorer outcomes; indeed, many cases that present to clinicians for retreatment have problems that can be traced to missed canals.
- To be successful, complex cases demand that the clinician apply all the available armamentarium to the problem, including a studied approach, microscopes, CBCT scans, and a commitment to solving the problem.
- Even in an impressive-looking obturation, not all the lateral anatomy can be filled.
- The residual debris in the canal can block the effective obturation of a space. Effective obturation depends on the effective debridement of the small anatomy, which is problematic.