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Significance of the Coronal Pulp Chamber Floor Anatomy in the Human Dentition: A Narrative Review Ajinkya M Pawar Shishir Singh Dental Update 2024 48:1, 707-709.
Authors
Ajinkya MPawar
BDS, MDS, Assistant Professor, Department of Conservative Dentistry and Endodontics, Nair Hospital Dental College and PhD Scholar, Department of Conservative Dentistry and Endodontics, TPCT's Terna Dental College and Hospital, Mumbai, India.
In root canal treatment, the foundation on which all surgical procedures are performed is a thorough knowledge of the anatomy of the pulp chamber and the root canal system. The endodontic triad comprises biomechanical preparation, microbial control and complete obturation of the root canal space. Knowledge of the pulp chamber floor anatomy is important in locating the numbers and orifices of root canals present within the tooth being root canal treated. This is particularly important while treating teeth that are heavily restored, mal-positioned, or calcified. The current review attempts to explain the complex anatomy of the pulp chamber floor and its significance in root canal treatment.
CPD/Clinical Relevance: To allow the location of all root canal orifices in the pulp chamber and to perform successful root canal treatment, knowledge of pulp chamber floor anatomy is essential. The clinician should consider that, as the external morphology of the tooth varies in individuals, so does the internal morphology.
Article
The pulp complex should be visualized as beginning occlusally at the pulp horns and ending at the apical foramina. In order to remove pulp tissue entirely from the pulp complex, the coronal portion must be accessed in a manner that will permit pulp removal and facilitate the location and debridement of the root canals without unnecessarily compromising the strength of the coronal enamel and dentine. The variation of the pulp chamber floor, especially in multi-rooted teeth, is a constant challenge for diagnosis and subsequent root canal treatment.1 Attempting to treat the root canal system without detailed anatomical information could be potentially disastrous. There is an abundance of literature describing root canal anatomies, but the studies that have considered pulp chamber anatomy have been very generic and offer little insight on how to determine the orifice number and location of root canals.2
One of the major reasons for root canal treatment failure is ‘missed canals.’ The access to the pulp chamber is also determined by a preset and well-defined set of laws. These are the laws of centrality, concentricity, cemento-enamel junction (CEJ), symmetries, colour change, and orifice location. CEJ, an anatomical landmark, still remains the pilot guiding towards an ideal access cavity preparation aiding the location of all the root canals.3
There is a generic description of the average number of canals in different teeth. While the average number of canals in a tooth is of some value, it may vary in the individual tooth of an individual person. The available literature regarding the location of canal orifices has been presented in an unsystematic manner.
Typically, it has been suggested that access to the cavity should be made in an approximate position in the clinical crown, and then a search for the orifices made in the hopes of finding them. However, locating canal orifices in teeth that are heavily restored, broken down due to extensive caries, or have had improper earlier access cavities is extremely problematical, as normal anatomy is often badly damaged.2 Also, factors such as physiological ageing, pathology and production of secondary and tertiary dentine may increase the difficulty in locating canal orifices.4,5,6
Clinically, there are a number of diagnostic measures that can be taken to locate root canal orifices, including multiple pre-operative radiographs, cone beam computed tomography (CBCT), examination of the pulp chamber floor with a sharp explorer, troughing of grooves with ultrasonic tips, staining the chamber floor with 1% methylene blue dye, performing the sodium hypochlorite ‘champagne bubble’ test and visualizing canal bleeding points.7
The aim of this review is to highlight the importance of the anatomy of the coronal pulp chamber floor.
Anatomy of the coronal pulp chamber floor
Knowledge of the anatomy of the tooth being root canal treated, with the anatomy of the adjacent tissue, is most important for successful removal of the pulpal tissue. For successfully removing the contents of an entire root canal system, the coronal pulpal chamber and the radicular pulpal tissue must be identified.
Krasner and Rankow formulated new laws, providing guidelines for locating the pulp chamber and root canal orifice. The existence of constant landmarks makes it easy to locate orifices systematically and more successfully, especially in cases where locating orifices has become difficult.8
The coronal anatomical laws have been proposed to aid in access cavity preparation and are discussed below.2
The law of centrality states that the floor of the pulp chamber is always located in the center of the tooth at the level of the CEJ (Figure 1). This law can be used as a guide to prepare to access the cavity. But care should be taken, as this law only applies at the level of CEJ and is not related to the occlusal anatomy of the tooth being root canal treated. This law may not apply when treating a tooth that is heavily restored with an oversized crown, since the location of the center of the tooth might be misleading.2
Figure 1. Coronally cut sample exhibiting law of centrality.
The law of concentricity states that the walls of the pulp chamber are always concentric to the external surface of the tooth at the level of the CEJ. This law helps the clinician in extending access to the cavity efficiently. If there is a presence of any bulge of the CEJ in a particular direction, the pulp chamber also extends in that direction (Figure 2).2
Figure 2. Coronally cut sample exhibiting law of concentricity.
The law of symmetry 1 states that, except for maxillary molars, the orifices of the canals are equidistant from a line drawn in a mesial-distal direction through the pulp chamber floor (Figure 3). The law of symmetry 2states that, except for the maxillary molars, the orifices of the canals lie on a line perpendicular to a line drawn in a mesial-distal direction across the centre of the floor of the pulp chamber (Figure 3).
Figure 3. Coronally cut sample exhibiting law of symmetry 1 (red line) and symmetry 2 (white line).
The law of colour change states that the colour of the pulp-chamber floor is always darker than the walls. The law of orifice location 1 states that the orifices of the root canals are always located at the junction of the walls and the floor. The law of orifice location 2 states that the orifices of the root canals are located at the angles in the floor-wall junction. The law of orifice location 3 states that the orifices of the root canals are located at the terminus of the root developmental fusion lines (Figure 4).
Figure 4. Coronally cut sample exhibiting law of orifice location 3. Arrows mark the developmental root fusion lines.
The law of orifice location 1 and 2 may be used to identify the number and position of the root canal orifices, as all the orifices are located along the floor–wall junction. These two laws, in conjunction with the law of colour change, are the only reliable indicator for the location of second canals in mesiobuccal roots of maxillary molars.9 The law of orifice location 2 may guide towards the actual location of the root canal orifices, with the vertices (ie a point where two or more lines/walls meet) and/or angles of the darker chamber floor specifying the position of the root canal orifices. In cases of calcified canals, the position of the vertex will dictate the penetration of the bur, aiding in removal of reparative dentine from above the root canal orifice (Figure 5). The laws of symmetry 1 and 2 (except for the maxillary molars), colour change, and orifice locations 1 and 2 can be applied to any tooth.2
Figure 5. Coronally cut sample exhibiting calcified pulp stone (arrow) and vertices on the pulp chamber floor.
Discussion
A major cause of failure in root canal treatment is the inability to locate, debride and obturate extra canals. There are numerous studies reported in the literature on the root canal anatomies of multi-rooted teeth (premolars and molars).10,11,12,13,14 These teeth often exhibit multiple canals. If they are considered to have multiple canals, knowledge of the coronal pulp chamber floor of these teeth is most important.15 If the clinician is not familiar with the chamber floor, the chances of missing root canals are high. Walton and Torabinejad16 and Ash and Nelson17 have rightly reported that the pulp morphology of teeth is often extremely complex and highly variable.
Distinct laws have been proposed for locating pulp chambers and the multiple orifices present on the pulp-chamber floor, on the basis of precise patterns and the relationship between the pulp chamber and the pulp-chamber floor. Knowledge of the laws of orifice location helps prevent clinicians from causing crown perforations in a lateral direction. For example, as the law of centrality states that the pulp chamber is always centrally located at the level of the CEJ, the operator can use the CEJ as a circular target regardless of how non-anatomical the clinical crown or restoration may be. Even if the crown sits at an obtuse angle to the root, the CEJ can still be a reliable landmark for locating the pulp chamber. Also, after restoration of a tooth, the occlusal anatomy may have no relevance to the position of the underlying pulp chamber.2
Many clinicians have preconceived ideas of the anatomy and position of the pulp chambers and root canals, based on the conventional clinical presentation of faultless teeth in textbooks. Gaining access to the pulp chamber is recommended from the external surface of the tooth to the internal surface (ie the pulp chamber), based on this ideal anatomy. However, this recommendation has little relevance when treating pretreated, restored, or crowned teeth, and may lead to perforation.
The first step in endodontic treatment is the preparation of the access cavity, which provides an opening in the dental crown that allows localization, cleaning, shaping, disinfection and obturation of the entire root canal system. An access cavity that has been prepared improperly in terms of position, depth, or extent will hamper the achievement of optimal results.18 The CEJ is the most accepted and established anatomical landmark and is regarded as the paramount landmark for locating the pulp chamber.2
The law of centrality helps to prevent coronal lateral perforations when gaining access to the pulp chamber, as it is located centrally at the level of the CEJ. The clinician may use the CEJ as a target irrespective of the anatomical alteration of the coronal structure.
The law of concentricity helps clinicians to extend their access appropriately. The clinician may refer to the bulge of the CEJ and extend the access cavity in that direction. For example, in cases where the tooth is narrow mesiodistally, the clinician can infer the pulp chamber is also narrow mesiodistally.
In order to be sure that the access cavity is adequate, the clinician needs to know the law of colour change.2 The access cavity is deemed complete when the clinician can successfully visualize the entire pulp chamber floor. The law states that the colour of the pulp chamber is always darker than the surrounding walls. As the cut walls are lighter, there is a junction, which is formed by light walls and the dark pulpal floor. If this junction is not observed at the pulp chamber floor, it is a hint to the clinician that the i cavity preparation is incomplete and the overlying tooth structure must be removed. Establishing this junction clearly helps in applying the laws of symmetry and orifice location to find the exact positions and numbers of orifices. Knowledge of the laws of symmetry 1 and 2 immediately indicates the presence of a fourth canal. Indeed, it not only implies the presence of a fourth canal, but exactly where it is located (Figure 6). The law of orifice locations 1 and 2 may be used to locate the position and number of root canal orifices, because all of the orifices are located along the floor–wall junction, and any black and white markings or indentations, observed anywhere else must be ignored to avoid any possible perforations. If the canal is calcified, then this position at the vertex will indicate with certainty where the operator should begin to penetrate with the bur to remove reparative dentine from the upper portion of the root canal. The law of orifice location 1 and 2, in conjunction with law of colour change, is often the only reliable indicator of the presence and location of extra canals.
Figure 6. Coronally cut sample exhibiting four canals.
In cases with anatomical variations, endodontic treatment initiation, instrumentation and completion may be carried successfully with the clinician being familiar with basic knowledge of the laws.4 While gaining access during root canal treatment, magnification with illumination by either dental operating microscope or dental loupes enhances the quality of vision for identifying the root canal orifices more easily.19,20
Each tooth demonstrates a variety of root canal configurations that must be thoroughly disinfected, increasing the success rate of root canal treatment. With the development of CBCT, it has become possible to visualize the anatomy and root canal system of the teeth, owing to the three-dimensional (3D) images obtained. Cases with unusual root formations, such as dens in dente (tooth within a tooth), multi-rooted lower premolars, C-shaped molars, or cases with excessively curved canals, may benefit from a CBCT scan. Many studies have used this technique to finvestigate the anatomy of the root canal system especially in multi-rooted teeth.21,22,23,24
This article correctly recommends the use of the CEJ as a reference level for correct access orientation. However, to use the CEJ as an anatomical reference, we suggest that beginners use retentive rubber dam clamps with narrow jaws, curved and slightly inverted, to help with gingival displacement when placed below the maximum diameter of the crown of the tooth being treated.
Conclusion
In spite of all of our best efforts, problems during root canal treatment can occur. The above description can help to overcome and remedy the most common problems that a practitioner might encounter. The observer should be cautioned, however, that the number of orifices does not necessarily correlate to the number of canals. Sometimes, more than one canal can be present in a single orifice.
