December 10, 2023
A single tooth represents a complex system of both hard and soft tissues. The upper two layers of the tooth are hard tissues, namely, enamel and dentin. Moreover, the hard tissue covering of the root(s) of the tooth is called the cementum. The soft tissue component is the pulp, that is at the core of the tooth, well protected by the enamel and dentin. It is the pulp that houses the blood vessels and nerves of the tooth.
The pulp is responsible for various functions of the tooth. This involves defensive, nutritive, formative and sensory mechanisms. The part of the pulp that lies in the crown of the tooth is called the coronal pulp. Whereas the part of the pulp that lies in the root of the tooth is called the radicular pulp. The junction that connects the coronal pulp and the radicular pulp is called the root canal orifice. But it is more specifically defined as the point from where the root canal begins.
A root canal orifice is an important landmark in operative dentistry. Root canal treatments are usually done to eliminate all the infective material from the root canals of the tooth. In order to do so, the dentist needs to first deroof the pulp chamber. Once the pulp chamber is removed, the dentist can locate the root canal orifices.
The number of root canal orifices depends on the type of tooth. It is not necessary that the number of roots always correspond to the number of root canal orifices. At times, the configurations can be such, that two orifices may eventually merge into a single canal or vice versa.
In most cases, the root canal orifices are equidistant from each other. However, this is uncommon in upper back teeth. When the dentist drills the tooth to gain access to the root canal, then the cavity thus made must be enlarged enough for proper visualisation of the floor. The root canal orifices are present at the junction of the walls and the floor of this cavity.
The root canal orifice is the point where the dentist introduces his instruments in order to clean and shape the root canals. In many cases the root canal orifices are too small and it might be difficult to pass an instrument through it. In such cases, an orifice opener bur is used to widen the orifice. The procedure to locate the root canal orifices is similar in deciduous or milk teeth as well. The only difference is that the orifices are located at a relatively higher position due to the decreased length of the tissues and hence are found earlier. On a digital radiograph, a close inspection of the pulpal floor might reveal a few blackish spots, that often correspond to the root canal orifices. This is particularly useful in cases where orifices are not located at the conventional areas.
There are two important mechanisms that need to be achieved after successful location of the root canal orifice. The first is to achieve a "glide path." The glide path is the passage made from the root canal orifice till the apex of the canal where it constricts. When any instrument is able to glide easily in this space, the canals can be cleaned effectively in a three-dimensional shape. The other important mechanism is gaining "straight line access." This means that when an instrument is introduced in the canal with the means of shaping it, the instrument should not bend till the firsr curvature of the canal is reached. This is ensured by removing any overhanging dentin near the orifice that hampers the direction of the instrument.
Certain irrigants like sodium hypochlorite and softening agents like ethylenediaminetetracetate (EDTA) can help in shaving off the dentin and the smear layer from the orifices. This helps in better visualisation of the root canal orifices. Following the completion of the cleaning and shaping of the canals, certain medicaments (obturating materials) fill the root canals from its apex till the orifice, thereby sealing it.
Root canal orifices are major landmarks on the pulp floor that helps in location of the root canals. The orifices guide the dentist in establishing the correct path of the root canal and understanding its configuration.