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Summary of some methods to find the root canal orifice

2021-06-02
The positioning of the root canal orifice is a key step for the correct positioning of each root canal. The pulp chamber and root canal of a single canal tooth are continuous tubular, which makes it difficult to identify the root canal orifice. For multiple teeth, there is a funnel-shaped root canal orifice, but the pulp chamber in the crown of the tooth must be carefully treated. The root canal orifice can only be found after the contents.

Clinically, if multiple root canal teeth are difficult to find the root canal orifice for some reasons, in addition to applying the knowledge of the anatomical shape of the pulp cavity of the tooth, the following methods can also be combined to help find the root canal orifice.

1. Multiple root canal teeth are often due to age-related changes or restorative dentin deposition, or pulpal stones, or pulp cavity calcification, or root canal morphology, etc., which makes it difficult to find the root canal orifice. You can use the three-dimensional tooth Three-dimensional anatomy, understand and see the anatomy of the pulp cavity from various directions and positions; and use X-rays taken by multiple angle projection methods to understand and point out the number, shape, position, and direction of the root and root canal And bending; the relationship between the root and the crown; the various possible variations of the anatomical morphology of the root and root canal, etc.

2. Remove the dentin collar covering the root canal orifice at the neck of the molar pulp cavity to fully expose the root canal orifice at the bottom of the pulp chamber.

3. After using a root canal irrigant that can dissolve and remove the necrotic tissue in the medullary cavity to thoroughly clean the medullary cavity, the root canal orifice is likely to be detected.

4. When detecting the root canal orifice, attention should be paid to selecting the dentin and restorative dentin covering the cementum in the darker part of the pulp chamber bottom for thorough exploration. And should pay attention to follow the direction of the root canal for exploration.

5. There are several developmental grooves at the bottom of the pulp chamber, all of which are related to the opening direction of the root canal, that is, they move along the developmental groove at the bottom of the pulp chamber to the orifice of the root canal. Therefore, use a very sharp root canal probe to scrape along the developmental groove, which is expected to open the tighter root canal orifice.

6. When a root canal has been pointed out, the possible positions of the remaining root canals can be estimated. If necessary, a small ball drill can be used to remove a small amount of dentin at the developmental groove where the root canal may or is expected to be located, and then use a sharp probe to try to penetrate the calcified area , To find the root canal orifice, remove the dentin collar of the tooth neck to expose the position of the root canal orifice. Pay attention not to deepen or flatten the developed groove excessively when drilling and grinding the developed groove, so as not to lose these natural signs and grind or puncture the root bifurcation area sideways.

7. Apply tincture of iodine to the bottom of the pulp chamber, and then wipe the bottom of the pulp with a slightly dry alcohol cotton ball to remove the iodine. The darker place is usually the root canal or developmental groove.

8. Transillumination: Use the light source of the optical fiber diagnostic instrument to transilluminate the hard tissue of the crown of the buccal and lingual tooth. The light enters the pulp cavity through the enamel and dentin, and the root canal orifice can be seen as a black spot; and the light source is approached from the soft tissue The root protrusion is transilluminated, and the light enters the pulp cavity through the soft tissue, cementum and dentin, which shows that the root canal orifice is brighter than the nearby pulp bottom.

There are several common techniques for finding less obvious root canal openings

1. The level of the pulp chamber floor is equivalent to the level of the enamel-cementum boundary. The formation of secondary dentin will not change this rule. Therefore, the enamel-cementum boundary can be used as a fixed anatomical landmark for finding and confirming the pulp chamber floor.

2. On the cross section of the tooth at the level of the enamel-cementum boundary, the shape of the pulp cavity is the same as that of the tooth section, and it is located in the center of the section, that is, the boundaries of the pulp chamber floor are equidistant from the outer surface of the tooth.

3. The formation of secondary dentin has a fixed position and pattern. The four side walls of the cheek and tongue, the top of the pulp chamber and the bottom surface of the pulp chamber are spherically formed in the mesial and distal sides of the pulp cavity.

4. Color law

(1) The color of the medullary chamber bottom is darker than the color of the medullary cavity wall, that is, the color of the medullary chamber bottom is black, and the color of the medullary chamber wall is white. The black and white junction is the boundary of the medullary chamber floor.

(2) The secondary dentin is lighter than the primary dentin, that is, the secondary dentin is white and the primary dentin is black.

6. Signs of sulcus fissure: There are dark sulcus fissures between the root canal orifices, and sometimes there is pulp tissue in the sulcus fissure. When the root canal orifice is heavily covered by calcification, remove the calcification along the direction of the fissure and find the root canal at the end of the fissure. This is a very quick and safe technique.

7. The root canal orifice must be located at the junction of the side wall of the medullary cavity and the floor of the medullary cavity.

8. The root canal orifice must be located at the corner of the bottom of the pulp chamber.

9. Symmetrical distribution of root canal orifices: For multiple teeth except maxillary molars, draw a mesiodistal center line at the bottom of the pulp chamber. The root canal orifices are distributed on both sides of the cheek and tongue and arranged symmetrically. That is to say, the distance between the buccal tongue root canal and the central line is the same. If there is only one root canal orifice, the root canal orifice must be located on the midline or near the central line and will not deviate much. According to this rule, it can be quickly judged whether there is a distal tongue root canal in the lower molars.

For lower incisors, 30% of Chinese have 2 root canals, of which the lingual root canal is often missed;

For maxillary premolars, the incidence of double root canals is more than 80%. Therefore, when the root canal is explored, two root canals are used as the target for positioning. The high incidence of wedge-shaped defects in the maxillary premolars leads to calcification of the buccal root canal and the buccal side. The root canal orifice is sometimes extremely biased to the buccal side, so clinical omissions often occur;

The incidence of multiple root canals near the buccal root of the maxillary first molar is about 60%, and the buccal palatal root canal, namely MB2, is often missed clinically.

For the mandibular first molar, if the distal root has two root canals, the mesial root generally has two or more root canals. At the same time, the incidence of independent distal tongue roots is higher than 30% because of the fact that the tooth roots are more than 30%. Located at the neck of the distal lingual axis, the root canal orifice is extremely close to the distal lingual side at the bottom of the medullary chamber. The root canal is slightly curved, which is easy to be missed clinically.

For the mandibular second molars, the incidence of C-shaped root canals is high in Chinese. The distal root canal and the proximal buccal canal are connected in a C shape, which has attracted great attention in clinical practice. On the contrary, the proximal root canal orifice is located near the lingual side and proximally. Below the tongue tip, and the root canal is small, it is easy to be missed clinically.

For variant roots and root canals, only through imaging diagnosis and analysis of variant root canal anatomy.

X-ray apical film is the main method to judge the missing root canal. It is recommended to use parallel projection technology for shooting, which is convenient for observing the trend and changes of the root shape and root canal image. If root variation is suspected, the projection angle can be changed to separate overlapping roots.

a X-ray of buccal and tongue; b X-ray of deflection angle projection

When the mandibular first molar has a distal root of the tongue, X-rays can often be used to observe the image of double roots in the distal; when the mandibular first premolar has more than 2 root canals, the main root canal images of the X-ray often show sudden Disappear or break.

a The image of the main root canal disappears (as shown by the black arrow); b The root canal confirms that the main root canal is bifurcated in the middle and lower segment

Treatment of omissions in the main root canal

The primary root canal omission must first be diagnosed through careful inspection to determine whether there is a missing root canal and which root canal is missing. If necessary, CT or dental CT scan can be used for inspection. Only after the positioning is clear can effective dredging be carried out. Generally, the recanalization rate of missing root canals is higher.

a CT scan showing double root canals of the maxillary lateral incisor; b X-ray film of the main tip file; c root filling film

For example, the study of MB2 root canal positioning and dredging found that 96% of maxillary molars have MB2 root canal orifices and 80% can be dredged. Although the use of a microscope is conducive to the exploration of MB2 root canals, some of them are still difficult to dredge. Studies believe that the reason why the MB2 root canal cannot be dredged may be due to the presence of obstructions such as bending, shoulders, or medullary stones, and debris.

Treatment of missing collateral root canals

The omission of the collateral root canal is difficult to avoid at the current level of treatment technology. The only treatment method is to strengthen the mechanical and chemical preparation of the root canal. Ultrasonic irrigation can be assisted to open the collateral root canal in the main root canal. The opening of the wall allows the disinfectant to enter the collateral root canal. It is recommended to fill the root canal with hot gutta-percha, so that the fluid gutta-percha and paste can fill the above-mentioned irregular areas.

a X-ray film of the initial tip file; b X-ray film of the root canal (the side branches of the root canal are shown by the arrow)

Dyeing method

Drop the dye into the pulp chamber, then rinse and dry the pulp chamber with water. The root canal where the root canal is missed usually has dye residue. For example, methylene blue is often stained blue due to the residual pulp tissue in the missing root canal. Iodophor, the omission of the root canal is darker in color.

Foaming test

After the pulp chamber is cleaned, drop the sodium hypochlorite solution and wait for a few minutes. Small bubbles can be seen from the mouth of the missing root canal.

Application of Microscope Ultrasound Technology

The microscope has the function of magnification and illumination, which can observe the condition of the floor of the medullary chamber more clearly. In general, the pulp chamber floor of multiple teeth is often depressed, and the deepest part of the depression is often the root canal orifice; the root canal orifice is often funnel-shaped; there is often a dark groove between the root canal orifices that is lower than the pulp chamber floor That is, the groove is developed, and the end of the groove is often the location of the root canal orifice. For the calcification of the pulp chamber or the presence of a large number of secondary dentin above the root canal orifice to form dentin overhangs, which are often chalky under the microscope, they are removed with an ultrasonic tip to expose the dark bottom of the pulp chamber underneath.

Attachment: Root Canal Orifice Location of Maxillary Molars

1. The mesial buccal canal orifice (MB) is located under the mesial buccal tip, and the distal buccal canal orifice (DB) is located in the far middle of the MB canal orifice, which is slightly more lingual than the position of the MB canal orifice. The palatal canal orifice (P) is the thickest, generally located below the mesial tip of the tongue.

2. Positioning the second canal (MB2) of the mesial buccal root is a difficult point in the preparation of this group of teeth. Sometimes the triangular crown entrance is often not enough to expose the MB2 canal. The MB2 canal orifice is usually located at 1.82mm on the lingual side of the MB canal orifice.

The method of positioning MB2: On the connection line between the MB root canal and the P root canal, draw a vertical line from the DB root canal to the MB-P connection. The intersection of the two lines is the location area of the MB2 root canal.

Root Canal Orifice Location of Mandibular Molars

1. The mesial root canal (MB) is located under the mesial buccal tip, and the mesial root canal (ML) is located on a straight line from the central sulcus to the mesial marginal ridge. The orifice of the distal buccal root canal (D) is often located below the intersection of the occlusal cheek groove, tongue groove and central groove.

2. The incidence of four canals is about 35%-43%, and the distal buccal canal orifice (DB) is often located in the mesial buccal side of the D canal. The positioning method of the distal root canal orifice: draw a vertical line to the distal center at the midpoint of the connection between the two mesial canals or follow the dark line of the mesial and distal canals on the bottom surface of the medullary chamber to explore the distance, if the distal root canal orifice is just right Located above the vertical line or at the end of the dark line, it is mostly a distal root canal; if the orifice of the distal root canal is on the side of the vertical line or dark line (mostly on the lingual side), it should also be on the opposite side (buccal side) ) Find the fourth canal (DB root canal).
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