The complexity of the root canal system of a tooth is far beyond our imagination. The success or failure of root canal treatment is largely determined by our accurate positioning and cleaning of the root canal length. The prerequisite for perfect cleaning and shaping is to obtain accurate root canal working length.
Four methods for locating the working length of the root canal:
1. Feeling method
2. X-ray positioning
3. Electronic measurement method, root apex locator
4. Paper tip method
The above four methods have their own advantages and disadvantages. When we choose different measurement methods, we must have a comprehensive understanding and mastery of them. Combining the above methods will achieve better results.
Features of the four technologies:
1. Tactile: lack of reliability for thin and curved root canals. Lack of feel when the apical foramen is too large. Strong dependence on the doctor’s experience.
2. Radiographic positioning: it is still the “gold standard” for root canal length positioning. It is often necessary to repeat the photographic determination multiple times, which is time-consuming.
3. Electronic measurement method (EAL): The apex locator dental equipment is convenient, and the accuracy varies according to different brands, but the overall accuracy and reliability are high. It takes some skill and learning to use well.
4, paper point method (paper point): suitable for use in specific situations.
The basic steps:
1. Pulp opening: Thoroughly clean the carious tissue and fillings, reduce the occlusal height, and have a good access channel.
2. Preliminary preparation: determine the number of root canals, understand and estimate the length and shape of the root canal (judgment of curved and thin root canals), prepare the root canal entry channel, determine the measurement of the main tip file, and clean up the contents of the root canal.
3. Choose different measurement methods for measurement: In particular, it should be noted that the preparation of the root canal entry channel has a very large impact on the measurement of the entire working length, but we often ignore this point.
Understanding of the basic anatomy of the root tip
1. Common anatomy rankings;
2. 33% of the apical foramen are not at the apical point of the root;
3. The significance of the anatomical statistical reference value of root canal length and root canal number.
How can I get the exact working length?
1. Tactile: Accumulation and experience of experience, referring to anatomical statistics.
2, X-ray positioning (Radiographic): combined with the feel method and other methods can improve the accuracy. The problem of image distortion at the tip: the tip of the file is not less than 1mm. Accurate images can be obtained only if ISO15# or above. The X-ray film positioning the file tip and root apex is considered to be in place, if it is greater than 2mm, it must be repositioned and confirmed by radiography again.
3. Paper point method (Paper point): (Buchan LS, 1991) Accuracy: ±0.25mm Most suitable for root canal positioning procedures with abnormally thick or lost more pointed holes: electrical measurement or estimation → minus 1mm → paper point Put it into the root canal to dry → insert the appropriate size paper tip until the tip is stained → take out and observe → measure the length.
4. Electronic measurement method (EAL, Electronic Apex Locator) has been widely accepted and used, and its accuracy is beyond doubt.
How to get an accurate reading:
1. Select the appropriate initial root canal file.
2. Remove at least 2/3 of the root canal content before measurement.
3. The medullary cavity is dry, and the inside of the tube is kept moist and lubricated, and there is no metal debris.
4. Make sure that there is no metal object or soft tissue touching the root canal file on the crown.
5. The initial root canal file is slightly exceeded and then withdrawn to the root apex for the exact length.
6. Repeated measurement and verification.
7. There will be “misreading” when entering the lateral branch root canal.
8. Combined with other methods or anatomical reference values, X-ray films and other data to make a comprehensive judgment.
The diagnostic value of the apex locator: it can be used for auxiliary diagnosis in patients with contralateral penetration and root fracture.
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