Endometric root canal length measurement (synonym: electrometric root canal length determination) is a diagnostic procedure that can be used to determine the preparation length of a root canal very accurately as part of a root canal treatment and thus makes an important contribution to its success. The aim of root canal treatment is to prepare and disinfect a root canal as completely as possible up to its apical constriction. At this narrowest part of the root canal, the root cementum lining the outside of the root usually merges with the intracanal root dentin and the pulp tissue (tooth pulp) with the mixed tissue of the periapex (root tip environment). The apical constriction does not coincide with the radiographic apex (root tip); rather, it is approximately 1 mm away from it. Whereas the position of the apical constriction has to be estimated in radiographic length determination and the practitioner has to feel the constriction with a great deal of dexterity in tactile length determination, electrometric length determination is now considered the most reliable measurement method. This is because the great advantage of modern endometry devices lies in the high accuracy with which they indicate apical constriction. They can determine it so reliably that overinstrumentation can almost certainly be ruled out.
Indications (areas of application)
The indication for electrometric length determination of a root canal arises in the context of any root canal treatment in which apical constriction is expected as a prerequisite for performing a correct measurement.
Contraindications
Correct measurements are made impossible by the following conditions:
- Resorptions caused by inflammation in the root tip area as well as roots not yet completed in growth do not have apical constriction
- Severe bleeding from the root canal leading to contact with the gingiva (gums) surrounding the tooth
- Deeply destroyed tooth crowns, leading to contact between the access cavity and the gingiva.
- In root fractures, the current is diverted away via the fracture gap
- Filling material remaining in the root canal during a revision (renewal of a root filling); filling material that cannot be completely removed blocks access to the apical constriction
- Metallic fillings or crowns with gingival contact conduct the current away. Measurement is only possible if contact of the root canal instrument with the metal can be avoided
Before the examination
Prior to the examination, access to the root canal(s) through the crown of the tooth must be exposed. Extirpation of pulp tissue (removal of pulp) not only in the crown area, but also in the root canal using an extirpation needle must precede the measurement, as well as preparation of the coronal third of the canal near the cavity. This is prepared in such a way that the root canal curvature is reduced and thus a straighter access to the further canal course and to the apical constriction is created.
The procedure
Endometry devices (synonym: apex locator) consist of a voltage source and a measuring instrument and operate with alternating current. The electrodes are, on the one hand, an instrument located in the root canal and, on the other hand, a counter electrode suspended in the corner of the mouth. Based on the knowledge that the electrical resistance between the oral mucosa and the desmodont (root skin, attached to the outer root surface in the root cementum) is constant, the endometry instrument measures the alternating current resistance between these tissues (tissue impedance). Using a canal preparation instrument inserted into the root canal, the endometry instrument measures the resistance between the tip of the instrument and the surrounding fluid (electrode impedance). In the area of apical constriction the resistance and thus the measurement signal is greatest, but below the constriction it is lowest, because there, beyond the narrow root canal in the area of the desmodont, the current can flow in all directions. Modern endometry devices work according to the relative impedance method. They have calibrated displays linked to a color code and an acoustic signal, with the help of which the practitioner can comfortably follow the path to the apical constriction and feel his way forward. New device types work with multiple frequencies and thus increase measurement accuracy.The following process steps are required for the measurement:
- Irrigation of the root canal with an electrically conductive liquid, for example with CHX (chlorhexidine).
- Drying the cavity, but not the root canal.
- Hanging the mucosal electrode in the moistened corner of the mouth.
- Attaching the root canal instrument (K-file ISO 008 to 020, depending on the device) to the clamp of the endometry device; the clamp must be placed between the handle and the silicone stopper
- Insertion of the root canal instrument into the canal to be measured.
- While following the indication or acoustic signal, advance the instrument until apical constriction is reached
- Once apical constriction is reached, adjust the silicone stop on the root canal instrument to a reference point in the area of the tooth crown that is clearly reproducible and easily visible to the operator (coronal reference point)
After the examination
After the examination, document the determined working length of the root canal instrument and the location of the reference point for any subsequent treatment sessions.
Possible complications
- The area of the root apex is multiform. Thus, in addition to the main canal with its foramen apicale (canal opening at the root apex), there may be side canals with accessory foramina (additional openings) that together form an apical delta. Each additional side canal, however, reduces the electrical resistance in the area of apical constriction, so that measurement errors are possible.
- A moist access cavity will result in false positive measurements.
- A channel that is too dry will give false negative results.
- Obliterated (closed by calcification) channels make measurement impossible.
