The fundamental operating principles of electronic root canal length measurement devices

By Neekofar M, Ghandi M, Hayes S, Dummer P

Date: 02/2007
Journal: JOE


•Goal of root canal treatment is to control infection through debridement, disinfection and filling of root canal system. (Lin et al 2005)

•Root canal treatment procedures should be limited within the root canal system. (Ricucci 1998)

Morphology of root canal terminus:

•Apex of the root canal narrows down then widens to form an hour glass shape (Kuttler 1958). This narrow part is considered the minor apical foramen and is located at the CDJ which many consider to be the terminus of the root canal. (Kuttler, Ricucci, Ponce and Fernandez) The wider part is the major foramen.

•Major apical foramen deviates from the apex of the root. Increased offset was reported with increasing age. (Stein and Corcoran 1990)

•Deviation of the foramen can occur due to pathological changes like external root resorption. (Maleug et al 1996)

•Theoretically, CDJ is the appropriate terminating point for root canal treatment procedures but it’s not clinically applied. Clinically applied practice, the minor apical foramen is more consistent feature (Katz, Ponce and Fernandez) that can be regarded as the narrowest portion of the root canal system and thus the landmark for end-point of root canal treatment.

Determining the root canal terminus:

•Root canal lengths determined by radiographs vary from actual root canal length by a considerable amount. (Kuttler et al)

Electronic Root Canal Length Measurement Devices:

•Their functionality is based on the fact that electrical conductivity of tissues surrounding the apex of the root is greater than conductivity inside the root canal system whether dry or wet canal with a non-conductive fluid. (Custer et al 1918)

Suzuki (1942) indicated that the electrical resistance between a root canal instrument inserted into a canal and an electrode applied to the oral mucous membrane registered consistent values.

•Based on these findings, Sunada (1962) reported that when the tip of an endodontic instrument had reached the periodontal membrane through the ‘apical foramen’, the electrical resistance between the instrument and the oral mucous membrane was a constant value.

•if perforation occurs, the reading on the device is similar to the reading at the apical foramen. (Sunada 1962)

•The device established a circuit in the mouth that originated in the device, ran through an endodontic file via the attached probe, and extended down the canal out of the foramen and into the periodontal ligament. The circuit continued through the patient’s mucosa and eventually completed the loop by running into the lip clip that was connected to the device through a return wire.

•Many different types of ERCLMDs.

•Mean distance between electronically located canal terminus and minor diameter was 1.03 mm for Endo analyzer and 0.19 mm for Root ZX. Ability  of the device to locate the apical constriction was 34.4% and 90.7% of cases respectively. (Welk et al 2003)

Pommer et al (2002) evaluated the effect of pulp vitality on accuracy of AFA Apex Finderand reported that vital cases had more accuracy than necrotic pulps.