Working Length Determination in Root Canal Treatment Part 2

Tear drop silicone – rubber stops have an added advantage because they do not have to be removed form the instrument during sterilization at 4500 F and tear drop tip can be positioned to indicate instrumental curvature
Rubber stops instruments have certain disadvantages like movement of up (or) down the shaft, leading to short (or) past the apical constriction and time consuming.

1) Grossman’s Method
2) Ingles Method:
Apical foramen
Apical constriction

Working length is determined only till the apical constriction and obturation is done till apical constriction

3) Xero-radiography – edge enhancement
Xero-radiography uses a uniformly charged selenium alloy photo receptor plate held in a light proof cassette.
Quick development (30 sec.)
Does not require wet chemical processing or dark room.

Good edge contrast so tissue appears sharper.

1/3rd the usual exposure time .
Xero-radiography uses a uniformly charged selenium alloy photo receptor plate held in a light proof cassette.
When exposed to x-rays ,the charge on the receptor is dissipated according to tissue density and a latent electrostatic image is formed.The latent image is transformed into a visible image by the deposition of specially pigmented particles attracted to the photo receptor plate.This visible image is then transferred into a bare sheet to produce a film of archival quality which can be viewed with reflected or trans illuminated light.
RVG system was developed by Dr. Francis Mouyen.
It has three components:
The radio component consists of a high resolution sensor
The ‘RADIO’ part consists of a conventional x-ray generator connected to a highly precise microprocessor timer for very short exposure times and an anatomically adopted sensor with rounded edges and angles. The sensor has a sensitive area of 17 X 26mm2 consisting of an exchangeable scintillation screen, a fiber optic, and a miniature charged coupled device imaging system.

The Visio portion consists of a video monitor and display processing unit.
The unit stores the incoming signals during exposure and then converts them point by point into one of 256 discrete grey levels. In real time the RVG is visualized four times larger than when compared to normal radiograph. Image can be stored point by point. In the zoom mode only apical portion can be seen.

Third component is the ‘Graphy.’ a high-resolution video printer that instantly provides a hard copy of the screen image
The unit consists of a digital mass storage unit that can be connected to various video print out (or) direct photographs of the screen may be made to provide an opportunity to access the radiographic information further.

RVG – Radio visiography
Radiographic images are obtained immediately
Developing time and film processing is eliminated
Radiation exposure is reduced from 50% to 90% compared to conventional film-based radiography.
High cost
Reduction in image quality when compared to conventional X-ray
Electronic method: Apex locator works on this method
All apex locator’s function by using the human body to complete an electrical circuit one side of the apex locator’s circuitry is connected to an endodontic instrument. The other side is connected to the patient’s body; either by a contact to the patient’s lip (or) by an electrode in the patients hand. The electrical circuit is complete when the endodontic instrument is advanced apically inside the root canal touches the PDL.the display on the apex locator indicates that the apical area has been reached.
WL is determined by comparing electrical resistance of periodontal membrane with that of the gingiva surrounding the tooth and both should be similar
Invented by Sunada in 1947.
It is an electronic device, to which an endodontic inst is attached and placed in a dry canal and slowly advanced till it contacts the periodontal ligament (apex) and at that point electrical resistance for both gingiva and P. Ligament shows similar reading
Three methods are used to signal the location of apical foramen;
a) the needle indicator at zero
b) the cessation of an audible tone
c) illumination of the apex indicator
Examples Neosono-M,Neosono-D,Formatron

1st Generation apex locators, also known as RESISTANCE apex locators.
Neosono ,Dentometer
Principles: measures opposition to the flow of direct current (or) resistance.

2nd second generation apex locators, also known as IMPEDANCE apex locators. THE ENDO ANALYZER , FORMATRON

Principle: Measures opposition to the flow of alternating current (or) impedance.

The 3rd generation apex locators are similar to 2nd generation except that they use multiple frequencies to determine the distance from the end of the canal. . ENDEX: (or) APIT , ROOT ZX

A fourth generation device and the unit use two separate frequencies 400 HZ and 8 KHZ similar to the 3rd generation units
The BINGO 1020 / RAY – PEX 4.

The Tri Auto ZX is primarily a cordless automatic, endodontic handpiece with a built in Root ZX apex locator

Only method that can measure length up to apical foramen, not to radiographic apex..
Easy and fast
Reduction of X-ray exposures
Artificial perforation can be recognized


Requires special device
Accuracy is influenced by electrical condition of canal
Difficult in teeth with wide open apex.
Inconsistent results in cases of vital teeth (except newly developed devices).
False when canal is wet ,in contact with metal ,in perforations,pulp in not completely removed
Audiometric method eg-Sono explorer
Is a variation of electronic method, uses low frequency oscillation sound to indicate the apical foramen.
Invented by Inoue in 1985.
In this method first the instrument is placed in the gingival sulcus and current is induced till the sound is produced, and then repeated by placing it in the root canal until the same sound is heard and thus W.L is measured.