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Working length

The document discusses methods for determining the working length in root canal treatment. It defines working length as the distance from a coronal reference point to the point where canal preparation and obturation should terminate. The key methods discussed are the radiographic method, using an electronic apex locator, and non-radiographic methods. Ingle's radiographic technique is described as the recommended method, which uses a preoperative radiograph and subtracts 1mm from the estimated working length to the radiographic apex. Terminating instrumentation between 0.5-1mm from the radiographic apex is advocated.

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WORKING LENGTH By Dr Ambalika Raj, 1st year MDS
CONTENTS • INTRODUCTION • DEFINITION • HISTORICAL PERSPECTIVE • ANATOMICAL CONSIDERATIONS • METHODS • CONCLUSION
INTRODUCTION
There are three distinct phases in the preparation of the root canal: 1) NEGOTIATION of the root canal and determination of the instruments’ working length 2) MAINTENANCE OF THE PATENCY of the apical foramen 3) ENLARGEMENT OF THE BODY of the canal. Files are used for the first two phases, reamers for the third. These instruments must be new, sterile, and re-sterilized whenever the need arises.
Furthermore, they must be precurved and equipped with rubber stops. One of the most important steps in canal preparation is the calculation of working length. The significances of this procedure are the following: 1. The calculation determines how far into the canal the instruments are placed and worked and thus how deeply into the tooth the tissues, debris, metabolites, end products, and other unwanted items are removed from the canal. 2. It will limit the depth to which the canal filling may be placed. 3. It will affect the degree of pain and discomfort that the patient will feel following the appointment. 4. If calculated within correct limits, it will play an important role in determining the success of the treatment and, conversely, if calculated incorrectly may doom the treatment to failure.
DEFINITION - The term ‘‘WL’’ is defined in the Glossary of Endodontic Terms as ‘‘the distance from a coronal reference point to the point at which canal preparation and obturation should terminate.’’
HISTORICAL PERSPECTIVE
In the early days of endodontic treatment, at the end of the nineteenth century, radiographs had not yet been applied to dentistry, and working length was usually calculated to the site where the patient experienced feeling for an instrument placed into the canal. Obviously this led to a multiplicity of errors. If vital tissue were left in the canal unextirpated, the resulting calculation would be too short. If a periapical lesion were present, the calculation could be much too long. Teeth with more than one canal in a root could also give inaccurate information.
With the advent of application of x-rays to dentistry by Kells in 1899, teeth treated without the benefit of radiographs, but evaluated by dental films, indicated these miscalculations. In this early portion of the 1900s, the popular opinion was that the dental pulp extended through the tooth, past the apical foramen into the periapical tissue, and that the narrowest diameter of the apical portion of the root canal was precisely at the site where the canal exits the tooth at the extreme APEX. In the 1920s,Grove concluded that pulp tissue could not extend beyond the CDJ because the cell unique to the dental pulp, the odontoblast, was not found past the CDJ. Hatton, and Grove, again, advised that preparation beyond the natural constriction of the CDJ would result in injury to the periapical tissues.
Kuttler, an endodontist from Mexico City,decided that filing to the radiographic apex was an unwise clinical procedure, contributing to postoperative pain and lowering the production of successful cases and undertook research on the anatomy of the apex. Other studies of the root tip, including histologic studies involving the soft and hard tissues of the apex, were reported and lent tremendous support to Kuttler’s views. Kutller's study is one of the most important papers that set proper standards for sophisticated, successful endodontic treatment, despite some minor errors.
Kuttler’s Study The apical foramen does not normally exit at the anatomic apex. It deviates by 0.5–3 mm. This variation is more marked due to continuous deposition of cementum in older patients. The distance of the minor diameter of the foramen from the cemental surface is at an average of 0.5 mm in young teeth and 0.75 mm in mature teeth.
Anatomical Considerations
Anatomic Apex: It is defined as the tip or the end of the root determined morphologically or in other words, refers to the vertex of the root and is also called geometric apex. Radiographic Apex: It is defined as the tip or the end of the root determined radiographically. Apical Foramen (Major Diameter): It is the main apical opening of the root canal. It is frequently eccentrically located away from the anatomic or radiographic apex and not necessarily coincide with the anatomic apex, depending on the apical curvature of the canal inside the root. Apical Constriction (Minor Diameter): It is the apical portion of the root canal having the narrowest diameter. Cementodentinal Junction: It is the region where the dentin and cementum are united. It is a histologic landmark.
Theoretically, the canal preparation should extend apically to the cementodentinal junction. This junction is located at or near the greatest constriction (minor diameter) of the apical foramen. The cementodentinal junction does not always coincide with apical constriction and may be located 0.5–3 mm short of the anatomic apex. Thus, it is clinically recommended to terminate instrumentation and obturation within 0.5–1.0 mm short of the radiographic apex.
USE OF REFERENCE POINTS In anterior teeth the other reference point is usually the incisal edge, but brokendown teeth may be measured from adjacent teeth or from some projecting portion of the remaining tooth structure. In bicanaled bicuspids the buccal canal is generally measured to the buccal cusp tip, but the palatal canal may use either cusp tip as reference. There may be a variance of at least 1 mm in length, depending on which reference point is used in measuring. Similarly, buccal canals of maxillary molars may be measured from either buccal cusp, mesial canals of mandibular molars from either mesial cusp, and so forth.
Schilder 70 states that canal preparation and obturation must be performed to the “radiographic terminus of the canal”, meaning the point at which the canal radiographically encounters the outline of the root. This derives from the following consideratons - 1.Clinically, it is easily identifiable by the dentist, by simply examining a properly-performed intraoperative radiograph 2. In 50% of cases , the canal ends at the anatomic or geometric apex or vertex of the root, and is thus identifiable radiographically. In these cases, using the radiographic terminus of the canal therefore entails neither overinstrumentation nor overfilling 3. If the emergence from the canal is not at the geometric apex of the root, but in a lateral position, it will always be identifiable radiographically if situated mesially or distally, as often happens.(about 40%)
• 4 If, the foramen is displaced buccally or lingually, it obviously will not be radiographically identifiable. In these cases, instrumentation at the radiographic terminus of the canal will lead to overinstrumentation , since there is a certain distance – which cannot be radiographically evaluated – between the vertex of the root and the apical foramen. This distance, measured by Dummer is 0.38mm
Advantages of filing upto radiographic apex In endodontic treatment, all materials, tissues, and debris from the canal must be removed. Many of the clinicians who believe this are not satisfied unless some excess material is pushed through the apical foramen, to indicate that the apical portion of the canal has been filled and thus has been sufficiently cleaned. They know that they are filing a bit too long, but they are willing to make this accommodation for the greater good of completely cleaning the canal. Another advantage of filing to the radiographic apex is that a small error in length calculation will not lead to an undesirably short filling with an apical segment of unprepared canal.
Disadvantages - Studies on success and failure, including those by Strindberg, Seltzer et al., and many others, have reported on the decrease in success when filling materials are passed into the periapical tissues, as is commonly seen in this method. Reports on postoperative pain also indicate an increase when canals are filed and filled to the radiographic apex as compared to within the body of the canal. In addition, the physical studies have indicated that when the canal exits eccentrically short of the root(very common in molar teeth, much less common in maxillary anterior teeth), as described by Levy and Glatt as well as others, preparation to the radiographic apex leads to an undesirable shape—a teardrop—which is very difficult to seal by any technique .
Methodological considerations Before determining a definitive WL, the coronal access to the pulp chamber must provide a straight-line pathway into the canal orifice. Modifications in access preparation may be required to permit the instrument to penetrate, unimpeded, into the apical constriction. The loss of WL during cleaning and shaping can be a frustrating procedural error. Once the apical preparation is over, it is useful to reassess the WL since the WL may shorten as a curved canal is straightened. WL may also be lost owing to ledge formation or blockage of the canal.
WL determination should be to the nearest 0.5 millimeter, which is the maximum resolution of the naked eye in working distance. The measurement should be made from a secure reference point on the crown in close proximity to the straight-line path of the instrument.
To achieve the highest degree of accuracy in WL determination, a combination of several methods should be used. The most common methods are radiographic methods, digital tactile sense, patients’ response to a file introduced into the canal, or a point to which a paper point can be placed and removed dry.
Requirements of an ideal clinical method for determining working length 1.Rapid location of the apical constriction in all pulpal conditions and all canal contents; 2.Easy measurement, even when the relationship between the apical constriction and the radiographic apex is unusual; 3.Rapid periodic monitoring and confirmation; 4.Patient and clinician comfort; 5.Minimal radiation to the patient; 6.Ease of use in special patients such as those with severe gag reflex, reduced mouth opening, pregnancy; and 7.Cost effectiveness.
The most appropriate technique for assessment of working length is by using a combination of electronic apex locator along with Ingle’s radiographic technique.
Methods of Determining The Working Length
Mainly 3 methods ( According to Grossman ) Radiographic method Electronic apex locators Nonradiographic methods ( not recommended )
According to Weine - 1. RADIOGRAPHIC APEX—FILING TO THE TIP OF THE ROOT AS SEEN ON THE X-RAY FILM. 2. A SPECIFIC DISTANCE FROM THE RADIOGRAPHIC APEX —ACCEPTING THAT FILING TO THE RADIOGRAPHIC APEX IS TOO LONG, A DISTANCE SHORT OF THAT, MOST OFTEN 1.0 MM, IS SELECTED. 3. ACCORDING TO THE STUDIES OF KUTTLER— EXAMINATION OF THE PREOPERATIVE RADIOGRAPH TO LOCATE THE MAJOR OR MINOR DIAMETER. 4. USE OF AN ELECTRONIC APEX LOCATOR—BY USING THE DIFFERENCE IN ELECTRICAL CHARGE BETWEEN THE TISSUES OF THE PERIODONTAL LIGAMENT AND THE SITES WITHIN THE CANAL.
1. Radiographic Methods 1. Ingle’s technique (Recommended) 2. Others – Best’s method – Bregman’s method – Bramante’s technique – Grossman’s method – Weine’s method 3. Kuttler’s method 4. X-ray grid method 5. Xeroradiography 6. Direct digital radiography
The following items are essential to perform radiographic WL estimation: 1. Good, undistorted, preoperative radiographs showing the total length and all roots of the involved tooth. 2. Adequate coronal access to all canals. 3. An endodontic millimeter ruler. 4. Working knowledge of the average length of all of the teeth. 5. A definite, repeatable plane of reference to an anatomical landmark on the tooth, a fact that should be noted on the patient’s record.
To secure reproducible reference points, cusps severely weakened by caries or restoration may be reduced to a flattened surface, supported by dentin. Failure to do so may result in cusps or weak enamel walls being fractured between appointments. Thus the original site of reference is lost – OVERINSTRUMENTATION and OVERFILLING.
Grossman's method The exact working length for each canal is determined by adjusting the length of insertion so the tip of the instrument ends 0.5mm from the root apex This length is later verified by placing instruments to the estimated working length in the root canal and taking an instrumentation radiograph. The original diagnostic radiograph is used to estimate the working length of the tooth from occlusal to root apex.
By measuring the length of radiographic images of both the tooth and the measuring instruments as well as the actual length of the instrument, the clinician can determine the actual length of the tooth by a mathematical formula. Actual length of tooth = ALI x RLT RLI ALT -Actual length of tooth ALI -Actual length of instrument RLT -Radiographic length of tooth RLI -Radiographic length of instrument
Ingle's radiographic technique Clinical Prerequisites - 1.Knowledge of average length of teeth 2.Instrument precurving 3.Stable occlusal reference point: – Anterior teeth → Incisal edges – Posterior teeth → Cusp tips 4.The reference point must be a definite and reliable point or surface to ensure exactness in all subsequent measurements. 5.Silicone stopper on the file is set to these reference points and the extent of the file from the bottom of the stopper to the tip of the instrument is used to determine the estimated working length.
Clinical Technique for Ingle's A working length instrumentation radiograph is taken to compare the exact position of the instrument in the root canal with the measured depth of insertion Precoronal enlargement of canal is done with Gates Glidden drill etc. Now the original diagnostic radiograph is used and the working length of tooth is estimated from occlusal surface to radiographic apex , and 1 mm subtracted from the WL obtained . Then it is removed from the canal and examined for any curvatures that were not apparent in radiograph. No. 6 , 8 or 10 K file is used and inserted into the root canal through the access cavity with a slight reaming motion to bypass any obstruction till it has reached the estimated working length.
SLOB technique may be used for better visualization of root canal and its terminus esp. When two root canals are present in a single root e.g. maxillary 1st premolar and they overlap each other. If apical root resorption is seen, the working length is reduced to 2 mm short of the radiographic apex .( WEINE ) If periapical bone resorption is evident in a radiograph, the working length should be reduced 1.5 mm short of the radiographic apex as the apical constriction would have been destroyed by the resorption. The working length should be established 0.5–1.0 mm shorter than the radiographic canal length because the actual length of the tooth is less than the radiographic image and the apical foramen is approximately 0.3 mm short of the actual root tip. The exact working length for each canal is determined by adjusting the length of insertion, so the tip of the instrument ends 0.5–1.0 mm from the radiographic root apex.
The buccal object rule - The rule is also termed as SLOB rule (same lingual opposite buccal). Stated more simply, Ingle’s rule is MBD: always shot from Mesial and the Buccal root will move to Distal. - As the X-ray tube head is moved from posterior to anterior, objects imaged on the film which are on the lingual aspects (palatal roots or mesial lingual roots or distal lingual roots) will be positioned mesially in the radiograph (the same position as the head tube). - Objects located in the buccal aspect will be shifted distally. - The palatal root will always shift on the same direction as the tube head. Therefore, the clinician can always determine the direction that the radiograph was taken by looking at the palatal roots of molars. Roots that are superimposed on a standard radiograph can be visualized when a mesial or distal view is taken.
- In general, the degree of horizontal angulation necessary to achieve a clear image will depend on the separation of the roots; the more parallel the roots (closer), the greater the alteration should be, while roots with a considerable divergence will require only a modest degree of horizontal angulation. - When the horizontal angulation is varied by 20 degrees to mesial, the zygomatic process is “moved” to distal of the first molar, and the distobuccal root is cleared of the palatal root.
The triangular scanning technique - This technique can be used to detect the exact position of root curvatures as well as iatrogenic errors such as ledges, creation of false canals during post space preparation and lateral perforations. - The technique involves the exposure of three films, one using the standard angulation and the others using mesial and distal angulations. -To interpret the data available from the three films correctly, it is necessary for each view to draw a diagram with two concentric circles where the outer circle represents the root contour and the inner circle represents the outline of the canal. - Each cross-sectional representation of the root is then divided into quadrants by two lines, one vertical dividing the root into mesial and distal halves, the other horizontal dividing the root into buccal and lingual halves. - A mesial angulation will superimpose the mesiobuccal (MB) and distolingual (DL) quadrants, while a distal angulation will superimpose the distobuccal (DB) and mesiolingual (ML) quadrants. -Data obtained from the three radiographs are transferred to the diagrams to produce a simple representation of the complex threedimensional architecture of the tooth
Kuttler's method According to Kuttler the narrowest diameter is definitely not at the site of exit of the canal from the tooth but usually occurs within the dentin, just prior to the initial layers of cementum. He referred to this position as the ‘minor diameter’ of the canal (apical constriction).
Technique for calculation of working length: Before starting endodontic treatment the dentist must identify the probable i.e. - The canal configuration present - The estimated length of the root - The site of exiting of the canal - The estimated width of the canal This is done by analyzing the pre-op radiograph available using both straight – for site (s) of exiting, root (s) length, canal (s) width & angled views – for canal configuration (s) and sites of exiting
The calculations dealing with the site of exiting of the canal (s) length & widths will help to identify the major and more often the minor diameter. The calculations dealing with the widths & length is valuable in making the calculation for working length. The basis for this method’s value is the measurement provided by Kuttler relating to the distance between the major diameter (site of exiting of the canal) and the minor diameter (i.e. the CDJ). In younger patients the distance between these two positions is approx 0.5 mm and in older patients due to increased build-up of cementum the distance is approx. 0.67 mm. Using the radiograph the dentist must locate the major diameter and then interpolate the position of the minor diameter or locate the minor diameter by seeing the funneled shape into the tooth from the site of the exiting.
Direct digital radiography (DDR) - Reliable method of WL determination. - This system consists of a programmed computerized receiver that processes signals from an intra-oral sensor that is stimulated by x-rays from a standard dental machine. - The computer-monitorised image then appears immediately upon the video monitor much like that in a large regular radiograph. - This image may then be varied in size (zoom in for enlargement), in contrast (gradations of grey) and finally it can be printed out. - The image can also be stored in computer for alter recall. - Two of the earlier models of the DDR system are the RVG (Radio - Visiography) developed by Dr. Francis Mouyan, a French dentist and VIXA (Video imaging X-ray application).
2 . Electronic apex locators These instruments are based on the principle that the electrical resistance between one electrode in the root canal and another applied to the oral mucosa registered consistent values. The tissue resistance of the periodontal membrane that surrounds the tooth is constant and is therefore the same at the gingival sulcus and at the apical foramen.
By measuring the depth of insertion of the endodontic file, one may determine the exact working length of the root canal When the endodontic file touches the soft tissues of the periodontal membrane, the electrical-resistance gauges for both oral mucosa and periodontal ligament would have similar readings. The attached file is slowly inserted into the root canal up to the estimated working length. One end is termed as a “lip hook” that is kept in contact with the oral mucosa of the patient while the other end is termed as “file holder” that is a probe which is attached to an endodontic instrument (K file or rotary file).
Classification of Electronic Apex Locators 1.Resistance-based electronic apex locator - 1st generation apex locator - based on resistance principle - work best in dry canals - inaccurate in presence of blood , pus, pulpal tissue - e.g. Root canal meter, endodontic meter and endodontic meter S II.
2.Low-frequency apex locator - Impedance based apex locator - indicate the apex when 2 impedance values approach each other. -had to be calibrated with periodontal sulcus prior to use. - technique sensitive - e.g. Sono explorer apex locator
3.High-frequency apex locator: - based on the principle that a high frequency (400 kHz) wave, as a measuring current, produces a more stable electrode. -perform even in the presence of electrolytes due to the presence of a special coating on the file. e.g. Endocater
4.Voltage gradient apex locator: - monopolar and bipolar electrodes were introduced which were coated with lacquer with separate electrodes applying the current and recording the voltage gradient. - not effective in constricted canals.
5.Dual-frequency apex locator: - determine the canal terminus as the difference between two impedance values at two different frequencies. - superior to other apex locators in the presence of fluids and electrolytes. -e.g. Endex apex locator
If the endodontic instrument overshoots the foramen, the needle passes to the yellow zone of the scale, while the acoustic signal remains steady When the apical foramen is reached, the sound becomes steady, and the needle is positioned on the red marking designated “APEX” . When the endodontic file is advanced toward the apical third, the needle moves into the green zone again, and the acoustic signal is once again emitted intermittently. When the “Reset” button is pressed, the instrument is calibrated, the indicator needle returns to the starting point, and the acoustic signal ceases. The clip is then connected to the file, and the indicator needle moves toward the green zone (Fig. 15.21 A), while an intermittent acoustic signal is emitted. Once the Apit/Endex is turned on and contact between the fifile clip and labial clip is established, the latter is attached to the patient’s lip and the file is introduced into the middle third of the canal.
6.Multiple-frequency apex locator: - uses two wavelengths: one high (8 kHz) and one low (400 Hz) frequency. - assesses the apical terminus by the simultaneous measurements of the impedance of two different frequencies that are used to calculate the quotient of the impedances. - e.g. Propex II
A newer advance is the integration of the apex locator with the battery-powered endodontic slowspeed handpiece.
Advantages of apex locator 1. The major advantage of the apex locator is that it supplies objective information with a high degree of accuracy. 2. Where radiographs are difficult to read accurately for calculation of working length. Such a situation often exists in maxillary molars, where the radiopaque structures of the malar process or floor of the maxillary sinus may superimpose the apices of the teeth, making radiographic calculation difficult. Mandibular tori may do the same for mandibular bicuspids and molars. 3.Patients who gag easily with radiographs also profit from preliminary use. 4.Locators also may be useful in verifying perforations of the root.
Disadvantages 1.The accuracy is somewhere in the low 90 percentiles. 2.Without a confirming radiograph, filing done to the incorrect length could cause an increase in postoperative pain and a decrease in success. 3.These machines to give incorrect or inaccurate readings because the battery may be low (check battery and replace frequently), too much tissue may remain in the canal (broach canal and use a Hedstrom file to verify that gross tissue is gone), the canal may be too wet (dry mildly with paper points) or too dry (irrigate mildly with peroxide or sterile water), the file may be too narrow (use a file that is slightly loose in the canal, not a size 10 each time; estimate first to chose the proper width), a blockage may be present (try to bypass CAREFULLY!), the lip clip may fall off (check that it is in place).
Current apex locators are sufficiently precise to allow WL determination, thus reducing the frequency of overinstrumentation when only radiographs are used. Even in cases of apical resorption and wide-open apices after root- end resection, these apex locators are shown to be accurate. Therefore, it seems warranted to focus on the electronically determined WL and to use the radiograph merely to avoid gross errors in case the apex locator does not appear to work correctly.
Apex locators versus radiographs It is a mistake to think that apex locators will eliminate radiographs during endodontic treatment. Excellent preoperative films must always be taken prior to any active treatment on the tooth. Apex locators cannot help the dentist determine canal width, canal curvature, or number of canals, and they can only partially help with sites of canal Division. These must be determined by radiograph. Fouad et al. stated that apex locators were not meant to replace radiographs, but to add to the information obtained by radiographs.
3. Non radiographic methods 1.Apex Finder 2. Audiometric Method 3. Tactile Method 4. Paper Point Evaluation Method
Paper point method In a root canal with an immature (i.e., wide open) apex, a relatively reliable means of determining WL is by gently passing the blunt end of a paper point into the canal after profound anesthesia has been achieved. The moisture or blood on the portion of the paper point that passes beyond the apex may be an estimation of WL or the junction between the root apex and the bone. In cases in which the apical constriction has been lost owing to resorption or perforation, and in which there is no free bleeding or suppuration into the canal, the moisture or blood on the paper point is an estimate of the amount the preparation overextended. This paper point measurement method is also a supplementary one.
Recent advances: 1. Tomography: - Is a radiographic technique that “slices” teeth in thin sections. - Computers subsequently reassemble the sections to generate a three-dimensional image. - Dental anatomy including bucco-lingual curvatures shapes of the root canal spaces and location of the apical foramen (which is important in determining or calculating the working length) can be visualized in the third-dimension. - Additional advantage in the elimination of angled radiographs; all angled views are captured in just one exposure.
2.Videography and Intra-Oral Cameras Intra-oral videography is a non-ionizing diagnostic imaging technique. Developers are using miniature colour CCD (charge coupled device) chips. With fiber optic probes to assemble video cameras small enough to transverse periodontal defects and identify vertical root fractures. These devices are useful in endodontics as they can display canal morphology as well aid in locating canal orifices. Perforations can be visualized by inserting the fiber optic probe down the suspected canal. These devices are connected to a computer that provides enhanced images for teaching and patient education.
3.DDR- Fourth generation DDR One of the more recent additions to Trophy’s fourth generation RVG systems is the capability of on screen point-to-point measurements using multiple additive points. This capability potentially allows for fast accurate working length estimation in roots demonstrating severe apical curvatures. The RVG on screen measurement utility allows for rapid additive multiple point measurement of digital images, automatically tallying the measurement points on screen to a tenth of a millimeter.
CONCLUSION It can be seen quite clearly that the procedure for calculation of working length should be performed with skill, using techniques that have been proven to give valuable and accurate results and by methods that are practical and efficacious. If this step is performed perfunctorily, without thought and skill, using techniques of dubious accuracy, many teeth so treated will be failures.

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Working length

  • 1.
  • 2.
    CONTENTS • INTRODUCTION • DEFINITION •HISTORICAL PERSPECTIVE • ANATOMICAL CONSIDERATIONS • METHODS • CONCLUSION
  • 3.
  • 4.
    There are threedistinct phases in the preparation of the root canal: 1) NEGOTIATION of the root canal and determination of the instruments’ working length 2) MAINTENANCE OF THE PATENCY of the apical foramen 3) ENLARGEMENT OF THE BODY of the canal. Files are used for the first two phases, reamers for the third. These instruments must be new, sterile, and re-sterilized whenever the need arises.
  • 5.
    Furthermore, they mustbe precurved and equipped with rubber stops. One of the most important steps in canal preparation is the calculation of working length. The significances of this procedure are the following: 1. The calculation determines how far into the canal the instruments are placed and worked and thus how deeply into the tooth the tissues, debris, metabolites, end products, and other unwanted items are removed from the canal. 2. It will limit the depth to which the canal filling may be placed. 3. It will affect the degree of pain and discomfort that the patient will feel following the appointment. 4. If calculated within correct limits, it will play an important role in determining the success of the treatment and, conversely, if calculated incorrectly may doom the treatment to failure.
  • 6.
    DEFINITION - The term‘‘WL’’ is defined in the Glossary of Endodontic Terms as ‘‘the distance from a coronal reference point to the point at which canal preparation and obturation should terminate.’’
  • 7.
  • 8.
    In the earlydays of endodontic treatment, at the end of the nineteenth century, radiographs had not yet been applied to dentistry, and working length was usually calculated to the site where the patient experienced feeling for an instrument placed into the canal. Obviously this led to a multiplicity of errors. If vital tissue were left in the canal unextirpated, the resulting calculation would be too short. If a periapical lesion were present, the calculation could be much too long. Teeth with more than one canal in a root could also give inaccurate information.
  • 9.
    With the adventof application of x-rays to dentistry by Kells in 1899, teeth treated without the benefit of radiographs, but evaluated by dental films, indicated these miscalculations. In this early portion of the 1900s, the popular opinion was that the dental pulp extended through the tooth, past the apical foramen into the periapical tissue, and that the narrowest diameter of the apical portion of the root canal was precisely at the site where the canal exits the tooth at the extreme APEX. In the 1920s,Grove concluded that pulp tissue could not extend beyond the CDJ because the cell unique to the dental pulp, the odontoblast, was not found past the CDJ. Hatton, and Grove, again, advised that preparation beyond the natural constriction of the CDJ would result in injury to the periapical tissues.
  • 10.
    Kuttler, an endodontistfrom Mexico City,decided that filing to the radiographic apex was an unwise clinical procedure, contributing to postoperative pain and lowering the production of successful cases and undertook research on the anatomy of the apex. Other studies of the root tip, including histologic studies involving the soft and hard tissues of the apex, were reported and lent tremendous support to Kuttler’s views. Kutller's study is one of the most important papers that set proper standards for sophisticated, successful endodontic treatment, despite some minor errors.
  • 11.
    Kuttler’s Study The apicalforamen does not normally exit at the anatomic apex. It deviates by 0.5–3 mm. This variation is more marked due to continuous deposition of cementum in older patients. The distance of the minor diameter of the foramen from the cemental surface is at an average of 0.5 mm in young teeth and 0.75 mm in mature teeth.
  • 12.
  • 13.
    Anatomic Apex: Itis defined as the tip or the end of the root determined morphologically or in other words, refers to the vertex of the root and is also called geometric apex. Radiographic Apex: It is defined as the tip or the end of the root determined radiographically. Apical Foramen (Major Diameter): It is the main apical opening of the root canal. It is frequently eccentrically located away from the anatomic or radiographic apex and not necessarily coincide with the anatomic apex, depending on the apical curvature of the canal inside the root. Apical Constriction (Minor Diameter): It is the apical portion of the root canal having the narrowest diameter. Cementodentinal Junction: It is the region where the dentin and cementum are united. It is a histologic landmark.
  • 14.
    Theoretically, the canalpreparation should extend apically to the cementodentinal junction. This junction is located at or near the greatest constriction (minor diameter) of the apical foramen. The cementodentinal junction does not always coincide with apical constriction and may be located 0.5–3 mm short of the anatomic apex. Thus, it is clinically recommended to terminate instrumentation and obturation within 0.5–1.0 mm short of the radiographic apex.
  • 15.
    USE OF REFERENCEPOINTS In anterior teeth the other reference point is usually the incisal edge, but brokendown teeth may be measured from adjacent teeth or from some projecting portion of the remaining tooth structure. In bicanaled bicuspids the buccal canal is generally measured to the buccal cusp tip, but the palatal canal may use either cusp tip as reference. There may be a variance of at least 1 mm in length, depending on which reference point is used in measuring. Similarly, buccal canals of maxillary molars may be measured from either buccal cusp, mesial canals of mandibular molars from either mesial cusp, and so forth.
  • 16.
    Schilder 70 statesthat canal preparation and obturation must be performed to the “radiographic terminus of the canal”, meaning the point at which the canal radiographically encounters the outline of the root. This derives from the following consideratons - 1.Clinically, it is easily identifiable by the dentist, by simply examining a properly-performed intraoperative radiograph 2. In 50% of cases , the canal ends at the anatomic or geometric apex or vertex of the root, and is thus identifiable radiographically. In these cases, using the radiographic terminus of the canal therefore entails neither overinstrumentation nor overfilling 3. If the emergence from the canal is not at the geometric apex of the root, but in a lateral position, it will always be identifiable radiographically if situated mesially or distally, as often happens.(about 40%)
  • 17.
    • 4 If,the foramen is displaced buccally or lingually, it obviously will not be radiographically identifiable. In these cases, instrumentation at the radiographic terminus of the canal will lead to overinstrumentation , since there is a certain distance – which cannot be radiographically evaluated – between the vertex of the root and the apical foramen. This distance, measured by Dummer is 0.38mm
  • 18.
    Advantages of filingupto radiographic apex In endodontic treatment, all materials, tissues, and debris from the canal must be removed. Many of the clinicians who believe this are not satisfied unless some excess material is pushed through the apical foramen, to indicate that the apical portion of the canal has been filled and thus has been sufficiently cleaned. They know that they are filing a bit too long, but they are willing to make this accommodation for the greater good of completely cleaning the canal. Another advantage of filing to the radiographic apex is that a small error in length calculation will not lead to an undesirably short filling with an apical segment of unprepared canal.
  • 19.
    Disadvantages - Studies onsuccess and failure, including those by Strindberg, Seltzer et al., and many others, have reported on the decrease in success when filling materials are passed into the periapical tissues, as is commonly seen in this method. Reports on postoperative pain also indicate an increase when canals are filed and filled to the radiographic apex as compared to within the body of the canal. In addition, the physical studies have indicated that when the canal exits eccentrically short of the root(very common in molar teeth, much less common in maxillary anterior teeth), as described by Levy and Glatt as well as others, preparation to the radiographic apex leads to an undesirable shape—a teardrop—which is very difficult to seal by any technique .
  • 20.
    Methodological considerations Before determininga definitive WL, the coronal access to the pulp chamber must provide a straight-line pathway into the canal orifice. Modifications in access preparation may be required to permit the instrument to penetrate, unimpeded, into the apical constriction. The loss of WL during cleaning and shaping can be a frustrating procedural error. Once the apical preparation is over, it is useful to reassess the WL since the WL may shorten as a curved canal is straightened. WL may also be lost owing to ledge formation or blockage of the canal.
  • 21.
    WL determination shouldbe to the nearest 0.5 millimeter, which is the maximum resolution of the naked eye in working distance. The measurement should be made from a secure reference point on the crown in close proximity to the straight-line path of the instrument.
  • 22.
    To achieve thehighest degree of accuracy in WL determination, a combination of several methods should be used. The most common methods are radiographic methods, digital tactile sense, patients’ response to a file introduced into the canal, or a point to which a paper point can be placed and removed dry.
  • 23.
    Requirements of an idealclinical method for determining working length 1.Rapid location of the apical constriction in all pulpal conditions and all canal contents; 2.Easy measurement, even when the relationship between the apical constriction and the radiographic apex is unusual; 3.Rapid periodic monitoring and confirmation; 4.Patient and clinician comfort; 5.Minimal radiation to the patient; 6.Ease of use in special patients such as those with severe gag reflex, reduced mouth opening, pregnancy; and 7.Cost effectiveness.
  • 24.
    The most appropriatetechnique for assessment of working length is by using a combination of electronic apex locator along with Ingle’s radiographic technique.
  • 25.
  • 26.
    Mainly 3 methods( According to Grossman ) Radiographic method Electronic apex locators Nonradiographic methods ( not recommended )
  • 27.
    According to Weine- 1. RADIOGRAPHIC APEX—FILING TO THE TIP OF THE ROOT AS SEEN ON THE X-RAY FILM. 2. A SPECIFIC DISTANCE FROM THE RADIOGRAPHIC APEX —ACCEPTING THAT FILING TO THE RADIOGRAPHIC APEX IS TOO LONG, A DISTANCE SHORT OF THAT, MOST OFTEN 1.0 MM, IS SELECTED. 3. ACCORDING TO THE STUDIES OF KUTTLER— EXAMINATION OF THE PREOPERATIVE RADIOGRAPH TO LOCATE THE MAJOR OR MINOR DIAMETER. 4. USE OF AN ELECTRONIC APEX LOCATOR—BY USING THE DIFFERENCE IN ELECTRICAL CHARGE BETWEEN THE TISSUES OF THE PERIODONTAL LIGAMENT AND THE SITES WITHIN THE CANAL.
  • 28.
    1. Radiographic Methods1. Ingle’s technique (Recommended) 2. Others – Best’s method – Bregman’s method – Bramante’s technique – Grossman’s method – Weine’s method 3. Kuttler’s method 4. X-ray grid method 5. Xeroradiography 6. Direct digital radiography
  • 29.
    The following itemsare essential to perform radiographic WL estimation: 1. Good, undistorted, preoperative radiographs showing the total length and all roots of the involved tooth. 2. Adequate coronal access to all canals. 3. An endodontic millimeter ruler. 4. Working knowledge of the average length of all of the teeth. 5. A definite, repeatable plane of reference to an anatomical landmark on the tooth, a fact that should be noted on the patient’s record.
  • 30.
    To secure reproduciblereference points, cusps severely weakened by caries or restoration may be reduced to a flattened surface, supported by dentin. Failure to do so may result in cusps or weak enamel walls being fractured between appointments. Thus the original site of reference is lost – OVERINSTRUMENTATION and OVERFILLING.
  • 32.
    Grossman's method The exactworking length for each canal is determined by adjusting the length of insertion so the tip of the instrument ends 0.5mm from the root apex This length is later verified by placing instruments to the estimated working length in the root canal and taking an instrumentation radiograph. The original diagnostic radiograph is used to estimate the working length of the tooth from occlusal to root apex.
  • 33.
    By measuring thelength of radiographic images of both the tooth and the measuring instruments as well as the actual length of the instrument, the clinician can determine the actual length of the tooth by a mathematical formula. Actual length of tooth = ALI x RLT RLI ALT -Actual length of tooth ALI -Actual length of instrument RLT -Radiographic length of tooth RLI -Radiographic length of instrument
  • 34.
    Ingle's radiographic technique ClinicalPrerequisites - 1.Knowledge of average length of teeth 2.Instrument precurving 3.Stable occlusal reference point: – Anterior teeth → Incisal edges – Posterior teeth → Cusp tips 4.The reference point must be a definite and reliable point or surface to ensure exactness in all subsequent measurements. 5.Silicone stopper on the file is set to these reference points and the extent of the file from the bottom of the stopper to the tip of the instrument is used to determine the estimated working length.
  • 35.
    Clinical Technique forIngle's A working length instrumentation radiograph is taken to compare the exact position of the instrument in the root canal with the measured depth of insertion Precoronal enlargement of canal is done with Gates Glidden drill etc. Now the original diagnostic radiograph is used and the working length of tooth is estimated from occlusal surface to radiographic apex , and 1 mm subtracted from the WL obtained . Then it is removed from the canal and examined for any curvatures that were not apparent in radiograph. No. 6 , 8 or 10 K file is used and inserted into the root canal through the access cavity with a slight reaming motion to bypass any obstruction till it has reached the estimated working length.
  • 36.
    SLOB technique maybe used for better visualization of root canal and its terminus esp. When two root canals are present in a single root e.g. maxillary 1st premolar and they overlap each other. If apical root resorption is seen, the working length is reduced to 2 mm short of the radiographic apex .( WEINE ) If periapical bone resorption is evident in a radiograph, the working length should be reduced 1.5 mm short of the radiographic apex as the apical constriction would have been destroyed by the resorption. The working length should be established 0.5–1.0 mm shorter than the radiographic canal length because the actual length of the tooth is less than the radiographic image and the apical foramen is approximately 0.3 mm short of the actual root tip. The exact working length for each canal is determined by adjusting the length of insertion, so the tip of the instrument ends 0.5–1.0 mm from the radiographic root apex.
  • 37.
    The buccal objectrule - The rule is also termed as SLOB rule (same lingual opposite buccal). Stated more simply, Ingle’s rule is MBD: always shot from Mesial and the Buccal root will move to Distal. - As the X-ray tube head is moved from posterior to anterior, objects imaged on the film which are on the lingual aspects (palatal roots or mesial lingual roots or distal lingual roots) will be positioned mesially in the radiograph (the same position as the head tube). - Objects located in the buccal aspect will be shifted distally. - The palatal root will always shift on the same direction as the tube head. Therefore, the clinician can always determine the direction that the radiograph was taken by looking at the palatal roots of molars. Roots that are superimposed on a standard radiograph can be visualized when a mesial or distal view is taken.
  • 38.
    - In general,the degree of horizontal angulation necessary to achieve a clear image will depend on the separation of the roots; the more parallel the roots (closer), the greater the alteration should be, while roots with a considerable divergence will require only a modest degree of horizontal angulation. - When the horizontal angulation is varied by 20 degrees to mesial, the zygomatic process is “moved” to distal of the first molar, and the distobuccal root is cleared of the palatal root.
  • 41.
    The triangular scanningtechnique - This technique can be used to detect the exact position of root curvatures as well as iatrogenic errors such as ledges, creation of false canals during post space preparation and lateral perforations. - The technique involves the exposure of three films, one using the standard angulation and the others using mesial and distal angulations. -To interpret the data available from the three films correctly, it is necessary for each view to draw a diagram with two concentric circles where the outer circle represents the root contour and the inner circle represents the outline of the canal. - Each cross-sectional representation of the root is then divided into quadrants by two lines, one vertical dividing the root into mesial and distal halves, the other horizontal dividing the root into buccal and lingual halves. - A mesial angulation will superimpose the mesiobuccal (MB) and distolingual (DL) quadrants, while a distal angulation will superimpose the distobuccal (DB) and mesiolingual (ML) quadrants. -Data obtained from the three radiographs are transferred to the diagrams to produce a simple representation of the complex threedimensional architecture of the tooth
  • 42.
    Kuttler's method According toKuttler the narrowest diameter is definitely not at the site of exit of the canal from the tooth but usually occurs within the dentin, just prior to the initial layers of cementum. He referred to this position as the ‘minor diameter’ of the canal (apical constriction).
  • 43.
    Technique for calculationof working length: Before starting endodontic treatment the dentist must identify the probable i.e. - The canal configuration present - The estimated length of the root - The site of exiting of the canal - The estimated width of the canal This is done by analyzing the pre-op radiograph available using both straight – for site (s) of exiting, root (s) length, canal (s) width & angled views – for canal configuration (s) and sites of exiting
  • 44.
    The calculations dealingwith the site of exiting of the canal (s) length & widths will help to identify the major and more often the minor diameter. The calculations dealing with the widths & length is valuable in making the calculation for working length. The basis for this method’s value is the measurement provided by Kuttler relating to the distance between the major diameter (site of exiting of the canal) and the minor diameter (i.e. the CDJ). In younger patients the distance between these two positions is approx 0.5 mm and in older patients due to increased build-up of cementum the distance is approx. 0.67 mm. Using the radiograph the dentist must locate the major diameter and then interpolate the position of the minor diameter or locate the minor diameter by seeing the funneled shape into the tooth from the site of the exiting.
  • 45.
    Direct digital radiography(DDR) - Reliable method of WL determination. - This system consists of a programmed computerized receiver that processes signals from an intra-oral sensor that is stimulated by x-rays from a standard dental machine. - The computer-monitorised image then appears immediately upon the video monitor much like that in a large regular radiograph. - This image may then be varied in size (zoom in for enlargement), in contrast (gradations of grey) and finally it can be printed out. - The image can also be stored in computer for alter recall. - Two of the earlier models of the DDR system are the RVG (Radio - Visiography) developed by Dr. Francis Mouyan, a French dentist and VIXA (Video imaging X-ray application).
  • 46.
    2 . Electronicapex locators These instruments are based on the principle that the electrical resistance between one electrode in the root canal and another applied to the oral mucosa registered consistent values. The tissue resistance of the periodontal membrane that surrounds the tooth is constant and is therefore the same at the gingival sulcus and at the apical foramen.
  • 48.
    By measuring thedepth of insertion of the endodontic file, one may determine the exact working length of the root canal When the endodontic file touches the soft tissues of the periodontal membrane, the electrical-resistance gauges for both oral mucosa and periodontal ligament would have similar readings. The attached file is slowly inserted into the root canal up to the estimated working length. One end is termed as a “lip hook” that is kept in contact with the oral mucosa of the patient while the other end is termed as “file holder” that is a probe which is attached to an endodontic instrument (K file or rotary file).
  • 50.
    Classification of Electronic ApexLocators 1.Resistance-based electronic apex locator - 1st generation apex locator - based on resistance principle - work best in dry canals - inaccurate in presence of blood , pus, pulpal tissue - e.g. Root canal meter, endodontic meter and endodontic meter S II.
  • 51.
    2.Low-frequency apex locator -Impedance based apex locator - indicate the apex when 2 impedance values approach each other. -had to be calibrated with periodontal sulcus prior to use. - technique sensitive - e.g. Sono explorer apex locator
  • 52.
    3.High-frequency apex locator: -based on the principle that a high frequency (400 kHz) wave, as a measuring current, produces a more stable electrode. -perform even in the presence of electrolytes due to the presence of a special coating on the file. e.g. Endocater
  • 53.
    4.Voltage gradient apexlocator: - monopolar and bipolar electrodes were introduced which were coated with lacquer with separate electrodes applying the current and recording the voltage gradient. - not effective in constricted canals.
  • 54.
    5.Dual-frequency apex locator: -determine the canal terminus as the difference between two impedance values at two different frequencies. - superior to other apex locators in the presence of fluids and electrolytes. -e.g. Endex apex locator
  • 55.
    If the endodonticinstrument overshoots the foramen, the needle passes to the yellow zone of the scale, while the acoustic signal remains steady When the apical foramen is reached, the sound becomes steady, and the needle is positioned on the red marking designated “APEX” . When the endodontic file is advanced toward the apical third, the needle moves into the green zone again, and the acoustic signal is once again emitted intermittently. When the “Reset” button is pressed, the instrument is calibrated, the indicator needle returns to the starting point, and the acoustic signal ceases. The clip is then connected to the file, and the indicator needle moves toward the green zone (Fig. 15.21 A), while an intermittent acoustic signal is emitted. Once the Apit/Endex is turned on and contact between the fifile clip and labial clip is established, the latter is attached to the patient’s lip and the file is introduced into the middle third of the canal.
  • 56.
    6.Multiple-frequency apex locator: -uses two wavelengths: one high (8 kHz) and one low (400 Hz) frequency. - assesses the apical terminus by the simultaneous measurements of the impedance of two different frequencies that are used to calculate the quotient of the impedances. - e.g. Propex II
  • 58.
    A newer advanceis the integration of the apex locator with the battery-powered endodontic slowspeed handpiece.
  • 59.
    Advantages of apexlocator 1. The major advantage of the apex locator is that it supplies objective information with a high degree of accuracy. 2. Where radiographs are difficult to read accurately for calculation of working length. Such a situation often exists in maxillary molars, where the radiopaque structures of the malar process or floor of the maxillary sinus may superimpose the apices of the teeth, making radiographic calculation difficult. Mandibular tori may do the same for mandibular bicuspids and molars. 3.Patients who gag easily with radiographs also profit from preliminary use. 4.Locators also may be useful in verifying perforations of the root.
  • 60.
    Disadvantages 1.The accuracy issomewhere in the low 90 percentiles. 2.Without a confirming radiograph, filing done to the incorrect length could cause an increase in postoperative pain and a decrease in success. 3.These machines to give incorrect or inaccurate readings because the battery may be low (check battery and replace frequently), too much tissue may remain in the canal (broach canal and use a Hedstrom file to verify that gross tissue is gone), the canal may be too wet (dry mildly with paper points) or too dry (irrigate mildly with peroxide or sterile water), the file may be too narrow (use a file that is slightly loose in the canal, not a size 10 each time; estimate first to chose the proper width), a blockage may be present (try to bypass CAREFULLY!), the lip clip may fall off (check that it is in place).
  • 61.
    Current apex locatorsare sufficiently precise to allow WL determination, thus reducing the frequency of overinstrumentation when only radiographs are used. Even in cases of apical resorption and wide-open apices after root- end resection, these apex locators are shown to be accurate. Therefore, it seems warranted to focus on the electronically determined WL and to use the radiograph merely to avoid gross errors in case the apex locator does not appear to work correctly.
  • 62.
    Apex locators versusradiographs It is a mistake to think that apex locators will eliminate radiographs during endodontic treatment. Excellent preoperative films must always be taken prior to any active treatment on the tooth. Apex locators cannot help the dentist determine canal width, canal curvature, or number of canals, and they can only partially help with sites of canal Division. These must be determined by radiograph. Fouad et al. stated that apex locators were not meant to replace radiographs, but to add to the information obtained by radiographs.
  • 63.
    3. Non radiographicmethods 1.Apex Finder 2. Audiometric Method 3. Tactile Method 4. Paper Point Evaluation Method
  • 64.
    Paper point method Ina root canal with an immature (i.e., wide open) apex, a relatively reliable means of determining WL is by gently passing the blunt end of a paper point into the canal after profound anesthesia has been achieved. The moisture or blood on the portion of the paper point that passes beyond the apex may be an estimation of WL or the junction between the root apex and the bone. In cases in which the apical constriction has been lost owing to resorption or perforation, and in which there is no free bleeding or suppuration into the canal, the moisture or blood on the paper point is an estimate of the amount the preparation overextended. This paper point measurement method is also a supplementary one.
  • 65.
    Recent advances: 1. Tomography: -Is a radiographic technique that “slices” teeth in thin sections. - Computers subsequently reassemble the sections to generate a three-dimensional image. - Dental anatomy including bucco-lingual curvatures shapes of the root canal spaces and location of the apical foramen (which is important in determining or calculating the working length) can be visualized in the third-dimension. - Additional advantage in the elimination of angled radiographs; all angled views are captured in just one exposure.
  • 66.
    2.Videography and Intra-OralCameras Intra-oral videography is a non-ionizing diagnostic imaging technique. Developers are using miniature colour CCD (charge coupled device) chips. With fiber optic probes to assemble video cameras small enough to transverse periodontal defects and identify vertical root fractures. These devices are useful in endodontics as they can display canal morphology as well aid in locating canal orifices. Perforations can be visualized by inserting the fiber optic probe down the suspected canal. These devices are connected to a computer that provides enhanced images for teaching and patient education.
  • 67.
    3.DDR- Fourth generationDDR One of the more recent additions to Trophy’s fourth generation RVG systems is the capability of on screen point-to-point measurements using multiple additive points. This capability potentially allows for fast accurate working length estimation in roots demonstrating severe apical curvatures. The RVG on screen measurement utility allows for rapid additive multiple point measurement of digital images, automatically tallying the measurement points on screen to a tenth of a millimeter.
  • 68.
    CONCLUSION It can beseen quite clearly that the procedure for calculation of working length should be performed with skill, using techniques that have been proven to give valuable and accurate results and by methods that are practical and efficacious. If this step is performed perfunctorily, without thought and skill, using techniques of dubious accuracy, many teeth so treated will be failures.