working length in endodontics , how to determine it

working length in endodontics , how to determine it

1. WORKING Length

2. CONTENTS INTRODUCTION DEFINITION ANATOMICAL CONSIDERATIONS METHODS OF DETERMINING WORKING LENGTH RADIOGRAPHIC METHODS ELECTRONIC APEX LOCATORS NON- RADIOGRAPHIC METHODS FAILURES IN WORKING LENGTH WORKING WIDTH CONCLUSION REFERENCES

3. INTRODUCTION DEFINITION The distance from coronal reference point to the point at which canal preparation and obturation should terminate. This is usually the apical terminus of the root canal, also termed as the minor constriction or the minor diameter of the apical foramen.

4. ANATOMICAL CONSIDERATIONS ANATOMIC APEX: It is defined as the tip or end of the root determined morphologically. RADIOGRAPHIC APEX: It is defined as the tip or end of the root determined radiographically.

5. APICAL FORAMEN (MAJOR DIAMETER): Main apical opening of the root canal. Frequently eccentrically located away from the anatomic or radiographic apex. APICAL CONSTRICTION (MINOR DIAMETER): The apical portion of the root canal having the narrowest diameter. Often 0.5-1.0mm short of centre of the apical foramen. The constriction widens apically to the foramen and assumes a funnel shape.

6. CEMENTODENTINAL JUNCTION: Region where the dentin and cementum are united. It is a histological landmark . CDJ does not always coincide with apical constriction and is located 0.5 -3 mm short of anatomic apex.

7. KUTTLER’S STUDY According to KUTTLER Narrowest diameter- apical constriction Average distance between minor and major diameter Young-0.524mm Older-0.659mm If file reaches major diameter exactly subtract 0.5mm from length in Young 0.67mm from length in Old

8. Distance between 1 and 2: The apical foramen deviates from the apex in 50-98% of the teeth. This deviation averages 0.3 to 0.6 mm but could be as much as 3 mm. Distance between 2 and 3: 0.5 mm in 18-25 y old, and 0.67 in 55+ y old. Distance between 1 and 3: 0.89 mm with a range of 0.1 to 2.7 mm.

9. DUMMER CLASSIFICATION

10. HISTORY End of 19th century: WL was calculated when file was placed in canal & patient experienced pain 1899 : Kells introduced X-rays in dentistry 1955 : Kuttler microscopically studied the microscopic anatomy of root tip, and decided that filling to the radiographic apex was an unwise clinical procedure, contributing to post operative pain. 1969 : Inove significantly contributed to evolution of electronic apex locators

11. SIGNIFICANCE OF WORKING LENGTH Determines how far into the canal the instruments are placed & worked & thus how deeply the tissues, debris, metabolites are removed . Limits the depth to which the canal filling may be placed. Affects the degree of pain & discomfort If calculated within correct limits-determines the success

12. REFERENCE POINT Is that site on occlusal or the incisal surface from which measurements are made. Do not use weakened enamel walls or diagonal lines of fracture This point is used throughout canal preparation & obturation.

13. Failure……….. LENGTH TOO LONG Perforation through apical constriction Overfilling or over extension Increased incidence of post operative pain. Prolonged healing period. Lower success rate, owing to incomplete regeneration of Cementum, Periodontal ligament and Alveolar bone

14. SHORT WORKING LENGTH Incomplete cleaning Underfilling Persistent discomfort Incomplete apical seal Existence of viable bacteria contributes to a peri-radicular lesion Lower success rate

15. METHODS OF WORKING LENGTH DETERMINATION GROSSMAN FORMULA INGLE’S METHOD WEINE’S METHOD BEST METHOD BREGMAN’S METHOD BRAMANTE METHOD GRID SYSTEM RADIOGRAPHY NON RADIOGRAPHICAL METHOD DIGITAL TACTILE SENSE APICAL PERIODONTAL SENSITIVITY PAPER POINT METHOD ELECTRONIC APEX LOCATOR RADIOGRAPHICAL METHOD

16. RADIOGRAPHIC METHOD

17. RADIOGRAPHIC METHOD Based on the tactile method. File is introduced into the canal until the practitioner believes that the narrowest part of root canal Then radiographed. Relation between tip of the instrument and the root apex determined Position of the file is changed

18. GROSSMAN’S METHOD According to Grossman An instrument extending to the apical constriction is placed into the root canal . - A mark or a stopper is placed at the occlusal or incisal table (detectable on radiograph)

19. GROSSMAN’S METHOD Actual length of the tooth Apparent length of tooth in radiograph Actual length of the instrument Apparent length of instrument in radiograph =

20. Wrong reading can occur because of : 1)Variations in angles of radiograph 2)Curved roots 3)A small error will be multiplied

21. INGLE’S METHOD Tooth length is measured in the pre operative radiograph 1 mm “safety allowance” is subtracted for possible image distortion Set the endodontic ruler at this tentative working length and adjust the stop on the instrument at that level and the instrument is inserted in the canal . On the radiograph the difference between the end of file and root end is measured and this value is either subtracted or added to the initial working length measurement depending on weather the file is short of apex or extended beyond apex.

22. From this adjusted working length 1mm “ safety allowance” is subtracted again to confirm with the apical termination of instrument Place the instrument with adjusting the stopper Take a confirmatory radiograph Record this final working length and the coronal point of reference on the patient’s record. Final working length may shorten by as much as 1 mm as a curved canal is straightened out by instrumentation, reconfirmed after instrumentation is completed.

23. WEINE’S METHOD Curved canal-The final working length may shorten by as much as 1mm as the curved canal is straightened out by instrumentation .

24. BEST’S METHOD In 1960 BEST described In this method -steel pin measuring 10 mm is fixed to the labial surface of the root with utility wax keeping the pin parallel to the long axis of the tooth A radiograph obtained. The radiograph is then carried to a gauge, which would indicate the tooth length.

25. BREGMAN’S METHOD Bregman (1950) 25mm length flat probes used Steel blade fixed with acrylic resin as a stop Leaving a free end of 10 mm for placement into root canal This is placed in the tooth until the metallic end touches the incisal edge or cusp tip of the tooth. Then a radiographic is taken

26. CRD=Real tooth length CRI = Real instrument length CAD= Apparent tooth length, seen in the radiograph. CAI= Apparent instrument length, seen in the radiograph. CRD = CRI X CAD CAI

27. BRAMANTE’S TECHNIQUE Probe was bent at one end -forming a right angle - this bend was inserted partially in acrylic resin- such that resin surface contacting tooth surface. Then the tooth is radiographed A-Internal angle of intersection of incisal U radicular probe segment. B-Apical end of the probe C-Tooth apex from radiographic image

28. CRD-Real tooth length CRS-Real probe length CAD-Tooth length in radiograph CAS-Instrument length in radiograph CRD - CRS x CAD CAS

29. KUTTLER’S METHOD According to Kuttler , canal preparation should terminate at apical constriction, i.e , minor diameter. Estimate length of roots from preop radiograph and canal width on radiograph. If canal is narrow, use 10 or 15 size instrument. Average width- 20 or 25 size and wide-30 or 35 size instrument. Insert selected file -take a radiograph. If file reaches major diameter, subtract 0.5mm from it for younger patients and 0.67 for older patients

30. X-RAY GRID METHOD Everett & Fixott in 1963. Grid consists of lines 1 mm apart running lengthwise and cross-wise. Every fifth mm is accentuated by a heavier line to make reading easier on the radiograph Millimetre grid is superimposed on the radiograph This overcomes the need for calculation. Not a good method if radiograph is bent during exposure

31. XERORADIOGRAPHY Better visualization of pulp chamber morphology, root canal configuration and root outline. According to Macro in 1984, Xeroradiography gave closer to accurate results in measurement compared to conventional radiographs. 35

32. DIRECT DIGITAL RADIOGRAPHY DDR digitizes ionizing radiation. Programmed computerized receiver that processes signals from an intra-oral sensor that is stimulated by x-rays from a standard dental machine. 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 ( Radiovisiography ) developed by Dr. Francis Mouyan , a French dentist and VIXA (video imaging x-ray application). 36

33. RADIOVISIOGRAPHY ( RVG ) RADIO PORTION Conventional X-ray unit with precise timer for short exposure Sensor to record images VISIO SECTION Video monitor holds the signal Display processing unit GRAPHIC PART Digital storage apparatus

34. ADVANTAGES Low radiation dose Darkroom not required Quality of the image is consistent Image distortion from bent films is eliminated DISADVANTAGES Expensive Large disk space required to store images Due to bulky sensor placement in mouth is difficult Soft tissue imaging is not very accurate

35. NON RADIOGRAPHIC METHODS

36. DIGITAL TACTILE SENSE Detect a sudden increase in resistance, as a small file approaches the apex. Increase in resistance as the file approaches the apical 2 to3 mm I. The unresorbed canal commonly constricts just before exiting the root . II. It frequently changes course in the last 2-3 mm. A narrowing presses more tightly against the instrument, whereas a curvature deflects the instrument from a straight path. Unreliable

37. APICAL PERIODONTAL SENSITIVITY File inserted into the canal up to the point where patient experiences pain or sensitivity, as the file reaches the periapical region. A file is advanced in a necrotic non-anaesthetized or completely prepared canal until the patient can feel it.

38. Botusanov and Vladimirov’s paper says this technique locates the “apex or 1.5 mm shorter than that” Their result is not surprising, since (1) a necrotic pulp frequently contains vital inflamed tissue that extends several mm into the canal, (2) it has been observed that, in an unanesthetized patient, an instrument has passed several mm out of the apex without being detectednly 25.6% of the time.

39. PAPER POINT METHOD To detect bleeding or apical moisture. A bloody or moist tip suggests an over extended preparation. The point of wetness often given an approximate location to the actual canal end point. A wet or bloody point - zipped or the apex perforated during preparation-----additional canal shaping in addition to adjustment of working length.

40. APEX FINDER M.M.Negm in 1982 Used to locate the apex as well as measuring the root length. Insertion of a fine plastic tapered bared shaft through a beveled tube into the root canal. When resistance to withdrawal is felt which indicates that some barbs have engaged the apical margin, the shaft is marked at the level of the cusp tip. The distance between the mark and the barbs, which caused the resistance, is measured . 45

41. AUDIO METRIC METHOD It is based on the principle of electrical resistance of comparative tissue using a low frequency oscillation sound to indicate when similarity to electrical resistance has occurred by a similar sound response. By placing an instrument in the gingival sulcus and including an electric current until sound is produced and then repeating this by placing an instrument through the root canal until the same sound is heard, one can determine the length of the tooth. 46

42. ELECTRONIC APEX LOCATORS The first reported use of electric current to measure root canal working length was in 1918 by Custer.

43. HISTORY 1918, Cluster - root canal length could be determined by using electrical conductance. 1942, Suzuki - electrical resistance between the periodontal ligament was equal to oral mucosa. 1960, Gordon - use of a clinical device for electrical measurement of resistance. 1962, Sunada –used a simple ohmmeter to study electrical resistance between the mucous membrane and the periodontium 48

44. 1969, Inove – incorporated the use of an audiometric component that permitted the device to relate the canal depths to the operator via low-frequency audible sounds. 1990, Yamashita - reported on a device that calculated the difference between two impedances from two different frequencies 1991, Kobayashi et al - eported on the ‘‘ratio method’’ for measuring the root canal length, ( Root ZX ) EALs with additional functions were developed in the late 1990s.- incorporation of endodontic handpieces 49

45. PARTS OF APEX LOCATOR It has four parts File File clip Lip clip Cord – which connects the three parts

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47. ADVANTAGES Decreases patient exposure Used to detect perforations Easy and fast Can be used in pregnant patients, children ,patients with gag reflex Particularly useful when the apical portion of the canal system is obscured by Impacted teeth, Tori ,Zygomatic arch ,Excessive bone density, Overlapping roots ,Shallow palatal vault

48. DISADVANTAGES Not 100% accurate Not useful in immature teeth, resorption May show inaccurate readings Cannot be used in patients with cardiac pacemakers

49. 1 st generation 2 nd generation 3 rd generation 5 th generation 4 th generation 6 th generation Based on resistance Impedance Frequency or comparative impedance Measures resistance and capacitance separately rather than the resulting impedance Based on dual frequency ratio type, Bluetooth technology Adaptive apex locators CLASSIFICATION 54

50. TYPES OF APEX LOCATORS BASED ON DIRECT CURRENT BASED ON ALTERNATING CURRENT ORIGINAL OHOMETER USED BY SUZUKI & SUNADA RESISTANCE TYPE IMPEDENCE TYPE FREQUENCY TYPE SUBTRACTION TYPE RATIO TYPE 2 FREQUENCIES 5 FREQUENCIES

51. FIRST GENERATION APEX LOCATORS Resistance apex locators Measure opposition to the flow of direct current or resistance. When the tip of the file reaches the apex in the canal, the resistance value is 6.5 kilo-ohms (current 40 mA)

52. F ound to be unreliable when compared with radiographs Eg : 1. Root canal meter- pain- high current. 2. Endodontic Meter and the Endodontic Meter S II ( Onuki medical Co.Japan ) 3.Dentometer ( Dahin Electro medicine, Denmark) 4.Endo Radar (Electronica Liarre , Italy).

53. INACCURATE READINGS Wet canals, Obstructed canals, Carious/ defective restorations, Perforations and in patients with Cardiac pacemakers. When the instruments came in contact with metallic restorations

54. SECOND GENERATION APEX LOCATORS Impedance apex locators T here is electrical impedance across the wall of the root canal due to the presence of transparent dentin T here is electrical impedance across the wall of the root canal due to the presence of transparent dentin Uses the mechanism that the highest impedance is at the apical constriction

55. SONO EXPLORER II: D eveloped by Inoue in 1971 Earliest of the Second-generation apex locators. SONO-EXPLORER M-III Meter to indicate distance to apex With an electrode connected to the dental chair and a sheath over the probe it was able to make measurements in canal even with conductive fluids present.

56. THE APEX FINDER: Has a visual digital LED indicator Self-calibrating. Compared to radiographic working length-accuracy at 67% ENDO ANALYZER: Combined apex locator and pulp tester.

57. DIGIPEX: It has a visual LED digital indicator and an audible indicator. It requires calibration. DIGIPEX II: It is a combination of the apex locator and pulp vitality tester. EXACT-A-PEX: it has a led display and an audio indicator.

58. THIRD GENERATION APEX LOCATORS Frequency dependent comparative impedance type Different sites in canal give difference in impedance between high (8 KHz ) and low (400 Hz) frequencies The difference in impedance is least in the coronal part of canal As goes deeper into canal, difference increases Greatest at the cementodentinal junction

59. These units have more powerful microprocessors and are able to process the mathematical quotient and algorithm calculation required to give accurate readings. Since the impedance of given circuit may be substantially influenced by the frequency and the current flow, these devices have been called “frequency dependent”

60. The device operates most accurately when the canal is filled with electrolyte such as saline or sodium hypochlorite. The disadvantage of this device needs “reset” or “calibrated” for each canal

61. EXAMPLES: Justy II (Yoshida Co., Japan) Apex Finder AFA Model 7005 (EIE Analytic Endodontics, USA). Apex Finder (Endo Analyzer 8001; Analytic Technology, USA). Neosono -D ( Amadent Medical and Dental, Co, USA) Apit 7 (Osada, Japan). ProPex (Dentsply- Maillefer , Switzerland) Bingo 1020 (Forum Engineering Technologies) Elements-Diagnostic ( Sybronendo ) Raypex_5, VDW, Munich, Germany).

62. ROOT ZX RAYPEX 5 PROPEX

63. ENDEX It uses a very low alternating current. The signals of two frequencies (5 and 1 khz ) File enters the coronal part of the canal- difference in impedances at the 2 frequencies is small. Instrument is advanced apically, the difference in impedance changes. As the apical constriction impedance values are maximum difference It is indicated on the analog meter and audio alarm. Accuracy was 96.5 percent (0.5 - 0.0 mm from apex).

64. Measures the two impedances at 2 frequencies (8 and 0.4 khz ) Described by K obayashi . Microprocessor in the device calculates the ratio of 2 impedances. The quotient of impedances is displayed on an lcd panel - represents position of instrument tip inside the canal Accuracy for the device ranged from 84 to 100% ROOT ZX

65. The root ZX mainly detects the change in electrical capacitance that occurs near the AC. The advantages of the ROOT ZX It requires no adjustment or calibration and can be used when the canal is filled with strong electrolyte or when the canal is “empty” and moist

66. Combination of apex locator and endodontic handpiece Tri Auto ZX, Endy 7000 , Sofy ZX Tri Auto ZX has 3 automatic safety mechanisms a. Auto start-stop mechanism : handpiece automatically starts rotation- instrument enters the canal and stops-instrument is removed. b. Auto-torque-reverse mechanism c. Auto-apical-reverse mechanism automatically stops and reverses rotation when instrument tip reaches a distance from the apical constriction-preset by clinician. prevents instrument beyond apical constriction Tri Auto ZX

67. Electronic measurement of root mode (EMR): Lip clip, hand file and file holder are used with apex locator in handpiece - determine the working length. Handpiece motor does not work in this mode 2. Low mode: Lower Torque used with small to mid sized instruments for shaping and cleaning the apical and mid-third sections All 3 automatic safety mechanisms are functional in this mode. The Tri auto Zx has four modes:

68. 3.High mode : The torque higher than low mode. Used with mid sized to large instruments for shaping and cleaning in mid third and coronal third sections All 3 automatic safety mechanisms are functional in this mode. 4. Manual mode: Highest torque . Auto-start stop and auto-torque-reverse mechanisms do not function. Large instruments for coronal flaring.

69. FOURTH GENERATION APEX LOCATORS Ratio type apex locators Determine the impedance at five frequencies Measures resistance and capacitance separately - than the resultant impedance value Have built in electronic pulp tester Can be different combination of values of capacitance and resistance that provides the same impedance and the same foraminal readin g

70. Examples AFA apex finder i-Pex Propex Elements Diagnostic Unit Bingo 1020/ Raypex - uses two separate frequencies 400 Hz and 8 KHz Root ZX II AFA apex finder

71. DISADVANTAGE Devices is that they need to perform in relatively dry or in partially dried canals. Heavy exudates or blood it becomes inapplicable

72. FIFTH GENERATION APEX LOCATORS Also called as dual frequency ratio type Developed in 2003 E-magic finder series Measures capacitance and resistance of the circuit separately. Supplied by diagnostic table that includes statistic of the file. They have best accuracy in any root canal condition (dry, wet, bleeding, saline, EDTA,NaOCl ). Provides with a digital read out, graphic illustration and an audible signal. Built in pulp tester

73. SIXTH GENERATION APEX LOCATOR S Adaptive type Continuously define humidity of the canal and immediately adapts to dry or wet canal. Possible to be used in dry or wet canals, canals with blood or exudates Example: Raypex 6

74. ADVANTAGES OF THE ELECTRONIC METHOD 1. Only method that can measure length up to apical foramen, not to radiographic apex. 2. Accurate 3. Easy and fast 4. Reduction of x-ray exposures 5. Artificial perforation can be recognized. 6. Procedures can be carried out in pregnancy.

75. DISADVANTAGES OF ELECTRONIC METHOD 1. Requires special device 2. Difficult in teeth with wide open apex. 3. Weak batteries can affect accuracy

76. RESISTANCE TYPE APEX LOCATORS ADVANTAGES 82

77. DISADVANTAGES

78. IMPEDANCE TYPE APEX LOCATOR ADVANTAGES 84

79. DISADVANTAGES

80. FREQUENCY DEPENDANT APEX LOCATORS ADVANTAGES DISADVANTAGES 86

81. CONTRAINDICATION 87 CARDIAC PACEMAKERS

82. OTHER USES OF ELECTRONIC APEX LOCATORS To detect root perforations to clinically acceptable limits Determine the location of root and pulpal floor perforations To detect horizontal fractures To confirm suspected periodontal or pulpal perforations during pinhole preparation Recognize any connection between the root canal & periodontal membrane such as root fracture, cracks & internal or external resorption . 88

83. Recent advances

84. TOMOGRAPHY “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. 90

85. VIDEOGRAPHY AND INTRA-ORAL CAMERAS Non-ionizing diagnostic imaging technique. Developers are using miniature colour ccd (charge coupled device) chips. With fiber optic probes to assemble video Identify vertical root fractures Display canal morphology as well aid in locating canal orifices. Perforations can be visualized Provides enhanced images for teaching and patient education. 91

86. DDR - FOURTH GENERATION More recent additions to trophy’s fourth generation RVG systems Capability of on-screen point-to-point measurements using multiple additive points. Fast accurate working length estimation in roots demonstrating severe apical curvatures. 92

87. RECEIVED: 14 MARCH 2023 REVISED: 12 APRIL 2023 ACCEPTED: 25 MAY 2023

88. 96 Received: 24 June 2021 Accepted: 6 August 2021 Published: 17 August 2021

89. THE FORGOTTEN DIMENSION: WORKING WIDTH Working width is defined as “initial and post-instrumentation horizontal dimensions of the root canal system at working length and other levels.” Minimum initial working width - initial apical file size which binds at working length. Maximum final working width corresponds to the master apical file size. Haga found that mechanical preparation of root canal to two sizes larger than the original was adequate

90. Walton’s histologic study showed that canals that were instrumented to three sizes larger still were not thoroughly cleaned. Horizontal dimension of RC system more complicated than vertical dimension However , preparing each canal to a specific apical diameter as per its initial apical size may better help the clinician to provide a more predictable canal preparation.

91. 99

92. FACTORS AFFECTING THE DETERMINATION OF MINIMAL INITIAL WORKING WIDTH AT WORKING LENGTH 100

93. MAXIWW- MAXIMAL INITIAL HORIZONTAL DIMENSION MINIWW- MINIMAL INITIAL HORIZONTAL DIMENSION

94. ELIMINATING OR MINIMIZING INFLUENCE OF THE AFFECTING FACTORS Circumferential instrumentation should be done to prevent dumbbell or key -hole effects , only way to properly clean and shape the canal. Proper selection of instruments- maximal flexibility, minimal taper, light speed. Early coronal flaring – widening of orifices to ensure effective irrigation, to minimize the interferences with tactile sensation.

95. Manual crown down instrumentation is more effective and efficient in cleaning flattened root canal than rotary instrumentation. Removal of infected dentin for successful treatment in infected canals.

96. SIGNIFICANCE To obtain apical stop which is round as possible so as to get an impermeable seal . So that the dentinal tubules at apical 1mm is devoid of any microorganisms . Apical preparation with large working width removes more bacteria than small apical preparation . It also permits irrigants to reach apex .

97. CONCLUSION The cementodentinal junction or minor diameter is a practical and anatomic termination point for the preparation and obturation of the root canal – and this cannot be determined radiographically. Modern apex locators can determine this position with accuracies greater than 90% No individual method is truly satisfactory in determining endodontic working length. Therefore, combination of methods should be used to assess the accurate working length determination

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