working length

working length determination in endodont

1. BY SHRUTI SUDARSANAN FINAL YEAR PART-II ROLL NO.-14 WORKING LENGTH DETERMINATION

2. DEFINITIONS WORKING LENGTH : According to endodontic glossary working length is defined as “ the distance from a coronal reference point to a point at which canal preparation and obturation should terminate”

3. REFERENCE POINT : is that site on occlusal or the incisal surface from which measurements are made. ANATOMIC APEX : tip or end of root determined morphologically

4. RADIOGRAPHIC APEX : tip or end of root determined radiographically . APICAL FORAMEN (major diameter): is main apical opening of the root canal. It is frequently eccentrically located away from the anatomic or radiographic apex. APICAL CONSTRICTION (minor diameter ): is apical portion of root canal having narrowest diameter. It is usually 0.5 to 1 mm short of apical foramen.

5. CEMENTODENTINAL JUNCTION: the region where cementum and dentin are united, the point at which cemental surface terminates at or near the apex of tooth. Location of CDJ ranges from 0.5-3mm short of anatomic apex.

6. SIGNIFICANCE OF WORKING LENGTH Determines how far into canal, instruments can be placed and worked. Consequences Of Over Extended Working Length : Perforation through apical constriction. Overinstrumentation Overfilling of root canal Increased incidence of postoperative pain. Prolonged healing period Lower success rate (because of incomplete regeneration of cementum , periodontal ligament and alveolar bone

7. Consequences Of Working Short of actual working Length Incomplete cleaning & instrumentation of canal. Persistent discomfort due to presence of pulpal remnants Under filling of the root canal. Incomplete apical seal. Apical leakage which supports existence of viable bacteria and contributes to poor healing and periradicular lesion

8. Causes of loss of working length: Presence of debris in apical 2/3 rd of canal Failure to maintain apical patency Skipping instrument sizes Ledge formation Inadequate irrigation Instrument separation canal blockage

9. WORKING WIDTH Definition : Working width is defined as “initial and postinstrumentation horizontal dimensions of the root canal system at working length and other levels” the minimum initial working width= initial apical file size which binds at working length and other levels The maximum final working width corresponds to the master apical file size

10. Reasons for widening root canal: To remove microorganism from the canal mechanically To increase the area of root canal for better irrigation To completely remove the pulp tissue To attain a sound apical stop so as to achieve a 3 dimensional seal. The round shape confirms to the round cross sectional tip of gutta percha

11. 2 guidelines for instrumentation: Enlarge the root canal atleast 3 sizes beyond the first instrument that binds the canal Enlarge the canal until it is clean. It is indicated by white dentinal shavings on the instrument flutes The main aim should be to remove the canal irregularities of dentin to make the canal walls smooth

12. Factors affecting size of working width Whether root canal is vital/non-vital Presence of periapical pathology Presence or absence of root resorption Canal configurations like C-shaped canal, bayonet canals, etc Presence or absence of isthmus

13. Advantages of narrow apex: Decrease risk of canal transportation Avoids extrusion of debris and obturating material Disadvantages of narrow apex Incomplete removal of infected dentin Not ideal for lateral compaction Irrigants may not reach the apical-third of canal Advantages of wide apex Complete removal of infected dentin Better disinfection of canal at apical third Disadvantages of wide apex Increased chances of extrusion of irrigants and oobturating material Not recommended for thermoplastic obturation More chances of preparation errors

14. METHODS OF WORKING LENGTH DETERMINATION Average root length from anatomic studies Radiographs Matematical method Tactile sensation Bleeding on paper point Apical periodontal sensitivity Electronic apex locator

15. RADIOGRAPHIC METHODS GROSSMAN FORMULA INGLE’S METHOD WEIN’S METHOD KUTTLER’S METHOD OTHER METHODS BEST’S METHOD BREGMAN’S METHOD BRAMANTE’S METHOD RADIOGRAPHIC GRID ENDOMETRIC PROBE DIRECT DIGITAL RADIOGRAPHY XERORADIOGRAPHY SUBTRACTION RADIOGRAPHY

16. RADIOGRAPHIC METHOD OF WORKING LENGTH DETERMINATION Two schools of thought are there: Cementodentinal junction is impossible to locate clinically and the radiographic apex is the only reproducible site available for length determination. Those who don’t follow this concept say that radiogrpahic apex is not reproducible. Its position depends on number of factors like angulation of tooth, position of ilmm , film holder etc . Two techniques used: Paralelling technique (superior) and bisecting angle technique

17. Before access opening, fractured cusps, weakened cusps are reduced to avoid fracture of weakened enamel during the treatment. This will avoid the loss of initial reference pont and thus the working length.

18. JOHN INGLE’S METHOD Pre-op radiograph is used to calculate the working length. Measure estimated working length from preoperative periapical radiograph It can be confirmed by placing an endodontic instrument (with stopper adjusted) into the canal and taking a second radiograph. Instrument inserted should be large enough not to be loose in the canal because it can move while taking radiograph and this may result in errors in determining its working length.

19. The new working length is calculated by adding or subtracting the distance between the instrument tip and desired apical termination of the root. Correct working length is finally calculated by subtracting 1mm from this new length.

20. Advantages Can see the anatomy of the tooth Can find out curvature of the root canal. Can see the realationship between the adjacent teeth and anatomic structures.

21. Disadvantages Varies with different observers. Superimposition of anatomical structures. Two- dimensional view of three-dimensional object. Cannot interpret if apical foramen has buccal or lingual exit. Risk of radiation exposure. Time consuming Limited accuracy

22. WEINE’S MODIFICATIONS Weine’s recommendations for determining the working length based on radiographic evidence of root or bone resorption If no root or bone resorption: preparation should terminate 1.0 mm short of the apical foramen (shorten the length by 1 mm) Bone resorption is present but no root resorption : shorten the working length by 1.5 mm Both root & bone resorption is present: shorten the length by 2.0mm

23. KUTTLER’S METHOD Canal preparation should terminate at apical constriction (MINOR DIAMETER) Locate major & minor diameter on preoperative radiograph. Estimate length of roots Estimate canal width Select the appropriate file and insert into the canal and take a radiograph. If file reaches major diameter, subtract 0.5 mm from it for younger patients and 0.67 for older patients.

24. Advantages: Minimal errors Has shown many successful cases Disadvantages: Time consuming and complicated Requires excellent quality radiographs

25. MATHEMATICAL METHOD OF WORKING LENGTH DETERMINATION GROSSMAN’S METHOD An instrument is inserted into the canal, stopper is fixed to the reference point and radiograph is taken Actual length of the tooth = ( apparent length of tooth in radiograph / apparent length of instrument in radiograph ) × actual length of the instrument. Disadvantages : wrong readings due to- Variations in angles of radiograph Curved roots S-shaped, double curvature roots.

26. RADIOGRAPHIC GRID By Everett & Fixott in 1963 A millimeter grid is superimposed on the radiograph. Advantages: Overcomes the need for calculation Disadvantages : Not good method if radiograph is bent during exposure.

27. ENDOMETRIC PROBE Uses the graduations on diagnostic file which are visible on radiograph. Disadvantage: smallest file size to be used is number 25.

28. Direct digital radiography Digital image is formed 2 types: Radiovisiography Phosphor imaging system

29. XERORADIOGRAPHY New method Without film, image is recorded on an aluminium plate coated with selenium particles. Advantages : Offers edge enhancement and good detail. The ability to have both positive and negative prints together . Improves visualization of files and canals. It is two times more sensitive than conventional D-speed films More sensitive

30. Disadvantages Since saliva may act as a medium for flow of current, the electric charge over the film may cause discomfort to the patient. Exposure time varies according to thickness of the plate. Process of development cannot be delayed beyond 15 min.

31. DIGITAL TACTILE SENSE Clinician may see an increase in resistance as file reaches the apical 2 to 3mm. Advantages: Time saving No radiation exposure Disadvantages: Inaccurate readings Narrow canals, one may feel increased resistance as file reaches apical 2 to 3mm. Teeth with immature apex, instrument can go periapically .

32. PERIODONTAL SENSITIVITY TEST Based on patient’s response to pain. Don’t always provide accurate readings In case of narrow canals , instruments may feel increased resistance as file approaches apical 2-3mm In case of teeth with immature apex, instrument can go beyond the apex In apical periodontal sensitivity test, In case of necrotic pulp: instrument can pass beyond apical constriction In case of vital or inflamed pulp: pain may occur several mm before periapex is crossed by the instrument

33. PAPER POINT MEASUREMENT METHOD Paperpoint is gently passed in the root canal to estimate the working length. Most reliable: open apex cases Moisture of blood present on apical part of paper point indicates that paper point working has passed beyond estimated working length. Used as supplementary method.

34. ELECTRONIC APEX LOCATORS Used as an adjunct to radiography Used to locate the apical constriction or cementodentinal junction or apical foramenand not the radiographic apex.

35. APICAL CONTROL ZONE : is the mechanical alteration of the apical terminus of the root canal space which provides resistance and retention form to the obturating material against the condensation pressure of obturation . The ability to distinguish between minor and major diameter is most important for the creation of apical control zone

36. Apex locators function by using human body to compete an electrical circuit. One side of apex locator circuit is connected to endontic instrument and other side is connected to patient’s body. Circuit is completed when endodontic instrument is advanced into root canal until it touches the periodontal tissues

37. COMPONENTS Lip clip File clip Electronic device Cord which connects above three parts

38. Advantages Provide objective information with high degree of accuracy Easy and fast Redction of exposure to radiation Perforation can be detected Can measure pulp space exactly to the constriction Can detect resorption and root fracture

39. Disadvantages Can provide inaccurate readings in following cases. Presence of pulp tissue in canal Too wet or too dry canal Use of narrow file Blockage of canal Incomplete circuit & low battery Chances of over estimation Immature apex Incorrect readings in teeth with periapical radiolucenies , and necrotic pulp associated with root resorption , etc.

40. Uses Provide objective information with high degree of accuracy When apical portion of canal system is obstructed. In patients who cannot tolerate X-ray film placement because of gag reflex Pregnant patients Detecting site of root perforations Children, disabled patients, patients who are heavily sedated. RCT of teeth with incomplete root formation.

41. Contraindications Patients who have cardiac pacemaker

42. CLASSIFICATION Based on type of current flow and opposition to current flow and number of frequencies involved First generation apex locator( resistance apex locator) Second generation apex locators ( impedence apex locators) Third genertion apex locators Fourth generation apex locators Combination apex locators and endodontic handpiece

43. FIRST GENERATION APEX LOCATORS (RESISTANCE APEX LOCATORS) Measures opposition to flow of direct current. i.e. resistance Principle: resistance offered by periodontal ligament and oral mucous membrane is the same. i.e. 6.5K ohms. Not used nowadays: blood, pus, chelating agents etc used within the canals can give false readings Technique Turn on the device and attach the lip clip near the arch being treated. Hold a 15 number file and insert it approx 0.5mm into sulcus of tooth. Adjust the control knob until the reference needle is centred on the metre scale and produces audible beeps. Note this reading

44. 4. Prepare the access cavity and apply rubber dam and remove pulp, debris etc. 5. Using preoperative radiograph estimate the working canal width. 6. Insert the file into canal unless the reference needle moves from extreme left to centre of scale and alarm beeps sound. Reset the stop at reference point and record the lengths. 7. Take the radiographs with file in place at the length indicated by apex locator. If length is longer or shorter, it is possible that preoperative film can be elongated or apex locator is inaccurate

45. Advantages Easily operated Possible to get objective information with high degree of accuracy Used when radiographs cannot be used accurately like Maxillary molars due to zygomatic process) Mandibular molars (obstruction due to mandibular tori ) Patient with gag reflex Digital read out Audible indication Detect perforation

46. Disadvantages Requires a dry field Many factors can lead to wrong reading like low battery, tissue present in canal, wet canal, too narrow canal or canal with blockage and problems of lip clip Patient sensitivity Requires calibration Cannot estimate beyond 2mm File should not contact metal restorations

47. SECOND GENERATION (IMPEDENCE APEX LOCATORS) Low frequency Introduced by Inoue Measures opposition to flow of alternating current or impedance. Indicates the apex when two impedance values approach each other.

48. Advantages Does not require lip clip. No patient sensitivity. Analog meter Detects perforations

49. Disadvantages No digital read out. Difficult to operate Canal should be free of electroconductive materials to obtain accurate readings. Requires coated probes Cannot use files

50. THIRD GENERATION (FREQUENCY DEPENDENT APEX LOCATOR) High frequency Based on the fact that different sites in canal give difference in impedance between high (8KHz) and low (400Hz) frequencies Is least in coronal part of canal As the probe goes deeper into canal, difference increases Greatest at cementodentinal junction These should be termed as ‘comparative impedence ” because they measure relative magnitudes of impedence which are converted into length information.

51. FOURTH GENERATION There can be different combination of values of capacitance and resistance that provides the same impedence . But te fourth generation apex locators measures resistance and capacitance separately rather than the resultant impedance value They are: AFA apex finder Elements diagnostic unit

52. COMBINATION APEX LOCATORS & ENDODONTIC HANDPIECE Tri Auto ZX is cordless electric endodontic handpiece with builtin root ZX apex locator It has three safety mechanisms: Autostart stop mechanism: handpiece starts rotation when instrument enters the canal and stops when it is removed. Autotorque reverse mechanism: handpiece automatically stops and reverses rotation when torque threshold (30gm/cm) is exceed. Prevents instrument breakage.

53. Autoapical –reverse mechanism It stops and reverses rotation when instrument tip reaches a distance from apical constriction taken for working length Prevents apical perforation

54. BASIC CONDITIONS FOR ACCURACY OF EAL Canal should be free from most of the tissue and debris Canal should be relatively dry No cervical leakage If residual fluid is present, it should be of low conductivity (5.25%NaOCl > 17%EDTA > saline) Proper adaptation of file to canal walls and periapex No blockages or calcifications in canals Battery of apex locator and other connections should be proper

55. BIBLIOGRAPHY TEXTBOOK OF ENDODONTICS- NISHA GARG & AMIT GARG

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