ELECTRONIC APEX LOCATOR (EAL)

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-Deepak Neupane

1. APEX LOCATOR DEEPAK NEUPANE  DEPARTMENT OF CONSERVATIVE DENTISTRY AND ENDODONTICS UCDS,BHAIRAHAWA

2. Electronic Apex Locators These are the electronic devices that have been developed for determining the working length of a root canal without resorting to radiography. Currently, Electronic Apex Locator (EAL) is the most optimal and accurate method to establish the root canal working length   Electronic apex locator (EAL) is used to locate the apical constriction or cementodentinal junction, apical foramen, but not the radiographic apex. Hence, the term apex locator is a misnomer one.

3. DEVELOPMENT CLUSTER (1918) : Proposed the concept of measuring the canal length electronically. SUZUKI (1942) : Principle and design of EAP. SUNADA (1962) : Introduction of first commercial EAL INOVE (1969) : Significant contribution in evolution of EAL. PRATTEN AND McDONALD (1996) : Compared the efficacy of three parallel radiographs and Endex apex locators in Cadaver.

4. Components of EALs 

5. Classification  According to Generations of EALs (Evolution of EALs)

6. McDonald's Classification (On the basis of type of current flow) TYPES OF APEX LOCATOR vvvO Based on Direct Current Based on alternating current Frequency Type Original OHM meter  Used by Suzuki and Sunada Resistance Type -Root canal meter -Endodontic meter Impedence type  - sonoexplorer Subtraction type -Endex - Neosonaultima EZ Ratio Type 2 Frequencies  5 Frequencies 

7. USES OF APEX LOCATORS  ‰ Provide objective information with high degree of accuracy  ‰ Useful in conditions where apical portion of canal system is obstructed by    • Impacted teeth   • Zygomatic arch    • Tori   • Excessive bone density    • Overlapping roots   • Shallow palatal vault  ‰ Useful in patients who cannot tolerate X-ray film placement because of gag reflex  ‰ Useful in pregnant patients, to reduce the radiation exposure 

8. ‰ Useful in children who may not tolerate taking radiographs, disabled patients and patients who are heavily sedated  ‰ Valuable tool for   • Detecting site of root perforations    • Diagnosis of external and internal resorption which have penetrated root surface   • Detection of horizontal and vertical root fracture     • Determination of perforations caused during postpreparation     • Testing pulp vitality

9. ContraIndications Older apex locators were contraindicated in the patients who have cardiac pacemaker functions. Electrical stimulation to such patients could interfere with pacemaker function. But this problem has been overcome in newer generation of apex locators.

10. MECHANISM OF ACTION OF APEX LOCATOR Root canals are surrounded by dentine and cementum that are insulators to electric current. At the apical foramen there is a small hole in which conductive materials within the canal are electrically connected to the periodontal ligament that is a conductor of electric current. The resistive material of the canal (dentine, tissue, fluid) with a particular resistivity forms a resistor, the value of which depends on the length, cross-sectional area and the resistivity of the materials . If an endodontic file penetrates inside the canal, and approaches the canal terminus, the resistance between the end of the instrument and the apical portion of the canal decreases, because the effective length of the resistive material inside the canal decreases .

11. Apex locators use the human body to complete an electrical circuit.One side of the circuitry is connected to an endo instrument & the other end to the patients body-(patients lip or by an electrode held in the patients hand).The impedance between the lip and the periodontal ligament (PDL) is a known value,6.5 KOhm so as the file tip is advanced toward the PDL, the EAL detects the changing impedance values and indicates the approach to the apex on its screen.

12. 1. First-generation apex locator (resistance apex locator)  • It is also known as resistance apex locator which measures opposition to flow of direct current, that is, resistance  • It is based on the principle that resistance offered by periodontal ligament, and oral mucous membrane is the same, that is, 6.5 kΩ  • Examples of 1st generation apex locators are root canal meter, endometric meter (Onuki Medical Co., Japan), Dentometer , Endo Radar.

13. ADVANTAGES  • Easily operated   • Digital read out   • Audible indication   • Detect perforation   • Can be used with K-file   • May incorporate pulp tester DISADVANTAGES   • Requires a dry field   • Patient sensitivity   • Requires calibration   • Requires good contact with lip clip   • Cannot estimate beyond 2 mm   •File should fit snugly in the canal    • File should not contact metal restorations

14. 2. Second-generation apex locator (impedance-based apex locator)/low-frequency apex locator   • Inoue introduced the concept of impedance-based apex locator which measure opposition to flow of alternating current or impedance  • This apex locator indicates the apex when two impedance values approach each other. Examples of second-generation apex locators are:  – Sonoexplorer  – Apex finder    – Exact-A- Pex    – Endoanalyzer (combination of apex locator and pulp tester)

15. ADVANTAGES • Does not require lip clip  • No patient sensitivity  • Analog meter  • Detects perforations  DISADVANTAGES  • No digital read out   • Difficult to operate   • Canal should be free of electroconductive irrigants and tissue fluids   • Requires coated probes

16. 3. Third-generation apex locator/high-frequency apex locator • It is based on the fact that different sites in canal give difference in impedance between high (8 kHz) and low (400 Hz) frequencies Various thirdgeneration apex locators are:  – Endex (Original third-generation apex locator)  – Neosomo ultimo EZ apex locator  – Mark V plus  – Root ZX   – Root ZX II    – Root ZX mini

17. ADVANTAGES  • Easy to operate   • Uses K-type file    • Audible indication   • Can operate in presence of fluids   • Analog read out  DISADVANTAGES  • Requires lip clip  • Chances of short circuit  • Needs fully charged battery  • Must calibrate each canal  • Sensitive to canal fluid level

18. ROOT ZX II 3 rd    Generation apex locator

19. 4. Fourth-generation apex locator   • Fourth-generation EAL measures resistance and capacitance separately rather than the resultant impedance value   • There can be different combination of values of capacitance and resistance that provides the same impedance and the same foraminal reading  • However, by using fourth-generation apex locator, this can be broken down into primary components and measures separately for better accuracy and thus less chances of occurrence of errors     Examples of fourth-generation apex locators are   - AFA apex finder   - i-Pex    -  Rayapex 4

20. The main problem with fourth-generation EALs is that they can perform well in relatively dry canals, so difficult to use in cases of heavy exudates or weeping canals.              AFA Apex fInder 4 th Generation apex locator

21. 5. Fifth-generation EALs (dual-frequency ratio type)  To overcome the disadvantages of previous generations of apex locators, fifth-generation EALs have been developed which are based on comparison of data taken from the electrical characteristic of the canal and additional mathematical processing. These show accurate reading in presence of dry, wet, saline, EDTA, blood, or sodium hypochlorite.      Examples of fifth generation apex locators are            Rayapex             Propex  II            Propex Pixi           I –ROOT 

22.                    JOYPEX 5 5 TH Generation apex locator

23. 6. Sixth-generation EALs (adaptive apex locators)  This apex locator is intended to overcome the disadvantages of fourth- and fifth-generation EALs.  It eliminates the need of drying the canals.   Examples of 6th generation apex locator are        -Adaptive apex locator       - Raypex 6 

24.                     RAYPEX 6 6TH Generation apex locator

25. ADVANTAGES OF APEX LOCATORS  • Provide objective information with high degree of accuracy  • Accurate in reading (90–98% accuracy)  • Some apex locators are also available in combination with pulp tester and can be used to test pulp vitality  DISADVANTAGES OF APEX LOCATORS  • Can provide inaccurate readings in the following cases:  – Presence of pulp tissue in canal  – Too wet or too dry canal  – Blockage of canal  – Incomplete circuit   – Low battery   • Chances of overestimation  • Incorrect readings in teeth with periapical radiolucencies and necrotic pulp associated with root resorption, etc. because of lack of viable periodontal ligament

26. CONCLUSION The electronic apex locators are now considered the most ideal method to measure the working length of a root canal.They can be used alone without the need of radiographs. However , It is recommended combined use of an apex locator along with the radiographic technique for accurate clinical measurement of Root Canal working length

27. Refrences -Text book of Grossman's Endodontic practice (14th Edition) -Text book of Endodontics (by Amit garg and Nisha Garg (4th Edition) -Goldman M,Pearson AH ,Darzenta N .Endodontic success