Working length determination /certified fixed orthodontic courses by Indian dental academy


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Working length determination /certified fixed orthodontic courses by Indian dental academy

  2. 2. Definition Working length is defined in the endodontic Glossary as “the distance from a coronal reference point to the point at which canal preparation and obturation should terminate”. The explicit location of the physiological apex of root canal is a prerequisite for a successful endodontic therapy.
  3. 3.  The anatomic apex is the tip or the end of the root determined morphologically, whereas the radiographic apex is the tip or end of the root determined radiographically. Root morphology and radiographic distortion may cause the location of the radiographic apex to vary from the anatomic apex. The apical foramen is the main apical opening of the root canal. It is frequently eccentrically located away from the anatomic or radiographic apex.
  4. 4.  An accessory foramen is an orifice on the surface of the root communicating with a lateral or accessory. The apical constriction (minor apical diameter) is the apical portion of the root canal having the narrowest diameter. This position may vary but is usually 0.5 to 1.0 mm short of the center of the apical foramen. The cementodentinal junction is the region where the dentin and cementum are united, the point at which the cemental surface terminates at or near the apex of a tooth - histologic landmark. The location of the cementinodentinal junction also ranges from 0.5 to 3.0 mm short of the anatomic apex.
  5. 5. MINOR DIAMETER The apical constriction is the narrowest part of the canal with the smallest diameter of blood supply, thus creating the smallest wound site and best healing condition. This anatomical landmark can be called the minor diameter of the canal. The minor diameter represents the transition between the pulpal and the periodontal tissue, located in the range of 0.5 to 1.0 mm from the external foramen or major diameter on the root surface.
  6. 6. Significance It determines how far into the canal the instruments are placed and worked, It limits the depth to which the canal filling may be placed, It affects the pain & discomfort for the patient, It determines the success of the treatment.
  7. 7. Methods Radiographic methods, • Ingle’s, • Grossman’s • Digital radiography/Xeroradiography Non-radiographic methods, • Digital tactile sense, • Apical Periodontal sensitivity, • Paper Point measurement, • Apex Locators Others.
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  11. 11. Apex Locators In 1918, Custer was the first to report the use of electric current to determine working length. The scientific basis for apex locators originated with research conducted by Suzuki in 1942. in vivo research on dogs using direct current discovered that the electrical resistance between the periodontal ligament and the oral mucosa was a constant value of 6.5 kilo-ohms.
  12. 12.  Sunada adopted the principle reported by Suzuki and was the first to describe the detail of a simple clinical device to measure working length in patients. He used a simple direct current ohmmeter to measure a constant resistance of 6.5 kiloohms between oral mucous membrane and the periodontium regardless of the size or shape of the teeth. The device used by Sunada in his research became the basis for most apex locators.
  13. 13. First-Generation Apex Locators. First-generation apex location devices, also known as resistance apex locators, measure opposition to the flow of direct current or resistance. When the tip of the reamer reaches the apex in the canal, the resistance value is 6.5 kilo-ohms (current 40 mA).
  14. 14. Second-Generation Apex Locators. Second-generation apex locators, also known as impedance apex locators. The major disadvantage of second-generation apex locators is that the root canal has to be reasonably free of electroconductive materials to obtain accurate readings. The presence of tissue and electroconductive irrigants in the canal changes the electrical characteristics and leads to inaccurate, usually shorter measurements.
  15. 15. Third-Generation Apex Locators The principle on which “third-generation” apex locators are based frequency of the electric current. In biologic settings, the reactive component facilitates the flow of alternating current, more for higher than for lower frequencies. Thus, a tissue through which two alternating currents of differing frequencies are flowing will impede the lower-frequency current more than the higher-frequency current.
  16. 16.  The reactive component of the circuit may change, for example, as the position of a file changes in a canal. When this occurs, the impedances offered by the circuit to currents of differing frequencies will change relative to each other. This is the principle on which the operation of the “third- generation” apex locators is based
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