Working Length Determination PDF

‫جامعة التحدي الطبية االهلية‬ ‫كلية طب وجراحة الفم واالسنان‬ WORKING LENGTH DETERMINATION Dr. Mohamed Faisal Lklouk ( BDS - MFDS RCSed ) Working length: Is the length to which the root canal preparation and obturation will terminate. The working length of a tooth is the length between an...

‫جامعة التحدي الطبية االهلية‬ ‫كلية طب وجراحة الفم واالسنان‬ WORKING LENGTH DETERMINATION Dr. Mohamed Faisal Lklouk ( BDS - MFDS RCSed ) Working length: Is the length to which the root canal preparation and obturation will terminate. The working length of a tooth is the length between an external reference point on the crown of the tooth, and the cemento- dentinal junction of the root. CDJ, the apical foramen,( the anatomical apex or the apical constriction) is 0.5 mm to 1 mm shorter than the radiographic apex. Biological rationale for working length: The optimum length is at the apical constriction Establishing a good working length of the tooth is the most important step in cleaning and shaping. It greatly facilitates accurate instrumentation and filling of the root canal. Over instrumentation Over instrumentation results in perforation of the apical foramen. Periapical tissue might become traumatized leading to post treatment inflammation, pain, and swelling. Necrotic material might be forced periapically with acute inflammation. Irrigant solutions or interacanal medicaments may leak through the foramen with subsequent irritation. Filling material may be extruded from the foramen and irritate the periapical tissue. Under instrumentation Instrumentation shorter than the cemento- dentinal junction. LEDGE FORMATION which will catch the instrument Bacteria or necrotic pulp will left beyond this point might case failure Short RC FILLING WITH SUBSEQUENT MICROLEAKAGE WICH MAY LEAD FAILURE Methods of working length determination 1. Average root length from anatomic studies 2. Radiographic method. 3. Electronic apex locator. 4. Tactile sensation. 5. Paper point. 6. Apical Periodontal sensitivity. Radiographic Method Preoperative radiograph 1- The number, size, shape, curvature and angulations of the root(s). 2- Presence of any periapical pathosis and degree of bone and root resorption if present. 3- Root obstructions by pulp stone or obliteration of the root by secondary dentin. 4- Presence of vertical or horizontal roots fracture. 5. Root resorption or immature root and open apex. 6- Old root canals treatment if present. 7- Estimation of the tooth working length. Radiographic Estimation of Working Length The estimated length is the length to which the initial file will be inserted into the canal, and then confirmed by a radiograph. If the estimated length is 21 mm. the stopper must be adjusted on the initial file shaft to be 21 mm away from the file tip, then the file is inserted into the canal and a confirmatory radiograph is taken. Considerations for radiographic estimation of the Working Length 1. Curved canal would indicate that you should place a bend in your instrument. 2. Elongated or shortened required that a new radiograph must be taken. 3. Examine the size and shape of the canals to determine if there is any indication that you might have difficulty getting the instrument to the desired length (1mm shorter than the radiographic apex) as: - very narrow root tip - apical bone &\or root resorption Bone and Root Resorption Normal case: 1mm from the apex Bone only (no root) resorption: 1.5 mm from the apex Bone and root resorption: 2 mm from the apex Selection of initial file for W.L. determination: Multirooted teeth: the canals are usually quite fine and generally a # 10 or 15 file should be used for length determination to prevent ledge of the canal(s). Single rooted teeth: have larger canals than the multirooted teeth. so, it will be possible to use larger file for length determination. In both anterior and posterior teeth the instrument of choice should be the instrument that would fit to the desired estimated length snugly enough to prevent it from dropping out. If the clinician use small instruments that are loose in the canal for length determination the following might result: a- the file might fall completely out of the canal. b- might slip partially out of the canal. Selection of the external reference point 1. In anterior teeth a incisal edge. In posterior teeth a cusp tip for each canal 2. Reference point should be easily checked. 3. It should be in sound tooth structure. 4. Avoid inclined planes as a reference point. 5. The file stopper must be rested in a straight position on the reference point. 6. If the canal is curved, a bend should be placed in the end of the file, and it should be placed after the stopper has been placed and the distance has been set. Initial radiograph with file in the canal Three possibilities may be faced at this step 1. The file tip is just on the cemento- dentinal junction (1mm shorter than the radiograph apex) 2-The file tip is at the radiographic apex or longer 3-The file tip is shorter than the radiographic apex by more than one millimeter. Confirming working length of tooth: 1.Reset the stop to the new estimated length. 2.Reinsert the file into the canal as done before to its new estimated length. 3.Take a new radiograph to confirm the length. 4.Examine the new radiograph to determine if the correct working length of tooth has been reached (just to the cemento-dentinal junction). If this length has been reached that is it, and this length should be recorded in the patient chart. 5.If the working length of tooth has not yet been reached, additional adjustment of the length must be done, until working length of tooth is reached and confirmed. Disadvantages of the radiographic method Health hazards The film reveals only 2-dimension picture for three dimensional object. This may lead to superimposition of root canals over each other in the radiograph, which may lead to inaccurate working length determination. Hence there was a need to develop a radiographic technique that can overcome this disadvantage which is called the buccal objective rule ( changing horizontal angulation ) OR (Tube-Shift). Tube-Shift Localization Clark’s SLOB Rule (Same Lingual Opposite Buccal) The SLOB rule is used to identify the buccal or lingual location of objects (impacted teeth, root canals, etc.) in relation to a reference object (usually a tooth). If the image of an object moves mesially when the tube head is moved mesially (Same direction), the object is located on the Lingual. If the image moves distally when the tube head moves mesially, the is located on the Buccal. Electronic apex locators 1. Determination of the working length 2. Avoid the hazards of exposure to multiple x-ray doses All apex locators function by using the human body to complete an electrical circuit. One side of the apex locator’s circuitry is connected to the patient’s body either by a contact to the patient’s lip or by an electrode held in the patient’s hand. The electrical circuit is complete when the endodontic instrument is advanced apically inside the canal until it touches the periodontal tissues. The display on the apex locator indicates that the apical area has been reached. Classification and Accuracy of Apex Locators Based on : 1. Type of current flow 2. Opposition to the current flow 3. Number of frequencies involved First-Generation Apex Locator: ( resistance apex locators) It 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). It had some problems. Today, most first-generation apex location devices are off the market. Second-Generation: (impedance apex locators) They measure opposition to the flow of alternating current or the impedance. 1.Sono-Explorer, one of the earliest of the second-generation apex locators. 2.The Digipex has a visual LED digital indicator and an audible indicator. 3.The Digipex II is a combination of apex locator and pulp vitality tester. 4.The Exact-A-Pex has an LED bar graph display and an audio indicator. 5.The Foramatron IV has a flashing LED light and a digital LED display. 6.The Apex Finder has a visual digital LED indicator. 7.The Endo Analyzer is a combined apex locator and pulp tester. Disadvantage of first & second generation apex- locators is that: 1.The root canal has to be free of Electroconductive materials to obtain accurate readings. 2.The presence of tissue and electroconductive irrigants changes the electrical characteristics and leads to inaccurate,( usually shorter measurements). 3.This created a Question : Should canals be cleaned and dried to measure working length, or should working length be measured to clean and dry canals? 3 rd generation apex locators (Frequency apex locators) OR (Comparative impedance apex locators): The 3 generation apex locator is based on the fact that, the reactive rd biologic components facilitates the flow of alternating current but more for the higher frequency current than for the low frequency current. The reactive component of the circuit may change ( e.g. as when the position of the file change in the canal ), so the impedances offered by the circuit to currents of different frequencies will change relative to each other and this is the principle on which the operation of the third generation apex locator is based. The 3rd generation apex locator need the canal to be flooded with electrolyte (saline or sodium hypochlorite ). As the instument is advanced apically, the difference in impedance values at the two frequencies ( 5 & 1 KHz ) is increased and reaches the maximum at the apex where an audio alarm is also heared. Combination of Apex Locator and Endodontic Handpiece has 3 automatic safety mechanisms: 1.Auto start – stop. 2.Auto torque reverse. 3.Auto apical reverse. Other uses of apex locators Detect root perforation. Detect ext. & int. root perforating resorption & pin and post perforations. Detect incomplete root formation. Contraindications of apex locators: Patients with cardiac pacemaker as in case of electric pulp tester and electrosurgical instruments. Limitations of apex locators: -In conjunction with radiograph, the apex locator is an effective method of determining the working length of tooth, but not as a sole method of working length determination. - These devices are most helpful in placing the first length determination file and it can guide the clinicians to develop his own tactile sense. - The early devices were inaccurate under certain circumstances, it had the disadvantage that if there is any periapical pathosis or when the canal is not completely dry it might lead to false reading. - More advanced devices could be helpful under these circumstances, but still cannot be the sole method on which one can rely in length determination. 3- Digital tactile sensation method This method is ineffective in case of : 1- immature apex 2- excessive root curvature 3- constricted canals throughout its course 4- Paper Point Method Can be used In: 1- A root canal with an immature (wide open) apex. 2- Apical root resorption. # After profound anesthesia has been achieved, gently pass the blunt end of a paper point into the canal. The moisture or blood on the portion of the paper point that passes beyond the apex may be an estimation of working length 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 is overextended. This paper point method is a supplementary one. 5- Apical Periodontal sensitivity method Any method of working length determination, based on the patient’s response to pain, does not meet the ideal method of determining working length. Working length determination should be painless. If an instrument is advanced in the canal toward inflamed tissue, the hydrostatic pressure developed inside the canal may cause moderate to severe pain. At the onset of the pain, the instrument tip may still be several millimeters short of the apical constriction. When the canal contents are totally necrotic however, the passage of an instrument past the apical constriction may evoke only a mild or possibly no reaction at all. This is common when a periradicular lesion is present because the tissue is not richly innervated.