Working Length Determination (PDF)

Objectives And Principles Of Intraradicular Cavity Preparation: Obtaining Working Length BDS8128 Date : xx / xx / xxxx Aims: The educational aims of this lecture are to explain the importance of obtaining working length in root canal preparation Objectives: On completion of this lecture, the stud...

Objectives And Principles Of Intraradicular Cavity Preparation: Obtaining Working Length BDS8128 Date : xx / xx / xxxx Aims: The educational aims of this lecture are to explain the importance of obtaining working length in root canal preparation Objectives: On completion of this lecture, the student should have an understanding of the optimal working length and different methods of obtaining it 1. Entry into R.C.S. 2. Prepation of shape that is easy to fill. 3. Proper obturation The primary objectives of cleaning and shaping are: 1-Remove the infected soft and hard tissue. 2-Give the disinfecting irrigant access to the apical canal space. 3-Create space for the delivery of medicaments and subsequent obturation. 4-Retain the integrity of radicular structures. Cleaning: Is the removal of all potential irritants from the root canal . This includes: 1- Infected material. 2- Organic remenants. 3- Microbes. The goal is achieved through Proper Instrumentation. Use Of Irrigants. Where it dissolute & detoxify debris Where Instruments Physically Remove Substance Inside The Canal Shaping: • Refers to the specific shape given to the canal, which is a continuously tapered from the canal orifice to the apical constriction Compatible with the filling material and techniques. Biological objectives for cleaning & shaping:  Totally clean root canal system of arganic and inorganic debris.  Avoid pushing debris beyond the apex.  Confine all your instrument within the root canal space.  Do no harm to the tooth or periodontium Mechanical objectives for cleaning & shaping:  Develop a continuous tapering conical form, from the canal orifice to the apical foramen.  Make the canal narrower apically with the narrowest cross section diameter at its terminus.  Preserve the natural curve, cross section & taper of the canal.  Preserve the apical foramen (Never transport foramen).  Creation of an apical stop. Mechanical objectives for cleaning & shaping: Use of a large or stiff instrument in a curved canal Zipping Apical Transportation Apical Perforation Principles Of Intraradicular Cavity Preparation (G.V black) 1. 2. 3. 4. Irrigation. Resistance form. Retention form. Extension for prevention. Resistance form This is achieved by enlarging the apical terminus of the canal while preserving the apical constriction Retention form This is achieved by enlarging the apical terminus so that the canal walls are parallel retaining the round cross section of the apical part of the canal Extension for prevention Extension of the preparation through the entire length and breadth. This is done by adjusting the proper working length and preparing all the canal walls circumferentially Resistance form Retention form How to determine ? The first step in cleaning & shaping is the determination of the working length  Working Length : It is measured from the reference point coronally till the apical constriction apically  Significance of working length determination: • Determines the instrument length in the canal. • Limits the depth to which the canal filling may be placed. • Limits postoperative pain & discomfort. Working length determination A. Landmarks Radiographic apex Apical constriction ( minor diameter): Apical portion of the canal having the narrowest diameter. It is usually placed 0.5- 1 mm short of the radiographic apex. Minor diameter widens apically to the apical foramen (major diameter). Cementodentinal junction (CDJ): The point at which the dentin and cementum unite (it doesn’t always coincide with the apical constriction). Radiographic apex: tip of the root determined radiographically (it doesn’t always coincide with the apical foramen in curved canals The optimum length is cleaning until the constriction. A. Landmarks Stopper Reference point File Reference point: it is the site on the incisal edge or the occlusal surface from which measurements are made. Working length determination B. Definitions Tooth length: length from reference point to radiographic apex. Instrumentation short of the apical constriction: 1- Improper cleaning and persistent infection. 2- Ledge formation & short filling leading to failure. Instrumentation beyond the apical constriction: 1- Irritation of the periapical tissues by instruments and filling materials. 2- Inability to compact the root canal filling materials. 3- Severe postoperative pain. Methods For Tooth Length Determination Methods For Tooth Length Determination include: • Radiographic method : (Ingle method) • Electronic Apex Locators • Tactile Sense • Paper Point. 1. Radiographic method ( Ingle method): The file is inserted to the estimated working length (EWL), which is determined by: a) Average length of the tooth. b) Preoperative radiograph. c) Tactile sensation. 1) Instruments: Steps of Ingle’s method: AWL 1) Initial measurement 23 -2 2) Radiographing 3 Possibilities for adjustment 3) Set instruments on AWL 21 flushing 19 +2 Variation in the position of the apical constriction in relation to the radiographic apex (weine modification) SLOB  Buccal object rule for tooth length determination for teeth having multiple overlapping canals.  This rule states that the most distant object from the cone moves towards the direction of the cone (Same Lingual Opposite Buccal) Limitations of Radiograph: 1. Two-dimensional image for a three-dimensional object. 2. Super imposition of anatomic structures. 3. Procedural errors during imaging & processing 4. Radiation hazards. 5. Difficult film placement in patients with high gagging sensation. 6. Time consuming. 7. Limited ability for proper determination of anatomic apex. 2. Electronic apex locator:  Electronic devices have been designed to determine the canal length , by reading the file tip at the apical foramen, as it has reached vital tissue. The principle is based on electrical resistance of different tissues, when circuit is complete resistance decreases & current begins to flow. 1-Oral soft tissues conduct electricity easily while hard tissues act as an insulator. 2-Apex locators have two electrodes, one touches the patient’s oral mucosa, while the second is connected to a file and introduced inside the root canal. 3-By passing the file inside the canal , a very small current exits between the 2 electrodes. (very high resistance) 4-The resistance decreases as the instrument moves down the canal and finally dropping as the file approaches the periapical tissues. This might be signaled according to the device by :  A beep or buzz A flashing light. A digital read out. Electronic apex locators: • Locates the minor diameter of the foramen ,end point of dentin. • Not affected by the presence of soft tissue fluids. • Minimizes radiation exposure. • Shortens the preparation time . • Affordable, accurate , painless and safe. • When the radiographic image of the root apices is unclear. • In case of suspected root perforation • For quick check of the working length during preparation phase. 3-Tactile Method: Some clinicians claim that it is possible to gauge the apical constriction of the root-canal system by tactile sense. There are several problems regarding this method: 1-First, not all teeth have an apical constriction due to the presence of apical resorption caused by apical periodontitis . 2-Ineffective in root canals with immature apex. 3- Inaccurate if the canal is constricted or when curvature is present. 4- The tactile detection of the apical constriction relies upon the selection of a file size that will first bind only at the apical constriction. 4-Paper Point Method: Another recommended method is the use of a sequence of paper points that show the position of the apical foramen. Mainly used in cases of canals with immature apex. However, it is unreliable by itself because of seepage of exudate or blood into the canal and by capillary action along the paper in case of inflammation . Combined methods for determining position of canal terminus Instrumentation Motions Basic Hand Files Motions 1)Linear motion: (Filing motion) • Push & Pull action against dentin wall. • Any type of file can do this action, but the best one is (H-file). • It is recommended for coronal 2/3 flaring. (Circumferential Filing) Rotation Motion: (Apical third preparation) 2) Reaming Motion: – Rotational motion in clockwise direction. Insertion- Rotation- Retraction (90-180) – Reamers & K- files are suitable for this motion. – It leads to formation of round cross section preparation to best fit master cone. 3) Quarter Turn & Pull Motion: – Combination of filing & reaming action. – It occurs by passive insertion of file, then apply quarter turn clockwise then pull. 4) Watch Winding Motion: – Suitable for Reamers & K-files. – Instrument inserted in the canal to desired length by clockwise/counterclockwise rotation of file. – Back & forth oscillation of a file through 30° - 60° of rotation – It is the motion used in the preparation of the apical part of the canal to preserve the round cross section. Watch Winding Motion Linear motion: (Filing motion) (Circumferential Filing) Aims: The educational aims of this lecture are to explain the importance of obtaining working length in root canal preparation Objectives: On completion of this lecture, the student should have an understanding of the optimal working length and different methods of obtaining it Reading material: -The dental reference manual, Geraldine M. Weinstein, springer 2017 (Chapter 12) -Essential skills for dentists, Peter A.Mossey et al, Oxford, 2006 (Chapter 2.6) -Endodontics, Kishor Gulabivala and Yuan-Ling NG, Mosby Elsevier 2014 -Harty`s endodontics in clinical practice, Bun San Chong, Elsevier 2017 -Clinical endodontics, Lief Tronstad, Thieme 2009 (main reference) Thank you Date : xx / xx / xxxx