Endodontic Instruments PDF

ENDODONTIC INSTRUMENTS CLASSIFICATION: 1. Diagnostic instruments: a. Visual Aids: include mirror and probe, trans-illumination, magnifying loops and surgical microscopes. b. Radiographic examination. c. Vitality Testing: Thermal pulp testing and Electrical pulp testing. 2. Isolating instruments. (Rubber dam) 3. Access cavity instruments 4. Working length instruments 5. Intra radicular instruments a. Extirpating. b. Exploring. c. Enlarging d. Obturating 6. Miscellaneous ISO GROUPING 1. Group I: Hand use only 2. Group II: Engine-driven latch type 3. Group III: Root canal points: gutta-percha, silver, 39 Diagnostic instruments: 1. Basic diagnostic tools: a. Mirror b. Endodontic prob and Periodontal prob. c. Tweezers. 2. Visual aids: a. Magnifying loops 2-6X b. Surgical telescope and Endoscope c. Dental operating microscope: (D.O.M.) 2-20X. d. Trans illumination: fiber optic high intensity to detect cracks and teeth crazing. 3. Sensitivity testing for pulpal tissue: a. Thermal sensitivity test: both hot and cold tools can be used for testing pulpal sensitivity (e.g.) hot gutta percha rods and cold anesthesia carpules. b. Electric pulp sensitivity testing: electric rod placed on the mid-facial region of the tooth to check current circuit presence. 4. Vitality testing of pulpal tissue: a. Laser Doppler flowmetry: records blood flow b. Pulse Oximetry: records oxygen saturation in RBCs. 5. Radio graphs: a. Plain R.G. and Digital R.G.: (Digora and Radio-Visio graph) b. 3 Dimensional imaging: i. Computed tomography scans. ii. Cone beam computed tomographic scans. 40 Isolating instruments: o Rubber dam 1. The patients are protected from the ingestion or aspiration of small instruments, dental fragments, irrigating solutions. 2. The opportunity to operate in a clean surgical field. 3. Retraction and protection of the soft tissues from the cutting action of the bur. 4. Better visibility. 5. Reduction of delays. Fig 1: Rubber Dam kit for endodontic use. Access cavity instruments: o Burs: Straight or tapered fissure burs (no. 557 or 701) and long shanked round burs (no.2, 4,6 and 8) for the preparation of the access cavity. 41 o Other stones were invented specially for the endodontic access cavity which is the Endo-Z bur (or stone) and the Martin access stone (endo access bur) Fig 2: Endo-Z bur Working length determination instruments: o Radio graph and files (ingles method) o Electronic apex locators. TRAY INSTRUMENT Endodontic instrument tray is a typical tray instruments already familiar in operative dentistry, however, many instruments have been specially adapted for endodontic use. Plastic instrument: The blade like end of this instrument is used to carry and place temporary filling materials. The opposite end is used as a plugger to condense filling material in the pulp chamber. 42 Locking pliers: For the handling of the absorbent paper points and filling materials. Locking pliers Endodontic explorer: The straight end is extra-sharp and long tipped to facilitate locating canal orifices. The L-shaped end aids in detecting unremoved portions of the pulp chamber. Endodontic explorer Spoon excavator: Extra-length, double-ended spoon excavator designed for endodontics, used for removal of caries, coronal pulp tissues and cotton pellets in the pulp chamber. Spoon excavator 43 Endodontic ruler: A ruler (half-millimeter increments) is used to measure intra-canal instruments and gutta percha. Endodontic ruler Endodontic syringes: is used for irrigation of the root canal. The needle tip is flat to prevent penetration into the smaller diameter canal orifices. Mosquito hemostat: Is included in the kit as an aid in holding radiographic films in the mouth. 44 INTRACANAL INSTRUMENTS Intra radicular instruments Intra canal instruments can be classified into: According to material of construction: 1. Carbon steel: very high cutting efficiency but very low corrosion resistance. 2. Stainless steel: medium cutting efficiency with higher corrosive resistance 3. Nickel titanium: a. Super elastic property (highest flexibility) b. Exotic metal doesn’t apply to the laws of metallurgy. c. Least cutting efficiency. 4. Diamond: abrasives diamond. According to use: 1. Exploring 2. Extirpating 3. Enlarging 4. Obturating According to energy supply 1. Hand driven instruments 2. Engine driven instruments a. Rotary instruments b. Vibratory instruments According to American dental association: 1. Group I: Hand use only 2. Group II: Engine driven instruments 3. Group III: Sonic and Ultra sonic devices 4. Group IV: Root canal points (Gutta percha points and paper points). 45 According to manufacturing technique: 1. Milling 2. Twisting 3. Stamping Extirpating instruments: Extirpation is the removal of vital pulp tissue as a whole; in one piece. Best instrument to extirpate is the Barbed (nerve) broach. Endodontic cutting files can also be used in extirpation and removal of pulp tissue from within the canal. Broaches are made from tapered soft steel shafts in a graduated series of sizes. Notching the shaft along its working length makes the small sharp barbs that are used in engaging the pulp and removing it. It also tends to weaken the shaft and so the instrument should never be forced into the canal otherwise the shaft may break. Since the barbs are inclined toward the handle of the instrument they resist withdrawal of the instrument when it is in tight contact with dentin. Force placed on the barbs can cause them to bend back and embed further into the dentin, so that even if the shaft can be removed intact, some of the barbs may break off in the dentin. The barbed broach is inserted into the canal until light contact is made and then withdrawn slightly. Then the instrument is rotated slightly to engage the soft tissue and withdrawn completely from the canal. It can also be useful for removing medicated cotton pellets from the pulp 46 chambers. Since the instruments are manufactured in a graduated series according to size, select a size smaller than the diameter of the canal. In very fine canals, especially premolars and molars; barbed broaches should not be used at all. Exploring instruments: They are instruments that are designed to explore and search for canal’s orifices in the pulp chamber’s floor after de-roofing. 1. Endodontic explorer 2. Smooth broach 3. Ultra sonics 4. Micro opener: (hand held K-file tip) 5. Microdebrider: (hand held H-file tip) Both are made of a stiffer material to help search for canal’s orifices. 47 fig : micro opener, micro debrider, endodontic explorer, smooth broach and ultra sonic tips used as exploration instruments. Enlarging instruments: 1. Reamers: Reamers are tapered, fluted intra-canal instruments that shave dentin when the sharp blades are rotated clockwise in the canal. Reamers are manufactured by pulling and twisting of a triangular cross sectional metal wire. The twisted metal then produces the flutes. The numbers of flutes twisted in the instrument are carefully controlled. Reamers generally have ½ to 1 flute per millimeter. The triangular shape blade with its acute angle results in a sharper blade than instruments made from square blanks. It a helical angle (the angle between the cutting 48 0 edge of the flute and the long axis of the instrument) 20 , this gives a general idea of the Fig: Reamer 2. Files: The most common types of files are the (k) type files, so called for the kerr manufacturing company that originally produced the instrument, and the (H) hedstrom file. These files act by scraping dentin from the walls of the canal in a rasping action. A reaming action can also be accomplished by slightly rotating the instrument. a) K - type file K-files are made in the same manner as the K-reamers. In general, the blade is ground into a square tapered blank cross sectional metal before the flutes are twisted. The square stock leaves more metal in the blade diameter resulting in a stronger instrument than blades twisted from triangular blanks but with lower flexibility. The cutting edge of the 90 blank is inherently less sharp than the more acute angles formed by the triangular blade. In the larger diameter files, some manufacturers use triangular blank because the flutes may be more readily twisted from that form. Files usually have 1 ½ to 2 ¼ flutes per millimeter. Fig: K- File 49 b) Hedstrom file: Hedstrom files are made by machine grinding the flutes into the metal stock. The flutes are formed into successively larger cones from the tip of the working blade to the handle, which remove dentin more efficiently than the k type file. The shaft of the Hedstrom file is weakened at the points where the metal is removed. For this reason the Hedstrom file must be used with a great care. It cuts only on the withdrawal stroke and should never be used in a reaming movement. H-File 50 STANDARDIZATION OF ROOT CANAL INSTRUMETS The intra-canal instruments until recently were not standardized in sizes or shape and the numbering system among manufacturers had no uniformity with regard to the diameter or taper of the working blade. Sizes were loosely numbered from one to twelve. Cleansing and shaping a canal accurately with instrument was difficult because the graduation from one diameter to the next were inaccurate. Under the direction of John Ingle, the standardization was accomplished by the following: 1. The working blade of any given instrument is 16 mm in length. 2. D 0: It is the diameter at a point where the instrument blades begin at the tip of the instrument and is measured in millimeters. 3. D16: is a point at which the working blades terminated and which is 16 mm from point D 0. Further more, point D16 is 0.32 mm greater in diameter than D 0. Thus by standardizing the length of the cutting blade and also the increase in diameter from D0 to D16 the taper from one millimeter to the next was uniform and depend on the following formula. D 16-D 0/ Length between D 0 and D 16 = 0.32 mm/16.0 mm = 0.02 mm/mm. Dimensional formula of files and reamers: D=diameter So, the taper of any given instrument is increased by 0.02 mm in diameter per each mm of length. 51 The instruments are numbered according to the diameter D 0 in mm x 100 e.g. if the diameter at D 0 is 0.30 mm the number given to the instrument is 30. The progressive increase in size from one instrument to the next is to be (transition between instruments): 0.02 mm. for sizes 6, 8, and 10, 0.05 mm from size 10 to size 60, 0.1 mm from size 60 to size 140. Standardized dimensions of root canal files and reamers were established by the ISO: 1. Tip. 2. Length of the blade 3. Taper. 4. Size. 5. Number. (of the same instrument) 6. Gradual increase in size. 7. Color Coding. (Of different instruments) Tip: Pointed (acute angle) 75 degrees ± 15 degrees. Length of blade: 16 mm Taper: D 16-D 0/ Length between D 0 and D 16 = = 0.02mm/mm Size: Diameter at D0 in mm. Number: Diameter at D0 × 100 Increase in size and Color-coding: listed in the following table. Accordingly, the number of each instrument can be indicated in a variety of ways: Metal handles may have the number inscribed on the end. While plastic handles are color coded in series. The color code is shown in the following table and should be memorized. 52 Standardized Diameter in hundredths of mm Color number D-0 D-16 6 Orange 0.06 0.38 8 Silver 0.08 0.40 10 Purple 0.10 0.42 15 White 0.15 0.47 20 Yellow 0.20 0.52 25 Red 0.25 0.57 30 Blue 0.30 0.62 35 Green 0.35 0.67 40 Black 0.40 0.72 45 White 0.45 0.77 50 Yellow 0.50 0.82 55 Red 0.55 0.87 60 Blue 0.60 0.92 70 Green 0.70 1.02 80 Black 0.80 1.12 90 White 0.90 1.22 100 Yellow 1.00 1.32 110 Red 1.10 1.42 120 Blue 1.20 1.52 130 Green 1.30 1.62 140 black 1.40 1.72 Handle style: 1. Style (D) long handled: i) They can be used only on maxillary anterior teeth. ii) It is not frequently used nowadays. 2. Style (B) short handled: i) Are made on metal or plastic handles ii) Handle configurations vary from a manufacturer to the other. 3. The measurement controls handle or test handle: It is fitted with a chuck that allows the operator to adjust length of blade projecting from the handle. 53 Length of the blade Files and reamers are made in a variety of lengths. The working part of the blade remains fixed (16 mm. in length) while the length of the instrument from D-16 to the beginning of the handle varies. The 31mm; length instrument is required for some maxillary canines and the shorter instruments are useful in molar areas where access is a problem. The most commonly used lengths are 21mm., 25 mm., 28 mm, and 31mm. instruments, when one considers the average length of teeth. Different length instruments Instruments stops: The importance of instrumentation to a known canal length has been stressed and there are several ways of marking instruments. They can be marked very simply by: 1. Using marking paste (a mixture of petroleum jelly and zinc oxide), which can be wiped off easily. So this method is not used today. 2. Either silicone or small rubber discs can be used as a stops some are teardrop in shape, with the point providing a reference guide for the 54 reinsertion of the instrument the same way each time, especially in teeth with curved canals. 3. A metal stop, which has the advantage that the stop fit the shaft accurately and firmly. 4. Test handle system consists of a handle marked in millimeters, which accepts special reamers and files of various sizes. The handle can be tightened so that the working part is clamped at a predetermined length. Different types of stops INSTRUMENTS USED FOR OBTURATION OF ROOT CANAL: Spreaders and Pluggers: The final stage of endodontic treatment is filling (obturation) of the canal with different materials. Gutta percha, is one of the most acceptable materials for filling root canals. It must be condensed into the root canal to fill the space completely. For this purpose, instruments called spreaders or pluggers are used. 55 1. Spreaders: Spreaders are long tapered instruments used to compress the filling material laterally against the canal walls. The spreader is then withdrawn and a cone of gutta percha is inserted into the space created by the spreader point. Finger Spreader Spreaders have a spear or rounded point-tip so they can be pressed deeply into the canal. Some spreaders are made with long handles but they are difficult to use in posterior teeth and for this reason; short handled (finger) spreaders are made for condensing filling material where limited access is present. Finger spreaders come in variety of sizes as indicated by the color coding of the instrument and / or the number written to the handle. 2. Pluggers: For filling techniques requiring a vertical condensation rather than lateral condensation, root canal pluggers are used. The working tip of root canal plugger is flat rather than having a pointed blade like a spreader to compress the gutta percha mass apically during the filling procedure. Like spreaders, they are supplied in long handled instruments or short handled (finger) pluggers, and represent a variety of sizes. 56 a b a: finger plugger, b: hand plugger (p) and spreader (s) 3. Lentulo spiral filler: These instruments are normally made from fine wire, which is twisted to form a tapered spiral, and attached to a bur shank. They are used to fill a root canal with paste medicament or with root canal sealer and they do this very efficiently in clockwise direction. However, when engine operated, they are dangerous because they are liable to fracture if they are wedged into the canal. Rotary Lentulo spiral Hand Lentulo spiral Modification of Intra-canal Cleaning and Shaping Instruments There are two major modifications: o Increase the file flexibility by change the file metals o Increase the file flexibility and cutting efficiency by change in file design (Hybrid instrument design). 57 Increase the flexibility by change in file metals: Since the introduction of Nitinol, which is a nickel-titanium alloy (NiTi), there are great advantages in the file flexibility 1. NiTi alloy has a very low modulus of elasticity. 2. NiTi files have 2-3 times elastic flexibility more than St.St. Files. This extraordinary flexibility allow the file to retain their curved shape rather than tending to straighten it self. 3. It also has a superior resistance to fracture in either clock wise or counter clockwise torsion. 4. NiTi files suffer no deformation where as Stainless steel files undergo permanent deformation between 30-40 degrees. 5. On the other hand, the cutting efficiency of NiTi files is only about 60% that of matching St.St. file. Modification of file design (Hybrid instruments): o Include: 1. Manufacturing. 2. Cross Section. 3. Tip design. 4. Length of cutting blade. 5. Depth and angel of blades. 6. Shaft design 7. Taper. 8. Numbering. 9. Flexibility. 58 1- Modification in Manufacturing: By Twisting: as K file or By milling: as Flex - R file. 2- Modification in cross section: Changes in instrument cross section; not only improve cutting ability, but also enhance flexibility by reducing the thickness of instrument along the cutting blade. There are different cross-sectional shapes for root canal cleaning and shaping instruments. They may be Square (K file), Triangular (Flexofile & Flex-R file), Rhomboid or Diamond (K flex file), Tear drop ( hedstrom file), or S-shaped (Unifile & S- file). The square blank produces the most rigid instrument; the triangular shape is more flexible while the rhomboid is the most flexible. The acute angle formed by the 2 high flutes of the diamond (rhomboid) shape in K- flex file increased sharpness and cutting efficiency. While the obtuse angle formed by the low flutes producing more area for increased debris removal.. Square C.S. Triangular C.S. 59 . Diamond C.S of K- flex file H-style file (note the Unifile Tear drop cross section (Upward) S-shape cross section 3- Modification in Tip Design: Altering the instrument tip from cutting aggressive tip to modified pilot non cutting tip permits the ability to enlarge a curved canal even along its inside wall completely to the apex without changing its original curvature Thus canal transportation, ledging, zipping and perforations will be minimized. As in Flex-R file, Uni file, A-file, Safety H-file and Canal Master system. 60 C A: H-file B: Safety H-file.C: modified non-cutting tip. 4- Modification in cutting blade: a) Length of cutting blade Another recent modification in instrument’s design depends on the cutting segment (cutting head) of the instrument and its blade. The cutting head is reduced from the standard length of 16 mm to 0.25 - 4 mm in some instruments. This effective, short, cutting blade enables the endodontist to feel the exact position and severity of canal curvature with better control, prevents instrument screw down the canal and reduces stresses on the instrument and the root. As in LightSpeed, Flexogates, and Canal Master instruments Short cutting head 61 b) Non cutting side of the blade This modification depends on presence of non-cutting side in the instrument blade to prevent stripping perforation in curved canal. This instrument has also non-cutting edge to prevent ledging in curved canal a b a: conventional H-file b: non cutting side H-file 5- Modification in depth /angle of blade: This modification depends on the steeper depth of the flutes by reducing the helical angle of the cutting blades from 70º in standardized instruments to 40º to cut more efficiently than the standardized one (A- file).The main advantage of this file is its use in curved canal because: 1 - The steep blades on the inner wall collapse and thus loose much of their cutting efficiency. 2- The blades on the external wall open up and more aggressively attack the dentin surface. 3- A non-cutting tip on the instrument also insures that the tip will follow the canal lumen and will not catch in the convex outer wall, starting a ledge or worth a perforation. H-file A-file 62 Difference in blade angle of standard Hedstrom file (left) with sharpened cutting tip, compared to steeper angle of blades of A file (right) a modified Hedstrom instrument. Note non-cutting tip. Hedstrom modified Hedstrom Action of standard hedstrom file vs. new A file in curved canal: A- on withdrawal, H file presents positive cutting action on internal wall of canal (arrows) where stripping perforation frequently occur, where as sharp tip tends to gouge and ledge into external wall. B- A file with very positive cutting angle blades is more aggressive on external wall (arrows) and less aggressive on internal wall owing to collapse of cutting blades. Non-cutting tip follows lumen without gouging or ledging. 6- Modification in Shaft design: Recently a smooth, flexible, non-cutting, taper-less shaft has been advocated for instrument’s design with its diameter is reduced to be smaller than that of the cutting head. This shaft design will increase its flexibility, maintain the original canal curvature, and provide a greater resistance to instrument fracture or separation. Additionally it leaves more room for debris and so the incidence of canal blockage is reduced. (e.g.) LigthSpeed and Canal Master instruments. 63 7- Modification in instrument taper: One of the recent advances in technology is the ability to manufacture endodontic files with increasing their tapering degree to have 4 %, 6%, 8% and may reach to 12% taper compared to 2 % taper of conventional endodontic instruments. The increase in taper has the following advantages: a) Allows the smaller files to function under reduced stress. b) Improves the tactile sensation at working length. c) Allows the file tip to act as a guide and prevent instrument binding at the tip. d) Allows greater coronal flaring e) The steeper angle of root canal instrument allows ample irrigation due to deep penetration of irrigating syringe into the canal. Finally, the greater taper of the instrument making the area of Variable VariableTapers Variable Tapers Tapers contact with the canal walls small, and therefore the contact pressure is Variable Tapers high and this gives the instrument greater cutting effectiveness. P R O F IL E O.S. : Angle T aper from 5 to 8% P RPORFOFIL ILE E O O.S.S. :. : Angle T aper from Angle T aper 5-8%from 5 to 8% 5 to 8% from 5 to 8% P R O F IL E O.SAngle. : Angle T taper aper P R O F IL E 0.6 : Angle T aper 6% PPRPRO FF IL ROOF ILILEEEAngle 0.6 : Angle T 0.6 0.6 :taper A ngle : Angle T 6% 6% T aper aper 6%6% aper P RPORFOILF IL E E 0.4 : Angle T 0.4 Angle : Angle T taper 4% aper aper 4% 4% P RPO F ILILEE 0.4 : Angle T R OF 4%4% aper 0.4 : A ngle T aper ISISO IS O Sstandard tandardAngle OS tandard taper : Angle T : Angle T 2%2% aper aper 2% IS O S tandard : A ngle T aper 2%2% Variable Tapers of endodontic IS O S tandard : Angle Tfiles aper 64 8- Modification in instrument Numbering system: A number of manufacturers have issued half sizes or intermediate sizes which named as "Golden medium sizes" as 12.5, 17.5, 22.5, 27.5, 32.5 and so on, to be used in shaping of extremely fine canals with less possibility of change canal curvature , ledge formation, and perforation. 9-Modification in instrument Flexibility: This involves modification in the material, modification in cross section, and modification in shaft design. ENGINE- DRIVEN INSTRUMENTS Engine driven instruments can be used in three types of contra angle hand pieces: a) A full rotary hand piece, either latch or friction grip type. b) A reciprocal quarter turn hand piece. c) A vertical strokes hand piece that imparts a vertical stroke but with an added reciprocating quarter turn. d) Sonic and Ultrasonic hand piece Rotary contra- angle hand piece instruments: Instrumentation with a full rotary hand piece is by straight – line drilling or side cutting. Special drills or reamers may be used to funnel out orifices for easier access, flare the coronal two third of the canal, or to prepare post space for final restoration of the tooth. Since most of these instruments do not bend, they should primarily be used in perfectly straight canals to avoid perforation of the canal. Used with Gates-Glidden drills, Pesso reamer, Canal Master, Orifice opener, and Rotary H type, U-type and K-type instrument. 65 Disadvantages of rotary instruments: 1. Loss of tactile sense 2. Ledge formation in curved canals 3. Perforation in curved canals 4. Instrument separation rate higher than hand driven instruments. A- Gates- Glidden drill: Gates Glidden (G.G.) drills are used for both initial opening of the canal orifices and deeper penetration in both straight and curved canals. They come in sizes 1 to 6 (50-70-90-110-130-150 #k sizes). B- Pesso reamer: 1- It is the most often used instruments in preparing the coronal portion of the root canal. 2- It is also used in preparing post channel preparation. 3- Safe ended Pesso reamer should be used to prevent lateral perforation. A: Gates-Glidden drill.B: Pesso reamer C- Orifice opener: It is more flexible than the G.G. but it is recommended to be used only in the straight portion of the canal. Orifice opener instruments come in sizes 25-70. They are used to create a funnel shaped opening into the root canal and to widen the coronal one third of the canal. So, canal opening is more easily located each time during the instrumentation phase. 66 Canal opening is easily located during the instrumentation phase. Funnel shaped orifice is even more important during the filling phase to prevent the fine tip of gutta percha cone to hit the pulpal floor, bent and fold back upon itself and the final root canal filling would then be short. D- Rotary H type, U-type and K-type instrument: 1. These types of file are designed to be used with rotary contra-angle. 2. Some types as LightSpeed, ProFile, Protaper, GT Rotary files, K3 rotary, Hero-642, ….. are made from nickel titanium alloy to increase flexibility and decrease the risk of instrument fracture during preparation. LightSpeed System 67 ProTaper system II-Reciprocating handpiece: 1- As Giromatic handpiece which accept only latch type instruments. 2- It makes a quarter turn motion about 3000 RPM which contra rotates the instrument through 90°. III-Vertical stroke handpiece: 1- It is driven either by air or electrically. 2- It delivers a vertical stroke ranging from 0.3- 1 mm. The more freely the instrument moves in the canal, the longer the stroke. Increasing vertical pressure will stop the vertical movement. 3- The hand piece has a quarter turn reciprocating motion that “kicks in” along with the vertical stroke. Reciprocal quarter turn Vertical movement with free rotation 68 IV-Ultrasonic and sonic handpieces: Instruments used in the handpieces that move near or faster than the speed of sound range from standard K-type files to special broach-like instruments. A-Ultrasonic handpiece: 1. The canal must be hand instrumented up to size 20 before the ultrasonic file has been used. 2. These handpieces all deliver an irrigant / coolant solution usually sodium hypochlorite, into the canal space while cleaning and shaping is carried out by a vibrating K-file. 3. The canals are better debrided with NaOCl if ultrasonic oscillation if is used at the conclusion of cavity preparation, this is because the heat generated from the movement increase the temperature of the irrigant solution which make it more effectively. Also the movement of the instrument pushes the irrigant solution to the irregular and deep area in the wall of the root canal, which are inaccessible by the ordinary way of irrigation. 4. The file must be small and loose in the canal particularly in curved canals. 5. The file’s shape is not adapted to the job “ K-file better cutting efficiency in up and down motion rather than side to side motion of ultrasonic hand piece.” 69 B- Sonic handpieces: 1- It attaches to the regular airline in the dental unit working at a pressure of 0.4 MPA. 2- It gives an oscillatory range of 1500-3000 cycles per second. 3- Tap water is used as an irrigant/coolant. 4- Specific types of file are used with sonic hand pieces as Rispi sonic, shaper sonic & trio sonic. All these instruments have safe ended non- cutting tips.1.5-2.0 mm in length. 5- As with the ultrasonic canal preparation, these instruments must be free to oscillate in the canal to rasp away at the wall and to remove necrotic debris & pulp remnants. 6- Also, the canal should be prepared with hand instruments up to size 20 before the use of #15 sonic file. 7- With 1.5-2.0 mm safe tips, the instrument begins its action away from the CDJ. This is known as the sonic length. Sonic oscillation A: RispiSonic, B: ShaperSonic, C: TrioSonic 70 The differences between Ultrasonic and Sonic instruments can be summarized as: Sonic Ultrasonic Less than 20 KHz From 20-50 KHz Air-powered Electrical powered Irrigant (water) Irrigant (NaOcl) Rispi & shaper K-flex & D-file Ex. MM 3000 Cavi-Endo 71 SHAPING AND CLEANING INTENDED LEARNING OBJECTIVES: 1. Recognize the root canal tretment principles. 2. Fulfilling biological and mechanical objectives in root canal treatment. 3. Knowing the limits of the procedure. 4. Mastering recent techniques for working length determination. 5. Utilizing principles of the radiograph to serve anatomical variations. 6. Understanding different instrumentation techniques. 7. Evaluating motorized shaping techniques. 8. Over viewing of rotary cutting systems in cleaning and shaping. INTRODUCTION: The ultimate goal in endodontic treatment is to perform a three dimensional fluid tight seal via obturation of the prepared pulp space both coronal and apically. Upon the completion of the coronal access cavity, the intra-radicular cavity preparation is initiated. The root canal system must be cleaned and shaped, cleaned of organic and inorganic irritants and shaped to receive a three dimensional hermetic filling. Definitions: 1. Debridement: is the cleaning of the inside of the necrotic root canal system. The principle of debridement is simple, instruments should cut through all the walls and loosen debris, irrigation solutions are then used to flush all the loosened and suspended debris from the canal space. 72 The chemical action of the irrigation further dissolves the organic remnants and destroys micro-organisms in what we call chemo- mechanical preparation of the canal. 2. Extirpation: is the cutting and removing of vital pulps. Extirpation on the other hand requires a specially designed instrument ( barbed broach) that penetrates the pulp Tissues, entangles the fibrous structure and removes it in toto (i.e.: as a whole). 3. Cleaning: Is the removal of all potential irritants from the root canal. This includes: Infected material, organic remnants and microbes. 4. Shaping: which refers to specific shape, a continuously tapered form from the canal orifice to the apical constriction, given to the canal to be compatible with the filling material and techniques. Treatment objectives: For better understanding of the proper cleaning and shaping we should first review our objectives. Herbert Schilder introduced these objectives more than 25 years ago. A. Mechanical objectives: a. Develop a continuously tapering conical form in the root canal preparation with the narrowest part apical and the widest part coronal. b. Preserve the natural curve, cross section and taper of the canal. c. Preservation of the apical foramen (never transport the foramen). d. Creation of an apical stop (seat) which help to confine the instruments and materials to the canal space and create a barrier against which gutta percha can be condensed. 73 B. Biological objectives: a. Total removal of organic and inorganic debris in root canal system. b. Avoid pushing the debris beyond the apex c. Confine all your instrumentation with in the root canal system d. Do not harm the tooth or the periodontium. In order to standardize the procedures G.V.Black have set certain principles and steps that are to be followed during cleaning and shaping of root canals: Principles for radicular cavity preparation (G.V. Black): o Irrigation. (Toilet of the cavity) o Resistance form. o Retention form. o Extension for prevention. 1) Irrigation: of the access preparation to eliminate as much debris as possible before introducing the enlarging instruments inside the canal. This will minimize the number of microorganisms to be forced apically, and hence minimize post operative pain, lubricate the canal for penetration by files and removes blood, pus or exudate so improves visibility and examination of the pulpal floor. 2) Resistance form: This is to be achieved by enlarging the apical terminus of the canal while preserving the apical constriction. Violating the apical constriction by over instrumentation leads to irritation of the periapical tissues by instruments and filling materials. In addition, the absence of an apical stop due to violation of the apical 74 constriction results in an inability to compact the root canal filling material. (Like condensing amalgam in a class II cavity without a matrix). 3) Retention form: This is achieved by enlarging the apical terminus of the canal while retaining its round cross-section. This shape provides an intimate contact between the dentin walls and the gutta-percha master cone (first fitting cone in the obturation process) thus preventing future leakage in the canal space. Coronal to this area of retention (2-3 mm above he working length), the cavity walls are flared where as the degree of flare depends on the filling technique to be used. Fulfilling the retention form is usually done by using the files &/or reamers in a reaming action (rotation). 4) Extension for prevention: This principle reflects the necessity for extension of the preparation throughout the entire length and breadth (increase the cutting tool’s size as to remove more dentin layers to ensure the removal of maximum amount of bacteria as possible) to ensure prevention of future problems. This is performed by adjusting the cutting tools to the proper working length and cutting the canal walls circumferentially with hand or rotary tools. Limitations: In the past, we have been thinking vertically, many students were taught that the first concern in root canal preparation was “working length”. We understand now that the critical issue is the three- dimensional cleaning. 75 Pulp space is a very difficult environment to work. Intra-canal instruments (files) are designed to enlarge a straight uniform slightly tapered space, which is not the case in root canals. Also files loose their flexibility by increasing their sizes and diameter meanwhile we have to widen root canals for cleaning and filling procedures. Knowledge of pulp space morphology shows that this space offers different levels of difficulty due to its complex anatomy. Difficulties faced in the root canal anatomy during cleaning and shaping procedures: 1) Pulp spaces are much wider in the bucco-lingual dimension than in mesio-distal dimension. 2) Cross-sections of root canals are rarely round along the entire length of the canal but rather oval, ovoid, elliptical, kidney-shaped and C-shaped. 3) Root canals exist in different types reflecting the presence of extra canals as second canal in mandibular incisors or second mesio- buccal canal in maxillary molars (Fig. 1). 4) Root canals might exhibit lateral or accessory canals along their entire length or in the furcation area. 5) All root canals show a degree of curvature, which might be in one plane, or curvatures at different planes. 6) The apical foramen may open at the root apex in a centric position or may open in any of the four planes (buccal–palatal-mesial- distal) surfaces of the root. 76 NB: Our main examination and evaluation tool (endodontists third eye) which is the radiographic examination may be very deceiving since it offers a two dimensional image for a three dimensional space. Root types: 1) Class I: Straight mature canals. 2) Class II: Curved mature canals. a. Slight. b. Moderate. c. Severe. d. Dilacerated (near the right angle) e. Bayonet or the double curve 3) Class III: Immature canals. a. Blunderbuss apex (old type of guns) canals seen in the early stage of root development where the canal diverges in an apical direction. b. Tubular canal in which the walls are parallel with no apical constriction. These conditions are usually met with in cases where traumatic injuries or pulp death have caused cessation of root growth before the root dentin fills in, tapers and constricts the canal lumen. Root canal types: fig (1) 1) Type I: One canal with one orifice and one apical foramen. 2) Type II: Two canal orifices that join into one with one portal of exit. 3) Type III: Two separate canals with two orifices and two apical foramina. 77 4) Type IV: One canal with one orifice that divides apically into two separate apical canals with two apical foramina, this canal type is often encountered in mandibular second premolars. Fig. 1:Different types of root canals showing the possibility of presence of more than one canal in the same root Instrumentation Procedures Intra-coronal preparation (access preparation) Tooth (working) length determination Pulp extirpation Intra-radicular preparation (cleaning & shaping) A proper access preparation is mandatory prior to canal instrumentation. Straight-line access allows files to be introduced without binding through the pulp chamber and into the canal. Endodontic access cavity should facilitate visual inspection of the pulp space, direct access to the canal orifices, complete control over the enlarging instruments and maximum convenience during the filling phase. 78 Tooth length determination (W.L.): Prior to cleaning and shaping of the root canal, the length of the root canal should be accurately measured. This length is measured from a point on the tooth’s coronal surface that is within the clinician’s field of view and goes apical reaching the apical constriction, which is 0.5-1 mm short of the anatomical apex. The apical constriction is the narrowest point of the canal beyond which the canal widens and develops a broad vascular supply. Therefore, from biologic and mechanical perspectives the constriction is the most rational point to end the canal preparation. Land marks: (fig 2) 1) Reference point: coronal point at which the stopper of the file rests. 2) Anatomical apical foramen (fig 3): which is at the Cemento- dentinal junction that should be 0.5-1 mm from the radiographic apex. Importance of working length determination: 1) Determines the instrument length in the canal 2) Limits the depth of the filling. 3) Limits the postoperative pain. 4) Determines the success of the case. 79 fig 2: showing the anatomical land marks upon which the working length is measured. Methods for W.L. determination: Determination of the length of the canal can be done either by the radiographic technique (Ingle's method) or by electronic devices for tooth length measurement (apex locators). 1) Radiographic method (Ingle’s method): The radiographic (R.G.) technique is considered the most widely used method. The first file (working length file) is inserted in the canal’s depth based on: 1) Length of the tooth in a preoperative R.G. 2) Average tooth length. 3) Tactile sense. The firmly attached rubber stopper on the file should be resting on a sound reference point e.g. cusp tip, incisal or canine tip. A radiograph with the file inside the canal is exposed, processed and examined. Working length should be 0.5-1 mm from the root apex. Adjust the length of the file according to the tooth length radiograph. 80 Plastic or rubber stoppers may be square shaped, triangular or pointed (directional) to mark the direction of the canal curve during instrumentation. Fig 3: Proper positions for the file tip in the canal to determine the working length. Notice the radiographic apex and the anatomical apex. 2. Electronic method (Apex locators): The idea behind these devices depends on the resistance of different tissues to electricity. Oral soft tissues conduct electricity easily while hard tissues act as an insulator. All apex locators in the market have two electrodes one touches the patient oral mucosa while the second is connected to a file and introduced inside the canal. By passing the file inside the canal a very small current exists between the two electrodes i.e. a very high resistance exists. This electrical resistance is very high as the file enters the enamel and dentin and decreases as the instrument moves down the canal and finally dropping as the file approaches the periapical tissues. Digital reading, light or sound is the indicators for different devices when reaching the end of the canal Old types of electronic apex locators were affected by presence of electrolytes, blood or saliva inside the canals, whereas recent types that depend on the electric impedance (difference in electric resistance 81 between the cervical and apical dentin) are said to be more accurate and work efficiently in presence of electrolytes, hypochlorite, blood and saliva. Fig 4: Electronic measurement of tooth length (apex locator) Electronic apex locators have been tested for accuracy against radiographic technique and both were found to be 80-90% accurate. However, radiographs supply the clinician with important data about canal curvatures, number and the condition of the surrounding soft and hard tissues. Modern devices such as the radio-visiograph (RVG) supplied with a sterilizable intraoral sensor allows the operator to utilize less dosage of x-rays (less hazards) and instantly view the image on a large computer monitor where it can be magnified, enhanced and stored. Improper tooth length determination will complicate the outcome of the treatment leading to failure of the case. This complication is reflected by either: 82 (i) Internal transportation: a condition in which canal will be prepared short of its real length leading to improper cleaning, persistent infection, ledge formation with subsequent under filling ending with failure. This error results from short working length determination and is also termed vertical under extension. (ii) External transportation: a condition in which enlarging instruments are extended outside the canal irritating the surrounding tissues. This situation leads to severe postoperative pain, persistent chronic inflammation with subsequent over filling ending by failure of the case. This complication results from over estimating the working length and is termed vertical over extension and results in a poor apical seal since the apical anatomical barrier against which condensation is made is destroyed. Advantages of electronic apex locators: 1. Locates the minor diameter of the foramen. 2. Not affected by the presence of soft tissues fluids. 3. Minimizes radiation exposure. 4. Shortens the preparation time. 5. Affordable, accurate, painless and safe. 83 IRRIGATION Chemical cleaning of the canal Irrigation is the first of four principles of the root canal preparation. Before, during and after the course of cleaning and shaping root canals should be washed out or irrigated with a solution capable of disinfecting them and dissolving organic matter. Although the major function of the irrigant is to flush debris from the canal, the irrigant should have additional properties that aid in cleaning and shaping. Irrigation is also mentioned as the first of the rules during preparation of the canals for a safe procedure due to its far most importance in the process of shaping and cleaning the canal. Rules for safe shaping and cleaning: 1. Always cut in a wet environment. (Use irrigation) 2. Never skip a file size. (Work in sequential order) 3. Always inspect the file before usage, and after use, to check for signs of deformation for discarding. Desired properties (functions &/or requirements) of root canal irrigants: 1. Tissue and debris solvent: The irrigant should have the ability to dissolve tissues either vital, necrotic or chemically fixed. 2. Lubricant: The irrigant should have a lubricating action to facilitate sliding of the instruments along the canal walls. 3. Antibacterial action: Ideal irrigant should have a bactericidal action against aerobic, anaerobic organisms and bacterial spores. 84 4. Removal of smear layer (if desirable): The smear layer is a microcrystalline layer of cutting debris covering the canal walls after canal preparation and its removal may aid in a better bonding between the sealer and canal walls. 5. Low toxicity: An ideal irrigant should have minimal or no toxic effect of the periapical tissues. 6. Availability, reasonable cost and adequate shelf life. Types of irrigants: 1. Sodium hypochlorite (NaOCL): The most popular and advocated irrigant is sodium hypochlorite (Clorox). The full concentration of sodium hypochlorite (5.25%) may be used, however it is recommended that it be diluted by an equal amount of water to have a concentration of 2.5%. This will decreases its toxicity, while retaining its action. Sodium hypochlorite is an excellent tissue solvent where its action may be increased by warming the solution, however, warming the solution affects its stability. Combining solutions of NaOCl and hydrogen peroxide causes foaming action for better removal of debris. Alternate use of NaOCl and EDTA is capable of removing the smear layer. Properties of NaOCl: 1. Gross debridement. 2. Antimicrobial. 3. Organic solvent 85 4. Lubricant. 5. Helps in smear layer removal. Smear layer: It is the microcrystalline layer covering the canal walls after canal preparation. Smear layer is a component of organic and inorganic layers, and to be totally removed we must dissolve the organic component by an organic solvent as NaOCl, and then react with its inorganic component using a chelating agent as EDTA to easily remove it from the canal. 2. Hydrogen peroxide (H2O2, 3%): A very popular irrigant, but unfortunately there is the fear of forcing it into the periapical tissues which will result in release of oxygen that will be trapped apically causing severe postoperative pain and emphysema. Caution is a must and pressure less irrigation technique should be followed to safely utilize this irrigant. Properties of H2O2: 1. Effervescence action, which is capable of removing loose debris from inside of the canal. 2. Release of nascent oxygen works against anaerobic microorganisms. 3. Quaternary ammonium compounds: 86 The most popular irrigant of this group is the 9-amino acridine. This irrigant is an antiseptic with low toxicity with no tissue dissolving property. 4. Chlorohexidine Gluconate (0.2%): This chemical was shown to have antibacterial action comparable to that of NaOCL but again it does not have tissue solvent action. 5. Saline: Its only action is the flushing of debris (mechanical debridement). It has no tissue solvent action, antimicrobial or even lubrication actions. 6. M-TAD: Mixture of doxycycline antibiotic, detergent for lubrication and citric acid for conditioning and smear layer removal. This mixture of the MTAD allows it to remove the smear layer alone with no need to other additives. 7. Chelating agents: Chelate: are compounds that can react with calcium, so their action in endodontics is to react with calcium ions & substitute it by sodium ions, which can bind to dentin to give soluble salt. Functions: o Enlarge narrow calcified canals. o Aid in removal of smear layer. 87 The most common Chelating agent used as an irrigant is Ethylene diamine tetra acetic acid (EDTA). EDTA: o Mechanical debridement. o Organic solvent o Inorganic solvent o Lubricant o Used in 17% concentration o Available in liquid or gel forms. RC-Prep: Is a paste composed of EDTA and urea peroxide. This paste when used with NaOCL is capable of removing the smear layer and produce bubbling action due to interaction of urea peroxide and NaOCl. This bubbling helps in loosening and floating of dentinal debris. EDTA-C: (EDTA & Cetramide) o Decrease the surface tension of the irrigant allowing it to flow more on canal walls. o Increase the antibacterial action. Glyde: (EDTA + CARBAMIDE PEROXIDE) 88 Methods of irrigation: The technique of irrigation is simple by using a plastic syringe and bending the needle to allow easier insertion inside the canal (fig 5). It is strongly recommended that the needle lie passively inside the canal as forceful irrigation can push the irrigant into the periapical tissues leading to severe complications. N.B. It must also be noted that it has been proven that the solution will only travel 2mm from the needle tip into the canal, therefore the deeper the tip of the needle goes into the canal the more effective the chemical cleaning and the antibacterial effect of the canal is. Fig 5: method of irrigation, the syringe with a bent needle and a cotton covering to prevent seepage of fluid. Goldman developed an irrigating needle (fig 6), which has a sealed end with ten side perforations along its length for side delivery of the irrigant. 89 Fig 6: types of needles used in endodontic irrigation Ultrasonic irrigation is considered the most effective method of root canal irrigation where the vibrational motion of the files inside the canal moves the irrigant in a vortex like motion cleaning areas, which cannot be reached, by the files. In addition, this motion causes warming of the irrigant thus increasing its action. A recent adjunct for cleaning and shaping is the Irrivac system, which is a combined irrigation needle with a suction tip for delivery of the irrigant and its rapid suction at the same time. The Vibrange syringe one of the recently introduced ultrasonic active irrigation methods A recent adjunct for cleaning and shaping is the Irrivac system, which is a combined irrigation needle with a suction tip for delivery of the irrigant and its rapid suction at the same time. The only draw back was the increased pressure that was induced during sending the irrigation solution into the canal, which may lead to bypassing the apical foramen and introducing the irrigation solution into the apical tissue, which will lead to serious complications. In addition to the Irrivac systems, disposable plastic tis of the Endo-Activator system was introduced as an efficient method for the 90 ultrasonic activation of the irrigating solution after its deposition inside the canals. (it doesn’t force or withdraw the irrigating solution in the canal) THE ENDO-ACTIVATOR HAND PIECE THE IRRIVAC SYSTEM THE VIBRANGE SYRINGE In summary, it appears that NaOCl 2.6% provides both excellent antimicrobial and tissue solvent action putting into consideration that the proper technique of irrigation is followed to avoid its toxic properties. If it is desired to remove the smear layer before obturation, EDTA should be used in combination with NaOCl. It should also be noted that debridement by irrigation is a function of volume, so at least two ml should be delivered each time of irrigation to be effective. 91 INTRACANAL MEDICATION: Intra canal medicaments are chemicals that are placed intra radicular between visits. Endodontics is one of the dental specialties that use antimicrobials as an adjunct in infection control in treatment of non- vital as well as in vital cases in medically compromised patients. Functions: 1. Anti-microbial activity in the pulp & peri-apex. 2. Neutralization of canal remnants to render them inert. 3. Control or prevention of post-treatment pain. Antimicrobials may be divided into chemotherapeutics (to be discussed separately), which are specific in action, and antiseptics, which are non-specific in action. Antiseptics may be classified into: I-Alcohols: ethyl and iso-propyle alcohols are used prior to obturation to dry the canal and remove the water content for better sealer adhesion. II- Phenolic compounds; phenol, camphorated phenol, camphorated monochlorophenol (CMCP) and formocresol {aldehyde ester, 19%formaldahyde,cresol 35%, water and glycerine46%} are locally acting antiseptics that work by denaturation and clumping of cell wall proteins thus altering the functions of bacterial cell wall causing bacterial death. They are vapor forming chemicals with different grades of spreading and dentinal penetration being maximum with formocresol followed by the CMCP and the least penetrating are the camphorated phenol and the phenol and thus they are the least potent and least irritant, yet all 92 phenolics are considered irritants and potentially carcinogenic which became a controversial issue in the past few years. III- Halogens; Iodine potassium iodide 2, 5% were also found very effective against the root canal flora without the periapical irritating quality of the phenolic derivatives so they are highly recommended as root canal medications, Hypochlorites as the sodium salt 0.5-5.25% has been discussed with root canal irrigants. IV- Calcium hydroxide; great interest is being directed towards calcium hydroxide in endodontics owing to its antimicrobial action, specially against the bacteriods of endodontic concern and its tissue dissolving action which encourages its use as intra canal medication and irrigant, also its osteogenic effect which encouraged its formulation as root canal sealers. V- Antibiotics; has been tried as intra canal medication but the fear of developing bacterial resistance jeopardizing the systemic use have led to the retreat of its local use. VI- Steroid / Antibiotics; the local use of steroids as intra canal medication was tried with successful results, however the fear of lowering the immunity in an already infected area have led to a combination of steroids to lower the inflammation and antibiotics to control the infection {Ledder mix}. 93 Intra-radicular preparation Shaping and cleaning of the root canal is achieved through two routes, the chemical cleaning (irrigation) and the mechanical removal of infected dentine by endodontic cutting instruments (enlarging files) Mechanical cleaning and shaping is done through two main methods, the basic instrumentation cutting motions, and the preparation techniques upon which the cutting motions are used. 1) Basic instrumentation motions, which is the type and direction of motion the operator performs while holding the tool and working the canal space, i.e.: vertical filing, rotation clockwise, counter clockwise and so on. Cutting of the root canal dentine is performed by moving endodontic instruments (files), against the dentin walls with pressure either in a linear motion (up and down) or rotation motion. 2) The preparation techniques, which are the sequence and steps taken for preparing the canal, i.e.: apical – coronal, coronal -apical or combined. "BASIC INSTRUMENTATION MOTIONS" 1) Filing motion: This is a linear motion in the form of push and pull action. It is the most efficient motion in cutting dentin. All types of files can be used with this motion; however, the H-file is considered the best as it has the highest cutting efficiency. This motion is recommended for enlarging the coronal 2/3 of the canal (circumferential filling) (fig 7). 94 Fig 7: picture representing the filing motion used in cutting of root canal. 2) Reaming motion: This is a rotation motion. The term ream indicates clockwise or right-hand rotation of the instrument. It is assumed that this motion produces round cross-section of the root canal, however, chances of the instrument to fracture is increased. Reamers and K-files are suitable for this motion, and its intended for use in the apical third to prepare circular cross sections to best fit the circular cross sections of the master gutta-percha cone. (Fig 8) Fig 8: picture representing the reaming motion used in cutting of root canal. 95 3) Turn and pull: This is a combination of reaming and filing where the instrument is inserted with a quarter turn clockwise (reaming) then the file is subsequently withdrawn (filing). (fig 9) 4) Watch winding motion: This is a rotation motion. The instrument is being inserted in the canal with a gentle clockwise/counterclockwise (30-60 degree) motion (right and left). Reamers and K-files are suitable for this motion (fig10). Fig 9: picture representing the watch winding motion used in cutting of root canal. 5) Balanced force: It is a rotation motion. It is identical to the watch winding in which the instrument is rotated right and left inside the canal until reaching the desired length. Now the instrument is rotated to the left (counter clockwise). This left rotation attempts to drive it out of the canal so, the clinician must apply apical pressure to prevent outward movement to obtain cutting. Simultaneous apical pressure and counter clockwise rotation of the file strikes a balance between the tooth structure and instrument. This balance keeps the instrument centralized inside the canal thus, minimizing the chances for canal transportation. This counter clockwise rotation that cuts dentin tends to push the dentin apically away from the file, so a clockwise turn is made to load the debris on the file 96 and pull it away. Flex-R-file (modified K-file) is the instrument of choice to be used with this motion due to its triangular cross section (less metal mass = more flexibility) and for its non-cutting tip (fig10). N.B: All rotation motions should be used in enlarging the apical 1/3 of the canal due to their ability to offer a round preparation. Fig 10: picture representing the balanced force cutting motion used in cutting of root canal. 97 Techniques for Instrumentation of the root canal Preparation of root canal systems includes both enlargement and shaping of the complex endodontic space together with its disinfection. A variety of instruments and techniques have been developed and described for this critical stage of root canal treatment. Techniques describe steps of the preparation. The root canal is divided into three parts, the apical, middle and the coronal part. Techniques differed from each other according to the part of the canal that the preparation starts with. Currently employed methods of canal preparation can be divided into two distinct approaches: those which prepare the coronal section of the canal system with large instruments and progress towards the apex (coronal-apical technique) and those which start at the apex with fine instruments and progress back towards the cervical orifice with larger instruments (apical-coronal technique). Furthermore, a hybrid technique might be used combining more than one technique. Any of the previously mentioned basic instrumentation motions can be used with any of these techniques. 98 1. The standardized technique, apical stop, (CIRCUMFERENTIAL FILING): a) Initial file determination: In this technique the working length is determined first and starting with the first file to bind at the working length (initial file). b) Cutting motion: The file is used in a filing motion along the whole circumference of the canal to plan all the surfaces till the file feels loose inside the canal, the canal is irrigated and the next file is used along the full length circumferentially till its loose, and so on the sequence is repeated, enlarging and washing the canal for at least three to four successive sizes larger than the initial size, till reaching the largest file used at the full length now termed the master apical file, according to which ,the master gutta perch point is selected. The main goal was to enlarge the canal along the whole length with establishing a definite apical stop while taking all file sizes to the full length regardless of the canal anatomy or the instrument flexibility. Master Apical file In addition to determining the correct length for canal preparation, a method of for calculating the correct degree of enlargement (extension for prevention) must be clarified. The optimal enlargement of each canal should be calculated separately; there is no hard fast rule that is universally acceptable. However, the initial size of file that binds at the apical portion of the canal is of great help in the determining the final canal size. 99 Master apical file (MAF) may be defined as a three sizes larger than the first file that binds at the full working length passively after straight- line access. It can also be called the largest file used at the working length passively after straight-line access. In other words, if a size 10 file put into a relatively small canal but is loose and does not remove dentin, it does not bind. In the same canal a size 20 or 25 files does work against the canal walls but does not reach the apical portion of the canal. A size 15 does reach the apical portion and the file cut against the wall; thus it is the initial size of that binds at the full working length, and the master apical file for this canal was size 30. N.B. Recent studies showed that the starting diameter of the apical portion of most canals is an average of a file size #25, this means that in order to clean the canal three sizes beyond the initial binding file, the minimum size of the master apical file will be size #35. Advantages of the standardized tech.: 1) Planning the whole circumference of the canal. 2) Simple to be used by inexperienced operators in straight canals Disadvantages of the standardized tech.: 1) Quiet damaging when used in curved canals, as increasing the size of the instruments decreases its flexibility (more mass = less flexibility) with subsequent indiscriminate increase in the stresses applied by the files on the canal walls, leading to areas of increased cutting (danger zones) and areas of less cutting ( safe zones) 2) Uneven planning and cleaning of the canal dentin with design errors in preparations as pear shaped, hour glass (ingle) and zipping (Weine) of the apical third of the canal. 100 Fig. 11: illustration of the dangerous zones and the safe zones in the root canal walls 2. Anti-curvature filing technique It is a modification of the standardized technique, which was developed to advise the operator to pull or drag the files in an anti- curvature direction to put more pressure and cut more in the safe zones and avoid the dangerous zones. 101 3. Step-back technique (Telescopic preparation/ Serial preparation): The "Step Back" method indicates that the dentist works from the bottom of the canal back towards the crown. It was first described by Clem 1969 and became popular as it creates smoother flow and a more tapered preparation. The advantage of this technique over the standardized technique is that it respects the canal anatomy, and the instrument flexibility. Only small and flexible instruments are taken to the full working length while larger stiffer instruments are stepped back and used in more coronal areas away from the maximum curvature of the canal. Cleaning and shaping of the root canal by the step-back technique is done after working length determination and initial binding file selection, which are two most important steps, and it includes three phases, in phase one the motion used is a rotation motion (reaming, watch winding or turn and pull motion) and its aim is to prepare the apical portion of the canal (apical preparation phase) starting by the initial file till reaching the MAF. The reaming motion used gives the canal a round cross section at the apical third; this allows complete friction between the canal walls and the master cone gutta-percha (same size and length of the master apical file), which also has a round cross section. This frictional fit gives the retention form of the root canal filling. In phase two the canal is enlarged with larger files in a step-back fashion; that is larger files move 1mm backward in a coronal direction in a series of steps. In phase three, the motion used is the filing motion around the circumference of the canal (circumferential filing). The aim of phase two 102 is to enlarge and flare the coronal two thirds of the canal (flaring phase). The technique is described as follows: File Number of File length in Phase Cutting motion type files canal 3 successive files after the All to the full I K-file Reaming motion initial binding working length file 3 successive Decrease 1mm Circumferential files after the from the II H-file filing motion master apical working length file with each file H-file/ Decrease 1mm 3 successive Gates Circumferential from the III files after Glidd. filing motion working length phase II Drills with each file Remember: I. Always keep the canal flooded with the irrigant and never force an instrument inside the canal. II. When working short than the full working length of the canal, dentin debris are susceptible of falling in the bottom of the canal and accumulating in the remaining of the working length which will cause canal blockage. So it is of most important in both phase II and III that canal be irrigated and the master apical file re-inserted into the full working length to re-assure that no blockage had occurred, upon retrieving the file, it is pressed on the side walls of the canal so as to remove and step or ledge that has been created during stepping back of the canal by the files. This is what we call "RECAPITULATION". III. Neglecting this phase would lead to formation of a series of ledges simulating an opened telescope and hence it was called the Telescopic preparation. 103 IV. Initial binding file is the largest file that can reach the full working length. V. Least size master apical file is size #35. Fig 12: illustrating the step back technique with the size #35 file as the MAF, #40-#50 in phase two and #55 the starting file of phase three 104 4. MODIFIED STEP- BACK TECHNIQUE: Indications: This technique may be used in less curved canals It simply involves establishing the proper working length, start to enlarge the canal with sequentially larger files, preparation of an apical seat with the MASTER APICAL FILE of an appropriate size using a reaming action to prepare a circular cross section at the apical third The working length is then shortened by 3-5 mms to leave what is known as the retention form with its circular cross section, then the rest of the canal is enlarged using either a rotary tool like the gates glidden drills, or using H-files in a circumferential filing manner. The amount of canal flare depends on the obturation technique to follow and the need for using posts. 5. THE CROWN- DOWN TECHNIQUE: Practitioners thought were pleased with the results of the step-back technique, yet it was found a lengthy boring procedure, and the evolution of the modern rotary tools together with the need to improve the quality of the preparation and to shorten the time of treatment have led to the development of the crown-down pressure less technique by Marshal. In other words the disadvantages of the step back technique is preparing the canal in a very long time, using increased number of tools, and still leading to errors (ledging, perforations & apical transportation) in curved canals. This technique depends on canal pre-flaring using either a rotary tool like the gates glidden drills or an H-file in a circumferential filing 105 technique, extending about 16 mm inside the root or at least the cervical and middle thirds of the canal. The second step is to penetrate the canal with a large file to the apical third with absolutely no apical pressure (i.e.): file # 35 or 40 depending on the size of the canal. This is followed by using sequentially smaller files (30-25-20-15) down the canal in what is known as waves of instrumentation advancing from the coronal to the apical direction. When the files reach 2-3mm shorter of the suggested average length (determined by the pre-operative radiograph) which is termed the Provisional working length a confirmatory working length radiograph is made for an accurate working length determination. The final step is to instrument the canal starting by large files and advancing apically using sequentially smaller files with no apical pressure.The second wave of instrumentation would be (40-35-30-25), the third would be (45-40-35-30), these waves are repeated till adequate apical preparation is reached and a MASTER APICAL file size is determined. The coronal pre-flare had led to a huge decrease in the amount of stress that is conveyed to the instrumentation files. When the file doesn’t bind to the canal coronal, and only cuts dentin apically this will lead to decrease in the surface area of contact between dentin and file surface leading to decrease in the stress and consequently in the rate of file separation. 106 Fig. (13): demonstrating the crown down pressure less technique. 107 ADVANTAGES OF THE CROWN-DOWN CONCEPT (CANAL PREFLARE) 1. Gross debridement of two thirds of the canal contaminants and so less microorganisms and debri is pushed apically and hence less liability to flare -ups and post operative pain. 2. Eliminates coronal and middle thirds dentin resistance to the files so improves tactile sensation since the first resistance encountered is the apical constriction. 3. Less stresses on the instruments results in less stresses on canal dentin and hence less liable to ledge or perforate the canal, also less likely to fracture the instrument. 4. Since coronal resistance is eliminated in the straight part of the canal the operator can better negotiate the apical curve with less stresses on the instrument. 5. Deeper penetration of the irrigation needles means deeper irrigation effect in the apical region, with formation of a large reservoir for the irrigant. 6. Preflaring with rotary tools shortens the preparation time so less fatigue to the patient and the operator. Although the crown down concept gained popularity for its benefits, it was found to b e time consuming so a hybrid technique was developed which is termed: the step-down technique. This technique depends on preflaring the canal from a coronal direction using engine driven instruments from the smallest to the larger (depending on the canal size). The working length is then properly established, and the apical third is prepared in a step- back manner. A small patency file is advanced to check for the patency and direction of the canal , the smallest gates size # 1,2 or 3 may be used to 108 reach the apical third or at least the mid –root as dictated by the canal anatomy and type of curve(in curved canals) ,this is followed by irrigation then the next size gates (# 2,3,or 4) may be used more cervically, again the canal is irrigated ,checked for patency and the larger drills used at the cervical third and canal orifice. The apical constriction may now be felt by tactile sensation and the proper working length radiograph is now made.The initial file is used with a watch-wind motion and sequentially larger files are used to reach the MASTER APICAL FILE, the apical third may now be flared by a step-back or a modified step-back techniques. Alternative techniques for cleaning and shaping Other approaches to canal preparation have been proposed. Because conventional preparation with hand instruments is somewhat difficult and time consuming, engine driven instruments have been suggested. Two types of motions are utilized either rotational motion or vibrational motion. I- Engine driven instruments utilizing rotational motion: These include large variety of special hand pieces that rotate back/forth or in a quarter turn or even up and down few millimeters. Tips mounted on these hand pieces are files or reamers with latches instead of handles. Rotational engine driven instruments were not widely accepted in the past due to problems that appeared when using them which included: 1. Less effective in canal debridement. 109 2. More tendencies for canal packing with dentin debris. 3. More tendency for ledges and perforations 4. More tendencies for canal straightening. 5. More tendency for instrument breakage. 6. Loss of operator sense of canal topography. However, the new generation of engine driven instruments were greatly modified and nowadays are comparable to hand instrumentation techniques. Modifications included: 1st- Modification in the hand piece: High torque Very low speed (300-1200 RPM) Steady rotation 2nd- Modification in the cutting tool: Nickel-titanium files (flexible) Increased taper II- Engine driven instruments utilizing vibrational motion: (Sonics & ultrasonic) Martin first introduced the utilization of vibrational motion in endodontics more than twenty years ago. The power source (electromagnetic or piezoelectric) is transferred to a special insert that holds a special instrument similar to a file. When the file is energized in a canal flooded with irrigant, the fluid motion helps loosening debris with better flushing of canal contents together with file scraping against the dentin wall. The results of the studies have shown that canal enlargement using sonics and ultrasonic may not be efficient as hand instrumentation and is 110 even less effective in small curved canals. However, flushing and disinfection appears to be very effective with the sonic or ultrasonic. SONICS ULTRASONICS SPEED 20 – 35 20,000 HERTZ < RANGE KILOHERTZ POWER PIEZO- COMPRESSED AIR SOURCE ELECTRIC RISPI & Shaper (R. K-TYPE& TOOLS Type) DIAMOND IRRIGANT WATER NaOCl BRAND MM 5000 ENDOSTAR Guidelines for instrumentation of difficult canals: The ideal canal enlargement would be the one that enlarges the canal while retaining the canal pre-operative shape. In a straight large canal this rule is easy to apply, but studies have shown that straight canals are the exception and the majority of root canals show a degree of curvature. When a file is inserted in a curved canal, elastic forces develop inside the instrument. These forces attempt to return the instrument to its original shape hence it is called “Restoring forces”. These forces act on the canal wall during preparation and influence the amount of dentin cut by the instrument. The restoring force is not equally divided along the length of the instrument being maximum at the instrument tip (Fig. H). This phenomenon is responsible for most of the procedural errors, which occur during canal enlargement. 111 These guidelines should always be remembered regardless of the technique of instrumentation used. 1. Always work files in a canal filled with irrigant. 2. Never skip intermediate instrument size during preparation 3. Never force files inside the canal to avoid instrument breakage or packing of debris in the apical region of the canal. 4. Precurving of instruments: a precurved file is a valuable tool for feeling canal passages and for moving around calcifications and ledges. In addition, a curved file helps alleviate the adverse effects of canal curvature. 5. Anti-curvature filing concept: this concept describes the action of pulling the files against the outside wall of the canal. This directionally applied pressure prevents straightening of midroot curvatures, which can lead to strip perforation 6. Radicular access: This procedure is employed nowadays in most instrumentation techniques. It describes enlarging the coronal 1/3 of the canal before initiating the cleaning and shaping. This can be accomplished either by rotary instruments (gatesglidden drills)(fig.6) or by circumferential filing using H-files. Termination of canal preparation How much should the root canal be enlarged? The answer is simple, canals should be enlarged enough to permit adequate debridement as well as manipulation and control of obturating materials and instruments. It is an interaction between three major factors: I – Canal anatomy: Curved canals (specially at the apical third) requires less widening, as using larger instruments will either damage the canal walls or will fracture. 112 II- Instruments used: Using more flexible designs and materials of construction allows the operator to enlarge the canal in the apical third to larger sizes, ie: for a severely curved canal having a regular K-st-st file may allow an apical preparation to size 25,where as having a k-flex st-st may allow an apical enlargement to size 30-35, while using one of the new NICKEL TITANIUM instrument systems may allow an apical preparation of the same curve to size 40-45. III – The operator skills: Experienced operators with wide range of skills are more able to deal with more complicated cases, where as less experienced practitioners are better advised to stick to the basic techniques to which they are more trained. Criteria for termination of canal preparation 1- Debridement: All walls should feel smooth along the whole length of the canal together with clean yellow dentin debris. 2- Apical preparation: An apical stop (apical control zone) should exist. This is tested by the failure of the master apical file to pass beyond the working length when a reasonable apical pressure is applied to it (RESISTANCE FORM). 3- Adequate taper: Selected obturating instrument (spreader or plugger) can reach easily to within 1-2 mm of the working length. 113 Procedural errors during cleaning and shaping: 1. Canal blockage 2. Ledge formation 3. Perforation 4. Instrument breakage Iatrogenic changes in root canal during cleaning and shaping do occur and especially in narrow curved canals. The majority of these complications occur as a result of improper control over the preparation instrument. These procedural errors include: Canal blockage This condition occurs when the operator feels that canal patency is lost during cleaning and shaping. Diagnosis * Full working length can not be reached. * At area of blockage canal feels sticky due to aggregation of debris. Etiology * Failure to maintain full working length during preparation. * Insufficient irrigation. * Failure to recapitulate during preparation. Treatment To solve this situation, the operator should irrigate the canal and start negotiating the canal at full working length using the initial file (smallest file reaching the working length). Ultra sonic irrigation may be very beneficial in steering back the accumulated debris and facilitate its removal by irrigants. Also the alternate use of hypochlorite/peroxide solutions with the resultant bubbling effect may help removal of the blocking debris. 114 II- Ledge formation This condition is noticed when the operator feels that full working length cannot be reached. Diagnosis * Loss of working length. * End of canal feels as a solid wall (non-sticky). * Radiographically file appears to leave the original path of the canal. Etiology * Insufficient irrigation. * Failure to recapitulate * Using large-sized instruments in small curved canals. * Skipping of instrument sizes during preparation. * Dry filing of root canals. To solve this situation, operator should irrigate the canal and try to relocate the original canal. This is done by placing a sharp bend at the file tip and trying to reinsert the file to its original canal through rotating the file all around. Treatment The last 1-2 mm of a file # 15. This tip is teased along the canal wall opposite to the wall which is expected to have the ledge until the full working length can be re-established. This is followed by filing of the wall which contains the ledge. III- Perforation This problem can occur anywhere along the length of the canal. Diagnosis *Sudden pain. *Sudden bleeding in a canal that is originally dry. *Radigraphically the file is seen projecting out of the canal when perforation is located in a favorable site to the x-ray beam. 115 * Insertion of a paper point along side the perforation will show a red spot {blood} corresponding to the perforation level. Etiology * Improper working length (apical perforation). * Boring through a ledge (side perforation). * Over enlargement of small canal leads to longitudinal perforation (strip perforation). Treatment * If perforation was apically, reestablish working length and create a new apical stop by enlarging the master apical file one or two sizes. * If perforation was side perforation, try to relocate the original canal and complete the cleaning procedure. The perforation can then be sealed during canal obturation or an external seal can be performed surgically. * Strip perforations are difficult to deal with. Obturate the canal and follow up the case. * Attempts to induce external calcific barrier by filling the canal with calcium hydroxide may be tried for three to six month and may last up to two years. * Failing cases may require surgical correction to seal the perforations externally. IV- Instrument breakage During instrumentation, fragment of the instrument can break inside of the canal. This fragment blocks the canal thus preventing routine cleaning and shaping. This condition is diagnosed as follows: * Sudden loss of working length (canal blocked). * Loss of a fragment of the instrument. * Radiographically instrument fragment can be seen. This condition occurs due to: 116 Frequent use of the instrument {instruments should be discarded before metal fatigue}. Using excessive force during instrumentation. Failure to inspect the instrument before use. Locking the instrument in a dry canal. Rotation in a counterclockwise direction. The prognosis of this condition depends on several factors: o Location of instrument (apical, middle or coronal). - Size of the instrument. o How much cleaning was performed apical to the broken fragment before instrument breakage. o The nature of the pulp disease (vital or non-vital case). The best correction of this error is to try to remove this fragment. If impossible, try to bypass it and complete the instrumentation procedure. Ultra-sonics may be of great value in trying to loosen the locked instrument and flush it out with irrigation. If also impossible, clean and obturate the canal to the level of the fragment and follow-up the case. Failing cases may require surgical intervention to retro-seal the apical root segment. 117

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