Techniques and Principles of Cleaning and Shaping

Principles of Cleaning
Nonsurgical root canal treatment is a predictable method of retaining a tooth that otherwise would require extraction. Success of root canal treatment in a tooth with a vital pulp is higher than that of a tooth that is necrotic with periradicular pathosis. The difference is the persistent irritation of necrotic tissue remnants, and the inability to remove the microorganisms and their by-products. The most significant factors affecting this process are tooth anatomy and morphology, and the instruments and irrigants available for treatment. Instruments must contact and plane the canal walls to debride the canal.
Morphologic factors such as lateral and accessory canals, canal curvatures, canal wall irregularities, fins, cul-de-sacs, and isthmuses make total debridement virtually impossible. Therefore the goal of cleaning not total elimination of the irritants but it is to reduce the irritants.
Currently there are no reliable methods to assess cleaning. The presence of clean dentinal shavings, the color of the irrigant, and canal enlargement three file sizes beyond the first instrument to bind have been used to assess the adequacy; however, these do not correlate well with debridement. Obtaining glassy smooth walls is a preferred indicator. The properly prepared canals should feel smooth in all dimensions when the tip of a small file is pushed against the canal walls. This indicates that files have had contact and planed all accessible canal walls thereby maximizing debridement (recognizing that total debridement usually does not occur).
Principles of Shaping
The purpose of shaping is to
1) facilitate cleaning and
2) provide space for placing the obturating materials.
The main objective of shaping is to maintain or develop a continuously tapering funnel from the canal orifice to the apex. This decreases procedural errors when cleaning and enlarging apically. The degree of enlargement is often dictated by the method of obturation. For lateral compaction of gutta percha the canal should be enlarged sufficiently to permit placement of the spreader to within 1-2 millimeters of the corrected working length. There is a correlation between the depth of spreader penetration and the apical seal.5 For warm vertical compaction techniques the coronal enlargement must permit the placement of the pluggers to within 3 to 5 mm of the corrected working length.6

As dentin is removed from the canal walls the root is weakened.7 The degree of shaping is determined by the preoperative root dimension, the obturation technique, and the restorative treatment plan. Narrow thin roots such as the mandibular incisors cannot be enlarged to the same degree as more bulky roots such as the maxillary central incisors. Post placement is also a determining factor in the amount of coronal dentin removal.

1. CLEANING AND SHAPING Dr. DHEERAJ GUPTA PG IIND YEAR

2. ROOT CANAL TREATMENT

3. INTRODUCTION Successful root canal treatment is an interplay of many procedures, of which shaping and cleaning play an important role. Early studies on prognosis of root canal treatment indicated that failures were mainly attributed to incomplete obturation. This was not true as obturation only reflects the adequacy of shaping and cleaning. Canals that are poorly obturated are often incompletely shaped and cleaned. Elimination (or significant reduction) of the inflamed or necrotic pulp tissue and microorganisms are the most critical factors.

4. DEFINITION Cleaning includes the removal of all organic debris, which could possibly serve as substrate for bacterial growth or as the source of periapical inflammation due to seepage of proteolytic breakdown products. Shaping implies the development of a unique shape for every root canal, directly related not only to the length but also to the position and curvature of each individual root and root canal

5. Root canal preparation has been described in many ways: • Canal preparation • Biomechanical preparation – involves biological and mechanical objectives in preparing root canal • Chemo mechanical preparation – a combination of mechanical instrumentation and chemical disinfection by chemical means. In 1974, Schilder introduced the term cleaning and shaping to the endodontic vocabulary. Human root rarely contains a single simple root canal. Accessory canals, lateral canals, fins, isthmus and apical delta contribute to the root canal system. Majority of these anatomical extensions are not accessible to instrumentation and are dependent on irrigating solution to flush through this system to dissolve organic debris and destroy the microorganisms at the same time. The current terminology for root canal preparation is not cleaning and shaping, but shaping and cleaning. Once shaped and cleaned, the root canal system is obturated to prevent entry of microorganisms, from apical and coronal aspects, and to entomb any remaining microorganisms to prevent their proliferation

6. Goals of Root Canal Treatment Major goals of root canal treatment are the following: Promote healing of periradicular lesions Prevention of periradicular disease Mechanical Objectives Biological Objectives Continuously tapering funnel from the apex to the access cavity Making the preparation in multiple planes, which introduces the concept of flow Making the canal narrower apically and widest coronally Avoiding the apical transportation of foramen Keeping the apical opening as small as possible Scrupulously remove all tissue debris, microbes and their by-products. Limit the instrumentation to within the root canal. An exception to this rule is the use of the ‘patency files’. Do not force necrotic material beyond the foramen. Enlargement of the canals should create space which acts as a reservoir for irrigants and intracanal medicaments to eliminate the bacteria and their by-products .

7. Radicular Preparation Instruments used in canal preparation are made of stainless steel or nickel–titanium (NiTi). These instruments are manipulated in the canal manually (hand) or mechanically (rotary or reciprocal). In the past, sonic and ultrasonic were used to prepare the canal.

8. Few terminologies:

9. Standardized Method • Introduced by Ingle as the first formal root canal preparation. • WL is determined and the initial apical file is selected. • Circumferential filing is done to increase the apical constriction two to three file sizes greater than the initial apical file to complete the preparation. It is the technique of inserting the file into the root canal to the working length, engaging it into the dentine wall by applying lateral pressure and withdrawing it. This procedure is performed around all the walls of the canal.

10. Standardized Method Advantages Disadvantages Easy to master. Preparation has the same shape, size and taper as a standardized instrument. Less time consuming. Stainless steel files should not be used in curved canals, because as the size of the instrument increases, flexibility decreases, resulting in mishaps (ledging, zipping, perforation). NiTi instruments reduce/ eliminate mishaps. Loss of WL due to the accumulation of dentine debris.

11. Step-Back Preparation (Telescopic Preparation or Serial Root Canal Preparation) Canal is shaped (with copious irrigation) from apex with a fine instrument, working backwards coronally progressively with larger instruments. Mullaney divided it into two phases: a. Phase I b. Phase II II-A II-B

12. Step-Back Preparation (Telescopic Preparation or Serial Root Canal Preparation) Phase I The canal is lubricated and explored using a patency file (#8/10 K-file). WL is determined (e.g. 20 mm). The first instrument that snuggly fits at apical constriction (initial apical file) is selected (e.g. ISO 15). The next size instrument (#20) is used to the same WL, in the same watch-winding motion till the instrument becomes loose, followed by irrigation. File #25 is used in the same manner to the WL to complete the apical preparation and the canal is irrigated. Phase II-A Next size file (#30) is used 1 mm short (i.e. 19 mm) of the actual WL with watch-winding motion till the instrument becomes loose and the canal is irrigated. The previous instrument (#25) is used to the actual WL (20 mm) to ensure the patency of the canal followed by irrigation. Sequential re-entry and reuse of each previous instrument is called recapitulation. The next instrument (#35) is used 2 mm short (i.e. 18 mm) of the WL in a lubricated canal in watchwinding motion till the instrument becomes loose. Till the straight midcanal is reached, where the instrument no longer fits snuggly.

13. Step-Back Preparation (Telescopic Preparation or Serial Root Canal Preparation) Phase II-B (Refining Phase) The last apical instrument (#25) is used to smoothen all the walls with push–pull strokes followed by copious irrigation.

14. Modified Step-Back Preparation After the enlargement of the apical stop, the step-back procedure begins 2 mm coronal to the apical foramen. This provides a short parallel retention form to the master GP point which snuggly fits in apical third. Advantages Disadvantages • Decreases apical transportation • Increases the percentage of canal walls being planed • Passing a pre-curved instrument in a coronally tight canal straightens the instrument, leading to ledge formation. • As it holds a minimal volume of irrigant, accumulation of dentinal mud leads to blockage of foramen. • WL is more likely to change as the coronal constriction is removed last.

15. Passive Step-Back Technique It is a combination of hand and rotary instrumentation. After estimating the WL with #15 K-file, insert #20, 25, 30, 35 and 40 files passively (may not reach the WL). GG drills are used for additional coronal enlargement. #20 K-file is inserted into canal up to WL and foramen is enlarged using watch-winding motion. Canal is then prepared with progressively larger instruments placed short of the WL. Advantages Gradual passive enlargement of canal in an apical to coronal direction Decreases incidence of procedural errors like transportation, ledge and zip formation Removal of debris and minor canal obstructions

16. Passive Step-Down Preparation (Crown-Down Preparation) This step focuses on opening and flaring the coronal third followed by middle third preparation and finally the apical third. Procedure • After preparing the access cavity under RD, coronal third is flared using GG drills #1, #2. • Apical instrumentation – two steps: • WL is determined. • Apical stop is prepared to size #25. • Remaining canal is shaped using step-down technique in which large files are used in the middle third followed by sequentially decreasing the size of the file as we approach the apical third.

17. Passive Step-Down Preparation (Crown-Down Preparation) Advantages • Provides straighter access to the apical region. • Most of the pulp tissue, debris and microbes are eliminated before apical instrumentation. • Eliminates dentinal interferences in the coronal third early in the preparation. • Allows deeper penetration of irrigating solutions. • Better control over apical instrumentation. • Less chances of change in the WL due to change in the canal curvature. • Less chances of instrument fracture. • Due to better tactile sensation, lodging and transportation is also reduced.

18. Crown-Down Pressure less Preparation • Coronal flaring is done with the GG drills, followed by larger files in the coronal third and then progressively smaller files are used in an apical direction without any pressure till the desired length is reached. Procedure • After application of the RD, canal patency is determined using #10 K-file. • Insert #35 file until it just binds and measure the length. This is known as radicular access length (RAL). • Coronal portion is flared using GG drill in a brush-out motion up to RAL. • #30 file is inserted and rotated clockwise slightly beyond RAL until resistance is felt and the canal is prepared till the instrument is loose. • The next smaller files are inserted in sequential order to a point 3 mm short of the radiographic apex (provisional WL). • Obtain a radiograph with the file at the provisional WL and estimate the true WL. The file that fits snugly at the true WL is the initial apical file. • Continue stepping down with smaller files to the true WL. • Apical stop is enlarged three times the initial apical file. • Finally the canal walls are finished by circumferential filing. Advantages • By eliminating the coronal constrictions, it reduces the effect of canal curvature and hence better tactile sensation. • Allows effective irrigation and hence the danger of pushing the debris beyond the apex is reduced (thus eliminating postoperative discomfort). • WL is less likely to change during apical instrumentation. • Holds larger volume of irrigants and hence helps in dissolution of pulp tissue in the apical and lateral canals. • Improves identification of foramen as it accepts larger files into the apical one-third, which is easier to visualize in the radiograph. • This technique reduces the risk of instrument fracture. • Precurved files remain curved, can be easily inserted and freely passed down the canal.

19. Hybrid Technique • Combination of step-down and step-back preparation is known as hybrid technique. • Patency of canal is checked with #10 K-files. • The canal preparation is done using hand/GG drills from coronal till point of curvature without excess apical pressure. • WL is determined. • Unprepared apical portion of the canal is prepared using step-back technique. • Recapitulation is done with patency file. • Copious irrigation is done at every step. • Blend the step-back with step-down preparation.

20. Double-Flared Technique • In this technique, canal is prepared with crown-down pressure less technique with copious amount of frequent irrigation. • Once WL is reached, foramen is enlarged to master apical size. • Canal is once again flared from apex using step-back method till the middle third which gives it a double flare. • Advantage Disadvantage Better cleaning with more volume of irritant exchange Excessive removal of dentine compromising the strength of the root

21. Balanced-Force Preparation • It is one of the methods used to prepare a curved canal without precurving the instrument. • This technique involves oscillation (reciprocation) of the instrument in clockwise and CCW directions. • Coronal flaring is done using crown-down technique followed by irrigation. • WL is determined. • Balanced-force movement of file is followed at the apical third of the canal.

22. Balanced-Force Preparation These include three phases: Phase I: file insertion – file is placed into the canal with light pressure until it binds against the wall. The file is then rotated clockwise through 60–90° so that the flutes engage the dentine and advance apically (clockwise rotation always advances the file apically as it engages the dentine). Phase II: file cutting – the file is now rotated 120–180° in CCW direction with apical pressure which prevents the movement of the file in the coronal direction. This breaks off the dentine engaged in the flutes with a clicking sound and enlarges the canal. c. Phase III: flute loading – a final clockwise rotation without apical advancement allows flutes to be loaded with debris and removed from the canal.

23. Balanced-Force Preparation • Thus, a balanced force is used to remove the dentine. • The preparation is done in crown-down technique by sequentially using smaller files till WL is reached. The apical width is then enlarged to master apical size. Advantages • It positions the instrument near the canal axis even in severely curved canals and avoids recognizable transportation of original canal path. • Works effectively without precurving (but might need a tip bend in sharply deviated apical foramen). • File cutting occurs only at the apical extent of the file.

24. Reverse Balanced-Force Preparation • Instrument used for reverse balanced-force technique is NiTi greater taper hand file. • Greater taper hand files can be used for reverse balanced-force technique, as the flutes of these files are machined in a reverse direction unlike the other files. The handle of these files is increased in size to make the reverse balanced-force manipulation easier. • Technique involves: • In reverse-balanced force, the file is used in 60° anticlockwise movement, followed by 120° clockwise movement with apical pressure using the GT files (largest [blue] to smallest [white]) in a crown-down sequence progressively towards the apex. • This procedure is repeated till the estimated WL using diagnostic radiograph is reached. • WL is determined. • 0.02 tapered ISO files are used to prepare the apical portion (balanced-force technique is used). • Radicular preparation is completed using the GT hand file of appropriate taper

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