Endodontic Triad [PDF]

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DEFINITION Access cavity preparation is defined as endodontic coronal preparation which enables unobstructed access to the canal orifices, a straight line access to apical foramen, complete control over instrumentation and to accommodate obturation technique. It is a well established fact that success of endodontic therapy depends on the main three factors: a. Cleaning and shaping b. Disinfection c. Three-dimensional obturation of the root canal system. Proper cleaning and shaping establishes the necessary conditions for next two factors. However, there is one step which precedes these factors, the error in this preliminary step would compromise the whole subsequent work. This preliminary step is the preparation of the access cavity, i.e. opening through the coronal portion of tooth which allows localization, cleaning, shaping, disinfection and a three-dimensional obturation of the



1.  Access Cavity Preparation



Endodontic Triad



•  Isolation •  Access opening •  Length determination



2.  Biomechanical Preparation •  Cleaning and shaping •  Irrigations •  Intracanal medicament



3.  Obturation Fig. 14.1: Pyramid of endodontic treatment



root canal system. Thus we can say that coronal access forms the foundation of pyramid of endodontic treatment (Fig. 14.1). As we have seen success of endodontic therapy depends on proper evaluation and thereafter placement of this step. Any improperly prepared access cavity can impair the instrumentation, disinfection and therefore obturation resulting in poor prognosis of the treatment. Before going for access cavity preparation, after evaluating other factors, a study of preoperative periapical radiograph is necessary with a paralleling technique.



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Radiographs help in knowing i. Morphology of the tooth (Fig. 14.2). ii. Anatomy of root canal system (Figs 14.3 and 14.4). iii. Number of canals. iv. Curvature of branching of the canal system. v. Length of the canal. vi. Position and size of the pulp chamber and its distance from occlusal surface. vii. Position of apical foramen. viii. Calcification, resorption present if any (Fig. 14.5).



The main objective of the access cavity preparation is to create a smooth, straight line access to the canal system and the apex. The optimal access cavity results in the straight entry into the canal orifices with line angles forming a funnel which drops smoothly into the canals (Fig. 14.6). Sometimes depending upon the location and number of canals, modification of the outline form may be needed. An ideal access preparation should have following qualities: 1. An unobstructed view into the canal. 2. A file should pass into the canal without touching any part of the access cavity. 3. No remaining caries should be present in access cavity.



Danica Anastasia



Access Openings Removal of the chamber roof and all coronal pulp tissue



General Principles •  Recommended shape for access of a normal tooth •  Assures correct shape and location, provides straight-line access to the apical portion •  Remove tooth structure that would impede the cleaning and Outline form shaping process



Locating all canals Unimpeded straight-line access of the instruments in the canals to the apical one third



Convenience form



•  Allows modification of the ideal outline form to facilitate unstrained instrument placement and manipulation



Conservation of the tooth structure



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Fig. 17.6: Radiograph showing obturated first molar



Caries removal



Root Canal System



plan the whole treatment so as to obtain the successful treatment results. The clinician should evaluate the tooth to be treated to ensure that the particular tooth has favorable prognosis. Before performing cleaning and shaping, the straight line access to canal orifice should be obtained. All the overlying dentin should be removed and there should be flared and smooth internal walls to provide straight line access to root canals (Fig. 17.8). Since shaping facilitates cleaning, in properly shaped canals, instruments and irrigants can go deeper into the canals to remove all the debris and contents of root canal. This creates a smooth tapered opening to the apical terminus for obtaining three-dimension obturation of the root canal system.



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•  Permits the development of an aseptic environment before entering the pulp chamber and radicular space •  Allows assessment of restorability before treatment •  Provides sound tooth structure so that an adequate restoration can be placed



Fig. 17.7: Doubling the file size apically, increases



Toilet of the cavity



•  Preventing materials and objects from entering the chamber and the surface area of foramen four times canal space Mechanical objectives of root canal preparation (given by Schilder) • The root canal preparation should develop a continuously tapering cone. • Making the preparation in multiple plane which introduces the concept of “Flow”. • Making the canal narrower apically and widest coronally. • Avoid transportation of foramen. • Keep the apical opening as small as possible.



Objectives of Biomechanical Preparation Biologic Objectives of Root Canal Preparation Biologic objectives of biomechanical preparation are to remove the pulp tissue, bacteria and their by-products from the root canal space.



Maxillary Anterior



Removal of overlying dentin get smooth smooth internal Fig. 17.8: Removal of overlying dentin to causes internal providestraight-line straight line access to root canalscanals walls walls and and provide access to root After obturation, there should be complete sealing of the pulp chamber and the access cavity so as to prevent microleakage into the canal system (Fig. 17.9). Tooth should be restored with permanent restoration to maintain its form, function and aesthetics and patient should be recalled on regular basis to evaluate the success of the treatment (Fig. 17.10). For past many years, there has been a gradual change in the ideal configuration of the prepared root canal. Earlier a round tapered and almost parallel shape was considered an ideal preparation but later when Schilder gave the concept of finished canal with gradually increasing the taper having the smallest diameter apically and widest diameter at the coronal orifice.



Maxillary Posterior



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Mandibular Anterior



Mandibular Posterior



Patency File



Working Length



•  Small K-File (#10 or #15) •  Passively extended slightly beyond apical foramen •  Suggested for most rotary technique •  Objectives:



Coronal reference point



Cleaning, shaping, and obturation point



Working Length



1.  Remove accumulate debris 2.  Maintain working length



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Textbook of Endodontics



was first introduced by John Ingle. Weine modified this subtraction rule (Figs 15.8A to C) as follows: a. If radiograph shows absence of any resorption, i.e. bone or root apex, shorten the length by 1 mm (Fig. 15.8A). b. If periapical bone resorption is present, shorten it by 1.5 mm (Fig. 15.8B). c. If both bone and root resorption is seen, shorten length by 2 mm. This is done because if there is root resorption, loss of apical constriction may occur in such cases (Fig. 15.8C). Electronic Apex Locators In curved canals, canal length is reconfirmed because final •  Patientsworking with gag reflex length may shorten up to 1 mm as canal is straightened and can’t films outtolerate by instrumentation. If root contains two canals, the cone be positioned at 20 to 30o horizontal deviation from •  Patientsshould with medical 204 the standard facial projection.



Length Determination Radiographic Evaluation •  Grossman formula •  Metode Ingle •  Metode Weine •  Metode Kuttler



problem that prohibit the holding ofRadiographic film/sensormethod of length determination 1. Measure the estimated working length from preoperative •  Patients with pacemaker periapical radiograph. (?) 2. Adjust stopper of instrument to this estimated working length



and place it in the canal up to the adjusted stopper. 3. Take the radiograph. 4. On the radiograph measure the difference between the tip of the instrument and root apex. Add or subtract this length to the estimated working length to get the new working length. 5. Correct working length is finally calculated by subtracting 1 mm from this new length. (Fig. 15.8) - subtract 1 mm - subtract 1.5 mm - subtract 2 mm



Advantages of radiographic methods of working length



determination Cleaning and Shaping 1. One can see the anatomy of the tooth



Principles of Cleaning •  Presence of clean dentinal shavings •  Color of the irrigant •  Canal enlargement 3 files sizes beyond the first instrument Do not correlate well with debridement



Grossman Method/Mathematic Method of Working Length Determination It is based on simple mathematical formulations to calculate the working length. In this, an instrument is inserted into the canal, stopper is fixed to the reference point and radiograph is taken. The formula to calculate actual length of the tooth Figs 15.8A to C: Modification in length by substraction is as follows: in case of root resorption



Grossman Formula Actual length of the tooth



Apparent length of tooth in radiograph = _____________________________________________ By above, we see those threelength variables are known and Actual length ofasthe Apparent of instrument instrument radiograph by applying the formula, 4thinvariable, i.e. actual length of tooth _______________________________



can be calculated.



• • •



10 or 15 size instrument. If it is of average wid or 25 size instruments. If canal is wide, use 30 instrument. Insert the selected file in the canal up to the estim length and1/22/19 take a radiograph. If file is too long or short by more than 1 mm f diameter, readjust the file and take second rad If file reaches major diameter, subtract 0.5 mm younger patients and 0.67 for older patients.



Advantages • Minimal errors • Has shown many successful cases • Rapid development of increases the chances o obturating material. Disadvantages • Time consuming and complicated • Requires excellent quality radiographs.



Actual length of the instrument × Apparent length of tooth in radiograph Actual length of tooth = ________________________________________________ Apparent length of instrument in radiograph



Disadvantages 1. Wrong readings can occur because of: a. Variations in angles of radiograph b. Curved roots c. S-shaped, double curvature roots. Kuttler’s Method According to Kuttler, canal preparation should terminate at apical constriction, i.e. minor diameter. In young patients, average distance between minor and major diameter is 0.524 mm where as in older patients it 0.66 mm. Working Length Determination



Modification in the length subtraction 1. No resorption 2. Periapical bone resorption 3. Periapical bone + root apex resorption



Disadvantages of radiographic methods of working length determination 1. Varies with different observers 2. Superimposition of anatomical structures 3. Two-dimensional view of three-dimensional object 4. Cannot interpret if apical foramen has buccal or lingual exit 5. Risk of radiation exposure 6. Time consuming 7. Limited accuracy



Technique • Locate minor and major diameter on preoperative radiograph Apical Fig. 15.3: Anatomy Minor apical diameter Principles • Estimate length of roots from preoperative radiograph. Fig. 15.2: Usually the reference point is highest point on incisal •  Purpose: facilitate cleaning • Estimate canal width on radiograph. If canal is narrow, use Disadvantagesedge ofofradiographic methods of working length anterior teeth and cusp tip of posterior teeth and provide space for placing 10 or 15 size instrument. If it is A of average width, use 20 determination Apex obturating 1. materials or 25 size instruments. If canal is wide, use 30 or 35 size Varies with different observers B Apical constriction 2. Superimposition of anatomical structures •  Maintain/develop a instrument. Therefore in case of teeth undermined cusps and fillings, canal 3. tapering Two-dimensional view of with three-dimensional object continuously funnel • Insert the selected file in the canalCup toRoot the estimated canal should be reduced considerably before preparation. Cannot interpret if apical foramen hasaccess buccal or lingual exit from canal 4.orifice totheythe apex length and take a radiograph. D Cementum 5. Riskshape of radiation exposure Anatomic is “tip or end of root determined morpho• If file is too long or short by moreE thanDentin 1 mm from minor •  Maintain original of apex root 6. Time logically”. consuming canal diameter, readjust the file and take second radiograph. F Apical foramen 7. Limited accuracy • If file reaches major diameter, subtract 0.5 mm from it for Radiographic •  Maintain apical foramen in itsapex is “tip or end of root determined radiographically”. younger patients and 0.67 for older patients. original position Grossman Method/Mathematic Method of Length Apical foramen is main apical opening of the root canal which •  Keep the Working apical opening as Determination Advantages located away from anatomic formulations or radiographic apex. small as possible It is basedmayonbesimple mathematical to calculate Apical constriction (minor diameter) isisapical portion into the • Minimal errors the working length. In this, anapical instrument inserted of root is canal havingto narrowest diameter. It ispoint usually 0.5 -1 mm canal, stopper fixed the reference and radiograph • Has shown many successful cases short of apical foramen (Fig. 15.3). The minor length diameter widens is taken. The formula to calculate actual of the tooth • Rapid development of increases the chances of retaining apically to foramen, i.e. major diameter (Fig. 15.4). obturating material. is as follows: 2. One can find out curvature of the root canal 3. We can see the relationship between the adjacent teeth and structures. of anatomic Shaping



Cementodentinal junction is the region where cementum and dentin united, Apparent the point atlength which cemental Actual length of thearetooth of toothsurface in radiograph _____________________________________________ = apex terminates at or near the of tooth. It is not always necessary Actual length of the Apparent length of instrument that CDJ always coincide with apical constriction. Location of instrumentCDJ ranges from 0.5 - 3 mm in radiograph short of anatomic apex (Fig. 15.5). _______________________________



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SIGNIFICANCE OF WORKING LENGTH • Working length determines how far into canal, instruments



Fig. 15.4: Anatomy of root apex



Disadvantages • Time consuming and complicated • Requires excellent quality radiographs.



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ally”.



of root canal system



iographic apex is “tip or end of root determined radiohically”. Fig. 17.3: Three-dimensional obturation of root canal system



cal foramen is main apical opening of the root canal which be located away from anatomic or radiographic apex.



cal constriction (minor apical diameter) is apical portion oot canal having narrowest diameter. It is usually 0.5 -1 mm t of apical foramen (Fig. 15.3). The minor diameter widens ally to foramen, i.e. major diameter (Fig. 15.4). Cementodentinal junction is the region where cementum dentin are united, the point at which cemental surface inates at or near the apex of tooth. It is not always necessary CDJ always coincide with apical constriction. Location of ranges from 0.5 - 3 mm short of anatomic apex (Fig. 15.5).



NIFICANCE OF WORKING LENGTH Working length determines how far into canal, instruments an be placed and worked. t affects degree of pain and discomfort which patient will xperience following appointment by virtue of over and nder instrumentation. f placed within correct limits, it plays an important role n determining the success of treatment. Before determining a definite working length, there should be straight line access for the canal orifice for unobstructed penetration of instrument into apical constriction. Once apical stop is calculated, monitor the working length periodically because working length may change as curved anal is straightened. Failure to accurately determine and maintain working length may result in length being over than normal which will lead o postoperative pain, prolonged healing time and lower uccess rate because of incomplete regeneration of ementum, periodontal ligament and alveolar bone. When working length is made short of apical constriction t may cause persistent discomfort because of incomplete



Fig. 15.4: Anatomy of root apex



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Fig. 17.2: Portals of communication of root canal system and periodontium



Mechanical Objectives (Schilder)



Fig. 15.5: CDJ needs not to terminate at apical constriction. CDJ needs not terminate at apical It can beto0.5-3 mm short of the constriction. apex



0.5 – 3 mm short of the apex



cleaning and underfilling. Apical leakage may occur into uncleaned and unfilled space short of apical constriction. It may support continued existence of viable bacteria and contributes to the periradicular lesion and thus poor success rate. Working Width Working width is defined as “initial and post instrumentation horizontal dimensions of the root canal system at working length and other levels”.



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The mechanics of cleaning and shaping may be viewed as an extension of the principles of coronal cavity preparation to the full length of the root canal system. Schilder gave five mechanical objectives for successful cleaning and shaping 30 years ago. The objectives taught the clinicians to think and operate in three dimensions. The objectives Schilder are: should 1.  given RC by preparation 1 . The root canal preparation should develop a develop a continuously continuously tapering cone (Fig. 17.4.) : This shape tapering cone mimics the natural canal shape. Funnel shaped preparation of canal should merge with the access cavity so that 2.  Making preparation multiple instruments will slide into the canal. Thus in access cavity and root canal preparation should form a continuous planes which introduces the channel. concept of “flow” 2. Making the preparation in multiple planes which introduces concept ofthe “flow”: This objective preserves 3.  the Making canal narrower the natural curve of the canal. apically and widest coronally 3. Making the canal narrower apically and widest coronally: create a transportation continuous tapers up toof apical 4.  ToAvoid thethird which creates the resistance form to hold gutta-percha in foramen the canal (Fig. 17.5). 4. Avoid of the foramen: There should 5. transportation Keep the apical opening asbe gentle and minute enlargement of the foramen while as(Fig. possible maintaining small its position 17.6).



Fig. 17.4: Prepared root canal shape should be continuous tapered



Fig. 17.5: Diagrammatic representation of objectives of canal preparation



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Biological Objectives Remove the pulp tissue, bacteria and their by-products from the RC



Preparation Techniques Apical to Coronal



Coronal to Apical



Conventional



Step-down



Step-back



Crown-down pressureless Hybrid technique



Modified step-back Passive step-back



Modified double flare Balanced force technique



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Watch Winding Textbook of Endodontics



•  Back-forth oscillation, right and left •  Angle of rotation 30o – 60o •  Efficient with K-type instrument •  Less aggressive



Fig. 17.17: Rotation of file in watch winding motion



4. Carve: Carve is performed with reamers to do shaping of the canals. In this a precurved reamer as touched with dentinal wall and canal is shaped on withdrawal. 5. Smooth: It is performed with files. In this circumferential motion is given to smoothen the canal walls. 6. Patency: It is performed with files or reamers. Patency means that apical foramen has been cleared of any debris in its path. BASIC PRINCIPLES OF CANAL INSTRUMENTATION 1. There should be a straight line access to the canal orifices (Fig 17.19). Creation of a straight line access by removing overhang dentine influences the forces exerted by a file in apical third of the canal. 2. Files are always worked with in a canal filled with irrigant. Therefore, copious irrigation is done in between the instrumentation, i.e. canal must always be prepared in wet environment. 3. Preparation of canal should be completed while retaining its original form and the shape (Fig. 17.20). 4. Exploration of the orifice is always done with smaller file to gauge the canal size and the configuration.



Fig. 17.18: Watch winding and pull motion



Watch Winding and Pull Motion In this, first instrument is moved apically by rotating it right and left through an arc. When the instrument feels any resistance, it is taken out of the canal by pull motion (Fig. 17.18). This technique is primarily used with Hedstroem files. When used with H-files, watch winding motion cannot cut dentin because H-files can cut only during pull motion. Motions of Instruments for Cleaning and Shaping For effective use of reamers and files, following six different motions are given. 1. Follow: It is performed using files during initial cleaning and shaping. In this file is precurved so as to follow canal curvatures. 2. Follow withdraw: It is performed with files when apical foramen is reached. In this simple in and out motion is given to the instrument. It is done to create a path for foramen and no attempt is made to shape the canal. 3. Cart: Cart means transporting. In this precurved reamer is passed through the canal with gentle force and random touch



Fig. 17.19: Straight line access to root canal system



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