Endodontic cleaning and shaping
This section gives a better understanding regarding the need for a proper cleaning and shaping of the canals together with the working length estimation, cleaning and shaping techniques, irrigants used and the possible trouble shoots.
1. Why is a reference point needed to calculate the working length?
The point from which the working length is measured should be a stable one that can be reproduced. One point of the measurement of working length is the anatomic apex and the other point may vary but it should be recorded for each tooth. In the anterior teeth, it is usually the incisal edge. For broken teeth, any projection on the remaining tooth structure is taken as the reference. For the posteriors, usually the cuspal tips corresponding to the canal are taken as the reference.
Ref: Franklin S.Weine,Endodontic therapy, Mosby , 6th Edn,261
2. Why apex locators cannot eliminate radiographs in endo, though they provide highly accurate information?
Pre operative radiographs are essential before any active treatment is started. Canal width, curvature and the number of canals cannot be found out with an apex locator and a radiograph is needed for that. They can only add to the information given by the radiographs.
Ref: Franklin S.Weine,Endodontic therapy, Mosby , 6th Edn,260
3. Why does a patient report with tenderness on a recently instrumented tooth?
Tenderness on the instrumented tooth may be due to overinstrumentation of the canal which can be confirmed by inserting a sterile paper point into the canal at a slightly more working length. When the paper point is withdrawn, there is a reddish brown discoloration that indicates seeping in the periapical area. A new shorter working length is calculated to prevent repeated irritation.
Ref: Franklin S.Weine,Endodontic therapy, Mosby , 6th Edn,252.
4. Why is the working length estimated cautiously in teeth with periapical radioluscency and resorption?
Radioluscent areas periapically are due to destruction of periapical bone by phagocytic cells. These cells may also destroy the root leading to root resorption. So while determining the working length in such teeth, an additional 0.5 mm is reduced from the calculated working length for teeth with periapical radioluscency and radiographic indication of apical resorption. If root resorption is extensive, upto 2 mm can be reduced from the working length to allow for the dentin matrix.
Ref: Franklin S.Weine,Endodontic therapy, Mosby , 6th Edn,251,252.
5. Why is the smear layer removed to achieve complete sealing of the canal?
The smear layer contains dentin debris, bacteria and its endotoxins and pulpal remnants . If it is not removed, the canal is not sealed completely and microleakage and failure can result. So it has to be removed to achieve complete sealing by using 17% EDTA flooded into the canal for 1 minute.
Ref: Stephen Cohen,Richard C.Burns,Pathways of the pulp, Mosby, 8th Edn,286.
6. Why is shaping of the canal essential to achieve a three dimensional seal?
Shaping removes the restrictive dentin, allow irrigants to work deeper and quicker so that it circulates into all the aspects of the canal. It also eliminates the pulp, bacteria and their endotoxins. When the contents of the canal are completely removed and the canal shaped, the source of irritation is removed and a perfect seal can be achieved.
Ref: Stephen Cohen,Richard C.Burns,Pathways of the pulp, Mosby, 8th Edn,235.
7. What is the role of calcium hydroxide as an Intracanal medicament in weeping canals?
Calcium hydroxide is placed in the canal after drying the canal with sterile absorbent points. A perfectly dry clean canal is seen in the next appointment which may be due to 3 reasons. The Ph of the periapical tissues might have been changed by the calcium hydroxide which is basic in nature. The calcifying potential of calcium hydroxide has started to build up bone in the lesion. The caustic action of calcium hydroxide burns out the residual chronic inflamed tissue.
Ref: Franklin S.Weine,Endodontic therapy, Mosby , 6th Edn,228
8. Why is EDTA inactivated after apical constriction is opened?
This is because the chelate may seep into the periapical tissue and damage the periapical bone. So after the appointment is completed, sodium hypochlorite is used to irrigate the canal where EDTA has already been used, so that it gets inactivated.
Ref: Franklin S.Weine,Endodontic therapy, Mosby , 6th Edn,226
9. Why chelating agents should be used cautiously?
Chelating agents are not used in blocked canals or canals with ledges, to locate the apex. Forcing a sharp instrument against a wall softened by a chelate may lead to a false canal formation. Also in curved canals, they can cause root perforation.
Ref: Franklin S.Weine,Endodontic therapy, Mosby , 6th Edn,225
10. Why hydrogen peroxide is not the last irrigant used in the canal?
It is because the nascent oxygen released may remain and after closure, it may build up pressure. So always sodium hypochlorite is used after hydrogen peroxide is used so that it reacts with the peroxide and liberates the remaining oxygen. Then the canal is given a closed dressing after drying with paper points.
Ref: Franklin S.Weine,Endodontic therapy, Mosby , 6th Edn,222
11. Why is hydrogen peroxide used as an irrigant?
Hydrogen peroxide, when it is in contact with the tissue, foams the debris from the canal. Also it liberates oxygen that destroys anaerobic micro organisms. It is specially used for draining canals that are left open because, the bubbling action dislodges food particles and other debris in the canal. Also, it is less damaging to the periapical tissues.
Ref: Franklin S.Weine,Endodontic therapy, Mosby , 6th Edn,222.
12. Why is the usage of irrigants important in a canal preparation?
Apart from removing the dentinal debris and preventing breakage of instruments in the canal, irrigants also are necrotic tissue solvents. They loosen the pulp tissue and micro organisms from the dentinal wall and are removed, especially in the accessory canals where reamers and files don’t fit. Some irrigants even have a bleaching action and decrease the chance of post operative darkening.
Ref: Franklin S.Weine,Endodontic therapy, Mosby , 6th Edn,222
13. Why Nickel Titanium files were introduced in endodontics?
The NiTi files have shape memory (ie) they return to their original shape even if bent severely and they are more flexible which facilitates them to be used efficiently in small curved canals.. But they do minimal canal preparation when used in hand. So they are used in mechanical handpieces to do a preparation faster.
Ref: Franklin S.Weine,Endodontic therapy, Mosby , 6th Edn,209
14. What are the common problems faced when a small, curved canal is cleaned and shaped?
The common problems that are faced are root perforation, ledging and instrument breakage due to forcing and driving the instrument, overuse of reaming action and over relying on chelating agents. Precurving of files, incremental instrumentation and flared preparations can prevent these problems.
Ref: Franklin S.Weine,Endodontic therapy, Mosby , 6th Edn,181-183
15. Why canal flaring is done with caution in small curved canals?
Overflaring of small curved canals can lead to a perforation into the periodontal space on the inner portion of the curve called Strip perforation, which may lead to a periodontal lesion or remain normal. To prevent this, anticurvature filing is done, so that the inner wall receives decreased rasping action.
Ref: Franklin S.Weine,Endodontic therapy, Mosby , 6th Edn,180
16. Why is the canal preparation flared?
When the preparation is flared at the orifice, smaller and more flexible files can be used at the apex, more dentin is available at the apex for dentin matrix, irrigants have more room to reach the irritants and the necrotic debris, wider orifice makes easy placement of finger spreaders and GP cones, in curved canals files are more effective and retain original canal shape and mainly a desired canal shape is obtained, narrow at the apex and wide at the orifice.
Ref: Franklin S.Weine,Endodontic therapy, Mosby , 6th Edn,176
17. Why is selection of initial apical file important?
The first file that binds at the apical portion of the canal, at the working length is the initial apical file. If a smaller instrument is chosen, it does not bind to the walls and it does not remove the dentin. If a larger instrument is chosen, it doesn’t reach the apical portion. So the initial apical file is selected which binds at the apex at the estimated working length. The canal is enlarged 3 times larger than the initial apical file.
Ref: Franklin S.Weine,Endodontic therapy, Mosby , 6th Edn,175,176
18. Why is a canal preparation done in a wet environment?
Preparations done in a dry canal leads to packaging of dentin chips and debris near the apical foramen which in turn prevents proper sealing. Heavy irrigation during preparation forces the debris to the chamber where they may be removed by aspiration or absorbent points. Also a wet canal is less likely to bind instruments and so fatigue of the files and breakage are reduced.
Ref: Franklin S.Weine,Endodontic therapy, Mosby , 6th Edn,175
19. Why are smaller size instruments used with care and periodically disposed?
Files 6, 8 and 10 are smaller size instruments and are discarded after the first appointment itself preferably because the flutes of the instrument may show signs of stress, fatigue and alterations of shape. If a fatigue instrument is repeatedly used in the canals, then it may break in the canal. So these instruments are checked every time they are removed from the canal by wiping clean with a sterile cotton role.
Ref: Franklin S.Weine,Endodontic therapy, Mosby , 6th Edn,174.
20. Why is the working length estimated before starting the instrumentation?
Working length is the length between the reference point and the anatomic apex of the tooth. It is calculated before instrumentation is started because overinstrumentation or repeated passage of an instrument through the apical foramen can cause flare ups and when apical constriction is lost, GP cannot be packed at the apex affectively. A measurement indicator or a stop is used to fix the working length. Also it determines the depth to which the instruments can be used, the depth to which the filling is placed, to reduce the pain and discomfort felt by the patient and above all it determines the success of the treatment.
Ref: Franklin S.Weine,Endodontic therapy, Mosby , 6th Edn,174
21. Why does a file have more cutting efficiency than a reamer?
Some of the principles of design are changed in a file to improve the cutting efficiency. A file has a square blank and twisted more to give increased number of cutting edges. 1 ½ to 2 ½ flutes are given per mm and thus the cutting edges are more. The cross sectional area of the file was greater than that of a reamer and it is less susceptible to fracture.
Ref: Franklin S.Weine,Endodontic therapy, Mosby , 6th Edn,168
22. Why does a barbed broach break easily in the canal?
Barbed broaches are tapered instruments of soft steel, notched by a shredder to produce sharp barbs extending from the shaft. This design makes it break easily since the notching weakens the shaft by providing a place for fracture if stress or torque is applied. So if hard surface of the dentin is felt, the instrument is not inserted any further.
Ref: Franklin S.Weine,Endodontic therapy, Mosby , 6th Edn,166.
23. Why are smooth broaches not used nowadays to check the patency of the walls?
Smooth broaches are not used nowadays for this purpose because inflammed or necrotic tissues may be forced through the apex. So tissue bulk is removed before any instrument is placed near the apex.
Ref: Franklin S.Weine,Endodontic therapy, Mosby , 6th Edn,166
24. Why is canal preparation important in endodontics?
The canal contents are removed by cleaning and shaping which include removal of pulp tissue, necrotic debris, microorganisms and affected dentin. The canal walls are also prepared to receive a filling material which seals the apical foramen and the lateral and accessory canals. A smooth, tapering preparation towards the apex is achieved by cleaning and shaping.
Ref: Franklin S.Weine,Endodontic therapy, Mosby , 6th Edn,165
25. Why are chelating agents preferred over caustic chemicals in enlarging sclerotic canals?
The caustic chemicals were non selective and destroyed anything that comes in contact including periapical tissue. Whereas the chelating agents act on the calcified tissues only and have little effect on the peraiapical tissues. The chelating agent is placed in the orifice of the canal that is sclerosed with an endo explorer or the flutes of an instrument.
Ref: Franklin S.Weine,Endodontic therapy, Mosby , 6th Edn,224,225.
26. Why is the term “cleaning and shaping” used while preparing the canal?
Preparation of the canal includes cleaning of all inorganic debris, organic substrates and microorganisms and shaping of the canal to facilitate the placement of permanent three dimensional filling and so is the term “cleaning and shaping”.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 396
27. What is the objective of cleaning and shaping of the canal?
Cleaning should remove the organic and inorganic material in the canal completely with no traces left out that could contribute to the growth of bacteria and generate products of tissue decomposition and destroy all the microorganisms in the canal. Shaping should result in a cavity form or shape that is simplest and most effective for a three dimensional obturation.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 396
28. How is the vital pulp tissue removed from the canal?
Broaches are used to remove the vital pulp tissue. It hooks and twists the pulp filament around itself so as to extract the pulp from the root canal. The instrument should never come into contact with the canal walls.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 397
29. What are the precautions to be followed while using the broach?
The broach must never be used in narrow or calcified canals, never introduced into curved canals or curved portions of straight canals and it is dangerous to introduce it to the apex.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 397
30. In which teeth can barbed broaches be used confidently?
In upper central incisors, canines, upper II premolars with single canal, palatal roots of upper molars and distal roots of lower molars.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 397,398
31. How is the barbed broach used in the canal?
The correct size of the broach is chosen wide enough to engage the pulp effectively. It is introduced for 2/3 of the length of the root canal and rotated at least 180o and then extracted. Another technique is two broaches can be introduced into the coronal two thirds of the canal and rotated around each other.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 397,398
32. How is necrotic pulp tissue and microorganisms removed from the canal?
Necrotic pulp tissue and micro organisms cannot be removed with a broach. Their removal is done by the use of irrigating solutions and the mechanical action of the endodontic instruments.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 398
33. What are the requirements of endodontic irrigating solutions?
• Ability to digest proteins and dissolve necrotic tissue. • Low surface tension and ability to reach the areas that cannot be reached by the instruments. • Must have germicidal and antibacterial properties. • Non- toxic and non- irritating to the periapical tissues. • Lubricating property. • Prevent discoloration of the tooth • Harmless to the patient and dentist • Readily available and in expensive.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 399
34. Which irrigant solution meets the requirements and widely used today?
Sodium hypochlorite is the irrigating solution that meets the requirements of irrigants and widely used today.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 399
35. Why is 3% hydrogen peroxide alternated with sodium hypochlorite while cleaning?
Alternating hydrogen peroxide with sodium hypochlorite facilitates mechanical removal of dentinal shavings. Oxygen is generated by chemical reaction between hydrogen peroxide and hypochlorite and effervescence is produced that pushes the dentin mud towards the access cavity where it is mechanically removed.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 406
36. What are the advantages of alternating use of hydrogen peroxide and sodium hypochlorite?
• It facilitates the mechanical removal of dentinal shavings. • Increases the permeability of the dentinal tubules. • It provides greater antimicrobial activity by the action of the generated oxygen on anaerobic bacteria.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 406,407
37. How does the lubricating action of sodium hypochlorite help for cleaning the canal?
The lubricating property of sodium hypochlorite helps for the introduction of instruments even in narrow and tortuous canal facilitating their work within the canal. It limits the engagement of instruments with the walls and reduces the risk of fracture.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 407
38. What are chelating agents?
Chelating agents are solutions used in endodontic practice that combine chemically with the calcium ions and thus soften the dentin.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 408
39. Which is the commonly used chelating agent?
EDTA is the commonly used chelating agent that combines with the calcium ions and causes the hydroxyapatite crystals to transform into the calcium salt of ethylene diamine tetra acetate.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 408
40. What is the purpose of cleaning and shaping?
The shaping process opens the root canal system for the irrigants and allows successive three dimensional obturation. The true agents of cleaning are the irrigants.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 410
41. Why is sodium hypochlorite not considered as ‘complete’ irrigant?
Though sodium hypochlorite is responsible for the deep cleaning of the root canal system, it cannot be considered ‘complete’ because it is not able to remove the smear layer produced during the instrumentation.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 410
42. How is the smear layer described?
The endodontic instruments cut the dentin and a consequence of this action is the smear layer. The debris that is formed is smeared and compacted against the canal surfaces during the instrument movement.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 410
43. What are the components of a smear layer?
The smear layer has 2 components, a thin layer that is 1-2 µ thick and forms a mat over the canal walls and the part the dentinal tubules forming plugs about 40µ deep.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 410
44. What is the role of the smear layer in endodontic treatment?
It is believed that the debris plug obstructs the dentinal tubules and reduces the permeability of the dentin thereby forming a barrier preventing the penetration of bacteria into the tubules. But the above statement is only partly true since the smear layer slows the passage of micro organisms in the dentinal tubules and does not block the tubules as a whole. Also the smear layer doesn’t allow the penetration of medication or obturation material into the tubules.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 411,412
45. How is the removal of the smear layer beneficial?
Removal of the smear layer improves the contact between the obturation material and canal walls and thereby the seal is also improved.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 412
46. What are the advantages of alternating sodium hypochlorite and EDTA during canal preparation?
Alternating the use of sodium hypochlorite and EDTA is more bactericidal than using hypochlorite alone. It enables sodium hypochlorite to carry out its function in depth while EDTA counters the smear layer formation during shaping. This way allows the hypochlorite to penetrate to those areas where it is impossible otherwise because of the smear layer. Also EDTA alternated with sodium hypochlorite prevents organization of the smear layer that occludes the dentinal tubules.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 413
47. How does temperature affect sodium hypochlorite?
Raising the temperature of the sodium hypochlorite potentiates the solvent action of sodium hypochlorite. When the temperature of sodium hypochlorite is raised to 500 c, there is a notable reduction of formation of the smear layer.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 413
48. How is the irrigant carried into the canal?
The irrigants are carried in 5 ml syringes with a fine precurved needle to aid its passage into the canal and should reach the maximum working depth without any obstruction from the canal walls.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 418
49. How is the irrigation carried out inside the canal?
The irrigation must be carried out without excessive pressure with a continuous movement of the needle up and down to reduce to a minimum risk of pressure extrusion of irrigant. The excess irrigant is constantly aspirated.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 419
50. What should be the shape of the prepared canal?
The prepared canal must be uniformly and progressively conical or a truncated cone shaped without ledges on its walls, with the thinnest section of the cone positioned apically and widest coronally.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 420
51. Why is a continuous taper essential for a prepared canal?
The continuous taper creates a resistance form to hold the gutta percha within the canal and eliminates the potential for overextensions.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 422
52. Why is apical control not possible in lateral canals while obturating?
The lateral canals are not instrumented and have no conicity. So apical control of the obturating material is impossible and leads to extrusion of sealer at their ends.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 422
53. Why should canal preparation be conical in all the planes?
The conical preparation of the canal must be in a mesio distal as well as bucco lingual planes so that the GP has a” flow” into the root canals. The original anatomy of the root canal has to be followed so that the curves are smooth in all the directions.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 423
54. How does excessive instrumentation affect the apical foramen?
Excessive or improper instrumentation may cause transportation of the apical foramen from its original position and the shape is modified.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 423
55. Why is the size of the apical foramen controlled?
The apical foramen must be kept as small as practical to obtain a better seal and to prevent extrusion of GP. It should be enlarged to the size that makes obturation easy.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 426
56. What happens if the apical foramen is enlarged excessively?
Excessive enlargement of the apical foramen may cause periodontal damage. It creates difficulty in obtaining a good seal and less apical control of the obturation, leading to overextensions.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 423
57. Why is accurate checking of the working length important?
The working length has to be determined accurately by electronic apex locators or by radiographic means so that the instruments are not extended beyond the foramen by which the nearby structures like the maxillary sinus or mandibular canal can be damaged. The rubber stops are always correctly positioned before starting the instrumentation.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 429
58. At what situations is the instrument allowed to go slightly beyond the apical foramen?
The instrument can be allowed slightly beyond the apical foramen when drainage is established for acute alveolar abscess or when caustic medications are injected for treating the lesion. Otherwise, the instrument should not go beyond the apex.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 429
59. How are the areas of the dentinal walls that doesn’t come into contact with the endodontic instruments cleaned?
The tissue debris in areas which do not come into contact with the endodontic instruments are removed by the digestive activity of 5% sodium hypochlorite heated at 500c that accompanies the instrumentation within the canal. It digests all the organic material within the canal.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 430
60. Why each canal in a multirooted tooth is prepared separately before proceeding to the next?
Each canal requires to own series of instruments, has its own length, reference points, curvature and orientation of apical foramen and it is difficult to bear all these in mind simultaneously for all the canals during instrumentation. So they should always be prepared individually and completely.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 430
61. How can the irrigants be potentiated?
The action of the irrigants can be potentiated by using ultrasonics to activate them.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 416
62. How does ultrasonics help for removing the debris?
Ultrasonics are combined with sodium hypochlorite to increase the effectiveness. They act by acoustic streaming or cavitation phenomena thereby help for removing the debris.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 416
63. What is acoustic streaming?
Acoustic vibrations with frequencies around 25,000 cycles/sec are transferred from the energy source via a transducer to the surrounding irrigant. By this there is a rapid movement of fluid particles around the object that vibrates. The temperature of the liquid surrounding the vibrating object is also increased. Thus it helps for removing the debris.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 416
64. How does cavitation remove the debris?
The ultrasonic vibrations cause a cavitation in which microbubbles are formed that gradually increases in the diameter until they collapse. Very effective small implosions are produced leading to irregular agitation of liquid resulting in removal of debris from within the canal.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 416
65. How is the combined action of ultrasonics and hypochlorite effective in removing the debris?
Ultrasonics when combined with sodium hypochlorite is extremely effective in the removal of organic substrate even in the areas where instruments were unable to contact the canal walls. Whereas when ultrasonics was used alone, some debris were found to remain in the instrumented areas of dentin.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 416
66. What is the importance of cleaning and shaping the canal?
Cleaning and shaping is the most important phase of root canal therapy since residual infection in the canal left out by improper cleaning and shaping may be a contributing cause for peripheral infection. So what is removed from the root canal is more important than what is placed inside.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 396
67. What is Preparing of the root canal?
Preparation of the root canal means cleaning of all inorganic debris, organic substrates and microorganisms and shaping to facilitate the placement of a permanent three dimensional filling.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 396
68. What are the precautions to be taken when sodium hypochlorite is used for irrigation within the canal?
The use of sodium hypochlorite should be limited to within the root canal and extrusion beyond the apical foramen should be avoided. The working length estimation is carefully done. Root canals should be irrigated gently and smaller needles that never engage the canal walls should be used. Visually, the reflux of the irrigating solution from the access cavity while being introduced into the canal has to be checked.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 405
69. What is the role of sodium hypochlorite within the canal as an irrigant?
The sodium hypochlorite within the root canal not only has a solvent action on the pulp but also keeps the dentinal debris in suspension, preventing blockage of the apical portion of the canal.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 406
70. Why is it said that cleaning is completed only after a complete shaping is achieved?
Since shaping facilitates cleaning, it allows a deeper and more apical penetration of the irrigating solutions and a deeper and more complete dissolution of the existing organic material. So complete cleaning is achieved after a complete shaping only.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 396
71. How is cleaning into all the aspects of the root canal anatomy achieved?
Cleaning all the aspects of the root canal is not achieved with files only. Files can clean the negotiable parts while the inaccessible parts of the root canal system such as the isthumus, resorption and the lateral canals are cleansed mainly by the irrigants. So it is clear that the files shape and the irrigants clean.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 397
72. What is barbed broach?
Barbed broaches are produced from a slightly conical, round metallic filament, that is notched in such a way as to create a ‘multiple barb’. It can fracture easily since it is a very delicate instrument.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 397
73. How is the size of the barbed broach important?
Choosing a correct size is important for a barbed broach. It should be wide enough to effectively engage the pulp but at the same time, not so wide that it can touch the canal walls. It cannot be used indiscriminately at any situation.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 397
74. How does Sodium hypochlorite act?
It acts as a solvent on necrotic tissues and tissue fragments that have lost their blood supply. It is ineffective on vital tissues with intact blood supply.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 400,401
75. Why is it important to know whether the canal been pretreated with medications?
Premedications with parachlorophenol or formaldehyde fix the tissue and make the activity of hypochlorite slow on the necrotic pulp tissue. Hence it should be kept in mind when cleaning the root canals.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 402
76. How does surface tension play a role for the efficiency of Naocl?
Sodium hypochlorite has a low surface tension and so it can reach areas beyond the reach of the instruments, lateral canals, resorptions etc. including the apical delta. Greater force is not necessary to inject hypochlorite into the root canal to make it reach the apex. It passively reaches the apex with the help of endodontic instruments. This makes it to integrate the most efficacious irrigation clinically.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 402,403
77. How does Naocl exhibit a germicidal action?
Naocl, when comes in contact with water, produces hypochlorous acid and sodium hydroxide. Then hypochlorous acid produces hydrochloric acid and oxygen. The free chlorine has germicidal properties when it combines with protoplasmic constituents, like proteins.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 405
78. How is Naocl useful as a sterilizing agent?
Naocl is indicated for sterilization of GP cones which cannot be heat sterilized. When the GP cones are immersed in hypochlorite for about 1 minute, they get sterilized completely without altering the physico - chemical structure.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 405
79. What are the points to be kept in mind when Naocl is used as irrigant?
When Naocl is used as an irrigant, it should be limited within root canal and not extrude beyond the apical foramen. Careful working length estimation, gentle irrigation of the canal using needles that do not engage the canal walls are to be checked. Also visual checking of reflux of the irrigant from the access while being introduced into the canal is done.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 405
80. What is the Physical - Mechanical role of hypochlorite in the root canal?
Apart from the chemical action in the canal, sodium hypochlorite keeps the dentinal debris produced during instrumentation in suspension thus preventing it from settling principally in the apical zone.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 406
81. What is the advantage of using EDTA as an irrigant together with Naocl?
Using EDTA together with Naocl allows filling of a greater number of lateral canals and opening of dentinal tubules. It provides a cleaner surface against which Gutta percha and the sealer will adapt.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 409
82. Why are chelating agents not used in canals with calcifications or obstacles?
Chelating agents are not used in canals that are unnegotiable due to calcifications or other obstacles because when the dentin is softened by the chelator, it is difficult to know whether the instrument is advanced in the original root canal or a false canal that is being made.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 410
83. When using EDTA with Naocl, why is irrigation ended with Naocl?
When alternating EDTA and Naocl, the final irrigation is always done with hypochlorite so that the acid along with its chelating action is neutralized.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 410
84. Where is the smear layer present in the canal?
The smear layer is present only on the surfaces of the canal where the endodontic instrument has been working contact and not in the other areas.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 411
85. How is the final rinse of the canal performed with ultrasonics?
At the end of shaping, ultrasonics can be used with a passive file in the canal that potentiates the action of EDTA and Naocl. These passive files are precurved and are about 2mm short of the apex. When placed in the canal with an irrigant, the ultrasonics is activated for 1 minute with 10% EDTA to remove all traces of smear layer and 3 minutes with 5% Naocl at 500 C to improve the completion of cleaning and to neutralize the acid.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 419
86. Why are ‘typical puffs’ of sealer present at the end of lateral canals?
The lateral canals are not instrumented and have no conicity and hence apical control of the obturation material is impossible in them. This leads to the presence of ‘puffs’ of sealers at their ends.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 422
87. Why is direct perforation common in upper lateral incisors?
In upper lateral incisors, the apical curvature is paltally oriented and is not radiographically appreciated. So when straight large instruments are used in such canals, the instruments are forced into the canal and screwed into the dentin resulting in a direct perforation. Similar errors can also occur in mesio buccal roots of upper molars and mesial roots of lower molars.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 425
88. How is direct perforation avoided?
Direct perforation is avoided by beginning the instrumentation with small pre curved files. The instrument should adapt itself to the anatomy of the canal eapecially in delicate zones like the apical one third.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 425,426
89. What is internal transportation of the canal?
When working within the canal is done short of the apex, the collagenous tissue, debris and dentin mud accumulate easily, blocking the canal till the apical foramen which is thus occluded. This is the internal transportation of the canal.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 426
90. What is the consequence of internal transportation?
Internal transportation of the canal is due to blockage of the apical foramen which leads to accumulation of pulp remnants and necrotic debris in the avascular root canal system. This is one of the factors for a persistent attachment apparatus disease. Also this may predispose to the formation of ledges, false paths and perforation.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 426
91. How is apical patency re established when there is an obstruction?
When the apical portion is obstructed, apical patency can be re-established by using generous sodium hypochlorite irrigations and trying to re negotiate the canal with the first instrument that was used (Recapituation).
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 426
92. Why are chelating agents contra indicated to re - establish apical patency?
In such situations of apical blockage, chelating agents are contra indicated because they pre dispose to the creation of a false canal or perforation.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 426
93. Why the apical foramen is kept as small as practical?
This is to obtain a better seal and to prevent extrusion of Gutta percha filling. The foramen must be cleansed and enlarged to a size that can be conveniently obturated without difficulty.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 426
94. Why is it dangerous to enlarge the foramen excessively?
Excessive enlargement of the foramen is done at the cost of periodontal damage and there is a greater difficulty in obtaining a good seal and less apical control of the obturation. Since a bigger foramen is a bigger area to be sealed, developing taper and preventing over extentions are more difficult.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 426,428
95. How does apical foramen enlargement vary in narrow and wide canals?
In narrow canals, the foramen has to be enlarged at least to a size corresponding to no. 20 file while in already wide canals the foramen has to be just cleaned without any enlargement; it should remain the same original size and shape.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 428
96. In which conditions, going beyond the apical foramen are allowed?
Foraminal patency is essential for the success of the treatment and this can be obtained by intentionally and passively inserting the tips of the no. 10 file to the foramen. The other situation when slightly going beyond the foramen is allowed is when trying to establish an endodontic drainage for acute alveolar abscess.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 429
97. How is pushing the infected material beyond the apex avoided?
Careful use of instruments within the root canal in such a way that they work only on withdrawl and do not exert piston like action will avoid pushing infected material beyond the apex.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 429
98. In multirooted teeth, why each canal requires separate care and attention?
Each canal in a mutirooted tooth, has its own length, reference points, own curvature, own orientation of apical foramen and requires particular angulation of the radiographic cone. Hence each canal requires its own series of instruments and attention and all cannot be worked simultaneously due to difficulty in remembering the various difficulties in the various canals.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 430
99. How is cleaning and shaping of each canal done in a multirooted tooth?
Cleaning and shaping of canals in a multirooted tooth is done in a single visit. It is not advised to proceed with the next canal till one is completed. Also same instruments should not be jumped from one canal to the other. If canals could not be prepared on the same day, some of them can be prepared on one day and the other canals in the subsequent visit. This applies to both vital and non vital teeth.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 430
100. Why are medications not placed in the canal after enlargement?
The medications placed within the canal act as irrigants where they penetrate apically and cause further formation of exudates in the periodontal ligament space, leading to periodonitis and discomfort for the patient. So it is preferred to place them in the chamber in the form of a cotton pellet moistened by the vapours of the medication.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 431