Schilders Technique for shaping the root canal system
Various techniques have emerged for cleaning and shaping the canals to aid in a perfect obturation and this section specifically deals with Schilder's technique for shaping which is widely accepted.
1. How is the amount of precurving determined?
The amount of precurving of an instrument is determined from the radiographic appearance of the degree of curvature of the root.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 438
2. How is precurving of an instrument important?
A file that is precurved easily passes through the obstacles and calcifications that are encountered during early probing of the canal. Also precurvature prevents the instrument from making ledges or false canals and also prevents transportation of the apical foramen.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 438
3. What is an endobender?
Endobender is an ideal instrument for precurving the endodontic instruments without minimally changing the blades; it bends the instruments depending on the curve radius at the point where the file is placed.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 439
4. How does a non precurved reamer introduced into a curved canal work?
A non precurved reamer introduced into a curved canal follows the curvature of the canal. It cannot rotate in its own axis, reproduces in space the curve that it has adopted, producing an hour glass effect in the canal. This increases the chance of lacerating the apex or creating ledges.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 439,440
5. What are rubber stops?
A non precurved reamer introduced into a curved canal follows the curvature of the canal. It cannot rotate in its own axis, reproduces in space the curve that it has adopted, producing an hour glass effect in the canal. This increases the chance of lacerating the apex or creating ledges.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 439,440
6. What are the requirements of rubber stops?
The rubber stops must easily be applied and easily movable when need arises. They should securely remain on the shaft of the instrument so that the same working length can be maintained consistently throughout the entire process of cleaning and shaping. The stop must be seated 90 to the long axis of the instrument. They should be made in such a way that it can be oriented in the direction of the precurvature.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 440
7. Why should the rubber stop be seated at 900 to the long axis of the instrument and not tilted?
If the stop is tilted or positioned obliquely, the working length of the instrument may vary by as much as 2mm.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 440
8. Why should the stops be directional?
The stop should be directional ie have the possibility of being oriented in the direction of precurvature since while the instrument is inserted inside the canal, one can know towards which side the precurvature faces so that it can be directed in the desired direction.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 440
9. How is the canal negotiated?
Negotiation of the canal is the most delicate phase of canal preparation where the precurved instrument is passively introduced into the root canal without forcing or pushing it. Simple back and forth motion is required with no rotation and then first instrument to enter the canal is the file which will never fracture when correctly used.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 440
10. How is the obstacle in the final mms of the canal interprated?
An obstacle in the final few mms of the canals is interpreted as calcified canals. But it is not so because diseases of the pulp progresses in the corono apical direction and calcifications cannot occur in the last few mms while the rest of the canal is pervious. So obstacles in the apical portion are indicative of a sudden, accentuated curvature of the canal and not calcifications.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 441
11. What are the possible happenings when a small instrument is forced into the root canal?
Forcing the instrument against the obstacle can cause bending and fracture of the instrument, mobilization of calcifications from the canal walls that could fall into the canal and obstruct it, creation of ledges, false canals or perforations all of which will lead to failure of the treatment.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 441
12. When is the rubber stop positioned?
When the instrument has reached the depth indicated by the pre op radiograph and confirmed with Electronic apex locator, the rubber stop is positioned against the chosen reference point that is stable and readily identifiable.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 441
13. When can an instrument be withdrawn from the canal after it has been introduced?
After verification of the working length, the instrument is made to work within the canal with small back and forth movements and it is withdrawn only after it has created enough space around itself so that it is loose within the canal which indicates that the canal is sufficiently enlarged and a file of the next size can be used.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 441
14. What is anatomic apex?
Anatomic apex is the tip or end of the tooth root as determined morphologically.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 444
15. What is radiographic apex?
Radiographic apex refers to the tip or the end of the root of the tooth as seen on a radiograph.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 444
16. What is apical foramen?
Apical foramen is the opening of the root canal on the external surface of the root and not necessarily coincides with the anatomic apex depending on the apical curvature of the canal inside the root.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 444
17. What are the advantages of electronic apex locators?
Electronic apex locators locate the apical foramen without taking the radiographic apex into consideration. They are useful in cases of hidden apices, pregnant women, uncooperative patients, handicapped or in situations where radiographs cannot be taken, diagnosing perforations, convergence of 2 canals into a single canal and lastly, they reduce the exposure to x rays.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 450
18. How are the electronic apex locators useful in diagnosing perforations?
When there is a perforation and when the instrument comes in contact with the PDL through the perforation, it registers the same electrical resistance as it would at the apical foramen. This is especially helpful in buccal / lingual perforations that cannot be detected radiographically.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 450
19. How is the convergence of 2 canals to a single canal diagnosed with apex locator?
In these conditions, a file is placed in the canal till the apex and the instrument is connected to another file that is introduced in the other canal. When these two instruments contact, the apex locator detects it and the diagnosis is made.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 450
20. What are the advantages of the latest generation apex locators?
The latest generation apex locators make use of a different principle and are not affected by the contents of the root canal and can perform accurately even in moist conditions.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 452
21. When do false positive responses occur in the latest generation apex locators?
The latest apex locators give inaccurate responses when the shaft of the file used for the measurement comes in contact with the metal of a coronal restoration or if there is a previous obturation within the canal that impedes the contact of the file with the surrounding dentin.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 452
22. How is the patency of the apical foramen maintained?
The files are introduced as far as the apex in such a way as to clean the foramen, enlarge it into a practical convenient size preventing dentin mud from obstructing it. The same working length is transmitted to the subsequent instruments before inserting into the canal. The files should be precurved and should not be forced into the canal rather they should enter the canal passively.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 456
23. Why is the GG drill used only after sufficient enlargement with hand instruments?
The GG drill can be used only after sufficient canal enlargement with hand instruments because introducing it into a narrow canal possess a risk of instrument fracture and formation of ledges and false canals.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 460
24. How does GG drill give a typical funnel shaped appearance?
The GG drill is introduced passively into the coronal third of the canal and applied carefully without making contact with the entire circumference of the canal. The drill is used with a brushing motion in apico coronal direction. This gives the canal a typical funnel shaped appearance.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 460,461
25. What are the points to be kept in mind when GG drills are used?
The drill is always used with the irrigating solution since it produces a large amount of dentin mud. After use also the canal is irrigated generously with the irrigants. Also the drill is very fragile and fractures easily if applied energetically to the canal wall or causes the shaft to bend while it is working.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 461
26. Why is the radiograph of the first instrument in the canal important?
The radiograph of the first instrument at the radiographic apex is important because it is the key as the accuracy of all subsequent works depend on it. The working length of all the other instruments depends on this measurement only. This is the preoperative radiograph and it needs to be satisfactory for proceeding with other instruments.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 465
27. How is the depth of entry of the first instrument into the canal determined?
The instrument is aligned on the radiographic image and shortened by 1mm. This reduction in 1mm is done to compensate for the errors in the radiograph and therefore there is no risk of over instrumentation.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 466
28. Why the radiograph or the use of an apex locator after the instrument is important nowadays?
This is done to check whether the working length is not changed. Though this can be verified using an apex locator, the radiographs allow to check the thickness of the dentin still present around the instrument and thus avoid stripping.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 466
29. Why is cleaning and shaping of confluent canals done carefully?
Cleaning and shaping of 2 canals in the same root that merge to a common foramen has to be done carefully to prevent tearing of the apical foramen or pointless weakening of the root, including stripping.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 466
30. How is the merging point determined in the confluent canals?
The GP cone of the appropriate size is inserted in one canal that is prepared and a small file in the other canal. When the small file touches the GP in the prepared canal, it leaves an impression on the GP and that is the point of confluence or the distance from the apical foramen.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 466
31. In confluent canals, why is the point of confluence taken as apical foramen for the second canal?
When the second canal is prepared, the working length is calculated till the point of confluence only since trying to reach the apical foramen from a different direction carries a risk of tearing of the foramen and breaking of the file. The preparation in this canal is therefore shorter when compared to the first canal and is less marked.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 466,467
32. What are the essentials before starting the endodontic therapy?
•Recent and up to date preop radiograph •Precurving of instruments with directional rubber stops. •Position of the instrument in the canal is ascertained with a radiograph. •In multirooted teeth, cleaning and shaping is performed for one canal at a time, starting from the easiest. •A series of new instruments for each canal in multirooted teeth •The use of electronic apex locator combined with a radiograph to check the working length. •Tactile sense alone is not trusted. •The next step is never started unless the preceding step has been completed.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 467
33. What are the requirements of an ideal root preparation?
Complete access, a continuous tapering shape, maintenance of the original anatomy and conservation of tooth structure are the ideal requirements of a root preparation.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 472
34. What is the importance of complete access in root canal preparation?
The unobstructed access to the root canal system provides freedom during cleaning and shaping, helps for removing the debris and provides an opportunity to compact the obturating material three dimensionally. Omission of creating a complete access is one of the causes of endodontic failure.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 472
35. How does continuous tapering govern the root canal preparation?
A continuous tapering canal allows convenient usage of instruments, aids in debris removal, helps for finishing and irrigation and prevents the displacement of filling material during compaction. It provides a clear access to the various reaches of the preparation that aids in the flow of irrigating solution to the anatomical complexities.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 472,473
36. What are R type hand instruments?
They are historically the oldest hand instruments. It is manufactured from a soft iron wire that is tapered and notched to form barbs rasps along its surface. They are used in the gross removal of pulp tissue from the root canal system.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 475
37. What are Headstorm files?
Headstorm files or H files are extremely efficient cutting instruments and cutting occurs in pull direction only. They are manufactured by grinding flutes into tapered round metal blanks to form a series of intersecting cones. They are available in 21, 25 or 31mm lengths. They are highly susceptible to fracture, if used aggressively.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 475
38. What is recapitulation?
It is an essential concept in cleaning and shaping procedure introduced by Schilder. It is the sequential re entry or re capture of that portion of the root canal system that has been previously enlarged during preparation. The previously used smaller instruments or the initial apical file are re inserted. This procedure removes the dentinal shavings that accumulate apically in the root canal system and prevents blockage. It also ensures a continuous tapering shape to the canal.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 482
39. Why reaming alone is contra indicated?
Reaming alone is contra indicated because instruments used in reaming motion transport the endodontic cavity preparation towards the inner wall of the curve of the root canal system. Alternatively, when filing is done, it maintains the original anatomy of the root canal system and a more ideal shape can be created.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 482
40. Why is the irrigant maintained as a reservoir during endodontic cavity preparation?
After the pulp is removed, the cavity is irrigated copiously with sodium hypochlorite and the irrigant is allowed to pool in the chamber forming a reservoir. This pooling of the irrigant provides a continuous floatation of the debris. Pre endodontic restorations and bands are used to establish and maintain the reservoir of irrigant.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 489
41. What is the importance of irrigation during endo cavity preparation?
Copious and thorough irrigation is important for endo cavity preparation since it is the procedure that provides the digestion and removal of organic debris within the secondary ramifactions and permits the flow of filling material to these areas. Repeated changing of the irrigating solution is also important.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 489
42. What is the role of the initial file passed into the root canal system?
The initial file that is passed into the root canal system is not a working instrument but it acts as a guide file that explores the canal configuration. The smallest instrument that the canal system can accommodate without resistance is chosen as the initial file.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 490
43. How is the initial file carried into the canal?
Usually a No.6 or No. 8 file is chosen and precurved to mimic the pathway of the original canal and gently manipulated in a watch winding motion. The direction, angulation and configuration of each curve is evaluated. Ramifactions not detected by radiographs are also searched for and other anatomic variations are also noted.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 490
44. Why usage of GG drills is considered to be safe?
GG drills have a non cutting tip and it prevents perforation. So it is considered to be safe and effective.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 492
45. What are the guidelines to be followed when GG drills are used?
GG drills are effective instruments to be used in the canal but have to be used only after preliminary enlargement to prevent ledging. They are non flexible instruments and should be used only in straight line. The initial drill is the smallest drill that engages the tooth structure and followed by the next larger size. They are used sequentially in a step back modality with cutting mainly on the outer walls of the curvature.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 492
46. How is the patency established after preliliminary enlargement?
The preliminary enlargement permits unimpeded access to the apical third. The patency of the apical foramen is established and checked using only passive strokes with the smallest and most delicate instruments. These instruments have to be precurved to negotiate the foramen and the complex bands that occurs in that region. No attempt is made to enlarge the apical foramen at this time.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 494
47. Why NiTi instruments are used with care during enlargement?
NiTi instruments are used with caution during enlargement since they can undergo spontaneous fracture and cannot be retrieved or bypassed easily.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 494
48. How are NiTi instruments used safely during enlargement?
NiTi instruments can be used safely after a pre-enlargement phase. Torque and speed control handpieces are also helpful. They are used in a sequence of largest to smallest instrument in a crown- down fashion. The sequence must be repeated twice since they are not as sharp as stainless steel instruments.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 494
49. What is blending?
A continuous tapering shape is essential for a perfect preparation and this shape is achieved by combining the apical, middle and coronal thirds of the preparation that have already been prepared by the pre- enlargement and enlargement phases. This is called as Blending. When those phases are performed judiciously, blending becomes simplified.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 496
50. What will happen if the apical foramen is displaced?
Displacement of the apical foramen leads to three errors – direct perforation, formation of ledges and creation of a tear drop foramen.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 502
51. How are the curves of the coronal third managed?
The curves of the coronal third are eliminated before commencing the normal cleaning and shaping.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 509
52. Why are the curves of the coronal third straightened?
Straightening the curves of the coronal third permits more direct access to the apical region, improves tactile sense and control while directing the files apically, eliminates the restrictive dentin in the coronal third, reduces the risk of ledges, transportation of apical foramen and stripping. It also allows deeper penetration of the irrigating solutions and better removal of debris and maintenance of working length throughout the procedure.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 510
53. What is anti curvature filing?
This method consists of working the endodontic instruments constantly against the external wall of the curve, with the goal to prepare the canal at the expense of the thickest portion of the root, staying away from the curve and bifurcation.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 512
54. What are safety zone and danger zones?
In cross section of the canals, safety zones are those areas far from bifurcation where the dentin is thicker and danger zones are the areas where the dentin is thinner and the canal closer to the periodontium.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 512
55. Which are the safety zones and danger zones in Upper and Lower molars?
The safety zone in the upper molar is the mesial wall of the mesio buccal root and that in lower molar is the mesial wall of the mesial roots. The danger zone in the upper molar is the distal wall of the mesiobuccal root and that in the lower molar is the distal wall of the mesial root.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 512
56. Why circumferential filing is not done in molars with curved roots?
In molars with curved roots, the canals are not in the central position rather displaced towards the bifurcation. Considering this circumferential filing is avoided since it can lead to excessive thinning of the root or even perforation from stripping in the area of bifurcation. During condensation of the obturating material, the thinned out wall may also fracture.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 512,513
57. What are the three distinct phases in the preparation of the root canal?
The three distinct phases are •Negotiation of the root canal and determination of instruments’ working length •Maintenance of patency of the apical foramen •Enlargement of the body of the canal.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 438
58. What are the points to be remembered regarding the endo instruments?
The files and reamers used must be new, sterile and should be re- sterilized whenever need arises. The instruments should be within the reach of the dentist and must be kept sterile throughout the procedure. They must be precurved and equipped with rubber stops.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 438
59. How is pre curving of an instrument done?
The precurving should coincide with the curve of the root canal. Precurving is done in a gentle and gradual way and must not be bent.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 439
60. How does a precurved reamer work?
When a precurved reamer is introduced into the canal and rotated, they describe a figure in space with a cutting edge superior to the original one of the straight instrument, described by schilder as “envelop of motion”.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 439
61. What should be done when an obstacle is sensed while negotiating the canal?
If an obstacle is sensed while negotiating the canal, the instrument should not be forced into the canal in an attempt to overcome it. Rather it should be removed from the canal and a greater degree of precurvature is given at the tip and probing is repeated with the consideration that the canal is patent at some point.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 441
62. What care is taken while an instrument is used within the canal?
The instrument should be used with great care, accompanied by generous irrigations. When original shape is altered, it should be substituted with a new instrument. It should be re precurved if if it is removed from the root canal in an attempt to reach the apex.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 441
63. When is the first intra operative radiograph taken?
When the instrument has progressed to the depth indicated by the pre op radiograph and the electronic apex locator, the rubber stop is positioned against the reference point that is stable and readily indentifiable and the first intra operative radiograph is taken to confirm the working length.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 441
64. Why is the instrument that is introduced into the canal not moved till a radiograph is taken?
The instrument that is introduced into the canal is not moved till a radiograph is taken to verify its position and the working length because if removed, it cannot be re introduced to the same point due to the debris that might have detached from the narrow wall, blocking the canal. Also back and forth motion of the instrument could create ledges or may damage the periapical tissues, if the initial assessment is wrong.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 441
65. What is the basic principle that the electronic apex locator works?
The apex locators are based on the principle that the electrical resistance between one electrode within the root canal and the other applied to the oral mucosa registered consistent values.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 448
66. Why should the apical foramen remain patent?
The foramen must not be obstructed by dentin mud, pulp residues or other irritating substances and it should always remain patent to avoid blockages, ledges and perforations. Also the patency of the foramen tries to retain the exudate if forms, within the canal itself rather than extending along the fibres of the periodontal ligament and thereby prevents the development of periodontitis post operatively.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 457
67. Why is it not advised to enlarge the foramen more than what is necessary?
Enlarging the foramen more than what is necessary increases the risk of transporting the foramen itself and increases the potential for overfilling and microleakege around the margin.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 458
68. What happens when an instrument encountering resistance is rotated forcefully?
If there is resistance to rotation and if the instrument is forcefully rotated, it is screwed into the canal to overcome the resistance. This should absolutely be avoided since it can result in formation of ledges, false canals, deformation of the blades or even fracture of the instrument within the canal.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 460
69. What is the purpose of drying the canal after irrigation?
The purpose of drying is to remove all the moisture from the canal and inside the dentinal tubules. Using paper points alone is not sufficient to achieve this. A rinse with pure alcohol is also carried out to dilute the watery content of hypochlorite. A weak stream of air can be directed inside the canal using special syringes. Once the canal is dry, it is ready to receive the obturating material.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 463
70. What are the factors that determine endodontic success?
Success in endodontics depends mainly on 2 factors: •The complete removal of the contents of the root canal system and •The complete obturation of the system.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 471
71. How is conservation of tooth structure important for an ideal root preparation?
Conserving the tooth structure provides resistance to fracture and decreases the incidence of perforation. Also maintaining the integrity of the apex keeps the apical foramen small and eliminates transportation of the apex, enhancing the opportunity to seal the apex.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 472
72. Describe the head of a GG drill.
The GG drills are available in stainless steel. The head is short and flame shaped attached to a shank. The tip has a non cutting surface to prevent perforation.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 476
73. Why is the usage EDTA an irrigant controversial?
Though EDTA is an effective chelating agent forming soluble calcium chelate, When exposed to dentin, these materials have an extended half life and they continue to react with the dentin after filing has taken place. They might predispose the root canal system to form ledges, transportation or perforation. So EDTA is considered to be controversial.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 479
74. What is the disadvantage of irrigants containing glycerol or glycerine?
Irrigants containing glycerine or glycerol can quickly form emulsions during root canal preparation which can obstruct the secondary anatomy like the lateral or accessory canals.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 479
75. What is elastic memory of endo instruments?
Root canal instruments are manufactured from straight metal blanks that are cut or wrought by twisting. These instruments are resistant to bending and will come back to their original shape very quickly during the instrumentation process. This is called elastic memory.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 481
76. How is the elastic memory of the instrument overcome?
The concept of elastic memory of the endodontic instruments can be overcome by overbending the instrument while it is being prepared for use, the degree and extent of which depends on the curvature of the canal and flexibility of that instrument.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 481
77. How is the sequence and frequency of recapitulation determined?
The sequence and frequency with which recapitulation is done is determined by the complexity of the anatomy of each root canal system. Desired result can be achieved by a continuous and painstaking utilization of this concept.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 482
78. What is the main objective of any filing technique?
The main objective of any filing technique is a purposeful motion that cleans and enlarges the endodontic cavity space harmlessly while maintaining the natural pathway of the space.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 482
79. How is the step back technique performed?
The smallest instrument that can effectively penetrate and enlarge the canal without forcible pressure is selected, followed by progressively larger and larger instruments. These instruments are stepped out of the canal as they increase in size. This stepping back produces a shape that conforms to the natural pathway of the canal and also creates a continuously tapering shape which is ideal for an endodontic cavity preparation.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 483
80. What are the various phases involved in canal preparation?
The technique can be divided into 6 phases: •Initial access and gross debridement •Preliminary enlargement •Establishment of patency •Enlargement •Blending and •Finishing and apical refinement.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 484
81. What is the purpose of the first phase of preparation (or) the initial access?
The initial access is an opening that will adequately accommodate the initial instruments without impingement or restriction and hence termed as initial access.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 486
82. What are the advantages of preparing the coronal and middle portion of the canal prior to apical enlargement?
Careful enlargement and debridement of the coronal and middle portion of the canal prior to enlargement of the apical portion can give several advantages like freedom and control of instrument cycles, coronal evacuation of contents of the canal, maintenance of large reservoir for irrigant, clear visibility and above all, a safe access to the foramen.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 486,487
83. Why is a safe access to the foramen critically important?
The instruments that arrive passively to the foramen are important for a safe access since the tip of the instruments that have been passed forcibly into the apex undergoes deflection and predisposes to an apical zip.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 487
84. Why the final phase of preparation is considered critical?
The final phase of preparation which finishes the walls and refines the apex is the most critical of the phases since it can be accomplished only after restrictive tooth structure has been removed. Only fine files are used to smooth the walls, especially the apical foramen. They have to be manipulated delicately to avoid over enlargement or transportation of the apex.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 488
85. What is the objective of preparing an access cavity?
The objective of access cavity preparation is to extend the opening to include the entire pulp chamber, obliterating the entire pulp horns and providing a slight divergence occlusally, not considering the occlusal anatomy or previous restorations. The opening is made through the enamel and the dentin and penetrates the roof of the pulp chamber.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 488
86. How is the chamber irrigated after initial access?
The chamber is irrigated using high volume syringes containing at least 2.5% of sodium hypochlorite. The solution is expelled from the syringe to the cavity using gentle pressure and suctioned away simultaneously. The needle of the syringe should never be inserted forcibly or locked in the canal.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 488
87. What is the sequence of usage of Gates Glidden drills?
The sequence and frequency of usage of Gates Glidden drills varies with the complexity of anatomy of each system and it is not fixed.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 488
88. During working length estimation, why is the pain response often misleading?
The pain sensation could be due to the pressure of the instrument in the canal even if the apical foramen is not reached. Or if vital pulp tissue is remaining within the canal, contact with it produces the pain. In a necrotic tooth, pain may even occur when the instrument is already far beyond the apical foramen. So pain response is often misleading.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 443
89. When does a Gates Glidden drill fracture?
The GG drills are fragile and when applied too energetically to a canal wall, it causes the shaft to bend while working. Fractures occur at the base of the long shaft and never at the head and the fractured portion can be removed with cotton pliers.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 461
90. What should be done when a ledge or obstacle is sensed during the process of recapitulation?
During recapitulation, if a ledge or obstacle is sensed, which impedes the proper use of other reamers, the process is stopped and a new recapitulation is started, beginning with the patency file.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 463
91. How is the number of recapitulation decided for a canal?
The number of recapitulations depends on the canal anatomy and the dentin thickness. Each recapitulation leads to removal of more dentin and care should be taken while working in teeth with thin roots as it may lead to perforation, stripping or radicular weakening or ultimately a root fracture.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 463
92. 5. Why is it difficult to cause a stripping in the mesiolingual canal of a lower molar?
The mesio lingual canal of a lower molar is more centrally placed with respect to the root and hence stripping cannot occur that easily.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 466
93. What is the pattern of serial instrumentation described by schilder?
The technique described by schilder starts with using progressively larger instruments working from the apical extent of the root canal coronally in a step back fashion. Files are used instead of reamers. The coronal portion is enlarged with Gates Glidden drills. Recapitulation with small preceding instruments to re establish patency is also done.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 470
94. How is the original anatomy of a canal maintained?
The original anatomy of a canal is maintained by removal of significant amount of the tooth structure from the upper and middle portions of the system at the expense of the outer walls of the curvature. Doing this provides a better access to the more complex anatomy apically by straightening the coronal third and parts of the middle third.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 473
95. What is the significance of root fractures?
Root fractures, if present, are usually the result of failure of the root to withstand masticatory stress after or a direct result of excessive condensation pressure during compaction of filling materials. These fractures occur in the weakest part of the root or the areas where overenlargement of the canal has occurred. Hence conservation of tooth structure is critical to the success of any endodontic procedure.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 474
96. Why are triangular files considered more desirable for cleaning and shaping?
The triangular files which are made from triangular blanks have small cross sectional areas. They are more flexible and less likely to fracture. They dislay larger clearance angles and more efficient during debridement.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 475
97. Why is the Gates glidden drill used only in a straight line?
The tip of the gates glidden drill has a non cutting surface to prevent perforation. The sides of the instrument are used for cutting and it is relatively rigid. Hence it can be used only in a straight line.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 476
98. What are the common lubricants used in sclerosed or calcified canals?
The most common agents used in sclerosed or calcified canals are EDTA, EDTA and cetrimide or EDTAC, urea peroxide, EDTA and urea peroxide or RC prep and urea peroxide in an anhydrous glycerine base or Gly-oxide.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 479
99. Why is precurving of endodontic instruments necessary?
To maintain the curvature of the root canal system and to capture the tortuosity in all the dimensions, the insturments are adapted to duplicate the original anatomy of the system and the directional shifts that occur during manipulation.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 481
100. Why is the tooth structure removed from the outer wall of the curve, while filing?
The tooth structure removed from the outer wall of the curve of the root canal system so that a straightest possible access to the foramen is gained.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol II; 482