Endodontic access cavity
Obtaining a straight line access to the canal system and the apex is the basic requirement of successful endodontic therapy and this section covers everything related to it starting from the need for a proper access cavity to the step by step procedures involved.
1. Why are access cavity preparations different from typical operative occlusal preparations?
The operative occlusal cavity preparations are based on the topography of the occlusal grooves, pits and fissures avoiding the underlying pulp. Whereas access cavities are designed to cover the pulp chamber fully, providing a straight line access to the pulp. If access preparations are restricted, then a direct access to the canal is not achieved, there is incomplete removal of the debris, insufficient dentinal wall preparation, failure to detect additional canals and improper condensation of obturating material.
Ref: Franklin S.Weine,Endodontic therapy, Mosby , 6th Edn,104,154.
2. When rotary endodontic instruments are used, why excess removal of coronal root dentin is not encouraged?
This is because, excess removal of coronal root dentin weakens the root walls, lateral or strip perforation can occur and the GP though well compacted, will not strengthen the root. Placement of a post also will not strengthen the root instead may lead to root fracture.
Ref: Stephen Cohen,Richard C.Burns,Pathways of the pulp, Mosby, 8th Edn,297
3. In a class III cavity with a carious exposure, why is the access not taken through the exposure?
In a class III cavity with a carious exposure, access to the pulp canal is not taken through the exposure. The caries is excavated and an interim restoration is placed and a straight line access is taken from the palatal surface of the tooth. This allows for completely involving the pulp chamber and a straight line entry to the canal space. Also the instruments are not bent and they take a straight pathway to the canal thereby preventing fracture.
Ref: Stephen Cohen,Richard C.Burns,Pathways of the pulp, Mosby, 8th Edn,179
4. Why is an access cavity preparation needed?
An access is prepared to create a smooth straight line path to the canal system and the apex. When it is correctly done, it allows for complete irrigation, proper shaping and obturation. Diagnostic radiographs help to estimate the pulp chamber position, calcifications in the chamber, canal length etc. which assist for gaining access into the pulp chamber.
Ref: Stephen Cohen,Richard C.Burns,Pathways of the pulp, Mosby, 8th Edn,174,179
5. What are the factors that determine the successful outcome of the endodontic treatment?
• Proper cleaning and shaping of the canal • Disinfection • Three dimensional obturation of the root canal system • Above all is the preparation of a proper access cavity.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;244
6. Why is thorough cleansing of the endodontic space important for a favorable outcome?
Proper cleansing of the endodontic space includes cleaning the root canal as well as the pulp chamber and the pulp horns. The pulp chamber roof is completely removed which allows removal of all the pulp tissue, calcifications, all residues or traces of old filling material. If the roof of the chamber is not removed, the contents may not be removed fully which may lead to contamination or infection of the endodontic space or discoloration of the endo treated tooth.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;244
7. How are endodontic probes useful in access preparation?
Endodontic probes help for the inspection and localization of canal openings. The probe explores the chamber floor and enters the canal openings displacing the calcific deposits obstructing them. They can also determine the angle between the root canals and the floor of the pulp chamber.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;246
8. Why should the access cavity be wide enough to permit the entry of the endo instruments?
This is because, a narrow access cavity allows working on only one wall of the canal and the other wall remains untouched, which may lead to deformations of the apical foramen. Also the friction of the instrument shaft against the coronal obstruction has to be overcome since the force required to do so impairs the ability to sense how much working portion of the instrument is engaged against the walls and this will lead to instrument fracture.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;247
9. How is the shape of the access cavity determined?
The shape of the access cavity should correspond to a slightly enlarged projection of the contour of the pulp chamber floor onto the occlusal surface of the tooth.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;248
10. Why is it necessary to have all four walls of the access cavity?
The four walls of the access cavity allow • Correct positioning of the rubber dam • Constant flooding of the pulp chamber with the irrigating solutions • Reproduction of stable reference points for the rubber stops on the instruments • Placement of temporary medication without affecting the adjacent tissues.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;249
11. Why does an access cavity not take a predetermined shape?
The shape of the access cavity is determined mainly by the anatomy of the pulp chamber so that good cleaning and shaping, disinfection and complete sealing are achieved without any hindrances.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;250
12. Why the access cavity is always prepared through the occlusal or the lingual surface?
It is so because, an approach other than the occlusal or the lingual would cause significant bending of the instruments which in turn results in inadequate cleaning and shaping of the canals and deformation of the apical foramen.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;250
13. How is the penetration phase important in the access preparation?
The penetration phase is the one in which the pulp chamber is entered by breaking the roof of the chamber with a bur. It creates a funnel shaped opening towards the outer surface for better visibility and orientation.
Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;250,251
14. What is the role of the enlargement phase in access preparation?
The penetration into the pulp chamber is enlarged in this phase in which the bur works on the dentinal walls with a brushing motion and removes all the overhangs of the dentin left behind in the preceding phase. A definitive form of the cavity begins to emerge at this phase.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;252
15. What is the role of the enlargement phase in access preparation?
Finishing the prepared access cavity is done with a non end cutting diamond bur to smoothen the walls of the access cavity so that the transition between the access cavity and the pulp chamber walls will be imperceptible to probing. Also the same bur is used for giving a slight flare to the access cavity in the most occlusal portion.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;252
16. What is the difference between the access shapes of a central and lateral incisor?
The access cavity of central incisor is roughly triangular in shape whereas that of the lateral is ovoid because the lateral incisor has two closely situated pulp horns or a single central horn.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;254,257
17. What are the pretreatments required for a tooth before beginning for endodontic therapy?
Pre endodontic management includes removal of all carious tissue, inadequate restorations and restoring the contacts and contours.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1; 331
18. Why is an access cavity prepared?
Preparation of access cavity is the preliminary step in endodontic treatment which allows localization, cleaning, shaping, disinfection and three dimensional obturation of the root canal system. The success of the endodontic therapy depends on the proper execution of this step.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;244
19. Why should the entire extent of the floor of the chamber be visualized through the access cavity?
The entire extent of the floor should be visualized as it helps in identifying the canal orifices. The floor has natural grooves, especially in the posterior teeth and the ends of the grooves are the canal orifices. Thus it helps for the localization of the canal orifices.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;245
20. Should the prepared access cavity remain unaltered throughout the treatment?
No, the cavity can be modified during the course of the treatment, if need arises. The cavity can be enlarged or even a cusp can be removed if required, to remove any hindrance that occurs. But to avoid enlarging the cavity intraoperatively, it is advisable to prepare wide, proper access cavities.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;247
21. How are the neighbouring canals protected while working on a canal?
Cleaning and shaping of a canal can cause the dentinal fragments or fragments of filling material to fall into the neighbouring canals. To prevent this, the adjacent canal openings can be closed with small cotton pellets.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;247
22. How is temporization important during the course of the endodontic therapy?
Temporization is very important to seal the medication within the canal, forming a hermetic seal to avoid any contamination from outside. It should remain unaltered and must not collapse into the chamber.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;247
23. How are the missing walls in an access cavity reconstructed?
Previous caries destruction would have caused breakage of one or more walls of the access cavity. These missing walls have to be reconstructed with the help of copper bands, orthodontic bands or any other method. All caries should be removed and the cavity should be restored back to form before starting access cavity. This step is termed as “Pre Endodontic Management.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;249
24. How does the shape of the access cavity differ from that in restorative dentistry?
In an amalgam cavity, the occlusal sulci, foci and fissures are involved avoiding the underlying pulp. But in endodontic therapy, the access must uncover the pulp by eliminating the entire roof of the pulp chamber. The external topography of the tooth determines the outline form of conservative cavity preparation. Whereas the internal anatomy of the pulp chamber determines the external outline of the endodontic access cavity
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;249,250
25. How is the penetration of the roof of the chamber felt?
When the roof of the chamber is penetrated during access preparation, there is a sensation of ‘falling into a vacuum’. When the chamber is very narrow or calcified, this sensation will be absent. In such cases, if drilling is continued for the vacuum sensation, it might result in perforation.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;250,251
26. Why are diamond burs preferred for access preparation than tungsten burs?
Diamond burs cut smoothly, vibrate less and better tolerated by patients. So they are preferred than the tungsten burs.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;251
27. How is the access opening shaped?
The opening must not be straight and long. For better visibility and orientation, it should be funnel shaped, opening towards the exterior. As the bur penetrates through the enamel, dentin and the chamber roof, it should be moved circularly to give the cavity a shape which is similar to the final one.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;251
28. Where is the access cavity initiated for upper central incisor?
The access cavity for upper central incisor is initiated by applying the bur occlusal to the cingulum, almost perpendicular to the palatal surface.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;253
29. Why is the cingulum chosen as the starting point in upper central incisor?
The cingulum is chosen as the starting point because in contrast to the gingival margin that can retract and the incisal margin that can abrade, the ridge remains constant throughout the patient’s life.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;253
30. In which conditions is the access cavity started at the incisal margin/ surface?
In very abraded teeth or in teeth with fractures of middle one third of the crown, the access is prepared entirely on the incisal surface.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;255
31. Why do lesions of endodontic origin in a lateral incisor often present in the palatal area?
The apical one third of the root of laterals may have a distal or a palatal curvature. The palatal curvature is not easily recognized radiographically. But lesions of endodontic origin in laterals present in the palatal area due to the palatal curvature.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;257
32. Where does the access cavity for canine begin??
For upper canine, the access cavity begins about half way up the crown on the palatal side. The shape of the access is oval with the diameter larger in the corono apical direction. Similar to incisors, if the tooth is abraded/ fractured then the incisal surface will be involved.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;258
33. How is the access oriented for an upper premolar?
The access cavity for an upper premolar is oriented buccolingually and not mesiodistally as in a restorative cavity, involving the two pulp horns present beneath the respective cusps.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;259
34. How is the presence of third canal diagnosed in an upper premolar?
In an upper premolar, 2 buccal canals can be suspected if the instrument that enters the root canal appears eccentric radigraphically with respect to the profile of the root. The second buccal canal may be present more distal to the first one. Radiographically, the course of the first canal is negotiated and then the second canal is located.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;262
35. What is the significance of the palatal root of an upper molar?
The palatal root is the longest and flat mesiodistally. The root is often curved buccally and this curvature is not appreciated radiographically. The orifice of the palatal canal is located beneath the mesio palatal cusp and the apical third of the canal may have lateral canals frequently. When there is difficulty in locating the canals, the palatal canal can be prepared first which is generally the widest, straightest and the easiest.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;266,267,274
36. Why is the lower central incisor graded as a difficult tooth?
The lower incisor is thin mesiodistally when compared to the bucco lingual width and this makes it very difficult to widen the canal completely in any direction. So it is graded under a difficult category.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;280
37. How does the mesiodistal thinness of the root of the lower central affect the access preparation?
The mesiodiatal thinness of the root affects the access cavity preparation because it may result in lateral perforation. Half way along the root, there is a concavity on both sides and excessive widening of the canal may result in stripping of the root.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;280
38. What is the shape of the access of a lower central incisor?
The access cavity of a lower central is either ovoid or elliptical extending almost from the incisal margin to the cingulum. In severely abraded or fractured teeth, the incisal margin is also involved.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;280,281
39. Why is careful radiographic examination of the lower central important?
The lower central incisor requires careful radiographic interpretation since it frequently presents with 2 canals that unite to a single foramen at the apical third. Failure to notice one canal necessarily will lead to a failure.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;281,283
40. Why is the lower first premolar considered as a very challenging tooth?
Because of its anatomical variability of having a single canal, 2 canals joining at the single foramen or a single canal bifurcating at the apex or 2 separate canals in 2 independent roots, it is difficult to perform proper treatment in lower first premolar.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;287
41. How is the bur oriented in lower first premolar for access preparation?
The bur is entered through the central groove inclined towards the buccal cusp. The lingual cusp being small is preserved. The bur is not oriented parallel to the long axis of the tooth since it may result in lingual perforation.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;288
42. How is the shape of the access of a lower first molar determined?
The access cavity shape of a lower first molar is not pre determined and it is determined by the anatomy of the pulp chamber floor. The shape should not be triangular rather it may be trapezoidal or quadrangular with rounded corners since the distal root usually has an extra canal, the distolingual canal. Preparation of a triangular access may affect the identification of the distolingual canal and also would hamper adequate cleaning and shaping if it is a single canal.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;291,292,294
43. When is the access cavity triangular for a lower first molar?
The access cavity of a lower first molar takes a triangular shape only when there is a single, roundish distal canal and no other extra canal present.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;295
44. What are the canal variations in a lower first molar?
Usually the lower first molar has 2 separate roots with a single canal in the distal root and 2 in the mesial root which mostly have separate foramen. The other variations are:1) Four canals in which the mesial has 2 canals and the distal has 2 canals. 2) A small separate root in the distolingual position with a second distal canal. 3) An extra canal in the mesial root along with the usually existing 2 canals and 4) An extra canal in the mesial root along with the usually existing 2 canals.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;291,292
45. Why the walls of the cavity are slightly flared with the occlusal surface wider than the floor?
The flaring of the access cavity walls will help for the retention of the temporary seal. If they are parallel or diverge apically, the forces of mastication would displace the temporary cement.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;247,248
46. Why is it sometimes difficult to negotiate the second mesiobuccal canal in an upper I molar?
Sometimes the tip of the file doesn’t progress apically and stops against the mesial wall due to sharp angulation in the mesial direction in the first 1-3 mm of the root canal. The mesial wall of the pulp has a dentinal shelf that hides the orifice of MB2. So before the canal is negotiated, the dentinal shelf in the mesial wall hiding the orifice of MB2 should be removed to get a straight line access into the canal.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;270
47. How is the curvature of the mesio buccal root of the upper I molar significant while cleaning and shaping?
The mesio buccal root is often curved distally in variable degrees. So the working length has to be modified accordingly and anticurvature filing is advised.
Ref: Endodontics,Arnaldo Castelluci,IL Tridente, vol 1;272