Access cavity preparation

Editor's Notes

1. It is well-recognized and universally accepted that a successful outcome in endodontic treatment essential- ly depends on three factors: 1)  cleaning and shaping 2)  disinfection 3)  three-dimensional obturation of the root canal system.
2. Caries and defective restorations remaining in an endodontic cavity preparation must be removed for three reasons:
3. The clinician uses the information from these assessments to choose the direction of initial bur penetration.
4. complete reliance on the occlusal anatomy is dangerous because this morphology can change as the crown is destroyed by caries and reconstructed with various restorative materials.
5. Preparation of an access cavity results in the removal of part of the central portion of the tooth thereby reducing the tooth’s resistance to occlusal stresses
6. Failure to follow this guideline results in treatment errors, including root perforation, misdirection of an instrument from the main canal (ledge formation), instru- ment separation, or creation of an incorrect canal shape (apical transportation).
7. ; this information can be used as an indicator of the direc- tion of the long axis of the treated tooth.
8. The clinician must take care to keep these instruments within the con nes of the canal system until the working length has been accurately determined. A lubricating agent (e.g., rC-Prep [Premier Dental Products, Plymouth Meeting, PA], a water-based preparation that will not congeal vital pulp tissue), may be used on instruments and introduced into the canal. Congealed pulp tissue may form a collagen plug that blocks the apex, preventing complete shaping and cleaning.
9. Enhanced vision allows the clinician to see internal dentin color changes and subtle landmarks that may not be visible to the unaided eye.
10. he clinician may want to retain the proximal portion of a class II restoration that extends subgingivally to aid in rubber dam isolation.
11. The clinician should measure the distance from the incisal edge to the roof of the pulp chamber on a dimensionally accurate pretreatment radio- graph and limit penetration to this distance
12. In vital cases, pulp tissue hemorrhage can impair the clinician’s ability to see the internal anatomy. In such cases, as soon as enough roof has been removed to allow instrument access, the coronal pulp should be amputated at the orifice level with an endodontic spoon or round bur and the chamber irrigated copiously with sodium hypochlorite. If the hemor- rhage continues, a tentative canal length can be established by measuring the pretreatment radiograph. A small broach coated with a chelating agent then can be introduced into the canal and rotated, thereby amputating the radicular pulp at a more apical level. This procedure is followed by irrigation with sodium hypochlorite.
13. Deflected instruments function under more stress than undetected instruments and are more susceptible to separation during the shaping and cleaning process
14. A ledge is an iatrogenically created root canal wall irregularity that may impede placement of an intracanal instru- ment to the apex. Transportation occurs in the portion of the canal apical to a curvature when canal wall structure opposite the curve is removed, tending to straighten the canal curvature. Zipping, or elliptication of the apical foramen, occurs when an overextended le transports the outer wall of the apical foramen
15. Proper restorative margins are important because anterior teeth may not require a crown as the nal restoration. De nite, smooth cavosurface margins allow the clinician to place and nish a composite resin nal restoration with the precision necessary to minimize coronal leakage
16. In mandibular first premolars the starting location is halfway up the lingual incline of the buccal cusp on a line connecting the cusp tips. Mandibular second premolars require less of an adjustment because they have less lingual inclination. The starting location for this tooth is one third the way up the lingual incline of the buccal cusp on a line connecting the buccal cusp tip and the lingual groove between the lingual cusps.
17. rarely are pulp chambers found mesial to this imaginary line.
18. The true three-dimensional position that teeth hold in each jaw cannot be assessed accurately by clinical or radiographic perspectives. Therefore, using the occlu- sal table of the tooth as a guide to the location of the chamber can be quite misleading. Figure 2 shows the lingual and mesial inclination of the mandibular molars, the mesial inclination of the maxillary molars, and the labial inclination of all the incisors
19. The outline form of the access cavity changes to a more oval shape as the tooth matures and the pulp horns recede because the mesial and distal pulp horns are less prominent.
20. Because of this oval shape, the clinician must take care to circumferentially le labially and palatally to shape and clean the canal properly.
21. As a group, the mandibular premolars are dif cult to treat. They have a high flare-up and failure rate. A possible explana- tion may be the extreme variations in root canal morphology in these teeth. counter this situation, the clinician may need to extend the lingual wall of the access cavity farther lingually; this makes the lingual canal easier to locate
22. Problems associated
23. In most cases, complete removal of large restorations is the wisest course , but the metal in the full veneer crown often masks the underlying pulp chamber
24. these spaces have adequate room to allow passage of millions of microorganisms. Chronic in ammatory processes (e.g., caries, medications, occlusal trauma, and aging) often cause narrowing of the root canal system
25. The best way to handle these problems is to prevent them from occurring. A thorough radiographic examination is crucial. The initial outline form occasionally can be created without the dental dam; this facilitates positioning of the bur with the long axis of the tooth. Bur penetration for both depth and angulation should be con rmed frequently with radiographs.
26. The designs of traditional endodontic cavities have remained almost unchanged for the past several decades. This is due to existing limitations in diagnostic and imaging techniques, which have created the need to delve into the variations and complexities of root canal anatomy more clinically.
27. While the apex of the root can be amputated, and the coronal third of the clinical crown removed and replaced prosthetically, the dentin near the alveolar crest is irreplaceable.
28. Clark-Khademi access preparation Drs. Clark and Khademi have described a concept of conservative endodontic access cavity preparation. 
29. When the authors first began to maintain a soffit, it seemed sloppy and contradicted the compulsive nature of traditional dentistry that has made complete deroofing a mark of a thorough clinician. The pulp seemed difficult to remove under the tiny eve and the removal of sealer and gutta percha was equally difficult.
30. The goal of the three-dimensional image assessment is to preclude clinically exploring the anatomy by removing dentin structure while focusing on the actual anatomy and practicing a precise approach for dentin conservation.
31. Even anterior teeth with no complex anatomy, variations, or unusual pathologies can benefit from preoperative CBCT, by certainty of its configuration, with no need for further exploratory structure removal, and by exact determination of the convenience point of approach—generally more incisal and round than traditionally described. This central maxillary incisor with a metal-free crown is a clear example. Conventional x-ray does not show the apical periodontitis present, nor can it be used to guide the approach through the reduced ceramic. 5-year follow-up.