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Except for the maxillary molars, the orifices of the canals lie on a line perpendicular to a line drawn in a mesial-distal direction across the centre of the floor of the pulp chamber.

1. INTRODUCTION The hard tissue that encompasses the human dental pulp takes on numerous configurations and shapes. A thorough understanding of the complexity of the root canal system is essential for understanding the principles and problems of shaping and cleaning, for determining the apical limits and dimensions of canal preparations, and for performing successful microsurgical procedures.

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5. DEFINITION

6. OBJECTIVES (ACC. TO RE WALTON)

7. RULES FOR PROPER ACCESS PREPARATION The objective of entry is to give direct access to the apical foramina, not merely to the canal orifice. Access cavity preparations are different from typical operative occlusal preparations. The interior anatomy of the tooth under treatment must be determined. Rubber dam – when canals difficult to find the rubber dam should not be placed until correct location has been confirmed Endodontic entries are prepared through the occlusal or lingual surface never through the proximal or gingival surface. As a part of access preparation, the unsupported cusps of posterior teeth must be reduced. (Franklin S. Weine )

8. A PREOPERATIVE PERIAPICAL RADIOGRAPH IS A MUST, PRIOR TO ACCESS CAVITY PREPARATION AN INTRA-ORAL PERIAPICAL RADIOGRAPH

9. DIVISIONS OF ACCESS CAVITY PREPARATION For sake of descriptive convenience Ingle has divided endodontic cavity preparation into

10. CAVITY EXPANSION TO ACCOMMODATE FILLING TECHNIQUES To make filling techniques more convenient or practical, outline form may have to be widely extended to accommodate these instruments

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12. COMPLETE AUTHORITY OVER ENLARGING INSTRUMENT If the instrument is impinged at the canal orifice by tooth structure the intervening tooth structure will dictate the control of the instrument. If the tooth structure is removed from the orifice so that the instrument stands free in this area of the canal the instrument will then be controlled by only two factors: the clinician’s fingers on the handle of the instrument and the walls of the canal at the tip of the instrument.

13. THE ROUND BUR No. 6 Only in large pulp chamber of molars Taurodontism No. 1 Used in the floor of pulp chamber to seek additional canal orifice. Eg MB2 Maillefer Endo-Z carbide fissure bur It is safe-ended and will not scar the pulpal floor. Moreover, it is longer bladed (9 mm) for sloping and funnelling the access cavity.

14. AIDS IN LOCATING ROOT CANAL ORIFICES Endodontic explorer Troughing of grooves with ultrasonic tips, Staining the chamber floor with 1% methylene blue dye, Performing the sodium hypochlorite ‘champagne bubble’ test and visualizing canal bleeding points are important aids in locating root canal orifices. Magnification and illumination

15. ACCESS PREPARATION GUIDELINES STEP 3: The roof of the pulp chamber is best perforated with a round bur. A no.2 bur ( anterior and premolar teeth) A no. 4 bur should be used in molar teeth. For teeth with porcelain crowns. The bur is best directed toward largest part of pulp chamber. In calcified, multi-rooted teeth, it is better to direct the access toward the largest canal.

16. ACCESS PREPARATION GUIDELINES STEP 4- Once the pulp chamber is located (with light upward pressure), the round bur is used to remove the roof of the pulp chamber from underneath; the “belly” of the bur should be used to cut on the outstroke. This should establish an initial outline form. The pulp chamber should be frequently flushed with sodium hypochlorite solution to remove debris and bacteria.

17. ACCESS PREPARATION GUIDELINES STEP 5- A sharp DG 16 double ended explorer is used to locate canal orifices. In heavily calcified teeth - transillumination, and the careful examination of internal dentin color. Once the canals are located, a no.10 or no. 15 K type of file is introduced into the canal to determine patency. Tooth length may be determined at this point.

18. ACCESS CAVITY PREPARATION FOR: Maxillary Lateral Incisors Shape of access cavity similar to maxillary central incisors,except that Smaller in size When pulp horns are present, shape of access cavity is rounded triangle If pulp horns are missing, shape is oval

19. ACCESS CAVITY PREPARATION FOR: Mandibular First Pre-molar Oval access cavity, wider mesiodistally Presence of 30 degree lingual inclination of crown to root,hence starting point of bur should be half way up the lingual incline of buccal cusp.

20. ACCESS CAVITY PREPARATION FOR: Mandibular Second Pre-molar Similar to mandibular first premolar Enamel penetration initiated in central groove dueto small lingual tilt Ovoid acess opening is wider mesiodistally

21. ERRORS OF ACCESS PREPARATION IN PRE-MOLARS

22. ACCESS CAVITY PREPARATION FOR: Maxillary First Molar Shape of pulp chamber –rhomboid; Palatal canal orifice located palatally , mesiobuccal canal orifice located under mesiobuccal cusp, distobuccal canal orifice located slightly distal and palatal to mesiobuccal orifice. A line drawn to connect all three orifices forms a triangle- molar triangle

23. ACCESS CAVITY PREPARATION FOR: Mandibular First Molar This tooth most frequently requires endodontic treatment. The access cavity, which should not be triangular, rather trapezoidal or quadrangular with rounded corners. The classical triangular shape would hamper the identification of the second distal canal.

24. ACCESS CAVITY PREPARATION FOR: Mandibular Second Molar The access cavity of this tooth is started from the central fossa, and it is created according to the same rules used for the first molar. Because of the slight distal angulation of its roots, the access cavity can, however, be less extensive in this case. The shape of the access cavity depends on whether there is one, two, three, or four canals; it may be round to oval, triangular, or quadrangular

25. ACCESS CAVITY PREPARATION FOR: Mandibular Third Molar The lower third molar may require endodontic therapy for the same reasons as the upper third molar. When it is the last distal abutment, this tooth acquires great importance. The most varied and bizarre root morphology can correspond to an almost normal coronal appearance . Nonetheless, this tooth can also be treated successfully by endodontic means. The same rules that apply to the other lower molars also hold for its access cavity.

26. ERRORS OF ACCESS PREPARATION IN LOWER MOLARS Overextended Perforation into furcation Failure to find a second distal canal Ledge formation caused by faulty exploration and using too large of an instrument.

27. RECENT ADVANCES IN CONCEPTS OF ACCESS OPENING

28. But why? Are endodontically treated teeth stiffer due to loss of structure?

29. If not… Are endodontically treated teeth stiffer due to loss of moisture?

30. Then… There definitely must occur some changes in the dentin quality?

31. RADIX ENTOMOLARIS AND RADIX PARAMOLARIS Supernumerary roots in mandibular molars

32. CHALLENGING ACCESS CAVITY PREPARATION Teeth with minimal or no clinical crown:-depth of penetration needed to reach the pulp canal is measured on the preoperative radiograph. Clinician should study their root angulation on preoperative radiograph. Heaviliy restored teeth:-here crown / root angulation is altered. As these restorations block the passage of light ,poor visibility. Most cases, restorations are removed for better visibility.

33. CHALLENGING ACCESS ACVITY PREPARATION Teeth with calcified canals:- here use of magnification and transillumination, as well as color changes and pulp chamber shapes, dyes and champagne test should be used. Calcified dentin must be slowly removed using ultrasonic tips. Angled direction radiographs are used A small K file #6 or #8 coated with chelating agent is used.

34. CHALLENGING ACCESS ACVITY PREPARATION Crowded teeth:-conventional access preparation may not be possible instead buccal access preparation may be treatment of choice. Rotated teeth:- have altered crown to root relationships, so it poses additional problems:- Failure to locate extra canals Excessive gouging of the coronal or radicular tooth structure Instrument separation in an attempt to locate the orifice Failure to debride all pulp debris from the chamber.

35. CONCLUSION Except for the maxillary molars, the orifices of the canals lie on a line perpendicular to a line drawn in a mesial-distal direction across the centre of the floor of the pulp chamber.