Preclinics of Conservative Dental Medicine · MU Sofia

38. Endodontic access cavity preparation and orifice enlargement in anterior and posterior teeth.

Explains how to prepare the access cavity step by step, from the pre-operative radiograph and caries removal through entry, penetration, deroofing and locating the orifices, then refining the walls. A table gives the outline and watch-points for each anterior and posterior tooth group, with a grid of occlusal and lingual outline diagrams. It also covers the burs and explorers used, the purpose and instruments of coronal flaring with Gates-Glidden drills and orifice shapers, and the main access errors such as perforation.

Inside: 7 sections · 1 labelled picture · 1 table · 17 flashcards · 7 min

Topic 38 of 53 in the MU Sofia syllabus for Preclinics of Conservative Dental Medicine (Dental Medicine, Year 3). The free AceMed note covers it in 7 sections, about 801 words (7 min of reading), with 17 flashcards.

In this note

  1. Introduction
  2. Steps of access preparation
  3. Access outlines by tooth group
  4. Burs and instruments
  5. Orifice enlargement (coronal flaring)
  6. Main mistakes
  7. Key points

Introduction

The access cavity is the opening through the crown that gives instruments a direct path into the pulp chamber and every canal; orifice enlargement (coronal flaring) then widens the canal entrances. Most missed canals, ledges, perforations and broken instruments go back to a poor access. Objectives of access: topic 37; canal anatomy: topics 35–36.

Steps of access preparation

The outline is set by the pulp chamber projected onto the crown surface – not by the caries, the old restoration or the shape of the crown.

  1. Pre-operative radiograph (parallel periapical): size and position of the chamber, calcifications, number and curvature of roots; measure the depth from the occlusal surface or incisal edge to the chamber roof and floor. Note crown tilt and rotation.
  2. Remove all caries and defective restorations and judge restorability; work under rubber dam. Leftover caries or leaking fillings contaminate the canals and hide the orifices.
  3. Entry point and bur angle. Anterior teeth: centre of the lingual (palatal) surface, incisal to the cingulum; the bur cuts through the enamel (about 1 mm) perpendicular to the lingual surface, then is turned parallel to the long axis. Posterior teeth: central fossa, bur parallel to the long axis, aimed at the largest canal (palatal in upper, distal in lower molars).
  4. Penetration – the "drop": when the bur breaks through the roof, resistance suddenly falls. In calcified chambers there is no drop, so compare the bur depth with the radiograph.
  5. Deroofing (unroofing): remove the entire roof including the pulp horns, with a round bur pulled outward from inside the chamber or a safe-ended (non-end-cutting) bur whose tip rests on the floor without cutting it.
  6. Locate the orifices with the endodontic explorer (DG-16). The floor is darker than the walls; orifices lie at the floor–wall junction, at the ends of its dark developmental lines. At the CEJ level the chamber lies in the centre of the tooth (Krasner and Rankow), so in tilted or crowned teeth the CEJ, not the crown, is the guide.
  7. Refine the walls: smooth, slightly divergent occlusally, no overhangs, until a small file (ISO 10–15) enters each canal in a straight line to the apical third or the first curve.

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