كلينكال هاند اوتس , مراجعة

2- Access cavity preparation (Clinical handout) l Endodontics series


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ACCESS CAVITY FOR ENDODONTICS

Modern concepts of endodontic access cavity

  •        Knowledge of the most likely internal anatomy known by preoperative radiograph (as curvature of root that may need some modifications in access cavity to avoid ledge formation, transportation, instrument separation or perforation) and basic knowledge about the anatomy.

  1.            Mostly upper incisors are type I, but may have dens invaginatus, while lower anteriors may have buccal and lingual canals (60%), and access cavity is triangular with base incisally and apex cervically, while in canines there is one pulp horn so access cavity is oval inciso-gingivally, upper premolars are oval bucco-lingually.
  2.            Anatomical variations in upper premolars: may have extra root with extra canal and it is called molarized premolar, for this variation access cavity become small triangle or T-shaped; 2 buccal canals and one palatal.
  3.            In lower premolars: may be with extra canals or c-shaped canals, for this variation you need to do more flaring, it can reach up to cusp tip to negotiate extra lingual canals with different directions.
  4.           Upper molars: access cavity is triangle from buccal cusp tips to the mesiobuccal groove to the mesiopalatal cusp in case of 3 canals, while if there are 4 canals, the access is quadrilateral with slight mesial extension to accommodate for MB2 canal.
  5.       Percentage of MB2 reaches 95% in upper 6, and 60% in upper 7.
  6.       MB canal is located below MB cusp tip, DB canal in front of MB groove  (between MB and DB cusps), palatal canal below base of mesiopalatal   cusp.
  7.      Upper 7 has more variations, it may have a single canal, double canals (access as upper premolars; oval buccolingually)

  •        Lower molars: mostly have 2 roots (mesial and distal), mesial roots always have 2 canals; MB (below MB cusp tip) and ML (1mm distal to central groove), with access cavity having rectangular shape.
  •      Variations in lower premolars: lower 7 may have 2 canals (mesial and distal) or single root with c-shaped canal.
  •      Extra-root as radix entomolaris which is usually located distolingial or radix paramolaris.
  •     Middle mesial canal, usually located in groove between MB and ML orifices, use ultrasonics to clean the groove. Mostly middle mesial canal is confluent with MB or ML canal.

2.     Remove decay, defective restoration or undermined/ weakened tooth structure to prevent any leakage and to evaluate restorability of the tooth.

  •        If undermined tooth structure is left after the first visit, it may fracture causing repetition of working length determination, and if the fracture is involving large area or causing a crack that propagates in different directions causing split tooth, this may lead to extraction of the tooth.

3.     Pre-access analysis by preoperative x-ray, to establish proper tooth long axis, as the tooth may be tilted and if it is accessed straight, cervical perforation may happen.

  •         Use radiopaque marker (stone, ultrasonic tip,..) to check the direction of the access angulation.
  •         Estimation of C-F (cusp-floor) distance, as long standing caries or restoration may cause pulp recession.

4.     Technical procedures preserving pericervical dentin that judges tooth restorability.

5.     Convenience for vision and instruments (I can’t treat what I can’t see).

6.     Inspection of the floor.


Technical procedures

  •        Removal of decay.
  •        Pre-endodontic build up.
  •        Access preparation (GED):

  1.            G: Geometrical design (start as a cavity as small as possible, then deepen it).
  2.            E: Exposure.
  3.            D: Deroofing.
  4.                How to differentiate between pulp horns and orifices?

  •         Depth of floor is at level of cervical line.
  •         Color change and dentin map.

Floor inspection (location of anatomy)

  •          MB2: in upper molars, it is located in the base of a groove from MB canal (comma shaped), at sub pulpal level. Its orifice is located at the point of intersection between an imaginary line from MB canal to palatal canal, with an imaginary perpendicular line from DB canal. Use endodontic probe or a curved file #10 to find a catch (entrance of the orifice), then use ultrasonic tips to remove dentin covering the orifice.
  •          Middle mesial (MM): between MB and ML canals in lower molars.
  •          Law of symmetry: if there is a canal buccal to a line dividing the tooth mesiodistally, there will be a canal lingual to this line (mirror), while if the canal orifice lies in the line, then it is a single canal.
  •          Convenience: slight flaring for vision and for instrument to move freely.

  1.            In lower anteriors, slight labial flaring is needed to negotiate lingual canal  if present.
  2.          In upper anteriors, lingual shoulder should be removed to allow file to be touching all walls of the canal.
  3.          Preserve pericervical dentin to avoid cervical fracture and vertical split.

Different cavity designs

  •        Traditional access: involves great flaring (butchering) for vision and for the instrument, it was used mainly before magnification as this design causes a decrease in fracture resistance of the tooth.
  •         Conservative cavity design: preserves bulk of cusps, marginal ridges and pericervical dentin to increase longevity of the tooth after endodontic treatment.
  •         Ultra conservative (Ninja) access: very narrow access cavity, but preoperative cone beam should be made to assess the presence of extra canals. Also, certain instruments with special properties should be used as there are very high stresses on the instruments.