Access Cavity Preparation 

 

:Definition

Before going for access cavity preparation, a study of preparative periapical radiograph is necessary with a paralleling technique.

An ideal access preparation should have following features:

• An unobstructed view into the canal.
• A file should pass into the canal without touching any part of the access cavity.
• no remaining caries should be present in access cavity.
• obturating instruments should pass into the canal without touching any portion of the access cavity.

:Objectives of access cavity preparation

:Direct straight line access to the apical foramen helps in

Improved instrument control because of minimal instrumemt deflection and ease of introducing instrument in the canal.

Improved obturation.

Decreased incidence of iatrogenic errors.

complete deroofing of pulp chamber helps in:

Complete debridement of pulp chamber.

Improving visibility.

Locating canal orifices.

Permitting straight line access.

preventing discoloration of teeth because of remaining pulpal tissue.

Conserve sound tooth structure as much as possible so as to avoid weakening of remaining tooth structure.

Clinical tips:

• Recommended access opening bur is round bur . It prevents the overpreparation. Once (drop in) into the pulp chamber is obtained, round bur is replaced by tapered fissured bur.
• Avoid using flat ended burs as these result in highly irregular access walls, causing multiple ledges.

Shape of pulp chamber is determined by:

• size of pulp chamber: In young patients, access preparation is wider than the older ones.
• shape of pulp chamber: Final outline form should reflect the shape of pulp chamber. It is triangular in anteriors, ovoid buccolingually in premolars and trapezoidal or triangular in molars.
• number, position and curvature of the canal: It can lead to modified access preparation , like Shamrock preparation in maxillary molar.

Laws of access cavity preparation for locating canal orifices:

• Law of centrality: Floor of pulp chamber is always located in the center of tooth at the level of cementoenamel junction.
• Law of cementoenamel junction: Distance from external surface of clinical crown to the wall of pulp chamber is same throughout the tooth circumference at the level of CEJ.
• Law of concentricity: Walls of pulp chamber are always concentric to external surface of the tooth at level of CEJ.
• This indicates anatomy of external tooth surface reflects the anatomy of pulp chamber.
• Law of color change: Color of pulp chamber floor is darker than the cavity walls.
• Law of symmetry: Usually canal orifices are equidistant from a line drawn in mesial and distal direction through the floor of pulp chamber.
• Law of orifice location: Canal orifices are located at the junction of floor and walls, and at the terminus of root development fusion lines.