05-07-2012, 11:12 AM
Access preparation in special situations
Access preparation in special situations.ppt (Size: 8.09 MB / Downloads: 243)
Introduction
Endodontic therapy is a micro neurologic surgical procedure. A thorough understanding of the canal anatomy followed by its complete debridement and filling is essential for a successful outcome. To achieve these objectives a well executed access preparation is essential which provides a straight line path to the apex and thereby increases the success rate of endodontic therapy.
Objectives of access cavity preparation
1. Straight line access
Benefits gained through this:
unobstructed access to canal orifice
direct access to apical foramen
complete authority over enlarging instrument
Ease of cleaning and shaping
Quality obturation
2. Removal of carious dentin and defective restorations
eliminate mechanically bacteria
eliminate the discolored tooth structure that may ultimately lead to staining the crown.
eliminate the possibility of any bacteria laden saliva leaking into the prepared cavity
3.Unroofing the pulp chamber
maximum visibility
location of canals
exposure of pulp horns
Access preparation guidelines
Internal anatomy dictates the access shape
Visualization of the location of pulp space
- B-L angulations
Coronal anatomy judged visually
Cervical anatomy is tactically determined using explorer
Palpation to determine the tooth location and direction
Diagnostic radiograph
2. Removal of any impinging restorative material.
3.Roof of the pulp chamber is perforated with a round bur. For teeth with porcelain crowns, a water cooled round diamond instrument should be used until dentin is reached ,this prevent fracture of the thin dentin.
4. Once the pulp chamber is located, 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 out stroke.
5. A sharp DG 16 double explored is used to locate canal orifices and to determine their angle of departure form the main chamber.
5.When canals are difficult to find the rubber dam should not be placed until correct location has been confirmed.
6. Access is through occlusal or lingual surface never through proximal or gingival surface.
7. As part of access preparation , the unsupported cusps of posterior teeth must be reduced.
Outline form
complete access for instrumentation from cavity margin to apical foramen. External form evolves from the internal anatomy of the tooth established by the pulp
Three factors to be considered:
size of the pulp chamber
Shape of the pulp chamber
No of individual root canals, their curvatures and their positions
Convenience form:
Important benefits gained through convenience form modifications
Unobstructed access to the canal orifice
Direct access to the apical foramen
Cavity expansion to accommodate filling techniques
Complete authority over the enlarging instrument
Anatomy of the pulp chamber
Krasner et al (JOE 2004) proposes certain laws which make for the specific, consistent location of landmarks.
Relationship of the pulp chamber to the clinical crown:
LAW of Centrality: the floor of the pulp chamber is always located in the center of the tooth at the level of the CEJ
Law of concentricity: the walls of the pulp chamber are always concentric to the external surface of the tooth at the level of the CEJ
Law of CEJ: CEJ is the most, consistent, repeatable landmark for locating the position of the pulp chamber.
Maxillary central incisor
Pulp chamber is centrally located
Broadest incisally
Has one root and one root canal
Access shape is triangular and is begin in exact centre of lingual surface (Lingual conventional access)
Lingual cingulum accessmannan et al) initial point of entry lingual surface, coronal to cingulum.Opening enlarged minimally to remove the entire pulp chamber roof cervico incisally and MD
Mandibular incisors
Smallest tooth in the arch
Narrow and flat in BL dimension
One root which is flat B-L ,
Benjamin and Dowson et al prevalence of 2 canals in mandibular incisors in 41.4%, of these only 1.3% had separate foramina
Incisor anatomy presents a challenge when making an access because of its small size and high prevalence of two canals
Traditional access - lingual ,because of esthetics and restorative reasons.
Disadvantage: the lingual canal is difficult to locate and instrument an artificial bulge of dentin remains making detection and debridement of the lingual canal more difficult.
Janik advocated extending the lingual access more toward the cingulum to aid in locating and debriding the lingual canal.
Clements and Gilboe labial endodontic access.
Mauger et al JOE 1999, advocate access in the incisal or facial edge of mandibular incisors.
Using a straight line access from the incisal or facial edge preserves the dentin in the cingulum area making for a stronger tooth