ACCESS CAVITY PREPRATION l Preclinical Endodontics MCQs

 ACCESS CAVITY PREPRATION l Preclinical Endodontics MCQ (multiple choice question) for dental students 

ACCESS CAVITY PREPARATION

The objectives of an ideal access cavity:

•         [ how good your access cavity determines how good the RCT will be]

1. Gives straight line access to the apical foramen [ unobstructed view of the canals] , The files should pass into the canal without touching any of the walls of the access cavity
2. Remove the entire roof of the pulp chamber so the pulp chamber can be debrided
3. Conserve as much tooth structure as possible

- Cemento dentinal junction:

• where the cementum meets the dentine usually 0.1 mm away from apical foramen.

- Isthmus:

• a narrow communication between 2 canals [ can be complete or incomplete]- contains pulp tissue and acts as a harbor for bacteria → has to be cleaned

 

Canal configurations

Type 1

• Single canal from the chamber to the apex

Type 2

• Two canals leaving the chamber but exiting as one canal

Type 3

• Two canals leaving the chamber and exiting as two separate foramina

Type 4

• one canal leaving the chamber and exiting as two separate foramina

 

Extra canals are mostly found in :

1.   Upper molars mostly have MB2
2.   Lower molars can have extra distal canal
3.  Mandibular incisors and premolars can have 2 canals 

ACCESS CAVITY DESIGN:

1. Before access – remove all defective restorations and caries -you can also check the depth of the preparation by aligning a bur next to a radiograph.
2. Walls of the pulp chamber are flared to give a funnel-shape with larger diameter toward occlusal surface.
3. Remove roof of pulp chamber completely so the pulp can be debrided completely – roof is removed in an upward cutting motion.
4. Access cavity is either lingual or occlusal never proximal or gingival.
5. If you need to gain access through a PFM restoration – use a round diamond bur to drill through the porcelain then switch to carbide to drill through the metal .

To find MB2 canal in upper molars:

• Mostly located between the MB and palatal canals • Good lighting + dry field

1.                         Look for a groove that extends from the MB orifice to the palatal surface.
2.                         Use a file # 8 or #10 to search for the canal in this groove [ many times the canal will be hidden by a  shelf of dentine that has to be removed using low speed hand piece 

Special cases

 Extensive restorations:

• Ideally the restoration should be removed completely before access cavity- if you prepare the access cavity through the restoration you will end up with :

1.  Coronal leakage [ the restoration loosens because of the vibration during drilling]
2.  Poor access and visibility
3.  Blockage of the canal because broken filling pieces may get stuck into the canal system
4.  Misdirection of bur → perforation

 

Tilted crowns:

• Sometimes you might need to open pulp chamber without the rubber dam so that the bur can be placed at the right angulation.
• Can lead to [ failure to locate the canals, gouging, perforations, instrument separation]

 

Calcified canals:

• Use special tips for ultrasonic handpieces -They allow precise removal of the dentin from the pulp floor – should be done under magnification and illumination
• Chelating agents also help in negotiating calcified canals

Sclerosed canals :

• Dyes can be used to located the canal
• Ultrasonic tips can be used
• Long shank low speed burs can be also used

Advancements in root canal prep :

Access cavity:

• Conical carbide burs :

1.     Self centering – safer and less invasive → will allow you to find calcified canals better than round burs.

• Ultra sonic tips: [ can be used in every step of RCT: access, irrigation, obturation]

1.      Used for: access refinement and finding calcified canals  removal of attached pulp stones / removal of posts / removal of broken instruments

• Terauchi file removal kit (TFRK) : to remove broken instruments 

Endodontic microbiology

The main objective of endodontic treatment = prevention or elimination of apical periodontitis

1.       Colonization = establishment of microorganisms in a host
2.       Infection= when bacteria damage the host and produce signs and symptoms
3.       Pathogenicity = the ability of a microorganism to cause a disease / virulence = the degree of pathogenicity under certain circumstances

 

Q:What are the defense mechanisms of DT to prevent bacterial entry if cementum is exposed?

• Outward flow of dentinal fluid
• Presence of Odontoblastic processes
• Presence of mineralized crystals and macromolecules like immunoglobins

 

N.B:

• A positive correlation exists between the number of bacteria in an infected root canal and the size of periradicular radiolucencies. [ the more the bacteria the larger the RL]
• No absolute correlation has been made between any species of bacteria and the severity of endodontic infections.
• when a PA granuloma forms → it prevents the spread of infection to the surrounding tissue [ a granuloma is the place where bacteria is killed]

 

Types of microorganisms present in bacterial infections:

1. Aerobes [ streptococci species]
2. An aerobes [ enterococci, bacteroides , actinomyces]
3. Fungi
4. Viruses – only in non – inflamed pulps of HIV / herpes pts
5. Spirochetes
6. Fusobacteria – associated with severe pain, swelling, flare ups

 

•         e.faecalis is mostly present in re infection cases – most resistant bacterial species .