Access cavities and isolation

Question 1

What treatment is used if the diagnosis is a healthy pulp?

Answer 1

None

Question 2

What treatment is used if the diagnosis is reversible pulpitis?

Answer 2

Pulpal irritant removed e.g. caries and tooth dressed

Question 3

What treatment is used if the diagnosis is irreversible pulpitis or necrotic pulp?

Answer 3

Commence root canal therapy (after determining the restorability of the tooth, periodontal condition and radiological investigation)

Question 4

Pre-operative radiographs:

Answer 4

At least 1 good quality periapical radiograph

• treatment tooth should be centrally located
• must have at least 3-4mm periradicular tissue visible
• taken with a film holder to minimise distortion
• a second film with a 15-20 horizontal parallax view (a bitewing or DPT view if avaliable can provide additional info)

Question 5

What should we look for on a radiograph?

Answer 5

• Previous disease and treatment (large amounts of caries, large restorations, previous pulp capping, previous extraction)
• Pulpal reactions (narrow chamber, narrow canal, internal resorption)
• Relationship to surrounding structures (Alveolar crest bone loss, general tooth form and length)
• Roots (number, shape and relations)
• Root canal patency (superimposition of 2 canals can make the outline indistinct in multirooted teeth)
• Coronal structure (previous treatment)
• Pulpal reactions (reparitive dentine in chamber)
• Tooth form and length

Question 6

What does a lack of straight access do?

Answer 6

Deflects the files - Groove filed down the labial wall of the canal

Question 7

When is the rubber dam applied?

Answer 7

After the access cavity has be drilled

Question 8

What is an access cavity?

Answer 8

• Removes the entire roof of the coronal pulp chamber and debride the chamber
• Allows ready access to all root canals with straight line access
• Allows placement of a temporary cement seal between visits
• Conserve tooth structure but still achieve goals
• cavity should be non undercut

Question 9

What is the shape of an access cavity determined by?

Answer 9

The position and number of pulp horns:

• Incisor = 3 horns and triangular shape
• Canine = 2 horns and oval shape
• Premolar = 2 horns and oval shape
• Molar = variable horns and are triangiular in shape

Question 10

What do the canals in an upper incisor like?

Answer 10

(pic)
n.b. pulp mimicks mamellons in newly erupted teeth
= kink at end of root
= >1 foamina at root (not always at the tip either, can be to one side!)

Question 11

What should an access cavity in the upper incisor look like?

Answer 11

(pic)

Question 12

How many root canals do second premolars usually have?

Answer 12

1 (often centrally located but if it has two there will be one in each cusp)

Question 13

What does a mandibular premolars root canals look like?

Answer 13

(pic)

Question 14

What should a mandibular premomalrs access cavity look like?

Answer 14

(pic)

Question 15

Which burs are used in access preparation?

Answer 15

Initial penetration = High speed small round (520) and tapered fissure (554)
Refinement of cavity = tapered fissure & round burs

Question 16

How can canals be located?

Answer 16

Using:

• knowledge of pulpal anatomy
• information from radiographs
• magnification techniques
• transillumination with white light
• canal probe (DG 16 probe - longer and sharper)
• fine endodontic hand instruments (ultra small size i.e. 6, 8)

Question 17

Which problems may there be to access?

Answer 17

• Crown in situ = loss of directional sense

- Obstruction within the canal = pulp stones, post crown, fractured instrument)

Question 18

What are the stages of making the access cavity?

Answer 18

• Check depth from reference point to roof of pilp chamber on a radiograph
• use tapered fissure bur to create outline into dentine
• continue in depth until pulp chamber is breached
• APPLY RUBBER DAM
• remove roof of pulp chamber using slow speed long shank round bur (cut from below the overhang upwards)
• gently flare the walls of the pulp chamber and access cavity outwards so greatest diameter is at tooth surface)
• clear debris from pulp chamber with an excavator
• irrigate using an ultrasonic scaler
• locate orifice of canal(s) and check straight line access
  (pic)

Question 19

It is mandatory that rubber dam isolation is used during all endodotnic procedures, what needs to be done to carious or poorlky filled teeth to allow satisfactory rubber dam isolation?

Answer 19

Should be re-restored

Question 20

What are the advantages of rubber dam?

Answer 20

• protects oro-pharynx
• protects soft tissues from caustic materials
• retracts soft tissues and tongue and improves access
• maintains clean, dry, aseptic working field free from salivary contamination

Question 21

What can be used to produce a rubber dam seal?

Answer 21

Ultradent Oraseal = Caulking agent

Question 22

What is the instrumentation stage of a root canal?

Answer 22

• Determine working length
• Shape anal (stepback or crown down) = narrowest part apically, widest part coronally, gradual outward flare)
• obturate

Question 23

How do we measure working length?

Answer 23

• tables of average length (makes huge assumption the dentist is working on the ‘average’ tooth
• apex locator
• radiography (estimate of the working length can be obtained by measuring a pre-operative radiograph)

Question 24

How does an apex locator work?

Answer 24

Measures electrical resistance with direct, alternating and high frequency currents = voltage gradients and calculates ration between impedences
n.b. the impedance between the apical tissues ad the mucosa to which the lip electrode is attached has been found to be a constant of 6.5 k ohms

Question 25

What are the problems associated with the use of apex locators?

Answer 25

• Wet canals (for absolute apex locator machines only) e.g. hypochlorite, pus or tissue exudate
• Heavily restored crown (all machines) e.g. amalgam or gold inlay
• poor contact of lip electrode

Question 26

How do we get the radiographic working length?

Answer 26

Measure from the fixed reference point incisally or occlusally to the radiographic apex of the root minus 1 mm

Question 27

Where is the canal terminus?

Answer 27

(pic)

= near the radiographic apex (1mm short of it)