Access cavities and isolation Flashcards
What treatment is used if the diagnosis is a healthy pulp?
None
What treatment is used if the diagnosis is reversible pulpitis?
Pulpal irritant removed e.g. caries and tooth dressed
What treatment is used if the diagnosis is irreversible pulpitis or necrotic pulp?
Commence root canal therapy (after determining the restorability of the tooth, periodontal condition and radiological investigation)
Pre-operative radiographs:
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)
What should we look for on a radiograph?
- 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
What does a lack of straight access do?
Deflects the files - Groove filed down the labial wall of the canal
When is the rubber dam applied?
After the access cavity has be drilled
What is an access cavity?
- 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
What is the shape of an access cavity determined by?
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
What do the canals in an upper incisor like?
(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!)
What should an access cavity in the upper incisor look like?
(pic)
How many root canals do second premolars usually have?
1 (often centrally located but if it has two there will be one in each cusp)
What does a mandibular premolars root canals look like?
(pic)
What should a mandibular premomalrs access cavity look like?
(pic)
Which burs are used in access preparation?
Initial penetration = High speed small round (520) and tapered fissure (554)
Refinement of cavity = tapered fissure & round burs
How can canals be located?
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)
Which problems may there be to access?
- Crown in situ = loss of directional sense
- Obstruction within the canal = pulp stones, post crown, fractured instrument)
What are the stages of making the access cavity?
- 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)
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?
Should be re-restored
What are the advantages of rubber dam?
- 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
What can be used to produce a rubber dam seal?
Ultradent Oraseal = Caulking agent
What is the instrumentation stage of a root canal?
- Determine working length
- Shape anal (stepback or crown down) = narrowest part apically, widest part coronally, gradual outward flare)
- obturate
How do we measure working length?
- 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)
How does an apex locator work?
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
What are the problems associated with the use of apex locators?
- 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
How do we get the radiographic working length?
Measure from the fixed reference point incisally or occlusally to the radiographic apex of the root minus 1 mm
Where is the canal terminus?
(pic)
= near the radiographic apex (1mm short of it)
