Clinical Amalgam Flashcards
What is amalgam?
“ An alloy of mercury with another metal or metals”
When might amalgam be used?
A direct restoration in moderate and large sized cavities in posterior teeth.
Core build ups when the definitive restoration will be an indirect cast restoration such as a crown or bridge retainer
When would amalgam not be used?
- If aesthetics are paramount to patient
- The patient has a history of sensitivity to mercury or other amalgam components
- Where the loss of tooth substance is such that a retentive cavity cannot be produced
- Where excessive removal of sound tooth substance would be required to produce a retentive cavity.
advantages vs disadvantages of amalgam?
ADVANTAGES
* Durable - long lasting
* Resistance to surface corrosion
* Shorter placement time than composite
* Radiopaque
* Economical
DISADVANTAGES
* Poor aesthetic qualities
* Does not bond easily to tooth substance
* Thermal diffusivity high
* Descructive prep
* Local sensitivity reactions (lichenoid lesiosn caused by type 4 hs reaction)
Retention form VS Resistance form
Retention form - features that prevent the loss of the restoration in direction of path of insertion
Resistance form - features that prevent loss of the material due to distortion or fracture by masticatory forces
What is the ideal resistance form?
Ideally the cavity floor should be approximately parallel to the occlusal surface with sufficient depth of the cavity to give adequate mechanical strength (approx 1.5 – 2mm)
The gingival floor of an interproximal box should be approximately 90 degrees to the axial wall. If it is greater this, it will create sloping inclined plane which makes the filling liable to slide out of the cavity.
What are amalgam cavity designs to treat interproximal caries?
- Self-retentive box preparation (minimal preparation box)
- Proximo-occlusal preparation
What are the advantages and disadvantages of a self- retentive box prep?
Advantages
* Less tooth tissue removed than with a proximo- occlusal preparation
* Reduced amount of amalgam placed
* Sound tooth tissue retained between proximal box and any occlusal cavity
Disadvantages
* Can be more technically demanding than proximo- occlusal preparation
* Further treatment of any pit and fissure caries may be required
What are the advantages and disadvantages of proximo-occlusal preparation?
Advantages
* (Should be) Very retentive
* Also treats any caries in pits and fissures
* Less or no opportunity for future caries in pits and fissures
Disadvantages
* Destruction of tooth tissue for retention
* Increased risk of weakening of the tooth
What are examples of additional mechanical retention tools?
- Include grooves or dimples within the cavity design
- Pin placement - titanium / stainless steel
(Pin use is controversial
Used to increase retention in large non-retentive cavities.)
Where should the pin be placed?
Place pin into dentine in the greatest bulk of the tooth.
Never in enamel or at the ADJ
Avoid the pulp and periodontal ligament
Pack amalgam around the pin
What are the intial and long term problems with pins?
Initial
Stress in tooth around the pin.
Cracking of dentine,
Sensitivity of tooth due to temperature transference
Long Term
filling can leak but will not fall out because of the pin
leading to secondary caries which can progress further into the tooth because of the pin
never use pins with composite resins
What should you check for finishing of prep?
- Ensure all caries is removed
- Smooth and round internal line angles
- Check and finish cavo-surface angles
- Smooth cavity margins
What does moisture contramination cause?
- Reduces Strength
- Increases creep
- Increases corrosion
- Increases porosity
- Critical but not as critical as in bonded composite restorations
What is used to seal dentine?
RMGIC
