Retaining large amalgam restorations Flashcards
Retention
Provided by convergent cavity walls
Loss of cusps gives loss of retention
Features to increase retention
Grooves Channels, slots Bonding Pins Use composite
Channels, slots etc
Use available tooth structure for retention
Slots
Amalgapins
Shelves
Slots
Inverted cone bur
Amalgapins
Minimum: 0.8mm diameter
2mm deep
Shelves
Need to be 2mm high?
Success
Place features where they will resist likely loads
Bonded amalgam
Other techniques are ‘invasive’
Risk to pulp and periodontium
A means to retain an amalgam restoration without macromechanical retention
Self curing
Bonds to dentine
Amalgam condensed into it whilst both unset to form mechanical interlock
Bonded amalgam: the process
Methacrylate or composite resin
HEMA: hydroxylethyl methacrylate
NMSA: N-methacryloyl 5-aminosalicylic acid
MDP: 10-methacryloyloxydecyl dihydrogen phophate
A bond to dentine and metal?
Bonded amalgam: clinical trials
Lower sensitivity?
Retention rates exceed that of pins
Less iatrogenic damage
Problems with bonding
Loss of bond layer
Oxygen inhibition
Weakening of amalgam
Adhesion to matrix band
Pins
Historically many forms Stainless steel self-tapping Must be surrounded by 0.5mm of sound dentine One per missing wall/ cusp Keep in axis of tooth
Location
Avoid:
- bifurcation
- curved roots
- thin dentine
- pulp
Pin placement
Maximise all other retention Find flat, anatomically safe location Mark centre with 1/2 round bur Select drill angle Drill hole Clean Place pin Adjust pin if required
Pain or bleeding
Pulp: endodontics
Perio: trim surgically if it protrudes