Retaining large amalgam restorations

Question 1

Retention

Answer 1

Provided by convergent cavity walls

Loss of cusps gives loss of retention

Question 2

Features to increase retention

Answer 2

Grooves
Channels, slots
Bonding
Pins
Use composite

Question 3

Channels, slots etc

Answer 3

Use available tooth structure for retention
Slots
Amalgapins
Shelves

Question 4

Slots

Answer 4

Inverted cone bur

Question 5

Amalgapins

Answer 5

Minimum: 0.8mm diameter

2mm deep

Question 6

Shelves

Answer 6

Need to be 2mm high?

Question 7

Success

Answer 7

Place features where they will resist likely loads

Question 8

Bonded amalgam

Answer 8

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

Question 9

Bonded amalgam: the process

Answer 9

Methacrylate or composite resin
HEMA: hydroxylethyl methacrylate
NMSA: N-methacryloyl 5-aminosalicylic acid
MDP: 10-methacryloyloxydecyl dihydrogen phophate
A bond to dentine and metal?

Question 10

Bonded amalgam: clinical trials

Answer 10

Lower sensitivity?
Retention rates exceed that of pins
Less iatrogenic damage

Question 11

Problems with bonding

Answer 11

Loss of bond layer
Oxygen inhibition
Weakening of amalgam
Adhesion to matrix band

Question 12

Pins

Answer 12

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

Question 13

Location

Answer 13

Avoid:

• bifurcation
• curved roots
• thin dentine
• pulp

Question 14

Pin placement

Answer 14

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

Question 15

Pain or bleeding

Answer 15

Pulp: endodontics
Perio: trim surgically if it protrudes

Question 16

Pins not advised presently

Answer 16

Often traumatic
Placement at high speed results in poor thread
Cause dentine fractures
Surplus lining reduces retentive action
Inappropriate with composite