retaining large amalgams

Question 1

What features increase retention?

Answer 1

Grooves
Channels
Bonding
Pins

Question 2

What is a slot?

Answer 2

Inverted cone bur

Circumferential ring inside dentine

Question 3

What is a pin?

Answer 3

Dent made into tooth with slight counter sink on pulpal aspect (to reduce stress
Small round bur
Minimum 0.8mm diameter and 2mm deep

Question 4

What are shelves?

Answer 4

Worked around periphery of tooth
W slightly undercut
At least 2mm high to reduce fracture

Question 5

What might make a restoration successful?

Answer 5

Place features where they’ll resist likely loads
Distribute forces around tooth
Consider direction of forces

Question 6

What is bonded amalgam?

Answer 6

Less invasive- less macro mechanical retention
Reduces risk to pulp and periodontium

Based off methacrylate or composite resins
To increase bonding eg. hydroxyethyl methacrylate (HEMA)

Self curing, bonds to dentine, amalgam condensed into whilst both unset to form micromechanical interlock

Maybe chemically bond- anaerobic setting (polymerisation happens faster in absence of O2)

Question 7

What is the evidence base of amalgam bonding?

Answer 7

Clinical trials

Reduces sensitivity?
Retention rates exceed that of pins
Less iatrogenic damage
Better restoration survival

Question 8

What are the problems w bonding?

Answer 8

Bond layer slightly soluble in water so can dissolve away at margin for recurrent caries

Oxygen inhibition might need an agent (oxiguard)

Weakening of amalgam- if too much bonding, gets incorporated

Might stick to matrix band which could stick to tooth

Question 9

What are types of pins?

Answer 9

Pushed in
Threaded in
Glued in
Stainless steel self tapping

Must be in sound dentine- must be surrounded by 0.5mm

One pin per missing wall/cusp

Keep in axis of tooth

Question 10

Where shouldn’t you put pins?

Answer 10

Bifurcation
Curve roots
Thin dentine
Pulp

Question 11

How are pins placed?

Answer 11

Maximise all other retention

Flat anatomically safe location 
Mark a centre w 1/2 round bur
Select drill angle
Drill hole
Clean
Place pin
Adjust pin if required

Question 12

Why aren’t pins advised?

Answer 12

Often traumatic 
High speed placements poor thread
Causes dentine fractures
Surplus lining reduces retentive action
Inappropriate w composite

Question 13

What should happen if the pin is misplaced in the tooth?

Answer 13

Pulp- endodontics

Periodontal ligament- cut flap surgically and cut down pin if it protrudes

Question 14

What is Nayyar core?

Answer 14

Done after endodontics
Cavities at level of pulp chamber filled with amalgam, can be covered w amalgam/composite
Core for indirect such as crown