Shade taking, impressions and diagnostic wax-up

Question 1

Problems with shade taking

Answer 1

Your colour perception
The lighting conditions
Translucency of tooth

Question 2

Shade guide

• what increases across
• what increases down

Answer 2

Value increases across

Chroma increases down

Question 3

3 easy steps for use of shade guide

Answer 3

Determine value
Determine chroma
Determine hue (yellower or redder)

Question 4

What is the use of a diagnostic wax-up?

Answer 4

Helps you, the technician and the patient see what’s possible. Allows planning and communication of

• aesthetics
• occlusion
• tooth reduction
• restoration type
• restoration design
• treatment plan

Question 5

Process of diagnostic wax-up

Answer 5

Study casts are produced
Ideally should be mounted on an articulator
Technician builds up proposed restorations in wax to a prescription
These can be used to identify problems with proposed plan

Question 6

How to articulate your models

Answer 6

Trim models
Find ICP position for models
Glue on disposable articulator

Question 7

Process of building up wax (diagnostic wax-up)

Answer 7

Use a clean carver

Add small amounts at a tie

Question 8

Impression materials for crowns

Answer 8

Silicones: addition or condensation
Polyethers
Polysulphides
Reversible hydrocolloids

Question 9

Addition-cured silicones are available in which forms?

Answer 9

Putty
Medium
Light
Ultra-light
(usually cartridge delivered for ease of mixing)

Question 10

Problems with addition-cured silicones
+
solution

Answer 10

Control of dimensional stability (low filler)
Flow of material into surface detail (high filler)
Control of material in tray/ mouth
SOLUTION: use two materials
-putty/ heavy-bodied material for bulk
-wash/ light=bodied material for detail
-or use custom tray to support medium-bodied material

Question 11

Addition-cured silicones: high filler content properties –>

Answer 11

Good dimensional stability but poor surface detail

Question 12

Addition-cured silicones: low filler content properties –>

Answer 12

Poorer (although still good) dimensional stability but good surface detail

Question 13

Techniques for silicone impression taking

Answer 13

Twin mix
Two stage (with or without spacer)
Monophase

Question 14

Technical considerations for silicone impressions

Answer 14

Air blows
Drag
Complete impression
Rigidity of material

Question 15

Technical considerations for silicone impressions: rigidity

Answer 15

If insufficient wash material, rigid putty will engage undercut area
When removing impression, model will break

Question 16

Two stage technique

Answer 16

Take an impression using putty with spacer
Once set, remove impression and discard spacer
Remove any large undercuts with scalpel
Fill space with the low viscosity material and re-seat impression
Once set remove completed impression