Sectional models and veneers

Question 1

Sectional model use

Answer 1

Indirect restorations are produce on a sectional model.
These models allow the die to be a separate, removable component while maintaining the die in the correct position in relation to the other teeth.

Question 2

How are sectional models produced?

Answer 2

They are produced in a hard material such as Class IV die stone, epoxy resin or equivalent that can withstand the production process without loss in accuracy

Question 3

Pinned systems

Answer 3

Technically difficult to use
Accurate
Time consuming

Question 4

Tray systems

Answer 4

Quick
Simple
Cheap
Less accurate

Question 5

Production of tray systems

Answer 5

The impression is trimmed to leave the teeth and 2-3mm of gingivae
The centre is also marked
Surface tension reducing solution is applied to allow the die material to flow readily
A plastic tray forms base which incorporates locating grooves and retaining lugs
Vacuum mixed die stone is vibrated into the impression after drying the silicone surface
The tray base is filled
The impression is turned on to the base, aligned and left to set
Once set, imp is removed
Model left to dry before sectioning and ditching

Question 6

Sectioning

Answer 6

The dies required are sectioned
This allows access to the margin and for the restoration to be seen from all aspects
The sections are made by making parallel cuts which allows all sections to be removed
Margins of the die and the adjacent teeth may be damaged easily by the blade

Question 7

Ditching

Answer 7

Refers to the removal of the gingival tissue around the die.
This allows the margin to be seen and accessed clearly.
A round bur is used to remove the material

Question 8

Die hardener

Answer 8

Typically die hardener used to increases abrasion resistance of the die stone
Ideal when using a blade near the margin

Question 9

Die spacer

Answer 9

Allows room for the luting agent
It is a thin layer of varnish added to the surface of the prep
Restoration is produced over the top

Question 10

What are veneers, what material are they made out of and how do they gain strength

Answer 10

Veneers, resin-bonded crowns, dentine bonded crowns
All-ceramic restorations with no substructure
Either: lithium disilicate or leucite or leucite containing feldspar
Gain strength by bonding to the tooth - must be able to etch and bond

Question 11

Methods of veneer production

Answer 11

Sintering ceramics
Pressing technique
CAD CAM

Question 12

Sintering ceramics

Answer 12

1. Ceramic particles are packed together on a refractory model to desired shape
2. Ceramic is fired at approx. 900C
3. Ceramic is trimmed, glazed & stained
4. Refractory is removed and the veneer fitted to the original model*.
   * Therefore the die must be duplicated which requires another stage in production and the associated errors.

Question 13

Platinum foil technique

Answer 13

a foil shell is created and used to support the ceramic particles in the furnace.
This technique was used extensively for the PJC which has now been superseded by high-strength substructure materials produced via alternative routes.

Question 14

Sintering production problems

Answer 14

Feather margins
Duplication of die in refractory material may introduce error
Refractory / ceramic compatibility is sensitive
Removing refractory from finished restoration
Fitting restoration to the original die

Question 15

Pressing technique

Answer 15

A wax pattern is produced of the desired shape either manually or via CADCAM
Use the lost wax process to convert the wax pattern into ceramic.
Pressing Ceramics - Lithium disilicate e.g. eMax
Once pressed the ceramic may be glazed or modified using sintering ceramics

Question 16

CAD CAM technique

Answer 16

Set margin
Cement lute
Design restoration
Send to production
Wax printing