CERAMICS

WHY DENTAL CERAMICS?

Low fracture toughness

Brittleness

High wear resistance

DRAWBACKS OF CERAMICS

a) anterior and posterior crown

b) veneer

c) post and core

d) fixed dental prosthesis

e) ceramic stain

f) glaze

Uses or indications

a) Ultralow fusing - <850

b) Low fusing - 850-1100

c) Medium fusing- 1101-1300

d) High fusing - >1300

Firing temperature

denture teeth

Medium- and high-fusing porcelains are used for the production of ____

crown and bridge construction

The low-fusing and ultralow-fusing types are used as veneering ceramics for ____ or ____

titanium and titanium alloys.

Some of the ultralow-fusing porcelains are used for

i. Casting

ii. Sintering

iii. Partial sintering and glass infiltration

iv. Slip casting and sintering

v. Heat press

vi. CAD-CAM milling

vii. Copy-milling

Processing method

i. Amorphous glass

ii. Crystalline

iii. Polycrystalline

Based on microstructure

i. Opaque

ii. Translucent

iii. Transparent

translucency

crystalline minerals and glass matrix.

Dental ceramics are mainly composed with

Glass modifiers

are used as fluxes

Boric oxide fluxes (B2O3)

can behave as a glass modifier to form its own glass network.

1. Cast metal ceramic restorations

2. Swaged metal ceramic restorations

CLASSIFICATION

a) Casting of molten metal

b) CAD-CAM machining

c) Electrolytic deposition techniques

d) Swaged metal processes

Copings and frameworks for metal-ceramic prostheses are produced by:

• A wax pattern of restoration constructed

• Cast in metal

• High melting temperature of alloys-

phosphate bonded investment

Most common method is melting and casting.

opaquer

• Mask/cover the metal frame and

prevent it from being visible

• Bond the veneering porcelains to the

underlying frame

Opaquer

thickness of approximately 0.3mm

Manipulation of Ceramic

Vibration

Spatulation

Brush technique

techniques

Build up of cervical porcelain

Build up body porcelain

Cut back

Build up enamel porcelain

Steps of Condensation

sintering

After the condensation and building of a crown it is fired to high density and correct form. At this stage the green porcelain is introduced into the hot zone of the furnace and the firing starts, the glass particles soften at their contact areas and fuse together. This is referred to as ____

Low Bisque: surface of the porcelain is very porous. At this stage the grains of porcelain will have started to soften. Shrinkage will be minimal and the fired body is extremely weak and friable. Lack translucency and glaze.

Medium bisque: surface will still be slightly porous but the flow of the glass grains will have increased. A definite shrinkage but lacks translucency and high glaze.

High bisque: surface of the porcelain would be completely sealed and presents a much smoother surface with a slight shine. Shrinkage is complete. Appears glazed.

THE STAGES IN MATURITY:

a) Lower firing shrinkage

b) Less porosity in the fired porcelain.

condensation provides two benefits:

• Removal of excess water allowing the porcelain object to gain its green strength.

• Preventing sudden production of steam that could result in voids or fractures.

• Ceramic particles held together in the “green state after all liquid has been dried off

Significance of pre-heating stage:

• reduce the strength due to formation of undesirable crystal phases at higher temperature [devitrification]

• increases the chances of slumping [eliminate the shape we made and leave a globule of ceramic].

what is overfiring?

The porcelain object will have a chalky white color overlaying its shade because light is reflected and scattered at boundaries between particles and at the surfaces of porosity

what is underfiring

• Natural/auto glaze

• Applied/add-on glaze

• Polishing

• Custom staining

PORCELAIN SURFACE TREATMENT

self glaze

No separate glaze layer

Chemical adhesion

Mechanical entrapment

Compression bonding

BONDING MECHANISMS