Chemistry of Dental Porcelain

Chapter 2

Introduction to Metal-Ceramic technology

Lin, Shih-Yun

This chapter reinforces the value of the continued use of the metal ceramic restorations.

Terminology Differences in Low-Fusing Dental Porcelains Classification of Dental Ceramics Chemical components of dental porcelain Low-fusing porcelains for metal-ceramic restoration

Ceramics

Glass

Glass ceramic

Dental ceramics

Porcelain

Dental porcelains

Art or technology of making objects of clay and similar materials treated by firing.

Earthenware Glazed porcelain Dental restorations

Inorganic crystalline materials that are fired at high temperature(sintered). Broad meaning

Too nonspecific to represent a particular dental product or even a particular category of nonmetallic materials

Including both products Veneer a metal substructure Comprise an entire restoration (substructure and veneer)

Compounds that contain metallic and nonmetallic elements.

• Weak structurally • require protection or strengthening

• Resist wear and mechanical forces • Harm to restorative materials and tooth

• Biocompatible • No break down or release elements

• Not transmit electric and thermal change • Protect sensitive pulpal and gingiva

• Withstand high temperatures • Within certain limits-no structural change

Amorphous(noncrystalline) inorganic material in which atoms and molecule are not arranged in a regular lattice structure as they are in crystalline solids.

lattice structure

Most are silicate family Based on silica (silicon dioxide, SiO2),

Found in nature as quartz

Retains a noncrystalline glass phase along with a partially crystallized ceramic phase. Crystal nucleation and growth in the glass matrix is controlled Stronger and tougher than glass phase along.

Ambiguous to apply to all types of ceramic dental products Anusavice: An inorganic compound of metallic and nonmetallic elements “formulated to produce the whole or part of a ceramic-based prosthesis.”

Ceramic materials initially derived from a combination of kaolin, quartz, and feldspar sintered at high temperatures.

高嶺土長石石英

Kaolin → Alumina

Materials science perspective An amorphous glass matrix and at least one crystalline phase such as leucite(K2O-Al2O3-4Si)2

白榴石

Ingredient (wt%) Early to 1800 High-fusing(wt%)

Feldspar 78 75 to 85

Quartz - 12 to 22

Alumina - ≤ 10

Kaolin 15.3 ≤ 3

Potash silicate 4.7 -

Dehydrated borax 2.0 -

Yamamoto, acknowledging the glass matrix and complex crystalline phase

Describe metal-ceramic porcelains as “Crystallized glass”

Composite structure of glasses, ceramics, or glass-ceramics Crystalline ceramic and glass-ceramic

Strengthen and toughen glass phase Ensure veneering materials compatible to substructure

Metallic oxides Opacity glasses and to add color

Fusion temperature(melting range) High Medium Low fusing

Vastly different application in dentistry Other classification methods are needed

Metal-ceramic restorations All-porcelain restorations

Land’s all-porcelain jacket crowns McLean’s aluminous porcelain jacket crowns

Contemporary metal-ceramic porcelains Improved esthetics Improved strength Increased linear (CTE) Coefficient of thermal expansion

熱膨脹係數

物體在單位溫度改變下，材料的長度改卛率。

Metal ↓

porcelain ↑

1838

Kaolin ↓, color & translucency ↑ Enamel crown Placing dental porcelain on a platinum foil

substrate Adapted metal foil to the prepared teeth No mechanical or chemical attachment

1886

Vacuum firing Atmosphere ↓, color & translucency ↑

Aluminum oxide addition Strength ↑

1949

Bonding low-fusing feldspathic porcelain to metal using a gold-based alloy

Cast metal substructures indirectly using the lost-wax technique

Chemical bond

control addition of leucite crystals feldspathic porcelain

low coefficient of thermal expansion(CTE) raise high enough to maintain a stable bond or attachment between ceramic veneer and the underlying metal

Dr Elias Wildman

Land

1956

Brecker

Dentists Supply Company(Dentsply)

1962

Weinstein

Land’s all-porcelain jacket crowns McLean’s aluminous porcelain jacket crowns

Late 1800s Low-fusing feldspathic porcelain

Complete dentures and individual denture teeth Disadvantages

No chemical bond Platinum foil removed

Lack strength and toughness Structural failures

Not gain widespread popularity

1965 Create special aluminous “core” porcelain

40%~50%(by weight) alumina Fired and veneered with thermally compatibly low-fusing body porcelain

Enamel porcelain Alumina free

Dentin porcelain 5%~10% alumina

Elimination of kaolin Addition of alumina Vacuum firing leucite-containing component

Esthetics Strength Raise linear CTE

Wildman 'reformulation vacuum firing metallic oxides

Proved opacity for masking Sufficient color for matching

Vacuum firing Alumina addition to quartz

McLean and Hughes Dispersion strengthening

Leucite crystals in the glass matrix High CTE(20 to 25x 10-6/℃) Weinstein, 1962

Mixture of 6 oxides

Fusion temperature Ultra low-fusing porcelains Contemporary classification f low-fusing porcelains

Fabrication method Crystalline phase(ie. Chemistry) Clinical application

ceramic particles fuse together range, not discreet temperature Pyroplastic flow(slumping)熱塑性流動

Gradually undergo over several hundred degrees

glass temperature(Tg) Solid to glass-supercooled liquid Significant increase in the ceramic’s CTE

Ultra low-fusing porcelains Contemporary classification flow-fusing porcelains

Denture teeth

Prefabricated pontic(trupontics)

Metal-ceramic & aluminous porcelains

Similar composition & microstructure

Manual processing Machine processing

Layering, pressing Copy-milling

CAM Slip casting, glass infiltration

CAD/CAM

Low-fusing ceramic porcelain

Strength Opacity Color CTE increased

Translucency Weaker

structure

Crystalline particle Glass matrix

All-ceramic systems Alumina, fluorapatite, leucite lithium disilicate , lithium phosphate, mica, spinel, zirconia

Clinical application Type of ceramic

Porcelain denture teeth High-fusing feldspathic porcelains (manufactured) Medium-fusing feldspathic porcelains (manufactured)

All-ceramic systems Based on alumina, feldspar, fluorapatite, leucite, lithium disilicate, lithium phosphate, mica, spinel, zirconia(heat-pressed, machined[CAM], sintered, and slip-caste)

Metal-ceramic porcelains

Low-fusing feldspathic porcelains(sintered)

Ultra low-fusing feldspathic porcelains(sintered)

Feldspar Potash feldspar Sodium feldspar

Quartz Alumina Kaolin Fritting and frits Phases of dental porcelains

leucite

Potassium aluminum silicate

鉀長石 K2O-Al2O3-6SiO2 Potash feldspar Orthoclase

Sodium aluminum silicate

鈉長石 Na2O-Al2O3-6SiO2 Sodium feldspar Albite

Forming the glass matrix Fritting and coloring process

Potash feldspar Sodium feldspar Lowers the fusion temperature More susceptible to pyroplastic flow

Potassium, sodium, calcium oxieds Fluexes Increase porcelain's CTE approach the higher CTE level of metal-ceramic alloys

Increase the porcelain's CTE by breaking up oxygen cross-linking

Too much oxygen cross-lining disrupted High-expansion dental porcelains Weaken restoration Cloddy appearance Difficult to glaze

SiO2, Silica High fusion temperature Serve as framework Stabilizing porcelain build up at high temperatures prevent pyroplastic flow during sintering strengthens the fire porcelain

Al2O3

Hardest and strongest oxide Naturally alumina

Water molecules, hydrated alumnia Pure alumina

Calcination process

Al2O3-2SiO2-2H2O Hydrated aluminum silicate Initially act as binder to increase the moldability of unfired porcelain

Enables the porcelain to be carved Opaque

Very small quantities

Glass modifiers Oxides of potassium, sodium, calcium

Opacifiers and pigments

Crystalline minerals Feldspar quartz alumina

High temperature Cold water Noncrystalline solids

Opaque, Dentin, Enamel Numerous color concentrates

Opaque and dentin color modifiers external colorants, colorless glaze

Viscosity Melting range Chemical durability Thermal expansion Resistance to recrystallization

Feldspar(長石)

Molten glass phase

Glass matrix 75-85%

raise CTE

Incongruent melting (分熔)

interspersed cooling

Overheating

Leucite crystals dissolve

CTE decreases, weakens the ceramic

How the porcelain being processed !

When porcelain cracking or bond failures occur...

Opaque porcelains Body porcelains Stains and glazes Optical qualities Color coding dental porcelain powders Starter or trial kits Requirements of a porcelain for bonding to metal Nondiscoloring dental porcelains Porcelain firing schedules

Vita 3D-Master

Bleaching guide

Vitapan classical

Ceramco 3, dentin porcelain

enamel porcelain

Dentin modifiers Mamelons, Add-on porcelains

Porcelain margins and gingival tissues

stains

Chromascop

(Ivoclar Vivadent)

Darker than body Removing and polishing Help select of body shades

Wet the metal surface and establish a metal-porcelain bond Mask the color of the metal substructure Initiate development of the selected shade

When opaque layer is fired Chemical bonds to form with oxides on the metal surface Metal-porcelain attachment is established

insoluble oxides

Tin dioxide (SnO2)

Titanium dioxide (TiO2)

Zirconium dioxide (ZrO2)

Cerium dioxide (CeO2)

Zircon (ZrO2-SiO2)

Rubidium oxide

(Rb2O)

Particle-size distribution Amount and color of the oxidized metal casting Light-colored surface oxides

Thin opaque layer

Opaque porcelains Foundation for a body shade

Altered by color modifiers and other additives to simulate natural fluorescence Color modifiers

Higher percentage of metallic oxides for more saturated color

Dentin porcelains Enamel porcelains Translucent porcelains Body modifiers

The bulk of the crown buildup for most metal-ceramic restoration Major determinant of the shade Discouraged terms: gingival porcelain, cervical porcelain Gingival porcelain

Less translucent, more saturated with color

Violet to gray range Illusion of translucency by virtue of their grayish or sometimes bluish hue Also as ”incisal porcelains”

Appreciation increased Not transparent Not allow the transmission of all light Give depth and natural enamel-like translucency without altering the body shade

Color concentrated Aid in internal color modification All body porcelains

Same basic chemical and physical properties Mix freely

Dentin porcelains Color predominant

Enamel and translucent Color reduced

Body modifiers Color intense

Yellow • Predominant color in most

teeth • Indium,

praseodymium(lemon) • Stable pigments

Green • Chromium oxide • Avoided in dental porcelain • Color of glass

White • Cerium dioxide • Titanium dioxide • Zirconium dioxide • Most popular

Black • Iron oxide

Gray • Platinum gray, diluting iron

oxide

Blue • Cobalt salts • Enamel shade

Surface characterization Modification for custom shade matching or harmonizing

Not to dilute color intensity Ensure fusion pint below maturation temperature of dentin and enamel porcelains

Generally colorless low-fusing porcelains Considerable fluidity at high temperature Fill small surface porosities , irregularities After firing—re-create the external sheen or glossy appearance of a natural tooth

Fluorescence Metamerism Opalescence

An object absorbs light an one wavelength and reflects it at another wavelength

300~400nm

absorb reflect

400~450nm

Blue or bluish white

Dentin exhibits more fluorescence than enamel Not all porcelains fluoresce In dark illuminated with fluorescent

PFM may appear dark compared to adjacent natural teeth

Rare earth oxides added mimic natural tooth Reduces metamerism

Metamerism the change in appearance of an object under varying light sources

Metameric pair

2 objects match in color under one light but differ in color under another light PFM in daylight/ dark with UV

Opalescence observation Light-scattering Sufficient daylight for light waves to be refracted in two ways

Low energy: blue / blue-white

High energy: orange-yellow orange-amber

Light-scattering abilities of translucent porcelain

Major: Enamel and translucent powders Opal porcelains

Reproduce natural teeth Enamel and translucent areas of teeth are more likely to demonstrate greater than dentin

Color code organic dyes to color code the porcelain powders

Dentin-pink, Enamel-blue Burn off on heating, not affect the shade

Color tags Without color differentiation

Difficult to track the placement of multiple shades of porcelain and internal color development until after a restoration has been fired

Typical kit Opaque porcelain, opaque liquid, dentin and enamel porcelains

New product introduction

Two features make low-fusing porcelains suitable for bonding to metal

High CTE(13.5 ~15.5 ×10-6/℃) Melt below the melting range of the alloy

High temperature can distort the metal and alter the fit of a restoration

“nongreening”? Fire on silver-containing alloys without risk of discoloring the ceramic veneer Don’t buy too much!

Furnace must be urged of any residual silver contamination prior to resuming work with metal-ceramic porcelain

1200℉→1800℉, 6 minute 100℉ per minute

649℃→982℃, 6 minute 55.5 ℃ per minute

Most manufacturers conversion100℉ as 55℃

Quickest way Multiply by 1.8, not add 32 Only calculating the rate of rise

Terminology Differences in Low-Fusing Dental Porcelains Classification of Dental Ceramics Chemical components of dental porcelain Low-fusing porcelains for metal-ceramic restoration Summary

Dental porcelain classification Chemical composition Low-fusing porcelains Various brans of dental porcelains differ in handling characteristics, ability to mask oxide layer, firing schedule

Chemistry of Dental Porcelain

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