Dental ceramicsSilicate ceramics and oxidceramics

Judit Borbély

Why use ceramics

n Biocompatibilityn Aestheticsn Durability

The biocompatability issue is essential to prevent adverse reactions within the patients

The use of dentally coloured glasses can provide replacement structures that can be made to imitate tooth structure in both colour, translucency and response to different lighting sources.

Improvements in fracture toughness, wear resistance, machinability, solubility and flexural strength

Ceramics used in dentistry

n Fillingsn Veneering metal

frameworksn All ceramic

restorationsn Denture teethn Implantsn Orthodontic brackets

Silicate ceramics

ESTHETICSn Feldspathic porcelainVeneering ceramics –

sintering n Glass CeramicCastable glasses-DicorPressed leucite system-

IPS Empress

Oxid ceramics

STRENGTHn Glass infiltrated Alumina

systemIn-ceram AluminaIn-Ceram SpinellIn –Ceram Zirconian Policrystal

ceramics:CAD/CAMCercon BaseDC-ZirkonLava Frame etc.

Glass matrix + Crystals§An overcooled liquid§Not crystalline, but still ordered structure§Silica tetrahedron network§Glass modifiers built in network

Most important crystals:n Leucitn Fluormican Aluminiumn Spinelln Zirconia

They determin the physical, chemical and optical

properties of the ceramics

(their composition varies in each type of ceramic)

Basic structure of dental ceramicsTwo different phases built by metallic (Al,Ca, Mg, K etc) and non-metallic (Si, O, B, F etc.) elements:

Feldspathic Porcelain:First used in dentistry

75%feldspar,22-25% quartz, 0-3% kaolin

First ceramic material in dentistry

Feldspathic Porcelain:derived from the natural mineral feldspar

n 75%feldspar,22-25% quartz, 0-3% kaolin¨ Feldspar:

Provides for transparency and influences the flow characteristics of the ceramics.

¨ Quartz (silicon oxide):Provides for adequate strength and also for transparency.

¨ Kaolin:Provides for the necessary opaque properties.

n Fritting:-cleaning and mixing raw materials, heating, melting, sudden cooling and grinding to fine powder

n Sintering:powder mixing with liquid, firing, powder particles stick together

n Shrinkage:appr. 30 vol%n Structure: leucite crystals in silica glass matrixn Disadvantage:brittle,hard,rigid

Veneering ceramicsn Used for the porcelain-fused-to-metal technique

n Based on modified feldspathic porcelainn Binding oxides for metal-ceramic bond

n Leucite content:thermal expansion coeff.

n Fusing temperature 200-250 C lower than metal framework (low fusing ceramics)

Synthetic ceramics (metal –ceramics)§No natural raw materials§Made of high purity chemicals§Tempering:guided heating process, to form certain type, size, amount and dispersion of crystals (micro-leucite crystals§Standard physical, chemical and optical properties§Standard quality§Low or ultra-low fusing temperature

Hydrothermal ceramics• tempering and fusing in high pressure

steam• Hydroxil ions built in glassy matrix• Compact and homogenous structure• Better fracture toughness and lower

hardness• Leucite content allows veneering

frameworks• Ultra-low fusing temp. Can be

achieved• Pure glass can be used for dental

purposes (one and only among dental ceramics)

The bonding of ceramic materials to alloys follows four principles:¨Shrinking the ceramic onto the metal frame - coefficient

of thermal expansion¨ Chemical bond The bond is formed by means of

oxygen bridges between the silicon atoms of the ceramic and the metal oxides of the alloy.

¨Mechanical retention is created through finishing and blasting of the frames-surface enlargement also takes place.

¨Bonding through adhesion takes place via intermolecular forces (VAN DER WAAL forces)

All ceramic restorations

All ceramic systems ?n Estheticsn Biocompabilityn No corrosionn No allergyn Optical properties (metal free

restorations can reproduce natural aesthetics )

Driving force for developments has been the immense difference in reliability betweenmetal-ceramic systems and all-ceramic systems and a public perception that metal-freerestorations are more aesthetic

n driving forces for developments:n Public perception that metal-free restorations are more

aestheticn Disadvantages of the metal ceramic systems include

radiopacity, some questions centring around metal biocompatibility and lack of natural aesthetics

n Difference in reliability between metal-ceramic systems and all-ceramic systems

advances in industrial ceramics have included improvements: fracture toughness, wear resistance, machinability, solubility, hardness and flexural strength

All ceramic restorationsLaboratory processing

n Silicate ceramics o Sinteringo Castingo Pressingo CAD/CAM

n Oxidceramics o infiltration and /or CAD/CAM technology

Sintering is a method for making objects from powder, by heating the material (below its melting point) until its particles adhere to each other

The base-material for heating ceramic on:

- platinum foil (removable heat-resistant cap from the gypsum cast)

- Heat resistant investment material made cast

- Hydrothermal glass/ Duceram LFC

§Sintering

under vacuum to prevent porosities

opaqueBase dentin

opaque dentin

dentin clear fluor-escence

enamel

n Casting (Dicor)Casting is a process by which a

material is introduced into a mouldwhile it is liquid, allowed to solidify inthe shape inside the mould, and thenremoved producing a fabricatedobject

Cast using lost-wax investment methodfollowed by heat-treatment toprecipitate a crystalline phase

§ Pressing (Empress)Pressed ceramic technology produces

consistently precise crowns byeliminating shrinkage, porosity and the inconsistency of brush build-ups

Tooth prep guidelines

Wax pattern

Investing

Preheating procedure

Ingots

Pressing

Préselő kályha

Silicate ceramics-Esthetics/Oxidceramics-Strength

Silicate ceramics Oxidceramics

Feldsparceramics

Glass ceramics

Hydrothermalceramics

Glass-infiltrated

ceramicsPolycrystallineceramics

Feldspathic porcelain Dicor Duceram LFC

In-Ceram Alumina

Aluminium-oxide ceramics

Synthetic ceramics

IPSEmpress Duceram MK

In-Ceram Spinell

Zirconium-dioxide ceramics

Veneering ceramics

In-Ceram Zirconia

sinteringcastingpressing

glass infiltration method

CAD/CAM CAD/CAMCAD/CAM

CAD/CAM

Images from KaVo Everest CAD/CAM system

nPolycrystalline materials: crystal phase > glassy matrixnGreater flexural strength and Fracture tougnessnHigh functional strength thanks to excellent physical propertiesnVery low transparency

Oxide ceramics

Types of Oxide ceramics :

n Glass infiltrated ceramicso In-ceram Aluminao In-Ceram Spinello In –Ceram ZirconiaØ Lab technology: Glass infiltration/CAD CAM

n Polycrystalline ceramicso Aluminium-oxide ceramicso Zirconium-dioxide ceramicØ Lab technology: CAD/CAM

Glass infiltrated oxide ceramicsn 1989 In-Ceram technique:

oxidceramics for crown and bridge substructures

n The cast alumina sintered and then infiltrated with a Lanthana based glass.

n glass infiltrated alumina core on which a feldspathic ceramic baked to provide the functional form and aesthetic component of the restoration

n In-Ceram use variations of alumina as a toughened and high strength underlying core to support feldspathic veneering porcelain which gives the final shape and aesthetic attributes required for the restoration.

¨ In-Ceram Alumina: anterior and posterior crown substructures and three unit anterior bridges Alumina is made of synthetically manufactured corundum which is extracted from bauxite

¨ In-Ceram Zirconia – aluminium oxide is reinforced with zirconium oxide and combines the fracture toughness of ZrO2 with the high flexure strength of AlO

¨ In-Ceram Spinell – aluminium oxide is reinforced with MgAl2O4 and offers anterior aesthetics: natural, translucent appearance, used for anterior crowns

Corundum=Aluminium oxide (Al2O3)

Spinell

Zirconia

CAD/CAM In-Ceram technique n aluminium oxide substructure is milled from industrially

manufactured, porously presintered ceramic blanksn The porosities are then sealed with glass infiltrationn Veneering ceramics with a thermal expansion coefficient

matched to that of the substructure material

Vita In-Ceram ceramic blanks and milled substructure

Polycrystalline oxide ceramics

n Aluminium-oxide ceramicsAluminium-oxide content

>73% n Zirconium-dioxide

ceramics¨ ZrO2 95%+ 5% Yttrium

§ Tetragonal Zirconium Polycrystals (TZP)

§ Phase transformation toughening :

5% Yttrium-oxide in addition, partially stabilised ZrO2

n ZrO2 exists in 3 forms (monoclinic, orthorhombic and tetragonal), each with a different crystal structure

n ZrO2 can be stabilized in its tetragonal high-temperature phase by addition of yttrium oxide

n When applying an external source of energy (for example in the case of a beginning crack) individual zirconium oxide grains are transformed locally and accompanied by an increase in volume to their stable mnoclonic form at room temperature= transformation strengthening

n Compressive stresses arising within the structure to prevent the growth of crack

n This phenomenon=tension expansion is only known in the case of steel

Ceramic steel

Zirconium-dioxide ceramics can not be formed by conventional lab technologies( sintering, pressing, casting).

CAD/CAM made it possible to work with a new generation of hard ceramics in dentistry. These materials cannot be cast so therefore must be machined. In order to machine something a cutting path is required. The cutting path is generated from digital scanned data.

n SCAN THE OBJECT

n CREATE DIGITAL DATA POINTS

n GENERATE CUTTING PATH

n MACHINE REPLICA OBJECT

Application of science to dentistry

n CAD/CAM systems mills the contour from:¨ Dense sintered ceramic blank or ¨ Presintered, porous ceramic blank-final sintering

required for improving mechanical properties.

Structure of porous ZrO2 before final sintering (A) densely sintered ZrO2 (B),Scanning elelectron microscop, magnification: 20.000X

n Green processing¨ Milling of presintered ceramic blocks ¨ advantage: easy to process, grinding instruments do not

have to be replaced that often¨ disadvantage: porous presintered zirconia shape shrinks

during final sintering- enlarged substructures= software calculated

n Hard processing¨ Milling of dense sintered ceramic blocks ¨ Takes more time, grinding instruments wear off

n HIP= Hot Isostatic Press : special sintering technique ¨ High temperature and pressure applied to densify the

material, gaining 20% more in strength

CAD/CAM technology

n Scanner- digital impression of the prepared teeth

n Software – CAD- digital cast on the screen

- virtual design of the modeln Milling unit – CAM

- computer aided milling unit (cnc)- grinding process

Thank You for Your attention