DR. RAZAN AL MGHAWICH

Ceramic Restorations

Dental Ceramics

is an inorganic material that contains metallic or semi-metallic elements with non-metallic elements (usually oxygen).

Theses elements can be Aluminum, calcium, titanium ,silicon, zirconium ,magnesium, phosphorous, potassium, lithium, sodium.

Dental ceramics

These materials can be defined by their inherent properties; they form hard, stiff, and brittle materials

This is due to the type of the atoms present, the nature of their inter-atomic bonding, which is ionic and covalent mostly ,& the shape of the atoms packed or held together

Other properties of ceramics are:Wear resistance, refractory (high melting point),

thermal insulators, non-magnetic, oxidation resistance, prone to thermal shock and chemically stable

Dental ceramics

Ceramics contains a crystalline phase and a glass (continues ) phase depending on structural arrangement of the atoms

In general, the more glassy the microstructure (i.e. non-crystalline) the more translucent it will appear, and the more crystalline, the more opaque

With a range from very translucent to very opaque. This is especially based on the silica structurea. Silicate Types:(1) Clays (hydrated alumino-silicates)with water(2) Feldspars (anhydrous alumino-silicates)no water(3) Quartz (silica)b. Non-silicate Types

Glass in general

Glass is an amorphous solid (non-crystalline) material that exhibits a glass transition

Glasses are typically brittle and can be optically transparent The most familiar type of glass is soda-lime glass, which is

composed of about 75% silicon dioxide (SiO2), sodium oxide (Na2O) from sodium carbonate (Na2CO3), lime (CaO)

In science, the term glass is defined in a broader sense, encompassing every solid that possesses a non-crystalline (i.e. amorphous) structure and exhibits a glass transition when heated towards the liquid state.

Quartz sand (silica) is the main raw material in commercial glass production

Quartz is the 2nd most abundant mineral in the Earth's continental crust, after feldspar.

It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2.

Crystalline in general

A crystal or crystalline solid is a solid material which constituent atoms, molecules or ions etc..,are arranged in an ordered pattern extending in all three spatial dimensions at a microscopic level

large crystals are usually identifiable by their macroscopic geometrical shape, consisting of flat faces with specific, characteristic orientations

The scientific definition of a "crystal" is based on the microscopic arrangement of atoms inside it, called the crystal structure.

A crystal is a solid where the atoms form a periodic arrangement

microstructure

Microscopically, a single crystal has atoms in a near-perfect periodic arrangement; a polycrystal is composed of many microscopic crystals (called "crystallites" or "grains"); and an amorphous solid (such as glass) has no periodic arrangement even microscopically.

crystalline polycrystalline amorphous

Feldspars

Feldspars (KAlSi3O8 – NaAlSi3O8 – CaAl2Si2O8) are a group of rock-forming tecto-silicate minerals

that make up as much as 60% of the Earth's crustin glassmaking, alumina from feldspar improves

product hardness, durability, and resistance to chemical corrosion, because it can crystallize

In ceramics, the alkalis in feldspar (calcium oxide, potassium oxide, and sodium oxide) act as a flux, lowering the melting temperature of a mixture.

Fluxes melt at an early stage in the firing process, forming a glassy matrix that bonds the other components of the system together

Classification based on the microstructural level

we can define ceramics by the nature of their composition of glass-to-crystalline ratio to four basic compositional categories, with a few subgroups:

composition category 1 – glass-based systems (mainly silica)

composition category 2 – glass-based systems mainly silica + crystalline fillers (typically Lucite, more recently, lithium disilicate)

composition category 3 – crystalline- based systems with glass fillers (mainly alumina)

composition category 4 – polycrystalline solids (alumina and zirconia) (no glass content at all only crystalline)

Other classification Systems for Dental Porcelains

1. Classification Based on Fusion Temperatures: High Fusing: 1288 - 1371 °C (2350 - 2500 °F), Used for :

Denture Teeth, Aluminous Cores Med Fusing: 1093 - 1260 °C (2000 - 2300 °F), Used

for :Porcelain jacket crowns, Inlays Low Fusing: 871 - 1066 °C (1600 - 1950 °F)Used for

Porcelain fused to metal Restorations

Classification Based on Application Design:a. Porcelain Core : Porcelain veneered onto porcelain coresb. Porcelain Inlays and onlaysc. Cast Porcelain : Cast porcelain crownd. Porcelain/Metal : Porcelain fused to metal

Classification Based on Usage of Low Fusing Porcelains

a. Opaque Porcelains = Low Fusing Glass + Opacifiers

b. Body Porcelains = Low Fusing Glass + Colorants (1) Incisal or Enamel= Low Fusing Glass +little colorant (2) Gingival or Dentin=Low Fusing Glass +yellow oxides (3) Modifiers =Low Fusing Glass + white/gray oxides

c. Stains or Glazes = Low Fusing Glass + Colorants

Related Definitions and Terminology

Condensation=Padding &/or packing of porcelain powders into position prior to firing

Biscuit =Cohesive powder compact at particle-to-particle contacts after initial fusion

Frit = An unfused or partially fused powder mass.

Firing = Heating of porcelain powder or biscuits to eliminate the porosity and form a completely solid mass

Soaking = Holding at a fixed firing temperature.

coefficient of thermal expansion= The degree of expansion divided by the change in temperature

Thermal expansion= the tendency of matter to change in volume in response to a change in temperature, through heat transfer

Feldspathic porcelains

Technically it is a glass rather than true porcelain( translucent)But since we want a crystalline phase with the amorphous

phase in dental porcelain we add feldsparfeldspar is the main component in it ,feldspar has a tendency

to form a crystalline phase (leucite)Feldspars (KAlSi3O8 – NaAlSi3O8 – CaAl2Si2O8) In addition feldspathic porcelains contain kaolin as a binder

(Al2Si2O5(OH)4)Quartz as a filler and strengthen agent Metallic oxides for opacity and color Some oxidative elements most present(tin, indium ,gallium)

for the porcelain to bond to the alloyUsed in porcelain fused to metal restorations

Leucite

Leucite is a rock-forming mineral composed of potassium and aluminum tecto-silicate K[AlSi2O6]

Leucite occur as a crystalline phaseIt has a large coefficient of thermal expansion

compared to glass

• Feldspar tend to form leucite when melted

• Feldspathic porcelain contain leucite crystalline phase

• Note : There is another type of glass based ceramic reinforced with luecite crowns used in all ceramic restorations

Porcelain fused to metal restorations

fixed restorations composed of a substructure metal layer and covered with 3 layers of feildspathic porcelain

The metal coefficient of thermal expansion should be higher than that of porcelain to place the porcelain in slight compression when cooled (which gives it a stronger state); the alloy part should expand more than porcelain when they are heated to the same temperature

Porcelain is stronger under compressive forces than under tensile forces

The metal alloy part is composed of Noble metals ( gold platinum, or palladium) they can be classified to : High noble alloys :contain 40 % or more noble

metals Noble alloys :contain 25 % to 40 % noble metal Base metal alloys: contain less than 25 % noble

metals

PFM

• The alloys should have high yield strength that minimize their permanent deformation under occlusal surface

• They should be stiff ( high modulus of elasticity ) that minimize their flexure especially their long span bridges

• Note: porcelain may fracture secondary to flexure or deformation of the metal substructure ,because of its low ductility

• Advantages of the added Metal substructure :• High strength. withstand stresses. Thermal compatibility. Less crack

propagation. High resistance to fracture. Give good marginal fit

Bonding porcelain to metal : Occurs via mechanical and chemical bonding Mechanical bonding : interdigitating between the opaque layer of

porcelain and the alloy which increases with surface roughness & wetting of the metal

Chemical bonding: occur via the oxide mixing layer (metal-oxide-porcelain) from the opaque layer and the metal; oxidation of metal is accomplished by heating the metal structure in a furnace before adding the porcelain

Porcelain fused to metal design

The metal part is the substructure and should be 0.5 mm in thickness

The metal-porcelain junction should be at least 1.5 mm away from the occlusal contact

All internal angles should be rounded to prevent stress concentration

The metal-porcelain junction should be at right angle to avoid porcelain fracture

the porcelain 1 to 1.5 mm (thickest at the occlusal contact ) build from 3 layers

The 3 layers of porcelain are :1- the opaque layer: masking the metal and the dark oxide layer, with minimum thickness of 0.1 mm2- body or dentine layer : the thickest used to build most of the crown gives the color and shade3- incisal or enamel porcelain : the most translucent layer to give a natural appearance

PFM failure

Mechanical or chemical failures

1- Metal failure: . Incomplete degassing . Incorrect metal conditioner . Reused metal alloy

2-Porcelain-to-Metal Fractures:(Most common site for short-term failures to occur. Most common for base metals.)a. (adhesive failure modes )Contamination of metal surface (oxide-metal interface failure )Contamination of oxide surface (oxide-porcelain interface failure)Porcelain metal interface failure : oxide layer wasn’t formed b. (Cohesive failure modes )Oxide- oxide failure : the oxide layer is too thick, Thick oxide layers should be sandblasted prior to porcelainizing to minimize the oxide thickness

Porcelain failure

A- porcelain fracture: (Most common site for long-term failures to occur. Design or fatigue problems.)1. Design or procedural errors:a. Too little bulk of metalb. Sharp angles in porcelainc. Improper margin designD. Inadequate framework design 2. Malocclusion or impact stresses3. Thermal contraction incompatibility:a. Built-in stresses generate cracks at poresb. Thermal fatigue propagates cracks

Porcelain failure

B- Intra-Porcelain Failures:1. "Gray or Black" shades in porcelain color: a. Insufficient opaque porcelain b. Improper opaque firing d. Porcelain oven contamination2. Porcelain surface cracks: a. Improper cooling rate b. Thermal cycling c. Over-glazed or under-fired porcelain d. Improper porcelain selection3. Porcelain surface roughness: a. Improper finishing and polishing agents b. Acid dissolution (topical fluorides)

REPAIR SYSTEMS:A. Silane + Acrylic (e.g., FUSION, George Taub Products, Inc.)B. Silane + Composite (e,g., PULPDENT Porcelain Repair Kit)C. Silane + Composite (e.g., MIRAGE PFM Repari)

Drawbacks of PFM restorations

Inadequate structure for ceramics - thickness of metal coping.

More occlusal clearance requiredTransparent metallic hue - anterior teeth Metal exposed in case of gingival recessionPatients allergy to metals especially base metal

alloys Casting procedural errors with metalsThe extra bonding failures at porcelain-metal

interface

All- ceramic restorations

In some hand-layered porcelain restorations , feldspathic porcelain is fused to aluminum oxide, glass-infiltrated aluminum oxide (alumina) or zirconium-oxide (zirconia) creating a high-strength, highly aesthetic, metal-free crown or bridge.

In other traditional restorations, this porcelain is layered onto a metal substructure and often display color brightness, an opaque "headlight", and dark oxide lines (a "black line" in the vicinity of the gum line).

As these dark metal substructures are not conducive to a natural appearance, metal-free restorations are typically more aesthetically pleasing to the patient

But as the PFM restorations having a different core porcelain material than the outer layer has a disadvantage of the chipping of the outer porcelain layer because the bond between the 2 layers is not as strong as wanted

All-ceramic restorations

monolithic restoration :it is fabricated in full from a single block of material.

The material used for this type of restorations has to be strong enough, especially for posterior teeth

Very strong porcelains are mostly opaque with no fluorescence

using a monolithic restoration means using one color from the cervical area to the occlusal and depending only on outer stains this whole process is considered less esthetic

Plus it can be abrasive of the opposing tooth Monolithic anterior crowns, with less occlusal stress can be

fabricated entirely from an esthetic porcelain material

All- ceramic restorations

All- Ceramic restorations

Glass ceramics with crystalline fillers

Glass ceramics with Leucite filler :E.x. IPS empress® :Can be press-ceramic or CAD/CAM machinable ceramic Provided as ingots or blocks Indications: Single-tooth restorations (Inlays,

onlays, veneers, anterior and posterior crowns)Not suitable for bridges or more than one unit

restoration ,because its toughness and strength range from medium to high

Glass ceramics with crystalline fillers

Glass ceramics with Lithium disilicate (LS2) fillers E.x. IPS empress 2® or IPS e.max®Supported with zirconium oxide for added strength , it may

also be used for bridges in the posterior area.either the press or the CAD/CAM technology Indications Thin veneers (0.3 mm) Minimally invasive inlays and onlays Partial crowns and crowns Implant superstructures 3-unit anterior/premolar bridges (only IPS e.max Press) 3-unit bridges (zirconium-oxide supported only IPS e.max

CAD)

Oxide Ceramics with glass infiltration

Example : Vident® all-ceramic In-ceram® products1-( VITA In-ceram Alumina)® Alumina based ceramic 75% Al2O3 with 25% glass

infiltrations single unit anterior or posterior crowns and three-unit

anterior bridges.

2-(VITA In-ceram Spinell)® spinell based caramics78% MgAl2O4 with 22%Glass

infiltration for single unit anterior crowns only

3-(VITA In-ceram Zirconia) ®56% Al2O3 ,24% ZrO2 with 20 % glass infiltration high level of translucency & flexural strength indicated for single unit posterior and three-unit posterior

bridges.All available in machinable block form for cerec inLaband other milling systems

Polycrystalline ceramics

Doesn’t contain a glass phase at all, usually made from alumina or zirconia oxides

Considered a very hard dental material so its used as a core layered with more esthetic other dental ceramics like fieldspathic ceramics, or can be used as monolithic crowns, Monolithic ceramic crowns tend to be dense in appearance with a high value and they lack translucency and fluorescence

Alumina cores without glass are produced by milling pre-sintered blocks of the material utilizing a CAD/CAM dentistry technique.

The zirconia substructure (core) is usually designed using CAD/CAM techniques of an impression, model or patient mouth, then its milled from a block of zirconia in a soft pre-sintered state, then sintered again in a furnace where it shrinks by 20% and reaches its full strength of approximately 850MPa.

Zirconia

Zirconia is the hardest known ceramic in industry and the strongest material used in dentistry

The zirconia used in dentistry is zirconium oxide which has been stabilized with the addition of yttrium oxide. its full name is yttria-stabilized zirconia or YSZ.

Advantage of zirconia cores : 1- allow light to pass as a normal tooth would and that gives

a natural look, unlike other metal cores that block the light. 2- The normal too hot/cold sensations that can be felt with

other crowns does not normally occur because of reduced thermal conductivity

disadvantage of core zirconia :bond strength of layered porcelain fused to zirconia core is not strong enough

Zirconia

1- tetragonal polycrystalline zirconia, partially stabilized with yttrium oxide there is pre-sintered zirconia and HIP (hot isostatic pressing) zirconia then

used with cad/cam technology has very high strength & toughness , suitable for posterior long span

bridges Its usually opaque Example : Lava™Zirconia from 3M™ESPE™ , (VITA In-Ceram) YZ™ Suggested indications Monolithic full-contour crowns.. 3,4 5- and 6-unit bridges. Curved and long-span bridges. Cantilever bridges. Inlay and onlay bridges. Anterior adhesive bridges. Primary crowns/Telescopes and Implant abutments.

Alumina

2- alumina oxide polycrystallineExample : (Vita In-ceram AL) ™= 100 %Al2O3 IPS e.max ZirCAD™Indicated for posterior crowns and bridgesHigh strength and toughness OpaqueFabricated by sintering and CAD/CAM technology

Note : alumina cores can be glass infiltered which has significantly higher porcelain bond strength over CAD/CAM produced zirconia and alumina cores without glass

Fabrication of dental ceramics

The traditional ceramic process generally follows this sequence:

Milling → Batching → Mixing → Forming → Drying → Firing → Assembly.

Milling is the process by which materials are reduced from a large size to a smaller size

Forming is making the mixed material into shapes. Forming can involve: (1) Extrusion, such as extruding "slugs" to make bricks, (2) Pressing to make shaped parts, (3) Slip casting

Sintering is the process of forming a solid mass of material by heat and/or pressure, without melting it to the point of liquefaction

CAD/CAM (computer-aided design and computer-aided manufacturing):

CAD/CAM dentistry uses subtractive processes (such as CNC milling) and additive processes (such as 3D printing) to produce physical instances from 3D models.

Two basic techniques can be used for CAD/CAM restorations:

- Chairside single-visit technique -Integrated chairside–laboratory CAD/CAM procedure

CAD/CAM

Increasing the speed of design and creationIncreasing the convenience or simplicity of the design,

creation, and insertion processesmaking possible restorations and appliances that

otherwise would have been infeasible. Utilizing in-office CAD/CAM restorations can be done

in a single patient visit.Reducing unit cost and making affordable restorations

and appliances that otherwise would have been prohibitively expensive.

However, to date, chairside CAD/CAM often involves extra time on the part of the dentist, and the fee is often at least two times higher than for conventional restorative treatments using lab services.

CAD/CAM

CAD/CAM use special partially sintered ceramic, which are fired again after machining.

CAD/CAM restorations created with glass-ceramic CEREC technology appear to last well, demonstrated excellent fit, strength and longevity

As adjunctive techniques, software, and materials improved, the chairside use of CAD/CAM (use within dental offices/surgeries) increased.

For example, the commercialization of Cerec by Siemens made CAD/CAM available to dentists who formerly would not have had avenues for using it.

CAD/CAM systems include a digital impression system, 3D dental design software and a chairside mill that function as a single system.

an image (scan) is taken of the prepared tooth and the surrounding teeth.

This image, called a digital impression, draws the data into a computer.

Proprietary software then creates a replacement part for the missing areas of the tooth, creating a virtual restoration.

This is called reverse engineering. The software sends this virtual data to a milling machine where

the replacement part is carved out of a solid block of ceramic or composite resin.

Stains and glazes are fired to the surfaces of the milled ceramic crown or bridge to correct the otherwise monochromatic appearance of the restoration.

aesthetic drawbacks:They rely mostly on superficial staining to

achieve a more natural appearance, unlike hand-layered porcelain restorations, which possess a deep-set coloration due to the multi-layering.