Lecture 11 & 12 - Metals in Dentistry (Slides)

8/3/2019 Lecture 11 & 12 - Metals in Dentistry (Slides)

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Metals in dentistry

Dental material


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General information

Alloy: a mixture of two or more metals

Pure metals are rarely used in dentistry because

they are weaker than they are when mixed withother metals.


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All metal casting

Classification of cast

restorations: Intra-coronal (e.g. inlay)

Extra-coronal (e.g.crown)

Cast metal alloys canbe used for bridges,

partial dentures


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Cast metal restorations


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Classification of dental casting alloy

(ADA) High noble alloys: What does noble mean?

Gold-platinum Does not corrode readily

Gold-palladium

Gold-copper-silver High noble: at least 60% noble

Noble alloys: (Au, Pd, Pt). 40% of which is gold.

Silver-gold-copper The remaining 40% is base metal

Palladium-copper (precious metals) Silver-palladium Noble: at least 25% noble (no gold

Base metal alloys requirements). 75% base metal

Ni-based (semiprecious)

Co-based

Ti-based


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Gold alloys (Au)

Most corrosion resistant

Pure gold is 24 karat,100%, or 1000 fine(percentage * 10)

Gold alloys classified: Hardness (resistance to

penetration)

Malleability (ability to beshaped by tapping)

Ductility (ability to beelongated)


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Platinum is not used much because:

Too expensive

High melting point

Difficult to mix with gold

Palladium is used more widely because: Good corrosion resistance

Increases hardness of alloy

Silver is precious but not noble because itcorrodes.


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Base metal alloys

< 25% noble metal

Primary base metals (non-precious): Copper

Silver

Nickel Tin

Zinc: added to decrease oxidation

Titanium

Stiffer than gold alloys, higher stress resistance

Added to gold alloy to increase hardness


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Base metal alloys

Drawbacks:

Difficult to finish and cut More equipment to manufacture

Higher casting temperature

Biocompatibility issues


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Crystal formation

Alloys start to form crystals as they cool down

after being poured into molds. Small crystals produce better qualities than

larger ones

Some alloys such as gold maybe reheated(annealing) to improve properties

Reheating base metal alloys is notrecommended.


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Porcelain bonded alloys

High noble

Noble Base metal

Composition is slightly modified to make them more

compatible with porcelain. How? Blended and mixed to withstand high temperature when

porcelain is fired (850-1350 C)

Small amounts of indium and tin are added to form oxideson metal surface to which porcelain is bonded

Silver and copper is not used to avoid green staining of

porcelain


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Porcelain fused to metal


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Porcelain bonding alloy

When PFM restorations are constructed,

layers of porcelain are fired in an oven on themetal base to cover the metals dark color

Body and incisal porcelain are added inlayers to simulate enamel and dentine colorsand translucency.

Porcelain and metal should have compatiblerates of thermal expansion or porcelain willcrack.


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Removable prosthetic casting alloys

Base metals used

Cobalt Iron

Titanium Beryllium

*Chromium Gallium

*Nickel Carbon

Aluminium molybdenum

Vanadium


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Continue,

Components areattached to prosthesis(precision and nonprecision attachments,bars) made from metalalloys :

High noble

Noble

Base metal


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Biocompatibility

Noble metals are more biocompatible than

base metals because they corrode less(corrosion products can cause allergy):

Nickel is associated with allergy (9-12% of

population), especially in women Seen on free gingival tissue in contact with metal

Mostly more sever with fixed prosthesis

Skin response may occur


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Continue,

Beryllium, added to Ni-Cr to reduce fusion

temperature and create smaller crystals: Can also cause allergy.

Inhalation can cause lung disease called

berylliosis


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SoldersAlloys that are used to join metals together or repair

cast restorations

Gold solders Silver solders

Join bridge units Used in ortho., paedo.

Add contacts Solder fixed space maintainer

components

Correct marginal deficiencies

Close holes from occlusaladjustment

Solder wire components toremovable ortho. appliances


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Solders

The solder alloy shouldhave a lower melting

temperature than the castrestoration.

For gold solders, the higher

the gold content the lowerthe melting range.

For silver solders, tin isadded to lower melting

temperature and improveflow.

Solder joint


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Wrought metal alloys

Are alloys that have been mechanically

changed into another form (can be shaped asa flat plate, or wire).

The resulting alloy, is harder and has a

greater yield strength (point at which a forceproduces permanent deformation).

Resistance to deformity can be modified byheating, annealing.


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Wire

Is a wrought metal which can be soft and easilyshaped or may resist bending as does as spring.

Used for clasps in partial dentures Stainless steel (iron, carbon and traces of Mn, Cr, Ni to

resist tarnish and rust)

Platinum-gold-palladium (PGP) Arch wires and ligature used in orthodontic

appliances

Arch bars and ligature wires used in oral surgery forfracture stabilization


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Wrought wires


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Endodontic files and reamers

Example of wrought metal alloy which have

been twisted to produce cutting edges Stainless steel

Nickel-titanium (more flexible)

Reamers are similar to files but with fewertwists and cut faster


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Endodontic files


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Metals used in orthodontics

Wires:

composed of base meta, stainless steel, cobalt-chrome-nickel, titanium, titanium-nickel.

Able to resist deformity. This resistance creates

memory in the wire, so it tries to reassume itsoriginal shape. That enables the wire to moveteeth.

Wires have different diameters (gauge), thethicker the wire the smaller the gauge


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Lingual retainer:


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Lingual retainer:

Used to maintain the position of teeth after orthodontic

treatment Adapted to the lingual surface of anterior teeth and bonded

with composite.

I l i l


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Implant materials

Used as anchors for prosthetic replacement

of missing teeth One or more single units as crowns or bridges

Support for dentures

Three main types:

Subperiosteal

Transosteal Endosseous


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S b i l


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Subperiosteal

Placed under periosteum(fibrous covering of bone)

and rests on the bone.

Placed in 3 stages:

Incision and flap reflection

Impression and closure ofwound & Framework castwith projection on which

prosthesis is attached 3rd incision and attachment

of framework

T l ( dib l l )


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Transosteal (mandibular staple)

In cases of severresorption of mandible

Needs intraoral andextraoral incisions

Seldom used due to itsinvasive nature

Consists of a beam

attached to metal rods

E d


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Endosseous

Most popular

Placed in bone May include surface

irregularities, screw like

threads, or a hollowcore with or without

holes on the side

These designs help tointegrate the implant

with bone


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A: Subperiosteal

B: Transosteal

C: Endosseous

Contin e


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Continue,

These implants are made of titanium ortitanium alloy, used for its biocompatibility:

Pure titanium is not as rigid as the alloy These implants are retained by intimate

contact with bone (osseointegration)

Some implants are coated with Calciumphosphate (hydroxyapatite) or plasma

proteins to improve osseointegration

Placement and restoration


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Placement and restoration

Incision and bone exposure

A hole is drilled that is slightly smaller thanimplant cylinder size so when implant isplaced it will have a frictional fit with bone.

Excessive heat should be avoided

Permanent restoration is attached to implant

core with a screw made of gold alloy


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Maintenance


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Maintenance

Maintenance


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Maintenance

Home care:

Disclosing agents: to visualize plaque Brushes:

Brushing should b done in different angels

Sulcular brushing

Toothpaste should b non-abrasive


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Flosses:

For plaque removal

Floss threaders are used to remove plaqueunderneath prosthesis.

Wooden sticks for plaque removal

Antibacterial agents:

Chlorhexidine gluconate used for a week (30seconds) after the second surgical stage whenimplant is uncovered or if inflammation occurs

Phenolic compounds

Hygiene visit


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Hygiene visit

Patient visit to dentist at 3-4 months intervals for:

Routine examination

Questions specific to implants: Soreness

Bleeding

Looseness

Radiographs to check bone level

Continue


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Continue,

Examine soft tissue for edema, erythema, bleeding

If scaling needs to be done, and titanium is exposed,plastic or gold and Teflon coated scalers can be used

Abrasive paste, steel curettes, ultrasonic scalers arenot indicated

Regular steel scalers can be used against a porcelainsurface

Implant failure


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Implant failure

Early failure is caused by failure of bone to

integrate with implant due to: Poor surgical technique

Generation of excess heat

Implant infection

Poor quality of bone

Placing load on implant too soon

Failure occurring after initial integration is dueto bacterial infection extending to bone

Endodontic posts


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Endodontic posts

Posts are metal or nonmetal rods placed inroot canal

The purpose of a post is to retain the corebuild up over which the crown is placed

Classification:

Active, engages canal surface with threads Passive post, cemented into the canal space

Classification by shape: Parallel

Tapered

Classification by material:


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Classification by material:

Metal Nonmetal

Classification by manufacturing method:

Custom made: made from a wax or resin patternmade directly on tooth or indirectly in lab. Usinglot wax technique. Core attached

Preformed: They rely for retention on shape, diameter, length, and

cementation.

Come in kits with drills specific to size of post

Core not attached, need to be made from amalgam,composite, hybrid GIC


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End of part one


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End of part one

References:

Chapter 8 metals in dentistry Dental materials, clinical applications for

dental assistants and dental hygienists

Lecture 11 & 12 - Metals in Dentistry (Slides)

Documents

Transcript of Lecture 11 & 12 - Metals in Dentistry (Slides)