Metals in Dentistry / orthodontic courses by Indian dental academy

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Metals in dentistry

Dental material

INDIAN DENTAL ACADEMY

Leader in continuing dental education www.indiandentalacademy.com


Lectures included in midterm exam 1. Amalgam 2. Composites 3. Glass ionomer cements 4. Adhesive systems and bonding in dentistry 5. Dental cements


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 with other metals.


All metal casting

Classification of cast restorations: Intra-coronal (e.g. inlay) Extra-coronal (e.g. crown)

Cast metal alloys can be used for bridges, partial dentures


Cast metal restorations


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


Gold alloys (Au)

Most corrosion resistant Pure gold is 24 karat, 100%, or 1000 fine

(percentage * 10) Pure gold is too soft, so, gold alloys were mostly

used Gold alloys classified:

Hardness (resistance to penetration) Malleability (ability to be shaped by tapping) Ductility (ability to be elongated)


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 it corrodes.


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


Base metal alloys

Drawbacks: Difficult to finish and cut More equipment to manufacture Higher casting temperature Biocompatibility issues


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 not recommended.


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 oxides

on metal surface to which porcelain is bonded Silver and copper is not used to avoid green staining of

porcelain


Porcelain bonding alloy

When PFM restorations are constructed, layers of porcelain are fired in an oven on the metal base to cover the metals’ dark color

Body and incisal porcelain are added in layers to simulate enamel and dentine colors and translucency.

Porcelain and metal should have compatible rates of thermal expansion or porcelain will crack.


Removable prosthetic casting alloys

Cobalt Iron

Titanium Beryllium

*Chromium Gallium

*Nickel Carbon

Aluminium molybdenum

Vanadium

Base metals used


Continue,

Components are attached to prosthesis (precision and non precision attachments, bars) made from metal alloys : High noble Noble Base metal


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


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


Solders Alloys 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 occlusal adjustment

Solder wire components to removable ortho. appliances


Solders

The solder alloy should have a lower melting temperature than the cast restoration.

For gold solders, the higher the gold content the lower the melting range.

For silver solders, tin is added to lower melting temperature and improve flow. Silver solders produce stronger joints and need lower heat to melt so they do not weaken the wire adjacent to solder joint.


Welding

Process of fusing two or more metal parts through the application of heat, pressure, or both, with or without a filler metal, to produce a localized union across an interface between the parts.

The welded point is susceptible to corrosion In soldering no fusion occurs, the gap

between the two joint parts is filled with molten metal.


Wrought metal alloys

Are alloys that have been mechanically changed into another form (can be shaped as a flat plate, or wire).

The resulting alloy, is harder and has a greater yield strength (point at which a force produces permanent deformation).

Resistance to deformity can be modified by heating, annealing.


Wire Is a wrought metal which can be soft and easily

shaped 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 for

fracture stabilization


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 fewer twists and cut faster


Endodontic files


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 its original shape. That enables the wire to move teeth.

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


Brackets and bands Cemented on teeth with bonding resin Retain the arch wire that has been shaped by the

orthodontists to guide the teeth into new position. The wire is held to brackets and bands by ligature wire or elastics

Made from stainless steel, the bracket has a slot into which the wire fits and 4 wings to hold the ligature or elastics



Lingual retainer: Used to maintain the position of teeth after orthodontic

treatment Adapted to the lingual surface of anterior teeth and bonded

with composite.


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



A: SubperiostealB: Transosteal C: Endosseous


Continue, These implants are made of titanium or

titanium 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 Calcium phosphate (hydroxyapatite) or plasma proteins to improve osseointegration


Placement and restoration

Incision and bone exposure A hole is drilled that is slightly smaller than

implant cylinder size so when implant is placed 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



Maintenance


Endodontic posts Posts are metal or nonmetal rods placed in

root canal The purpose of a post is to retain the core

build 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: Metal Nonmetal

Classification by manufacturing method: Custom made: made from a wax or resin pattern

made directly on tooth or indirectly in lab. Using lot 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



Lectures included in the midterm exam next Thursday Amalgam Composite Glass ionomer cements Adhesives in dentistry Dental cements


References: Chapter 8 metals in dentistry Dental materials, clinical applications for

dental assistants and dental hygienists

End of part one

Thank you

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Metals in Dentistry / orthodontic courses by Indian dental academy