Metals in dentistry Dental material

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

NOBLE METALS & ALLOYS NOBLE METALS ARE ELEMENTS WİTH A GOOD METALLİC SURFACE THAT RETAİN THEİR SURFACE İN DRY AİR. THEY HAVE A GOOD RESİSTANCE TO OXİDATION , TARNİSH AND CORROSION DURİNG HEATİNG. Group A Ruthenium 2310c Rhodium 1966c Palladium 1553c a.w. 100 12/13 g/cm3 Group B Osmium Iridium Platinium Gold a.W 190 19-23 g/cm3 GOLD PLATİNUM PALLADİUM IRIDIUM RHODIUM OSMIUM RUTHENIUM

GOLD Soft, malleable, ductile Yellow. İt must alloyed with silver or palladium Small amounts of impurities have a pronounced effevt on the mechanical properties of gold and its alloys. %0.2 lead = brittle Calcium = improves the mechanical prop., of gold foil. It can be produced as foil by a process known as gold beating. 0.0025 mm

Platinum Bluish white metal Ductile and melleable Has a widw using area in dentistry as ametal for metal reinforced ceramics As posts and pins Adda greatly to the hardness and elastic qualities of gold.

Palladium White metal but darker than platinum Its density little more than half that of platinum and gold Is not used in the pure state in dentistry

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) The higher the gold content in gold alloys, the more burnishing can be accomplished.

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 Base metals used Cobalt Iron Titanium Beryllium *Chromium Gallium *Nickel Carbon Aluminium molybdenum Vanadium

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 Gold solders Silver solders Join bridge units 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. Soldering procedure: the components to be joined are invested in a special soldering investment gypsum in the proper relationship. A flux is added to remove oxides and improve flow of solder alloy. (containing borax). Alloys are heated until red, then solder is added until it melts and flows to cover exposed area.

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: Subperiosteal B: 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

End of part one References: Chapter 8 metals in dentistry Dental materials, clinical applications for dental assistants and dental hygienists