Alloys and metals

Palladium hardens the alloy, confers tarnish-resistance to Ag-Au alloys, whitens gold, decreases greening of silver and red color of copper, and lowers the coefficient of thermal expansion.

Legacy cements include zinc polycarboxylate, zinc phosphate, and conventional glass ionomer cement (GIC).

Highest gold content is 88%, lowest is 66%.

Sandblast the area (e.g., with ProphyJet), use a metal primer, apply a layer of resin cement followed by a layer of composite, and then go through the normal workflow when the patient returns.

35-65% cobalt, 28-30% chromium, and 3-6% molybdenum

200-340 MPa

0.3 mm

The modulus of elasticity of titanium is higher than gold but lower than chromium.

Increased hardness but low sag resistance, limited to crowns on 3-unit FPD

Molybdenum acts as a grain-refiner, increases corrosion resistance and strength, and decreases the thermal expansion coefficient, which is good for compatibility with porcelains.

Copper (Cu)

Mechanical bonding and chemical bonding

To raise thermal expansion to be compatible with the metal substructure

Silicon and manganese improve castability by increasing the fluidity of the molten alloy and act as deoxidizers.

Contemporary cements include resin, RMGIC (resin-modified glass ionomer cement), self-adhesive composite resins, and compomers.

They form an oxide layer that acts as an adherend for porcelain bonding.

Better adaptation of the crown.

18%

Ni-Cr alloys are mainly used for small castings such as crowns and fixed partial dentures (FPDs) due to their ease of finishing and polishing compared to Co-Cr.

High rigidity, high sag resistance, and a coefficient of thermal expansion that matches porcelain

Silver can pick up oxygen when molten, leading to pitting and surface roughening, cause green discoloration of porcelain, and lower tarnish resistance.

Copper is important for heat treatment.

Post and core, crowns, bridges, and partial denture frameworks.

Any water-based cements that undergo an acid-base setting reaction, as well as resin cements.

Carbon forms discontinuous carbides at the grain boundaries, increasing hardness, strength, and yield strength, but decreases ductility.

Gold is expensive due to its tarnish and corrosion resistance, ductility, but it has low elastic modulus, low sag resistance, and low strength and hardness.

Au-Cu (Gold-Copper) alloy

Cobalt increases strength, hardness, and modulus of elasticity.

Because of their excellent biocompatibility, corrosion resistance, and mechanical properties.

Titanium can be added up to 5% in Co-Cr-Mo-Ti alloys.

CP-Ti can undergo alpha, near-alpha, alpha-beta, or beta phases.

If the chromium content exceeds 30%, it causes casting difficulties and forms a more brittle sigma phase.

Aluminum forms Ni3Al, which increases tensile and yield strength.

Segregation of aluminum during casting that corrodes during service and the use of alkaline denture cleaners.

Their high hardness can be problematic as it may wear down the natural tooth in the opposing arch.

Chromium is essential for corrosion resistance as it forms a passive Cr2O3 layer which is thin, uniform, non-porous, and adherent.

Zinc phosphate is considered a good choice because it is cheap, easy to use, and suitable for crowns that are already opaque.

Copper, silver, iron, and tin.

Casting titanium is problematic due to internal porosity within the clasp assembly, which can lead to fractures.

All-ceramic crowns have better aesthetic qualities, can be supragingival, withstand corrosion better, have greater biocompatibility, bond to tooth structure for extra strengthening, and provide better thermal and electrical insulation.

Titanium forms a protective oxide layer (~10 nm) which promotes plaque adherence to frameworks more than other base metal frameworks.

Adding different stabilizers allows temperature manipulation to achieve desirable properties in titanium.

1. Discuss the bonding strategies of three different materials to enamel and dentine, including treatment for the tooth side and restoration side and the type of cement used. 2. Compare the mechanical integrity of different types of CAD/CAM materials and their reinforcement strategies, such as zirconia.

The opacifier layer, often containing ZnO and other oxides, is crucial for bonding PFM crowns.

To ensure that the porcelain is placed under compression if it shrinks slightly less than the metal

Beryllium lowers the fusion temperature of the alloy by 100°C, improves fluidity and castability, refines grain size, increases strength, and promotes the formation of a stable metal oxide for porcelain bonding.

Iridium acts as a grain refiner, adding strength to the alloy.

Nickel provides strength, hardness, modulus of elasticity, and ductility but to a lesser extent than cobalt, and it can cause nickel allergies.

They have a higher percentage of elongation, making clasps easily adjustable but requiring careful denture design to achieve rigidity.

By ceramic locking on cooling due to the difference in coefficients of thermal expansion

Wettable, soluble in porcelain, and should not react with or discolour the porcelain

Silver discolours ceramics and has a high coefficient of thermal expansion

Nitrogen from ambient air improves the quality of casting.

By carat (24 parts by weight) and fineness (pieces per thousand, e.g., 999.9).

Chemically using hydrofluoric acid (HF) or mechanically using grit-blasting or rotary instruments.

Fe, Indium, Sn

Noble metals, Au-Pt-Pd, Au-Pd-Ag, Pd-Ag

Metal collars are more conservative but unaesthetic, suitable only posteriorly and subgingivally, while ceramic collars offer a balanced compromise of aesthetics and conservation, ideally equigingival.

Titanium is the most biocompatible metal used in dental alloys.

Cheaper, high elastic modulus, and less saggy