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• Dental hygienists need knowledge of dental materials

Agencies Responsible for Standards

• ADA (American Dental Association)
• FDA (Food and Drug Administration)
  • Class I
  • Class II
  • Class III
• International Organization for Standardization

Dental Materials Classifications

• Preventative/therapeutic materials
• Restorative materials (indirect and direct)
  • Permanent
  • Temporary (provisional)
  • Intermediate
• Auxiliary materials
• Examples:
  • Preventative: sealants, fluoride
  • Restorative: fillings, crowns
  • Auxiliary: wax, alginate, stone

Biocompatibility

• Dental materials must have biocompatibility
• Reactions to avoid:
  • Post-op sensitivity
  • Hypersensitivity
  • Irritation
  • Toxicity
• Adverse response refers to these reactions

Force, Stress, & Strain

• Force (aka load) is important in dental materials
  • Tensile Force
  • Compressive Force
  • Shearing Force
• Torsion (torque) is a twisting force that includes both compressive and tensile components
• Flexure is a bending force that includes compressive, tensile, and shearing components

Properties of Dental Materials

• Stress results to resist force, measured in psi or Mpa
• Strain is the amount of change force produces in an object
• Resilience is the energy needed to permanently deform a material
• Fracture toughness is energy needed to fracture material
• Ultimate strength is the point of fracture
• Fatigue Failure is resulting fracture from repeated stress causing small flaws over time
• Creep is small changes in shape from continuous compressive force
• Stress relaxation is like creep, a slow decrease in force over time
• Stress concentration is stress focused around defects

Moisture and Acid Considerations

• Solubility is desirable when low
• Water sorption is undesirable
• Corrosion is undesirable

Galvanism

• Galvanism is when electrical current transmits via electrolyte solution between two dissimilar metals.
• Galvanic shock stimulates the tooth pulp
• Metals conduct electricity well, while polymers/ceramics conduct poorly

Temperature Impacts

• Dimensional change occurs, expanding with heat and contracting with cold
• Coefficient of thermal expansion (CTE) measures the change in volume/length in relation to temperature
• Percolation is repeated shrinking/expanding, resulting in oral fluids entering gaps
• Thermal conductivity is the rate of heat flow through material over time
• Exothermic reaction is a chemical reaction that produces heat

Retention

• Retention is the ability to maintain position without displacement under stress
• Retention is achieved through mechanical, chemical adhesion, or bonding
• Bonding happens through acid etching the rough surface, where the bonding material locks into place

Factors Affecting Bond Strength

• Wetting is the degree a liquid adhesive can spread over a surface
• Wettability is determined by contact angle between liquid and surface
  • Low contact angle is better wetting, whereas high contact angle is poor wetting
• Viscosity is resistance of liquid to flow
  • Viscosity can affect wetting and film thickness
  • High viscosity equals poor flow, while low viscosity equals good flow
• Film thickness is the minimal thickness of material
• Surface characteristics, like cleanness, moisture, texture, etc., also impact bond strength

Microleakage

• Microleakage can affect the longevity of restorations
• Fluids/microbes leak into the interface, causing recurrent caries, stain, and sensitivity
• The interface is the space between the tooth and restoration

Esthetics & Color

• Hue is the dominant color
• Chroma is the intensity of color
• Value is the light vs. dark
• Transparent items allow light to go through
• Opaque items do not allow light to go through

Primary Bonds

• Primary bonds are strongest and involve sharing or transferring electrons
  • Covalent bonds: Two nonmetal atoms sharing outer shell electrons
  • Ionic bonds: Electron given up by one atom and accepted by another
  • Metallic bonds: Electrons shared by all atoms in the material (sea of electrons)

Secondary Bonds

• Secondary Bonds are also known as van der Waals forces
• Secondary Bonds do not share or transfer electrons
• Secondary Bonds are weaker than primary bonds
• Forces of attraction in alike molecules
• Created by dipoles
• Dipole- electrons unequally shared between atoms causing (+) and (-) charged ends
• Ex: Hydrogen bonds (dipole-dipole forces), permanent dipoles, temporary dipoles

States of Matter

• Gas has the weakest attraction
• Liquid has a stronger attraction than gas, but is weaker than solid
• Solid has the strongest attraction
  • Crystalline solids are ordered, in a specific arrangement (3D cube)
  • Amorphous solids have irregular patterns (dry ice, polymers)

Physical Properties & Related Terms

• Melting/boiling point aids in identifying material; some do not melt or boil, but decompose
• Vapor pressure is a measure of liquid's tendency to evaporate
  • A high vapor pressure evaporates faster at room temperature
• Density is the amount/mass in a given volume
• Viscosity is the resistance of liquid to flow
• Thermal conductivity is the rate of heat flow through material over time
• Thermal expansion measures the change in volume/length in relation to temperature (CTE)
• Color

Mechanical Properties & Related Terms

• Hardness is resistance of a solid to wear and abrasion, measured by severity of indentation
• Stress is an object resisting force
• Strain is the amount of change force produces in an object
• Fatigue is repeated stresses over time causing failure
• Ultimate strength is the amount of stress on material at time of break
• Toughness is the ability of material to absorb energy without fracture
• Ductility is pulling or stretching under tensile stress
• Malleability is the ability to handle compressive forces
• Durability is the ability of material to withstand damage due to pressure or wear
• Abrasion resistance the ability to withstand friction, scraping, or

More Mechanical Properties & Related Terms

• Elasticity is non-permanent deformation and material recovers completely
• Elastic limit is when the material does not return to original shape
• Plastic deformation is permanent deformation
• Young's modulus measures the resistance of a material to being deformed
• Stiffness is lack of elasticity
• Resilience is the amount of energy a material can absorb without permanent deformation
• Toughness is the ability of material to absorb energy without fracture

Mixing Times

• Mixing time is the time to achieve homogeneous mix
• Working time is the mixing to hard stage, so it is important to move fast
• Initial set time is the end of working time
• Final set time is the conclusion of reaction from mixing, permanent state of material results

Dental Materials

• Metals are have metallic bonds
  • Metals have high thermal conductivity, are ductile and opaque with luster
  • Ex: amalgam, implants, crowns, bridges
• Ceramics have ionic bonds
  • Ceramics are strong yet brittle, insulators with high melting point and low thermal cond
  • Chemical rx break old bonds/form new, sometimes transparent
  • Ex: crowns, veneers
• Polymers possess long chains of repeating covalent bonds
  • Polymers exhibit great strength in one direction, cross links in chains = stiff, strong material
  • Ex: denture base + teeth, temp. crown

Other Materials Used

• Composites are made of 2+ different materials (polymer + ceramic fiberglass)
  • Materials act as a team
  • A property lacking in one is enhanced by the other(s), lightweight and strong
• Colloids are not true solutions, but a mix of gases, liquids, and solids
  • One material is suspended in another
• Emulsions consist of 2 liquids that do not blend (think oil/water)

Detecting Restorations

• Includes using:
  • Tactile sense
  • Light
  • Drying
  • Magnification
  • Radiographs