what kinds of bonds are there?
Primary (strongest)
-Ionic
-Covalent (strongest)
-Metallic
Secondary
Primary bonds
Strongest, involve exchange of electrons.
Three types:
Ionic bonds: give e-'s to another atom.
Covalent bonds: when two atoms share e-'s. (strong)
Metallic bonds: shared lattice of positive e-'s.
Secondary bonds
Weak, Often leads to deformation or fracture.
No sharing of electrons
Longevity
How long a dental material can last. Can be...
Permanent restoration, (many years)
Temporary/provisional restoration, (several months-year)
Intermediate restoration. (several years)
Direct Restorative materials
Constructed directly in the mouth.
Indirect Restorative Materials
Made indirectly on a replica of the patient's oral tissues.
Ex: partials, dentures, crown
Catalyst
Responsible for speed at which reaction occurs.
Often liquid component
Base
Main/supporting ingredient for material
Reactions
Can be physical or chemical.
Can also be Chemical set, Light-activated, Dual set.
Chemical reaction
The formation of new primary bonds
Physical reaction
Rearrangement, doesn't change what the chemical is.
Mixing time
Length of time to bring components to a homogenous mix
Working time
time permitted to manipulation material in the mouth
Initial set time
Begins when material no longer can be manipulated in mouth
Final set time
occurs when material has reached its ultimate state
Force
Any push or pull on matter
Stress
Internal force, which resists applied force.
Strain
Change produced within material that occurs as the result of stress.
Biting force
Measure of strength of muscles of mastication during normal chewing.
Normal masticatory forces on the occlusal surface of molar teeth:
Average 90 to 200 pounds per square inch.
Can increase as much as 28,000 pounds per square in on a cusp tip.
Denture wea
Flexural/bending stress
Bending caused by a combination of tension and compression.
Fatigue failure
Fracture resulting from repeated stresses that produce microscopic flaws that grow.
Ultimate strength
Maximum amount of stress a material can withstand without breaking.
Tensile stress
Pulling apart (like when chewing food)
Compressive force
Pushing together (like when you crunch down on something hard)
Shear force
Grinding side to side
Proportional limit
the greatest stress a structure can withstand without permanent deformation.
Resilience
ability of a material to absorb energy without permanent deformation
Toughness
ability of a material to resist fracture
Elasticity
Ability of a material to recover shape completely after deformation from applied force
Ductility
Amount of dimensional change a material can withstand without breaking
Malleability
Ability to be compressed and formed into something else without breaking.
Hardness
Measure of the resistance of a metal to indentation, scratching, or abrasion.
Stiffness
Materials resistance to deformation.
Measured by Young's elastic modulus - Stiffer materials have a higher modulus.
Thermal Change
Change in temperature in oral cavity resulting from hot or cold product.
Major concern:
-Contraction and expansion.
-Need to protect pulp from thermal shock from extreme temperature differences.
Contraction and Expansion
Ideal material --> contracts and expands at rate similar to tooth
Coefficient of Thermal Expansion (CTE)
Measure of expansion of material per degree in temperature change when compared to material's original size.
Microleakage
Leakage of fluid and bacteria caused by microscopic gaps occurring at the interface of the tooth and restoration margins.
Percolation
Movement of fluid within microscopic gap of restoration margin.
Result of differences in expansion and contraction rates of tooth and restoration with temperature changes associated with ingestion of cold or hot fluids/food.
Thermal Conductivity
Rate that heat flows through a material over time.
Galvanism
Phenomenon of electric current being transmitted between two dissimilar metals
Galvanic shock
current resulting in the stimulation of the pulp. Example: metal fork touching a metal restoration
Corrosion
Deterioration or dissolution of the metal to a chemical attack (acid) or electrochemical reaction with other metals due to the moisture and acid present in the oral environment.
Tarnish
Surface
phenomenon. Thin layer of corrosion forming over metals as outermost layer undergoes chemical reaction.
Often appears dull, gray, or black coating over metal
Solubility
Degree to which a substance will dissolve in given amount of another substance
Ideal for oral cavity? Does not dissolve easily
Adhesion
Strength that causes unlike materials to adhere to each other
Without, microleakage can occur and restoration can come out
Affected by Wetting, Viscosity, Surface irregularities, Film thickness
Application Properties
Techniques used in application help determine the properties of that application.
Properties affecting application properties:
-Flow
-Adhesion including wetting and viscosity
-Retention
-Curing
Hue
Dominant color of that wavelength
Chroma/saturation
Intensity or strength of a color
Value
How light or dark a color is
Wetting
Ability to flow over a surface.
Consideration in wetting: hydrophilic or hydrophobic material?
Viscosity
Material's ability to flow.
Retention
Ability to maintain position without displacement under stress.
May be:
1) Mechanical retention -> places undercuts in preparation
2) Chemical retention -> works through adhesion and bonding
3) Combo
Opaque
Not see through, all the light is absorbed.
White on a radiograph
Transparent
See through, Light passes through.
Black on a radiograph.
Metamerism
Colors look different under different light sources.
Standardized measure of color needed.
Detection of Restorative Materials
Identification
Tactile evaluation
Visual evaluation
Radiographic evaluation
Translucent
Partially see-through.
Light is only partially absorbed.
Between opaque and transparent