Chapter 2: Structure of Matter and Principles of Adhesion Flashcards
The state of a material is a function of ________.
Temperature
(The more energy that is put into a material by increasing its temperature, the more difficult it is to keep the atoms or molecules in close proximity to one another.)
INFO ONLY: The study of dental materials of necessity requires a basic knowledge of matter particularly solids if the properties of the material are to be understood.
Change of State of Matter
What happens when heat is applied to atoms or molecules of a solid?
It moves apart or it expands.
(The addition of sufficient heat causes a solid to melt and become liquid. Further addition of heat to a liquid causes it to vaporize and become gas. Increasing the energy within a given material through the application of heat can have a destabilizing effect on both its structure and dimensions.)
Thermal energy required to convert a solid to a vapor.
Heat of Vaporization
What do you call the heat energy RELEASED as solid changes to liquid?
Latent Heat of Fusion
What do you call the heat energy REQUIRED to change solid to liquid?
Fusion temperature
The force required to free atoms or molecules from a liquid and become gas.
Vapor Pressure
What do you call the process of changing solid into gas?
Sublimation
What is the bonding force that holds the atoms together?
Cohesive Force
The force of attraction between the molecules or atoms on two different surfaces as they are brought into contact.
Adhesion
The force of attraction between the molecules or atoms within a given material (not on the surface).
Cohesion
Two Types of Bonds
- Primary Bonds
- Secondary Bonds
This bond is chemical in nature. It holds the atoms of solids together which makes it stronger and stable.
Primary Bonds
This bond is characterized by physical forces. They hold the atoms of liquids together, therefore it is weak and unstable.
Secondary Bonds
This bond is also called chemical bonds.
Primary Bonds
Three Different Types of Primary Bonds
- Ionic Bonds
- Covalent Bonds
- Metallic Bonds
IMC ⛪
A strong and stable bond which results from sharing of electrons between to atoms.
Covalent Bond
This bond is an interaction between a positively and a negatively charged atom.
Ionic Bond
[One atom donates its electron to another and both atoms become stable through the linkage. These bonds are not relied on heavily because they often are unstable in water.
Ex. Sodium (+) and Chloride (-)
Gypsum, GIC, Polycarboxylate cemens (-) and Tooth Structure (+)]
This bond involves many atoms sharing all of their outer (valence) electrons with their neighbors.
Metallic Bond
(The arrangements is very strong and stable, with the shared electrons free to move between and among the billions of atoms that make up the solid, never being tightly held to any specific atom. This accounts for the ability of a metal to conduct electricity and heat readily.
Ex. All metallic dental materials)
This bond involves weaker attractions of charge.
Secondary Bonding
(These interactions keep the molecules or atoms in a liquid from dispersing and becoming gas, but they generally are not strong enough to keep the liquid confined without external container.)
This bond is also responsible for the adhesion between a liquid and a solid or between two solids that are not chemically attached.
Secondary Bonding
Ex. Dental Polymers
Types of Secondary Bonding
- Van der Waals
- Hydrogen Bonding
Types of Hydrogen Bonding
- Intermolecular Hydrogen Bonding
- Intramolecular Hydrogen Bonding
Attraction between atoms, molecules and surfaces caused by correlations in the fluctuating polarizations of nearby particles.
Van der Waals Bonding
It is the attractive interaction of a hydrogen atom with an electronegative atom, like nitrogen, oxygen or fluorine.
Hydrogen Bond
They are weaker than primary bonding because they are intermolecular rather than intramolecular.
Van der Waals
TRUE OR FALSE: The hydrogen must be covalently bonded to another electropositive atom to create the bond.
FALSE
The hydrogen must be covalently bonded to another ELECTRONEGATIVE atom to create the bond. These bonds can occur between molecules (intermolecularly), or within different parts of a single molecule (intramolecularly).
Which bond is stronger that a Van der Waals but weaker than covalent or ionic bonds?
Hydrogen Bond
This type of bond occurs in both inorganic molecules such as water and organic molecules such as DNA.
Hydrogen Bond
Responsible for the high boiling point of water (100’C). This is because of the strong hydrogen bond.
Intermolecular Hydrogen Bonding
Partly responsible for the secondary, tertiary, and quaternary structures of proteins and nucleic acids.
Intramolecular Hydrogen Bonding
A limiting factor that prevents the atoms or molecules from approaching each other too closely.
Interatomic Distance
As two atoms come closer together, the energy does not change a great deal initially, after which the energy increases rapidly since the resultant repulsive force increases rapidly with little change in interatomic distance. The minimal energy is the condition of equilibrium or the equilibrium interatomic distance.
Bonding Energy
The atoms at a temperature above absolute zero are in constant state of vibration, the average amplitude (extent) of which will depend upon the temperature. What kind of energy is this?
Thermal Energy
(The higher the temperature, the greater the amplitude and the greater the kinetic energy or internal energy.)
Continuous increase in temperature = Increase in interatomic space.
What happens when this energy occurs?
Change of State
(Solid-liquid; liquid-gas)
Temperature, Amplitude, Interatomic Spacing, Internal Energy = ?
Thermal Expansion
The force required to move atoms away from their equilibrium spacing.
Melting Temperature
(A high melting point is accompanied by a greater stiffness.)
The characteristic that determines the rate at which heat flows through a material. Heat is conducted from one atom or molecule to the next.
Thermal Conductivity
(The number of free electrons influence thermal conductivity.)
TRUE OR FALSE: Metals have many free electrons.
TRUE
They contain many free electrons and therefore good conductors of heat and electricity.
Any arrangement of atoms in space such that every atom is situated similarly to every other atom. It may be a result of primary or secondary bond.
Space Lattice or Crystal
Molecules are disturbed at random but with regular arrangement.
Amorphous Materials (Non-crystalline structures)
Example of Crystalline Structures
Metals
Examples of Non-Crystalline Structures
Waxes
Glass
Dental Synthetic Resins
The process of spreading through something else.
Diffusion
This happens when atoms change position in pure solids even under equilibrium conditions.
Self-diffusion
TRUE OR FALSE: Diffusion rates for given substance depend primarily on the temperature.
TRUE
The higher the temperature, the greater will be the rate of diffusion.
Diffusion rate depends upon:
Atom Size
Interatomic
Intermolecular Bonding
Lattice Imperfection
The amount of diffusion that takes place across a given unit area thru unit thickness of the substance in one unit time.
Coefficient of Diffusion (D)
TRUE OR FALSE: Most crystalline solids at room temperature = Low Coefficient of Diffusion (D)
TRUE
However, metals at high temperature may change radically by atomic diffusion.
TRUE OR FALSE: In non-crystalline solids, diffusion may occur at a more rapid rate often evident at room temperature or body temperature.
TRUE
Strong attachment of one substance to another can also be accomplished by what type of bonding?
Mechanical Bonding
Example of Mechanical Bonding
- Acid Etching Technique
Can be through:
- Screws
- Bolt
- Undercuts
- Penetration of Adhesive into microscopic or submicroscopic irregularities in the surface of the substrate
The energy at the surface of a solid where outermost atoms are not equally attracted in all directions.
Surface Energy
The attraction that atoms and molecules on the surface of the liquid have for one another.
Surface Tension
The surface atoms or molecules are strongly held together and do not want to be displaced.
High Surface Tension
The extent to which an adhesive will spread out on a surface.
Wetting
The angle formed by the adhesive with the adherend at their interface.
Contact Angle
TRUE OR FALSE: The size of the contact angle is the measurement of the wettability of the solid.
TRUE
Types of Wetting
- Good Wetting
- Poor Wetting
The contact angle is below 90°, with the best spreading to an angle approaching 0°.
Good Wetting
The Contact Angle is obtuse.
Poor Wetting
TRUE OR FALSE: The surface energy and the adhesive qualities of a given solid can be reduced by any surface impurities.
TRUE
The greater the surface energy, the greater will be the capacity for adhesion. An adhesive with a low surface tension and an adherend with a high surface energy provide the best possible situation for good adhesion.
Factors that affect wettability:
- Contamination of the Surface
- Surface Imperfections
- Fluidity of the Adhesive
- Low Surface Energy of Solids
Lack of adhesion between restoration and tooth results to:
- Continuing tooth sensitivity
- Recurrent caries
- Deterioration at the margins of the restoration
This reduces the surface energy of the enamel so that it retains less plaque, reducing enamel solubility to acid and resulting to reduction in dental caries formation.
Fluoride Application
What causes the microleakage or higher incidence of marginal caries around restorations?
Many restorative materials have higher surface energy that the tooth surface margins of restoration has greater tendency to accumulate debris.
