chapter 2: materials science and dentistry

gases

the weakest bond type between molecules, no molecular organization → fills shape of the container they fill

liquids

weaker bond than solids, stronger than gas and maintain a fixed volume but take the shape of their container

short-range order: consistent spatial relationship among atoms or molecules 5 to 10 neighbors apart (lacks long-range order)

solids

strong attraction between atoms and molecules (help maintain shape and resist external forces)

crystalline or amorphous

crystalline solids vs amorphous solids

crystalline solids have long range order (consistent spatial relationship of atoms or molecules repeated millions of times) and short range order (attraction between atoms and molecules 5-10 atoms/molecules apart) (small neighborhoods)

amorphous solids only have short range order- as strong as crystalline but may be irregular or disorganized (ex: glass or dental mirror)

positive charges attract _____ and vice versa

positive repels _____

negative repels _____

negative

positive

negative

primary bonds

strong bonds that involve the transfer or sharing of electrons between atoms(ex: ionic, covalent, metallic)

valence electrons

electrons in the outer shell of atoms and are involved in chem reactions and atomic bonding

ionic bonds

primary bond where an electron is given up by one atom and retained by another

force between ions falls rapidly with increasing distance

covalent bonds

primary bond where two atoms share a pair of electrons to achieve stability- the orbital surrounds both atoms together

results in molecules

metallic bonds

primary bond where electrons are shared by all the atoms that make up that object and allow for electrical conductivity and malleability, as well as a high density of atoms.

“positive cores in a cloud of negative mobile valence electrons”

secondary bonds

weak attractions that form when electrons are not shared evenly (not real chemical bonds like ionic or covalent) → partial charges

permanent and fluctuating dipoles

permanent dipole

occurs in a molecule where there is a permanent uneven distribution of electron density due to differences in electronegativity between atoms.

positive and negative ends

hydrogen bonds

special permanent dipole

hydrogen has only one electron- when it is taken away the nucleus is left partially unshielded but the bonds created with other atoms are stronger than other secondary bonds

fluctuating dipole

occurs when the constantly moving electrons in a symmetrical atom or molecule become unevenly distributed, creating temporary positive and negative regions.

four categories of materials

metals

ceramics

polymers

composites

(types of atoms and bonds determine the strength of a material)

metals

metallic bonds, some have covalent or ionic bonding

enables the atoms of metals to slide past one another without causing breakage

ex: ortho wires, clasps on partial dentures, gold foil restorations that are packed into place

ceramics

ionic bonding

makes materials strong yet brittle

strength of bonds necessitates high temp to process ceramic materials

varying shades of white, translucent property

polymers or plastics

long chain covalent bonding of the backbone with different types of bonds coming off of the backbone

allows atoms to slide past one another (more flexible)

can be heated causing the material to be more flexible/moldable (whitening/fluoride trays/mouth guard)

composites

usually a mix of polymer and a ceramic

2 or more materials (called phases) are put together

end result= final product is better and stronger than either of the individual phases were to begin with

colloids

two phase material, mixture of solid, liquid, and gas

one phase does not overpower another (suspension- one material suspended in another)

emulsion- a type of colloid made of 2 liquids that do not blend together

can transform from a liquid to a gel (hydrocolloid impression material does this)