dental 2 Flashcards
3 physical properties of dental material
mechanical
electrical
thermal
what are the different mechanical properties?
strength
hardness
elasticity
plasticity
what are the different mechanical strengths
tensile
compressive
shear
what are the test for hardness
brinell vicker knoop rockwell share A
what does mechanical elasticity test
elastic modules
resiliance
what does mechanical placticity test for
ductility
percent elongation
yield strenth
what do the electrical and electrochemical physical properties mesure
electrode potential
electrical resistivity
what do thermal propoties mesure
thermal expansion heat flow ( thermal conductivity and diffusivity )
atom
smallest electroneutral part of chemical element which preserves its chemical properties
mass number
atomic number
mass- neutrons
atomic- electrons
simple substance
atoms of 1 in the same chemical element
what are the different states of material
gas
liquid
solid( crystalline and amorphous )
7 different crystal lattice
cubic, rhombic, monoclinic, hexagonal, tetragonal, triclinic and rhombohedral
what is allotropy
ability to change crystal lattice depending on the temp e.g carbon- graphine and dimond
what is amorphous
random molecular formation as fluids with high dentisty and vicocity
thermodynaically unstable
when heated it softens lowering the viscosity
e.g of am amorphoges and lattice
wax- 52 degrees amorphous material,
36 degrees -crystal
what is the force that holds atoms together
cohesive forces
what is cohesion
force/ molecular attreaction between molecules or atoms of the same substance
classification of interatomic bonds
primary and secondary
primary interatomic bonds
ionic
covalent
metalic
secondary interatomic bonds
hydrogen
van der waals forces
what is an ionic bond
the mutal attraction between and positive and negativly charged element
e.g of ionic bonding
sodium chloride (na+ cl-)
Na contains one valence e- in the outer shell
and chlorine has seven electrons in the outer shell .
transfer of Na valence e- to cl results in a dtable compound
where can you find ioinc bonding in dentistry
some gypsum and phosphate based cement in their crystalline phases
what is a covalent bond
are the results of electron sharing between 2 valence electrons by adgacent atoms.
e.g of covalent bonding
hydrogen molecule (H2) single valence elctron is shared with the other combining atom, causeing the valence shells to become stable
what are metallic bonds
characterized by electron sharing and formation of a “gas” or “cloud” of electrons that bonds the atoms (which become positively charged because of the electron gas formation) together in the lattice
what are interatomic secondary bonds
dont share electrons, instead the charge variation among molecules induce polar forces that attract the molecule
water in hydrogen bonding
2 hydrogen atoms bonded to 1 oxgen therfore
the p+ of the hydrogens pointing away from the O arnt shilded by the electrons making the poton side positivly charged
on the opposite side the elctrons that fill the outer orbit of oxygen provide a negative charge. a permanent dipole exits represnting asymmetric molecule
what happens when multiple H2O molcules mix
positive hydrogen is attrected to the negative oxygen part of its neighboring molecule producing hydrogen bridges
what are Van der Waals forces
form the basis of all dipole attractions
in symmetric molecules e.g inert gas, the electron feild constantly fluctuates so that it becomes momentarily positive or negative. the fluctuating dipole attracts similar dipoles.
what is water sorption of a material
represent the amount of water aDsorbed on the surface and aBsorbed into the body of the material during fabrication.
e.g of water sorption
of denture arcylic- is mesured gravemetrically in μg/mm3 after 7 days in H2O
What is crystalline
having molecules arranged in a regular 3 dimensional pattern
e.g metal
charecteristics of crystalline
microscopic range order periodic crystal structure have definite shape and volume small no of defects in the structure sharp and well-defined melting points
what is amorphous
Atoms in crystalline solids exhibit an ordered
arrangement, whereas atoms in amorphous solids lack this long-range periodicity.
charecteristics of amorphous
lots of structre defects
no set shape
mechanical hardness
isotrope property
