Ch. 5, 36, 32 Flashcards
polymers
materials made of large, long molecules formed by chemically reacting molecular building blocks called monomers; common polymers or plastics include polyethylene, Plexiglas
polymerization
links monomers together to produce polymer
thermoplastic
can be heated and molded to shaped after polymerization reaction
thermoset polymers
polymers with a cross-linked rather than a linear structure tend not to melt, rather they decompose, can’t be heated or molded, tend to be stronger, most dental resins are cross-linked and are therefore thermoset
free radicals
the polymerization reaction of acrylic resins is called free radical or addition polymerization; a free radial or unpaired electron is involved in reaction and one monomer is added at a time to polymer chain as reaction proceeds
initiation
first step in addition polymerization; first formation of free radicals then the free radical reacts with a monomer molecule to start a growing chain
propagation
second step in addition polymerization, which is the growth or lengthening of the chain; involves adding the 2nd, 3rd, 4th, and later monomers to the growing chain until that chain is hundreds/thousands of monomers long
termination
two free radicals at the ends of two growing chains may react; if they do, they will form a carbon-carbon bond; at this point, no free radicals are left to continue growth of the chain
heat activated acrylic resins
typically use benzoyl peroxide as the initiator, heat is the activator, in hot water bath; most complete and partial dentures use heat-activated acrylic resins for denture base
chemically activated
use BPO as initiator, tertiary amines as activator; used to make temp crows, ortho retainers
light activated
use several activator and initiator chemicals; the activator absorbs light and then reacts with the initiator; supplied as single paste
dual-cure
have both chemical and light-activated capabilities
working time
can occur very rapidly, an inhibitor, typically hydroquinone reacts with the first free radicals that are produced during the initiation process, this reaction competes with polymerization process and wins
percolation
repeated expansion and contraction can open and close gaps at the margin of a restoration, can result in leakage and recurrent caries
macrofilled composite
first type of dental composite, large size of filler particles in macrofilled composites results in a restoration that feels rough to explorer and can appear rough to the eye
microfilled composite
particle size far smaller, will polish smooth and lustrous
hybrid composite
are strong and polish well
flowable composites
flow into cavity prep b/c of lower viscosity, used as initial increment then covered with a hybrid material
condensable composites
have a filler particle feature that inhibits the filler particles from sliding by one another
finishing composite
contours are corrected while margins and irregularities are smoothed
polishing composite
produces smooth lustrous finish
evaluating restoration
it is useful to dry tooth, then visually inspect the contours to detect anatomical form, chips, voids, strains, or defects, check occlusion, look at margins, check with dental floss
scalpel blade
most effective instrument to remove interproximal overhangs and flash
flame-shaped finishing burs
can be used to smooth contours and margins and remove overhangs
finishing disks
useful when the restoration extends onto the facial or lingual surface thereby allowing access to the area
finishing strips
the center contains no abrasives, position the strip both on tooth structure and restoration and gently pull strip over surface
egg or football shaped finishing burs
can be used to complete all occlusal finishing
finishing points and cups
used to smooth the surface and grooves
flame shape finishing burs
can be used to contour surfaces, smooth margins, and remove flash
debonding
complete removal of the composite and cement material from enamel surfaces after appliances are removed
debonding procedure
identify resin, remove resin bulk, final finishing
tips for clinician during debonding
during use of bur, apply air frequently to dry tooth and examine surface; make sure the pt moved his or her tongue over each tooth surface slowly to detect any residual resin, emphasize importance of office and home fluoride to remineralize enamel after debonding; begin the stroke with the bur at the cervical portion of the resin and move toward the incisal or occlusal surface to avoid accidental trauma to gingiva
