Dental Materials Midterm
Shear
(slip) stress occurs when parts of an object slide by one another
Resilience
- the ability to absorb energy and not become deformed -measured as the area under the stress-strain curve up to the yield point
Non aqueous elastomeric impression materials
-polysulfides - condensation silicones -polyethers -additional silicones
Aqueous elastomeric impression material
Alginate (irreversible hydrocolloid) Agar (reversible hydrocolloid)
Amalgam
An alloy of mercury
Composite
An esthetic restorative material composed of a bonding agent and tooth-colored filler particles
[(CaSO4)2 1/2H2O]
Gypsum rock -calcium sulfate dihydrate
Elastomeric
Having both viscosity and elasticity
Surfactant
Increase wetting and decrease bubbles. Reduce the contact angle of gypsum products on the surface impression
Viscosity
Resistance to flow
Malleability
a materials capacity to be shaped by force or pressure
Elasticity
a measure of push or pull -When force is removed, the object returns to its original shape
Sol state
a solution of one material dissolved in another
Microchemical
bonding using surface irregularities smaller than can be see by the naked eye or felt with an explorer - more evenly distributed than macro
Wetting and contact angles
brings material into intimate association with the surface so that chemical and micro mechanical bonding can occur -A low contact angle, such as a drop of water on most plastics, indicates poor wetting -Ex) gypsum product is poured into an impression, when poor wetting occurs bubbles will likely result -good wetting of gypsum will have fine details of impression
Finishing
contour are corrected while margins and irregularities are smoothed using burs, a cup, or abrasive disks
Syneresis
contraction of a gel due to the loss of a solvent -Fluid lost by solid; water lost from alginate:desorption
Radiolucent
dentin, pulp, composite, cements, sealants, porcelain, other cements
Radiopaque
enamel, dentin, amalgam, cast gold, implants, composite, glass ionomer, cements, bands, gutta-percha, sealants, porcelain, other cements
Fatigue
failing after being stressed repetitively for a long time
Condensation silicone
hydrophobic, and setting process is the result of a condensation reaction -An alcohol by-product rather than water is formed -Cleaner materials to use but are difficult to pour without voids or bubbles -Must be poured without delay
Macromechanical
materials used for bonding that are on a larger scale -EX) screws, bolts, nails -In micro mechanical force is more evenly distributed on the joint
hysteresis
melting and gelling at different temperatures- ex) hydrocolloid does not melt at the same temperature it gels
Trituration
mixing of two materials into one -EX) mixing alloy with the liquid mercury
Micro leakage
passage of oral fluids/bacteria into and out of tooth structure due to marginal gap or failure of marginal (restorative) seal
Compression
pushing or crushing stress
Obtundent
reduces irritation - Ex) eugenol is a phenol derivative that is antibacterial and also obtudent to the pulp
Inelastic impression materials
set hard and rigid compared with elastic impression materials and would "lock" around the teeth -plaster -wax and impression compound -Zinc oxide- eugenol (ZOE)
Bases
stronger and thicker than a liner -provides thermal insulation, may be used in conjunction with a liner
Imbibition
the absorption of water/swelling/distortion
Adhesion
the chemical attraction between online molecules (Tape)
Proportional limit
the force at which a material cannot return to its original shape
Tensile
the force needed to stretch a material to the point of fracture
Biocomaptability
the lack of harmful effects to the patient
Gelation
the process of gelling (solidified by cold)
Working Time
the time that is needed to condense and carve -the working time of amalgam is not controlled by the dentist but rather by light-activated composites
Endosseous
type of implant that involves cutting a hole into the alveolar bone and then pressing or screwing in the implant
Liner
used to protect the pulp from chemical irritation -may stimulate secondary dentin formation or release fluoride -too thin to provide thermal insulation
