thermoplastic
property of becoming softer upon heating and harder upon cooling with the process being reversible
NaPO4
the retarder that is used to control set time
Examples of elastic non-aqueous material
Polysulfide rubber impression material
Polyether rubber
How can the set time be controlled by the operator?
1)Increase/decrease the temp of the water and/or environment
2) Proportions of water & powder affect the time & strength
How is plaster made from gypsum?
Gypsum is heated in atmospheric pressure & produces beta-hemihydrate
Dry strength
after free water has evaporated; 2x stronger than wet strength; after 24 hrs
Wet strength
free water not evaporated; before 24 hrs; gypsum product cannot be subjected to high stress during this period
Irreversible hydrocolloid
alginate
Which requires more water for mixing: Plaster or stone?
Plaster because it has more porous particles than stone
Dental impression
negative reproduction of the mouth, dentition, and oral structures
Die
working model of a tooth or teeth (strongest model)
Cast
working model or mouth
Model
used for study and observation only
3 contraindications for placing implants
smoking
diabetes
periodontal disease
3 types of bleaching available to patients
in office
take home-professional supervision
independently home applied
4 disadvantages of alginate impression material
Restricted to use of gypsum for replicas
Does not transfer detail like agar or rubber
Must pour immediately for accuracy
Low tear resistance
Factors affecting setting time
Manufacturing process
Water/powder ratio
Mixing process
Temperature
Addition of retarder & chemicals
What three things affect the abrasion process?
Size of abrasive particles
Pressure of abrasive against surface
Speed of abrasive
A rough surface in a restoration is undesirable because:
1) Food debris and plaque can easily cling to it
2) Irritation and recession of soft tissues can occur in proximity to it
3) It is responsible for acceleration of corrosion of metallic restoration
The rate of abrasion is increased by:
1) greater pressure on the abrasive tool
2) greater speed on the abrasive tool
Final polishing of a dental amalgam to the smoothest surface is achieved by:
use of tin oxide
Prophy paste
Use should precede application of a fluoride gel to make enamel accessible and more reactive to the fluoride
Components of dentifrice
abrasive
therapeutic agent
humectant
siveetner??
3 common amalgam failures
-secondary or recurrent decay around restoration
- bulk fracture
-marginal breakdown
Sol state
solution of one material dissolved in another
Gel state
two phases exist
Irreversible hydrocolloid
hydrocolloid that sets via a chemical reaction; commonly called alginate; does not reverse
Reversible hydrocolloid
gels by a physical change; agar or agar-agar; goes back to sol state when heated, changes to a gel when cooled
surfactant
reduce the contact angle of the mixed gypsum product on the surface of the impression; wetting increases; bubbles decrease
Alginate impression material is:
easy to use
Elastomeric
Impression materials that have mechanical properties permitting considerable elastic deformation but that return to their original form are:
warm water will
cool water will
shorten the gelation time
lengthen the gelation time
Agar
impression material set by physical means
syneresis
when an agar impression slightly contracts and exudes water
working time
length of time from the start of the mix until the setting mass reaches a semihard state
final setting time
represents the length of time from the start of the mix until the setting mass becomes rigid and can be separated from the impression
potassium sulfate
commonly used accelerator
Potassium sulfate & borax
suitable accelerator and retarder for gypsum products
Plaster
weakest gypsum product
add powder to the water
best way to make gypsum products
study models/study casts
positive reproductions of patients dental arches and surrounding tissues
2 1/2 inch
the combined thickness of a maxillary and mandibular model
hydrophilic
water loving-material or surface is readily wetted by water as indicated by a low contact angle of water on the surface
hydrophobic
water hating-material or surface not readily wetted by water in the form of a drop with a contact angle greater than 90 degrees measured internally to that drop
custom tray compliance
1) better compliance
2) better application of a substance
3) less risk of tissue trauma
imbibition
absorbs additional water if given the chance
hybrid, microfill, and fine
describe the size of the particles used as fillers; hybrid is the strongest
colloid
two phase material, mixture of gases, liquids, or solids at microscopic level
forms beta hemihydrate; plaster
gypsum heated in atmospheric pressure
forms alpha hemihydrate; dental stone
gypsum heated in steam pressure
forms alpha hemihydrate; die stone
dental stone is dehydrated in calcium chloride to yield smoother particles
Plaster and Dental stones are:
chemically IDENTICAL; only shapes of powder particles are different
Plaster
used for study models
Dental stone
used for full arch impressions, mouth protectors, bleaching trays
Die Stone (High Strength Dental Stone)
crowns, bridges, onlays, inlays, partials (anything indirect)
gypsum
the only material that can be used in hydrocolloid impressions
Rubber based impressions
-Never store or immerse in water
-Poly ether and addition silicones are most accurate, least dimensional change;most expensive
-Auto mix is available for most
-Temperature and humidity effect all
-Poly ether and addition silicones are used for bite regist
Disinfection of rubber materials
gluteraldehyde, phenols, chlorine dioxide
Polyether impression material
-Better stability and mechanical properties (than polysulfides or condensation silicones)
-Shorter working times
-Greater stiffness�will lock into undercuts
-Extremely accurate�good for bite registration
-Polyether and addition silicone more wettable (mor
Silicone rubber impression material
-Fairly short working and setting times
-Moderate flexibility and tear strength
-Less shrinkage upon setting
-Less flow and permanent deformation
-Addition silicones are the most accurate
-Expensive compare to hydrocolloids
-Hydrophobic
-Wet poorly, stone
Polysulfide impression material
compared to hyrocolloid:
-More flexible
-Less dimensional change
-More resistant to tearing
-Horrible taste and smell
-Difficult clean-up
-2 paste system (base and catalyst)
-3 viscosities: lite, regular, heavy bodied base
Endosseous implant
screwed or pressed into a hole that is cut into the man or max (reside inside bone)
Transosteous implant
requires extra oral incision under chin
subperiosteal
implant rests on bone under the periosteum; requires multiple surgeries