Test One: Denture Base Materials Flashcards
In terms of elastic modulus, tensile strength, and compressive strength, how does acrylic compare to dentin, amalgam, and enamel?
Low to high
Elastic modulus: acrylic, dentin, amalgam, enamel
Compression strength: acrylic, dentin, enamel, amalgam
Tensile strength: acrylic, enamel, amalgam, dentin
How does acrylic resin hardness compare with that of tooth structure or other restorative materials?
PMMA is very soft compared to other materials. Composite is twice as hard, amalgam is five times, enamel is fifteen times
What type of filler is used for dentures?
pre-polymerized PMMA, which undergoes no further polymerization upon curing of the denture base resin to reduce shrinkage
What are heat and chemically cured denture base materials composed of?
POWDER LIQUID
PMMA beads MMA monmer
Pigments Glycoldimethacrylate (x-linker)
Plasticizers Hydroquinone (inhibitor)
BPO *(Tertiary amine, only if chemically cured )
What is the use of tin foil substitute?
To prevent the resin from adhering to the gypsum mold so that the processed denture could be removed from the master cast
What are the stages of the powder/liquid mixture and when should it be packed into the flask?
Sandy, sticky/stringy, doughy (this is when it should be packed), and rubbery
Stringy stage still has monomer separated and rubbery will not compress as well
Heat cured denture base material
0.5% linear shrinkage, high average degree of polymerization, low residual monomer, enhanced physical properties but heat can cause warpage of the denture base
Chemically cured denture base
0.2% linear shrinkage, more residual free monomer, lower strength properties
Fluid pour denture base
High polymerization shrinkage, highest amount of residual monomer, air bubbles and voids and teeth shifting, poor strength, lower abrasion resistance, and decreased color stability
What causes residual stress in denture base materials?
Heat cured repair will release residual stresses and distort the denture base.
Proper curing schedules for heat processed acrylic resins
65° C bath for 90 minutes, then 100° C for 1 hour to cure the thinner sections
Or 74° C bath for 9 hours
What happens if a packed denture flask is placed immediately into boiling water?
the combined effect of the water temperature and the curing exotherm of thick sections will cause the monomer to boil (100.3°C), resulting in porosity in
thick denture sections as opposed to the absence of porosity in the thin sections. These porosities result in greatly decreased strength values.
What is the best way to repair Heat cured dentures?
The broken parts need to be flasked to repair
How do repair resins adhere to old resins?
Mechanically
Pros and cons of MMA-butadiene-styrene rubber-reinforced acrylics
Disadvantages: lower color stability, higher solubility, greater water sorption
Advantage: these products tend to absorb a great deal of energy prior to fracture which reduces chance of breaking
Pros and cons of Polycarbonate resins
Advantages: designed to have a higher impact strength than the rubber-reinforced acrylics. They absorb less water than the acrylic resin. Disadvantage: must be injection molded at high temperature and pressure.
Pros and cons of vinyl resins
Disadvantages: injection molded at high temperatures, and the high costs of associated equipment.
Advantage: average molecular weight is high resulting in elevated glass transition
temperature
Pros and cons of metal base dentures
advantages: better fit due to the greater accuracy of the lost-wax process, improved sensation of “taste” resulting from the conduction of heat through the metal denture base.
Disadvantage: Relining is not possible, necessitating a complete remake of the
prosthesis when the ridge has resorbed.
How are denture bases relined/rebased?
Mouth cured, lab cured, soft acrylic, and lab cured silicon reliners. Rebasing replaces the entire denture base which decreases chance of changing occlusion–good with porcelain denture teeth
Tissue conditioners
Made of pmma,a solvent and a plasticizer. “Setting” occurs by an increase in viscosity from the wetting of the powder particles. They must be replaced frequently due to leaching of the plasticizer which decreases flexibility
Indications for denture base adhesive
- as an emergency measure to stabilize ill fitting dentures,
- for patients with very flat ridges,
- with edentulous patients having a cleft palate
- in patients with post cancer prosthesis.
Mechanism of action for powder type denture base adhesives
The powders contain vegetable gums or ethylene oxide polymer which produce a mucilaginous gel
when added to water. This viscous, sticky mass adheres both the denture base as well
as to the oral mucosa.
