Polymers
Linear shrinkage
-1-2% -exerts significant effects upon denture base adaptation and occlusion
Soft liners
-2 types: silicon is auto or heat polymerized, soft is auto or heat polymerized -used to improve the comfort or fit of an old denture until a new one is made -provides comfort for pts who cannot tolerate occlusal pressure -replaced in 3 months
Milled provisionals materials
-PLA: poly lactic acid filament -PEEK -PMMA blocks and pucks
Polymerization via microwave energy
-a conventional microwave is used to supply thermal energy required for polymerization -special flask -very quick -can cause over heating and boiling of monomer, leads to porosity
Short curing cycle
-about 2.5 hours -flask in water bath, increase temp gradually from room temp to 65C in 30 mins -keep at 75C for 1.5 hrs, keep boiling for 30 mins
Volumetric shrinkage
-about 7% -fit of denture is not impacted because the shrinkage is uniform
Long curing cycle
-about 9 hours -put flask in water bath, increase temp gradually from room temp to 65C in 30 mins -raise to 80C within 8 hours, keep boiling for 30 mins -best for bulky prosthetic
Tissue conditioners
-absorbs some energy from masticatory forces, shock absorber -promote healing of the inflamed tissue -placed for 2-3 weeks at a time
Customized provisional types
-acrylic: methacrylate -composite: bis
Hard reline advantages
-allows dentist to reline a removable prosthesis directly in the mouth -procedure is faster than the lab one -does not result in any clinically significant dimensional change
Repairing resins
-can be heat, light, or self cured -self cure is easiest to use -heat and light activated need water baths and light chambers -heat generated can cause stress release and distortion
Chemically activated denture base resin
-chemical cure, self cure, auto cure, cold cure -two paste system: base is benzoyl peroxide initiator, catalyst paste is tertiary amine activator
Preformed provisional advantages
-convenient -save time -no stent needed -useful in emergency situations
Problems with soft liners
-does not bond to acrylic denture base -degrades in the presence of water -swells and changes dimensionally -cannot be cleaned effectively -pts have bad taste and odor, c albicans can grow -leaching of plasticizer can cause hardening
Heat curing
-exothermic reaction, but not above 100C otherwise monomer boils off -better color stability due to absence of tertiary amines
Bis GMA composite provisional disadvantages
-expensive -single units only -single shade
Injection molding
-flasking method -sprue is attached to wax denture, leads to a channel -resin is mixed and injected into the mold cavity
Fluid resin technique steps
-for chemical activated resins 1. complete tooth arrangement in a fluid resin flask 2. removal of tooth arrangement from reversible hydrocolloid investment 3. preparation of sprues and vents 4. repositioning of the prosthetic teeth and master cast 5. introduction of pour type resin 6. recovery of the completed prosthesis
Internal porosity
-form of void or bubbles within the mass of polymerized acrylic -confined to thicker part of denture -from vaporization of unreacted monomers and low molecular weight polymers, when temp is past boiling for monomers -can be avoided by using long and low temp curing cycles
Injection molding advantages
-good clinical accuracy -tooth movement is minimized -homogenous denture base -low free monomer content -good impact strength
Bis acryl composite provisional advantages
-good marginal fit -good transverse strength -low exothermic reaction -low shrinkage
Methyl methacrylate provisional advantages
-good marginal fit -good transverse strength -polishable -durable
Injection molding disadvantages
-high equipment cost -difficult mold design -less craze resistant -specialized flask -requires deeper prep of the post palatal seal to ensure contact of the polymerized denture base within the pts palatal tissues
Methyl methacrylate provisional disadvantage
-high exothermic reaction -high shrinkage -free monomer -low abrasion resistance
Thermoplastic resin properties
-high molecular weight copolymers, not monomers -no residual monomer -non toxic or allergenic -high biocompatibility and keeps it shape
Bisacryl resin
-in preloaded syringes or cartridges, auto mixing tips -self cure -low shrinkage during set -low exothermic reaction
External porosity
-lack of homogeneity -lack of adequate pressure -can be avoided by using proper powder liquid ratio and mixing it well, pack in the dough stage
Poly ethyl methacrylate provisional disadvantages
-less transverse strength -less fracture toughness
Bis GMA composite provisional advantages
-low exothermic reaction -low shrinkage -adaptable intra orally -no mixing needed -easy to repair -polishable
Milled provisional blocks advantages
-marginal fit -flexural strength -internal fit -hardness
Liquid of PMMA
-methyl methacrylate: resin -dibutyl phthalate (plasticizer) -glycol dimethacrylate (crosslinker) -hydroquinone (inhibitor)
Customized provisional advantages
-more versatile -better contour, occlusion, and marginal adaptation
Milled provisional blocks disadvantages
-more wastage -cost -in office availability limited
Nylon advantages
-no free monomer -soft and flexible -high impact and fatigue strength -less gingival inflammation -better pt acceptance -less bulky or thinner -better aesthetics
Bisacryl resin disadvantages
-not as tough as PMMA -not for long term -more expensive -thick oxygen inhibited layer, less stain resistant -flowable does not bond to it well
Bis acryl composite provisional disadvantages
-not easy to repair -more expensive -limited shades -less stain resistance -brittle
Poly ethyl methacrylate provisional advantages
-polishable -low exothermic reaction -good stain resistance -low shrinkage
Powder of PMMA
-poly methyl methacrylate: resin -benzoyl peroxide: initiator -dibutyl phthalate: plasticizer
Thermoplastic materials
-polyamides: nylon, used the most -acetylates -thermoplastic acrylics -polyolefins -polyesters
Hard reline disadvantages
-possibility of chemical burn due to acrylic heating -high polymerization temps -poor color stability -porosity
Provisional restoration uses
-protects the prepared abutment teeth -aids in reestablishing occlusal parameters -maintains esthetic and oral functions -preserves perio health
Nylon disadvantages
-provisional applications -does not bond well to acrylic -absorbs water and discolors -high surface roughness -technique sensitive -difficult to adjust and polish -less stiff -lack rigidity
Light activated denture base resin
-single component resin in sheet and rope form, stored in a lightproof pouch -high molecular weight polymer, less shrinkage -polymerized in a light chamber -used for record bases
Preformed provisionals types
-stainless steel -polycarbonate
Heat activated denture base resin
-thermal energy is required, immerse in water bath -above 60C benzoyl peroxide decomposes to yield species containing free radicals -the free radicals react with monomers to initiate chain growth polymerization
Thermoforming resin
-transforming a plastic sheet into a 3D shape using heat, vacuum, and pressure -essix sheets for retainers, bleaching trays, ortho aligners, occlusal splints, stents for implants
Relining
-used for temporarily resurfacing the tissue side of the denture -3 types: tissue conditioner, soft liner, hard reline
Thermoplastic nylon
-used the most -no allergy issues, no metal -good thermal and chemical resistance -manipulated by injection molding to make a flexible denture -low free monomer content -good impact strength
Compression moldings steps for resin
1. mix resin and bend into a horseshoe shape, place in mold cavity 2. the flask is put together and pressure is applied 3. excess resin is removed from flask 4. flask is transferred to a flask carrier and pressure is maintained
Polymer and monomer steps in setting
1. sandy: no interaction at molecular level 2. stringy: few polymer chains 3. dough: more polymer chains, can manipulate at this stage 4. rubbery: evaporation of free monomer, resistant to chemical deformation 5. stiff: mass rebounds when stretched
Compression molding steps before resin
1. tooth arranged 2. master cast is embedded in stone 3. occlusal surfaces of teeth are exposed to allow for denture recovery 4. fully flasked 5. separate flask after wax is melted out 6. place alginate separating medium for resin
Polymer to monomer ratio
3:1 by volume -excess monomer increases shrinkage
Bis acryl composite provisional brand
Integrity, luxatemp, protemp 2 -self or dual cure
Methyl methacrylate provisional brand
JET -self cure
Poly ethyl methacrylate provisional brand
SNAP -self cure
Polymerization shrinkage
acrylic can shrink due to thermal shrinkage upon cooling, or polymerization shrinkage
Type 2 denture base resin
auto polymerization
Polymethyl methacrylate biologic properties
biocompatible, non irritant, nontoxic, non carcinogenic
How does PMMA grow
chain growth
Porosity
heat activated dentures have different porosity, can be from rapid heating, insufficient mixing, or insufficient pressure
Type 1 denture base resin
heat polymerizable
Polymethyl methacrylate mechanical properties
high elastic modulus, proportional limit and resilience, adequate abrasion resistance, fatigue and impact strength
Polymethyl methacrylate other properties
inexpensive, easy to manipulate and repair, easy to clean, longer shelf life
Polymethyl methacrylate chemical properties
insoluble, non reactive, compatible and bond artificial teeth and liners
Type 4 denture base resin
light activated
Polymethyl methacrylate physical properties
low specific gravity, dimensional stability, good thermal conductor, coefficient of thermal expansion is close to teeth, thermal stability, radio opqaue
Type 5 denture base resin
microware cured
Bis GMA composite provisional brand
protemp crown -light cure
Type 3 denture base resin
thermoplastic blank or powder
Polymethyl methacrylate esthetic properties
translucency ability to tine and pigment to match color of teeth and gums
Hard reline
when a patient needs a new denture but can't for some reason, can do chair side or send to lab
