W3: Denture Base Materials Flashcards
What impacts can tooth loss have on the quality of life?
The impact of tooth loss on the quality of life is emotional and psychological health problems, joint and jaw disorders, as well as premature aging.
What is vulcanite?
Vulcanite was a rubber material that was hardended through a process and then used as a denture base (it was a successful material but had limitations).
What are the ideal properties for a denture base material?
Natural appearance (colour and translucency)
Easy processing (for consistent and good results)
Easy to clean
Easy to repair
Inexpensive
Long shelf life
Biocompatible (to the oral cavity)
Persistant to bacterial contamination
High strength, stiffness, hardness, toughness and
impact strength
Low density (not too heavy)
Radiopaque (to appear on radiographs)
High thermal conductivity
Dimensionally stable
Accurately reproduces surface detail
What does PMMA stand for?
Polymethyl Methacrylate
When are acrylic polymers used?
Acrylic polymers are used in prosthetic dentistry (articifcal teeth), denture repairs, crown and bridge facings, temporary crowns, impression trays, cleft palate obturators, and orthodontic devices
What are conventional dentures made of?
PMMA (highly crosslinked with polymer chains of varying lengths) and residual monomer
Why is PMMA the most popular base material for conventional dentures?
PMMA as a base material has advantages including good aesthetics, fit accuracy, stability in the oral cavity (biocompatible), easy to work with clinically and in the laboratory (easy manipulation), and is an inexpensive production.
What are the two forms PMMA can be supplied in?
- Powder and liquid
- Gel
What is the composition of the powder in heat cure acrylic?
Powder composition:
PMMA granules/beads
Initiator (benzoyl peroxide)
Pigments/dyes (cadium salts)
Optical opacifiers (titanium dioxide/zinc oxide)
Radio opacifiers (Ba, bismuth, zirconyl dimethacrylate)
Plasticizers (ethyl acrylate, dibutyl phthalate)
Synthetic fibers (nylon)
What does benzoyl peroxide do?
Benzoyl peroxide (initator) starts the setting process
What do cadium salts do?
Cadium salts (pigments/dyes) add colour to the material
What does titanium dioxide or zinc oxide do?
?
Titanium dioxide/zinc oxide (optical opacifiers) are related to light. If the optical opacifiers are too translucent, there is an issue with light.
What do Ba, Bismuth, and zirconyl dimethacrylate do?
?
Ba, Bismuth, and zirconyl dimethacrylate (radio opacifiers) make the acrylic material visible on radiographs.
What do ethyl acrylate and dibutyl phthalate do?
Ethyl acrylate and dibutyl phthalate (plasitcizers) add flexibility to the acrylic material.
What does nylon do?
Nylon (synthetic fibers) add colour and strength?
?
What is the composition of liquid in heat cure acrylic?
Liquid composition:
Methyl methacrylate monomer (MMA)
Inhibitor (hydroquinone)
Crosslinking agent (diethylene glycol dimethacrylate)
What is the boiling point of heat-cure acrylic?
MMA boiling point is 100.3°C
What is the glass transition temperature of acrylic?
PMMA Tg is around 105°C
What is the flexural strength range of PMMA?
70-127 MPa (ASTM D790)
*ASTM is a testing method that determines the flexural properties
What is the flexural modulus of heat cure acyrlic?
More than 2 (>2) GPa
How much residual monomer can be in heat-cure acrylic?
Less than (<) 2.2
What is the water sorption of heat cure acrylic?
Less than (<) 32 μg/mm3
What is the solubility of heat cure acrylic?
Less than (<) 1.6μg/mm3
Which type of PMMA form does vinyl acrylic present as?
Gel form
What is the composition of gel form PMMA?
Same composition of powder-liquid PMMA PLUS light activator.
Which denture base is light-cure?
Gel form PMMA (i.e need to cure gel)
Which light is gel-form PMMA cured by?
Ultraviolet light
Are self-cure acyrlic resin and cold acrylic resin the same?
Yes
Self-cured (cold) acrylic resin
What is the composition of self-cured acyrlic resin?
Same as that of heat cure acrylic resin PLUS a tertiary amine (e.g. sulfinic acid or dimethyl-p-toluidine)
What is the composition of self-cured acrylic resin?
Smaller bead size
Shorter average chain length
High residual monomer
Lower strength properties
Lower colour stability
Lower glass transition temperature around (75-80ºc) compared to heat-cure acrylic resin
What are visible light-cure resins similar to in dentistry?
Restorative composite (because of the matrix)
What is the matrix of visble light-cure resin based on?
Urethame dimethacrylate (has colloidal silica which control material abilty to flow)
Which photoinitiator is included in the visible light cure resin?
Comphoroquinon (allows the material to set)
What are three more types of acyrlic resins?
Microwave cure acrylic resin
Rapid heat-polymrtized resins
Pour type denture resins
Which areas requirement of denture base materials does PMMA lack?
Strength, stiffness, hardness and toughness
Inhibit bacterial growth
Thermal conductivity
Retention to other polymers, porcelain and metals
Radio-opacity
What are the advantages of PMMA?
Excellent aesthetics
Easy and cheap to process
Low density
What are the disadvantages of PMMA?
Low strength and toughness
Suceptible to distortion
Prone to discolouration
Low thermal conductivity
Radiolucent
How can acrylic materials modified?
Rubber reinforced
Fiber reinforced
Paritculate reinforced
Give examples of rubber reinforced acrylic materials?
Rubber reinforce (high impac resin) includes rubber particle reinforcement (butadiene-syrene) and acrylic-elastomer copolymer (MMA-butadiene or MMA-buadiene-styrene).
Give examples of fiber reinforced acyrlic materials?
Carbon, acrylic, GF, Aramid, Nylon, PEF, and UHMWPEF
Give examples of particulate reinforced denture base materials?
Silica, alumina, glass flakes, nanoclay, titanium and zirconium oxide
What is Polyamide?
Nylon
*1950s
What are the brand names for nylon dentures?
Valplast (Valplast Int. Corp., USA) and Flexiplast (Bredent, Germany)
What is the composition of Nylon dentures?
Crystaline polymers with weak bonding between chains
What are the advantageous properties of nylon dentures?
Non-brittle (high-toughness)
Flexible Material
Comfortable and aesthetic clasps
Less allergenic than PMMA
What are the disadvantageous properties of nylon dentures ?
Low flexural strength
Low fatigue resistance
Low surface hardness
Difficult to perform repairs and relines (have to completely replace denture often)
Retains staining
Retains biofilms
Difficult to polish
Lacks rigidity and occlusal rests (risks occlusal instability and sinking with Kennedy Class I and Class II cases as well as peridontally affecetd abutment teeth)
What is Polyoxymethylene?
Acetal Resin
Similar to nylon polymeric structure
*1986
What are the advantageous properties of acetal resin dentures?
High modulus of elasticity
High strength
Heat resistant
Organic solvent resistant
Oil resistant
Water resistant
Monomer-free
What is acetal resin dentures a safe alternative for?
Acetal resin dentures are a safe alternative for patients allergic to PMMA.
What are the advantageus properties of acetal resin compared to nylon
Acetal resin material has minimal prosities therefore resisting the accumulation of biological material. This minimizes (lessens) the risk of bad odour and staining of the acetly resin material (unlike nylon).
What are Aryl Ketone Polymer (AKP) dentures?
AKP dentures attempt to bridge the gap between metal Removeable Partial Dentures (RPDs) that can be too rigid and other polymer frameworks that can be too flexible.
How are the clasps of AKP dentures compared to metal clasps?
AKP clasps are less retentive but more durable than metal clasps. This means that although clasp retention may not be as good to that of metal frameworks, the clasps may not break if moved out of design range (unlike metal clasps) and are more bendable/are more giving if needing adjusment (?).
How are AKP dentures manufacutred?
CAD-CAM
What are 3 other advantageous properties of AKP dentures?
Fully biocompatible
Lightweight (increase patient satisfaction)
Heat reistant (can be autoclaved)
What are the advantages PEEK?
Highly bicompatible (no free monomer)
Good mechanical properties
High-temperature resistant
Chemical stability
Increased colour stability (better than PMMA)
Milled/heat pressed
What can PEEK dentues be used an alternative for?
PEEK dentures can be used as alternative to Chobalt-Chrome (Cr-Co) dentures. This denture base material has clasps more flexible than Cr-Co and can be used in areas where there are deeper undercuts. This means that PEEK dentures can be designed to benefit tooth support.
What are the clinical applications of PEEK dentures?
Implant abutments, crowns, fixed bridges and removable dentures.
Which arch and which instance are Every Denture used for?
Every Denture is an upper acrylic partial denture that is used for the replacemet of anterior teeth (Kenndy IV classification).
What are characteristics of Every Denture?
Every Denture has:
-Artifical teeth with a smaller occlusal table and wide embrassures
-Point contact between abutment and denture teeth (reduces lateral stresses)
-Posterior wire stops (to prevent distal drifting of posterior teeth and to increase denture retention)
-Flanges (to increase bracing and open design between tooth/saddle)
What are the adverse reactions to PMMA?
Irritant contact dermatitis
Allergic contact dermatitis
Describe in detail irritant contact dermatitis (include where it is most common, how it occurs, and protection measures)
Which type of Allergy is irritant contact dermatitis to PMMA?
Irritant conact dermatitis is most common in dental laboritories. It may be associated (occur) with regular contact of handiling the monomer and powder dough. Protection measures include avoiding direct contact, rubber gloves (but may not provide sufficent protection), barrier creams, and utilizing the dust exhaust fans.
Type I
Describe in detail allergic contact dermatitis (include, where it is most common, how it occurs, and protection measures)
Allergic contact dermatitis may be common with patients (?), is usually associated (occurs) with the release of residual monomer. Protective measure include ensure full denture cure.
Which type of PMMA does allergic contact dermatitis worsen with?
Self (cold) - cure acrylic resisns
Which type of Allergy is allergic contact dermatitis?
Type IV (delayed hypersensitivity)
If a patient has allergic contact dermatitis to PMMA, what ther materials can be considered?
Polycarbonate, nylon
Which 3 instances are denture lining materials used?
To restore denture fitness (hard relining)
To relieve pressure over inflammed tissues or make functional impressions (tissue conditioner)
To provide patient comfort with a soft liner (soft reline)
When are hard lining denture materials indicated?
When the denture has a lack of fitness
Which material can be used as a denture hard reline?
Conventional denture base resin
*often PMMA
What are the methods to performing a denture hard reline?
Direct (chair side)- chemical-cure
Indirect (lab)- heat-cure
What are the two types of chemical-cure denture hard liners?
- Powder + MMA (+ Di-n-butylphtalate) (tissue irritant)
- Powder + BMA less (tissue irritant)
What are the disadvantages of direct (chair side) hard lining denture materials?
Disadvantages of the direct method:
Low glass transition temperature of chemical-cure resin
High porosity of chemical-cure resin
Tends to increase vertical dimension (VD)
Tends to decrease the Free Way Space
Can change the anterio-posterior position of the denture
When are tissue conditioners indicated?
Healing after extraction or surgery (cushioning)
Relining of immediate dentures (cushioning)
Recovery of traumatized tissues (cushioning)
Making functional impressions
What is the composition of tissue conditioners?
Powder + liquid
Powder- PMMA (no initiator)
Liquid- alcohol (ethyl alcohol) + plasticizer (e.g. buthylphthalyl buthylglycolate)
NO MONOMER, NO CHEMICAL REACTION, NO IRRITATION
How long after do tissue conditioners harden and why?
Tissue condtioners become hard after 3-14 days due to loosing plasticizer and alcohol
How often should tissue conditioners be replaced?
Every 2-3 days when used as a tissue conditioner
Should tissue conditioners be used for short-term use or long-term use only?
SHORT-TERM USE ONLY
What are the two different types of soft liners?
Soft liners (temporary)
Soft liners (permanent)
What are the indictions for temporary soft liners?
- When frequent replacement is difficult
- Provisional improvement of fitness before defenitive denture constructures
- Assesment of patient response to soft liners
Describe the viscoelasticity property of temporary soft liners and its added benefit
The viscoelasticity property is harder at setting but remain soft for 2-3 months. This allows the temporary soft liner to be used as a permanent soft cushion for patients unable to tolerate hard dentures.
What are two types of permanent (long lasting) soft liners?
Acrylic
Silicone
What is the composition of acrylic permenent (long lasting) soft liners?
Acrylic: can be chemical-cure or heat-cure
Composition:
Powder (polyethyl) or polybutyl-mathacrylate (+BPO)
and
Monomer butyl-mathacrylate + plasticizer
What are two forms of curing silicone permanent (long lasting) soft liners?
Chemical cure
Heat cure
What is the composition of heat cure silicone permanent (long lasting) soft liners?
Composition of heat cure:
Single paste- vinyl terminated polydimethylsilxane + silica + filler particles + heat activated peroxide
What is the composition of chemical cure permanent silicone (long lasting) soft liners?
Composition of chemical cure:
condensation and addition polymerization
What are the relative merits of silicone based soft liners?
Highly resilient
Retains softness longer
Weak bond to acrylic
Suceptible to candida growth
Poor tear strength
Poor wettability
No permanent deformation
Requires regular replacement
High water sorption
More elastic
What are the relative merits of acrylic based soft liners?
Not as resilient as silicone
Harden with time due to plasticizer leaching
Resistant to bacerial growth
Excellent bond to acrylic
Acceptable tear strength
Suceptible to creep
Good wettability
Requires regular replacement
More vicoelastic
What is the contraindication to silicone liners
Xerostomia -> chaffing and irritation
What is a polymer?
Polymer is a distinc repeating group of atoms called monomer
What is addition polymerization?
Addition polymerization occurs when a reaction between two molecues produces a larger molecule WITHOUT the elimination of a smaller molecule or by prodcut.
What are the steps of addition polymerization?
Activation
Initiation
Propagation
Termination
What is a commonly used free redical producer and an INITIATOR in addition polymerization?
Benzoyl peroxide
What are activators in addition polymerization?
Heat
Chemical compounds (tertiary amines)
Light (radiation)
= produce free radicals describes
What is condensation polymerization?
Condensation polymerization occurs when a reaction between two molecures produces a larger molecule WITH the elimination or production of a smaller molecule
What controls the properties of polymers?
Molecular strength of repeating units
Molecular weight (average MW)
Chain length
Degree of chain branching
Crosslinking
Filler or plasticizer
What are the benifits of cross-linking a polymer?
Cross-linking can make the polymer rigid, brittle, and strong.
What are two different types of polymers?
Thermoplastic
Thermosetting
Describe thermoplastic polymers
Thermoplastic polymers are softened at glass transition temperature (Tg) and molded to shape when required.
Describe thermosetting polymers
Thermosetting polymers are manufactured partly polymerized (powder). Heating after molding will complete polymerzation. These polymers are highly cross-linked and cannot bet softened.
What is glass transition temperature (Tg)?
Glass transition temperature (Tg) is the temperature at which polymer chains flow past each other.
- relates to thermoplastic polymers
What are two different polymer structures?
Amorphous polymers
Crystalline polymers
Describe amorphous polymers?
Amorphous polymers are polymers that contain amorphous regions where molecules are randomly arranged.
Describe crystalline polymers?
Crystalline polymers are polymers with crystalline regions where molecules are arranged in a partial pattern
Which polymer structure has a limited use in dentistry and why?
Crystalline polymers have a limited used in dentistry because of opacity and processing conditions.
Which type of structure are dental polymers mostly?
Amorphous
What are the dental applications of polymers?
PMMA (hompolymer)
Polyacrylic acid/Hydroxy Methylmethacrylate (copolymer)
pure resin e.g PMMA
composute e.g. restorations (tooth fillings)
?
