Biomaterials Flashcards
What is material:
strength?
resilience?
toughness?
tensile strength?
compressive strength?
Strength = ability to absorb a lot of stress before breaking (total stress absorbed before #)
Resilience = stress absorbed that can be released again
Toughness = energy absorbed in total until the material fractures
Tensile strength = ability to be pulled or stressed
Compressive strength = ability to withstand stress when squashed.
Why does thermal conductivity matter in restorations?
Restorative materials should expand when heated as much as enamel and dentine.
If not, gaps will form at the edge of restorations, allowing bacterial invasion.
What is the elastic modulus?
What is the elastic region and plastic region?
Young’s modulus.
Measure of how flexible or rigid a material is.
Elastic region: if material is released, it return to its original shape with no deformities.
Plastic region: material is permanently deformed and does not go back to original shape/size
What is corrosion?
The deterioration of intrinsic properties in a material due to environment.
- Due to oxidation in metals.
Can cause failure of metals and alloys due to:
> Loss of material bulk
> Deterioration of mechanical properties
> Leaching of corrosive products.
Conducting material + reactive material + electrolyte = corrosion
What is passivation?
Protecting coating of the material, rendering the material inert.
Why may a filling break which has been there for years?
Because small forces applied over the years, the material became fatigued and fractures due to molecular change in the material (as supposed to a single event with great force).
If apply a stress to material below the yield stress, eventually will become fatigued and fracture.
What is galvanic corrosion?
Movement of electrons from anode to cathode.
- the more electronegative material is the anode, this material corrodes.
- requires two or more inhomogenous metals/alloys to be in contact.
How can you reduce pit corrosion?
Polish amalgam surface to remove oxidation layer.
What is:
- tarnish?
- discolouration?
- dissolution?
- erosion?
- sorption?
- Tarnish = surface discolouration on the metals/alloys due to sulphides and chlorides
- Discolouration: due to extrinsic and intrinsic staining
- Dissolution: solubility, measure of the extent to which material will dissolve
- Erosion: dissolution and surface wear
- Sorption: usually with polymers, associated with dimensional change and flexibility loss.
What metals does amalgam contain? %? purpose?
- Mercury (Hg) = 44-48%
- ~ 400mg in one capsule - Silver (Ag) = 30-35%
- Tin (Sn) = 9-15%
- decreases reaction rate = increased clinical working time - Copper (Cu) = 0-15%
- eliminates gamma-2 phase by converting it to gamma-1
What is amalgam? What are the good and bad properties of amalgam?
An alloy, a mixture of metals (mercury, silver, tin, copper).
Good properties:
- High tensile and compressive strength
- Good working time
- Good longevity
Bad properties:
- Poor aesthetics
- Not adhesive - relies on mechanical retention
- Destructive cavity prep
- Mercury use
How does amalgam set?
What does adding copper do?
Trituration initiated when the alloy powder encounters the elemental mercury (Hg) in the amalgamator:
Ag3Sn + Hg –> Ag3Sn (y) + Ag2Hg3 (y1) + Sn7-8Hg (y2)
y = gamma phase = Ag3Sn
y1 = gamma -1 phase = Ag2Hg3
y1 = gamma -2 phase = Sn7-8Hg
Adding copper impacts the setting reaction:
Converts gamma 2 to gamma 1
Why is copper in amalgam fillings useful?
Adding copper converts gamma 2 to gamma 1.
Sn7-8Hg + AgCu –> Ag2Hg3 + Cu6Sn5
Useful as gamma 2 is most prone to corrosion since highest in electronegativity.
- Eliminating the gamma 2 reduces the chances of galvanic corrosion or creep (protrusion of the amalgam from the cavity).
High copper amalgam has low creep value due to little/no gamma-2 phase.
What are the properties of amalgam?
High compressive and tensile strength
Strong
Prone to corrosion (galvanic corrosion)
Good conductor
Amalgam is prone to creep
Under trituration can result in amalgam that sets too quickly.
y-gamma and y-gamma 1 have high corrosion resistance. y-gamma 2 has low corrosion resistance.
y-gamma has high strength. y-gamma 1 and y-gamma 2 have low strength
What is amalgam creep?
Protrusion of the amalgam from the cavity. It is the physical property of a material to deform over time due to constant application of force or stress.
This can lead to flow of material –> ditching –> secondary caries.
What are the advantages and disadvantages of amalgam bonding agents?
They reduce microleakage and allow adhesion to dental hard tissues as well as increasing strength.
But time consuming and costly.
What are the different types of amalgam cut?
- Lathe cut = made into an ingot and cut into a lathe –> irregular chippings
- Spherical = molten and sprayed where it solidifies to form round droplets
- Admix amalgam contains both lathe-cut and spherical cut particles.
What is light-cured resin-based composites?
A filler polymer material that is strong and durable with outstanding aesthetics. Reason to fail - 2* caries.
What is the composition of light-cured resin-based composites?
- Filler particles
> Silica or quartz
> they are the largest component (silicon dioxide and glass filler particle)- (silica and quartz are chemically identical (both silicone dioxide) but with different crystalline structures (quartz is a specific crystal structure of silica))
- Large resin monomers (high viscosity, large molecules)
> Urethane dimethacrylate (UDMA)
> Bisphonol-A glycidyl methacrylate (Bis-GMA) - Smaller resin monomers that act as ‘dilutents’ to reduce viscosity
> TEGDMA (triethylene glycol dimethacrylate)
> MMA (methyl methacrylate) - Coupling agent
> Silane molecules
- bonds the resin to filler (by establishing covalent bond) - Heavy metal-containing fillers (for radiopacity)
- Photoinitiator/activator
> Photoinitiator - Camphorquinone- produces free radicals to allow the polymerisation to start
> Chemical activator where light can’t access - benzyl peroxide
- produces free radicals to allow the polymerisation to start
- Inhibitor/retarding agent
> hydroquinone
- prevents premature polymerisation
What are compomers?
They are a material combination of composite and glass ionomer. They require bonding agents for good dental surface retention.
Also called Polyacid-modified composite resin.
What are hybrid ionomers?
Contain 80% glass ionomer and 20% composite.
Don’t require a bonding agent for retention
They release fluoride, bonding agent may reduce the fluoride received.
Good for high caries patients.
Useful when light curing access is difficult.
How do resin based composites set?
Resin based composites exhibit a command set (usually 20-40 sec).
Polymerisation is initiated when the composite is exposed to blue light (470nm)
The photons stimulate camphorquinone to release free radicals.
This initiates the polymerisation of the resin monomers.
Polymerisation inhibited by oxygen (apply translucent strip on top of restoration surface to exclude oxygen).
Exhibit a limited depth of cure, some light is absorbed, transmitted or scattered.
What can incomplete polymerisation of composite result in?
Reduced strength and bond strength
Decreased marginal integrity and increased wear.
Water sorption and leaching of uncured monomers.
What factors influence the depth of cure?
- Shade
- Filler loading
- Filler size
- Powder/intensity of curing light
- Distance between curing light and composite
- Time of cure
- Oxygen inhibition (inhibits depth of cure
How do you compensate for limited depth of cure and what is another advantage of this?
To compensate for limited depth of cure, cure using increments.
This also reduces setting shrinkage (typically 2-4% shrinkage).
(when monomers join together to form the polymer, they get closer together. Thus, less gaps = shrinkage).
What are the properties of composites?
- Poor compressive strength (weakest after amalgam, dentine and enamel).
- Relatively high tensile strength (stronger than enamel)
- Can have a good adhesive. bond to enamel and dentine
- Good aesthetics
- Moderate wear resistance (but can be worn by opposing teeth)
- Staining (at margins or at rough surface)
- Shrinkage of 2-4% during polymerisation, with shrinkage reduced by increased filler (causes lower coefficient of thermal expansion though)
- Water sorption (leads to deterioration)
What is the composite bond strengths to enamel and dentine?
Enamel - 20-30 MPa
Dentine - 3-11 MPa
What layer can impact the bonding of a restoration material?
Smear layer
- Tissue debris over the tooth surface when tooth tissue is cut. Contains debris produced by reduction or instrumentation of enamel, dentine or cementum.
It is calcific in nature and obstructs the bonding of restoration material with underlying tooth tissue.
What is the hybrid layer in composite restorations?
Area which the resin of restorative material has interlocked with collagen of dentine by providing micromechanical retention.
What acid does etch contain?
Function of etch?
Phosphoric acid 36%
Increases surface area for bonding
What does enamel bonding agents contain?
Enamel bonding agents (e.g. Bis-GMA) consists of unfilled resin and is extremely moisture sensitive.
What do dentine conditioners do?
Dentine conditioner (acid/conditioner) remove/dissolve smear layer by removing most of the hydroxyapatite and expose a microporous network of collagen resulting in diffusion-based bonding.
Conditioned dentine surface is difficult to wet with bonding agents
> Primers increase the surface free energy (wet) dentine
> Primers increase the wettability of dentine surface which allows the resin to spread and penetrate the tubular dentine
> Improving the bonding of the subsequently applied adhesive resin
> The resin used in them are hydrophobic
What do dentine bonding agents do?
Form a link between the resin primer and the restorative material .
Form resin tags in dentine tubules.
Stabilise the hybrid layer.
What is Glass Ionomer cement?
Acid-base cement material composed mostly of glass filler particles in a polymer matrix.
What are GIC’s used as?
- A restorative material, mainly for where moisture control is difficult.
- For wear cavities close to gingival margin
- Lining material under amalgam and composite (lining/base)
- Luting material (attaches prosthesis to tooth structure).
- Temporary restoration
- As pit and fissure material (e.g. Fuji Triage)
- As permanent direct restorative material in primary and permanent teeth.
What is the composition of GIC? (4) (2 additionals)
- Polyacid (typically polyacrylic acid)
- Glass filler particles (silica-alumina-calcium fluoride flux)
- Tartaric acid - initially retards the setting, so viscosity is lower for longer, followed by a much more rapid set (snap set).
- Water - needed to initiate the process.
Additional/minor components in GIC glass fillers are:
> sodium and aluminium fluoride (act as a fluoride source)
> calcium and aluminium phosphates (act as a fluxes)
What is snap-set of GIC due to?
Tartaric acid
Extends working time
Shorter setting time
How does GIC set?
- Dissolution
- Polyacrylic + water –> poly acid
> Dissociates so hydrogen ion are released.
> H+ ions attack the glass filler particles and cause them to start to dissolve.
> Ions of Na, Ca, Al, F ions dissolve leaving a layer of silica outside the filler particles, but Zn does not get released when GIC sets.
> When F- ions leach out the GIC, hydroxyl ions replace them. - Gelation
- Ca2+ released from dissolution cross-link the negatively charged polyacid chains
- Ca2+ is divalent, and so 2 polyacid chains to 1 Ca2+ ion. - Hardening
- Al3 are also released from dissolution stage
- Al ions are released more slowly than Ca ions and so Ca ions initially link polyacid chains.
- Al is trivalent and so can displace the Ca ions - linking 3 polyacid chains per 1 Al ion.
What is the role of tartaric acid in GIC?
It is a chelator, so can sequester other ions, removing them from other chemical reactions.
Chelates Ca2+ during dissolution phase.
Make it less likely that polyacid chain will be linked by Ca ions compared to Al ions.
Makes gelation phase shorter and hardening phase occur more quickly.
What are properties of GIC?
- GIC releases fluoride. Hydroxyl ions replace the fluoride ions which leach out.
- It is an initial burst of high fluoride release, followed by a longer low release.
- Fluoride reservoirs can be topped up by exposure to fluoride in the mouth.
- Setting reaction takes up to 7 days to be complete, therefore varnish use to protect GIC
How does GIC adhere to enamel and dentine?
- Hydrogen bonding to collagen (dentine)
- Bonding direct to hydroxyapatite via calcium
What is the relative compressive strength + tensile strength of enamel, dentine, composite and GIC?
Compressive strength:
1. Amalgam (400-500 MPa)
2. Dentine (300 MPa)
3. Enamel (260 MPa)
4. Composite (180-200 MPa)
5. GIC (120-140 MPa)
Tensile strength
1. Dentine (100 MPa)
2. Amalgam (50 MPa)
3. Composite (40 MPa)
4. Enamel (10 MPa)
5. GIC (5 MPa)
What is macroscopic vs microscopic mechanical retention?
Macroscopic = undercuts
Microscopic = etching
How do conditioners, primers and sealers help with resin-based composite dentine bonding?
- Condition: cleans, opens tubules and dissolves hydroxyapatite exposing collagen.
- Primer: (M-S-R) methacrylate-spacer-reactive, they are dissolved in a solvent.
- Sealer: unfilled or lightly filled resin, wets the surface of the dentine.
Can get combined conditioners and primer ‘self-etching primer’ = two stage bonding.
What are mucostatic impression materials?
Materials that don’t compress the soft tissues e.g. Alginate.
Mucostatic impression is an impression taken with the mucosa in its resting state. It provides a good fit at rest and therefore good retention.
What is mucocompressive materials?
Mucocompressive impressions are an impression taken when the denture-bearing area is subjected to compressive force.
This reults in a denture that is maximally stable during function but not at rest.
What are rigid imp materials vs elastic materials?
Rigid materials cannot engage undercuts, only used for complete dentures.
Elastic materials can engage undercuts.
- Hydrocolloids: agar and alginate
- Elastomers: polyether, silicones and polysulfides.
How does condensation cured and addition cured silicones set?
Condensation cured, requires activator (TES, get a small alcohol by-product due to OH terminal groups)
Addition cured, required platinum catalyst and silanol, produces no by-product due to C=CH2 terminal groups.
What are 2 different types of fissure sealants?
- Resin based materials
- Light cured = bis-GMA/UDMA based with diluent
- Auto-cured = methacrylate based - GICs: both conventional and resin-modified (auto-cured)
What are properties of fissure sealants?
- Longevity (lasts 5-7 years)
- Newer materials show improved retention
- No clear advantage of fluoride release
- Failure most likely to happen within a year of placement
How much does Fl Varnish reduce caries risk?
Produces a mean reduction in caries of 37% in primary teeth and 43% in permanent teeth if applied >2 times/year.
Can arrest existing lesions on the smooth surface of primary teeth and roots or permanent teeth.
How can you apply fluoride varnish?
Dry teeth with cotton wool rolls/3 in 1 syringe
Apply a small amount of fluoride varnish with microbrush to pits, fissure and carious lesions.
What post-treatment advise do you give after fluoride varnish?
Avoid eating, drinking and rinsing for 30 minutes.
Eat only soft food in the following 4 hours.
Brushing can recommence on the day following application.
What are contraindications of fluoride varnish?
- Ulcerative gingivitis
- Stomatitis
- Asthma
What is the composition of stainless steel?
- Iron - bulk component
- Carbon - helps increase in strength but can make more brittle (0.25%)
- Chromium - becomes corrosion resistant - passivation (11%)
- (Nickel) - stabilises structure at room temperature
What is Panavia?
A self-dual curing resin-based adhesive.
Used for crown and bridge, veneers, inlays and onlays.
It can stick anything to pretty much anything.
What can Panavia adhere to?
- Metals and alloys, including titanium and amalgam
- Metal oxide ceramics, including zirconia
- Silicate ceramics
- Composites
What are the properties of panavia?
- Radiopaque (contains barium glass)
- Heavy filled (large particle sizes)
- Has a film thickness of 24 ym
- Leaches fluoride
- May be auto-cured or light-cured.
Zinc phosphate cement:
1. indications
2. contraindications
3. composition
- cementing metal crowns and bridges of non-vital teeth.
- cavity liner
- cementing metal crowns and bridges of non-vital teeth.
- Vital teeth (acidic)
- Ceramic restorations
- Exothermic set
- Solubility, may dissolve
- Vital teeth (acidic)
- Zinc oxide + phosphoric acid.
Zinc polycarboxylate cement:
1. indications
2. contraindications
3. composition
- Metal crown and bridges
- Porcelain restorations
- Antibacterial cavity liner - Titanium restorations
- Zinc oxide + polyacrylic acid
GIC (Fuji) cement:
1. indications
2. contraindications
3. composition
- Metal, porcelain and ceramic restorations.
- Fissure sealants
- Cavity liners
- Erosion lesions - Liner must be placed close to the pulp
- low fracture toughness and brittle - Polyacrylic acid, Glass Silica flux, Water, Tartaric acid.
RMGIC cement:
1. indications
2. contraindications
3. composition
- Lining cement
- Cavity liners
- Able to bond to composite - All ceramic crowns and veneers
Zinc Oxide Eugenol cement:
1. indications
2. contraindications
3. composition
- Temp-bond - Temporary crowns and bridges.
Cavity liner
Pulp soother. - Weakest of cements. Low strength and soluble.
- Zinc Oxide + Eugenol
Resin cement:
1. indications
2. contraindications
3. composition
- Indirect restoration of crowns, inlays, onlays.
- High tensile strength, least soluble, high micromechanical bonding. - Unable to use if ZOE was temp material.
- Must be light cured
- Possible pulp irritant.
- Metal posta nd core - Panavia (MDP + y MTPS) Dual cured resin
M - S - R
Modified ZOE cement:
1. indications
2. contraindications
3. composition
- Cavity bases
- Do not adhere chemically to tooth
- Zinc oxide + eugenol + MMA + hydrogenated resin
When would you use setting CaOH and non-setting CaOH as a pulp cap?
- Setting calcium hydroxide (life) is used as an indirect pulp cap if cavity is very close to pulp.
- Non-setting calcium hydroxide is used for direct pulp capping.
Calcium hydroxide is pH 11, bacteriostatic as it absorbs the CO2 of pathogens. Promotes the formation of calcified barrier.
How does CaOH act as a pulp cap?
Calcium hydroxide is pH 11, bacteriostatic as it absorbs the CO2 of pathogens.
Promotes the formation of calcified barrier.
Why should zinc phosphate not be used on vital teeth?
It is a pulpal irritant due to pH 2-4.
How does ZOE act as a pulp soother?
90% zinc oxide + 10% magnesium oxide = powder.
Eugenol mixed with oil = liquid.
Antibacterial and pulpal soother as pH 6-8.
Inhibits resin setting so cannot be used with composite or to cement indirect with resin-based cements.
Used base under filling materials, soothing temp filling and indirect pulp capping.
What is the composition of porcelain?
- Kaolinite
- Quartz (SiO2)
- Feldspar
- Borax reduces melting temperature, with metal oxides used for opacity. Has low thermal conductivity which is good for pulpal health but may lead to stress and fractures.
Alginate
- composition?
- use?
A. irreversible hydrocolloid
B. impression material
Alveogel
- composition?
- use?
a. Butamben, iodoform, and eugenol
b. dry socket medicament
Amalgam
- composition?
- use?
a. 42% amalgam, 59% silver, 13% copper, 28% tin
b. restorative material
Aquacem
- composition?
- use?
a. GIC: calcium-aluminium-fluoro-silicate flux, polyacrylic acid, tartaric acid, water
b. Luting material for crowns and bridges
Clearfil
- composition?
- use?
a. Dual-cure composite cement
b. cementation of restorative work
Corsodyl
- composition?
- use?
a. Chlorhexidine digluconate 0.2%
b. - antibacterial and plaque protective
- thrush, trauma, hygiene and ulcers.
Duralay
- composition?
- use?
a. quick cure lab pattern resin
b. tapered and telescope crowns
Duraphat
- composition?
- use?
a. 50 mg/ml 2.26% (22,600ppm NaF)
b. Fluoride varnish for high caries patients
EDTA (glide)
- composition?
- use?
a. 17% EDTA + carbamide peroxide in water soluble base.
b. - Cleans and lubricates dental canals
- Effervescent properties with NaOHCl
- Chelating agent
Etch
- composition?
- use?
a. 37.5% phosphoric acid
b. improves micromechanical retention of materials to enamel and dentine.
Delton
- composition?
- use?
a. GIC light cured
b. Fissure sealant
Fuji II
- composition?
- use?
a. Radiopaque light cured reinforced GIC
b. Class III and IV restorations
Hypocal
- composition?
- use?
a. non-setting calcium hydroxide
b. cavity lining
- direct pulp and indirect pulp capping
- pulpotomy
- induced closing root apex
Kalzinol
- composition?
- use?
a. Zinc oxide eugenol cement.
b. - base under fillings (pulpal soother)
- temporary seal for medicament dressing
- indirect pulp capping
Ketac
- composition?
- use?
a. GIC (calcium-aluminium-fluoride-silicate), tartaric acid, polyacrylic acid, water.
b. Class III and V fillings and temp restorations
Ledermix
- composition?
- use?
a. calcium chloride and zinc oxide.
- Demeclocycline hydrochloride: An antibiotic
- Triamcinolone acetonide: An anti-inflammatory corticosteroid
b. Pulpitis prophylactic treatment.
Acute pulpitis and acute periodontitis.
Life
- composition?
- use?
a. Setting CaOh
b. direct and indirect pulp-capping
cement base for amalgam restorations
MTA
- composition?
- use?
a. mineral trioxide aggregate
b. strong impermeable barrier for apexification as root-end filling.
root perforations
Oraseal
- composition?
- use?
a. caulking paste
b. applied when need rubber dam seal
Panavia F.20
- composition?
- use?
a. Dual-curing resin-based cement.
Contains HEMA, 5-NMSA and MDP
b. cementing metal, composite and silanated porcelain.
Point 4
- composition?
- use?
a. light cured resin-based composite
b. direct restorations
Zinc polycarboxylate
- composition?
- use?
a. Zinc oxide + magnesium oxide + polyacrylic acid
b. cementation of crowns, bridges and inlays.
cavity lining and temp filling in primary teeth
requires CaOH liner due to exothermic set
Telio
- composition?
- use?
a. monomer matrix of methacrylate. fillers are silicone dioxide and copolymers
b. temporary filling material
Tempbond
- composition?
- use?
a. self-curing zinc-oxide eugenol
b. temporary cement
Retraction cord
- composition?
- use?
a. 15.5% ferric sulphate
b. tissue managment
Tubliseal
- composition?
- use?
a. zinc oxide eugenol (radiopaque)
b. root canal sealer
Viscogel
- composition?
- use?
a. plasticised acrylic containing ethyl alcohol
b. tissue conditioner, temporary soft denture liner
Zinc phosphate
- composition?
- use?
a. zinc oxide + magnesium oxide. phosphoric acid liquid.
b. cement for crowns and bridges.
can cause pulpal irritation.
cavity lining under amalgam.
