Materials Science Flashcards
Aprismatic enamel can be found where?
25 micron layer on the surface of the tooth
What type of etch pattern is poor for retention?
Type 3 - irregular
What is the bond strength between enamel and resin?
20-25 MPa
What are the organic components of dentine?
Collagen
Proteins
Chondroitin Sulphate
Mucopolysaccharide
As you get deeper into dentine, what do you expect to see?
Denser Tubules: therefore more moisture
Secondary and Tertiary dentine
What are the 3 sources of moisture on dentine?
Triplex
Oral Humidity
Dentinal Tubules
What is in smear layer?
Tooth fragments Organic matter Bacteria Blood Crevicular Fluid Saliva Collapsed Collagen
How large is the ion-exchange layer in GIC?
0.5-1 microns
What is the main ingredient for wet bonding primers?
Acetone- used to chase water
Why is acetone based primers less effective?
Overwet dentine causes water blisters
Water is trapped between dentine and resin
Poorer physical properties
Very technique sensitive
HEMA creates a bond between dentine and adhesive resin. Which functional group of the primer bond with the dentine surface?
-OH Group
T/F: 1st generation adhesives had bonding to both enamel and dentine
False: enamel only
T/F: 5th Generation Adhesives is a 2-step resin with Self Etch/Prime + Adhesive
False, 5th generation is Total Etch with combined Primer/Adhesive
Which generation is 3 step Etch-and-Rinse adhesive?
4th Generation: Etch > Primer > Adhesive
What is an example of a 8th Generation universal adhesive?
G-Premio
G-Bond is an example of what generation adhesive?
7th Generation: combined self etch/primer/adhesive
T/F: Monomers (BIS-GMA, UDMA, TEGDMA) all have double carbon bonds at both ends
True
T/F: HEMA is exclusively hydrophilic
False - HEMA has both hydrophobic and hydrophilic ends but is overall hydrophilic
Why is self etch less effective than total etch?
pH is higher (1-2) vs total etch (pH 1), so smaller resin tags are created
What is considered a gold standard adhesive?
4th Generation 3 step.
What are the 3 components of a self-etch primer?
Adhesive Group that creates bond to dentine and enamel
Spacer Group: influences flexibility, solubility, wetting behaviour
Polymerizable Group
Microscopically what would a mild pH self-etch (pH 2) result in
Remaining resin impregnated smear layer
Shallow resin tag formation
Why might phase separation of adhesion occurs
Ingredients in all-in-one adhesives are inherently unstable
Excessive water content causes separation of bis-GMA and HEMA
What factor could affect permeability of the hybrid layer?
Trapped air bubbles
What is a main difference in ingredients of a 7th generation adhesive
No HEMA: 4-MET monomer used instead (G-Bond)
What monomers are used in G-Premio and what sort of bonding is it?
4-MET, MDP, MDTP
Chemical Bonding
What are the steps to apply G-Premio?
Total etch: Etch with 37% H3PO4 for 15s; Self-etch: no etching
Apply G-Premio to all surfaces and leave for 10 sec
Dry for 5 sec at MAX air pressure
Light cure for 10 sec
Apply resin composite
What operator aspects would make G-premio preferential for treating hypersensitivity?
- One Step
- No wash steps required
- Better Patient Comfort
What is the main difference between 5th and 6th generation Adhesives?
5th Generation: Total Etch + Primer/Adhesive combination
6th Generation: Self Etch/Primer combination + Adhesive
What are problems with etch-and-rinse adhesives (4-5th Generation)?
- Incomplete infiltration of primer into demineralized collagen
- Long-term water sorption into the hybrid layer with HEMA based adhesives
What are problems with self-etch adhesives (6-7th Generation)?
- Formation of water blisters at the resin/ dentine interface
- Semi-permeable membranes
- Greater failure rates and poorer bonding strengths than etch-and-rinse adhesives
What is an example of an adherent?
Resin Composite, Acrylic, Ceramic
What is an example of an adhesive?
Adhesive Resin, Silane Primer
What is an example of an adherend?
Enamel, Dentine, Ceramic
Define Macromechanical bonding
Visible interlocking between dissimilar materials
Define Micromechanical bonding
Microscopic mechanical interlocking between dissimilar materials
How would you repair a fractured ceramic crown with CR?
Roughen porcelain surface - 24% hydrofluoric acid . Use silane bonding agent to bond porcelain to CR (as silane can bond resin cements to ceramic)
What are the 4 types of adhesion in dentistry?
Macromechanical
Micromechanical
Interfacial
Chemical
How would you repair exposed metal on a fractured PFM (Porcelain Fused to Metal) crown?
Sandblasting then Metal Primer
What is interfacial adhesion?
A broad term describing adhesion between two very dissimilar materials, and is a combination of mechanical and chemical adhesion
What are the 4 layers in a metallic crown?
- Gold Alloy + Underlying Metal Primer
- Resin Cement
- Dentine Primer/Adhesive
- Enamel / Dentine
What are the 4 layers when doing a Ceram-Metal Bridge?
- Ceramic Crown + underlying silane layer
- Resin Cement
- Primer / Adhesive
- Enamel
What is a metal primer and why is it needed?
Bi-directional bonding to both:
- Resin Bond via carbon double bonds to vinyl/methacrylate groups
- Metal Bond via a carbonyl (double oxygen bond) group
What is adhesive failure?
Breakage of bond between the materials
What is cohesion failure?
Breakage within the material themselves
What are the 6 conditions for optimal adhesion?
- Large surface area
- Clean bonding surfaces
- Close contact between surfaces
- Good wetting of adhesive - needs low viscosity to flow
- Dimensionally stable adhesive
- Correct protocols for bonding
What stimuli can cause dentinal hypersensitivity?
Thermal Evaporative Tactile Osmotic Chemical
What is the most common area for dentinal hypersensitivity?
Buccal aspects at the cervical regions of permanent teeth
What are 4 clinical causes of dentinal sensitivity?
- Tooth Wear
- Recession
- Periodontal Disease
- Periodontal Therapy
Which occupation in Australia is at high risk for dentinal hypersensitivity?
Wine Tasters (79%) #firstworldproblems
What are the 2 categories of treatment options for dentinal hypersensitivity?
- Tubule occlusion by adhesion of exogenous materials
2. Modification of nerve excitability
How does Potassium Nitrate (Sensodyne) modify nerve excitability to reduce dentinal sensitivity?
High K+ ions outside nerve membranes blocks repolarisation phase of AP, thereby blocking pain impulse
Which exogenous materials aid in remineralising exposed dentinal tubules in the treatment of dentinal hypersensitivity?
- High concentration Fluoride dentifrices
- Bioglass (Si gel > CaPO4 > Hydroxyapatite)
- RMGIC/GIC restorations
- Tooth Mousse Plus
Which exogenous materials aid in physically occluding exposed dentinal tubules in the treatment of dentinal hypersensitivity?
- Stannous Fluoride
- Resin Sealants
- CR/RMGIC/GIC Restorations
- Arginine
What are 2 high risk groups for Dentinal Hypersensitivity via Tooth Wear?
Patients with GORD
Wine Tasters
Dentine is porous biomaterial that contains numerous tubules filled with fluid. How do tubule diameter and density change from superficial to deeper dentine?
Tubules increase in diameter and increase in density.
What are the 3 dentinal hypersensitivity theories?
- Dentinal Receptor Theory (debunked)
- Odontoblast Transducer Theory (debunked)
- Hydrodynamic Theory
Dentinal hypersensitivity is a common conditions that can present management dilemma to clinicians. What type of treatment is considered most common and conservative but effective in its management?
Frequent home application of toothpaste (Sensodyne, Stannous Fluoride)
What are 3 prevention measures for minimising dentinal hypersensitivity?
- Remove causal factors (Tooth Wear, Erosion, Gingival Recession)
- Analysis of Dietary / Lifestyle factors / Medications
- Salivary Protection
How does Duraphat work in the mouth?
Deposition of CaF2 globules on the tooth surface within a resin layer at neutral pH.
When pH lowers and becomes acidic Hydroxyapatite is formed
What is an example of a nanofil composite resin?
Filtek Supreme
What are 4 factors associated with the cavity prep that can affect adhesion to tooth structure
- Smear Layer
- Cavity Size
- Moisture
- Foundation of bonding substrate
What are desirable properties for a resin composite?
- Aesthetics
- Durability
- Ease of Handling
- Low Shrinkage
- Wear Resistance
- Radiopacity
- Anticariogenic (Fluoride Release)
- Biocompatibility
What were the key properties of first generation posterior CRs in the 1960-80s?
Macrofils - to give strength and durability
- Poor Aesthetics
- Hard to Polish
What are the features of current generation of “universal” resin composites?
- Nanohybrid/Nanofil resins
- Low shrinkage formulations
What do monomers become when light cured?
Polymers
What is an example of an interfacial phase in a Resin Composite?
Silane Coupling Agent
What are the components of a nanofil resin composite such as Filtek Supreme?
- Larger Nanocluster Particles: agglomerates of Zr/Si nanoparticles fused together
- Nanomers: SiO2 particles
- Resin: BisGMA, UDMA, TEGDMA, PEGDMA (low shrinkage)
- Silane: coupling agent fills up porous areas
What are indications for Flowable resin composite?
- Suitable in non-load bearing areas
- Repairing old resin composites
- Fissure Sealant
- Filling voids
What are indications for Packable resin composites?
Adaptation to tight proximal tooth contacts
What are the properties of packable resin composites?
- Higher average filler content (80%)
- Larger filler particle size
- High Compressive Strength
- High Wear Resistance
- Prone to surface roughening
- Poor Polish Retention
What is required for a polymer to be formed?
- Monomer
2. Free radical: that is produced either by light, heat or a chemical reaction
What are the 4 stages of a polymer reaction
- Initiation Stage
- Propagation Stage
- Transfer Stage
- Termination Stage
What is there less polymerisation shrinkage in bulk fills?
The monomer chains are far larger, since there are less monomer molecules overall, the % of polymerisation is less
What is elastic modulus?
Defines a material’s rigidity.
Elastic Modulus = Stress / Strain
What is the elastic limit?
The point where the material loses its elastic capacity to bear stress.
(The point on the True Stress-Strain Curve when parabolic curve becomes linear)
When does Post-Gel Shrinkage Strain occur?
Occurs after the material has lost its ability to flow. It typically occurs up to 24 hours after light curing
Which direction does Polymerisation shrinkage occur?
Shrinkage occurs towards the light source
How do you clinically prevent problems with polymerisation shrinkage?
Opposite layering of CR and incremental light curing
What is Compressive Strength?
Ability of materials to resist a load that tend to shorten/compression it
What is Tensile Strength?
Ability of material to resist load to elongate/stretch it
When is diametral tensile strength tested?
When the material is brittle and can’t be gripped by normal tensile strength tests
What is flexural strength?
Ability of material to withstand bending/flexural stress without it breaking
What is the difference between 2 and 3 body tooth wear
Presence of a 3rd body at the interface: food, toothpaste, tooth chips, F, CPP-ACP particles
What are examples of extrinsic erosive substances?
1) Carbonated Drinks (Carbonic/Phosphoric acids)
2) Citric Acid
3) Sour Candies (Citric/Malic Acid)
What are examples of intrinsic erosive substances?
Stomach acid via GORD or induced vomiting
What are the classic symptoms of GORD?
Acid Regurgitation
Heartburn
What is GORD?
Gastroesophageal Reflux Disease (GORD): Condition where the reflux of stomach contents causes troublesome symptoms and complications
Why is sleep reflux worse than normal reflux?
Far more extensive damage due to high duration of contact of acids and lowered Defense Mechanisms during sleep
1) Decreased Salivary Flow during sleep
2) Decreased heartburn: conscious trigger to deal with the reflux
3) Decreased Swallowing
4) Decreased Esophageal Peristalsis response
What are 3 manifestations of prolonged GORD?
Reflux Esophagitis (Mucosal Erosion)
Barrett’s Oesophagus
Oesophageal Adenocarcinoma
How does Barrett’s Oesophagus manifest?
Constant insult causes metaplasia of respiratory epithelium to transition to intestinal mucosa - with the presence of infolding and goblet cells
Oesophageal Adenocarcinoma is a progression of what?
Barrett’s Oesophagus: ongoing metaplasia causes neoplastic differentiation. This has a poor prognosis neoplasm with high risk factors for males over 60 and patients that are obese.
Would CPP-ACP or Fluoride dentifrices be effective for sleep GORD?
Unlikely, sleep reflux often results in pH drops below 1. CPP-ACP / Fluoride are effective defenses when acid attacks are with the caries range of pH 4-5, with some limited defense at pH 3.
What are the main ways to treat oral aspects of GORD
1) Remove the Cause
2) Medical Management
3) Control adjunct Tooth Wear aspects - construct a nightguard
4) Reinforce Oral Defenses: retain biofilm overnight, increase saliva, remineralisation agents
5) Defer restorative treatment until erosion is resolved
Which tooth material is easiest to bond to?
Prismatic Enamel that is not affected by quantitative defects such as fluorosis/hypoplasia
What is cementum hard to bond to?
High organic component formed by extrinsic and intrinsic fibres
Is it harder or easier to bond to dentine the deeper you go?
More difficult: high density of dentinal tubule meaning increased dentinal fluid and moisture
What 4 factors of cavity preparation will influence the success of bonding?
1) Presence of moisture
2) Resistance and retention
3) Removal of smear layer + pellicle
4) Poor foundation of the bonding substrate (eg retained infected dentine)
Why is Aprismatic enamel harder to gain retention to restorative materials
Surface is more resistant to etching - erodes whole layer rather than creating porosities for resin tags
How much enamel is removed by 37% orthophosphoric acid etching?
10-20 microns of enamel
What is the bond strength between enamel and GIC?
10-12 MPa
What is the bond strength between enamel and RMGIC?
15-20 Mpa
What is the difference between dry and wet bonding with primers
Wet Bonding: dentine is not desiccated and primer displaces water to support collagen
Dry Bonding: fibres are rehydrated and stiffened by the hydrophilic primer
Why is wet bonding no longer preferential for primers?
1) Technique Sensitive
2) Acetone content evaporates from containers if not used regularly
3) Overwet dentine increases risk of water blisters
4) Poorer physical properties, leading to weaker bonds
What is the long term disadvantage of dry bonding primer?
Moisture sorption from HEMA over the long term breaks down the hybrid layer
What are the 3 main reasons for microleakage?
Moisture Contamination
Insufficient Dentine Etch
Polymerisation Shrinkage
What is nanoleakage?
Submicron channels that allow passage of fluids - this can happen in both wet and dry bonding techniques
What is the difference between adhesive and cohesive failure?
Adhesive: failure in bond between materials
Cohesive: failure in material themselves
