Hard stuff Flashcards

1
Q

Define alloy, and explain how the strength of dental amalgam is affected by different components of alloy

A
  • Alloy: a metal made by combining two or more metallic elements, especially to give greater strength or resistance to corrosion
  • Spherical alloys: require less mercury/ smaller surface area easier to wet
  • Admixed alloys: require more mercury/ lathe-cut particles more difficult to wet
  • Low copper alloys: has a gamma 2 reaction. This makes it weak and soft. It corrodes fast, and corrosion yields Hg which reacts with more gamma 2.
  • High copper alloys: Reduces creep and prevents gamma-2 formation.
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2
Q

Interpret characteristics of different types of Composite Resin

A

Microhybrid Composite Resins:
• Stronger than microfilled
• Can be used in both anterior and posterior teeth
• Most have medium viscosity

  1. High-viscosity packable Composites
    • Filler particles - 80% in volume
    • Indicated for the re-establishment of the contour and proximal contacts in Class II
    • Due to its high viscosity, subject to layering problem, one increment may not completely join into another leaving gaps and porosities
  2. Low-viscosity: Flowable Composites
    • Filler particles - 50% in volume
    • Inferior mechanical properties
    • Greater degree of polymerisation shrinkage

Nanofilled Composite Resins:
• Consist of nanomers and ‘nanoclusters’ as the fillers
• Nanoclusters are clusters of primary zirconia/silica nanoparticles fused together at points of contact, and the resulting porous structure is infiltrated with silane

Nanohybrid Composite Resins:
• Nano-sized particles in CR formulation
• Composites present similar mechanical and physical properties to those of microhybrid
• Better polish and gloss retention than microhybrid

Bulk fill composites:
• Developed to speed up placement process
• Can place one large increment and cure
• Depth of cure is 4mm or more (light can reach that deep)
• To achieve this, manufacturers have increased the translucency or reduced the amount of filler or change the chemical make up
• Has limitations on proximal box of Class II cavities: more than one increment should be used in proximal box
• Polymerisation shrinkage has been reduced by adding special modifiers
• Shrinkage about 1.3% to 2.4%
• May need to be covered by a nanocomposite to achieve aesthetics and wear resistance
• Shades are limited

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3
Q

Describe the following properties of composite Resin:

  • Biocompatibility
  • Degree of conversion
  • Water sorption
A

Biocompatibility:
• Newly placed composite can release chemicals. This can diffuse through dentinal tubules into pulp causing an inflammatory reaction
• Unbound monomers can be dissolved out by water or solvents in the diet, degrading overtime
• Bisphenol A, a polymer in some composites and fissure sealants, may induce cellular changes
• By product of polymerisation may cause soft tissue reaction resemble lichen planus – lichenoid reactions

Degree of conversion:
• Degree of conversion indicates the percentage of carbon-to-carbon double bonds that have undergone conversion to single bonds during polymerisation
• The higher the rate of conversion, the physical and mechanical properties improve which will be stronger and resist wear better

Water sorption:
• Water causes some hydroscopic expansion of the composite over the first week after placement
• The resin matrix absorbs water from the oral cavity over time
• The greater the resin content, the more water is absorbed
• Microfilled and flowables tend to have greater water sorption
• Water softens the resin matrix, leads to degradation of restoration

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4
Q

What is the purpose of a primer? Describe what it’s made of, and it’s bonding mechanism.

A
  • The primer contains hydrophobic and hydrophilic methacrylate monomers copolymerizes with the adhesive which is unfilled resin
  • The primer bonds to both dentine and resin
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5
Q

What are issues with self etch?

A
  • Is the enamel adequately etched?
  • Dissolved calcium and phosphate ions in the adhesive attract more water than the 3 step adhesives: ↓ resin-dentine bond
  • Acid in etch & rinse and self-etch bonding agents can activate matrix metalloproteinases (MMP’s) in dentine which results in the breakdown and loss of collagen fibres within the hybrid zone
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6
Q

What factors that determine the shade of composite resin?

A

Translucency

Opacity

Type and intensity of illumination

Metamerism

Contrast

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7
Q

Define:

  • Value
  • Chroma
  • Hue
A
  • Value: is the degree of lightness or darkness of a colour (Black has value zero, and pure white has value 10)
  • Chroma: Strength or intensity of a colour (For example, lemon yellow has a high chroma, while a banana yellow has lower chroma)
  • Hue: the types of colours in the wheel
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8
Q

Define:
Centric occlusion
Lateral occlusion

A
  • Centric occlusion: ideally upper and lower teeth are in contact. Teeth are in contact uniformly and with equal pressure. It is in its habitual position “feels right”
  • Lateral excursion or movement: mandibular movements - left and right from centric occlusion
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9
Q

List indications for polishing dental restorations

A
  • Detected by radiographs
  • Dental floss fraying
  • Patient complaining of ‘food impaction’
  • Gingival tissues appear inflamed in the area
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10
Q

Compare setting reactions of different types of Glass Ionomer Cement

A

Auto-cure
Stage 1: Dissolution (immediate – minutes)
• Hydrogen ion from the polyacrylic acid attacks the glass surface
• Calcium/ Strontium, aluminium and fluoride are released

Stage 2: Precipitation (minutes – 24 hours)
• Calcium/ Strontium and aluminium ions binds to polyanions
• The calcium chains form first, producing a clinically early set within 4-10 minutes, but they are relatively fragile and highly soluble in water
• The aluminium chains form over the next 24 hours which are strong and insoluble, providing the major physical properties of the GIC

Stage 3: Hydration (24 hours – months)
• Cross-links continue to develop and are progressively hydrated making them more rigid

Light initiated autocure:
• A red dye (ferric oxide) is incorporated in the glass ionomer.
• After irradiation from the halogen light , the acid-base reaction – already on it’s way- will take place more rapidly.
• The pink shade absorbs heat energy easily, which accelerates the setting
reaction to 40 sec, compared with 1 min 40 sec without light
• The material is light-activated, but there Isn’t any resin
• Is highly bactericidal due to a high fluoride release
• Can be used as fissure protection, root surface protection or as a lining material

Light- cure
Resin-Modified Glass Ionomers sets partly
• An acid- base reaction between polyacrylic acid and Fluoro -aluminosilicate glass
• Photo- initiated polymerisation of HEMA monomer by camphoroquinone
• Oxidation- reduction reaction polymerisation of HEMA monomer

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11
Q

Recognise new technologies and products available (poly-acid composite resin).

A
  1. “Compomer”
    • A compomer is a composite resin that uses an ionomer glass
    • It has a small quantity of dehydrated polyalkenoic acid that is incorporated with the filler particle
    • The acid-base reaction doesn’t occur until for some time after placement so it is not possible for a compomer to bond to tooth structure through an ion exchange mechanism
    • Small fluoride release sometime after placement but no ion exchange layer
    • Not heavily filled with filler particles, resistance to wear is low, should not be used on heavy occlusal load
  2. Giomers:
    • A hybrid material: glass ionomer and composite. It is resin-based with pre-reacted glass ionomer particles (PRG).
    • Claims to have properties of GIC such as fluoride release, fluoride recharge and Composite such as excellent aesthetics, easy polishability
    • Allows ion releases and recharge, neutralise acid contact
    • It requires etching and resin/primer for placement
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12
Q

State and describe the coats used on GIC

A

Vaseline:
* Prevents water and saliva contamination to GIC during first 24 hours of treatment

GC Fuji Coat:

  • Protects GIC against humidity and dehydration, and gives it a smooth glossy surface
  • 10 seconds

G-Coat Plus:
* Self etching, enabling strong adhesion to tooth surfaces surrounding restorations

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13
Q

Examine the setting mechanism of Composite Resin

A
  1. Initiation: Initiate through light curing, chemical curing or dual cure
  2. Propagation:
    ○ The resin monomers bis-GMA have double carbon to carbon bonds
    ○ When the monomers are attacked by the initiators, the carbon-to carbon bond splits
    ○ When the bond splits, the molecule is left with a carbon-carbon single bond and a free radical
  3. Termination
    ○ The now single bonded carbons causes the monomers to bond to other monomers
    ○ They continuously bond and add to the polymer chain
    ○ Each linkage leaves a free radical available for further reaction
    ○ However, not all monomers are converted to polymers
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14
Q

List 2 types of paste to paste formulations, and describe them.

A

Fuji Lining LC Paste Pak
• Dispensed in right ratio

Vitrebond Plus LC

Description:
• RMGIC
• Liner in Paste/Paste formula • Wash and dry cavity, no need to condition
• Manufacturer’s instructions state that the use of polyacrylic acid conditioner results in decreased adhesion of Vitrebond Plus LC
• Cure for 20 secs

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15
Q

What is a EQUIA system?

A
  • Combines the characteristics of Fuji IX Extra and G-Coat plus
  • G-Coat plus can infiltrate the GIC surface, thus filling cracks and porosities
  • The newest ones are EQUIA Forte Fil and EQUIA Forte Coat
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16
Q

Describe EQUIA Forte Fil and EQUIA Forte Coat

A

EQUIA forte fil
• Glass Hybrid technology: enhanced physical properties for superior wear resistance, fracture toughness and durability
• Conventional glass particles + ultrafine highly reactive glass particles
• High molecular weight polyacrylic acid which increases ion availability to make the matrix stronger
• Stronger than Fuji IX extra

EQUIA Forte Coat
• Stronger than G-coat because of a new chemistry that polymerises to produce a tougher resin matrix
• Produces smooth surface finish and high lustre coating
• Toughens, protects and polishes

17
Q

Describe Fuji VIII

A
  • Auto-cure, resin reinforced GIC
  • Resin content is 9% by weight; Fuji II is about 4-5%
  • Resin reinforced helps to improve bond strength
  • Heat can accelerate setting
  • Less viscous than Fuji IX
  • Cannot polish until 6 minutes after mix
  • Used in sandwich technique
18
Q

Describe Fuji bulk

A
  • Conventional GIC
  • Fast setting, ready, start of mix to finish in 2 minutes
  • Reduce risk of contamination
  • The most acid-resistant conventional GIC
  • High molecular weight polyacrylic acid with new glass filler