Hard stuff Flashcards
Define alloy, and explain how the strength of dental amalgam is affected by different components of alloy
- 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.
Interpret characteristics of different types of Composite Resin
Microhybrid Composite Resins:
• Stronger than microfilled
• Can be used in both anterior and posterior teeth
• Most have medium viscosity
- 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 - 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
Describe the following properties of composite Resin:
- Biocompatibility
- Degree of conversion
- Water sorption
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
What is the purpose of a primer? Describe what it’s made of, and it’s bonding mechanism.
- The primer contains hydrophobic and hydrophilic methacrylate monomers copolymerizes with the adhesive which is unfilled resin
- The primer bonds to both dentine and resin
What are issues with self etch?
- 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
What factors that determine the shade of composite resin?
Translucency
Opacity
Type and intensity of illumination
Metamerism
Contrast
Define:
- Value
- Chroma
- Hue
- 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
Define:
Centric occlusion
Lateral occlusion
- 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
List indications for polishing dental restorations
- Detected by radiographs
- Dental floss fraying
- Patient complaining of ‘food impaction’
- Gingival tissues appear inflamed in the area
Compare setting reactions of different types of Glass Ionomer Cement
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
Recognise new technologies and products available (poly-acid composite resin).
- “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 - 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
State and describe the coats used on GIC
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
Examine the setting mechanism of Composite Resin
- Initiation: Initiate through light curing, chemical curing or dual cure
- 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 - 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
List 2 types of paste to paste formulations, and describe them.
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
What is a EQUIA system?
- 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
