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Questions and Answers
What is a significant issue commonly associated with polymerisation in composite resins?
Which type of resins is noted for being the most commonly used in composite restorations?
What primary characteristic distinguishes ORMOCER® resins from acrylic resins?
Which additive is used to control viscosity in ORMOCER® resins?
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Which of the following types of resins is developed primarily to minimize polymerisation shrinkage?
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What polymerisation method is commonly initiated by blue light in dental composite materials?
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What is the role of filler particles in composite resins?
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Which monomers are commonly blended into acrylic resins to improve their flowability?
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What is the polymerisation shrinkage percentage of silorane-based resins compared to acrylic-based composites?
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Which type of polymerisation occurs with silorane-based resins?
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Which of the following factors does NOT influence the stress of silorane-based resins during polymerisation?
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What is a significant advantage of ring-opening polymerisation in silorane-based resins?
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Which of the following statements about ORMOCER® resins is FALSE?
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Which polymerisation process is characterized by low shrinkage and is light-initiated in silorane-based resins?
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What is one reason silorane-based resins are less frequently used in clinical practice compared to acrylic resins?
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Which property is mainly associated with acrylic-based composites that has been improved in modern formulations?
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What is the primary result of polymerisation shrinkage during the formation of a polymer?
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Which type of polymerisation primarily occurs in the curing of dental polymers?
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What is the effect of increasing the degree of conversion (DC) on polymerisation shrinkage?
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Which component is primarily responsible for the shaping and adaptation of dental composites before hardening?
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Which of the following monomers is most commonly used in the formulation of dental composite resins?
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What is a key characteristic of dimethacrylate-based resins after curing?
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What role do flexible low molecular weight monomers play in the formulation of dental composites?
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Which of the following monomers possesses a more flexible backbone compared to bis-GMA?
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What is a common property observed in high molecular weight resin components?
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Which type of polymer is specifically noted for having lower polymerisation shrinkage than traditional methacrylate-based resins?
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Study Notes
Non-Acrylic Resins
- ORMOCER® resins are inorganic-organic copolymers, combining reactive organic species with a siloxane network.
- Polymerisation occurs through addition reactions, allowing for low shrinkage and superior aesthetics.
- TEGDMA serves as a viscosity controller, balancing the viscosity similar to bis-GMA.
- Filler particles are necessary to enhance strength in ORMOCER composites.
Dental Composite Resins
- Organic resin enables flow and shaping within cavities until polymerisation.
- Blue light facilitates free radical polymerisation, turning composite resin into a rigid solid.
- Common dimethacrylate monomers include bis-GMA, UDMA, TEGDMA, and bis-EMA.
- Larger, rigid monomers in resins increase viscosity; flexible, low molecular weight monomers improve flowability.
- Modified dimethacrylate monomers have been created to minimize polymerisation shrinkage and stress.
Polymer Science
- Polymers are large macromolecules formed by repeating covalent links of monomers.
- Characteristic properties are influenced by the chemical structure, including the types of monomers and their organization.
- Addition polymerisation (chain-growth) and condensation polymerisation (step-growth) are the two main reaction types.
- Polymerisation shrinkage results in volume reduction and internal contraction stress, exacerbated by higher degrees of conversion and lower molecular weight monomers.
Silorane-Based Resins
- Silorane monomers undergo ring-opening polymerisation, which reduces volumetric shrinkage to less than 1%.
- Utilizes light-initiated and cationic polymerisation, eliminating unreacted layers that can trap oxygen.
- Comparable strength to acrylic resins, but less frequently used due to advancements in stress-reducing acrylics.
ORMOCER® Resins
- Stand for ORganically MOdified CERamic, functioning as "all-ceramic direct fillings."
- Designed to minimize issues like microleakage and secondary caries, hence no traditional monomers are present.
Resin Matrix in Dental Composites
- The resin matrix surrounds filler particles and is a fluid mixture of monomers that harden upon activation.
- Dimethacrylate-based resins dominate, providing the chemically active component for shaping before curing.
Acrylic Resins Chemistry
- Difunctional monomers in acrylic resins can link with multiple other monomers forming crosslinked structures during curing.
- Crosslinking increases molecular weight and rigidity, enhancing wear resistance but also limiting polymerisation.
Commonly Used Monomers
- Bis-GMA is the primary monomer due to its high viscosity and strength, necessitating blending with other monomers for workability.
- EGDMA and TEGDMA, flexible low molecular weight monomers, are incorporated to reduce viscosity and improve handling, though they contribute to higher shrinkage.
- Current formulations often include UDMA and bis-EMA, which offer similar strength with better flow properties due to their molecular structure.
Desired Properties of Dental Composite Resins
- Focus on achieving low shrinkage, adequate strength, optimal flowability, and resistance to wear.
- Aim for minimal microleakage and high aesthetic quality in restorative applications.
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