Composites

• What type of material are dental resin composites?

  Plastic
• Dental resin composites are made of co-polymerised methacrylate-based resin chains embedding inert filler particles
• What are the major resin monomers used in dental composites?

  Aromatic or aliphatic dimethacrylates
• Dimethacrylates are used in dental composites because the double bond in each methacrylate group can be broken during polymerisation.
• An example of a high molecular weight resin monomer is Bisphenol A-glycidyl methacrylate, also known as Bis-GMA
• What are filler particles in dental composites typically made from?

  Silica or quartz
• Filler particles in dental composites reduce polymerisation shrinkage
• Match the type of filler particle with its property:

  Spherical ↔️ High polishability

  Irregular ↔️ Fracture toughness
• Diluents are added to dental composites to reduce their viscosity and improve filler dispersion.
• Which diluent is commonly used in dental composites?

  Triethylene glycol dimethacrylate (TEGDMA)
• Inhibitors are added to dental composites to prevent premature polymerisation
• What is the role of silane coupling agents in dental composites?

  Improve adhesion
• What is the most commonly used photoinitiator in dental composites?

  Camphorquinone
• Camphorquinone has a bright yellow color, which can affect composite shades.
• Trimethylbenzoyl-diphenyl-phosphine oxide (TPO) is being tested as an alternative photoinitiator because it is colorless.
• Why are radio-opacifiers added to dental composites?

  Distinguish from tooth tissue
• Free radical addition polymerisation in dental composites can be light-activated or dual-cured.
• What initiator is used in chemical activation of dual-cured composites?

  Benzoyl peroxide
• Light-activated polymerisation allows unlimited working time before curing begins.
• Steps in the light-activated polymerisation of dental composites:

  1️⃣ Initiation: Free radicals are produced on irradiation

  2️⃣ Propagation: Free radicals attack double bonds of methacrylate groups

  3️⃣ Chain generation: Monomer free radicals are created
• What is the typical polymerisation shrinkage percentage in dental composites?

  2-3%
• Polymerisation shrinkage in dental composites can lead to gap formation between the tooth tissue and composite.
• Why is incremental placement necessary during photopolymerisation of dental composites?

  Limited depth of cure
• Hydroscopic water absorption can lead to expansion and degradation of dental composites.
• The coefficient of thermal expansion of dentine is approximately 18.
• What is the purpose of the air-inhibited layer on top of newly placed dental composites?

  Allows incremental build-up
• The degree of cure in dental composites typically ranges from 40-78%, leaving residual uncured monomers.
• Uncured monomers in dental composites can cause hypersensitivity.