Resin Composite Restorations Overview

Resin Composite Restorations

• Resin composites are esthetic restorative materials
• Composites are composed of two or more insoluble constituents
• They provide superior or intermediate properties
• Resin composites are widely used in anterior and posterior teeth restorations

Composition

• Resin composites consist of an organic resin matrix and inorganic filler particles
• The particles are bonded by an organic coupling agent

The Organic Resin Matrix

• The matrix is the continuous phase to which other ingredients are added
  • High molecular weight monomers:
• Commonly Bisphenol glycidyl methacrylate (BisGMA) and Urethane dimethacrylate (UDMA)
• These are extremely viscous
• Viscosity reduces the amount of filler that can be incorporated
  • Low molecular weight monomers:
• Examples include Triethylene glycol dimethacrylate (TEG-DMA)
• This monomer lowers viscosity, improving wettability which in turn improves mechanical properties, but increases polymerization shrinkage and water sorption
  • Activator/Initiator system:
• Can be chemically cured (auto or self-cure, but not used currently)
• Can be photochemically cured (single paste containing a photo-sensitive chemical like camphorquinone)
• Can be dual cured (using both photo and chemical mechanisms)
  • Inhibitors:
• Prevent spontaneous polymerization, improving shelf-life and working time
  • Pigments:
• Metal oxides provide different shades and opacity matching tooth color and translucency

The Inorganic Fillers

• Fillers are the dispersed phase, improving strength, wear resistance, and optical characteristics
• They decrease polymerization shrinkage, coefficient of thermal expansion, and water sorption
• However, they increase viscosity
  • Types of fillers:
• Crystalline (like quartz): Stronger and harder, but difficult to finish and polish, often used in silicate glass composites
• Non-crystalline (like glass): More common filler type in current composites
  • Filler particle size and loading:
• Smaller particles improve polishability and wear resistance but increase viscosity
• High filler loading enhances mechanical properties

The Coupling Agent

• An organo-silane is used to bind filler particles to the organic resin matrix
• One end of the molecule forms siloxane bonds with silica filler's hydroxyl groups
• The opposite end allows copolymerization with the matrix monomers
• This is critical for stress transfer between resin and filler phases increasing strength, rigidity, and wear resistance
• Also prevents water from penetrating between resin and filler interface

Classification and Types of Resin Composites

• Classification by filler size:
• Macrofilled
• Microfilled
• Hybrid
• Nanofilled
• Classification by filler loading and consistency:
• Packable
• Flowable
• Classification by resin type:
• Regular methyl methacrylate
• Silorane

Steps of Application

• Selection of resin composite type
• Shade selection
• Isolation of operatory field
• Liner/base application (if needed)
• Matricing and wedging
• Applying adhesive system
• Packing and curing composite
• Finishing and polishing

Advantages of Resin Composites

• Superior esthetic quality
• Satisfactory physical and mechanical properties
• Conserve and reinforce tooth structure
• Low thermal conductivity
• Easy to repair

Disadvantages of Resin Composites

• Questionable adaptation to tooth structure due to high polymerization shrinkage and poor wettability
• Potential for high occlusal wear in areas of high stress
• Hydrolytic instability in oral fluids
• High technique sensitivity
• Lack of anticariogenic potential

Indications of Resin Composites

• All cavity preparations (carious or non-carious)
• Esthetic enhancement (shape, size, diastema closure, veneers)
• Core build-up material under crowns and bridges
• Cementation of indirect esthetic restorations (resin cement)
• Restorations, periodontal splinting, and orthodontic bracket bonding

Contraindications of Resin Composites

• Patients with poor oral hygiene and high caries index
• Poor operatory isolation or site access
• Patients with heavy occlusal stresses (bruxism)

Cavity Preparation Design for Resin Composites

• Modified classic cavity design for bonding to enamel and dentin
• Preservation of tooth structure: Outline limited to defective enamel and dentin, no extension in depth or width
• Beveled cavo-surface angle: Enamel walls beveled at 45° for increased bonding surface area, micromechanical retention, and marginal sealing. Important for stress-bearing areas (posterior teeth)