Advancements in Resin Composites

Riyadh Colleges of Dentistry and Pharmacy.

Biomaterial, Restorative Division

DENC 613 (Level 11)

Craig's Restorative Dental Materials (Thirteenth Edition) Chapter 9 2013Dr. Abdul Qadir Abdul Wahid

What are Composites ?

• The concept of a composite biomaterial, can be described as a solid that contains two or more distinct constituent materials or phases when considered at greater than an atomic scale

What are Resin Composites ?

• In dentistry, the term resin composite generally refers to a reinforced polymer system used for restoring hard tissues, for example, enamel and dentin

Resin Matrix

• METHACRYLATE MONOMERS• LOW-SHRINK METHACRYLATE MONOMERS• LOW-SHRINK SILORANE MONOMER

METHACRYLATE MONOMERS

• 2,2-bis[4(2-hydroxy-3-methacryloxy-propyloxy) phenyl] propane (Bis-GMA)

• Urethane dimethacrylate (UDMA). • Triethylene glycol dimethacrylate (TEGDMA),

or Bis-EMA6 • Addition Polymerization

Bis-GMA Structure

UDMA Structure

TEGDMA Structure

Bis-EMA6 Structure

LOW-SHRINK METHACRYLATE MONOMERS

• Low volumemetric shrinkage and polymerization stress of composites

• Some examples include the use of dimer acids, incorporation of cycloaliphatic units, and photocleavable units to relieve stress after polymerization

LOW-SHRINK SILORANE MONOMER

• Chemical building blocks siloxane and oxirane (also known as epoxy)

• Ring opening Crosslinking

• Specific adhesive system is used

Structure of silorane

Ring- opening Vs. Linear additionRing- openingLess shrinkage Addition:

shrinkage

TYPES 0F COMPOSITES

• MACROFILLED• MICROFILLED• HYBRID AND MICROHYBRID • NANOCOMPOSITES • PACKABLE • FLOWABLE• LABORATORY• CORE BUILDUP

Macrofilled Composites

• Average filler size 20 to 30 μm. • Opaque• Low resistance to wear• No longer in clinical use

Microfilled Composites

• Average Particle size 0.4μm• Best polish• Best esthetics • Higher shrinkage

Hybrid & Microhybrid Composites

• The hybrid composites • Particle sizes: 2 to 4 μm & 0.04 to 0.2 μm. • The microhybrid composites• Particle sizes: 0.04 to 1 μm. & Microfine Silica• Good clinical wear resistance and mechanical

properties (High strength & High modulus)• Suitable for stress-bearing applications. • Lose their surface polish with time and become

rough and dull.

Nanocomposites

• Nanofills. Particle size: 1-100 nm • Nanohybrids. Particle size: 0.4 to 5 microns • ability to control and manipulate structures

at the atomic and/or molecular scale • High polish• High strength• High modulus

Nanocomposites

• The size of nanomeric particles is below that of visible light (400-800 nm), which provides the opportunity of creating highly translucent materials

• The surface area to volume ratio of the nanoparticles is quite large. The sizes of the smallest nanoparticles approach those of polymer molecules so they can form a molecular scale interaction with the host resin matrix.

Nanocomposites

Packable composites

Particle sizes: 0.04 μm & 0.2-20 μm • Packable• Less shrinkage• Lower wear

Flowable composites

Particle sizes: 0.04 μm & 0.2-3.0 μm

• Syringeable• Lower modulus • Higher wear

Laboratory composites

Particle sizes: 0.04 μm & 0.2-3.0 μm

• Best anatomy and contacts• Lower wear • Lab cost• Special equipment• Requires resin cement

DENTAL LABORATORY COMPOSITES

-Indirect Composite Veneers, Inlays and Onlays

Indirect composite: Tooth prepared for MOD composite inlay. Polyvinyl siloxane die of thpreparation from an alginate impression. Composite inlay prepared outside of the mouth at chairside. Composite inlay after cementation with a resin cement.

Core Buildup Composites

• Available as self-cure, light-cured, and dual-cured products.

• Core composites are usually tinted (blue, white, or opaque) to provide a contrasting color with the tooth structure

Core Buildup Composites

MEGAFILL MACROFILL MIDIFILL MINIFILL MICROFILL NANOFILL

NotShown

NotShownDifferent

Filler ParticleSizes

HYBRID(MIDIFILL)

HYBRID(MINIFILL)

MixturesOf Filler

Sizes

Hetero-geneousMIDIFILL

Hetero-geneousMINIFILL

Hetero-geneousMICROFILL

NotShown

NotShownMixtures

Of Pre-CuredPieces of

Composite

FILLER PARTICLESSchematic Examples

HOW DO YOU MAKE FILLERS?• Crushing, Grinding, Sieving• Vapor Phase Condensation• Sol-Gel Precipitation

HHYBRID MICROFILLED NANO

Working and Setting Times

• Light-cured composites “on demand” setting

• Chemically activated composites 3 to 5 minutes.

Polymerization Shrinkage and Stress

• Volumetric shrinkage contraction stresses (13 Mpa)

• These stresses severely strain the interfacial bond between the composite and the tooth

• 2-mm increments + polymerizing each increment independently can reduce the net effect of polymerization shrinkage.

Thermal Properties

• The linear coefficient of thermal expansion (α) of composites is higher than Enamel & Dentine

• Cyclic Thermal stresses place an additional strain on the bond to tooth structure & can lead to material fatigue and early bond failure.

Water Sorption

• The water sorption of composites with hybrid particles (5 to 17 μg/mm3) is lower than that of composites with microfine particles (26 to 30 μg/mm3)

Solubility

• The water solubility of composites varies from 0.25 to 2.5 mg/mm3

• Breakdown and leakage can be a contributing factor to the reduced resistance to wear and abrasion of composites.

Color and Color Stability

• Stress cracks within the polymer matrix and partial debonding of the filler to the resin as a result of hydrolysis tend to increase opacity and alter appearance

• Change of color and loss of shade match with surrounding tooth structure are reasons for replacing restorations

Mechanical Properties

Depth of Cure (Light-Cured Composites)

• Standard exposure time = 20 seconds. • Light shades of resin 2 or 2.5 mm• Opaque shades 1 mm• Darker shades exposure time

recommendation = 40 seconds

Radiopacity

• Very difficult to locate enamel-composite margins radiographically because of the relatively low radiopacity of composites

• Modern composites include glasses having atoms with high atomic numbers, such as barium, strontium, and zirconium.

Wear Rates

• Over an 18-month period, a loss of surface contour >50 μm is accepted

• Nanofilled composite showed wear resistance similar to natural human enamel

(in a 3-year and 5-year clinical study)

Biocompatibility

• Nearly all of the major components of composites (Bis-GMA, TEGDMA, and UDMA, among others) are cytotoxic in vitro if tested as the bulk monomer

• Curing of composite + presence of Dentine barrier limits the exposure of pulp to the released components

Biocompatibility

• The use of composite materials as direct pulp-capping agents poses a higher risk for adverse biological responses, because no dentin barrier exists to limit exposure of the pulp to the released components.

• Studies have proved that bisphenol A is estrogenic in vitro tests