Lecture 6- resin composites

Resin Composites – Applications (Uses in Dentistry)

• Direct Restorations

  • Placed directly in the cavity (anterior & posterior).

  • Includes Class I–V restorations.

• Indirect Restorations

  • Lab-processed, then cemented.

  • Inlays, onlays, veneers, crowns.

• Base-Up / Build-Up

  • Core build-ups under crowns.

  • Replace large missing tooth structure.

• Sealants

  • Preventive application for pits and fissures.

• Cements

  • Used as luting agents for indirect restorations (inlays, onlays, veneers).

• Repair of Restorations

  • Add composite to fix chipped or defective existing restorations.

• Provisional Restorations

  • Short-term crowns, bridges, or fillings.

Delivery Forms

• Single paste (light-cure): syringes, compules (single dose).

• Dual-paste (chemically/dual-cured): automix or manual mix.

Composite

compound of two or more materials with properties superior/intermediate to individual constituents.

Composition of composite (5)

resin matrix, filler particles, coupling agent, Optical Modifiers, Initiators/Accelerators

1) Resin matrix is made up of (3)

• Bis-GMA (hard, solid)

• UDMA

• TEGDMA (runny/flowable)

  *resin material is hydrophobic must keep composite dry to work

2) Filler Particles:

• Quartz, silica, lithium aluminum silicate, zirconia, barium/strontium/zinc/ytterbium glasses.

• Improve strength, reduce shrinkage & water sorption.

• without filler particles resin chains will curl up -> swells

3) Coupling Agents:

• Silanes → bond inorganic filler particles to resin matrix.

4) Optical Modifiers:

• Pigments, opacifiers, fluorescence, opalescence → match enamel/dentin shades.

5) Initiators/Accelerators:

• Chemical: benzoyl peroxide + amine

• Light: camphorquinone (blue ~468 nm), Lucirin TPO (violet ~370 nm), phenylpropanedione

• Dual-cure = combination

Polymerization

• a chemical process where small molecules, called monomers, link together to form long chains of larger molecules, called polymers

• Free radical chain reaction (double bond breaks → reactive site).

• 50–70% (not all monomers react) bec now maxtrix is more hard less free space

Polymerization stages: (3)

initiation → propagation → termination

Polymerization Issues:

• Problems:

  • Oxygen-inhibited layer (soft, unpolymerized surface).

  • Inhibition by eugenol (temp fillings) or peroxide (bleaching).

• Shrinkage:

  • Always occurs; direction depends on cavity shape and bonded walls (C-factor).

  • Higher C-factor = more stress/debonding risk.

Oxygen-inhibited layer is formed by:

the atmosphere has oxygen that reacts with free radicals in the composite

Two options with oxygen inhibited layer:

• Remove: (best because OIL is bad) when surfaces of restorations exposed to air (done building up)

• Leave: surface will be covered with more layers (NOT done with build up) *Overfill slightly → polish later

Polymerization shrinkage:

• Stress can debond at margins, cause staining, sensitivity.

• Reduced by:

  • Smaller filler size

  • Special monomers

  • Soft-start curing lights

  • Incremental layering (2 mm layers, low C-factor).

c-factor 5/1 highest stress in class ___&___ c-factor 1/6 lowest stress in class ___

I & V, VI

C- Factor

• ratio of bonded / unbonded surfaces

• lower C factor = lower stress

• less walls = less likely to break because no air in between

Layering techniques

vertical, horizontal, oblique, cusp build-up

*b has high c factor lots of stress on the walls so not very good technique

Types of Filler Composites

• Macrofilled: >5 µm, 60–80% wt.

• Microfilled: 0.04–0.6 µm, 35–85% wt., very good polishable.

• Hybrid: 0.04–15 µm, 70–80% wt.

• Fine/Microhybrid: 0.04–1 µm, 70–80% wt.

• Nanohybrid/Nanofilled: 0.002–0.075 µm, ~75–79% wt., strong + great polishable.*

*we use nanofilled

Shade & Optical Properties

• Shade guides → dentin & enamel shades.

• Fluorescence: absorbs energy, emits longer wavelength.

• Opalescence: scatters shorter wavelengths, gives natural look.

• Opacity: resistance to light passage; increases with age.

• Spectrophotometer: objective shade mapping.

Light Curing

• Blue light (~468 nm) used for polymerization.

• Curing modes: standard, high power, extra power, polywave.

• Barriers: sleeves, films for infection control.

• Important: match light wavelength with composite’s initiator system.