Composite Restoration - Steps and Formula

Composition Formula of Composite Resin

1. Organic Resin Matrix (10-30% by volume)

• Bis-GMA (Bisphenol A-Glycidyl Methacrylate) - the most widely used monomer, developed by Bowen (1962)
  • Formula: C29H36O8 (MW ~512 g/mol)
• TEGDMA (Triethylene Glycol Dimethacrylate) - diluent monomer that reduces viscosity
• UDMA (Urethane Dimethacrylate) - used in some modern systems
• Bis-EMA - less water absorption than Bis-GMA

2. Inorganic Filler (60-90% by volume)

• Quartz, barium glass, silica, zirconia, or strontium glass particles
• Determines mechanical properties and radiopacity

3. Coupling Agent (Silane)

• 3-methacryloxypropyltrimethoxysilane - bonds filler to matrix
• Enables stress transfer between filler and matrix

4. Initiator-Accelerator System

• Light-cured: Camphorquinone (0.2%) + amine co-initiator (DMAEMA)
  • Absorption peak: 468 nm (blue light)
• Chemically cured: Benzoyl peroxide + tertiary amine
• Dual-cure: Both systems combined

5. Inhibitor

• BHT (butylated hydroxytoluene) - prevents premature polymerization

6. Pigments/Opacifiers

• Titanium dioxide (TiO2) and ferric oxide for shade matching

Polymerization Reaction

C=C (methacrylate double bond) → -C-C- (polymer chain)

Light → Camphorquinone* → free radicals → monomer activation → chain propagation → cross-linked polymer

• Polymerization shrinkage: 1.5-5% by volume (major drawback - causes marginal gap and stress)
• Degree of conversion: ideally >65%

Clinical Steps of Composite Restoration

Step 1 - Diagnosis and Treatment Planning

• Select shade using a shade guide before drying the tooth (dry teeth appear lighter)
• Select composite type: flowable for small cavities/liners, packable/condensable for posterior, nanofill/nanohybrid for anterior

Step 2 - Isolation

• Rubber dam preferred (best moisture control)
• Cotton rolls + retraction cord as alternative

Step 3 - Cavity Preparation

• Remove caries with round bur at slow speed
• No need for extensive "extension for prevention" (unlike amalgam)
• Conservative preparation - follow caries outline
• No undercuts needed (composite bonds micromechanically)
• Create bevels at cavosurface margin (enamel only, 45°) for anterior teeth - increases bond surface area

Step 4 - Pulp Protection (if needed)

• Deep cavity (< 0.5 mm from pulp): calcium hydroxide liner (Dycal)
• Moderate depth: glass ionomer cement base
• Avoid ZOE (zinc oxide eugenol) as eugenol inhibits polymerization

Step 5 - Etching (Total-Etch Technique)

• Self-etch systems (no separate etch step): use acidic primers that etch and prime simultaneously
• Selective-etch: etch enamel only, self-etch primer on dentine

Step 6 - Priming

• Primer contains hydrophilic monomers (HEMA - hydroxyethyl methacrylate)
• Penetrates the demineralized dentine collagen to form a hybrid layer (Nakabayashi's hybrid layer)
• Applied in multiple coats, air-dried gently
• Do not light cure at this stage

Step 7 - Bonding Agent Application

• Apply adhesive (hydrophobic resin) over primed surface
• Air-thin to 2-5 micron thickness
• Light cure for 10-20 seconds (creates the bonded base)

Step 8 - Matrix and Wedge Placement (for proximal cavities)

• Sectional matrix (e.g., Palodent) or Tofflemire band
• Wooden or plastic wedge at gingival embrasure - separates teeth, adapts matrix, prevents gingival overhang

Step 9 - Composite Placement (Incremental Layering)

• Place in 2 mm increments maximum - prevents incomplete polymerization at deeper levels
• First increment: oblique/diagonal to reduce C-factor stress at walls
• C-factor (configuration factor) = bonded surfaces / unbonded surfaces
  • High C-factor = more polymerization shrinkage stress
  • Incremental technique reduces effective C-factor

1. Small horizontal layer on gingival floor (1 mm) → cure
2. Oblique increment on one proximal wall → cure
3. Oblique increment on other proximal wall → cure
4. Final occlusal increment → cure

1. Dentine shade body layer → cure
2. Enamel shade layer → cure
3. Optional: translucent/effect shade at incisal edge

Step 10 - Light Curing

• Light intensity: minimum 400-600 mW/cm² (conventional halogen); LED units 1000-3000 mW/cm²
• Protect patient and operator eyes from blue light

Step 11 - Finishing

• Remove matrix band and wedge
• Check occlusion with articulating paper
• Use finishing burs (12-fluted), fine diamonds, or sandpaper discs
• Contour and shape anatomy

Step 12 - Polishing

• Polishing cups, points, and discs (Sof-Lex, Polydisk sequence)
• Sequence: coarse → medium → fine → superfine
• Final polish with polishing paste or aluminum oxide
• Apply surface sealant (optional) to seal microporosities at margins

Summary: Key Formulas to Remember

Classification of Composites by Filler Size

Shade Selection in Composite Restoration

The Vita Classical Shade Guide (Most Widely Used)

• 1 = Lightest
• 2 = Light
• 3 = Medium
• 4 = Darkest

Vita 3D Master Shade Guide (More Precise)

1. First match value (lightness) - most critical dimension
2. Then match chroma
3. Then match hue

Rules for Shade Selection

When to Select

• Before starting the procedure - wet tooth
• Before rubber dam placement
• Before prolonged drying (dry teeth appear 1-2 shades lighter)
• Under natural daylight or color-corrected lighting (5500K)

How to Select

1. Clean the tooth (remove plaque/stains)
2. Hold shade tab at same distance and angle as the tooth
3. Glance quickly (first impression) - do not stare (eye fatigues in ~5 seconds)
4. Use the cervical, body, and incisal thirds separately
5. Involve the patient in selection (especially anterior)

Zones of a Tooth - Layered Shade Technique

Optical Properties to Understand

Practical Tips

• Most common shade in adults: A3 or A3.5
• Most common in young patients: A1 or A2
• Chameleon effect: composite adapts slightly to surrounding tooth color after placement due to light scattering - final shade appears after 24 hours
• Rubber dam effect: tooth dehydrates under rubber dam, appears lighter - place composite slightly lighter than selected shade OR rehydrate before final check
• Stump shade: for crown work or veneers, record the prepared tooth shade too, as it affects the final restoration appearance

Quick Summary

VITA Classical:  A (red-brown) | B (red-yellow) | C (grey) | D (red-grey)
                 1=light → 4=dark

Most used:  A2, A3, A3.5

Key rule:  Select shade WET, in natural light, BEFORE isolation
           Value > Chroma > Hue (in order of importance)