Composit restoration. Steps and formula
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The library does not have a dedicated dental/restorative dentistry textbook. I'll answer from established clinical knowledge, which is well-settled for this topic.
Composite Restoration - Steps and Formula
Composition Formula of Composite Resin
Composite resin has three main components:
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
The free-radical addition polymerization:
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)
| Parameter | Enamel | Dentine |
|---|---|---|
| Agent | 35-37% phosphoric acid | 35-37% phosphoric acid |
| Time | 15-30 seconds | 10-15 seconds (shorter to prevent over-etching) |
| Rinse | 15-20 seconds | 15-20 seconds |
| Result | Chalky white frosted appearance | Moist/slightly wet surface |
- 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
Posterior Class II layering sequence:
- Small horizontal layer on gingival floor (1 mm) → cure
- Oblique increment on one proximal wall → cure
- Oblique increment on other proximal wall → cure
- Final occlusal increment → cure
Anterior layering (for aesthetics):
- Dentine shade body layer → cure
- Enamel shade layer → cure
- Optional: translucent/effect shade at incisal edge
Step 10 - Light Curing
| Composite Type | Curing Time | Tip Distance |
|---|---|---|
| Regular | 20-40 seconds per 2 mm increment | ≤ 2 mm |
| Bulk-fill | 20-40 seconds per 4 mm increment | ≤ 2 mm |
| Flowable | 20 seconds | ≤ 2 mm |
- 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
| Item | Detail |
|---|---|
| Bis-GMA monomer | C29H36O8 |
| Etchant | 35-37% H3PO4 |
| Enamel etch time | 15-30 sec |
| Dentine etch time | 10-15 sec |
| Max increment thickness | 2 mm (4 mm for bulk-fill) |
| Curing wavelength | 468 nm (camphorquinone) |
| Min light intensity | 400 mW/cm² |
| C-factor | Bonded surfaces / Unbonded surfaces |
| Polymerization shrinkage | 1.5-5% by volume |
Classification of Composites by Filler Size
| Type | Filler Particle Size | Use |
|---|---|---|
| Macrofill | 10-100 µm | Rarely used now |
| Microfill | 0.01-0.1 µm | Anterior, high polish |
| Hybrid | 0.6-1 µm + large | Universal |
| Nanofill | < 100 nm | Anterior (superior aesthetics) |
| Nanohybrid | Nano + micro | Most versatile, current gold standard |
| Bulk-fill | Variable | Posterior, 4 mm depth curing |
Shade?
Shade Selection in Composite Restoration
The Vita Classical Shade Guide (Most Widely Used)
Shades are organized into 4 hue groups based on color:
| Group | Hue | Description |
|---|---|---|
| A | Reddish-brown | Most common in natural teeth |
| B | Reddish-yellow | Yellowish tint |
| C | Grey | Greyish tone |
| D | Reddish-grey | Rare, darker grey-red |
Within each group, numbers indicate value (brightness):
- 1 = Lightest
- 2 = Light
- 3 = Medium
- 4 = Darkest
So: A1 (lightest reddish-brown) → A2 → A3 → A3.5 → A4 (darkest)
Vita 3D Master Shade Guide (More Precise)
Organized by 3 dimensions of color:
| Dimension | Scale |
|---|---|
| Value (Lightness) | 1 (brightest) to 5 (darkest) |
| Chroma (Saturation) | 1 (low) to 3 (high) |
| Hue | M (middle), L (left/yellow), R (right/red) |
Example: 2M2 = Value 2, Middle hue, Chroma 2
Selection order in 3D Master:
- First match value (lightness) - most critical dimension
- Then match chroma
- 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
- Clean the tooth (remove plaque/stains)
- Hold shade tab at same distance and angle as the tooth
- Glance quickly (first impression) - do not stare (eye fatigues in ~5 seconds)
- Use the cervical, body, and incisal thirds separately
- Involve the patient in selection (especially anterior)
Zones of a Tooth - Layered Shade Technique
A natural tooth has 3 optical zones:
| Zone | Location | Shade Characteristic | Composite Used |
|---|---|---|---|
| Cervical | Gingival 1/3 | Highest chroma, most yellow/opaque | Higher chroma or cervical shade |
| Body | Middle 1/3 | Base shade - matches overall tooth | Dentine shade (A2, A3) |
| Incisal | Incisal 1/3 | Most translucent, bluish/grey | Enamel or translucent shade |
This is why single-shade placement looks flat - layering mimics natural depth.
Optical Properties to Understand
| Property | Definition | Clinical Relevance |
|---|---|---|
| Hue | The color itself (red, yellow) | A, B, C, D groups |
| Value | Brightness/lightness | Most important for matching |
| Chroma | Intensity/saturation of color | Number within group |
| Translucency | Light transmission | Incisal third matching |
| Fluorescence | Glow under UV light | Natural teeth fluoresce; composite should too |
| Opalescence | Blue reflected, orange transmitted | Gives incisal edge life |
| Metamerism | Color match changes under different light | Check shade under multiple light sources |
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)
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