Dental Composite Lecture – Part 2 Review

Seven Key Properties of Dental Composites

• Linear Coefficient of Thermal Expansion (LCTE)

• Measures dimensional change with temperature.

• Ideal restorative material should match enamel LCTE; current composites ≈ 3× higher → greater marginal gap risk.

• Enamel naturally resists distortion while chewing hot/cold foods; composites may distort under extreme conditions.

• Water Sorption (Water Absorption)

• Indicates how much water a composite absorbs over time.

• High water uptake degrades color, texture and strength (parallels acrylic dentures that discolor/perforate after 5–10 yrs).

• More filler ⇢ lower sorption.

• Wear Resistance

• Ability to resist surface loss from chewing/brushing.

• Affected by filler size, shape, amount, restoration location, and occlusion.

• Macro-fillers = bigger “gravel” ⇒ bigger voids when lost; micro-fillers = “cement powder” ⇒ minimal voids.

• Class I restorations (occlusal table) wear faster than Class V (cervical) due to direct occlusal forces.

• Modern composites approach amalgam durability yet still short of the gold standard.

• Surface Texture / Polishability

• Smooth surfaces promote gingival health; roughness traps plaque and causes overhang-like irritation.

• Smaller fillers ↑ polishability; nano-fill & nanohybrid provide mirror-smooth finishes.

• Radiopacity

• Needed to differentiate restoration from caries on radiographs (caries = radiolucent).

• Achieved by adding radiopaque fillers (e.g., barium glass) that reflect X-rays.

• Modulus of Elasticity (Young’s Modulus)

• E = \frac{\text{stress}}{\text{strain}}

• High E ⇢ rigid; low E ⇢ flexible.

• Microfills have low E – good for Class V where tooth flexure/abfraction occurs, preserving bond integrity.

• Solubility

• Measures dissolution in oral fluids.

• Composites display no clinically significant solubility in saliva under normal conditions.

Polymerization & Shrinkage Phenomena

• Polymerization (Light-activated hardening) triggered by blue LED curing units.

• Polymerization Shrinkage

• Occurs as resin chains link; volume contracts.

• Bulk-fill → composite pulls from cavity walls ⇢ marginal gaps.

• Incremental technique (≤ 2 mm layers) allows each layer’s shrinkage to be compensated by the next.

• Clinical impacts: gaps on root surfaces ↑ micro-leakage/recurrent caries.

• Shrinkage Prevention Strategies

• Use adhesive bonding to strengthen interface.

• Incremental layering + separate cures.

• Place RMGI liner on root surfaces as stress-breaker.

• Alternate flowable (flexible, small filler) and packable (strong, carve-able) layers.

• Configuration Factor (C-Factor)

• \text{C-factor}=\frac{\text{Bonded surfaces}}{\text{Unbonded surfaces}}

• ↑ C-factor → ↑ internal stress during cure.

• Class I: C=5 (high risk); Class IV: C=0.25 (low).

• Minimization: soft-start curing modes, flowable liners, incremental placement.

• Shrinkage by Resin Chemistry

• Bis-GMA/UDMA hybrids: 2.4–2.8 %

• Microfill & flowable: higher (less filler).

• Silorane-based: ≈ 0.7 % (special bonding system required).

Polymerization Methods

• Modern blue LED units (portable, durable) replaced QTH & plasma arc; modes: soft-start, high-intensity, pulse.

Clinical Use Considerations

Indications

• Class I-VI direct restorations
• Core build-ups post-RCT
• Sealants & preventive resin restorations
• Esthetic veneers, contouring, diastema closure
• Cementation for indirect inlays/onlays
• Temporary restorations; periodontal splinting with fiber & resin

Contra-Indications

• Inadequate moisture control (e.g.
– uncooperative pediatrics)
• All occlusal load on single restoration
• Operator unwilling/unskilled in adhesive protocols
• Margins extending far onto root without RMGI liner

Advantages

• Highly esthetic (wide shade range)
• Conservative prep (only defective tooth removed)
• Insulating, no galvanism
• Versatile & repairable – polymers bond to polymers

Disadvantages

• Gap formation risk at root margins
• Technique & moisture sensitive → longer chair time
• Less wear resistance vs amalgam in bruxers
• Higher LCTE than enamel → marginal leakage if poorly managed

Clinical Technique: Step-by-Step

1. Examination, Dx, treatment plan (coordinate whitening beforehand).

2. Local anesthesia (routine in West; optional cost-saver & depth indicator in Philippines).

3. Prophylaxis with pumice (avoid fluoride/glycerin pastes before bonding).

4. Shade selection BEFORE drying; use natural/neutral light; cervical → darker.

5. Isolation

   • Preferred: rubber dam (demo forthcoming).

   • Alternative: cotton rolls + high suction; may add retraction cord.

6. Pre-wedge for proximal preps; assess occlusion; mark contacts pre-dam.

7. Prepare cavity – only carious tissue removed (except large Class III/IV may need dovetails, pins).

8. Etch (37 % phosphoric), rinse, dry (do NOT desiccate), apply bonding agent twice, gentle air-thin, light-cure.

9. Incremental composite insertion (≤ 2 mm), light-cure each, maintain orientation of light to surface.

10. Build anatomy; final cure.

11. Finish & polish (fine diamonds, discs, strips); check/adjust occlusion in centric & excursions.

12. Fluoride varnish optional; document shade, lot #, curing time.

Troubleshooting & Common Problems

Matrix & Isolation Systems

• Conventional Tofflemire vs Triodent V3 sectional system (super-curved bands, wave wedge, NiTi ring).

• Bands have S-curve & marginal ridge contour; wedge provides seal + papilla relief; NiTi ring grants 60–80 µm separation.

• Yellow "narrow" ring works distal to canine & for pediatric/bicuspid; rings can butterfly/stack for MODs.

• Wedge guard protects adjacent tooth during prep then detaches, wedge left for restoration.

Ethical & Practical Notes

• Technically possible to layer new composite over old (polymer–polymer affinity) yet ethically clinician should remove old restoration before refurbishing.
• Use cavity varnish ONLY under metal (\"V\" for varnish, \"M\" for metal mnemonic).
• RMGI or flowable liners act as stress-breakers and fluoride source on root surfaces.
• For bruxers or heavy occlusion, consider amalgam (where legal) or ceramic/onlay rather than composite.

Numerical & Statistical References

• LCTE: composite ≈ 3 × enamel.
• Shrinkage: Bis-GMA/UDMA 2.4–2.8 %, Silorane 0.7 %.
• C-factor: Class I = 5, Class IV = 0.25.
• Separation with V3 rings: 60–90 µm (green ring 60–80 µm; yellow 70–90 µm).
• Recommended increment thickness ≤ 2 mm.

Connections & Broader Context

• Builds on prior Dental Materials lectures (Doc Jill) – reinforces terms LCTE, modulus, sorption.
• Aligns with OPD-1 concepts (overhang removal, Class cavity design, polymerization shrinkage).
• Ethical shift away from amalgam due to mercury concerns; composites continuously refined to meet wear benchmarks.
• Public health note: cost limits rubber dam use in the Philippines, influencing isolation strategies.
• Environmental/occupational safety: LED light eye protection, avoidance of mercury.

Philosophical & Ethical Implications

• Esthetic dentistry balances minimally invasive philosophy against longevity & patient economics.
• Decision to re-use old composite or replace reflects duty of care vs convenience.
• Material science advances (silorane, nano-fillers) exemplify continual pursuit of biomimicry – striving for enamel-like behavior with biocompatibility.

Quick-Fire Exam Reminders

• \text{C-factor}=\frac{\text{Bonded}}{\text{Unbonded}} – higher ⇒ more shrinkage stress.
• Silorane shrinkage ≈ 0.7 % (lowest).
• Flowable + Packable layering = stress-breaking sandwich.
• Class I wears more than Class V; macrofill loses big chunks like asphalt gravel.
• Use RMGI liner when margins on root.