Overview of Restoration Materials

Restoring lost tooth structure following caries, trauma, or iatrogenic tooth loss represents routine operative dentistry practice. Multiple restoration material options exist, each with distinct mechanical properties, clinical handling characteristics, longevity expectations, and cost implications. Selection requires understanding material properties, clinical performance data, patient preferences, and cavity classification demands.

Contemporary material science provides restorations capable of outstanding clinical longevity when properly selected, prepared, and placed. However, no single material universally outperforms all others in all situations—the ideal material varies based on specific clinical parameters.

Direct Composite Resin

Composite resins consist of bis-GMA or UDMA resin matrices containing 50-80% silicon dioxide and other filler particles by weight, providing volume. Fillers are classified by size: macrofilled (10-100ÎĽm), microfilled (0.04-1ÎĽm), and nanofilled (0.05-0.1ÎĽm). Contemporary composites typically use hybrid or nanofilled formulations balancing strength, esthetics, and handling.

Composition and Properties

Resin Matrix Bis-GMA (bisphenol A glycidyl methacrylate) provides the backbone of most composite matrices. This resin exhibits high strength but limited flowability and filler incorporation capacity. UDMA (urethane dimethacrylate) offers superior flex strength and lower shrinkage compared to bis-GMA. Many contemporary composites incorporate both resins to optimize properties. Filler Particles Silica-glass fillers occupy the majority of restoration volume. Filler size directly affects clinical properties—larger fillers provide greater strength but compromise surface polish and esthetics. Smaller fillers (nanofilled) achieve superior esthetics and surface characteristics but may sacrifice strength slightly. Shrinkage Composite undergoes polymerization shrinkage of 3-6% by volume upon light-curing. This shrinkage creates internal stress and can produce marginal gaps. Shrinkage increases with greater restoration volume and higher filler loading. Incremental (layered) placement technique reduces stress by limiting shrinkage in individual increments.

Clinical Properties

Advantages:
  • Excellent esthetics with natural-color matching capability
  • Direct placement without laboratory fabrication
  • Conservative preparation (less tooth removal than amalgam)
  • Repairable—can be resurfaced or re-contoured without replacement
  • Adhesive bonding provides micromechanical retention
  • Superior patient acceptance
Disadvantages:
  • Technique-sensitive—requires meticulous isolation, moisture control, and application
  • Polymerization shrinkage and microleakage risk if not properly placed
  • Relatively low wear resistance—marginal degradation and surface roughness develop over years
  • Susceptibility to staining and color change, particularly in smokers or coffee/tea drinkers
  • Limited longevity compared to amalgam in high-stress posterior teeth
  • Cost higher than amalgam

Clinical Longevity

Contemporary systematic reviews demonstrate composite restoration survival rates of:

  • 5-year survival: 88-95%
  • 10-year survival: 70-85%
  • 15-year survival: 50-70%

Posterior composites show slightly lower longevity than anterior composites. Restoration longevity depends significantly on:
  • Cavity size (larger restorations fail more frequently)
  • Dentin bonding quality (single-step adhesives show lower longevity than total-etch systems)
  • Incremental placement technique (layered placement shows superior longevity)
  • Patient habits (smokers, individuals consuming staining beverages show faster degradation)

Indication and Contraindication

Indications:
  • Anterior caries restorations
  • Small to medium posterior caries
  • Esthetic demands requiring tooth-colored restoration
  • Conservative preparation preferred
  • Patients with documented resin allergy (when composite is free of problematic components)
Contraindications:
  • Large posterior caries where composite bulk exceeds optimal thickness
  • Severe attrition cases where minimal tooth structure remains
  • Cases where long-term longevity is paramount (patient age, restoration risk)
  • High-stress situations (significant posterior functional cusp coverage)

Dental Amalgam

Amalgam consists of a mercury liquid combined with a powder alloy mixture (typically silver-tin-copper), creating a plastic mass that sets to a hard, metallic restoration. Despite decades of controversy regarding mercury content, controlled studies demonstrate no adverse health effects from properly placed and maintained amalgam restorations.

Composition and Properties

Alloy Composition The powder component comprises silver (40-70%), tin (12-32%), copper (4-30%), and smaller amounts of zinc and indium. These elements provide the mechanical properties; mercury is merely the matrix carrier. Setting Mechanism Mixing mercury with the alloy powder initiates phase changes. Initially plastic, the mixture gradually sets over 6-24 hours through gamma phase transformation. Setting is not instantaneous—final hardness develops over days. Strength Amalgam develops substantially greater compressive and tensile strength compared to composite resin. Amalgam exhibits minimal creep (permanent deformation under load). Wear resistance is superior to composite.

Clinical Properties

Advantages:
  • Superior longevity—10-30+ year clinical lifespan is routine
  • Excellent wear resistance
  • Lower technique sensitivity—moisture contamination does not prevent adequate set
  • Lower cost than composite or ceramic
  • Ease of manipulation and placement
Disadvantages:
  • Metallic appearance unacceptable for esthetic demands
  • Nonbonded restorations require aggressive preparation and retention form
  • Tooth discoloration from metallic ions (silvering effect on enamel)
  • Expansion upon setting can create marginal discrepancies
  • Removal is destructive—requires additional tooth removal to gain access
  • Maintenance involves managing corrosion over years
  • Recurrent decay beneath margins is common after 10+ years

Clinical Longevity

Amalgam restorations demonstrate:

  • 10-year survival: 85-90%
  • 20-year survival: 60-75%
  • 30-year survival: 40-50%

The most common reasons for replacement are secondary decay (40%), fracture of restoration margin (30%), and secondary fracture of tooth structure (20%).

Indications and Contraindications

Indications:
  • Large posterior restorations requiring maximum longevity
  • Situations where moisture control is difficult
  • When cost is the primary concern
  • High-risk caries patients where rapid replacement expense is prohibitive
Contraindications:
  • Anterior visible teeth
  • Esthetic-conscious patients
  • Patients with documented mercury sensitivity (extremely rare)
  • Small restorations where composite performs adequately

Glass Ionomer Cement

Glass ionomer consists of fluoro-alumino-silicate glass powder mixed with polyalkenoic acid liquid, producing a cement with unique properties including bioactive fluoride release and chemical adhesion to tooth structure.

Composition and Properties

Glass ionomers release fluoride continuously, providing anticariogenic effects particularly in high-risk patients. The cement chemically bonds to tooth structure, eliminating the need for mechanical retention.

Initial and Final Setting Glass ionomers set chemically at room temperature without light-activation (though light-activated versions are available). Setting is gradual—moisture protection is necessary immediately post-placement. Mechanical Properties Glass ionomers exhibit lower mechanical strength compared to composite or amalgam. Compressive strength ranges 150-200 MPa versus 350-550 MPa for amalgam. Brittleness makes glass ionomers susceptible to fracture in stress-bearing regions.

Clinical Properties

Advantages:
  • Fluoride release provides anticariogenic benefit
  • Chemical adhesion to tooth structure
  • Moisture tolerance compared to other materials
  • Low technique sensitivity
  • Inexpensive
  • Biocompatibility
Disadvantages:
  • Low mechanical strength limits use in stress-bearing areas
  • High solubility initially—moisture exposure during setting compromises restoration
  • Relatively short clinical longevity (3-5 years typically)
  • Surface degradation and erosion over years
  • Limited esthetic capability (opaque, monochromatic)
  • Difficult to achieve precise contours

Clinical Longevity

Glass ionomer restorations show:

  • 3-year survival: 60-80%
  • 5-year survival: 40-60%

Longevity depends significantly on moisture exposure during setting and early post-operative period. Proper moisture protection dramatically improves outcomes.

Indications and Contraindications

Indications:
  • Primary dentition restoration (temporary nature acceptable)
  • High caries risk patients benefiting from fluoride release
  • Root surface lesions and cervical caries
  • Base liner under composite restorations
  • Temporary restorations
  • Pediatric patients where cooperativity is limited
Contraindications:
  • Stress-bearing areas or large carious lesions
  • Posterior teeth requiring high strength
  • Situations where longevity exceeds 5-7 years

All-Ceramic and Porcelain Restorations

Ceramic materials (porcelain, lithium disilicate, zirconia) are fabricated indirectly in a laboratory following tooth preparation and impression. These restorations provide superior esthetics and longevity compared to direct materials.

Material Types

Feldspathic Porcelain Traditional porcelain composed of feldspar, silica, and kaolin, processed through high-temperature firing. Excellent esthetics with superior color matching. Lower strength than contemporary ceramics; susceptible to fracture under concentrated loading. Leucite-Reinforced Ceramic (IPS Empress) Addition of leucite crystals (10-35% by volume) increases strength versus feldspathic porcelain. Strength remains 160-170 MPa—moderate compared to zirconia. Good esthetics with improved strength. Lithium Disilicate (IPS e.max) Contemporary ceramic with lithium disilicate crystals (30% volume). Strength reaches 350-400 MPa. Excellent esthetics with superior strength. Currently popular for full-coverage crowns and large inlays. Zirconia (Yttrium-Tetragonal Zirconia Polycrystal) Transformation-toughening mechanism gives zirconia exceptional strength (900-1400 MPa). Highly resistant to fracture. Lower esthetics—often layered with porcelain for color/esthetic enhancement. Increasingly popular for posterior crowns and bridges.

Clinical Properties

Advantages:
  • Superior esthetics with natural translucency
  • Excellent color stability—no discoloration over decades
  • Outstanding longevity—15-20+ years routine
  • Excellent wear characteristics—does not cause opposing tooth abrasion
  • Biocompatible with excellent tissue response
  • Low plaque accumulation compared to composite
Disadvantages:
  • Higher cost than direct materials
  • Requires tooth preparation and multiple appointments
  • Irreversible—tooth structure cannot be recovered if restoration is damaged
  • Potential for fracture if prepared inadequately or subjected to excessive lateral forces
  • Complex repair if marginal failure develops—often requires replacement rather than repair

Clinical Longevity

All-ceramic restorations demonstrate:

  • 10-year survival: 90-95%
  • 15-year survival: 85-92%
  • 20-year survival: 80-88%

Longevity depends on ceramic material, preparation geometry, and cement selection. Zirconia and lithium disilicate show superior longevity compared to feldspathic porcelain.

Indications and Contraindications

Indications:
  • Anterior esthetic demands requiring maximum longevity
  • Posterior teeth requiring maximum strength and esthetics
  • Multiple tooth restorations where color stability is paramount
  • Patients with demanding esthetic standards
Contraindications:
  • Single posterior tooth restorations in bruxism patients (fracture risk with zirconia)
  • Patients unable to tolerate multiple appointments
  • Situations where cost must be minimized

Gold Restorations

Gold alloys (typically 80%+ gold, 15-20% copper, small percentages of other elements) represent the highest quality restoration material available in dentistry.

Composition and Properties

Gold alloys exhibit exceptional corrosion resistance, excellent longevity, minimal wear to opposing teeth, and superior marginal adaptation when properly constructed.

Mechanical Properties: Compressive strength exceeds 350 MPa. Creep is minimal. Ductility allows adjustment without fracture. Wear of opposing teeth is minimal.

Clinical Properties

Advantages:
  • Unparalleled longevity—40+ year restorations are documented
  • Minimal corrosion and biocompatibility
  • Superior marginal adaptation
  • Minimal opposing tooth wear
  • Adjustable without fracture
Disadvantages:
  • High cost (gold price fluctuations make budgeting uncertain)
  • Metallic esthetics unacceptable for visible teeth
  • Requires expertise—not all laboratory technicians excel at gold fabrication
  • Difficult to repair if marginal failure develops

Clinical Longevity

Gold restorations show:

  • 10-year survival: 95%+
  • 20-year survival: 90%+
  • 30-year survival: 85%+

Indications and Contraindications

Indications:
  • Posterior large restorations in high-stress situations
  • Patients prioritizing longevity above cost
  • Cases where esthetics permit metal visibility
Contraindications:
  • Anterior esthetic zones
  • Cost-conscious patients

Selection Criteria by Cavity Classification

Class I Cavities (Occlusal Surfaces)

Amalgam: Excellent choice for large, deep occlusal caries. Superior longevity and strength. Composite: Acceptable for small-medium occlusal cavities. Esthetic advantage minimal (occlusal surfaces not visible). Consider patient preference and cost. Indirect (Inlay/Crown): Consider for very large occlusal defects. Superior longevity justifies cost and appointments.

Class II Cavities (Occlusal-Proximal)

Amalgam: Gold standard. Superior longevity documented. Composite: Acceptable for small-medium cavities. Moisture control and proximal access are challenges. Indirect (Inlay): Superior for large cavities and posterior aesthetic demands.

Class III and IV Cavities (Anterior-Proximal/Incisal)

Composite: Excellent choice. Esthetics essential. Glass Ionomer: Acceptable for root surfaces. Indirect (veneer): Consider for large anterior cavities or high esthetic demands.

Conclusion

Optimal restoration material selection requires understanding material properties, clinical longevity evidence, and individual case parameters. Contemporary practice increasingly emphasizes evidence-based material selection informed by systematic reviews and clinical outcomes research. The ideal restoration provides optimal longevity, esthetics, and functional outcomes while respecting biological principles and patient preferences.