The use of composite materials for direct reconstruction in the anterior and posterior parts of the dentition..pdf

Components of Composite Resin

  • 1. Organic resin matrix

    • composition: Monomer, Initiator, Inhibitors, Pigments

  • 2. Inorganic filler

  • 3. Coupling agent

  • 4. Initiator-accelerator system

Monomer in Composite Resins

  • Functions:

    • Binds filler particles together

    • Provides proper workability

  • Typical Monomers:

    1. Bis-GMA

    2. UEDMA

    3. TEGDMA

Polymerization Reaction

  • Description: An exothermic reaction post light/chemical activation, where monomers convert to polymers.

  • Effects:

    • free volume decrease (in polymer) - as the polymer chain rotation = restricted compared to unpolymerized monomers

    • Decrease in molecular vibration and intermolecular distances

    • Transition from paste/pregel state → viscous solid

  • Three Stages:

    • Initiation, Propagation, Termination

  • strategies to minimise polymerisation contraction :

    • Filling monomer resins with prepolymerized resins

    • Maximizing inorganic filler content

    • Utilizing high molecular mass methacrylate monomers

  • polymerisation shrinkage:

    • Range: 1.35% to 7.1% (typically around 2-3%).

    • Issues: Leads to adhesion failures associated with the degree of monomer to polymer conversion.

    • recommendations addressing polymerisation shrinkage:

      • Use of "soft-start" polymerization

      • Incremental layering technique to reduce shrinkage effects

      • Application of stress-breaking liners (filled adhesive, flowable composites, resin-modified glass ionomers)

      • Use of non or low-shrinking restorative materials

C-Factor (Configuration Factor)

  • Definition: The ratio of bonded to unbonded surfaces in a tooth preparation.

  • Higher C-factor increases potential for bond disruption from polymerization effects.

  • Examples:

    • Class IV restoration (1 bonded, 4 unbonded): C-factor 0.5 (low risk)

    • Class I restoration (5 bonded, 1 unbonded): C-factor 5 (high risk)

    • 1: pits fissures (post.), lingual (ant.); 2: proximal (post) 2; 3: proximal (ant.) 2; 4: proximal + incisal edge (ant.); 5: gingival 1,9; 6: cusps

Resin Matrix

  • Contains activator/initiator systems for curing.

  • Curing reactions can be chemical or visible-light activated.

Inorganic Filler

  • makes up major part of composite ( by volume or weight)

  • Role: Reinforces resin matrix, controls volume shrinkage (polym.) , and provides certain degree of translucency.

  • Composition: Glasses with high atomic number atoms (e.g., barium, strontium, zirconium) for radiopacity during X-rays.

  • Size: Influences surface smoothness (larger particles = rougher surfaces).

  • Filler Content: Increased filler % lowers resin content → reduced shrinkage and adjusting thermal expansion coefficient closer to tooth structure + improved hardness, strength, handling and abrasion resistance

Coupling Agent

  • Purpose: Binds filler to resin matrix, enhances mechanical properties of composite, and minimizes filler plucking during clinical wear.

  • Functions:

    • Distributes stress among particles and polymer

    • Creates a hydrophobic environment lowering water absorption of composite

Advantages of Composite Materials

  1. Aesthetic appeal

  2. Conserves tooth structure

  3. Insulative properties

  4. Repairable

  5. Can be polished in one appointment

Disadvantages of Composite Materials

  1. Polymerization shrinkage

  2. Time-consuming and expensive

  3. Technique sensitive

  4. Difficult finishing and polishing

  5. Lacks direct adhesion to tooth structure

  6. Higher coefficient of thermal expansion than tooth structure

Indications for Use

  • Suitable for Class I, II, III, IV, V, and VI cavities

  • Can be utilized as foundations or core buildups; sealants + preventative resin restorations; and esthetic enhancements such as veneers, tooth contour modifications, diastema closures

  • Recommended for cements in indirect restorations

  • temporary restorations

  • Used in periodontal splinting

Contraindications for Use

  1. High caries incidence/poor oral hygiene

  2. Teeth under heavy/abnormal occlusal stress

  3. Difficult access or isolation

  4. Subgingival difficulties

  5. Patient allergy/sensitivity to resin composites

Classification of Composites

  • Composites are primarily classified based on inorganic filler size, amount, and composition.

Handling Characteristics and Properties

  • Types:

    • Multipurpose: High strength, high modulus

    • Nanocomposite: Best polish, high strength, high modulus

    • Microfilled: Best polishing, best esthetics, higher shrinkage

    • Packable: Less shrinkage, lower wear

    • Flowable: Syringeable, lower modulus, higher wear potential

    • Laboratory: Best anatomy, requires lab costs and specialized cement

Specific Composite Brands

  • Neo Spectra ST (Dentsply Sirona):

    • Nano-ceramic, light-cured, radiopaque, universal comp. suitable for direct/indirect restorations, available in HV and LV (Low visc) viscosities.

    • comprises barium glass, prepolymerised filler + ytterbium fluoride

  • Charisma Classic (Kluzer):

    • Radiopaque, light-cured, microhybrid composite with BIS-GMA matrix, contains 60% inorganic volume. indicated for Class I-V, direct composite veneers, shape corrections of teeth, splinting of teeth loosened by trauma / periodontal disease, primary teeth restoration, repairs of porcelain/ composite

  • SDR (Dentsply Sirona):

    • one-component, light-cured, Flowable-like characteristics , fluoride-containing composite, ideal for class I and II cavities, self-leveling feature allowing adaptation to cavity walls, one universal shade, controlled polymerisation (modulator helps monomers form more relaxed network) → less shrinkage stress

Restorative Techniques for Posterior Teeth

  • Horizontal Layering Technique: Involves layers <2.0 mm thick, can increase C-factor and shrinkage stresses between opposing cavity walls

  • Oblique Layering Technique: Uses wedge-shaped increments to reduce C-factor and distortion. each increment photocured 2x (through cavity wall + occlusal)

  • Vertical Layering Technique: Small increments placed vertically to minimize gaps from polymerization shrinkage. polym: from behind the wall (e.g. if inc: buccal: place on lingual wall + cure outside lingual wall),

  • Successive Cusp Buildup Technique: Individual cusps restored progressively to maintain tooth morphology.

  • Bulk-Fill Techniques: Allows filling cavities in increments of around 4 mm for efficiency. more grey-ish. modifications: bulk and body

    • flowable bulk-fill material (dentin) + conventional composite (compensates for absorbtion of light → not so grey) to provide resistance to masticatory loads.

Restorative Techniques for Anterior Teeth

  • Dual-Shade Layering Technique: Utilizes dentine and enamel shades for a natural appearance.

  • Polychromatic Layering Technique: Employs various composite shades to achieve aesthetic restorations, requiring a solid understanding of material and optical properties.

  • Considerations: Selecting the right chroma and opacity to match natural tooth structure.