Material Science of Resin-Based Composites

Material Science of Resin-Based Composites & Compomers

• This presentation covers the material science of resin-based composites and compomers, focusing on their use in dentistry.

Key Concepts

• Clinical question: Indicates a question related to the clinical application of the material.
• Clinical consideration: Highlights important clinical factors to consider regarding the material.
• Materials question: Indicates a question about the material's properties.

Learning Objectives

• Recognize the scientific principles underpinning dental composite resin materials.
• Identify the constituents of dental composite resin materials.
• Outline the processes used in etching and bonding of dental composite resin materials to tooth tissue.
• Outline the limitations of dental composite resin materials.

Outline

• Constituents
• Types of composites
• Compomers
• Etch and bond systems
• Polymerisation
• Limitations
• Clinical applications

MCQs - Question 1

• Which term describes the process of small molecules (monomers) joining to form a large molecule (polymer)?
• Correct Answer: Polymerisation

MCQs - Question 2

• Which characteristic best describes dentine compared to enamel?
• Correct Answer: Contains odontoblastic processes

MCQs - Question 3

• Which property is most critical for a restorative material placed in posterior load-bearing areas?
• Correct Answer: High compressive strength

MCQs - Question 4

• What best describes the smear layer on dentine surfaces?
• Correct Answer: A layer of debris created during tooth preparation

MCQs - Question 5

• What is the main reason for applying a bonding agent to etched dentine before placing composite resin?
• Correct Answer: To seal dentinal tubules and prevent sensitivity

MCQs - Answers

• Polymerization: The chemical process where monomers link to form polymers.
• Dentine: Vital, sensitive tissue with tubules.
• Enamel: Acellular, less sensitive tissue.
• Smear layer: Debris from tooth preparation.
• Bonding agent: Seals dentinal tubules to prevent sensitivity.
• Composite resin: Contains a resin matrix reinforced with inorganic fillers.

Introduction

• Composite materials are mixtures of multiple chemical phases.
• Restore function and aesthetics of damaged or decayed teeth.
• Shift from amalgam fillings to tooth-coloured restorations.
• Demand for materials that mimic natural tooth appearance.

Organic Resin Matrix

• Bis-GMA (Bisphenol A-Glycidyl Methacrylate): High molecular weight reduces shrinkage; provides rigidity.
• UDMA (Urethane Dimethacrylate): Increases flexibility and toughness, enhances handling.
• TEGDMA (Triethylene Glycol Dimethacrylate): Lowers viscosity, improves flow and adaptation, used as a diluent.

Inorganic Filler Particles

• Quartz: Improves wear resistance (hard).
• Silica: Provides translucency and polishability.
• Glass: Barium or strontium glasses add radiopacity.
• Functions: Enhance mechanical properties (strength), reduce shrinkage and expansion, influence esthetics.

Coupling Agents

• Silane coupling agents chemically bond inorganic filler to organic resin matrix; improve mechanical properties, prevent filler dislodgment, and water penetration.

Initiators and Accelerators

• Camphorquinone: Primary photoinitiator activated by visible light.
• Tertiary Amines: Co-initiators to accelerate polymerisation.
• Phenylpropanedione: Alternative initiator for improved color stability.

Additives

• Pigments: Metallic oxides (iron, titanium) adjust shade and translucency.
• Ultraviolet Absorbers: Prevent discoloration from UV exposure.
• Inhibitors: Hydroquinone extends shelf life by preventing premature polymerisation.

Constituents

• Organic resin matrix: Bis-GMA, UDMA, TEGDMA
• Inorganic filler particles: Quartz, silica, glass particles
• Coupling agents: Silane coupling agents
• Initiators and accelerators: Camphorquinone, tertiary amines
• Additives: Pigments, inhibitors, UV absorbers
• Others: Stabilizers, optical modifiers, plasticisers

Macrofilled, Microfilled, Hybrid Composites

• Filler size, Advantages, Disadvantages, Applications
• Characteristics and mechanical properties of each composite type

Flowable and Packable Composites

• Flowable: Lower filler content, increased flow, good adaptation
• Packable: Higher filler content, stiff consistency, mimics amalgam handling; difficult adaptation

Compomers

• Composite resins modified with polyacid groups, incorporate features of composites and glass ionomer cements, resin matrix with acid-functional monomers, fluoride-releasing glass fillers.

Compomers (Cont.)

• Properties: Fluoride release (anti-cariogenic), handling (easy to manipulate), aesthetics (tooth-coloured, acceptable translucency).
• Uses: Pediatric dentistry, Class III and V restorations, orthodontic cementation.
• Limitations: Lower strength compared to composites, potential for water uptake and expansion.

Etching Process

• Purpose: Enhance adhesion, remove smear layer, increase surface energy.
• Etching agents: Phosphoric acid (35-37%).

Procedure (Etching)

• Enamel etching: Apply etchant for 15-30 seconds.
• Dentine etching: Apply for 10-15 seconds.
• Rinsing: Rinse thoroughly for at least 10 seconds.
• Drying: Air dry enamel, keep dentine moist.
• Etching patterns: Type I, II, III

Bonding Process

• Purpose: Establish strong bond, prevent microleakage, distribute stress.
• Bonding systems: Total-etch (etch-and-rinse), self-etch, universal adhesives

Application Steps (Etching, Primer, Adhesive)

• Etching: Procedures
• Primer application: Apply generously, allow thinning to evaporate solvents.
• Adhesive application: Apply uniformly.

Polymerisation

• Free radical polymerisation: Initiation (photoinitiators), Free radicals, Degree of conversion.
• Exothermic reaction: Heat generated during polymerization must be controlled.

Polymerisation Shrinkage

• Mechanism: Monomer conversion to polymers reduces free volume.
• Consequences: Gap formation at tooth-restoration interface, internal stress leading to enamel cracks.
• Strategies to minimize shrinkage: Incremental layering, modified curing techniques, low-shrinkage materials.

Composite Layering Technique

• Why composite increments should not exceed 2 mm: Ensure proper light penetration and complete polymerization.

Limitations

• Polymerization shrinkage
• Wear resistance
• Technique sensitivity
• Discoloration
• Longevity

Clinical Applications

• Anterior restorations: Class III, IV, and V restorations, veneers, diastema closures.
• Posterior restorations: Conservative preparations, elimination of undercuts, use of sectional matrices, attention to occlusal anatomy.
• Minimally invasive dentistry: Prevention, sealants, early lesions, indirect composite restorations (inlays, onlays, veneers).

Materials in SDLE/PDSE

• List of materials and manufacturers used in SDLE/PDSE.

Summary

• Composite resins harden via light-activated polymerization.
• Bonding involves mechanical and chemical adhesion.
• Main composite components are resin matrix, fillers, and coupling agents.
• Etching creates micro-retentions, enhanced by bonding agents.
• Different composites cater to specific clinical requirements.
• Advanced composites improve properties and ease of use.
• Proper techniques lead to successful, durable restorations.

MCQs - Question 6

• Which component in dental composite resins is primarily responsible for reducing polymerization shrinkage?
• Correct Answer: Inorganic filler particles

MCQs - Question 7

• What is the main function of silane coupling agents in composite resins?
• Correct Answer: Bond inorganic fillers to the organic resin matrix.

MCQs - Question 8

• Which factor most significantly contributes to postoperative sensitivity following composite resin restorations?
• Correct Answer:Polymerisation shrinkage causing microleakage.

MCQs - Question 9

• In the context of composite resin restorations, what does the term "degree of conversion" refer to?
• Correct Answer: The percentage of monomer units converted to polymer.

MCQs - Question 10

• What is the main limitation of compomers compared to traditional composite resins?
• Correct Answer: Lower mechanical strength and wear resistance.

MCQs- Answers (Cont.)

• Inorganic filler particles: Reduce shrinkage by occupying space in the resin matrix.
• Bonding agents (silane coupling agents): Create chemical bonds between inorganic fillers and the organic resin matrix.
• Polymerization shrinkage: Creates gaps and microleakage leading to potential sensitivity.
• Degree of conversion: Percentage of monomers converted into the polymer network.

This quiz explores the material science of resin-based composites and compomers with a focus on their applications in dentistry. Participants will assess their understanding of the properties, clinical considerations, and processes involved in using these materials in dental practices.