Glass Ionomer Cements - University of Plymouth 2024-25 PDF

Material Science of Glass Ionomer Cements Dr Alex Cresswell-Boyes [email protected] Key Clinical question. If you see this icon a question related to the clinical aspect of the topic will be asked. Clinical consideration. If you see this icon some key clinical consider...

Material Science of Glass Ionomer Cements Dr Alex Cresswell-Boyes [email protected] Key Clinical question. If you see this icon a question related to the clinical aspect of the topic will be asked. Clinical consideration. If you see this icon some key clinical considerations to be made aware of regarding the topic. Materials question. If you see this icon a question related to the materials aspect of the topic will be asked. Learning Objectives  Recognise the scientific principles underpinning the use of glass ionomer cements.  Identify the constituents of glass ionomer cements.  Outline the limitations of GICs and RMGICs.  Describe the appropriate selection of materials for applicable clinical situations. Outline  Setting reaction.  Ion release.  Components.  GICs vs. RMGICs.  Material selections and clinical considerations. MCQs – Question 1 Which tooth structure is primarily composed of hydroxyapatite crystals? A. Enamel B. Dentine C. Cementum D. Pulp E. Periodontal ligament MCQs – Question 2 What is the smear layer in the context of tooth preparation? A. A layer of plaque accumulated on tooth surfaces B. A thin layer of debris on dentin surfaces after cavity preparation C. A protective protein layer naturally present on enamel D. A layer of cementum covering the root surfaces E. A biofilm formed by oral microorganisms MCQs – Question 3 What is the primary reason for using a rubber dam during restorative dental procedures? A. To provide better access to posterior teeth B. To retract soft tissues and improve visibility C. To prevent contamination from saliva and moisture D. To reduce patient discomfort during drilling E. To enhance the curing of light-activated materials MCQs – Question 4 What is the primary role of fluoride in dental materials? A. Enhances the aesthetic appearance of restorations. B. Acts as a catalyst in polymerisation reactions. C. Provides antibacterial action against periodontal pathogens. D. Inhibits demineralisation and promotes remineralisation. E. Increases the mechanical strength of the material. MCQs – Question 5 Which of the following best describes an acid-base reaction? A. A reaction where an acid donates electrons to a base. B. A neutralisation reaction forming a salt and water. C. A reaction involving oxidation and reduction processes. D. A process where a base releases hydrogen ions. E. A polymerisation reaction initiated by light. MCQs – Answers 1. A. Enamel. Enamel is the outermost layer of the tooth and is primarily composed of hydroxyapatite crystals, making it the hardest substance in the human body. 2. B. Removing the smear layer and enhancing bonding. Cavity conditioners remove the smear layer and modify the tooth surface, enhancing the chemical bond between the glass ionomer cement and the tooth structure. 3. C. To prevent contamination from saliva and moisture. A rubber dam isolates the operative field from saliva and moisture, which is critical for the success of many restorative procedures, especially those sensitive to moisture. 4. D. Inhibits demineralisation and promotes remineralisation. Fluoride helps prevent dental caries by inhibiting demineralisation and enhancing remineralisation, making it a key component in preventive dentistry. 5. B. A neutralisation reaction forming a salt and water. An acid-base reaction in dental cements involves the neutralisation between an acid (e.g., polyacrylic acid) and a base (e.g., glass powder), resulting in the formation of a salt (the set cement) and water. Introduction  Introduced in the early 1970s by Wilson and Kent.  Developed as a biocompatible alternative to silicate cements.  Combines beneficial properties of silicates and polycarboxylate cements.  Widely used for restorative Photo: © van Noort & Barbour 2023 procedures, luting agents, and liners. Scientific Principles of GICs  Acid-Base Reaction:  Setting occurs through a neutralisation reaction.  Polyacrylic acid reacts with ion- leachable glass.  Chemical Bonding:  Forms ionic bonds with calcium ions in tooth enamel and dentine.  Results in adhesion without the need for a separate bonding agent.  Fluoride Release:  Provides anticariogenic properties.  Acts as a reservoir for long-term fluoride ion release. Photo: © GC Europe 2024 Acid-Base Reaction Mechanism  Initial Stage (Dissolution):  Mixing glass powder with liquid initiates the reaction.  Hydrogen ions from the acid attack the glass surface.  Gelation Phase:  Release of metal ions (Ca²⁺, Al³⁺) leads to cross-linking.  Formation of a hydrogel matrix entrapping unreacted glass particles.  Final Maturation (Hardening): Photo: © van Noort & Barbour 2023  Gradual increase in strength over 24 hours.  Water plays a crucial role in the setting How does the setting reaction impact and maturation process. clinical procedures? Requires careful timing to prevent premature set or extended working time. Dissolution (Ion Leaching)  Initiation of Setting Reaction:  Acid Attack on Glass Particles:  Upon mixing, polyacrylic acid dissociates, releasing hydrogen  The acid-base reaction begins with ion ions (H+). leaching.  H+ ions attack the surface of the glass powder particles.  Essential for Cross-Linking:  Releasing calcium (Ca2+), aluminium (Al3+), fluoride (F-), sodium  Released metal ions are crucial for (Na+) and silicate ions (SiO44-). subsequent matrix formation.  Working Time Influence: Glass + H+ → Ca2+ + Al3+ + F- + SiO2  The rate of ion release affects the working and setting times.  Clinical Relevance:  Mixing Technique: Proper mixing ensures uniform ion release and optimal consistency.  Temperature Sensitivity: Higher temperatures can accelerate the reaction, reducing working time.  Handling: Efficient manipulation is needed before the material thickens. Photo: © van Noort & Barbour 2023 Gelation (Initial Set)  End of Working Time:  Formation of Initial Matrix:  Rapid viscosity increase signals that  Released Ca2+ ions cross-link with manipulation should cease. carboxylate groups (R-COO−) on  Material Becomes Unworkable: polyacrylic acid chains.  The gelation stage limits further shaping of the restoration.  Sensitivity to Moisture:  Material is vulnerable to contamination 2 R-COO- + Ca2+ → (R-COO)2Ca during this phase.  Clinical Relevance:  Placement Efficiency: Material must be placed and contoured before gelation.  Isolation Importance: Prevents saliva or moisture from interfering with the setting process.  Surface Protection: Applying a protective coating can safeguard against early moisture exposure. Photo: © van Noort & Barbour 2023 Hardening (Maturation)  Increase in Mechanical Strength:  Aluminum Cross-Linking:  Al3+ ions progressively replace some Ca 2+ ions in the matrix.  Restoration gains strength over time,  Development of a Rigid Structure: becoming more resistant to wear.  Formation of a stable, hardened polyacrylate salt matrix.  Completion of Setting Reaction:  Full maturation may take 24 hours or 3 R-COO- + Al3+ → (R-COO)3Al longer.  Reduced Sensitivity:  Hardened material is less susceptible to moisture and dehydration.  Clinical Relevance:  Delayed Finishing: Final polishing should be postponed until sufficient hardness is achieved.  Patient Instructions: Advise patients to avoid stressing the restoration during initial hours.  Longevity of Restoration: Proper maturation contributes to the durability of the restoration. Photo: © van Noort & Barbour 2023 Adhesion to Tooth Structure  Chemical Adhesion:  Carboxyl groups in polyacrylic acid chelate with calcium in hydroxyapatite.  Micromechanical Interlocking:  Minimal, as GICs do not require etching.  Clinical Implications:  Reduced risk of microleakage. Photo: © van Noort & Barbour 2023  Preservation of tooth structure How does GIC adhesion reduce due to minimal preparation. microleakage? Chemical bonding minimises gaps between restoration and tooth. Fluoride Release and Recharge  Initial Burst Effect:  High fluoride release immediately after placement.  Sustained Release:  Continuous, low-level fluoride release over time.  Recharge Capability:  GICs can absorb fluoride from external sources (e.g., toothpaste).  Benefits: Photo: © Nayak et al. 2019  Inhibits enamel demineralisation. What happens to the mechanical properties of  Promotes remineralisation of affected GICs with time as ions are released? The leaching of ions like fluoride, while beneficial for caries areas. prevention, can lead to slight degradation of the cement matrix. This may result in reduced strength and wear resistance over extended periods, potentially affecting the longevity of the restoration. Constituents of GICs Component Role/Function - Source of Metal Ions: Provides essential ions (Ca²⁺, Al³⁺, F⁻) for the acid-base Glass Powder (Calcium setting reaction.  Glass Powder: Fluoroaluminosilicate - Mechanical Strength: Contributes to the structural integrity of the set cement. Glass) - Fluoride Release: Supplies fluoride ions for anticariogenic effects.  Composition: - Translucency: Affects aesthetic properties of the cement.  Calcium fluoroaluminosilicate - Acid Component: Reacts with the glass powder in the acid-base setting reaction. - Chelation and Cross-Linking: Carboxylate groups (−COO−) bind with metal ions to glass. Polyacrylic Acid (PAA) form a cross-linked matrix.  May contain strontium for - Adhesion to Tooth Structure: Facilitates chemical bonding via ionic interaction with calcium ions in enamel and dentin. radiopacity. - Setting Control: Extends working time and sharpens the setting reaction.  Function: Tartaric Acid - Enhances Properties: Improves mechanical strength and handling characteristics by  Source of ions for cross- promoting efficient cross-linking of the matrix. - Reaction Medium: Essential for ionization of acids and dissolution of glass particles. linking. Water - Ion Mobility: Facilitates the movement of ions during the setting process.  Provides mechanical strength. - Hydrogel Formation: Maintains the hydrogel structure of the set cement. - Radiopaque Agents: Addition of elements like strontium or barium increases  Liquid Component: Fillers and Additives radiopacity for radiographic visibility.  Polyacrylic Acid: - Pigments and Opacifiers: Adjust shade and translucency to improve aesthetic outcomes.  Usually 50% aqueous solution. Polycarboxylic Acid - Modified Acids: Copolymers like itaconic acid or maleic acid are added to improve  Molecular weight affects Copolymers the physical properties and handling characteristics of the cement. Antimicrobial Agents (in - Examples: Addition of chlorhexidine or silver particles. viscosity and working time. Some Advanced GICs) - Role: Provides antibacterial properties to reduce the risk of secondary caries.  Tartaric Acid: - Examples: Polyethylene glycol or similar agents. Dehydration Inhibitors - Role: Prevents rapid water loss during the setting reaction, ensuring proper  Typically 5–10%. maturation of the cement.  Enhances setting characteristics. Role of Tartaric Acid  Setting Control:  Delays initial setting, allowing extended working time  Improved Properties:  Enhances mechanical strength by promoting efficient cross- linking  Clinical Advantage: Photo: © van Noort & Barbour 2023  Facilitates easier manipulation and placement When might adjusting setting time be clinically necessary? In complex restorations requiring longer manipulation. Types of GICs  Conventional GICs:  Basic formulation with standard properties.  Resin-Modified GICs (RMGICs):  Incorporation of hydrophilic resin monomers (e.g., HEMA).  Dual-setting mechanism: acid-base and light-curing.  High-Viscosity GICs:  Increased powder-to-liquid ratio. Photo: © van Noort & Barbour 2023  Enhanced wear resistance and strength.  Metal-Reinforced GICs:  Addition of metal particles (e.g., silver alloy).  Improved toughness for core build-ups. Resin-Modified GICs Component Role - Source of Metal Ions: Provides essential ions (Ca²⁺, Al³⁺, F⁻)  Composition: Conventional GIC for the acid-base setting reaction. - Fluoride Release: Supplies fluoride ions for anticariogenic effects.  Conventional GIC components - Examples: Hydrophilic monomers like HEMA (hydroxyethyl methacrylate). plus resin monomers. Resin Components (in RMGICs) - Dual Setting Mechanism: Allows both acid-base reaction and light-activated polymerisation. - Improved Properties: Enhances mechanical strength,  Advantages: aesthetics, and immediate set upon light curing. - Light-Curing Agents: Substances like camphorquinone initiate Initiators and  Faster setting with light activation Accelerators (in RMGICs) polymerisation of resin components upon light exposure. - Chemical Accelerators: Amines that speed up the curing process, ensuring a prompt set.  Improved aesthetics due to better translucency.  Enhanced physical properties (e.g., flexural strength).  Considerations:  Potential for resin-related issues When should RMGICs be selected over conventional GICs? (e.g., sensitivity). When improved strength and aesthetics are needed. Properties of GICs  Biocompatibility:  Minimal pulpal irritation.  Suitable for use as liners or bases.  Thermal Expansion:  Coefficient similar to natural tooth structure.  Reduces stress at the restoration-tooth interface.  Radiopacity: Photo: © Farag & Amer 2011  Enhanced with additives (e.g., How does thermal expansion compatibility strontium). benefit restorations?  Aids in radiographic evaluation. Reduces stress and risk of debonding under temperature changes. Limitations of GICs  Mechanical Properties:  Lower compressive and tensile strength compared to composites.  Susceptible to fracture under high occlusal loads.  Aesthetic Limitations:  Opaque appearance.  Limited color matching capabilities.  Setting Sensitivity: Photo: © Young & Nelson 2023  Moisture contamination can disrupt setting.  Dehydration leads to crazing and Why might GICs not be suitable for load-bearing cracking. restorations? They have lower fracture toughness and may fail under stress. Limitations of RMGICs  Polymerisation Shrinkage:  Can lead to marginal gaps.  Water Sorption:  Absorption of water over time may affect dimensional stability.  HEMA Content:  Potential for allergic reactions in sensitive patients.  Wear Resistance: Photo: © Stearn 2023  Less resistant compared to resin composites in high-stress What is a potential drawback of areas. polymerisation shrinkage?? It can create gaps leading to microleakage and secondary caries. Moisture Sensitivity Management  Isolation Techniques:  Use of rubber dam or cotton rolls.  Protection During Setting:  Application of varnish or unfilled resin over restoration surface.  Delayed Finishing:  Allow initial set before contouring to prevent disruption. Photo: © Nasser 2021 Why is protecting GICs from dehydration important? Prevents cracking and ensures proper maturation. Aesthetic Considerations  Colour Stability:  Susceptible to staining over time.  Surface Texture:  Rougher finish compared to composites.  Indications:  More suitable for posterior restorations or non-esthetic Photo: © Young & Nelson 2023 zones. What factors contribute to the opacity of GICs? The composition of glass particles and lack of resin components. Clinical Applications of GICs  Restorative Material:  Class III and V cavities, especially in cervical regions.  Temporary restorations.  Luting Agent:  Cementation of crowns, bridges, and orthodontic brackets.  Base or Liner:  Under amalgam or composite restorations. Photo: © Nisha & Amit 2011  Provides thermal insulation and fluoride release.  Fissure Sealants: How do GICs function as luting  In cases where moisture control is agents? challenging. They adhere to both tooth structure and restorative materials. Material Selection Criteria  Patient Factors:  Age: Ideal for pediatric patients due to fluoride release.  Caries Risk: High-risk patients benefit from anticariogenic properties.  Tooth Factors:  Cavity Size and Location: Best for small to moderate lesions in low-stress areas.  Substrate Condition:  Suitable for root caries and lesions near the gingival margin.  Clinical Environment:  Situations with compromised isolation where resin composites are contraindicated. Photo: © Burke et al. 2023 Appropriate Material Selection  Conventional GICs:  Root surface restorations.  Non-load-bearing areas.  RMGICs:  Patients requiring improved aesthetics but with limitations for composite use.  Intermediate restorations in primary teeth.  Not Recommended For:  Large posterior occlusal restorations in adults.  Areas subjected to high masticatory forces. Photo: © Young & Nelson 2023 Handling and Placement Techniques  Tooth Preparation:  Minimal invasive approach.  Beveling not required due to chemical adhesion.  Cavity Conditioning:  Application of 10% polyacrylic acid for 10–20 seconds.  Rinsing and gentle drying to remove smear layer.  Mixing and Placement:  Follow manufacturer's instructions for powder-to-liquid ratio.  Avoid over-mixing to prevent air entrapment.  Finishing and Polishing:  Delayed for 24 hours in conventional GICs to allow maturation.  Immediate finishing possible with RMGICs due to light-curing.  Materials in SDLE/PDSE Type of Material Material's Name & Manufacturer Source Fuji IX (GC) Glass ionomer cement SDLE, PDSE Aquacem (Dentsply) Resin-modified glass ionomer Fuji II LC (GC) SDLE, PDSE cement Summary  GICs set through an acid-base reaction forming a durable hydrogel matrix.  Chemical adhesion to tooth structure via ionic bonds with calcium ions.  Calcium fluoroaluminosilicate provides essential ions and strength.  Polyacrylic acid initiates setting; tartaric acid optimises working time and enhances properties.  Inhibits demineralisation and promotes remineralisation for caries prevention.  Lower fracture toughness compared to composites; not ideal for high- stress areas.  Requires strict isolation during setting to prevent weakening.  Suitable for Class III and V restorations, luting agents, bases, and liners.  Ideal for patients with high caries risk due to sustained fluoride release. References  Berg, J. H. (2002). Glass ionomer cements. Pediatric Dentistry. PDF Link  Anusavice, K. J., Shen, C., & Rawls, H. R. (2012). Phillips' Science of Dental Materials. Elsevier.  Powers, J. M., & Wataha, J. C. (2015). Dental Materials-E-Book: Foundations and Applications. Elsevier.  Sidhu, S. K., & Nicholson, J. W. (2016). A review of glass-ionomer cements for clinical dentistry. Journal of Functional Biomaterials. PDF Link  Van Noort, R., & Barbour, M. E. (2023). Introduction to Dental Materials-E- Book. Elsevier. MCQs – Question 6 Which ions are primarily involved in the cross-linking process during the hardening stage of GICs? A. Sodium ions (Na⁺) B. Potassium ions (K⁺) C. Calcium ions (Ca²⁺) D. Fluoride ions (F⁻) E. Hydrogen ions (H⁺) MCQs – Question 7 In GICs, what is the primary function of water? A. Acts as a solvent for the resin components B. Facilitates ion mobility and is essential for the acid-base reaction C. Increases the viscosity of the cement D. Enhances aesthetic properties by improving translucency E. Provides radiopacity for radiographic detection MCQs – Question 8 Which property of GICs closely matches that of tooth structure, reducing stress at the restoration interface? A. Compressive strength B. Thermal expansion coefficient C. Elastic modulus D. Surface hardness E. Water sorption rate MCQs – Question 9 Which of the following best describes a limitation specific to RMGICs compared to conventional GICs? A. Increased moisture sensitivity during setting B. Potential for polymerisation shrinkage leading to marginal gaps C. Lower fluoride release over time D. Less adhesion to tooth structure E. Incompatibility with light curing units MCQs – Question 10 Over time in the oral environment, what happens to the mechanical properties of GICs as ions are released? A. Mechanical properties significantly increase due to ongoing maturation B. Mechanical properties remain unchanged as ion release doesn't affect the matrix C. Mechanical properties may gradually decrease due to matrix degradation from ion leaching D. GICs become harder and more resistant to wear over time E. GICs dissolve completely due to continuous ion release MCQs – Answers 6. C. Calcium ions (Ca²⁺). These ions cross-link with polyacrylic acid chains, forming the hardened cement matrix. 7. B. Facilitates ion mobility and is essential for the acid-base reaction. Water allows acid ionisation and ion movement necessary for setting​. 8. B. Thermal expansion coefficient. Matching thermal expansion minimises stress from temperature changes. 9. B. Potential for polymerisation shrinkage leading to marginal gaps. Resin components can shrink upon curing, creating gaps. 10. C. Mechanical properties may gradually decrease due to matrix degradation from ion leaching. Ion release can slightly degrade the cement matrix, reducing strength over time. Feedback – YourVoice We are continuously improving your learning experience through plenaries and their delivery. We would appreciate your feedback on what you found effective and what could be improved. Please scan the QR code below or click on the yellow icon to visit the YourVoice site.