Bases, Liners & Varnishes - Dr Alex Cresswell-Boyes 2024-25 PDF

Material Science of Bases, Liners & Varnishes 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 cons...

Material Science of Bases, Liners & Varnishes 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 bases, and linings e.g. Ca(OH)2/ZnOEug/ZnO/ ZnP. ▪ Recall the constituents of bases and linings. ▪ Outline the advantages and limitations of bases and linings. ▪ Describe the appropriate selection of materials for applicable clinical situations. Outline ▪ Vases, liners & varnishes. ▪ Pulp protection. ▪ Constituents and properties. ▪ Advantages and limitations. ▪ Clinical application and material selection. MCQs – Question 1 Which part of the tooth contains nerves and blood vessels, making it sensitive to stimuli? A. Enamel B. Cementum C. Dentin D. Pulp E. Alveolar Bone MCQs – Question 2 Why is it important to protect the dental pulp during restorative procedures? A. To prevent tooth discoloration B. To avoid pain and maintain tooth vitality C. To enhance enamel hardness D. To improve saliva production E. To reduce tooth mobility MCQs – Question 3 Which property is essential for a material used to fill cavities to withstand chewing forces? A. High solubility B. Low viscosity C. High compressive strength D. Low thermal conductivity E. Translucency MCQs – Question 4 Which of the following is a common cause of postoperative sensitivity after a dental restoration? A. Overhanging restorations B. Excessive polishing C. Microleakage at the restoration margins D. Proper occlusion E. Use of fluoride toothpaste MCQs – Question 5 Why is thermal conductivity an important consideration for restorative materials? A. To enhance aesthetics B. To prevent thermal shock to the pulp C. To improve adhesion D. To reduce setting time E. To increase hardness MCQs – Answers 1. D. Pulp. The pulp is the innermost part of the tooth containing nerves and blood vessels, providing nutrients and sensory function to the tooth. 2. B. To avoid pain and maintain tooth vitality. Protecting the pulp prevents irritation or damage that can cause pain or lead to the death of the pulp tissue, necessitating more extensive treatment. 3. C. High compressive strength. Materials with high compressive strength can withstand the forces of mastication without deforming or fracturing. 4. C. Microleakage at the restoration margins. Microleakage allows bacteria and fluids to penetrate the interface between the tooth and restoration, leading to sensitivity and potential secondary caries. 5. B. To prevent thermal shock to the pulp. Materials with low thermal conductivity protect the pulp from temperature extremes by insulating against hot and cold stimuli. Bases & Liners Defined ▪ Bases: Materials applied in thick layers to replace missing dentine, provide thermal insulation, and distribute stress. ▪ Linings (Liners): Thin coatings applied to seal dentine tubules, protect pulp tissue, and sometimes release therapeutic agents. ▪ Varnishes: Solutions of resins in Photo: © Denteach 2021 volatile solvents applied to seal dentine tubules and reduce How do bases differ from liners in application? microleakage. Bases are thicker layers replacing dentine, while liners are thin coatings primarily for sealing and pulp protection. Role in Restorative Dentistry ▪ Pulp Protection ▪ Thermal insulation. ▪ Chemical protection from restorative materials. ▪ Barrier against bacterial ingress. ▪ Enhancement of Restoration Longevity Photo: © Nisha & Amit 2011 ▪ Reducing microleakage. ▪ Minimising postoperative Why is sealing dentine tubules important? sensitivity. It reduces fluid movement and sensitivity, preventing bacterial penetration that could harm the pulp. Pulp-Dentine Complex ▪ Sensitivity of pulp tissue to external stimuli. ▪ Importance of preserving pulp vitality. ▪ Mechanisms of Protection ▪ Thermal Insulation: Preventing thermal shock from hot and cold stimuli. ▪ Chemical Protection: Neutralising acidic components from restorative materials. Photo: © Peters et al. 2021 ▪ Sealing Dentin Tubules: Reducing fluid movement and bacterial penetration. ▪ Stimulating Reparative Dentine: Inducing tertiary dentine formation to protect the pulp. Calcium Hydroxide (Ca(OH)2) ▪ Properties Component Base Paste: Role/Function ▪ High alkalinity (pH ~12). Calcium Hydroxide Provides high alkalinity (pH ~12), stimulates tertiary ▪ Antibacterial activity. Zinc Oxide dentine formation, and offers antibacterial properties. Acts as a filler to improve handling and strength. ▪ Stimulates tertiary dentine formation. Glycol Salicylate Reacts with calcium hydroxide to form a hard-set ▪ Uses material. Catalyst Paste: ▪ Direct and indirect pulp capping. Calcium Tungstate Radiopacifier to make the material visible on radiographs. ▪ Protective liner under restorations. Titanium Dioxide Additional radiopacifier and filler for opacity. ▪ Forms Available Zinc Stearate Acts as a lubricant to improve mixing and handling. Ethylene Toluene Plasticiser to adjust consistency. ▪ Chemical-cured (self-setting) – two Sulfonamide paste system. ▪ Light-cured formulations. Component Role/Function Same as above; provides high pH and stimulates dentine Calcium Hydroxide formation. Methacrylate Resin Polymerisable resins that allow light curing and What role does material pH play in pulp Monomers hardening of the material. protection? Photoinitiators (e.g., Initiate polymerisation upon exposure to light of specific High pH materials neutralise acids and have antibacterial Camphorquinone) wavelengths. effects, aiding in pulp health. Fillers (e.g., Barium Provide radiopacity and adjust viscosity and strength. Sulfate, Silica) Zinc Oxide Eugenol (ZnOEug or ZOE) ▪ Properties Component Role/Function ▪ Sedative effect on pulp tissue. Powder: Primary reactive ingredient; reacts with eugenol to form a ▪ Good sealing ability. Zinc Oxide set material. ▪ Low compressive strength. White Rosin Enhances strength and reduces brittleness; improves handling. ▪ Uses Zinc Acetate Acts as an accelerator to speed up the setting reaction. ▪ Temporary restorations. Polyethylene Glycol Modifies setting time and consistency. ▪ Base material under non-resin (optional) Liquid: restorations. Acts as the liquid component; reacts with zinc oxide; ▪ Not recommended under resin-based Eugenol provides sedative effect on pulp and antibacterial composites due to inhibition of properties. Acts as a plasticiser to improve flow and handling polymerisation. Olive Oil (optional) characteristics. ▪ Types ▪ Type I: Temporary cements. ▪ Type II: Permanent luting agents. ▪ Type III: Temporary fillings and bases. Why avoid ZOE under resin-based composites? Eugenol inhibits polymerisation of resin composites, compromising the restoration. Modified Zinc Oxide Eugenol (EBA Cement) ▪ Properties Component Powder: Role/Function ▪ Enhanced mechanical strength Zinc Oxide Primary reactive ingredient as in conventional ZOE. compared to conventional ZOE. Alumina Increases strength and hardness; improves abrasion resistance. ▪ Reduced solubility. Quartz (optional) Enhances mechanical properties and durability. ▪ Better abrasion resistance. White Rosin Same as in ZOE; improves handling. ▪ Modifications Liquid: Eugenol Reacts with zinc oxide; provides sedative effect. ▪ Addition of Ethoxybenzoic Acid Ethoxybenzoic Acid (EBA) Replaces some eugenol; increases strength and reduces solubility of the set cement. (EBA). Olive Oil (optional) Plasticiser to adjust consistency. ▪ Inclusion of alumina fillers. ▪ Uses ▪ Permanent luting cement. ▪ Base material under restorations Eugenol can have an inflammatory where increased strength is response. required. Eugenol at higher concentrations or with prolonged exposure, it becomes cytotoxic to pulp cells. This cytotoxicity irritates the pulp tissue, leading to inflammation. Zinc Phosphate Cement (ZnP) ▪ Properties Powder: Component Role/Function ▪ High compressive strength. Zinc Oxide Main reactive ingredient; reacts with phosphoric acid. ▪ Exothermic setting reaction. Magnesium Oxide Silica (optional) Controls setting time and influences strength. Acts as a filler to improve physical properties. ▪ Initial low pH (potential pulp Bismuth Trioxide (optional) Provides radiopacity. irritation). Liquid: ▪ Uses Phosphoric Acid (~50- Reacts with zinc oxide to form a hard matrix; provides 60%) acidity for the reaction. ▪ Base material under amalgam Water (~30-35%) Medium for the acid-base reaction; influences ionisation and setting time. restorations. Aluminium Phosphate Acts as a buffer to control pH and setting characteristics. ▪ Luting agent for crowns and (optional) bridges. ▪ Composition ▪ Powder: Zinc oxide, magnesium oxide. What precaution is needed when ▪ Liquid: Phosphoric acid, water, using ZnP near the pulp? buffers. Use a liner to protect the pulp from its initial low pH and exothermic setting reaction. Zinc Polycarboxylate Cement Component Role/Function ▪ Properties Powder: Zinc Oxide Primary reactive ingredient; reacts with polyacrylic acid. ▪ First cement to exhibit true Magnesium Oxide Modifies setting time; improves strength. Tin Oxide (optional) Enhances mechanical properties and radiopacity. chemical adhesion to tooth Bismuth Oxide (optional) Provides radiopacity. structure. Liquid: Reacts with zinc oxide to form a cross-linked matrix; ▪ Moderate compressive strength. Polyacrylic Acid provides chemical adhesion to tooth structure. Copolymers of Acrylic Acid ▪ High viscosity upon mixing. (e.g., Itaconic Acid, Maleic Acid) Modify viscosity and setting characteristics; enhance adhesion. ▪ Minimal pulp irritation due to large Water Solvent for the acid; essential for the acid-base reaction. molecular size of polyacrylic acid. ▪ Uses ▪ Luting agent for crowns, bridges, What is a handling challenge with and orthodontic bands. this cement? ▪ Base material under restorations. High viscosity and short working time require quick and precise application. Glass Ionomer Cements (GIC) ▪ Properties Component Role/Function Powder: ▪ Chemical bond to tooth structure. Fluoroaluminosilicate Glass Primary reactive component; releases fluoride ions; reacts with polyacrylic acid. ▪ Fluoride release (anticariogenic Calcium Fluoride (part of Provides source of fluoride for release; contributes to glass) anticariogenic properties. effect). Contributes to the strength and translucency of the Aluminium Oxide ▪ Thermal expansion similar to dentine. Liquid: cement. ▪ Uses Polyacrylic Acid Reacts with glass powder to form a cross-linked matrix; provides adhesion to tooth structure. ▪ Bases and liners under restorations. Tartaric Acid Controls setting characteristics; extends working time ▪ Restorative material for non-stress- and sharpens setting reaction. Solvent for the acid; necessary for the ionisation and Water bearing areas. reaction with glass powder. ▪ Luting agent for crowns and bridges. ▪ Advantages ▪ Biocompatibility. ▪ Reduced microleakage. How does GIC benefit patients with high ▪ Versatility in clinical applications. caries risk? By releasing fluoride, it helps prevent secondary caries around restorations. Resin-Modified Glass Ionomer Cements (RMGIC) ▪ Properties Component Role/Function ▪ Combines properties of GIC and resin Powder: Same as conventional GIC powder with possible inclusion of photo-reactive fillers. composites Fluoroaluminosilicate Same role as in GIC; fluoride release and reaction with ▪ Improved mechanical properties Glass Liquid: acid. ▪ Dual setting mechanism (acid-base Polyalkenoic Acid Modified Allows for both acid-base and light-cured polymerisation reaction and light-curing) with Methacrylate Groups reactions. ▪ Uses HEMA (Hydroxyethyl Methacrylate) Monomer that facilitates resin polymerisation; improves adhesion. ▪ Liners and bases under resin Photoinitiators Initiate light-activated polymerisation process. restorations Tartaric Acid Same as in GIC; controls setting characteristics. ▪ Restorative material for class V Water Necessary for acid-base reaction and ion transport. lesions ▪ Advantages ▪ Enhanced strength and wear resistance ▪ Better esthetics compared to Why choose RMGIC over conventional conventional GIC GIC? It offers improved mechanical properties and can be light- cured for faster setting. Adhesive Resin Liners ▪ Properties Component Bis-GMA (Bisphenol A Role/Function ▪ Low-viscosity resin systems. Glycidyl Methacrylate) UDMA (Urethane Main resin monomer; provides structural backbone. Alternative resin monomer; affects viscosity and ▪ Penetrate and seal dentine Dimethacrylate) flexibility. HEMA (Hydroxyethyl Low-viscosity monomer; promotes penetration into tubules. Methacrylate) dentine tubules; enhances adhesion. ▪ Compatible with resin-based Photoinitiators (e.g., Camphorquinone) Initiate polymerisation upon light exposure. composites. Solvents (e.g., Ethanol, Acetone, Water) Enhance penetration into dentine; evaporate during curing. ▪ Uses Fillers (optional) May contain nanoparticles to adjust viscosity and improve mechanical properties. ▪ Liners under composite Adhesion Promoters (e.g., Enhance chemical bonding to tooth structure. 4-META, MDP) restorations. ▪ Sealing hypersensitive dentine. ▪ Types When are adhesive resin liners ▪ Self-etching primers. preferred? ▪ Total-etch adhesives. Under resin restorations requiring strong adhesion and dentine sealing. Cavity Varnishes ▪ Properties Component Role/Function ▪ Solutions of natural or synthetic Natural Resins (e.g., Copal Form a thin film upon solvent evaporation; seal dentine Resin) tubules. resins in organic solvents Synthetic Resins (e.g., Polyurethane, Polystyrene) Alternative to natural resins; provide sealing effect. ▪ Form thin films upon solvent Volatile Solvents (e.g., Dissolve resins; evaporate after application, leaving a evaporation Ether, Chloroform, Acetone) resin film. ▪ Provide temporary seal ▪ Uses ▪ Under amalgam restorations to reduce microleakage ▪ Not recommended under resin composites ▪ Limitations ▪ Soluble in oral fluids Why are varnishes used under ▪ Limited longevity amalgam but not composites? They reduce microleakage under amalgam but interfere with composite bonding.  Comparison Temporary Material Base Liner Varnish Indications for Use Properties Material - Direct and indirect pulp capping - Low compressive strength Calcium Hydroxide No Yes No No - Deep cavities near the pulp - High pH (~12), providing antibacterial properties - Stimulates reparative dentine formation - Poor mechanical strength; not suitable as a base - Sedative temporary restorations - Low to moderate compressive strength - Base under amalgam restorations - Sedative effect on pulp due to eugenol Zinc Oxide Eugenol Yes Yes No Yes - Eugenol inhibits polymerisation of resin composites; not recommended under resin - Temporary cementation restorations - Base under restorations requiring improved strength - Improved strength and hardness compared to conventional ZOE Modified Zinc Oxide Yes Yes No Occasionally - Reduced solubility Eugenol - Luting agent for crowns and bridges - Contains eugenol; may inhibit resin polymerisation - Base under amalgam restorations - High compressive strength Zinc Phosphate - Low tensile strength Yes Rarely No No Cement - Luting agent for crowns, bridges, and orthodontic bands - Exothermic setting reaction - Initial low pH; potential for pulp irritation if not properly insulated - Bases and liners under restorations - Moderate compressive strength Glass Ionomer - Luting agent for crowns and bridges - Chemical adhesion to tooth structure Yes Yes No Yes Cement - Restorative material for non-stress-bearing areas - Fluoride release provides anticariogenic effect - Temporary restorations - Coefficient of thermal expansion similar to tooth structure - Bases and liners under composite restorations - Improved mechanical properties over conventional GIC Resin-Modified - Restorative material in low-stress areas - Dual setting mechanism (acid-base reaction and light-curing) Glass Ionomer Yes Yes No No - Fluoride release Cement - Class V restorations - Better aesthetics and wear resistance than GIC - Liner under composite restorations - Low viscosity resin Adhesive Resin - Sealing hypersensitive dentine - Bonds micromechanically and chemically to tooth structure No Yes No No Liners - Compatible with resin-based composites - Enhancing bond strength between tooth and restoration - Provides sealing of dentine tubules to prevent sensitivity - Under amalgam restorations to reduce microleakage - Thin resin film formed upon solvent evaporation Cavity Varnishes No No Yes No - Sealing dentine tubules - Soluble in oral fluids; temporary effect - Not recommended under resin restorations - Minimal mechanical strength; does not reinforce tooth structure - Base under restorations - Moderate compressive strength Zinc - Luting agent for crowns, bridges, and orthodontic bands - Chemical adhesion to enamel and dentine via chelation with calcium ions Polycarboxylate Yes Yes No Yes - High viscosity upon mixing Cement - Patients with pulp sensitivities or near pulp exposures - Biocompatible; minimal pulp irritation due to large polyacrylic acid molecules that do not penetrate dentinal tubules Advantages ▪ Pulp Protection ▪ Sealing Ability ▪ Thermal insulation (bases like ▪ Reduction of microleakage ZnP, GIC). (adhesive resins, varnishes). ▪ Chemical barrier (varnishes, ▪ Prevention of postoperative liners). sensitivity. ▪ Biological Effects ▪ Fluoride Release ▪ Antibacterial action (Ca(OH)2). ▪ Anticariogenic properties (GIC, ▪ Sedative effect on pulp (ZOE). RMGIC). ▪ Stimulating reparative dentine formation (Ca(OH)2). Limitations ▪ Mechanical Weakness ▪ Interference with Restorative ▪ Low compressive strength Materials (Ca(OH)2, ZOE). ▪ Inhibition of resin polymerisation ▪ Not suitable in areas under heavy by eugenol-containing materials. occlusal stress. ▪ Initial Pulp Irritation ▪ Solubility ▪ Low pH materials (ZnP) can ▪ Potential dissolution over time irritate the pulp if not properly (varnishes, some liners). insulated. ▪ Loss of seal and protection. ▪ Technique Sensitivity ▪ Proper mixing ratios required (ZnP). ▪ Moisture control necessary (GIC). Decision-Making Process ▪ Assess Cavity Depth ▪ Patient Factors ▪ Deeper cavities require more ▪ Allergies, sensitivities, caries protective measures. risk. ▪ Consider Pulp Status ▪ Clinical Technique ▪ Vital vs. non-vital pulp affects material choice. ▪ Familiarity with material ▪ Compatibility with handling. ▪ Equipment availability (e.g., Restorative Material ▪ Avoid materials that interfere light-curing units). with the restoration (e.g., eugenol under composites). Clinical Examples Case Scenario 1: Deep Carious Lesion Case Scenario 2: Restoration with Near the Pulp Amalgam in a Shallow Cavity ▪ Assessment ▪ Assessment ▪ Risk of pulp exposure. ▪ Minimal risk to pulp. ▪ Need for pulp protection. ▪ Need for microleakage reduction. ▪ Material Selection ▪ Material Selection ▪ Liner: Calcium hydroxide for pulp ▪ Varnish: Cavity varnish applied to capping. dentine surfaces. ▪ Base: Glass ionomer cement to provide ▪ Rationale bulk and seal. ▪ Varnish reduces microleakage under ▪ Rationale amalgam. ▪ Ca(OH)2 stimulates reparative dentine. ▪ Quick and easy application. ▪ GIC provides additional sealing and fluoride release.  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 Reinforced zinc oxide-eugenol IRM (Dentsply) SDLE, PDSE Temporary enamel substitute or Biodentine (Septodont) SDLE, PDSE permanent dentine substitute Polycarboxylate cement Poly-F (Dentsply) SDLE, PDSE Zinc phosphate cement Detray Zinc Cement (Dentsply) SDLE, PDSE Dycal (Dentsply) SDLE Ca(OH)₂ liner Life (Kerr) PDSE Summary ▪ Protect the pulp, provide thermal insulation, and enhance restoration longevity in restorative dentistry. ▪ Calcium Hydroxide: Liner for deep cavities; stimulates reparative dentine; antibacterial. ▪ Zinc Oxide Eugenol: Base, liner, temporary filling; sedative effect; not suitable under composites. ▪ Glass Ionomer Cement: Base, liner, luting agent; releases fluoride; chemically bonds to tooth structure. ▪ Zinc Phosphate Cement: Base under amalgam; high compressive strength; requires pulp protection due to initial acidity. ▪ Cavity depth, pulp status, restorative material compatibility, and patient-specific considerations. ▪ Provide pulp protection, reduce microleakage, prevent postoperative sensitivity, and support restorative materials. ▪ Potential issues with mechanical strength, solubility, and compatibility with certain restoratives. References ▪ Draheim, R. N. (1988). Cavity bases, liners and varnishes: A clinical perspective. American Journal of 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. ▪ Chandak, M. S., Chandak, M., & Nikhade, P. P. (2020). Role of Liners in Restorative Dentistry. Journal of Evolution Medical Dental Sciences. PDF Link ▪ Van Noort, R., & Barbour, M. E. (2023). Introduction to Dental Materials-E-Book. Elsevier. MCQs – Question 6 Which material is most suitable for direct pulp capping to stimulate reparative dentin formation? A. Zinc Phosphate Cement B. Calcium Hydroxide C. Zinc Oxide Eugenol D. Glass Ionomer Cement E. Cavity Varnish MCQs – Question 7 Which of the following materials releases fluoride, providing an anticariogenic effect? A. Zinc Oxide Eugenol B. Calcium Hydroxide C. Glass Ionomer Cement D. Zinc Polycarboxylate Cement E. Adhesive Resin Liner MCQs – Question 8 Why is zinc oxide eugenol not recommended under resin- based composite restorations? A. It lacks sufficient strength. B. It causes tooth discolouration. C. It inhibits polymerisation of resin composites. D. It is too acidic for use under composites. E. It releases fluoride that interferes with composites. MCQs – Question 9 What is the primary function of cavity varnish when applied under amalgam restorations? A. To reinforce the tooth structure B. To provide thermal insulation C. To release fluoride D. To reduce microleakage by sealing dentine tubules E. To stimulate secondary dentine formation MCQs – Question 10 In which scenario is calcium hydroxide contraindicated as a base material? A. Shallow cavities with no pulp exposure B. Deep cavities requiring pulp capping C. Areas under heavy occlusal stress D. When using amalgam restorations E. In primary teeth MCQs – Answers 6. B. Calcium Hydroxide. Calcium hydroxide is ideal for direct pulp capping because its high pH stimulates odontoblast activity, promoting reparative dentine formation and protecting the pulp. 7. C. Glass Ionomer Cement. Glass ionomer cements release fluoride ions over time, which helps to prevent secondary caries by inhibiting demineralisation and promoting remineralisation of tooth structure. 8. C. It inhibits polymerisation of resin composites. Eugenol interferes with the free radical polymerization of resin-based composites, leading to incomplete curing and compromised restoration properties. 9. D. To reduce microleakage by sealing dentine tubules. Cavity varnish forms a thin film that seals dentine tubules, reducing microleakage and postoperative sensitivity under amalgam restorations. 10. C. Areas under heavy occlusal stress. Calcium hydroxide has low compressive strength and is not suitable as a base in stress-bearing areas; it is best used as a liner in deep cavities near the pulp. 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.