Material Science of Bases, Liners & Varnishes

Topic covers bases, liners, and varnishes in material science.
Key learning objectives include recognizing scientific principles, recalling constituents, outlining advantages/limitations, and describing material selection.
An outline includes vases, liners, varnishes, pulp protection, properties, advantages/limitations, and clinical applications.
Clinical questions, considerations, and material questions will be part of the learning assessment.
A multiple-choice question (MCQ) regarding which tooth component (enamel, cementum, dentin, pulp, alveolar bone) contains nerves and blood vessels will be asked.
Another MCQ investigates the importance of protecting the dental pulp during restorations (preventing tooth discoloration, maintaining tooth vitality, enhancing enamel hardness, improving saliva production, reducing tooth mobility).
A third MCQ concerns a necessary property of materials used to fill cavities, to withstand chewing forces (high solubility, low viscosity, high compressive strength, low thermal conductivity, translucency).
A further MCQ addresses a cause of postoperative sensitivity after a dental restoration (overhanging restorations, excessive polishing, microleakage at the restoration margins, proper occlusion, use of fluoride toothpaste).
A fifth MCQ details why thermal conductivity is critical in restorative materials (enhancing aesthetics, preventing thermal shock to the pulp, improving adhesion, reducing setting time, increasing hardness).
The pulp is the innermost part of the tooth, containing nerves and blood vessels (important for tooth sensitivity).
Protecting the pulp prevents irritation and damage, preventing pain and extensive treatment.
Materials should have high compressive strength to withstand chewing forces, without deforming or fracturing.
Microleakage allows bacteria and fluids to enter restoration sites, causing sensitivity and secondary caries.
Thermal conductivity in restorative materials helps protect the dental pulp from temperature extremes (hot and cold stimuli).
Bases are thick materials that replace missing dentine, insulating thermally, and distributing stress.
Liners are thin coatings that seal dentine tubules, protecting the pulp.
Varnishes are solutions of resins in volatile solvents, which seal dentine tubules and reduce microleakage.
Calcium hydroxide has high alkalinity and antibacterial activity, stimulating tertiary dentine formation, and used for direct/indirect pulp capping and protective lining.
Zinc oxide eugenol offers a pulp-sedative effect, good sealing, but low compressive strength, unsuitable under resin-based restorations.
Modified zinc oxide eugenol offers enhanced strength and reduced solubility.
Zinc phosphate cement provides high compressive strength but has an initial low pH (potentially irritating to the pulp).
Zinc polycarboxylate cement adheres chemically to tooth structure.
Glass ionomer cement (GIC) is biocompatible, releases fluoride, and has similar thermal expansion to dentine, ideal for bases/liners/luting agents.
Resin-modified glass ionomer cement (RMGIC) combines the properties of GIC and resin composites, offers enhanced strength, and can be light-cured.
Adhesive resin liners have low viscosity, penetrate and seal dentinal tubules, compatible with resin-based composites, and suitable for sealing hypersensitive dentine.
Cavity varnishes are solutions of resins, form thin films, and seal dentine temporarily, suitable for reducing microleakage in amalgam restorations.
Selecting materials entails assessing cavity depth, pulp status, compatibility with restorative materials, patient factors (allergies, sensitivities), and familiarity with material handling and equipment.
Deep caries lesions require more protection (e.g., calcium hydroxide for pulp capping).
Amalgam restoration in a shallow cavity (e.g., varnish to reduce microleakage).
The lecture lists several materials by type, material name, and manufacturer.

MCQ Answers

Direct pulp capping: Calcium Hydroxide
Fluoride release: Glass Ionomer Cement
Zinc oxide eugenol under resin composites: It inhibits polymerisation of resin composites.
Cavity varnish function: To reduce microleakage by sealing dentine tubules.
Calcium hydroxide contraindication: Areas under heavy occlusal stress.