Classification of root canal filling materials
Root canal materials are functionally divided into sealers and fillers (bulk-filling materials). A high-quality material must not resorb, change volume, discolor the tooth, or cause allergies, while providing good adhesion and an antiseptic effect.
Based on their physical and mechanical properties, they are classified into:
- Plastic non-setting pastes (based on calcium hydroxide, antibiotics, and oils). Used exclusively for temporary filling (up to 2 months) in the treatment of periodontitis. They are permeable to fluids and resorb over time.
- Plastic setting cements. These include zinc-phosphate, zinc oxide-eugenol, polymer resins, resorcinol-formalin pastes (which discolor the tooth and are therefore only suitable for multi-rooted teeth), and glass ionomer cements.
- Rigid materials (various intracanal posts).
Presentation forms and types of glass ionomer cements (GIC)
Glass ionomers are one of the most important groups of cements in modern dentistry. They can set via a classic acid-base reaction or feature a dual/triple setting mechanism (hybrid cements with resin modification that also cure via light).
Main presentation forms:
- Powder-liquid — classic system for manual mixing.
- Water-set cements — components are supplied as a powder mixed with distilled water. They have a longer shelf life but exhibit high initial acidity.
- Capsules — precise factory dosing of powder and liquid for ideal properties.
- Paste-in-paste / tubes — convenient light-cured forms (e.g., Ionoseal, Septocal LC).
Advantages and biological effects of GIC
The popularity of glass ionomers is due to their high biocompatibility and unique chemical composition. Large macromolecules of polyacrylic acid do not penetrate deeply into dentin, protecting the pulp from irritation.
Main advantages of the material:
- Chemical adhesion. Bonding to the tooth occurs via the formation of chelate compounds with calcium of hydroxyapatite and hydrogen bonds with dentin collagen.
- Caries-static effect. The cement acts as a fluoride donor. It forms acid-resistant fluorapatite, catalyzes mineralization, alters the electrical potential of the enamel (preventing bacterial adhesion), and blocks their lactic acid production.
- Physical properties. GICs feature high compressive strength, low polymerization shrinkage, and a coefficient of thermal expansion nearly identical to tooth tissues. Their low modulus of elasticity allows them to compensate for composite stress when used in the sandwich technique.
Handling characteristics and potential errors
Despite numerous advantages, traditional GICs are brittle, slow-setting, and extremely moisture-sensitive. Their final shade stabilizes only after 24 hours.
Important preparation and placement rules:
- Cavity preparation should be minimally invasive. It is not necessary to excise healthy tissue for prophylactic purposes, create retention points, or bevel enamel.
- For non-carious lesions (cervical wedge-shaped defects), the cavity is not prepared, but simply cleaned with an abrasive paste.
- The cavity is conditioned with polyacrylic acid (to remove the smear layer) and rinsed.
- Overdrying the dentin is strictly prohibited! GICs are hydrophilic. Overdrying the tissues causes a rapid fluid movement within the tubules, odontoblast aspiration, and stretching of the nerve fibers. The result is acute postoperative pain.
- Mixing (on average 30–60 seconds) and placement are performed with a plastic spatula, as the cement adheres to metal.
- After placement, the restoration must be coated with a surface protection varnish to shield it from saliva.
Briefly: answers to topical questions
What is the chemical composition of the powder and liquid in a traditional glass-ionomer cement?
The chemical composition of a traditional glass-ionomer cement includes a glass-based powder and a liquid containing acids.
- Powder — consists of fluoroaluminosilicate (aluminosilicate) glass particles.
- Liquid — contains polyacrylic and tartaric acids in the presence of water; acrylic, itaconic, and maleic acids are also specified among the alkenoic monomers.
An acid-base reaction occurs when the components are mixed. The structure of the set cement contains glass particles, silica gel, and a matrix of cross-linked polyacid chains.
What are the indications for the use of zinc phosphate cements?
Indications for the use of zinc phosphate cements include their use as temporary restorations and base liners.
- Temporary delayed restorations — placed for a period ranging from several months to 1 year.
- Base liners — used for dentin protection; when restoring with silicate and silicophosphate cements, a base liner is used, most commonly zinc phosphate cement.
Zinc phosphate cements have limited use due to their short working time.
What classes of materials are used as endodontic sealers?
Various classes of plastic setting filling materials are used as endodontic sealers (sealing and filling materials).
- Zinc phosphate cements — have a short working time.
- Zinc oxide-eugenol based pastes — include products such as Endomethasone and Tubliseal.
- Calcium hydroxide based pastes — may contain tricalcium phosphate or hydroxyapatite.
- Synthetic and epoxy resin based pastes — for example, AH Plus or Topseal.
- Resorcinol-formalin based pastes — used in multi-rooted teeth.
- Glass-ionomer cements — rarely used.
What are the contraindications for the use of glass-ionomer cements?
Sources do not provide an exact list of contraindications for glass-ionomer cements, but the following limitations are indicated:
- Cavities with high occlusal load — the use of traditional glass-ionomer cements is limited due to their brittleness.
- Overdrying of dental tissues — when working with glass-ionomer cements, it is strictly forbidden to overdry the dental tissues or treat them with alcohol, as this can lead to postoperative hypersensitivity.
To avoid confusing the functions of canal materials, rely on English terminology: a sealer (to seal) coats the walls, while a filler (to fill) creates a dense framework inside the canal.
Class and exam questions
Why shouldn't a traditional GIC filling be polished immediately after placement?
The chemical setting and color stabilization process of traditional glass ionomer takes a long time. Finishing is strictly permitted only after 24 hours, otherwise the material structure will be disrupted.
Why is conditioning performed before placing the cement?
The conditioner (10–25% polyacrylic acid) is needed to dissolve the smear layer and release calcium ions. This ensures full chemical adhesion of the material to the cavity walls.
Can glass ionomers be used on occlusal surfaces?
Traditional GICs have increased brittleness, so their use in areas with high occlusal load is limited. However, modifications with the addition of silver alloy or hybrid resins exist for these purposes.
What else to study on this topic
- Indications for GIC use: from tunnel preparations to the ART technique
- Sandwich technique: rules for combining glass ionomer and composite
- Composition and properties of non-setting temporary endodontic pastes
- Mechanism of odontoblast aspiration during dentin over-drying
- Chemical composition of hybrid GICs and the dual-cure mechanism
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