Modeling materials

Silicophosphate cements: declining classics

After setting, this material forms a specific conglomerate: a silicic acid gel penetrated by crystals of phosphate cement setting products. The main visual advantage of this group is pronounced radiopacity.

In modern practice, they are extremely rarely used for treating permanent teeth (Class I, II, and V cavities). Dentists prefer stronger and highly aesthetic composites or amalgam. Silicophosphates are used only when contraindications to newer materials exist or they are unavailable, as well as in pediatric dentistry for filling primary teeth.

Working features:

• The material is introduced into the cavity in several portions, each of which must be thoroughly condensed.
• Strict rule: a base liner (usually zinc-phosphate cement) must be preliminarily applied to the bottom and walls of the cavity to protect the pulp.
• Market representatives include Russian "Silidont-2" and "Lacto-dont", "Beladent", as well as foreign capsule systems Silicap, Infantid, Zumikolor Cement, and Posterit Cement.

Polycarboxylate cements: composition and application

These materials are available as a classic powder-liquid system. The powder is a finely ground clinker obtained by sintering oxides: about 90% zinc oxide and 10% magnesium oxide. Aluminum oxide (up to 40%) and stannous fluoride are added to some preparations. The liquid is a 40–50% aqueous solution of polyacrylic acid.

Material properties: Pros include excellent chemical bonding with tooth tissues (formation of carboxylate group bonds with calcium and chelate bonds with metals), a neutral pH level (6.5–7.0), biocompatibility, and low toxicity. Cons include susceptibility to saliva (solubility), low mechanical strength, and poor aesthetics.

Working technique:

1. The powder is mixed with 2–3 drops of liquid for exactly 30 seconds. A metal spatula and a smooth glass slab are used, with components dispensed using a special measuring scoop.
2. The criterion of readiness is a thick, viscous mass with a characteristic gloss.
3. The cement is introduced into the cavity in strictly one portion.
4. The working time is about 3 minutes. If this time is missed, the mass transitions to a rubber-like state, begins to string, and becomes completely unusable.

Polycarboxylates are used for base liners, as well as for cementing orthodontic appliances, inlays, and small fixed partial dentures (up to three units). Popular products include "Belokor", Aqualox, and Pory-F Plus (both mixed with water), Durelon, Adhesor Carbohine.

Glass ionomer cements (GICs): composition and evolution

GICs are a broad class of modern dental materials created by merging silicate and polyacrylic systems. They are actively replacing outdated cements. The first commercial product—the aluminosilicate polyacrylic cement ASPA-IV—was developed by researchers A. Wilson and B. Kent in 1971.

Traditional GICs also consist of powder and liquid. The powder is produced by fusing components at extreme temperatures (1000–1300 °C), followed by cooling and grinding. Particle size depends on the intended use: 40–50 µm for restorative work, and finer fractions (20–25 µm) for liners and luting.

The liquid for GICs is a solution of acrylic and itaconic (or maleic) acids (47.5–50%). A 5% tartaric acid solution serves as a crucial modifier: it accelerates the extraction of ions from the glass, regulates medium pH, and optimizes the setting process.

Setting mechanism and ion exchange of GICs

The basis of powder-liquid interaction is a classic acid-base reaction. The setting process proceeds in three successive phases:

1. Dissolution (hydration and leaching). The acid attacks the surface layer of the glass particles. Hydrogen protons diffuse into the glass, forcing aluminum, calcium, sodium, and fluoride ions outward.
2. Gelation (primary gel formation). Lasts about 7 minutes. At this stage, polyacid molecules cross-link with each other via calcium ions. The structure is still unstable.
3. Hardening (maturation). Cross-linking of the chains occurs via trivalent aluminum ions. A rigid spatial polymer structure is formed. This phase is fully completed only after 24 hours.

The secret of reliable GIC adhesion lies in chemical ion exchange with tooth tissues. Polyacrylic acid penetrates the enamel and dentin structure, displacing phosphate ions (PO₄³⁻). To maintain electrolytic balance, these phosphate ions bind with calcium ions. At the microlevel, dentin tubules are sealed, and a super-strong ion-enriched layer forms at the interface.

The hardened glass ionomer consists of fluoroaluminosilicate glass particles surrounded by a silica gel shell, embedded in a uniform matrix of bonded polyacids (ionomer).

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Classification of glass ionomer cements by application (according to J. McLean, 1988) — aesthetic and reinforced restorative GICs.
• The chemistry of complex chelate bond formation between polycarboxylate cements and hard tissue proteins.
• Detailed algorithm for dispensing and mixing polycarboxylate systems using a measuring scoop and dropper.
• Effect of GIC powder particle size (40–50 µm vs 20–25 µm) on the physical and mechanical properties of the material.

Other topics in "Chapter 8. Dental Materials"

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.