Main groups of filling materials
Depending on the clinical situation, various compositions are used to close carious cavities. All materials can be divided into several key categories:
- Temporary fillings and dressings. Used for short-term cavity sealing. Inserted using special instruments.
- Therapeutic and base liners. Placed on the bottom of the cavity to protect the pulp and provide a therapeutic effect.
- Permanent materials. Designed for long-term tooth restoration.
Classical materials include dental cements. Among them, phosphate, silicate, and silicophosphate cements are distinguished. Each of them has its own indications and limitations. For example, silicate cements possess both pronounced positive and negative properties that determine a narrow range of their application. A special place is occupied by glass ionomer cements (GICs), which are classified according to their functional purpose.
Amalgam is a traditional material that requires amalgamation and trituration (mixing) processes. When working with it, it is necessary to strictly observe the optimal filling thickness. Amalgam has a number of advantages, but also significant disadvantages.
Composite materials
Modern composites are standardized according to ISO requirements. Their structure invariably includes a polymer matrix (organic matrix), and silanes are used to ensure a reliable bond between components.
According to the activation method, the following are distinguished:
- Chemically cured composites. Require specific preparation and placement steps.
- Light-cured composites. Differ in a different direction of polymerization shrinkage and provide more time for modeling.
According to the filler particle size, composites are divided into macrohybrid (macrofilled), microhybrid (microfilled), and hybrid. Each group has unique physical properties and strict indications for use.
The adhesive protocol when working with composites includes the stage of "total etching" of hard tissues, which is necessary to create a micro-relief. As a result of the interaction of the adhesive with tooth tissues, a so-called "hybrid layer" is formed, ensuring reliable fixation of the restoration. An important step is also the preliminary cleaning of the tooth surface and the competent selection of the restoration material color to achieve high aesthetics.
Artificial abrasive materials
Various abrasives are used for processing metal structures, plastics, and finished fillings:
- Electrocorundum. Obtained by reductive smelting of bauxite with coke in electric furnaces. Contains 94–97% aluminum oxide (the higher it is, the higher the hardness of the material), as well as impurities of iron, titanium, and silicon. Excellent for processing steel, bronze, and cast iron, as well as for profile grinding work.
- Silicon carbide. Synthesized by the reduction of silicic acid with carbon. Used for working with brittle and viscous surfaces.
- Boron carbide. It is the hardest of artificial abrasives. It often replaces diamond dust and is used in the form of pastes for polishing extra-hard alloys.
Abrasive finishing materials and pastes
For fine grinding and polishing (gloss enhancement), powders, micropowders, and fat-based pastes (stearin, paraffin, wax) are used:
- Iron oxide (hematite) and crocus: natural and artificial materials for manual polishing. The hardness of crocus depends on the darkness of its color.
- Chromium oxide: fine gray powder (formed by burning tin), ideal for delicate items.
- Vienna lime: obtained from dolomite, extremely unstable in air and requires storage in airtight vessels.
- Magnesia (magnesium oxide): soft flaky powder. When mixed with aluminum oxide and Vienna lime, it forms "white polish".
GOI paste has gained the greatest popularity. Its composition includes 8 parts of chromium oxide, 10 parts of stearin, 5 parts of melted fat, as well as silica gel (2 parts) and kerosene (2 parts). For polishing plastics, ordinary chalk in the form of an aqueous slurry is generally used.
Physics and tools of grinding
The quality of finishing largely depends on the linear speed of the abrasive movement. With slow movement, the grain removes a thick chip, but is subjected to severe destructive stress. With rapid rotation, the chip is smaller, and tool wear is reduced. It is important to remember that the linear speed during polishing must always be higher than during grinding.
Tools for machine processing are selected based on the relief of the product:
- Felt wheels (felt bobs) — for flat and smooth surfaces.
- Bristle disc brushes — for complex openwork structures.
- Cloth (madapallam, flannel) and string wheels — for final gloss enhancement.
Specifics of work in the oral cavity: The processing process is always accompanied by thermogenesis (heat generation due to friction and deformation). In the oral cavity, it is strictly forbidden to apply excessive pressure on the tool. This can lead to bur breakage, overheating, and trauma to tooth tissues. When grinding plastic elements, water cooling is mandatory to avoid softening and deformation of the base.
Briefly: answers to topical questions
What are the requirements and features of the application of materials for root canal filling?
Before root canal filling, mechanical and drug treatment, as well as thorough drying of the canal, are mandatory. All points are inserted into the canal strictly with a paste: the paste is called a sealer (sealant), and the point is called a filler. For filling, in particular, methods of lateral compaction of cold gutta-percha and vertical condensation of heated gutta-percha are used. When filling a root canal, the root canal filler is chosen one size smaller than the last root canal reamer used. With proper obturation, the filling material densely fills the entire canal and reaches the physiological apex; unfilled apical space and the extrusion of material beyond the root apex into the periodontium are unacceptable.
What else to study on this topic
- Technique of insertion and modeling of chemically and light-cured composites
- Amalgamation and trituration processes
- Classification and indications for the use of therapeutic liners
- Properties and clinical purpose of glass ionomer cements (GICs)
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