Dental material
Dental products are specially fabricated materials, designed for use in dentistry. There are many different types of dental products, and their characteristics vary according to their intended purpose.
Temporary dressings
A temporary dressing is a dental filling which is not intended to last in the long term. They are interim materials which may have therapeutic properties. A common use of temporary dressing occurs if root canal therapy is carried out over more than one appointment. In between each visit, the pulp canal system must be protected from contamination from the oral cavity, and a temporary filling is placed in the access cavity. Examples include:- Zinc oxide eugenol—bactericidal, cheap and easy to remove. Eugenol is derived from oil of cloves, and has an obtundant effect on the tooth and decreases toothache. It is suitable temporary material providing there are no biting forces on it. It is also contraindicated if the final restorative material is composite because eugenol adversely effects the bond/polymerization process; also, when applied directly on the pulp tissue, it can produce chronic inflammation and result in pulp necrosis. Brands include Kalzinol and Sedanol.
Cements
- Zinc oxide cement—self setting and hardens when in contact with saliva. Example brands: Cavit, Coltosol.
- Zinc phosphate cement
- Zinc polycarboxylate cement—adheres to enamel and dentin. Example brand: PolyF.
- Glass ionomer cement
- Resin-based cement
- Copper-based cement
Impression materials
Because patients' soft-tissue undercuts may be shallow or deep, impression materials vary in their rigidity in order to obtain an accurate impression. Rigid materials are used with patients with shallow undercuts, while elastic materials are used with patients with deep undercuts, as the material must be flexible enough to reach the end-point of the undercut.
Impression materials are designed to be liquid or semi-solid when first mixed, then set hard in a few minutes, leaving imprints of oral structures.
Common dental impression materials include sodium alginate, polyether and silicones. Historically, plaster of Paris, zinc oxide eugenol and agar were used.
Lining materials
Dental lining materials are used during restorations of large cavities, and are placed between the remaining tooth structure and the restoration material. The purpose of this is to protect the dentinal tubules and the sensitive pulp, forming a barrier-like structure. After drilling the caries out of the tooth, the dentist applies a thin layer to the base of the tooth, followed by light curing. Another layer might be applied if the cavity is very large and deep.There are many functions to dental lining materials, some of which are listed below:
- Lining materials protect the weak tooth from post-operative hypersensitivity, reducing patient discomfort and allowing the tooth to heal at a faster rate after the procedure.
- Some dental restorative materials, such as acrylic monomers in resin-based materials and phosphoric acid in silicate materials, may pose toxic and irritable effects to the pulp. Lining materials protect the tooth from such irritants.
- Lining materials serve as an insulating layer to the tooth pulp from sudden changes in temperature when the patient takes hot or cold food, protecting them from potential pain resulting from thermal conductivity.
- Lining materials are electrically insulating, preventing corrosion by galvanic cell where two dissimilar metals are placed next to each other.
Types
Calcium hydroxide is a relatively low compressive strength and a viscous consistency, making it difficult to apply to cavities in thick sections. A common technique to overcome this issue is to apply a thin sub-lining of calcium hydroxide, then build up with zinc phosphate prior to amalgam condensation. This generates a relatively high pH environment around the area surrounding the cement due to calcium hydroxide leaking out, thus making it bactericidal.
It also has a unique effect of initiating calcification and stimulating the formation of secondary dentine, due to an irritation effect of the pulp tissues by the cement.
Calcium hydroxide is radio-opaque and acts as a good thermal and electrical insulation. However, due to its low compressive strength it is unable to withstand amalgam packing; a strong cement base material should be placed above it to counter this.
Calcium silicate-based liners have become alternatives to calcium hydroxide and are preferred by practitioners for their bioactive and sealing properties; the material triggers a biological response and results in formation of bonding with the tissue. They are commonly used as pulp capping agents and lining materials for silicate and resin-based filling materials.
It is usually supplied as two pastes, a glycol salicylate and another paste containing zinc oxide with calcium hydroxide. On mixing, a chelate compound is formed. Light-activated versions are also available; these contain polymerization activators, hydroxyethyl methacrylate, dimethacrylate which when light activated will result in a polymerization reaction of a modified methacrylate monomer.
Polycarboxylate cement
Polycarboxylate cement has the compressive strength to resist amalgam condensation. It is acidic, but less acidic than phosphate cements due to it having a higher molecular weight and polyacrylic acid being weaker than phosphoric acid. It forms a strong bond with dentine and enamel, allowing it to form a coronal seal. In addition, it is an electrical and thermal insulator while also releasing fluoride, rendering it bacteriostatic. It is also radio-opaque, making it an excellent lining material.
Care has to be taken in handling such material, as it has a strong bond with stainless steel instruments once it sets.
Polycarboxylate cement is commonly used as a luting agents or as a cavity base material. However, it tends to be rubbery during its setting reaction and adheres to stainless steel instruments, so most operators prefer not to use it in deep cavities.
It is usually supplied as a power containing zinc oxide and a liquid containing aqueous polyacrylic acid. The reaction consists of an acid base reaction with zinc oxide reacting with the acid groups in polyacid. This forms a reaction product of unreacted zinc oxide cores bound by a salt matrix, with polyacrylic acid chains cross linking with zinc ions.
Glass ionomer
Glass ionomer has the strongest compressive and tensile strength of all linings, so it can withstand amalgam condensation in high stress bearing areas such as class II cavities. GI is used as a lining material as it is very compatible with most restorative materials, insulates thermally and electrically, and adheres to enamel and dentine. GI lining contains glass of smaller particle sizes compared to its adhesive restorative mix, to allow formation of a thinner film. Some variations are also radiopaque, making them good for X-ray cavity detection. In addition, GI is bacteriostatic due to its fluoride release from un-reacted glass cores.
GIs are usually used as a lining material for composite resins or as luting agents for orthodontic bands.
The reaction is an acid-base reaction between calcium-aluminum-silicate glass powder and polyacrylic acid. They come in a powder and liquid which are mixed on a pad or in capsules which are for single usage. Resin-modified GIs contain a photoinitiator and an amide, and are light cured with a LED light curing unit. Setting takes place by a combination of acid-base reaction and chemically activated polymerization.
Zinc oxide eugenol
Zinc oxide eugenol has the lowest compressive and tensile strength of the liners, so its use is limited to small or non-stress-bearing areas such as Class V cavities. This cavity lining is often used with a high strength base to provide strength, rigidity and thermal insulation. Zinc oxide eugenol can be used as linings in deep cavities without causing harm to the pulp, due to its obtundant effect on the pulp as well as its bactericidal properties due to zinc. However, eugenol may have an effect on resin-based filling materials, as it interferes with polymerization and occasionally causes discoloration. Caution could therefore be exercised when using both in tandem. It is also radio-opaque, allowing fillings to be visible by X-rays.
Zinc oxide eugenol is usually used as a temporary filling/luting agent due to its low compressive strength making it easily removed, or as a lining for amalgam as it is incompatible with composites resins.
It is supplied as a two paste system. Equal length of two pastes are dispensed into a paper pad and mixed.
| Agent | Advantages | Disadvantages |
| Calcium hydroxide |
| |
| Polycarboxylate cement | ||
| Zinc oxide eugenol | ||
| Glass ionomer |