Introduction
Clinical restorative materials are used mainly to rebuild defects in hard dental tissues. They are divided into three groups: dental cements, composite materials and dental amalgams.
Requirements
- Mechanical properties close to those of enamel and dentin, which is called mechanical biomimetics.
- Thermal insulation. A conductive material needs an insulating base.
- Thermal and volume changes like those of the tooth. A mismatch strains the bond and can crack tooth walls.
- Esthetics: color, the opacity of dentin, and the translucency, fluorescence, opalescence and gloss of enamel, with lasting color.
- Biological safety: no permanent or irreversible injury.
- A sound, durable, tight bond to the tooth.
- Low solubility in saliva, dentinal fluid and gingival fluid.
- Good handling: easy dosing and mixing, enough working time, fast setting and a long shelf life.
- Biological activity: stimulating repair and increasing the resistance of the tissues.
- No pores, and a surface that polishes perfectly.
Why dentin matters
Dentin is permeable because of its tubules. There are about 20,000 per mm² near the enamel and over 50,000 per mm² near the pulp, where they are also wider. They take up 1% of dentin near the enamel but 22% near the pulp, so the closer a material is to the pulp, the more harm it can do.
- Diffusion permeability: ions and molecules move through the dentinal fluid.
- Convective permeability: pressure, such as when seating a crown, pushes toxic products toward the pulp.
Cutting tooth tissue leaves a smear layer 0.5 to 10 µm thick. Its plugs reduce permeability and act as a barrier.