A course in Dental Composites page 3 (Cements)-DoctorSpiller.com

A course in composites pages 1234567891011

Dental Cements and the composite restorations derived from them

Interestingly, all dental cements, and all tooth colored filling materials are made of combinations of only two different powders ( top row), and four different liquids (left column) .  In most cases, the chemical combination of the various powders with the various liquids creates a  material which begins as a paste and “sets” as a hard cement.  Most of these materials are water soluble during the setting phase, but become waterproof after they become hard.

cementtableThe glass powder that is used in the production of both Silicate cement and Glass Ionomer cement is made from a glass made with Sodium Fluoride and stabilized with minimal alumina.  It is technically known as Alumino-Fluoro-Silicate glass.  This glass is ground into a very fine powder.  While this glass is stabilized to make it insoluble in water, it is formulated to remain partially soluble in very highly acidic solutions.  (It is not soluble in saliva or in any food or liquid that can be consumed by mouth.)  By the use of various trace metals, zirconium, and other components, the glass can be fabricated to match the various colors and opacities of tooth structure.  The major characteristic of this type of glass, however is its ability to partially dissolve and form a hard, waterproof matrix when mixed with either of the two types of acids shown in the table above. This glass is discussed in more detail on the  Alumino-Fluoro-Silicate glass cements page. Alumino-Fluoro-Silicate glass (powder)

Note:  Resin composite fillings and cements are filled with glass particles, but the glass in these materials does not chemically react with the surrounding matrix and does not need the same formulation as the Alumino-Fluoro-Silicate glass described here.

Zinc Oxide powder

The zinc oxide powder used in dental cements is plain, powdered ZnO.  It is an opaque white color, and has antiseptic properties.  It is familiar to most mothers as the component in diaper rash ointment (Desitin) that makes it white.

Phosphoric Acid

Pure anhydrous phosphoric acid is a white solid that melts at 42.35 °C to form a colorless, viscous liquid.  It is highly water soluble, and the form used in mixing with the powders presented here is 37% H2PO4:

H3PO4(s)   + H2O(l)  <=> H3O+(aq) + H2PO4(aq)

Polyacrylic Acid

Polyacrylic acid is a polymer of Acrylic Acid.  This means that it is composed of chains of the molecule acrylic acid strung together like beads.  Acrylic acid has the formula CH2=CHCH3.   It is a clear liquid and has a thick, syrupy consistency.

Eugenol

Eugenol is a clear to pale yellow, oily liquid extracted from certain essential oils, especially from clove, nutmeg, cinnamon, basil and bay leaf.  It is the main constituent in oil of clove.  It has been used for centuries in dentistry because it has anesthetic and antiseptic qualities which make it ideal for treating painful lesions in the mouth.  We still use it today, on strips of iodoform gauze, to treat dry sockets.  When mixed with zinc oxide powder, it creates ZOE, the quintessential temporary filling that has been used in decayed teeth to reduce toothache pain since the late nineteenth century.

Next page==>Zinc Oxide cements

A course in composites pages 1234567891011