SILICATE CEMENT

ANSI/ADA specification number-9

INTRODUCTION

•The use of dental cements as a restorative material began with the use of silicate cement. At that time it was considered to be more aesthetic than amalgam.

CompositionCompositionPowder-it consists of Silicate glass.The glass for Silicate cement was made

by fusing the compounds of Silica(SiO2), Alumina( Al2O3), Fluoride compounds like Sodium Aluminium Fluoride (Na3AlF6) and Calcium salts at approximately 14000c.

Liquid-it consists of aqueous solution of phosphoric acid.

Setting reaction

Stages of setting..

• Mixing-the initial contact of powder and liquid components.

• Working-it involves the ion migration during the powder dissolution.

• Setting-this consists of the metal phosphate dissolution.

The set cement structure

• The set cement consists of unreacted powder particles interspersed in an alumino-phosphate gel.

ManipulationManipulation

• The powder and liquid is dispensed on a cool glass slab. The cooling of the glass slab is done so that it can prolong the working and setting time and also permits the operator to incorporate maximum amount of powder in the mix. The liquid should not be dispensed onto the slab until mixing is to be initiated because water will be lost to air by evaporation.

• The P:L ratio is 2.0 or higher by weight.

• The powder is divided into three increments as indicated in the instructions. small quantities are incorporated initially with a brisk spatulation and a small area of mixing slab should be used to minimize water loss.

• Mixing of the powder is to be done for 90-120 seconds until a desired consistency is obtained. However a desired consistency is always obtained by incorporation of more powder and not by allowing a very thin mix to stiffen.

• The setting reaction is exothermic and is technique sensitive.

• The setting time is 2-6minutes.

• Temperature of the glass slab and water content is an important consideration.

PropertiesProperties

Strength-it is considered as the most brittle material but relatively strong in compression but weak in tension after it sets.

Solubility-it has a high rate of disintegration over time

It has anticariogenic potential.

Setting time at 37O2-6 minutes

Minimum compressive strength 170 MPa

Maximum film thickness 25 µm (for luting the prostheses)

Maximum Solubility 0.2% by weight

Disadvantages

Advantageso It has highly

acidic pH thus acts as a pulpal irritant.

o It has a high disintegration rate in the oral cavity.

o It is highly esthetic.

o It has a high compressive strength of 170Mpa

Uses of silicate cement

Not used nowadays..Initially it was used in restorations in esthetic parts of the oral cavity.

Zinc silicophosphate

cement.

ANSI/ADA specification number-21

Composition

• Powder-acid soluble aluminosilicate glass and zinc oxide.

• Liquid-aqueous solution of phosphoric acid.

• The cement is essentially a mixture of zinc phosphate cement and silicate cement.It is also considered as a modification of zinc phosphate cement.

Advantages of this combination

Fluoride release.Translucency is obtained for better esthetics in comparison to zinc phosphate cement.

It is similar to that of silicate cement except that the zinc ions are also involved.

Variables affecting mixing of cements in general.

Mixing time Make sure to follow the manufacture’s

directions for the mixing time, working time, and delivery time.

Humidity If the clinical area is warm or humid,

premature exposure of the cement to these environments can create a loss of water from the liquid or an addition of moisture to the powder.

• Powder to liquid ratio– Incorporating too much or too little powder will

alter the consistency.

• Temperature– Some types of cements put off an exothermic

reaction.