The effects of boric acid and phosphoric acid on the compressive strength of glass-ionomer cements

Summary 

Objectives

Both boric acid (H₃BO₃) and phosphoric acid (H₃PO₄) are components of dental cements, commonly incorporated into glass (as ingredients in the melt) and occasionally added to the powder or liquid components. This study investigated the effect of boric acid addition to an experimental glass-ionomer powder and the effect of phosphoric acid addition to a glass-ionomer liquid on the 24-h compressive strength.

Methods

Boric acid powder was added in various concentrations to an experimental glass-ionomer powder and, separately, phosphoric acid was added to an experimental glass-ionomer liquid. Powders and liquids were dosed into capsules at various powder:liquid ratios and cements thus formed were assessed for 24-h compressive strength.

Results

Incorporation of boric acid in glass-ionomer powder resulted in a pronounced decrease (p<0.05 at 1% boric acid) in compressive strength. Addition of phosphoric acid produced initially stronger cements (up to 13% increase at 1% phosphoric acid) before also declining.

Significance

The incorporation of less than 2% w/w phosphoric acid in glass-ionomer liquids may improve cement strengths without compromising clinical usefulness. The incorporation of boric acid in glass-ionomer cements is contraindicated.

Keywords: Dental material, Glass-ionomer, Phosphoric acid, Boric acid, Compressive strength, Fluoride glass, Polyalkenoate cement