Assessment of Re-mineralising Dental Composites Through ISO Testing

Objectives:

The aims of this study were to assess light curing re-mineralising dental composites using ISO standard methods.  The effect of reactive calcium phosphate filler on polymer based composites was measured through flexural strength, physical and chemical properties.  

Methods:

Composites containing 10 and 20 wt.% calcium  phosphate (CaP) ( 1:1 weight ratio of mono-calcium phosphate and β-tri-calcium phosphate) were prepared. Flexural strength, depth of cure, water sorption, and solubility were tested according to ISO 4049:2009. Polymerisation shrinkage was obtained from paste versus set material densities and monomer conversion by FTIR. Re-mineralising capability was quantified by using scanning electron microscopy (SEM) and Raman spectroscopy to assess hydroxyapatite (HA) precipitation on the composite surfaces in simulated body fluid (SBF).  

Results:

The results shown in table 1 demonstrate that water sorption, solubility, and flexural strength of the composites depend on CaP content but are all well within ISO requirements. Formulations appeared to absorb more water in SBF than in H₂O. The 20 wt.% CaP Composite had a higher net weight loss in H₂O than in SBF whilst solubility of the 10 wt.% CaP composite appeared slightly negative in both medium. This may be a consequence of the test method being unable to remove some absorbed water that is bound in the reactive filler.  As the monomer conversions are high, the solubility would primarily reflect net dissolution of CaP rather than monomers.

Table 1: Assessment results

SEM with Raman confirmed HA precipitated on both material surfaces after 7-day's soaking in SBF. The layer formed on the 20 wt.% CaP composite was denser and thicker than that on 10 wt.% CaP composite.

Conclusions:

The water sorption and solubility test according to the current ISO standard has limitations with re-mineralising composites. The results can only be understood with aid of SEM and Raman.