The optimisation of the initial viscosity of an encapsulated glass-ionomer restorative following different mechanical mixing regimes

Summary 

Objectives

An optimisation of the mixing ratio of an encapsulated glass-ionomer restorative in terms of compressive strength, working characteristics and pore distribution following mechanical mixing with different mixing machines was undertaken.

Methods

Mean compressive fracture strengths, standard deviations and associated Weibull Moduli (m) were determined from series of 30 encapsulated specimens with varying powder/liquid mixing ratios. Working characteristics were assessed using an oscillating rheometer and scanning electron microscopy and image analysis was used to investigate the influence of the mixing ratios and mixing regime on the pore distribution.

Results

Cement mixing regime or reducing the powder/liquid mixing ratio did not have any significant influence on the compressive strength. Utilising the one-way ANOVA and Tukey test comparisons at P<0.05 the cement manipulation regime significantly increased the compressive strength on increasing the powder content of the capsule by 10% (G110) when a combination of rotational and centrifugal action rather than vibration were employed. Utilising a Rotomix^® at a powder content of G110 was beneficial in reducing porosity levels within the restorative investigated compared with a conventional mixing machine. Increasing the powder content reduced the working characteristics regardless of the mixing regime.

Significance

The increased reliability of encapsulated restoratives reported in the literature following mixing with a combination of rotational and centrifugal compared with vibrational action was only evident when the powder content of the restorative under investigation was increased by 10%. The finding suggests that the initial viscosity of the cement mass of the Ketac^®Fil Plus Aplicap^® as supplied by the manufacturer may not have been optimised.

Keywords: Glass-ionomer restorative, Initial viscosity, Weibull statistics, Compressive strength, Porosity, Working characteristics