Recommended Mixing Equipment for Dental Composites

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Dental composites are synthetic polymers filled with reinforcing glass and/or ceramic particles.

A typical mixing procedure starts with blending two or more monomers often of significantly different viscosities. Various particle size fillers are then added to the liquid binder and mixed under vacuum until a homogenous paste is obtained. High amounts of fillers render most dental composites very abrasive. Initiators, inhibitors and pigments may also be added to the hardenable paste.

Ross Double Planetary Mixers

Double Planetary Mixers are well-proven equipment for the preparation of dental composites. Traditional designs move materials by rotating two rectangular-shaped paddles on their respective axes as they orbit on a common axis. The blades contact virtually every point of the batch in just 36 revolutions, imparting a very thorough but gentle mixing action. The typical viscosity range of these stirrers goes up to around 2 million centipoise.

Newer design helical blades offer improved mixing and easier handling of viscosity peaks as high as 6 million centipoise. The first of its kind, Ross High Viscosity "HV" Blades (US Patent No. 6,652,137) feature a precisely angled contour which generates a unique mixing action: the sweeping curve firmly pushes batch material forward and downward, keeping it within the mixing zone at all times. The helical flights pass each other in a slicing motion, enabling them to move through a viscous batch without substantial spikes in power draw and amperage.

Mixing abrasive composites in a conventional stainless steel mixer leads to discoloration of the paste (stainless steel particles are incorporated into the formulation). The slightest contamination is not acceptable in dental composites wherein precise optical characteristics are critical. Ross Double Planetary Mixers are used worldwide for various abrasive materials and these are commonly either hard-chrome plated or coated with Kynar (polyvinylidene fluoride) or aluminum oxide.

The ideal mixing equipment for this application must be capable of handling a wide range of viscosities and highly abrasive formulations.