Many papers published in this and other international journals investigate resin composites , a major class of dental restorative material. But some writers refer to them as composite resins. Are these terms equivalent – or not? And does it matter? The issue may seem trivial, but I have been asked for guidance on the subject; hence this Editorial.
In the expression “resin composite”, the word composite is a noun and resin is an adjective qualifying the noun. It tells us what kind of composite we are dealing with. According to the Oxford English dictionary, composite means: “made up of various parts”, especially of a synthetic building material “made up of recognisable constituents”.
This understanding is taken up in the wider field of materials science, where composite materials consist of two or more distinct phases. Normally one of these is a continuous phase (or matrix) and the other phase(s) are dispersed phases, i.e. dispersed within the matrix.
From a materials science perspective, many distinct dental materials are classifiable as “composites”, including glass ionomer (polyalkenoate) cements and some impression materials. Materials science also considers quite different composites, such as “metal matrix composites”, where the continuous phase is metallic. Moreover, many ceramic materials, including some used in dentistry, have both continuous and dispersed phases. However, majority usage within dentistry conventionally confines the term composite to materials that have a polymeric (organic) matrix and a particulate inorganic glass phase, possibly with the addition of fibers. These are designated resin composites or equivalently polymeric composites [ ]. Other, more specific terms are used, acceptably, such as dimethacrylate composites [ ]. However, resin is quite a useful term because it is applicable to both the pre-cure and post-cure organic component of such composites. Specifically, it can refer to the monomer mixtures, as formulated by the manufacturer, and also to their polymerised condition when they then constitute a matrix.
If we now consider the alternate term: composite resin , then the noun is resin and that is modified by the adjective composite (made up of various parts). And indeed, these resins are almost always monomer mixtures, such as bis-GMA and TEGDMA. So, according to those definitions, the term “composite resin” can properly designate an unfilled resin, such as a sealant.
It follows that the terms resin composite and composite resin are not equivalent. The former is strongly to be preferred and the designation composite resin is to be discouraged.
Within the context of a dental research paper, concerning resin composites, it is not necessary to continue using the full expression “resin composite” multiple times within the text. It is acceptable to say “composite” for brevity. Alternatively, some may prefer to use the acronym RBC (resin-based composite).
A further point is that some authors use the term resin(s) when actually they mean resin composite(s) or RBCs. This seems to happen particularly if their focus is upon light curing or photo-polymerization. Admittedly it is the resin or monomer phase that is polymerised. However, the light transmission and thus the photo-cure characteristics are significantly modified by the presence of dispersed “filler” particles. The term resin composite or the acronym RBC should also be used in such contexts since the abbreviation “resin” is rather sloppy and incomplete.