As I’ve mentioned on Part 1, one of the components of composite resins is the Oligomer Matrix commonly called Resins. Resins is the liquid or the organic part made of polymerizable monomers that upon exposure to visible light, it catalyzes the formation of active centers, typically radical contents that induces its polymerization. These resins are composed commonly of either or a combination of the following:

(1) Bis-GMA- It is Bisphenol A-Glycidyl Methacrylate
(2) TEGDMA- Is Triethylene Glycol Dimethacrylate
(3) UDMA- Urethane Dimethacrylate

What is its significant to us when we buy our dental composites and its clinical value to our practice?

(1) The volume of the resins found in our composite resins affects its viscosity. The more volume of a specific resin content found particularly Bis-GMA, the more viscous it becomes. For example composite resins are commonly composed of 75% Bis-GMA and 25% TEGDMA, the result is that the viscosity is like honey but if you make it 50% Bis-GMA and 50% TEGDMA, the viscosity is like a thin syrup. Its clinical significance is that it allows us to increase filler loading in our restoration. In other words, the less viscous our composite, the more fluid it becomes. Moreover, the volume ratio of resins to its fillers also differentiates the classification of composite resins to microfilled, packable, microhybrid, flowable, sealant and no-resin composite resins.

(2) The sole presence or combinations of these resins also affects handling properties of our composite resins. Sometimes we complain about its stickiness or being too dry. It is because composite resins are commonly made of Bis-GMA. It is highly viscous, thus, any viscous material will affect the way it can be handled. The more viscous it is, the more it becomes dry if we don’t properly store them and vise-versa. Thus, it is normally mixed with TEGDMA.

Its combination will also affect the increase or decrease of water sorption, decrease or increase the composite’s general mechanical properties and affects color stability. The less viscous your composite resin is, the lesser its strength and color stability. That’s why some sealants are available in colorless. Why its high water sorption is a problem when we use sealants as preventive restoration when the cavity preparation is not totally dry. It is critical that we make sure that the area we are sealing is totally void of moisture. The best way to make sure that your sealants will not fail is to properly isolate the area with the use of rubber dam. There are some manufacturers who sells a product to evaporate moisture on the cavity like PrimaDry or make the sealants less hydrophobic in nature.

In my humble opinion, based on my observations, I prefer using flowable composites rather than sealants as preventive measures in restorations. It has higher mechanical properties and provide better seal. More so, there a lot of flowable composites that provides continuous fluoride release which takes care of making sure that our restoration will do as we intend it to be which is preventive on this case.

(3) Composite resins basically becomes expensive in price based on the components that the manufacturer used in making them. Bis-GMA monomers are relatively cheaper. But, there’s another component that’s developed which has higher flexural strength, elastic modulus and hardness. This is UDMA. Another is the ethoxylated version of  Bis-GMA which is BisEMA (Ethoxylatedbisphenol Dimethacrylate). BisEMA has reduced viscosity and has better mechanical properties. All these other components makes the composite in higher quality but places it in a much higher price value.

(4) Depending on what type and volume combination of these resins along it coupling agents will also affect the time of its polymerization. We have a tendency as dentists to prefer quicker polymerization of our composite resins because we want our procedures to be done as quick as possible too. However, each composite resins we handle requires variation of time to exposure to light and this also depends on the type and quality of light we use. Thus, when we buy composite resins because it states there we can cure it on 3-5 seconds only, we also have to consider if the light we use is capable to cure it as such. If we don’t cure properly our composite resins, these monomers become a health risk much deadlier than what we worry about mercury in our amalgam restorations. Not only our restorations become weaker if we don’t cure it properly but it also put our patients’ at risks with uncured monomers.

(5) Depending on the content and volume of these monomers, it is also important that we take into consideration how we store them. That’s why it is critical that we read the manufacturer’s instruction in regards to storage particularly the temperature it should be stored. We have heard that some composite resins don’t need to be refrigerated. That maybe true as long as the temperature you store your composites is according to the temperature stated in its instruction. Remember, our country is either dry or wet in season, and, this affect the level of room temperature we have in our clinics as well as the level of its humidity. All of these will affect the handling properties of your composite resins as well as its shelf-life.

If we try to read the components of our composite resins, it becomes totally complex and confusing. In the end, what is important to us is what matters to us when we do our restorations. If its handling properties you need to consider, then, personally I like the properties of composite resins with UDMA or with TEGDMA in as much composition with Bis-GMA. I also make sure that my composite resins are totally sealed with their caps and stored in my refrigerator for longer shelf-life. I take it out from the fridge 30 minutes or 1 hour prior to its use, so, I can avoid problems with its handling. If its hardness, flexural strength and color stability we are concerned about, then I prefer microhybrids rather than used microfilled or nanohybrids or even packable composite resins for that matter. If it is aesthetics, well, everyone is into nanohybrids but I still prefer microhybrids of higher quality as it provide both strength and aesthetics. When you buy your composite resins, do glance first its components and see if it will do deliver your preferences first before you consider the price. Because the value of its price is dependent on whether or not it can truly produce what you want during your treatment and your patients’ satisfaction in the end.