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31 May 2020 | Australasian Dental Practice

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Omnichroma - A composite resin game changer from Tokuyama

By Dr Timothy Stolz

For better or for worse is a pledge many of us make when we state our marriage vows and married we are, as dental practitioners, to the most ubiquitous material in modern dentistry... composite resin. For better or for worse.

Patient demand for more aesthetic materials has presided over the demise of amalgam - not to mention concerns over mercury - and so we have seen the rise and rise of composite resin as a restorative material. Originally developed for anterior fillings, in the early days it was more terrestrial than celestial. However, through generations of research and development, it has morphed into a super-performer and its range of applications is now broader than a pre-election political promise.

Bonding to etched enamel early in its infancy, it now bonds to both enamel and dentine, and those bond strengths have increased with each new product launch. Intrinsic material strength (both compressive and shear) has increased, wear rate has decreased, polymerisation shrinkage reduced, colour stability improved, particle size varied, flowable materials introduced... the list goes on.

So much of this R&D has been driven by the recognition that composite is now the go-to material for the majority of drill-and-fill dentistry and the market is huge. For the practitioner who understand the material's physical properties, it has an almost unlimited range of applications in its current forms. From Class I to Class V restorations, coronal build-ups of heavily worn or broken teeth, porcelain repair, aesthetic veneering of anterior teeth, gap closure, interim rehabilitation of complete dentition, core build-ups, cementation, spread it on your toast... again the list goes on.

Perhaps the only frontier left in the Wild West of this ceramic/resin melange was the problem of colour. The way colour has been traditionally delivered to match all the shades on a Vita guide is to add different tints to the resin. This means that you need to keep a suitcase full of different colours for that "just-in-case'' patient. Inevitably, as clinicians, we will use about three shades routinely and the rest will lie sulking in the corner of the suitcase until they are past their use-by date, then to be thrown out. I doubt there's a practice in Australia that hasn't had to throw out expired composite and if they haven't, check your suitcase now!

Colour: The last frontier

The Wild West was opened up and tamed by the likes of dudes with money like Buffalo Bill and Wild Bill Hickok. The Wild Bill Hickok in the composite story is the Tokuyuma Company, who have produced a composite that addresses the colour problem front and square. If you've not heard of the Tokuyama company, it has already has form. They're the ones who developed the first composite with spherical nano particles, which had exceptional polishability. This technology has been incorporated in subsequent products they have produced (Estelite Sigma Quick, Estelite Omega, Estelite Asteria, Estelite Flow Quick, Estelite Bulk Fill Flow), with outstanding physical properties.

The latest iteration is Omnichroma and it signals the opening up of the final frontier. They have developed a one-size-fits-all composite, where there is just one shade. Yep, I'll say it again - JUST ONE SHADE. How the hell does that work? They have a system which they call "STRUCTURAL COLOUR" where the colour is generated by the interaction of light with the microscopic structure of the material. The shade and size of the structure affects the wave length of light as it exits the material, exhibiting specific colours. What happens is that the filler particles are grown to a very specific size and shape. They are 260nm in diameter and once again, spherical. They start off as a seed particle on which materials accrete through a chemical process known as the SO-GEL method, much like a pearl grows when an oyster is seeded with an irritant like a grain of sand. All the filler particles are kept to the uniform size of a 260nm. There are no added tints, as with composites we traditionally use.

This process produces a composite that mimics all the colours on a Vita Shade Guide. One composite, sixteen colours, a true chameleon composite which blends properly with the colour of the surrounding tooth.

But wait, there's more

In addition, Tokuyama's Omnichroma's polishability is better than most other composites and the high polish is achieved more quickly than others as well. Most composites have fillers which consist of ceramic particles that are produced by smashing the glass. This produces particles with jagged and rough edges, which means more rapid wear of the composite material as the filler particles get torn from the resin matrix and the ragged edges cause more abrasion of the opposing teeth. Because Omnichroma has spherical particles, it, along with one or two others, has the lowest wear rate and the lowest abrasion of opposing teeth by far. Strength and polymerisation shrinkage are on par with other modern composites.

What's in it for me?

It's time to "Cross the Rubicon". The Rubicon is a river which was the boundary between ancient Rome and Pompey which Julius Caesar crossed in 49 BC, signalling an irrevocable decision to start a war. While unlikely Omnichroma will be the cause of a war, it's fair to say that the development of this material can allow you as a clinician to make an irrevocable change.

Shade matching composite accurately to tooth structure has been fertile ground for disaster until now. Omnichroma has an exceptional ability to adopt the colour of the surrounding teeth. This takes the heat out of decision making, which if wrong, means re-applying a layer of composite again, at best, and at worst, starting again. This is both frustrating and time-consuming. With Omnichroma, this will not happen. The freakish ability of the material to produce structural colour and adapt to different tooth shades is a big step in the development of composite resins, at a time when most improvements have been no more than incremental. Combine this with the simplicity and cost-saving of a one-colour system and Tokuyama have come up with a winner with Omnichroma. With Omnichroma, you will be more efficient. With Omnichroma you will never throw out expired composite again!

About the author

Dr Tim Stolz is a Geelong-based general dentist of 40+ years' experience, with the last 30 years having an emphasis on reconstructive and implant dentistry.

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