New Aura in aesthetic dentistry

During the 1950's and 1960's, Rafael Bowen's work with acrylics and epoxy resins1,2 led to the development of Bis GMA resins (or more accurately Bis Phenol A Glycidyl Methacrylates) which when modified with cross linking polymers and combined with glass particles, led to the "birth" of the modern dental composite. The chemistry is complex and over the past four decades, no material in dentistry has undergone an evolution process quite like composites and their "dental marriage" partner, the bonding resin.

Numerous posterior composites such as microfills, hybrids, nano hybrids and their "cousins" such as the compomers have emerged. The restorative dentist is not surprisingly often confused by the sheer numbers and types of different materials available to use. The leading dental companies of the world literally year on year launch new improved composites and/or bonding resins. Physical characteristics including bond strengths, abrasion resistance, polishability, microleakage and shrinkage or more aesthetic considerations such as chroma, hue, value, translucency and fluorescence have led to the average practitioner having to develop the knowledge of a materials scientist coupled with the skills and finesse of a leading artist and sculptor to understand and take advantage of this constant change. Material selection comes down to faith in a company, the handling characteristics, the aesthetic result obtained and a belief in the longevity of the life of the restoration produced.

Searching for the ideal composite

A search was undertaken to find a new composite material that had the ideal properties for both strength and aesthetics with ease of use for clinicians. SDI has emerged as an innovative company and their managing director, Jeffrey Cheetham, had an almost Martin Luther King-like dream to manufacture the "perfect resin composite" with the highest aesthetic potential. No tall order then! The basic premise was to perfectly match the colour of all teeth of all patients with the lowest number of syringes. Not even the least cynical member of the profession can be blamed for having thoughts of, "heard it all before" and if such a product existed, would it end up as another box of composite material to use for a while before ending up at the back of the proverbial cupboard!

Philosophy behind the Aura composite: Aesthetic layering

To understand the philosophy of developing such a material, it is important to truly understand what actually determines the colour of a tooth. The colour is determined by several factors - 95% of the colour is determined by the dentine and only 5% by the enamel, so not surprisingly the main determinant of the colour of a composite restoration will be related to the shade of the bulk of the material forming the restoration, often referred to as the dentine shades. The outer enamel shades, as in "mother nature", are translucent. Many of the systems currently available are arguably overly complicated with too many different shade combinations. Combining multiple shades, whether by multiple layering of different shades or kneading more than one shade together, is very difficult to do well and in any case, becomes impractical in a normal working situation. The practitioner may have liked to produce a "Van Gogh" masterpiece, but usually only has the time to craft a rapidly produced restoration.

Dentine and enamel shades

The Aura system, for reasons of simplicity, has only 7 dentine shades (Db, D1, D2, D3, D4, D5, D6 and D7) and 3 enamel shades (E1, E2 and E3). One might reasonably expect there to be 21 different combinations, but thankfully, only 9 are of clinical interest. Practitioners are more than experienced in observing the lighter and whiter teeth of the younger patient with translucent incisal edges and the yellower and darker shades of the older patient. Consequently, when choosing shades for teeth for a directly produced restoration, it is often less of a discussion of chroma, hues and opalescence but a decision taken almost subliminally. Good lighting is essential for choosing shades and a need to look at colours both under natural and artificial conditions goes without saying, but the use of gadgets such as spectrophotometers really have little place when preparing direct composite restorations. Therefore, with a single word answer, is Aura revolutionary in redefining the goal posts for aesthetic dentistry? "NO!"... unequivocally... nor does it claim to be...

Shade selection

Selecting the shade of the restoration should be undertaken prior to the placement of the restoration.³ It is best to do a trial mock-up and cure this onto the tooth prior to commencing the restoration. There are multiple options for choosing the shades and a few trial mock-ups are the best. It is best to show the patient the options for the layering and involve the patient in the decision for the final shade. As the layering technique involves a build up from darkest to lightest shade, using multiple shades will bring the restoration to life.⁴ However, if the restoration is too thin for a large build up, the multipurpose MC shade can be selected.

Benefits of Aura

So what are the benefits of the Aura system over much of the competition? Though multiple layers⁵ of different colours can be used to mimic nature as near as possible, for the most part, it will be used in simple 2-layer combinations. Furthermore, whilst the majority of dentists are using single shade composites for restorations, they will layer them in a few increments⁶ because of curing considerations and so it should not be very difficult to alter behaviour and place the dentine shades for the deeper layers and the enamel shades for the outermost layers, especially if there are enhanced aesthetic results and happier patients!

Conclusion

SDI have produced a very easy to understand shade card which shows the necessary combinations of enamel and dentine composites to produce the equivalent shade of the widely known "Vita" shade guide. It is also possible to master the different combinations of the dentine and enamel shades to produce optimal aesthetic results. That is the "beauty" of this system; it can be used either by the "true artist" or the "decorator" of the profession and either way, one will produce better aesthetic results than they have performed previously.

About the authors

Dr Linda Greenwall runs a multidisciplinary practice in Hampstead, London. She is the founder of the British Dental Bleaching Society (BDBS) and lectures extensively around the world on the subject of tooth bleaching. She is also the editor-in-chief of Aesthetic Dentistry Today magazine.

Dr Jeremy Cooper (UK) is a full-time general dental practitioner based in Salford, Manchester, United Kingdom.

References

1. Bowen RL ( 1956) Use of Epoxy Resins in restorative Materials J Dent Res 35:360-9.
2. Bowen RL ( 1963) Properties of silica- reinforced polymer for dental restorations JADA 66:57-64.
3. AHN Akbar , K Moharamzadeh, Wood DJ, Van Noort R (2011) Relationship between Color and Transluscency of Multishaded Dental Composite Resins. International Journal of Dentistry.
4. Blank JT (2012) Histological layering techniques for Composites. Dentistry Today (Dentistry today.com).
5. N Fahl ( 2006) A polychromatic composite layering approach for solving a Complex Class IV/Direct Veneer- Diastema Combination PPAD ( Practical Procedures and aesthetic dentistry)18:10 A-G.
6. Christensen G (1999) Sorting out the confusing array of resin-based composites in dentistry. J Am Assoc 130:275-277.