From Volume 46, Issue 4, April 2019 | Pages 363-368
This paper details the history of the introduction of visible light curing into dentistry. This history provides an excellent example of ‘out of the box’ lateral thinking translation of innovative scientific technology into dentistry. Visible light curing is an important UK contribution to the recent history and current practice of dentistry, with several million visible light curing procedures being carried out globally on a daily basis.
Visible light curing − activation of the polymerization of a material by means of light included in the visible spectrum, followed in the wake of ultraviolet light activated materials suffering a demise, largely caused by concerns over the hazards of exposure to ultraviolet radiation1 and limited depth of cure.2 The motivation to find an acceptable, user friendly means of light-activation in dentistry stemmed from market appeal for the desirable qualities of photo-activated materials, notably a one component formulation, as distinct from two components − base and catalyst − in chemically-cured systems, an opportunity for extended working time, and a ‘command set’.
In the early 1970s, two chemists at the ICI Petrochemical and Polymer Laboratory in Runcorn, Edward (Ed) Dart and Joseph (Joe) Nemcek, developed a visible light-activated (alpha)-diketone/amine catalyst system − an innovation which was granted a patent in 1976.3 Ed and Joe had been looking for a novel way to cure acrylic resins, specifically acrylic paint to be used to paint car bodies. Subsequent to the approach having been found difficult to apply, in particular in difficult to access, rust-prone areas of car bodies, new applications were sought for the Dart/Nemcek catalyst system. These included the development of resins used in fibre optic systems and in the manufacture of fan blades for jet engines.
The first suggestion of the possible use of visible curing in dentistry is credited to a chemist working in ICI Corporate Laboratories in the late 1970s, Dr Joseph (Joe) Jaworzyn (deceased). It is understood that the idea came to Joe when being treated by his dentist for the placement of a tooth-coloured restoration in one of his upper anterior teeth. Speculative, feasibility studies involved Joe and colleagues in refining the Dart/Nemcek catalyst system − the subject of a patent granted in 19784 and combining it with appropriate biocompatible resins − urethane di-methacrylates being developed by one of Joe's colleagues, Dr Mike Knight. The outcome of Joe Jaworzyn's work was a prototype visible light-cured resin composite which was considered to have potential for dental applications. Joe's final act in the process was to persuade an Operating Division of ICI to follow his work with the development and funding of a programme to translate the prototype material into a viable product (Figure 1).
Medical Aids in the Pharmaceutical Division of ICI, headed up by Mr Alan Vernon, took on the challenge posed by the Jaworzyn prototype. Dr John Yearn (Figure 2), recently moved to Medical Aids from the ICI Petrochemical and Polymer Laboratory, was tasked to lead the project. At that time, Dr Yearn had no knowledge of dentistry, other than as a patient; however, following bench demonstrations of the handling and ‘command set’ of the Jaworzyn prototype resin composite, he quickly realized the opportunity to produce novel restorative systems with relatively high filler loadings and favourable mechanical and clinical properties. Impressed by the outcome of subsequent initial evaluations and informal market enquiries, John Yearn undertook, amongst a number of other ‘blue sky’ responsibilities, to develop a new product proposal to be put to the Pharmaceutical Division Board of Directors.
To understand opportunities for visible light-cured, resin-based materials in dentistry better, John Yearn made contact with the local dental school − The University Dental Hospital of Manchester (UDHM), formerly the Turner Dental School. John Yearn's first point of contact in UDHM was Professor Alan Grant, Professor of Prosthetic Dentistry, including Dental Materials Science. Concurrently, John Yearn spent many hours in libraries learning about various aspects of dentistry, talking to local general dental practitioners (GDPs) and working with the ICI Corporate Laboratory Business Group to develop a business case to create marketable products based on the Jaworzyn prototype. Given considerable enthusiasm for, in particular, the prospect visible light-cured restorative systems, with the caveat from GDPs that the proposed new concept products should aim to be ‘quicker, easier and cheaper’, together with a workable business case, John Yearn's proposal was supported, and he had a new job heading up the project, line managed by John Colville, who replaced Alan Vernon, who died in a road traffic accident. Many years later, John Yearn disclosed that the ‘to develop, or not develop’ decision had been a close-run affair, with a number of the Directors being sceptical about a speculative business venture in the highly specialized world of dentistry.
John Yearn's first action in his new role, which commenced in 1974, was to establish a small research team. The first recruits were Dr Robert (Bob) Denyer and his two assistants Rod Traynor and Geoff Cole from ICI Corporate Laboratories. They were allocated a small ground floor laboratory in ICI Pharmaceuticals Mereside Research Facilities outside Alderley Edge in Cheshire, to await completion of new laboratories on the ICI Macclesfield site. Next, John Yearn had to recruit an individual capable of developing a light source to cure (polymerize) the proposed visible light-cured products. This individual was Ray Jones, again from ICI Corporate Laboratories. Ray worked closely with ICI Pharmaceutical Division instrument engineers to develop a suitable unit, building on experiences in dentistry with ultra-violet photoactivation units. Critically, the unit had to emit light in the range of 440 nm−480 nm wavelength in sufficient intensity to cure <3 mm of material in circa 60s.
Another important step for John Yearn was to strengthen links with UDHM. One of Professor Alan Grant's postgraduate students, Dr Mohammed Bassiouny, who had recently completed his MSc by research, was recruited to undertake PhD studies based on the development of visible light-cured composite systems. Mohammed Bassiouny was soon joined by Gordon Smith and Nairn Wilson, lecturers in Conservative Dentistry at UDHM, to provide clinical expertise in various aspects of operative dentistry and develop clinical trials of potential products. Dr Bassiouny's work ranged from physical and mechanical testing of prototype materials to determining an optimal finishing technique for use clinically.
What followed was a period of very intense, fast moving product development, including scaling up the production of the resin work undertaken in conjunction with ICI Organic Division at Blackley, extensive toxicology testing under the auspices of Dr Anne Charlesworth, laboratory, physical properties testing and clinical simulation, not to forget all the electo-engineering development which went into creating the first visible light-curing unit.
Looking back, the development team was very close knit, efficient and effective, with none of the countless problems encountered ever being allowed to become a barrier to realizing the collective goal of creating a novel, single paste formulation, visible light-cured, tooth-coloured composite capable of challenging the then market leading two paste, chemically cure composite, ADAPTIC (Johnson & Johnson, New Jersey, USA).
At one and the same time, Dr Robin Davies, who had previously been a senior clinical academic in Periodontology at UDHM, was leading an ‘Oral Health Project’ team in the Pharmaceutical Division of ICI working on the research and development of Corsodyl mouthwash and related products.
Being a true team leader, John Yearn, now line managed by Arthur Mason, volunteered to receive the ‘first in man’ visible light-cured composite restoration. As commemorated by a 25th anniversary plaque in UDHM, this event took place in what was known as ‘Side Surgery 1’ of the UDHM Department of Conservative Dentistry the late morning of 24th February 1976. The restoration, a replacement of a failing cervical (Class V) acrylic resin restoration in an upper right first premolar, was placed by Mohammed Bassiouny, with Gordon Smith and Nairn Wilson in attendance. The restoration, which was placed without rubber dam isolation, or acid etching and an intermediate resin, let alone dentine bonding, which had not been introduced at that time, was, in John Yearn's words, ‘acceptably smooth, but flat opaque white in appearance’ (Figure 3). The prototype material and light-curing unit used in the placement of the ‘first in man’ visible light-cured composite restoration are illustrated in Figures 4 and 5. While the simple ‘scrape testing’ indicated restorations of <2.5 mm in depth could be cured by a 30s exposure to the prototype light,5 a 60s exposure was used to ensure polymerization within the body of the material.
Subsequent to the placement of the ‘first in man’ restoration, a priority was to improve the translucency of the material. This was achieved by switching from a single glass filler to a blend of different glass fillers with a much higher refractive index. In the process, the material benefited from being rendered radio-opaque. As with all composite restorative systems available at the time, a single shade was considered sufficient. The goals for the further refinement of the material and light-curing unit were as follows.
Working in partnership with Johnson & Johnson, ICI launched the first commercially available light-cured composite, Fotofil, and associated light-curing unit (Figure 7) at an international symposium held at Guy's Dental Hospital on 27th January 1978. Remarkably, this event took place 23 months only after the ‘first in man’ placement of a visible light-cured composite restoration.
The symposium, chaired by Dr Richard Norman, then Director of Clinical Research, Johnson & Johnson Dental Products, included presentations by Drs John Yearn, Bob Denyer, Mohammed Bassiouny, Anne Charlesworth, together with papers by Professor John Bates (University of Cardiff; co-author Dr W (Bill) Douglas) and Dr Harold Wilson (University of Birmingham), who had undertaken academic consultancy work in the development of the Fotofil system. A panel of general dental practitioners (R Moule, W Peberdy and P Skinner), who had undertaken some practice-based evaluations of Fotofil, shared their clinical experiences with Fotofil with the invited audience of circa 200 participants from around the UK and Europe. Proceedings of the symposium were produced and disseminated by Johnson & Johnson.6
Soon thereafter, Bassiouny and Grant published a paper in the British Dental Journal reporting a ‘clinical open assessment’ of Fotofil.7 This paper was followed several months later by a presentation by Nairn Wilson and Gordon Smith at the 1979 General Assembly of the International Association for Dental Research in New Orleans8 and a related paper co-authored by Gordon Smith and Nairn Wilson reporting the initial findings of the first clinical trial of Fotofil.9 Related papers were subsequently published by Nairn Wilson and Gordon Smith between 1980 and 1984.10,11,12
Concurrent work was carried out on developing prototype visible light-cured fissure sealing systems, both filled and unfilled, and a visible light-activated orthodontic bracket bonding resin. The clinician in the latter programme of work was Michael (Mike) Read, a consultant orthodontist at UDHM. Neither of these workstreams resulted in the production of any commercial products, given a decision to focus available resources on the development of restorative systems.
Despite its novel features, favourable independent testing and, by standards of the late 1970s early 1980s, good aesthetic outcomes (Figure 8), Fotofil, for various, principally commercial reasons, was not a great marketing success, other than in the UK.
However, the experience gained and lessons learnt in developing and bringing Fotofil to the market provided a powerful springboard, largely funded by royalties on the ICI photoinitiation catalyst system, for the subsequent development and marketing of a series of novel restorative systems by what was then known as ICI Dental, which, in 1981, acquired its own marketing team, headed up by Glynn Heselwood. Glynn, in addition to his many, different contributions to the commercialization of ICI Dental visible light-activated restorative systems, took over responsibility for the marketing of ICI's Corsodyl products. Another hugely important addition to John Yearn's team was Tom Roberts who, from 1981, led the innovative, fast-moving, ground-breaking, basic research which facilitated the development of, amongst other products, Occlusin (ICI Dental, Macclesfield, UK) and subsequently Opalux (ICI Dental, Macclesfield, England), which were successfully marketed, together with the Luxor light (ICI Dental, Macclesfield, England) developed by the ICI Dental light-curing unit team, which continued to be led by Ray Jones (Figure 9). Occlusin was the subject of the most extensive clinical trial programmme ever undertaken in the field of dental biomaterials science.13 Notable amongst the related products was Epitex, a composite finishing system, which enjoyed sales which exceeded all expectations.
Looking back, the rate of innovation and pace of development within ICI Dental was very fast. Following the launch of Fotofil, essentially all the major manufacturers of dental composite systems sooner or later introduced one or more visible light-cured restorative systems. The resultant competition was a major driving force in the development of ICI Dental, which went on to acquire Coe Dental Laboratories, based in Chicago, before itself being acquired by GC Corp, Japan in the late 1980s.
Visible light curing is now integral to the practice of dentistry, with many different applications and certain issues.14 LED technology has largely replaced the use of filtered halogen lamps in light-activation units,15 and most of the light-activating handpieces are now cordless, rechargeable units. Today, it is estimated that several million visible light-curing procedures are carried out globally on a daily basis. Despite such widespread use, stemming from the ‘bright idea’ of Joe Zaworzyn, and voluminous research over the last 30−40 years, visible light curing is not without its limitations and drawbacks. The limitations centre on depth and sufficiency of cure, especially when preparations are very deep, and the key drawback relates to shadowing in difficult to access and undercut situations, compromising curing, the basis for the concept of ‘soggy bottom’ restorations, fuelling the view that ‘light curing may not be as simple as it seems’.16
Dentistry and countless patients have benefited greatly from Joe Jarworzyn's ‘bright idea’ and the subsequent work of, in particular, the close-knit team led by Dr John Yearn. Visible light curing is set to continue to play a major role in dentistry for the foreseeable future and may yet find new applications in oral healthcare provision; for example, in 3D photopolymer printing processes. The failed car paint to everyday use in dentistry stories provide excellent examples of ‘out of the box’, lateral thinking translation of innovative, scientific technology into dentistry. Visible light curing is an important UK contribution to the recent history and current practice of dentistry. Hopefully, this article will ensure credit where credit is due to the people behind the inception and initial development of the innovation.
