RESEARCH INTERESTS

Colin Robinson is Emeritus Professor of the Dental Institute at Leeds. Professor Robinson's long-standing research interests lie in the biochemistry of mineralised tissue, morphogenesis, morphostasis and pathology, comprising the initiation and growth of mineral phases, interaction with extracellular matrices and their chemical and physical characterisation. This includes the effects of fluoride and other extraneous components. More recently, attention has been focused on novel physical technologies (AFM, CFM, SNOM). Work also includes oral soft connective tissues, salivary rheology and the interaction of oral biofilms with both natural and artificial substrates. Professor Robinson is a Founder Fellow of the Academy of Medical Sciences. He has considerable international involvement in oral and dental research: Secretary General and past president of the European Organisation for Caries Research (ORCA), past president of the British Division of the International Association for Dental Research (IADR), and former Chairman now honorary life member of the Mineralised Tissue Group of the IADR. He is also a corresponding honorary member of the Finnish Dental Society. Professor Robinson received the ORCA Rolex prize in 1982 for outstanding work on the basic biology of dental enamel and in 1992 received the IADR Distinguished Scientist Award for outstanding research in mineralised tissues. He served on the steering group for the Pan European Federation of Societies for Dental Research, UK Forum for Dental Research and is a member of The Advisory Board to the Research Councils (MRC). Professor Robinson is an affiliate senior member of staff at the Forsyth Dental Centre Boston, US. He was also Chairman of the Association of Basic Science Teachers in Dentistry. SCIENTIFIC INTERESTS -: Summary: Biomineralisation Fluoride and Fluorosis Dental Plaque Biofilms Dental Enamel Formation Filling Without Drilling Photodynamic Therapy for Dental Plaque BIOMINERALISATION Hydroxyapatite Crystal Formation- Fusion of preformed subunits stabilizing amorphous nuclei Freeze etching work (Robinson et al 1981) suggested that developing enamel substructure comprises spherical subunits with a diameter similar to the width of enamel crystals. From this it was concluded that these may reflect original nucleating centres containing amorphous or short range order calcium phosphates stabilized by matrix protein components. Degradative processing of the matrix by endogenous metalloproteases (MMP20) and a phosphatase could facilitate mineral precipitation. Fusion of such units would lead to the long crystals characteristic of enamel. AFM data supported this view in that morphology of early crystals comprised a linear succession of roughly spherical swellings. These disappeared as crystals grew in thickness but were replaced regular bands of positive charge similar in width to the original spheres. Smooth hypoplastic amelogenesis imperfecta revealed short fragments of crystals suggesting the defect resulted in non fusion of these early units. The spherical units themselves contained smaller chemically defined domains each sphere or charged band comprising a hexagonal cluster of smaller spheres. These appeared to be protein binding sites possibly for modulating proteins but may also represent initial nucleation sites. Selected relevant references: 1981 Robinson, C., Fuchs, P. and Weatherell, J.A. The appearance of developing rat incisor enamel using a freeze fracturing technique. J Crystal Growth, 53, 160-165 1998 Brookes S.J., Kirkham J., Shore R.C., Bonass W.A., Robinson C., Enzyme compartmentalization during biphasic enamel matrix processing. Connective Tissue Research Vol 39 (1-3) pp 89-99 (393-403) 1998 Kirkham J., Brookes S.J., Shore R.C., Bonass W.A., Smith D.A., Wallwork M L., Robinson C., Atomic force microscopy studies of crystal surface topology during enamel development. Connective Tissue Research Vol 38 (1-4) pp 89-100 2001 Wallwork ML, Kirkham J, Zhang J, Smith DAM, Brookes SJ, Shore RC, Wood SR, Ryu O & Robinson C. Binding of matrix proteins to developing enamel crystals; an atomic force microscopy study. Langmuir, 17. pp 2508 -2513 2003 Robinson C., Shore R.C., Wood S.R., Brookes S.J., Smith D.A. M., Wright J.T., Connell S., Kirkham J., Subunit structures in hydroxyapatite crystal development in enamel: implications for amelogenesis imperfecta. Connective Tissue Research 44 (suppl 1) pp 1-7 2004 Robinson, C., Connell, S., Kirkham, J., Shore, R.C., and Smith A. Dental enamel- a biological ceramic: regular substructures in enamel hydroxyapatite crystals revealed by atomic force microscopy.J. Mater. Chem., 2004, 14, 2242 - 2248 2005 Robinson C, Connell S, Brookes SJ, Kirkham J, Shore RC, Smith DAM Surface chemistry of enamel apatite during maturation in relation to pH: implications for protein removal and crystal growth. Archs Oral Biol; 50: 267-270. FLUORIDE AND FLUOROSIS Fluoride alters pK of crystal surfaces such that protonation is more difficult. Growth is altered and crystal surfaces are rougher at the molecular level. More protein binding results perhaps further affecting crystal growth. Recent work using the Atomic Force Microscope has shown that protonation of the surface of apatite is a first step towards ultimate loss of mineral ions. The pK of the apatite surface being about 6 compared with 6.8 for phosphate in solution. The presence of small amounts of fluoride had a dramatic effect on this phenomenon reducing the pK by an order of magnitude. The significance of this is that the surface is much more difficult to protonate. This will have significance for protein binding especially by surface cations, perhaps leading to protein retention seen in fluorotic tissue and reducing crystal growth. 1975 Weatherell, J.A., Deutsch, D., Robinson, C. and Hallsworth, A.S. Fluoride concentrations in developing enamel. Nature 256, 230-232 1990 Robinson, C. and Kirkham, J. Effect of fluoride on developing mineralised tissues. J Dent Res 69, 685 - 691 2001 Kirkham, J., Zhang J., Wallwork M., Smith D.A.M., Brookes S.J., Shore R.C., Wood, S.R., and Robinson C., The Effect of fluoride on the surface topology of developing enamel crystal. Caries Research 35, 50-56 2004 Robinson, C., Connell. S., Kirkham, J., Brookes, S.J., Shore, R.C., Smith, A.M. The effect of fluoride on the developing tooth. Caries Res. 38, 268-276 CARIES FLUORIDE, CARBONATE AND MAGNESIUM Analysis of the histological zones of caries lesions revealed massive loss of carbonate and magnesium at the first visible stage together with an increase in fluoride. Removal of destabilising components and increase in fluoride lead to re-deposition in the dark zone. Dark zone eventually dissolves due to lower pH near the lesion body. 0.05 ppm fluoride in saliva induces a delay in mineral loss. This limits duration in acid lowering net mineral loss. Very small amounts of fluoride in the saliva are associated with dramatic effects in caries reduction. The reasons are not clear elevation from about 0.02ppm to 0.05ppm seem to be most dramatic. A direct effect on mineral solubility is possible but the data is not too convincing. However, recent data has shown that at 0.5 ppm there may be an initial delay in mineral ion loss from enamel possibly due to delayed protonation of the crystal surface (see Atomic Force data above). The significance of this is that since acid production is episodic, any delay in loss of mineral ions would reduce the duration of acid exposure, an important parameter in caries and would lead together with slower dissolution to reduced mineral loss. 1982 Robinson, C., Weatherell, J.A. and Hallsworth, A.S. Alterations in the composition of permanent human enamel during carious attack. In: Demineralisation and Remineralisation of the teeth. Eds S.A Leach and W. M. Edgar pp 209 - 223 IRL Press 2001 Robinson C., Kirkham J., Shore R.C., Brookes S.J., Wood S.R., and Strafford S.M., The Chemistry of Enamel Caries. Critical Reviews in Oral Biology & Medicine, 11, pp 481-495 DENTAL PLAQUE BIOFILMS Plaque architecture contain channels and voids, surface area to mass is greater on outside due to frond like structures. Penetration of most materials is limited over short tooth brushing times A technique for recovering natural biofilms developed in the mouth on natural surfaces has been developed (Robinson et al 1997). This permitted studies of untouched intact plaque biofilms. Data revealed that dental plaque biofilms contain channels and voids often reaching as far as the enamel surface. Surface area to mass increase from surface to interior. Penetration profiles, for example of fluoride, fell steeply from outer surface to the interior; kinetic uptake experiments over very short periods (tooth brushing) revealed penetration only into the outer third or so of the biofilms. This seems to be related to the surface to to mass ratio. (See image above) Amine fluorides showed similar behavior but use of tracers showed that much of this was confined to the biomass surface. Hydrophobic triclosan on the other hand seemed to penetrate the biomass possibly locating near bacterial cells. Restricted uptake may relate to the limited efficiency of such therapeutics. DNA checkerboard has suggested that there is no obvious relationship between biofilm depth and species present. Obligate anaerobes were evenly distributed throughout the biofilm depth. 1997 Robinson C., Kirkham J., Shore R.C., Bonass W.A., Brookes S.J., Kusa L., Nakagaki H., Kato K., and Nattress B.R., A method for the quantitative site-specific study of the biochemistry within dental plaque biofilms formed in vivo. Caries Res 31, pp 194-200 1997 Kato K., Nakagaki H., Takami Y., Tsuge S., Ando S., Robinson C. A Method for Determining the Distribution of Fluoride, Calcium and Phosphorus in Human Dental Plaque and the Effect of a single in vivo Fluoride Rinse. Archs Oral Biol, Vol 42, No 7, pp 521-525 2000 Wood S.R., Kirkham J., Marsh P.D., Shore R.C., Nattress B and Robinson C., Architecture of Intact Natural Human Plaque Biofilms studied by confocal laser scanning microscopy. Journal of Dental Research 79 (1) pp 21-27 2002 Wood SR, Kirkham J, Shore RC, Brookes SJ and Robinson C. Changes in the structure and density of oral plaque biofilms with increasing plaque age. FEMS Microbiol Ecology 39: 239-244. 2004 Watson. P.S., Sissons, C.H., Devine, D.A., Shore, R.C., Kirkham, J., Nattress, B.R., Marsh, P.D., Robinson, C. Minimising prion risk without compromising microbial composition of biofilms grown in vivo in a human plaque model. Letters in Applied Microbiology, 38, 211-216 2005 Yamamoto K, Arai K, Fukazawa K, Fukui K, Nagamatsu K, Kato K, Nakagaki H, Robinson C. Effect of plaque fluoride released from a glass-ionomer cement on enamel remineralization in situ. Caries Res. Mar-Apr; 39(2):157-60. 2005 Watson PS, Pontefract HA, Devine DA, Shore RC, Nattress BR, Kirkham J, Robinson C. Penetration of fluoride into natural plaque biofilms. J Dent Res May; 84(5):451-5. 2005. Robinson C, Watson PS. Penetration of therapeutic agents through natural plaque biofilms. In Biofilms, Persistence and Ubiquity, The Biofilm, Club, Eds. Mcbain, A, Allison D, Pratten J, Spratt D, Upton M and Verran J.; 343-353. 2005 Watson PS, Robinson C, The architecture and microbial composition of natural plaque biofilms. In: Biofilms Persistence and Ubiquity. The Biofilm Club, Eds. McBain A, Allison D, Pratten J, Spratt D, Upton M, and Verran J. ; 273-285. DENTAL ENAMEL FORMATION Much of Profesor Robinson?s early work was directed towards a site specific location of chemical changes which occcur during enamel development, specifically relating changes in chemistry to accompanying histological change. Much of this was summarised in a textbook edited by Porfesor Robinson and Oral Biology staff. Work with radioactive phosphate located active mineral ion uptake adjacent to a discrete white opaque zone of tissue. This turned out to be the beginning of the maturation stage and resulted from tissue fluid replacing degraded matrix protein. The uptake of mineral represented massive crystal growth into the fluid filled space. Analysis of mineral content confirmed this view as a large increase occurred concomintant with the uptake of radioactive tracer. This was preceded by a massive loss of organic matrix components. Work was extended to enamel from a wide range of species and revealed an identical pattern although the timescale for each species was remarkably different. An elegant study when both enamel organ and enamel were dissected in 100ug samples along the same developing tooth showed a precise relationship between the shortening of ameloblasts, final loss of protein and massive mineral uptake. FILLING WITHOUT DRILLING First published in,1976 (see reference)Professor Robinson put forward the idea that instead of drilling out the porous enamel of carious lesions, that these small pores could be infiltrated with organic polymers which would polymerise within the lesion pores. This would occlude space preventing further ingress of acid or loss of mineral as well as providing mechanical support. In pursuance of good clincial procedure, this would minimise removal of sound tissue. The infiltration process could also be applied to very restricted fissures and to junctions between restorations and tooth tissue as well as exposed porous dentine. Water based polymers were preferred since it would not be possible to dry lesions completely. Later work showed that contemporary adhesive materials may be just as effective. Infiltration by polymers which would encourage remineralisation has also been explored. Slow release of, for example, fluoride, antibacterials and anti inflammatories was also shown to be possible and would widen the applications of this technique. 1976 Robinson, C., Hallsworth, A.S., Weatherell, J.A. and Kunzel, W. Arrest and control of carious lesions; A study based on preliminary experiments with resorcinol- formaldehyde resin. J Dent Res 55 812-818 1975 Robinson, C., Hallsworth, A.S., Kunzel, W. and Weatherell, J.A. Zur Definition qualitativer Anforderungen an locale kariesprventiva. Zahn-Mund- und Kieferheilkunde 63 829-835 2001 Robinson C, Brookes SJ, Kirkham J, Wood SR, Shore R.C. In vitro studies of the penetration of adhesive resins into artificial caries-like lesions. Caries Res 35 136- 14 2007 Kirkham, J.; Firth A.J.; Vernels, D.; Boden N.; Robinson, C.; Shore, R.C.; Brookes, S.J.; Aggeli A. Self-assembling peptide scaffolds promote enamel remineralisation. Journal of Dental Research, 86(5), pp.426-430. PMID: 17452562 [PubMed - indexed for MEDLINE] PHOTODYNAMIC THERAPY FOR DENTAL PLAQUE Work with plaque biofilms produced in vivo was extended to examine the effects of photosensitisers on inhibition of plaque bacteria actually in the mouth. In this context, Professor Robinson instigated the use of a current disclosing soution i.e. one used to visualise plaque. This solution, containing the photosensitiser erythrosine, already was known to penetrate plaque and its clearance for use in the mouth made it an ideal candidate for clinical use; now being exploited by the Leeds Dental Institute. (PhD Thesis Daniel Metcalfe, University of Leeds). 1999 Wood S.R., Nattress B., Kirkham J., Shore R.C., Brookes S.J., Griffiths J., Robinson C.,. An in vitro study of use of Photodynamic Therapy for the treatment of natural oral plaque biofilms formed in vivo. Journal Photochem. Photobiol B: Biol 50 pp 1-7 2006 Metcalf D. Robinson, C. Devine D. Wood, S. Enhancement of erythrosine-mediated photodynamic therapy of Streptococcus mutans biofilms by light fractionation Journal of Antimicrobial Chemotherapy 58 (1): 190-192.