2nd European GIC

Chlorhexidine acetate release from four glass-ionomer-cements using HPLC: 

Introduction Previous work on resin-modified glass-ionomer cements (RMGIC) has shown that they leach hydroxy ethyl methacrylate (HEMA), one of their ingredients, depending on the curing rate1. It is also well established that conventional GICs and RMGICs can release fluoride ions, one of their component ingredients, over a prolonged period2. Further, it has been shown that fluoride ions can be added during the mixing phase of GICs leading to increase in fluoride release3. The mechanism of fluoride release is thought to be a diffusion process4 though Williams suggested that this may be a special case for fluoride5. Previous work on release of Chlorhexidine acetate (CHA) incorporated in AH2 cement resulted in only 3 – 10% of the incorporated species being released6. The reason for such a small release is unclear though many explanations have been purported such as CHA occupying preferred “strong-binding” sites, the release being that of ‘free’ CHA. G. Palmer, F. H. Jones and G.J. Pearson* Department of Biomaterials, Eastman Dental Institute 256 Gray’s Inn Road, London, WC1X 8LD *Department of Biomaterials in Relation to Dentistry ,Queen Mary & Westfield College, London, UK Results Affiliate of University College London Discussion Release In all cases, when more CHA was included in the glass, more was released although only a small amount of the added material was released (Table 2). The profiles for CHA release from AH2 cement and MP4 cement both have in common a linear portion (more clearly defined at higher concentrations) before levelling off. These two glasses have sodium in common. These differ from the other two glasses, LG30 and LG26, in which sodium is absent. In these, the curves show a gradual decrease in rate of release from t = 0 to the end of the experiments at approximately t = 60 h1/2 (150 days). Variations in batch (2) for MP4 and LG30 showed different release levels possibly dependant on the age of the glass, interestingly, they showed similar same release profiles. Compressive Strength For AH2, MP4 and LG26 as the percentage of added species was increased, so the compressive strength was reduced (Table 2). For the LG30, however, there was no perceivable trend. The compressive strengths show marked reduction with the exception of the LG30 cement. LG30 is the only glass without sodium and fluoride species; it is possible that CHA undergoes some form of ionic reaction with cements containing sodium and fluoride. The absence of these in LG30 means that different release profiles may be observed. Materials and Methods The materials used in this study were four glasses7 (Table 2) AH2, MP4, LG30 and LG26; freeze dried PAA (Advanced Health Care) and CHA (batch 93E213). A range of weights from 0.5% to 10.0% of CHA were added to the powder component of the mixture while maintaining the PAA : glass ratio of 1:4 (by weight) and blended powder : water ratio of 7:1(by weight). HPLC release The cement paste was packed into a split ring between glass slides. Any excess material was expressed through the split. The mould assembly was placed in an incubator at 37ºC for 1 hour. After this, the specimens were removed from the mould and weighed (±0.0001g) prior to immersion in 20 ml of distilled water. The samples were placed in an incubator at 37ºC and the storage pots agitated periodically. At regular intervals, 25mm aliquots were taken and added species concentrations of the solutions were determined by HPLC (Table 1). HPLC was carried out using external standards. Thus added species release from the cement (mg CHA / gram cement) were determined. Compressive Strength Experiments to determine the effect of added species content on compressive strength were carried out. Specimens were made in split steel moulds of 4mm diameter and 6mm height, left at 37 °C for 1 hour, then removed and placed in water at 37 °C for 48 hours before being tested to failure in compression on a universal testing machine (Instron 4500, Instron Ltd, Coronation Way, High Wycombe, England ) at 1mm per min. Conclusions The addition of CHA during mixing leads to rapid release of material into solution for all four GICs studied. The release profile depends on the composition of the glass component of the GIC. The mechanical properties also depend on the composition of the GIC. On the addition of CHA, compressive strengths were significantly decreased for GICs containing Na+ and / or F-. Most of the CHA remained bound up in the cement. References 1 G. Palmer, H.M. Anstice, G.J. Pearson, The effect of curing regime on the release of hydroxyethyl methacrylate (HEMA) from resin-modified glass-ionomer cements. Journal of Dentistry, 1999;27;303-311. 2 A. Musa, G.J. Pearson, M. Gelbier. In vitro investigation of fluoride ion release from four resin-modified glass polyaleknoate cements. Biomaterials 1996;17;1019-1023. 3 K.P. Thevadass, G.J. Pearson, H.M. Anstice, E.H. Davies. A method for enhancing the fluoride release of a glass-ionomer cement. Biomaterials 1995;16;1-5. 4 W.M. Tay, M. Braden. Fluoride ion diffusion from polyalkenoate (glass ionomer) cements. Biomaterials 1988;9;456-6. 5 J.A. Williams, R.W. Billington, G.J. Pearson, Comparison of ion release from a glass ionomer cement as a function of the method of incorporation of added ions. Biomaterials 1999;20;589-594. 6 G. Palmer, F.H. Jones, R.W. Billington and G.J. Pearson. Chlorhexidine release from an experimental glass ionomer cement. Biomaterials; 2004;25;5423-5431. 7 R.W. Billington, P.C. Hadley, M.R. Towler, G.J. Pearson, J.A. Williams, Effects of adding sodium and fluoride ions to glass ionomer on its interactions with sodium fluoride solution. Biomaterials, 2000;21:377-383. Aims The aim of this study was to investigate the use of four GIC cements containing vacuum dried poly(acrylic acid) (PAA), as a release agent for CHA using high-performance liquid chromatography (HPLC). The cements differed in the presence or absence of sodium, fluoride and phosphorous ions. The differing release profiles of CHA from these may give an indication as to the mechanism involved in the release of CHA. For Oral Health Care Sciences http://www.eastman.ucl.ac.uk Eastman Dental Institute Chlorhexidine acetate release from four glass-ionomer-cements using HPLC Table 2 The composition of the four cements in terms of their ionic species present, together with the maximum amount of CHA released from 10% CHA-containing GICs and the overall Change in compressive strength on going from the 0% to the 10% CHA cement Amount of CHA released from the four different cements http://www.eastman.ucl.ac.uk