The impact of iodoform on the hydration, bioactivity and antimicrobial properties of White Portland Cement

Iodoform (CHI3) is a potential radiopacifying agent for use in Portland cement-based root-filling materials. During this study, the impact of 20 wt% iodoform on the hydration and setting of white Portland cement (WPC) was monitored by powder X-ray diffraction, 29Si magic angle spinning nuclear magnetic resonance spectroscopy and Vicat apparatus. The presence of 20 wt% iodoform reduced the initial and final setting times of WPC from 150 to 121 min and 200 to 165 min, respectively. Iodoform had little impact on the products and extent of hydration after 7 days of curing; although, it did cause a reduction in the mean silicate chain length of the C-S-H gel (from 4.11 to 3.47 units). Both iodoform-blended and unblended cement pastes exhibited similar in vitro bioactivity, with the formation of crystalline hydroxyapatite on their surfaces within 1 day of exposure to simulated body fluid. An inhibition zone assay confirmed that WPC possesses intrinsic antimicrobial activity against S. aureus, P. aeruginosa and E. coli, which is significantly enhanced in the presence of iodoform. This study indicates that iodoform may be a suitable radiopacifying agent for Portland cementbased dental restoratives; although, further work is required to determine its long-term stability within the cement matrix

Hydrothermal synthesis of lithium silicate (Li2SiO3) from waste glass: a preliminary study

Current environmental directives to conserve resources and to divert waste streams have generated significant interest in mineral recycling. In this respect, this preliminary study has demonstrated that lithium metasilicate can be prepared by hydrothermal reaction between waste container glass and lithium hydroxide solutions at 100 °C. Minor proportions of calcium hydroxide, calcite, lithium carbonate and tobermorite were also produced during the reaction. Percentage crystallinity and proportion of lithium metasilicate in the reaction product were found to increase as functions of lithium hydroxide concentration (between 1 and 4 M). This research has also shown that the lithium metasilicate phase can take up 6.4 mmol/g of Zn2+ ions after 24 h during batch sorption. Further work to optimise the yield and to appraise the antimicrobial properties of Zn2+-bearing lithium metasilicate is now warranted

A 12-week assessment of the treatment of white spot lesions with CPP-ACP paste and/or fluoride varnish

This 12-week clinical study evaluated the impact of 10% CPP-ACP and 5% sodium fluoride varnish regimes on the regression of nonorthodontic white spot lesions (WSLs). The study included 21 children with 101 WSLs who were randomised into four treatment regimes: weekly clinical applications of fluoride varnish for the first month (FV); twice daily self-applications of CPP-ACP paste (CPP-ACP); weekly applications of fluoride varnish for the first month and twice daily self-applications of CPP-ACP paste (CPP-ACP-FV); and no intervention (control). All groups undertook a standard oral hygiene protocol and weekly consultation. Visual appraisals and laser fluorescence (LF) measurements were made in weeks one and twelve. The majority of WSLs in the control and FV groups exhibited no shift in appearance, whereas, in the CPP-ACP and CPP-ACP-FV groups, the lesions predominantly regressed. The visual and LF assessments indicated that the extent of remineralisation afforded by the treatments was of the following order: control ~ FV < CPP-ACP ~ CPP-ACP-FV. Self-applications of CPP-ACP paste as an adjunct to standard oral hygiene significantly improved the appearance and remineralisation of WSLs. No advantage was observed for the use of fluoride varnish as a supplement to either the standard or CPP-ACP-enhanced oral hygiene regimes

Melting behaviour of triblock polymers (poloxamers) in supercritical CO2

Carbon dioxide (CO2) is the most commonly used SCF because of the relatively mild operating conditions (31.1°C and 72.8 bar) and easily tuneable properties. Moreover, the ability of CO2 to act as a solvent and solute has made it highly desirable in the field of excipient processing, particle formation and drug encapsulation. The dissolution of CO2 is known to affect glass transition or melting temperature of polymers and fats [1]. In this work, the effect of the dissolution of liquid (l.CO2) or supercritical (sc. CO2) was studied on the melting point of various poloxamers (Pluronic™ F77, F127, F38, F68, F108) at the pressure ranging from 70 to 250 bar in a supercritical phase monitor. The treated and untreated samples were analysed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC)

The hydration chemistry of ProRoot MTA

‘Tooth-coloured’ ProRoot MTA is an endodontic cement comprising an 80:20 wt% mixture of white Portland cement (WPC) and bismuth oxide. The setting reactions within this cement system are not currently well understood. Accordingly, this research monitors the early hydration chemistry of ProRoot MTA by X-ray diffraction, solid state nuclear magnetic resonance and Fourier transform infrared spectroscopies, and isothermal calorimetry. The initial rate of hydration is rapid with 40% having reacted within the first 24 h; it then slows considerably such that within 3 days the hydration reactions are 58% complete and only increase by a further 1% within one week. The relatively fast reaction of alite to form C-S-H gel and portlandite, and the development of the calcium aluminosulphate phases, are as would be anticipated for the hydration of pure WPC. These findings confirm that bismuth oxide is an inert additive which does not participate in the hydration reactions

Bioactivity and antimicrobial properties of chitosan-tobermorite membranes

Tobermorite (Ca5Si6O16(OH)2.4H2O) is a layered calcium silicate hydrate phase whose bioactivity and biocompatibility with respect to bone and dental tissues are documented. Chitosan is a biodegradable mucopolysaccharide derivative that has been evaluated as a tissue scaffold material for the in situ regeneration of bone and periodontal structures. Recent studies have shown that tobermorite-chitosan composites are potential candidates for use as biodegradable guided tissue regeneration (GTR) membranes [2,3]. During the GTR process, a membrane is used to isolate the exposed root surface from invasive epithelial and gingival tissues in order to enable the slow-growing periodontal ligament and hard tissues to regenerate. Resistance to potentially pathogenic oral bacteria is a highly desirable property of GTR membranes which are prone to biomaterial-centred infection. Silver (Ag+), copper (Cu2+) and gallium (Ga3+) ions are reported to confer antimicrobial activity when incorporated into bioactive materials [1,4,5]. In the present study, tobermorite was synthesised and ion-exchanged with Ag+, Cu2+ or Ga3+ ions. The in vitro bioactivity and antibacterial properties of solvent-cast tobermorite-chitosan composite membranes were then evaluated with respect to their potential use as GTR membranes to repair damaged periodontal structures

Enamael Protection by Hydroxyapatite Toothpaste

Tooth enamel comprises ∼90% substituted hydroxyapatite (Ca10(PO4)6(OH)2), HAP, which is continually subjected to consecutive cycles of dissolution and recrystallisation. Initial dental caries is denoted by non-cavitated white spot lesions (WSLs) when net demineralisation occurs. Commercial products such as toothpastes, mouthwashes and chewing gums that release bioavailable calcium, phosphate and/or fluoride species have been shown to facilitate the remineralisation and repair of initial WSLs. In this respect, synthetic HAP particles can be incorporated into toothpastes to exploit both their abrasive and remineralising properties. The present study investigates the potential of a toothpaste containing micron-sized HAP particles (mirasensitive hap+®, Hager Werken, Germany) to repair WSLs in human enamel under optimum pH-neutral conditions and to protect the enamel exposed to an aggressive acid-challenge regime in vitro

Interactions of Cr3+, Ni2+ and Sr2+ with crushed concrete fines

The underutilized cement-rich fine fraction of concrete-based demolition waste is a potential sorbent for aqueous metal ion contaminants. In this study, crushed concrete fines (CCF) were found to exclude 33.9 mg g-1 of Cr3+, 35.8 mg g-1 of Ni2+ and 7.16 mg g-1 of Sr2+ from ~1000 ppm single metal nitrate solutions (CCF:solution 25 mg cm-3) under static batch conditions at 20 °C after 3 weeks. The removal of Sr2+ followed a pseudo-second-order reaction (k2 = 3.1 x 10-4 g mg-1 min-1, R2 = 0.999), whereas, a pseudo-first-order model described the removal of Cr3+ (k1 = 2.3 x10-4 min-1, R2 = 0.998) and Ni2+ (k1 = 5.7 x 10-4 min-1, R2 = 0.991). In all cases, the principal mechanism of interaction was the alkali-mediated precipitation of solubility-limiting phases on the surface of the CCF. Four consecutive deionized water leaching procedures (CCF:water 0.1 g cm-3) liberated 0.53%, 0.88% and 8.39% of the bound Cr3+, Ni2+ and Sr2+ species, respectively. These findings indicate that CCF are an effective sorbent for the immobilization and retention of aqueous Cr3+ and Ni2+ ions, although they are comparatively ineffectual in the removal and sustained exclusion of Sr2+ ions. As is commonly noted with Portland cement-based sorbents, slow removal kinetics, long equilibrium times, associated release of Ca2+ ions, high pH and formation of loose floc may preclude these materials from conventional wastewater treatments. This notwithstanding, they are potentially suitable for incorporation into permeable reactive barriers for the containment of metal species in contaminated groundwaters, sediments and soils

Enamael Remineralisation by Arginine-Calcium Carbonate Toothpaste

White spot lesions (WSLs) are the first visual indication that the dynamic processes that maintain healthy tooth enamel have shifted in favour of demineralisation. It is possible to reverse this early stage of enamel caries with good oral hygiene and home-use products that enhance the bioavailability of salivary calcium, phosphate and fluoride species. Arginine (C6H14N4O2), a conditionally essential α-amino acid, is metabolised by oral bacteria to generate ammonia which protects enamel from acid-erosion. It also forms complexes with Ca2+ ions which increase the bioavailability of calcium and promote remineralisation. The present in vitro study investigates the potential of a commercial arginine- and calcium carbonate-bearing toothpaste (Colgate Sensitive Pro-Relief, Colgate-Palmolive (UK) Limited) to repair WSLs in human enamel under optimum and aggressive acid-challenge conditions