Ronald Verbeeck

Synthesis and thermal properties of poly(ethylene glycol)-poly(ϵ-caprolactone) copolymers

Abstract Three different types of polyester—polyether copolymers were synthesized by PEG initiated ring-opening polymerization of ϵ-caprolactone: an A-B and an A-B-A block copolymer and an (A)2-B star copolymer, where A is a poly(ϵ-caprolactone) (PCL) and B is a poly(ethylene glycol) (PEG) block. The monomer to initiator ratio was varied to obtain copolymers with different PCL block length and weight fraction ranging from 68–85 wt%. These PCL-PEG copolymers were characterized by means of g.p.c., n.m.r., d.s.c. and WAXD. In all types of copolymer the PCL constituent crystallizes first when cooling from the molten state. This leads to significant undercooling and imperfect crystallization of the PEG block. The mutual influence between PCL and PEG constituents is significantly stronger in the A-B-A block copolymers, having a central PEG block, and in the (A)2-B star copolymers. The effect of the PCL/PEG ratio on the melting and crystallization behaviour of the copolymers was investigated. The results obtained demonstrate that the thermal properties and morphology are affected significantly by the chain length of the PCL and PEG constituents in the copolymers and by the type of copolymers (sequence of the different blocks).

The effect of tooth size discrepancy on occlusion: An experimental study

The purposes of this experimental study are the following: (1) to compare the anterior and overall tooth size ratios reported by Bolton to values reported in epidemiologic studies, (2) to assess the accuracy of tooth size discrepancy measurements, (3) to investigate to what extent generalized tooth size discrepancy affects occlusion, (4) to investigate the effect of leveling the curve of Spee, and (5) to evaluate the effect of extraction therapy of 4 premolars on occlusion. For the first part of the study, Boltons mean anterior and overall tooth size ratio (as well as the extraction values) were compared with calculations derived from 4 publications reporting mean mesiodistal tooth width by using the t test (P </=.05). The second part of the study was carried out on a setup made from 1 dental cast of a male patient judged to have an ideal occlusion at the end of a nonextraction treatment. Our data reveal (1) no significant difference between the overall tooth size ratios of the Bolton values compared to 4 studies, but the anterior ratios were significantly different, (2) high reproducibility (99%) of tooth size discrepancy measurements, (3) that severe tooth size discrepancy affects the occlusion only a little, (4) that an excessive (6 mm) curve of Spee creates the poorest setup result, and (5) that extraction therapy only slightly affected the final occlusion. The effect of generalized tooth size discrepancy appears to be limited.

In vivo behaviour of three calcium phosphate cements and a magnesium phosphate cement

Three types of calcium phosphate cements and one magnesium phosphate cement were implanted subcutaneously in rats under exclusion of direct cellular contact. Retrieval times were either 1, 2, 4 or 8 weeks. Before and after retrieval the compressive strength, the diametral tensile strength, the quantitative chemical composition, the qualitative phase composition, the FTIR spectrum and the microstructure were determined. The three calcium phosphate cements maintained their strength during implantation. The phase DCPD was completely transformed into a Na- and CO3-containing apatite, the phases DCP and CDHA only partially. It could not be ruled out that OCP is also transformed into a bone-mineral-like apatite to a certain extent. That this latter process occurs much faster during the turn-over of living bone, is probably due to the very small crystal size of the OCP particles in bone.

The Short-term Fluoride Release of a Hand-mixed vs. Capsulated System of a Restorative Glass-ionomer Cement

The present study investigated whether variability in fluoride release was reduced by use of a capsulated system as compared with a hand-mixed system based on the same qualitative and quantitative glass-ionomer formulation. Five operators independently prepared five disks of each type of glass-ionomer restorative filling material. The amount of fluoride released in water by each specimen after 1, 2, 3, 7, and 14 days was determined. The variance and the mean value of the fluoride release at a given time were independent of the operator, regardless of the glass-ionomer system considered. However, the variance and the mean value of the fluoride release at a given time were considerably greater for the capsulated system than for the hand-mixed system. A regression analysis further showed that the cumulative amount of fluoride released, [F], as a function of the time t conformed to [F] = a[1- exp (-bt)] + ct0.5 for each glass-ionomer specimen, suggesting the simultaneous occurrence of two processes. Whereas the parameter b was the same for the hand-mixed and capsulated system and was independent of both a and c, the latter parameters were positively correlated. Moreover, the values for a and c were significantly greater for the capsulated system. On the basis of these results, it is concluded that the mixing process drastically influences the short-term as well as the long-term fluoride release.

Biodentine™ material characteristics and clinical applications: a review of the literature

IntroductionBiodentine™ is a new version of calcium silicate-based inorganic cement.AimThe aim of this review is to provide a detailed analysis of the physical and biological properties of Biodentine™ and to compare these properties with those of other tricalcium silicate cements viz. mineral trioxide aggregate (MTA) and Bioaggregate™ (Bioaggregate).Study designA comprehensive systematic literature search for all publications to date was performed on 20th November 2013 by two independent reviewers in Medline (PubMed), Embase, Web of Science, CENTRAL (Cochrane), SIGLE, SciELO, Scopus, Lilacs and clinicaltrials.gov using the search terms Biodentine, “tricalcium silicate”, Ca3SiO5, “dentine substitute”, “dentin substitute” and RD 94. In addition to the electronic search, hand searches and reference searches were performed to include articles published in journals that were not indexed in Medline. Randomised control trials (RCT), case control studies, case series, case reports, in vitro studies, animal studies and short communications in English language were considered for this review.ConclusionsConsidering the superior physical and biologic properties, Biodentine™ could be an efficient alternative to MTA to be used in a variety of clinical applications. There appears to be a wide range of clinical applications where Biodentine™ could be used in the field of endodontics, dental traumatology, restorative dentistry and pediatric dentistry. Although it seems to be good clinical practice, currently there is little clinical evidence to support all potential indications.

Conversion of octacalcium phosphate in calcium phosphate cements

This study investigated the in vitro conversion reaction in calcium phosphate cements (CPCs) containing octacalcium phosphate (OCP) as one of the reagents. OCP is known to be a precursor for apatite formation in vivo. The reaction products were characterized using infrared spectroscopy and X-ray diffraction. Although the conversion of OCP into hydroxyapatite is thermodynamically favorable, OCP only yields apatite formation in CPC provided it is combined with a highly soluble Ca(2+) and OH(-) releasing reaction partner. In this respect, tetracalcium phosphate is a promising compound. Adding small amounts of monocalcium phosphate monohydrate can stimulate the setting through intermediate brushite formation. The preparation method of OCP might drastically affect the performance of the cement. The reaction path of the setting of these CPC probably does not conform to the singular point principle described in the literature, and an in situ hydrolysis of OCP to apatite is conceivable. Simulation of apatite formation using OCP as the precursor and/or seed in CPC might be beneficial for some biomedical applications.

Reactivity of Fluoride-containing Calcium Aluminosilicate Glasses Used in Dental Glass-ionomer Cements

The glass component critically determines the properties of glass-ionomer cements (GIC). However, the exact relationship between the composition of the glass and these properties is not yet fully understood. To investigate this relationship, we studied the reactivity of glasses used in commercial GIC in acetic acid solutions, using a pH-stat method. Qualitative differences in the leaching behavior of these glasses can be explained by different pre-treatments. Acid-washing and silanization modify the surfaces of the glass particles, thus inducing a delay of the leaching process, whereas untreated glasses exhibit a fast initial leaching, but their acid reactivity slows very soon. Quantitative differences in acid reactivity can be correlated with the mean chemical composition of the glasses. In this respect, the leaching tends to increase with an increasing ratio of network-dwelling cations to Al 3+ ions. These results provide a fundamental basis for the explanation, prediction, and control of cement properties as a function of glass characteristics.

Changes in surface hardness of conventional restorative glass ionomer cements

The effect of a contact with an aqueous solution on the surface hardness of glass ionomers has been investigated in a few studies and for a limited number of formulations. As there is no information on the long-term changes of the surface hardness in this respect, the aim of this study was to determine these long-term changes in 10 conventionally setting glass ionomer formulations after storage in water as compared to maturation in a humid atmosphere (85% RH). After setting for 15 min different series of glass ionomer specimens were stored at 37 degrees C in both experimental media for 1, 7, 28 and 140 days. At the end of the specific maturation times, the mean surface hardness was determined on the basis of Knoop Hardness (KHN). Data were analyzed using ANOVA. In a humid atmosphere the surface hardness generally increases rapidly initially, followed after 1 day by a more gradual increase. In contact with water, the hardness also increases up to one day but not to the same extent. The surface hardness then remains constant or slightly decreases. Evidence of a detrimental softening of the surface ascribed previously to the loss of matrix forming ions was not found. A surface erosion is not likely to occur.

Infrared Spectrometric Study of Acid-degradable Glasses

The composition of glasses used in glass-ionomer cements affects their leaching behavior and hence the properties of the cement. The aim of this study was to correlate the composition and leaching behavior of these glasses with their infrared absorption characteristics. The wavenumber of the absorption band of the Si-O asymmetric stretching vibration ῡAS shifts to a higher value with decreasing content of mono- and bivalent cations in the glass. This effect can be ascribed to the influence of these extraneous ions on the glass network order and connectivity. Preferential leaching of these ions induces an increase of ῡAS and a general modification of the band profile. The results can be correlated with the x-ray diffraction characteristics of the glass. A decrease in the Si-O-Si angle could be caused by a decrease in the distortions in the (arrangement of the) SiO4 tetrahedra; the tetrahedra as well as their arrangement can be distorted.

Effect of acetic acid on the fluoride release profiles of restorative glass ionomer cements

OBJECTIVES This study investigates the fluoride release of glass ionomers in an acetic acid solution in order to substantiate a model according to which the short-term release results from an elution of loosely bound fluoride and the long-term release from an erosive leaching of the glass particles in the bulk of the cement. METHODS Individual fluoride release profiles of five specimens of 10 acid-base setting restorative glass ionomers were obtained by determining the amounts of fluoride released by each sample at 37 degrees C in consecutive elutions for up to 140 days with 25 ml of a 0.01 mol/l acetic acid solution with pH = 4. Differences in the fluoride release profiles were determined with a Multivariate Data Analysis on the basis of a Principal Component Analysis. RESULTS The fluoride release profiles of the 10 glass ionomers can be classified into five distinct groups which are characterized by a cumulative fluoride release described by the equation [F]c = [F]l t/(t + t1/2) + beta square root of t. The parameters ([F]l, t1/2) and beta are characteristic for the materials in the groups, and refer to the short-term and long-term fluoride release, respectively. The acidic solution enhances both processes compared to an elution in water, the effect being more pronounced for the long-term release. SIGNIFICANCE The fluoride release mechanism is intrinsically the same as determined for elutions in water. The increased amount of fluoride released under acidic conditions, especially in the long term, corroborates that an erosive leaching of the glass particles in the bulk of the cement accounts for the long-term fluoride release.