Auger electron spectroscopy of dentin: elemental quantification and the effects of electron and ion bombardment

Lacunar-canalicular bone remodeling: Impacts on bone quality and tools for assessment

Osteocytes can resorb as well as replace bone adjacent to the expansive lacunar-canalicular system (LCS). Suppressed LCS remodeling decreases bone fracture toughness, but it is unclear how altered LCS remodeling impacts bone quality. The first goal of this review is to assess how LCS remodeling impacts LCS morphology as well as the composition and mechanical properties of surrounding bone tissue. The second goal is to compare tools available for the assessment of bone quality at length-scales that are physiologically-relevant to LCS remodeling. We find that changes to LCS morphology occur in response to a variety of physiological conditions and diseases and can be classified in two general phenotypes. In the 'aging phenotype', seen in aging and in some disuse models, the LCS is truncated and osteocytes apoptosis is increased. In the 'osteocytic osteolysis' phenotype, which is adaptive in some physiological settings and possibly maladaptive in others, the LCS enlarges and osteocytes generally maintain viability. Bone composition and mechanical properties vary near the osteocyte and change with at least some conditions that alter LCS morphology. However, few studies have evaluated bone composition and mechanical properties close to the LCS and so the impacts of LCS remodeling phenotypes on bone tissue quality are still undetermined. We summarize the current understanding of how LCS remodeling impacts LCS morphology, tissue-scale bone composition and mechanical properties, and whole-bone material properties. Tools are compared for assessing tissue-scale bone properties, as well as the resolution, advantages, and limitations of these techniques.

Self-assembly of dental surface nanofilaments and remineralisation by SnF2 and CPP-ACP nanocomplexes

Dental caries, erosion and hypersensitivity are major public health problems. SnF₂ is used widely in oral care products to help prevent/treat these conditions. Casein phosphopeptide-stabilised amorphous calcium phosphate nanocomplexes (CPP-ACP) are a biomimetic nanotechnology of salivary phosphopeptide-ACP complexes that deliver bioavailable calcium and phosphate ions to promote dental remineralisation (repair). We show here using in vitro studies and a double-blind, randomised controlled, cross-over design in situ clinical trial that SnF₂ and CPP-ACP interact to form a nanofilament coating on the tooth surface and that together they are superior in their ability to promote dental remineralisation. Sn(II) by cross-linking the CPP-ACP helps to stabilise the complexes which improves delivery to the tooth surface and enhances binding and ion incorporation into tooth mineral. The combination of SnF₂ and CPP-ACP in oral care products may significantly improve their efficacy in prevention/treatment of dental caries/erosion and hypersensitivity.

Ca/P concentration ratio at different sites of normal and osteoporotic rabbit bones evaluated by Auger and energy dispersive X-ray spectroscopy

Osteoporosis is a systemic skeletal disorder associated with reduced bone mineral density and the consequent high risk of bone fractures. Current practice relates osteoporosis largely with absolute mass loss. The assessment of variations in chemical composition in terms of the main elements comprising the bone mineral and its effect on the bone's quality is usually neglected. In this study, we evaluate the ratio of the main elements of bone mineral, calcium (Ca), and phosphorus (P), as a suitable in vitro biomarker for induced osteoporosis. The Ca/P concentration ratio was measured at different sites of normal and osteoporotic rabbit bones using two spectroscopic techniques: Auger electron spectroscopy (AES) and energy-dispersive X-ray spectroscopy (EDX). Results showed that there is no significant difference between samples from different genders or among cortical bone sites. On the contrary, we found that the Ca/P ratio of trabecular bone sections is comparable to cortical sections with induced osteoporosis. Ca/P ratio values are positively related to induced bone loss; furthermore, a different degree of correlation between Ca and P in cortical and trabecular bone is evident. This study also discusses the applicability of AES and EDX to the semiquantitative measurements of bone mineral's main elements along with the critical experimental parameters.

Bisphosphonate incorporation in surgical implant coatings by fast loading and co-precipitation at low drug concentrations

The objectives of the present work was to evaluate the possibility for fast loading by soaking of bisphosphonates (BPs) into hydroxylapatite (HA) implant coatings biomimetically grown on crystalline TiO(2) surfaces, and also investigate the influence of different BP loading concentrations in a buffer during co-precipitation of a calcium phosphate containing layer onto these surfaces. The co-precipitation method created coatings that contained BPs throughout most of the coating layer, but the presence of BPs in the buffer hindered the formation of a bulk HA-layer, thus resulting in very thin coatings most likely consisting of islands built up by a calcium phosphate containing BPs. The coatings biomimetically grown on TiO(2) surfaces, were shown to consist of crystalline HA. Soaking of these coatings during 15 min only in a low BPs concentration containing buffer yielded a concentration on the coating surface of the same order of magnitude as obtained with soaking during 60 min in significantly higher concentrated buffers. This could be of advantage during surgery since the operating surgeon could make a fast decision whether or not to include the drugs in the coating based on the need of the particular patient at hand. The BPs present on the surface of the fast-loaded HA coatings were found to be strongly bound, something which should be beneficial for in vivo use. Both the co-precipitation method and the fast loading by soaking method investigated here are promising techniques for loading of BPs onto surgical implants. The simplicity of both methods is an advantage since implants can have spatially complicated structures.

Bone calcium, phosphorus detection by Auger electron spectroscopy

Auger electron spectroscopy was used to detect calcium and phosphorus of cortical bone from rat femoral neck and rear tibia. Spectra were taken from bone pieces as well as from disks prepared from grinded bone material. Experimental conditions were found whereby the samples could be analyzed without conductive coatings. The results of this preliminary investigation demonstrate that Auger electron spectroscopy can be used to study bone mineral elements.

SEM–EDX study of prepared human dentine surfaces exposed to gingival retraction fluids

OBJECTIVES

To evaluate the effects of gingival retraction fluids (GRF) on prepared dentine surfaces, and to test the null-hypothesis that prior exposure of dentine surfaces for prolonged period to any of the fluids evaluated does not influence acid-etching of the exposed surfaces.

METHODS

The investigation was carried out using SEM and energy-dispersive X-ray analysis (EDX). The GRF studied were Hemodent (HMDT), Astringedent (AST) and Ultradent buffered 25% Aluminium Chloride (ULTB). Longitudinal sections of 220-grit ground dentine surfaces were exposed to GRF for 0.5-, 1-, 2- and 5-min (n=4 each). Another group of samples was produced by 20s application of 35% phosphoric acid (PA) on GRF-pretreated dentine. Control samples were not exposed to GRF. Differences in etching effect-a function of the Ca-contents detected by EDX, were analysed using Friedman's and Wilcoxon's rank test (P<0.05).

RESULTS

The SEM demonstrated the presence of a relatively non-porous amorphous dentine matrix, but many of the dentine tubule orifices remained occluded. Granular precipitates, which remained even after acid-etching, were noted on surfaces exposed to Hemodent for 5 min. Characteristic crystal growth was observed on surfaces exposed to Astringedent for 1- or 2-min prior to acid-etching. The EDX data demonstrated that there were differences in resulting Ca-content; ULTB >AST>HMDT>ULTB+PA>HMDT+PA>AST+PA>PA, but AST and HMDT were not significantly different.

CONCLUSIONS

The exposure of dentine prepared surfaces to these three GRF altered its morphology and reduced the dentine's susceptibility to acid-etching, thus the null-hypothesis is rejected.

Current concepts on adhesion to dentin

This review examines fundamental concepts in bonding to dentin. Emphasis is placed on the structure and permeability characteristics of dentin and how they may influence its interaction with adhesive resin. Several new techniques to examine the interfaces between resin and dentin are reviewed along with some of their limitations. The advantages and disadvantages of acid etchants/conditioners vs. self-etching conditioners/primers are discussed. The problems of matching the surface tension of resin-bonding systems to the surface energy of the substrate are reviewed in terms of wetting the various components of dentin. The problems associated with matching the permeability of intertubular dentin to the diffusibility of bonding reagents are explored. Speculation is advanced on how to ensure polymerization and wetting of dentinal collagen. Theoretical problems associated with dentin bonding and with bond testing are reviewed to encourage future research in this rapidly developing area.

Quantitative analysis of the dentin adhesive interface by Auger spectroscopy

The ultimate success of a dentin adhesive bond is dependent in large part on specific conditions at the interface between the tooth and the adhesive. Most current dentin adhesive systems use some sort of pre-treatment to demineralize the first few microns of the dentin surface, leaving a meshwork of collagen into which the adhesive resin can penetrate, infiltrate, and polymerize. The general hypothesis tested in this experiment was that the penetration and distribution of adhesive resin into the demineralized zone are a function of the conditioner used as a pre-treatment for the adhesive application. Four commercially available adhesive systems were modified to incorporate hydroxyethylthiomethacrylate (HETMA), a sulfur-substituted, traceable analogue of 2-hydroxyethylmethacrylate (HEMA), thereby allowing for a qualitative measurement of the amount and distribution of monomer in the treated dentin substrate by energy-dispersive x-ray spectroscopy (EDS) and a quantitative measurement by Auger electron spectroscopy (AES). The dentin pre-treatments investigated were: (1) 10% citric acid/3% ferric chloride, (2) 10% maleic acid, (3) 2.5% nitric acid, and (4) an alcoholic solution of HEMA with a phosphorus acid ester. These pre-treatments were applied to freshly extracted teeth that had been sectioned to expose the dentin and ground to simulate the smeared layer. After the appropriate pre-treatment was applied, a 10% (v/v) solution of HETMA in acetone was applied to the surface, followed by the corresponding adhesive resin, which was then polymerized. The samples were then processed for observation by scanning transmission electron microscopy (STEM), AES, and STEM/EDS analysis. The results indicated significant differences in the ability of HETMA to penetrate the dentin surface conditioned by the four pretreatments investigated here. This study also demonstrated that AES and STEM/EDS could be used in a correlative fashion to determine the distribution of HETMA within or adjacent to the treated dentin surface.

The effects of ion sputtering on dentin and its relation to depth profiling

Characterization of the dentin surface and the dentin/adhesive interface is fundamental to investigations concerning adhesive bonding to dentin. It has been shown that good adhesive bonding depends on both the structure and composition of the dentin surface. A combination of ion sputter etching and Auger electron spectroscopy can be used to obtain surface composition and elemental depth profiles at interfaces. This investigation was conducted to examine the changes induced in human dentin by ion sputtering under conditions commonly encountered during depth profiling. The sputtering was conducted with argon ions at 7.5 keV and an ion flux ranging from 10(18)-10(19) ions/m2s. The amount of material sputtered was calculated from profilometer measurements of the sample surface. The surface composition was monitored by Auger electron spectroscopy. The results indicate that, under these conditions, collagen was removed at a much faster rate than hydroxyapatite, causing the surface composition of dentin to change during the sputtering process. The sputter yields for hydroxyapatite and collagen were found to be 5 and 28 atoms/ion, respectively, at a sputter angle of 45 degrees. At a sputter angle of 29 degrees, the yields were 2 and 25 atoms/ion, respectively. Both the changes in composition of dentin and the measured sputter rates are in agreement with the behavior predicted by a theoretical model for two phase materials (Blaise, 1978; Blaise et al., 1978).