Biomedical subjects

G Eliades

Publications and source records attributed to G Eliades.

At least 19 recordsLinked to original sources

PubMed2006

Surface characterization of precious alloys treated with thione metal primers.

OBJECTIVES: To characterize the effect of two thione metal primers with phosphate groups on the surface morphology and composition of two noble prosthodontic alloys. METHODS: Cast specimens from Argen 81(Au-Pd) and Argipal (Hi-Pd) alloys which were ground, polished and ultrasonicated in water, were divided in two groups (2 x 3) and treated with single layers of Alloy Primer (AP) and Metal Primer II (MP) primers respectively. The treated alloy surfaces were washed off with acetone and then examined by polarized light microscopy (PLM), reflection FTIR microspectroscopy (FTIRM) and X-ray photoelectron spectroscopy (XPS). RESULTS: After AP treatment, PLM revealed a crystalline phase (VBATDT) dispersed in an amorphous phase (MDP plus soluble VBATDT) on both the alloys tested. MP demonstrated a fibrial arrangement with the most dense structure found on the Hi-Pd alloy. FTIRM failed to clearly resolve the presence of SH peaks on alloy surfaces. Moreover, NH and PS peaks were identified denoting the presence of original thione tautomers. In both primers, phosphates were detected in a dissociative state (-PO(3)(2-)). FTIR molecular mapping confirmed separation of VBATDT from MDP and MEPS from residual MMA. XPS showed that on alloy surfaces approximately 50% of sulphur was in the sulphide state, the rest being organic sulphur. AP showed higher sulphide percentage than MP on both alloys and higher sulphide percentage on the Au-Pd alloy (p<0.05). CLINICAL SIGNIFICANCE: Phase separation of the primer components on alloy surfaces may adversely affect their clinical performance. Sulphide formation on alloy surfaces was confirmed only by XPS under ultra-high vacuum and not by environmental techniques like FTIR; this poses serious questions on the chemical bonding capacity of these primers with the noble alloys tested under environmental conditions.

Crystallization↗

PubMed2005

In vitro degradation of polyurethane orthodontic elastomeric modules.

The objectives of this study were to investigate the structural characteristics of orthodontic polyurethane elastomeric modules and their changes produced by mechanical and chemical ageing. Three products were tested (Generation II, Dentaurum, Alastic). For each product four groups of modules were studied under the following conditions: as-received (A(0)); after 3 weeks stretching at 50% elongation in air (B(0)); after 3 weeks immersion in an ethanol/water solution (3:1 v/v) to induce accelerated ageing (A(1)); and after 3 weeks immersion in the ethanol/water solution at 50% elongation, as above (B(1)). The chains and the solution extracts were characterized by micro-MIR FTIR spectroscopy. Specimens of group B(0) exhibited changes in peak intensities relative to the control group (A(0)), attributed to molecular orientation of poly (methylene glycol) soft segments and chain extenders such as butanediol. Moreover, group B(0) showed differences in the omega(CH(2))b peak at 1364 cm(-1), attributed to oxidative degradation of alpha-methylene groups by formation of ester, carboxylic acid or aldehyde groups due to hydrogen abstraction. Comparison of A(1) and B(1) groups with the controls (A(0), B(0)) showed no major differences between their respective spectra, apart from the loss of the 1639 cm(-1) peak attributed to ethylene NN bis (stearamide) wax. However, comparison of the spectra of the extracts from the elongated modules with the extracts of the controls revealed differences in the concentration of alcohol and alkene groups. The structural changes identified were the same in all the products tested and may indicate degradation mechanisms that could potentially hold intraorally.

Elastomers↗

PubMed2004

Tensile properties of orthodontic elastomeric chains.

The purpose of this investigation was to assess the permanent elongation, tensile strength and toughness of elastomeric chains. Two types (open and closed chains, i.e. with and without an intermodular link) of three brands of elastomeric module yielding six groups were included in the study. Specimens with equal numbers of loops were measured and classified into four groups based on their ageing state: (a) as-received; (b) subjected to a 24 hour steady strain in air determined as 50 per cent of original length; (c) exposed intraorally for 24 hours; and (d) retrieved following 3 weeks of intraoral exposure. All specimens were subjected to tensile stress and their behaviour was analysed with three-way ANOVA and Tukey's multiple comparison test at alpha = 0.05 level of significance, with brand, type (open or closed chains), and treatment variables serving as discriminating variables. Modular geometry or design were found not to have significant effects on elongation, probably due to the substantial variation in chain shape, modular size, and link length among products of the same category. Similarly, no correlation was identified between specimen treatment and the tensile strength of elastomers. The toughness results were not consistent with the group rankings for tensile strength, probably because of variation in the elastic and plastic deformation of specimens upon loading.

Analysis of Variance↗

PubMed2003

Multi-technique characterization of retrieved bone cement from revised total hip arthroplasties.

The purpose of this study was to assess the chemical composition, structure and degree of double bond conversion of retrieved bone cement from 29 total hip replacement revision arthroplasties, employing a multi-technique approach. Scanning electron microscopy revealed a porous cement surface, which replicated the characteristics of bone or femoral stem surface irregularities. Fourier transform infrared spectroscopy indicated that the retrieved bone cement samples were covered by a well-organized proteinaceous film rich in amides and alcohols, probably because of the adsorption of species from body tissues and fluids. X-ray fluorescence spectrometry showed the presence of potassium, sodium, calcium and phosphorus, implying the development of a mineralization process of the adsorbed biofilm. X-ray microtomography demonstrated a dense porous network in the bulk material comprised of macropores with a mean diameter >1 mm. FTIR analysis of the degree of double bond conversion of retrieved samples was in the order of 70%, similar to that of samples prepared in vitro in air, but 30% lower relative to their counterparts mixed in vitro and set in water. The effect of the adsorption of species onto bone cement surface on the reactivity of the material with the surrounding tissues and materials, is currently unknown. The results of this investigation reveal that the in vivo aging pattern of bone cements may involve alterations, which cannot be simulated under current in vitro protocols, emphasizing the necessity for adopting in vivo approaches including retrieval studies in assessing bone cement properties.

Journal Article↗

PubMed2002

Moisture-insensitive adhesives: reactivity with water and bond strength to wet and saliva-contaminated enamel.

The purpose of this study was to investigate the reactivity with water of a moisture-insensitive orthodontic primer (Transbond MIP), in conjunction with a no-mix orthodontic adhesive (Unite), and a moisture-insensitive adhesive (Smartbond), and to assess their bond strength to wet and saliva-contaminated enamel relative to the conventional application of the no-mix adhesive. The reactivity of the moisture-insensitive products with water was investigated by micro-multiple internal reflectance Fourier transform infrared spectroscopy (micro-MIR FTIR). Sixty premolars were divided into two groups of 30 teeth each and, on the buccal enamel surfaces, a standardized volume (0.1 ml) of water or fresh whole saliva was applied. Standard edgewise stainless steel brackets were then bonded to enamel surfaces as follows: (a) Unite, (b) Unite with the Transbond MIP, and (c) Smartbond. The brackets were debonded under shear force at a speed of 2 mm/min and the debonded enamel surfaces were subjected to fractographic analysis. The statistical analysis of the bond strength values was performed by two-way ANOVA with condition (water, saliva) and adhesive type serving as discriminating variables (n = 10, alpha = 0.05). The results of the fractographic analysis were evaluated by chi 2 test (alpha = 0.05). FTIR analysis showed that only Smartbond set in the presence of water. Application of water in Transbond MIP increased the extent of carboxyl ionization without inducing any setting reaction. Transbond MIP did not improve bond strength values when combined with the no-mix adhesive. Most adhesive-enamel condition combinations showed a trend to present lower bond strength in the presence of saliva; however, this was not confirmed statistically. Fractography of enamel and bracket base surfaces showed that Unite + Transbond MIP resulted in the most adhesive fractures (leaving no resin on enamel surface), whereas Smartbond presented the highest frequency of cohesive fractures (adhesive left on bracket and enamel surfaces).

Adhesives↗

PubMed2001

Heterogeneous distribution of single-bottle adhesive monomers in the resin-dentin interdiffusion zone.

OBJECTIVES: The purpose of this study was to investigate whether monomer separation occurs in single-bottle adhesives applied on acid-etched dentin surfaces. METHODS: Smear-layer covered dentin specimens produced from sound premolars, were acid-etched and analyzed by micro-MIR FTIR spectroscopy, before and after treatment with the single-bottle adhesives One-Step, Prime and Bond 2.1, Scotchbond 1 and Syntac-Sprint. The difference spectra (etched, and primed minus etched of the same dentin surfaces) were plotted and compared with original adhesive spectra. The C=C/C...C (aromatic adhesives) and C=C/C=O (aliphatic adhesives) peak area ratios were used to evaluate the extent of monomer separation relative to original adhesive spectra at the uppermost 2 microm of the resin-dentin interdiffusion zone. Three dentin specimens were used for each adhesive. One-way ANOVA and Newman-Keuls tests were performed to assess the statistically significant differences (alpha=0.05). RESULTS: All the adhesives demonstrated separation of monomer components on etched dentin ranging in mean values from 68.7 to 81.9% relative to reference. High molecular weight hydrophobic (i.e. BisDMA, BisGMA, BisGMA adducts) and hydrophilic monomers (i.e. BPDMA) predominated at the region probed. Prime and Bond 2.1 demonstrated the highest extent of monomer separation. SIGNIFICANCE: Heterogeneous monomer distribution following application to etched dentin may affect the curing performance of single-bottle adhesives within the resin infiltrated region and consequently, the mechanical and chemical stability of the network formed.

Acid Etching, Dental↗

PubMed2001

Intraoral aging of the inner headgear component: a potential biocompatibility concern?

The effect of intraoral aging of biomaterials on the modification of their surface properties has mostly been unknown. The purpose of this study was to investigate and characterize surface alterations of retrieved inner face-bow headgear components. Specimens were prepared from 3 areas of retrieved headgear wires: inner-outer face-bow soldered junction, buccal segment, and projection entering the buccal tube. Specimens from as-received headgear wires that matched the brand and size of the retrieved wires were also fabricated; all specimens were then subjected to multitechnique characterization. Optical microscopy revealed extensive biofilm islands of amorphous precipitants and accumulated microcrystalline particles. Micro-multiple internal reflectance Fourier transform infrared spectroscopy investigation of the retrieved wire samples demonstrated the presence of a proteinaceous biofilm, the organic constituents of which were mainly amide, alcohol, and carbonate. Scanning electron microscopy and radiographic microanalysis showed that the elemental species precipitated on the material surface were mainly calcium and phosphorus, forming calcium-phosphorus precipitates with thicknesses reaching 300 microm, whereas radiograph fluorescence spectrometry provided evidence of integument calcification through identification of calcium and phosphorus peaks. The clinical implication of the aging pattern that was identified relates to the potential protective role or induction of disintegration by the biofilm adsorbed on the wire that affected the biocompatibility of the alloy. Whereas further investigation is suggested for the clarification of the effect of intraoral aging on ionic release, the results of this study emphasize the necessity for the incorporation of in vivo approaches, including retrieval analyses, in the study of the biologic performance of orthodontic materials.

Adolescent↗

PubMed2001

Comparison of enamel colour changes associated with orthodontic bonding using two different adhesives.

The purpose of this study was to evaluate the enamel colour changes associated with bonding of brackets with a no-mix (one-phase) adhesive resin (Unite) and a glass-ionomer adhesive (GC Fuji Ortho). Thirty recently extracted premolars were used in the investigation. Black rectangular pieces of adhesive tape with a 3-mm diameter window were used to standardize the enamel surface intended for analysis. The teeth were divided into two groups of 15 teeth each, brackets (Starfire TMB) were bonded with the two adhesives, and the enamel surfaces were colourimetrically evaluated at three time intervals: (a) before bonding (baseline), (b) following debonding and cleaning, and (c) after artificial photo-ageing for 24 hours. The CIE colour parameters (L*, a*, b*) were recorded and averaged for each material, interval group, and the corresponding colour differences (delta E) were calculated. The results were statistically analysed using two-way ANOVA repeated measures, and Scheffé multiple range test at alpha = 0.05 level of significance. All differences noted exceeded the threshold for clinical detection (delta E = 3.7). The highest differences were recorded for the baseline-debonding interval for both adhesives used. No difference was found with respect to delta E between etching-mediated and no etching-mediated bonding implying that the debonding cleaning process involving adhesive grinding may be more invasive relative to acid etching with regard to enamel colour alterations.

Acid Etching, Dental↗

PubMed2001

Ease of use versus clinical effectiveness of restorative materials.

"Ease of use," as applied to dental materials and techniques, means different things to different people. Factors that may contribute to ease of use include a minimum number of application stages, easy application and shaping ability, quickness of use, lack of stick, and moisture sensitivity. Ease of use may also imply that a material or technique does not cause stress for the dentist and patient, is cost effective, is easy to learn, and should provide the operators with a sense of satisfaction with their work. Similarly, "clinical effectiveness" of the treatments prescribed for patients is not always capable of being accurately defined. Suggested factors that may contribute to clinical effectiveness include a lack of patient complaints with respect to longevity and/or cost, no secondary caries, and preservation of the remaining tooth structure during functional loading. Ease of use and clinical effectiveness are not necessarily related, but they must be combined for a technique to be successful. The achievement of this demands a partnership between clinicians, manufacturers, and patients.

Chemical Phenomena↗

PubMed2000

Light intensity effects on resin-composite degree of conversion and shrinkage strain.

OBJECTIVE: The aim of this study was to investigate the relationship between the degree of conversion (DC) and shrinkage strain values of two representative resin-composites when irradiated by two light intensity levels, for different time periods. METHODS: The DC of Z100 and Tetric Ceram was measured by FTIR spectroscopy immediately post-cure and shrinkage strain values were obtained continuously for 30 min from photoinitiation with the bonded-disk technique. All samples were photopolymerized at an initial temperature of 23 degrees C with the Elipar Highlight unit under the following modes of variable light intensity (I) 40 s at 750 mW/cm2; (II) a two-step 'soft-start' irradiation mode of 10 s at 200 mW/cm2 plus 30 s at 750 mW/cm2; (III) 40 s at 200 mW/cm2; and (IV) 10 s at 200 mW/cm2. Temperature effects of the light and curing exotherm were not eliminated. RESULTS: Mode II of irradiation did not reduce the DC for each material, relative to the values obtained with mode I (p > 0.05). The corresponding shrinkage strain values after 30 min were also not significantly different (p > 0.05). However, the effects of reduced light intensity levels for 10 s and 40 s (modes III and IV), were in agreement with previous findings implying reduced shrinkage strain levels. For both resin composites, data from all curing times and light-intensities gave a linear regression relationship (with r2 > 0.99) between the bonded-risk shrinkage strain versus DC values. SIGNIFICANCE: For the materials and light-intensities studied, the correlation between DC and shrinkage strain values means that some reductions in the problems of shrinkage may be achieved by an acceptable reduction in DC. However, this must also be consistent with generating adequate curing performance in the resin-network. Nevertheless, DC is not the exclusive parameter describing network character and a fuller understanding of the latter is an important research goal.

Analysis of Variance↗

PubMed2000

Surface characterization of retrieved NiTi orthodontic archwires.

The structure and morphological condition of retrieved NiTi orthodontic archwires was evaluated and any possible alterations in the surface composition of the alloy following 1-6 months in vivo were characterized. NiTi wires (GAC, German Orthodontics, ORMCO) of various cross-sections were collected through a retrieval protocol and were subjected to multi-technique characterization. Optical microscopy revealed islands of amorphous precipitants and accumulated microcrystalline particles. Micro MIR-FTIR investigation of the retrieved samples demonstrated the presence of a proteinaceous biofilm, the organic constituents of which were mainly amide, alcohol, and carbonate. Scanning electron microscope and X-ray microanalysis showed that the elemental species precipitated on the material surface were Na, K, Cl, Ca, and P, forming NaCl, KCl, and Ca-P precipitates. Increased intra-oral exposure was consistently associated with the presence of a mature film, while evidence of alloy delamination, pitting, and crevice corrosion, as well as a notable reduction in the alloy grain size was observed. Intra-oral exposure of NiTi wires alters the topography and structure of the alloy surface through surface attack in the form of pitting or crevice corrosion or formation of integuments. Further in vivo research is required to resolve the implications of the described ageing pattern in the corrosion resistance of the alloy, the potential for nickel leaching, as well as bracket-archwire friction variants.

Alcohols↗

PubMed2000

Degree of cure of orthodontic adhesives with various polymerization initiation modes.

The purpose of this study was to estimate the degree of cure (DC) of a light-cured, and a two- and a one-phase (no-mix) chemically-cured, as well as a dual-cured commercially available orthodontic adhesive resin. Forty stainless steel brackets were divided into four groups of 10 brackets each, and the bracket bases were covered with a standardized volume of adhesive. They were then pressed firmly onto a yellowish background surface of 75 per cent reflectance covered with cellulose film to facilitate detachment of the system and recovery of the set material. The visible light- and dual-cured adhesives were photopolymerized by irradiation from the incisal and cervical edges of the bracket for 10 seconds each, while another group of ceramic brackets was used to assess the differential interference of transparent relative to opaque material in the DC. Micro-multiple internal reflectance Fourier transform infrared spectroscopy was employed for the estimation of the DC of the adhesives (alpha = 0.05, n = 10), utilizing a method proposed previously. The dual-cured product demonstrated the highest DC followed by the light-cured combined with the ceramic bracket, and the no-mix and the chemically-cured adhesives. The combination of the metallic bracket with the light-cured product resulted in a DC comparable with that of the chemically-cured material.

Analysis of Variance↗

PubMed1999

Multitechnique characterization of articular surfaces of retrieved ultrahigh molecular weight polyethylene acetabular sockets.

The articular surfaces of 10 retrieved ultrahigh molecular weight polyethylene acetabular sockets were studied by optical microscopy, X-ray fluorescence spectrometry, multiple internal reflectance FTIR spectroscopy, scanning electron microscopy, and wavelength dispersive X-ray microanalysis. The results revealed characteristic wear patterns including polishing, scratching, pitting, cratering, folding, shredding, burnishing, cracking, embedding of particles, and development of acquired biofilms with various degrees of mineralization. The biofilms formed were mainly of proteinaceous origin, and mineralized regions were composed of calcium phosphates with carbonate impurities. The crystallinity of the polyethylene at the articular surfaces was enhanced compared to the bulk, which was possibly due to the cold work produced in vivo. The mineralized regions were classified into two groups based on the grey levels of the backscattered images obtained. The high-contrast regions that were mainly composed of Ca and P with traces of Al and Si were associated with bone fragments; the low-contrast regions composed of K, Na, Ca, Mg, Si, Al, Fe, Cl, and P were associated with acquired biofilm calcification, which implies the active engagement of biofilms in the long term performance of acetabular sockets in vivo.

Aged↗

PubMed1999

Effect of dentin primers on the morphology, molecular composition and collagen conformation of acid-demineralized dentin in situ.

OBJECTIVES: The purpose of this study was to assess the effect of two commercial primers and distilled water on the morphology, molecular composition and collagen conformation of acid-demineralized dentin in situ. METHODS: Dentin specimens etched with Scotchbond Etchant were imaged by tapping mode AFM and analyzed by MIR-FTIR spectroscopy. They were then primed with Scotchbond Multi-Purpose Plus Primer, Scotchbond 1 Adhesive or distilled water and imaged and analyzed again. The chemical modifications induced on the uppermost 2 microns of primed dentin were studied after water and original primer subtraction. The conformational changes of type I collagen at this region were evaluated by deconvoluting the amide I band components. The absorbance ratio An(1655/1627) was used to semiquantitatively assess, on a relative basis, the extent of collagen denaturation. RESULTS: All the priming treatments swelled the collapsed dentin collagen left after etching. No evidence of primary bonding was found after priming treatments, while approximately 50% of the conditioned dentin collagen appeared denatured. Treatment with distilled water did not change the status of denatured collagen, however, application of the commercial primers refolded the alpha-helix to approximately 95% of the extent found on the native reference dentin. SIGNIFICANCE: The dynamic response of dentin collagen to demineralization and priming treatments reveals the critical role of some primers in rapidly restoring the conformational status of acid-denatured collagen. Implementation of reactive adhesive groups in alpha-helix recovery may provide an associative means of modifying the mechanical properties of the demineralized collagen based on the extent of their intermolecular bonding.

Acid Etching, Dental↗

PubMed1999

Structural conformation of in vitro and in vivo aged orthodontic elastomeric modules.

The objectives of this study were to investigate the structural characteristics of open and closed elastomeric modules in the as-received condition, and following (a) 24-hour in vitro loading determined as a 50 per cent extension relative to their original length; (b) 24-hour intra-oral exposure; (c) 3-week intra-oral exposure. Ten specimens of each type (open and closed) of the three brands of elastic chains were included in the study (total of 60). All specimens were subjected to (a) optical transmission microscopy utilizing phase contrast and polarized light modes, (b) micro MIR FT-IR spectroscopy, and (c) scanning electron microscopy and electron probe X-ray microanalysis. Stretched elastomers demonstrated a honeycomb pattern of filament detachment corresponding to strained areas. The chains possessing a well-differentiated inter-modular link presented higher strain concentration gradients located in the link. Phase contrast imaging revealed that the stress adsorption mechanism of these materials involved macromolecular chain orientation and elongation co-axially to the applied load. The specimens retrieved after 24 hours had acquired a proteinaceous film rich in alcohol groups with minimal evidence of phosphate mineralization, while the 3-week retrieved specimens presented precipitation of Ca- and P-forming calcium phosphates. The high protein content of the biofilm organized on the surface of these materials, as well as the calcification pattern found, were similar to a non-specific mechanism of film adsorption of biomaterials exposed to body fluids. The results have clinical implications for aspects of retraction control through sliding mechanics with the use of elastomeric ligatures, and the potential detrimental effects on dental and periodontal tissues such as decalcification and gingival inflammation, respectively. In addition, the experimental protocols adopted for the in vitro study of the force decay of elastomerics should be modified to include parameters pertinent to adsorption phenomena and calcification processes documented to occur in vivo.

Biofilms↗

PubMed1999

Effect of chelating agents on the molecular composition and extent of decalcification at cervical, middle and apical root dentin locations.

The aim of this study was to investigate the interaction of two chelating agents used in endodontic treatment with dentin from different root locations. Standardized cervical, middle and apical root dentin specimens were prepared and subjected to treatment with 15% neutral EDTA and RCPrep. Following rinsing with water, dentin surfaces were studied by reflected light optical microscopy and micro-MIR FTIR spectroscopy, while the wash-off extracts were analyzed by atomic absorption spectrometry (AAS) to determine the content of calcium and phosphorus. Neutral EDTA removed the smear layer and opened tubules while RCPrep did not. FTIR measurements showed higher decalcification of dentin surfaces after neutral EDTA treatment although its effect was reduced at apical regions. AAS measurements of calcium and phosphorus confirmed the higher dentin dissolution potential of EDTA at cervical and middle root dentin locations. The results of the present study implied different reaction modes for the two chelating agents tested which might affect the efficiency of the chemo-mechanical preparation when these agents are used.

Analysis of Variance↗

PubMed1999

Effect of aluminium oxide sandblasting on cast commercially pure titanium surfaces.

Studies on the titanium porcelain interface have shown the presence of alumina, attributed mainly to the sandblasting procedure. In this study, an investigation of the effect of the sandblasting procedure on the microstructure and roughness of a cast commercially pure titanium surface was undertaken using three different particle size alumina powders. The analysis showed that in all cases alumina particles are embedded into the surface layer of titanium. The use of a large particle size alumina seems to be advantageous in reducing the weight of alumina remaining on the titanium surface and while increasing the surface roughness, thus promoting mechanical interlocking with porcelain.

Aluminum Oxide↗

PubMed1998

Acid-base reaction and fluoride release profiles in visible light-cured polyacid-modified composite restoratives (compomers).

OBJECTIVE: The aim of the study was to evaluate the extent of the acid-base reaction and F- release in Compoglass (Vivadent) and Dyract (Dentsply/DeTrey) restoratives. METHODS: For evaluation of the extent of the acid-base reaction, two groups of three specimens (7 mm x 5 mm x 1 mm) were prepared for each material. The first group was immersed in distilled water, while the second was kept in dark and dry conditions. Micro-MIR FTIR spectroscopy was used to determine the extent of the acid-base reaction on directly irradiated material surfaces immediately after irradiation and following water storage for 30 min, 3 d, 1, 2, 4, 8 and 12 wks. The in-depth extent of the acid-base reaction of the specimens stored in water for 4 weeks was studied by sequential spectra acquisition after removal of the uppermost 20, 70, 100, 240 and 400 microns layer by controlled grinding and 1 wk re-immersion in water of the 400 microns reduced specimens. For the F- release measurements, five disk-shaped specimens (10 mm x 1.5 mm) were prepared from each material and stored in distilled water. The amount of F- released for the storage periods reported above was measured using an ionometer with an F- electrode. Statistical analysis was performed by ANOVA, Scheffé's test and regression analysis. RESULTS: Storage in water promoted the development of an acid-base reaction on directly irradiated surfaces which reached a saturation point after 4 weeks. Depth profiling of the 4 wk immersed specimens revealed high salt concentration at the uppermost 100 microns layer. Re-immersion in water for 1 week of the 400 microns reduced specimens increased the salt concentration again at the uppermost region. Statistically significant differences were found in the acid-base rates and the in-depth salt yields between the materials (p < 0.05). The fluoride release after a 1 week initial "bursting" period was stabilized below 2 mg l-1 (p > 0.05) in both products. No positive correlation was found between acid-base reaction and fluoride release. SIGNIFICANCE: The development of a carboxylate-rich surface layer on polyacid-modified composite restoratives after water storage may explain their lower wear resistance compared with resin composites. The dynamic nature of these surfaces may provide several advantages regarding their interaction potential with hard dental tissues and their anticariogenic properties, but also some disadvantages concerning the quality of the surface texture obtained.

Alkalies↗