Effect of curing mode on the conversion and IIT-derived mechanical properties of core build-up resin composites.

The aim of the study was to evaluate the degree of conversion and the mechanical properties of five composite core build-up materials polymerized in dual-curing and self-curing modes. The materials tested were: Clearfil DC Core Plus (CF), Gradia Core (GC), Luxacore-Z Dual Smartmix (LX), Multicore Flow (MC) and Paracore (PC). Disk-shaped specimens were prepared from each material; half the specimens were light-cured, whereas the rest were only self-cured. After a 3-week storage period (dark/dry/37 °C) the Martens Hardness, Indentation Modulus, and Elastic Index were determined by instrumented indentation testing (IIT), while the degree of conversion was assessed by ATR-FTIR spectroscopy. Statistical analysis was performed by 2-way ANOVA and post-hoc testing (α = 0.05). The dual-curing mode resulted in statistically higher Martens Hardness and Elastic Index than the self-curing mode in most materials but showed insignificant differences in Indentation Modulus. MC and PC demonstrated significantly higher degree of conversion in both curing modes. Overall, the self-curing mode was inferior to the dual-curing in conversion and mechanical properties for most products, despite their differences in monomer composition and filler loading.

Comparative evaluation of topographical data of dental implant surfaces applying optical interferometry and scanning electron microscopy.

OBJECTIVE: Comparability of topographical data of implant surfaces in literature is low and their clinical relevance often equivocal. The aim of this study was to investigate the ability of scanning electron microscopy and optical interferometry to assess statistically similar 3-dimensional roughness parameter results and to evaluate these data based on predefined criteria regarded relevant for a favorable biological response. METHODS: Four different commercial dental screw-type implants (NanoTite Certain Prevail, TiUnite Brånemark Mk III, XiVE S Plus and SLA Standard Plus) were analyzed by stereo scanning electron microscopy and white light interferometry. Surface height, spatial and hybrid roughness parameters (Sa, Sz, Ssk, Sku, Sal, Str, Sdr) were assessed from raw and filtered data (Gaussian 50µm and 5µm cut-off-filters), respectively. Data were statistically compared by one-way ANOVA and Tukey-Kramer post-hoc test. For a clinically relevant interpretation, a categorizing evaluation approach was used based on predefined threshold criteria for each roughness parameter. RESULTS: The two methods exhibited predominantly statistical differences. Dependent on roughness parameters and filter settings, both methods showed variations in rankings of the implant surfaces and differed in their ability to discriminate the different topographies. Overall, the analyses revealed scale-dependent roughness data. Compared to the pure statistical approach, the categorizing evaluation resulted in much more similarities between the two methods. SIGNIFICANCE: This study suggests to reconsider current approaches for the topographical evaluation of implant surfaces and to further seek after proper experimental settings. Furthermore, the specific role of different roughness parameters for the bioresponse has to be studied in detail in order to better define clinically relevant, scale-dependent and parameter-specific thresholds and ranges.

Comparative analysis of the mechanical properties of fiber and stainless steel multistranded wires used for lingual fixed retention.

OBJECTIVE: To evaluate the effect of different resins used for the co-polymerization of EverStick fiber-reinforced fixed orthodontic retainer on its mechanical properties and to compare the mechanical properties of these configurations to commonly used multistrand wires. MATERIALS AND METHODS: Ten 0.0175-in. WildCat (WC175), ten 0.0215-in. WildCat (WC215) three-strand twisted wires and thirty EverStick fibers were tested in this study. The EverStcik fibers were equally shared in three groups (n=10). The samples of first group (ESRE) were polymerized employing Stickresin (Light cure enamel adhesives), the second one (ESFT) employing Flow Tain (Light cured composite), whilst the specimens for the third group (ES) were not combined with resin. All samples were loaded in tensile up to fracture in a universal tensile testing machine and the modulus of elasticity, tensile strength and strain after fracture were recorded. The same groups were also tested employing Instrumented Indentation Testing (IIT) and Martens Hardness (HM), Indentation Modulus (EIT) and elastic index (ηIT) were determined. The results of tensile testing and IIT were statistically analyzed employing one way Anova and the Student Newman Keuls test (SNK) at a=0.05 level of significance. RESULTS: WC175 and WC215 showed higher modulus of elasticity and tensile strength but lower strain after fracture compared to Everstic groups. IIT illustrated significantly higher values for HM, EIT, and ηIT for WC groups compared to ESRE, ESFT and ES. ESFT showed higher HM and elastic index compared to ESRE and ES, a finding which is attributed to the fact the FlowTain is a filler-reinforce composite with higher hardness compared to unfilled resins. SIGNIFICANCE: Multistrand wires demonstrated higher values in mechanical properties compared to EverStick ones. The co-polymerization with difference resins does not affect the tensile properties of Everstic, however the use of a light cured composite has a beneficial effect on hardness.

Viscoelastic properties of orthodontic adhesives used for lingual fixed retainer bonding.

OBJECTIVE: To evaluate the viscoelastic properties of two experimental BPA-free and one BisGMA-based orthodontic resin composite adhesives for bonding fixed retainers. METHODS: A commercially available BisGMA-based (TXA: Transbond LR) and two bisphenol A-free experimental adhesives (EXA and EXB) were included in the study. The viscoelastic behavior of the adhesives was evaluated under static and dynamic conditions at dry and wet states and at various temperatures (21, 37, 50°C). The parameters determined were shear modulus (G), Young's modulus (E) under static testing and storage modulus (G1), loss tangent (tanδ) and dynamic viscosity (n*) under dynamic testing. Statistical analysis was performed by 2-way ANOVA and Bonferroni post-hoc tests (α=0.05). RESULTS: For static testing, a significant difference was found within material and storage condition variables and a significant interaction between the two independent variables (p<0.001 for G and E). EXA demonstrated the highest G and E values at 21°C/dry group. Dry specimens showed the highest G and E values, but with no significant difference from 21°C/wet specimens, except EXA in G. Wet storage at higher temperatures (37°C and 50°C) adversely affected all the materials to a degree ranging from 40 to 60% (p<0.001). For dynamic testing, a significant difference was also found in material and testing condition groups, with a significant interaction between the two independent variables (p<0.001 for G1 and n*, p<0.01 for tanδ). Reduction in G1, and n* values, and increase in tanδ values were encountered at increased water temperatures. SIGNIFICANCE: The apparent detrimental effect of high temperature on the reduction of properties of adhesives may contribute to the loss of stiffness of the fixed retainer configuration under ordinary clinical conditions with unfavorable effects on tooth position and stability of the orthodontic treatment result.

Histochemical changes of occlusal surface enamel of permanent teeth, where dental caries is questionable vs sound enamel surfaces.

AIM: This in vitro study was to classify questionable for caries occlusal surfaces (QCOS) of permanent teeth according to ICDAS codes 1, 2, and 3 and to compare them in terms of enamel mineral composition with the areas of sound tissue of the same tooth. METHODS: Partially impacted human molars (60) extracted for therapeutic reasons with QCOS were used in the study, photographed via a polarised light microscope and classified according to the ICDAS II (into codes 1, 2, or 3). The crowns were embedded in clear self-cured acrylic resin and longitudinally sectioned at the levels of the characterised lesions and studied by SEM/EDX, to assess enamel mineral composition of the QCOS. Univariate and multivariate random effect regressions were used for Ca (wt%), P (wt%), and Ca/P (wt%). RESULTS: The EDX analysis indicated changes in the Ca and P contents that were more prominent in ICDAS-II code 3 lesions compared to codes 1 and 2 lesions. In these lesions, Ca (wt%) and P (wt%) concentrations were significantly decreased (p = 0.01) in comparison with sound areas. Ca and P (wt%) contents were significantly lower (p = 0.02 and p = 0.01 respectively) for code 3 areas in comparison with codes 1 and 2 areas. Significantly higher (p = 0.01) Ca (wt%) and P (wt%) contents were found on sound areas compared to the lesion areas. CONCLUSIONS: The enamel of occlusal surfaces of permanent teeth with ICDAS 1, 2, and 3 lesions was found to have different Ca/P compositions, necessitating further investigation on whether these altered surfaces might behave differently on etching preparation before fissure sealant placement, compared to sound surfaces.

Setting characteristics of a resin infiltration system for incipient caries treatment.

OBJECTIVES: This study investigated the curing efficiency, the extent of atmospheric oxygen inhibition to the polymerization reaction and the mechanical properties of a new resin-infiltration system for caries treatment. METHODS: The curing efficiency was estimated by measuring the percentage degree of cure (%DC) of thin resin films (h: 150µm, Ø: 5mm, n=3), 10min after 40s exposure to a quartz halogen bulb (750mW/cm2) light curing unit (Optilux 501, Demetron/Kerr, USA), in the absence of O2, by micro ATR-FTIR spectroscopy. The extent of O2 inhibition on resin film setting (width in µm) was assessed by transmission optical microscopy on thin films (h: 150µm, Ø: ∼7mm, n=5) placed between two transparent cover slips and exposed to air from lateral sites. For each sample the extent of inhibition was measured at 5 different locations. The mechanical properties were tested employing Instrumented Indentation Testing according to ISO 14577:2002. Resin specimens (h: 2mm, Ø: 10mm, n=5) were prepared employing cylindrical teflon moulds enclosed in transparent matrix strips and glass slides as before. The measurements were performed employing a Vickers indenter attached to a universal hardness testing machine (ZHU2.5/Z2.5 plus test Xpert software, Zwick/Roell, Ulm, Germany). The parameters tested were Martens Hardness (MH), Vickers Hardness (VHN), Indentation Elastic Modulus (EIT) and elastic to total ratio of indentation work (ηIT). For all these tests, specimens of a conventional light-curing bonding resin (HB-Heliobond, Ivoclar-Vivadent, FL) prepared as above were used as control. Student t-test was used to identify statistically significant differences between the two materials in the parameters tested (a: 0.05). RESULTS: The results of the materials tested were: (a) [% DC]; IC: 57.4±1.5, HB: 59.8±2.4, (b) [Width of O2 inhibition/µm]; IC: 33.1±6.5, HB: 23.6±4.4, (c) [MH/N/mm(2)] IC; 116±16, HB: 261±35, (d) [VHN]; IC; 15.4±2.5, HB: 22.1±1.8, (e) [EIT/(GPa)]; IC; 2.3±0.4, HB: 7.5±0.5, and (g) [ηIT (%)] IC; 50.3±3.4, HB: 35.1±1.9. The IC presented no significant difference in terms of % DC, higher thickness of the inhibited layer, lower MH, VHN, EIT and greater ηIT values than HB. CONCLUSIONS AND CLINICAL SIGNIFICANT: The resin-infiltrating system for incipient caries treatment demonstrated the same curing efficiency with a conventional unfilled bonding resin, but exhibited higher extent of oxygen inhibition, lower hardness, lower elastic modulus and higher plastic to elastic indentation energy.

The effect of polishing technique on 3-D surface roughness and gloss of dental restorative resin composites.

The aim of this study was to compare surface roughness and gloss of resin composites polished using different polishing systems. Five resin composites were investigated: Filtek Silorane (FS), IPS Empress Direct (IP), Clearfil Majesty Posterior (CM), Premise (PM), and Estelite Sigma (ES). Twenty-five disk specimens were prepared from each material, divided into five groups, each polished with one of the following methods: Opti1Step (OS), OptiDisc (OD), Kenda CGI (KD), Pogo (PG), or metallurgical polishing (ML). Gloss and roughness parameters (Sa, Sz, Sq, and St) were evaluated by 60°-angle glossimetry and white-light interferometric profilometry. Two-way analysis of variance was used to detect differences in different materials and polishing techniques. Regression and correlation analyses were performed to examine correlations between roughness and gloss. Significant differences in roughness parameters and gloss were found according to the material, type of polishing, and material/polishing technique (p< 0.05). The highest roughness was recorded when KD was used (Sa: 581.8 [62.1] for FS/KD, Sq: 748.7 [55.6] for FS/KD, Sz: 17.7 [2.7] for CM/KD, and St: 24.6 [6.8] for FS/KD), while the lowest was recorded after ML (Sa: 133.6 [68.9] for PM/ML, Sq: 256.5 [53.5] for ES/ML, Sz: 4.0 [1.3] for ES/ML, and St: 7.1 [0.7] for ES/ML). The highest gloss was recorded for PM/ML (88.4 [2.3]) and lowest for FS/KD (30.3 [5.7]). All roughness parameters were significantly correlated with gloss (r= 0.871, 0.846, 0.713, and 0.707 for Sa, Sq, Sz, St, and gloss, respectively). It was concluded that the polishing procedure and the type of composite can have significant impacts on surface roughness and gloss of resin composites.

Monomer conversion in dual-cured core buildup materials.

OBJECTIVES: To examine the impact of self-curing (SC) and light-curing (LC) mechanisms on the curing efficiency of dual-cured buildup restorative materials (DCB). METHODS: The DCB materials tested were: Clearfil DC Core Automix (CD), Cosmecore DC (CM), LuxaCore DC (LX) and MultiCore DC Flow (MC). The SC material Clearfil Core New Bond (CN) and the LC material Clearfil Photo Core (CP) were used as controls. Specimens (Ø=4 mm, d=1 mm, n=4) of DCB materials prepared without light-exposure were tested after 10-, 20-, 30- and 60-minutes of storage in dark and dry conditions (37°C), whereas DCB specimens light-cured immediately after mixing (20 seconds, 850mW/cm2) served as a reference. The amount of remaining C=C bonds (%RDB) was measured on the bottom specimen surfaces using ATR-FTIR spectroscopy. One-way ANOVA and multiple comparison tests were used to evaluate the statistically significant differences (α=0.05). RESULTS: Polymerization mode had a strong effect on the polymerization efficacy of the DCB materials (p<0.0001). The control materials (CN, CP) performed better than the DCB materials (p<0.0001), except for LX in the LC mode. LX and MC showed better SC conversion during the initial 20-minute period. After 60 minutes, the %RDB values of CM were still above 60%, whereas in CD and LX, they reached the level of LC specimens. CONCLUSIONS: The LC initiation mechanism of the DCB materials that were tested resulted in better C=C conversion when compared to their native SC mechanisms. The SC and LC control materials performed better than the DCB materials, with the exception of LX in the LC mode.

A metallurgical characterization of ten endodontic Ni-Ti instruments: assessing the clinical relevance of shape memory and superelastic properties of Ni-Ti endodontic instruments.

AIM: To evaluate the elemental composition, microstructure and hardness of Ni-Ti endodontic instruments and to assess the relevance of shape memory and superelastic properties. METHODOLOGY: Ten brands of Ni-Ti endodontic instrument were evaluated (EndoSequence, Ergoflex K, FlexMaster, Hero 642, Hyflex X-File, K3 Endo, Liberator, NRT, Profile and ProTaper). After embedding in resin and metallographic preparation the elemental composition, structure and hardness were evaluated employing SEM/energy-dispersive X-ray spectrometer (EDX), X-ray diffraction (XRD) and microhardness measurements. The results of elemental composition and hardness were analysed statistically by one-way anova followed by SNK test (alpha : 0.05). The correlation between Ni content and microhardness was examined by the Pearson test. RESULTS: The instruments comprised of Ni (52.1-56.2%wt) and Ti (43.8 to 47.9%wt) and were classified in four different Ni content groups: ProTaper, Liberator, ProFile and K3 demonstrated higher Ni content than Hylfex X-File but lower than Hero 642, NRT and Ergoflex. EndoSequence and FlexMaster had the highest Ni content. XRD analysis revealed the presence of the austenitic structure in all instruments. Vickers hardness values ranged from 312 (K3) to 376 VHN (Endosequence). No correlation (r(2) = 0.026) was found between Ni content and hardness among the instruments tested. Microstructural and hardness data confirm that the Ni-Ti instruments were manufactured by cold worked Ni-Ti and do not posses shape memory or superelastic properties. CONCLUSIONS: The endodontic instruments tested were manufactured from cold worked Ni-Ti wires and thus have neither shape memory nor superelastic properties.

Bond strength and interfacial characterization of eight low fusing porcelains to cp Ti.

OBJECTIVES: The aim of this study was the interfacial characterization and the determination of bond strength of commercially available low fusing dental porcelain for Ti. METHODS: Eight materials were included in this study: Duceratin, Duceratin Plus, Initial Ti, Ti-22, TiKrom, TitanKeramik, Triceram (powder) and Triceram (paste). Eight ISO 9693 bond characterization specimens from each porcelain were prepared according to manufacturers' instructions. One specimen from each group was embedded in acrylic resin and after metallographic preparation was studied under an SEM. Interfacial characterization was carried out with Backscattered Electron Imaging and X-ray EDS analysis operating in line scan mode. Metal-ceramic specimens were tested in three point bending at a crosshead speed of 1.5mm/min according to ISO 9693 requirements. Additionally the fracture mode (adhesive-cohesive) of all specimens was evaluated employing SEM/EDS analysis. The results of bond strength and adhesive percentage were statistically analysed with one-way ANOVA and SNK multiple comparison test (a=0.05). Additionally the possible correlation between the bond strength and fracture mode was also tested using Pearson test. RESULTS: Interfacial characterization showed the mutual diffusion of Ti, Si, O and La along the Ti-ceramic interface. Only in Tricerap (paste) Zr showed an increased concentration at the interface. The results of bond strength classified the materials in the following decreasing order: TiKrom>Duceratin>InitialTi>Duceratin Plus>Ti-22>Triceram(paste)>Triceram(powder)>TitanKeramik. No correlation (r=0.132) between the fracture mode and bond strength of the selected material denoting that the fracture mode is irrelevant with the bond strength of Ti-ceramic joint and thus the former should not be applied for comparison among different materials. SIGNIFICANCE: According to the results of this study the materials tested provided great difference in interfacial analysis and bond strength with metallic Ti.

Surface characterization of zirconia dental implants.

OBJECTIVES: The aim of the study was to characterize the chemical composition, microstructure and roughness of two commercially available zirconia dental implants (WhiteSky and Zit-Z). METHODS: The chemical composition of the cervical collar and threaded root parts of the implants (n=2) were studied by XPS and HV-EDX. LV-SEM was used for morphological assessment, Raman microanalysis for microstructural characterization and optical profilometry for surface roughness measurements. XRD, HV-EDX and Raman microanalysis of bulk regions (longitudinal sections) were used as reference. RESULTS: XPS showed the presence of C, O, Zr and Y (collar) plus Al (root) at implant surfaces. More C (10-26at%) and a lower Al/Zr ratio were found in WhiteSky (1.05 vs 1.26 in Zit-Z). Zr, Y and Al were detected in single, fully oxidized states. The same elements, plus Hf, were identified by HV-EDX at bulk and surface regions, with a Al/Zr ratio higher in WhiteSky (0.17 vs 0.09 in Zit-Z). Na, K and Cl contaminants were traced at implant root parts by both methods. XRD analysis of cross-sectioned specimens revealed the presence of monoclinic and tetragonal zirconia along with cubic yttria phases. Raman microanalysis showed that the monoclinic zirconia volume fraction was higher at root surfaces than the collar. No monoclinic phase was found at bulk regions. Significantly higher Sa and Sq values were recorded in WhiteSky than Zit-Z, whereas Zit-Z showed higher Rt value. SIGNIFICANCE: The differences found between the implants in the extent of carbon contamination, residual alumina content, tetragonal to monoclinic ZrO(2) phase transformation and 3D-roughness parameters may contribute to a substantial differentiation in the cellular and tissue response.

Surface characterization and force relaxation of retrieved silk sutures.

AIM: To investigate the relaxation of as-received and retrieved silk sutures and characterize the compositional and structural changes occurred during service. MATERIALS AND METHODS: Silk sutures were tested in three conditions: (a) as-received, (b) retrieved from the oral cavity of patients, and (c) retrieved from extraoral sites of patients following 4 days. Specimens of the first group were fabricated by tying a knot on a plastic cable of 5 mm diameter. Specimens (n = 6) of groups (b) and (c) were placed in the appropriate surgical site and retrieved. Specimens were subjected to Fourier transform infrared spectroscopy for the characterization of molecular composition; low vacuum scanning electron microscopy (LV-SEM) to investigate the morphological variation; and energy dispersive X-ray microanalysis to assess the elemental composition of integuments formed onto the materials. To investigate the stress relaxation of elastics, a portable test assembly was developed to monitor the force exerted by a stretched suture for a period of 4 days. RESULTS: Retrieved specimens demonstrated absorption of proteinaceous matter comprising of amide I and II and alcohol, as well as precipitation of Mg, Si, Cl, and Ca for the extraorally aged specimens and additional K and P for the intraorally exposed sutures. Aged specimens showed swelling and disorganization and rupture of suture bundles. Stress relaxation data were indicative of no difference between the three groups, which relaxed at 30% of the initial value, whereas the curves showed similar slopes. SIGNIFICANCE: Significant relaxation was found for silk sutures, which seems to be independent of surgical site.

Characterization and in vitro estrogenicity of orthodontic adhesive particulates produced by simulated debonding.

OBJECTIVE: To investigate the structure and composition of ground orthodontic adhesive particulates produced under simulated clinical conditions and assess their estrogenic action in vitro. MATERIALS AND METHODS: A chemically cured and a light-cured adhesive were included in the study. Specimens were prepared by simulating bonding procedures, covering the bracket base surface with cellulose films to detach the full set material. The adhesives prepared under this method were grounded in glass chambers with an 8-fluted tungsten carbide on a high-speed handpiece; a new bur and different chamber was used for each adhesive sample and grindings were performed on different days to avoid contamination of the room. The adhesive particulates produced were subjected to FT-IR spectroscopy for the molecular characterization of particles; scanning electron microscopy for the morphologic condition and structure; and X-ray microanalysis for the elemental composition of the particles. Amounts of the ground adhesives were immersed in saline for 1 month at 37 degrees C. Eluents from solution of the two adhesives were added to media of an estrogen-responsive cell line derived from human breast adenocarcinoma (MCF-7), to assess the estrogenicity. Positive (estradiol and bisphenol-A) and negative (saline) controls were used; all assays were repeated four times and the results were averaged. Estrogenicity data were analyzed with one-way ANOVA and the Tukey test at the .05 level of significance. RESULTS: The study of the composition of particles revealed compounds related to monomers with no major differences noted. Significant structural alterations were observed between the materials studied, with the chemically cured adhesive having larger particles. The ground samples contained Si, Na and Al apparently deriving from fillers, whereas large Ba fillers were identified only in the chemically cured group, whereas no distinct molecular variation was noted between the set material and its corresponding particulate form. Both chemically cured and light-cured adhesives exhibited an estrogenic action through induction of the proliferation rate of MCF-7 cells (160% and 128%, respectively, compared to control). SIGNIFICANCE: Apart from the potentially hazardous action of adhesive particulate aerosol produced by grinding, composite resin particulates may act as endocrinological disruptors.

Effect of blue light on the proliferation of human gingival fibroblasts.

OBJECTIVES: Previous studies have reported that blue light, under conditions similar to those used for orthodontic bonding, influences several aspects of cellular physiology. The purpose of this study was to investigate the effect of the exposure to blue light curing sources, i.e. halogen, light emitting diode (LED) and plasma arc irradiation, on the proliferation of human gingival fibroblasts. METHODS: Primary cultures of human gingival fibroblasts were exposed to halogen, LED and plasma arc irradiation for 240, 180 and 120 s, respectively. The effect of blue light on DNA synthesis and cell proliferation was estimated by tritiated thymidine incorporation and direct cell counting, respectively. The possible involvement of an oxidative stress on the effect of blue light irradiation was studied by using N-acetyl-cysteine. Finally the formation of DNA double-strand breaks after irradiation was studied by immunofluorescence with an antibody against histone H2A.x phosphorylated in Ser139. RESULTS: Blue light showed no immediate effect on the regulation of DNA synthesis. However, exposure of cells to these light sources inhibits cell proliferation measured one week after irradiation. This phenomenon is not attributed to the formation of DNA double strand breaks and cannot be annulled by N-acetyl-cysteine. SIGNIFICANCE: The results presented here indicate a mild inhibition of gingival fibroblasts' proliferation after exposure to blue light and necessitate further study to clarify the exact mechanism underlying this effect.

Oestrogenicity of orthodontic adhesive resins.

The purpose of this study was to assess the oestrogenic action of a chemically cured, no-mix (Rely-a-Bond) and a light-cured (Reliance) orthodontic adhesive resin. The adhesives were bonded to 40 stainless steel maxillary incisor brackets (Diamond) divided into two equal groups, employing a method which simulated the clinical handling of materials. In total, three series of specimens were prepared for each adhesive-bracket group. All specimens were immersed in normal saline. Samples of eluent were removed from each group at 1 day and 1 week following incubation and tested for oestrogenicity by measuring their effect on the proliferation of the oestrogen-responsive MCF-7 breast cancer cells, while an oestrogen-insensitive cell line (MB-231 human breast adenocarcinoma) was used as a control. Three-way analysis of variance with adhesive, concentration of eluent, and immersion period were used as discriminating variables. No evidence was found of stimulation of proliferation of these cells, indicating the absence of any oestrogenicity of orthodontic adhesive eluents.

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.

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.

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.

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.