Francesca Antoniolli

Contraction stress of low-shrinkage composite materials assessed with different testing systems

OBJECTIVES The contraction stress of a silorane-based material and a new low-shrinkage nanohybrid composite were compared to three conventional dimethacrylate-based resin composites using two different measuring systems. It was hypothesized that the silorane-based material and the low-shrinkage nanohybrid composite would exhibit lower contraction stress than dimethacrylate-based composites irrespective of measuring system. METHODS The materials tested were Filtek Silorane LS (3M ESPE), Venus Diamond (Heraeus Kulzer), Tetric EvoCeram (Ivoclar Vivadent), Quixfil (Dentsply DeTrey), and Filtek Z250 (3M ESPE). Shrinkage stress was assessed using a stress-strain analyzer consisting of two opposing attachments, one connected to a load sensor and the other fixed to the device, or a system fixed to a universal testing machine with an extensometer as a feedback system. All specimens were light-cured with 20 J/cm(2); the contraction force (N) generated during polymerization was continuously recorded for 300 s. Contraction stress (MPa) was calculated at both 40 s and 300 s. Data were statistically analyzed by three-way ANOVA and Tukeys post hoc test (alpha=0.05). RESULTS Venus Diamond exhibited the lowest stress under both experimental conditions. Stress values scored as follows: Venus Diamond<Tetric EvoCeram<Filtek Silorane LS<Quixfil<Filtek Z250 (p<0.05). Stress values measured with the stress-strain analyzer were significantly lower than those measured with the universal testing machine with feedback. SIGNIFICANCE The hypothesis was partially rejected because only Venus Diamond exhibited the lowest stress values among the tested materials. Contraction stress was higher for all composites when measured in a test system with a feedback. This study confirms that simply reducing the shrinkage does not ensure reduced stress development in composites.

Degree of conversion of Filtek Silorane Adhesive System and Clearfil SE Bond within the hybrid and adhesive layer: An in situ Raman analysis

OBJECTIVES To examine the degree of conversion (DC) of the adhesive interfaces created by Filtek Silorane Adhesive and Clearfil SE Bond using micro-Raman spectroscopy. METHODS The adhesives were applied on human dentin in accordance with manufacturers instructions. Specimens were cut to expose the bonded interfaces to the micro-Raman beam (Ranishaw InVia; laser wl 785 nm). Raman spectra were collected along the dentin/self-etching primer/adhesive interface at 1 microm intervals. The relative intensities of bands associated with mineral (P-O functional group at 960 cm(-1)) and adhesive (C-C-O group at 605 cm(-1)) components within the bonded interface were used to detect monomer penetration into the dentin matrix and to calculate the degree of conversion (C=C at 1640 cm(-1) as reaction peak, C-C-O at 605 cm(-1) as reference peak). Data were statistically analyzed with two-way ANOVA. RESULTS DC of Filtek Silorane Adhesive was 69+/-7% in the adhesive layer, increasing (p<0.05) to 93+/-5% in the primer and 92+/-9% in the hybrid layer. Clearfil SE Bond showed a DC of 83+/-3% in the hybrid and 85+/-3% in the adhesive layer. Thus, Filtek Silorane Adhesive showed a higher DC than Clearfil SE Bond in the hybrid layer (p<0.05), but a lower DC in the adhesive (p<0.05). SIGNIFICANCE As high DC is a fundamental pre-requisite for the stability of the bond over time, this study supports the hypothesis that optimal stability of Filtek Silorane Adhesive can be obtained. However, further research is needed to investigate the mechanical properties of the hybrid layer created by Filtek Silorane Adhesive and its long-term stability.

Effect of Two In-office Whitening Agents on the Enamel Surface In Vivo: A Morphological and Non-contact Profilometric Study

This study evaluated the morphological effects produced in vivo by two in-office bleaching agents on enamel surface roughness using a noncontact profilometric analysis of epoxy replicas. The null hypothesis tested was that there would be no difference in the micromorphology of the enamel surface during or after bleaching with two different bleaching agents. Eighteen subjects were selected and randomly assigned to two treatment groups (n=9). The tooth whitening materials tested were 38% hydrogen peroxide (HP) (Opalescence Xtra Boost) and 35% carbamide peroxide (CP) (Rembrandt Quik Start). The bleaching agents were applied in accordance with manufacturer protocols. The treatments were repeated four times at one-week intervals. High precision impressions of the upper right incisor were taken at baseline as the control (CTRL) and after each bleaching treatment (T0: first application, T1: second application at one week, T2: third application at two weeks and T3: fourth application at three weeks). Epoxy resin replicas were poured from impressions, and the surface roughness was analyzed by means of a non-contact profilometer (Talysurf CLI 1000). Epoxy replicas were then observed using SEM. All data were statistically analyzed using ANOVA and differences were determined with a t-test. No significant differences in surface roughness were found on enamel replicas using either 38% hydrogen peroxide or 35% carbamide peroxide in vivo. This in vivo study supports the null hypothesis that two in-office bleaching agents, with either a high concentration of hydrogen or carbamide peroxide, do not alter enamel surface roughness, even after multiple applications.

Influence of different initiators on the degree of conversion of experimental adhesive blends in relation to their hydrophilicity and solvent content

OBJECTIVES The aim of this study was to compare the curing reaction of five experimental adhesive blends containing different photo-initiating systems. The hypothesis tested was that degree of conversion (DC) of resin blends is affected by resin type, solvent content and photo-initiating system. METHODS The experimental methacrylate resin blends were ranked from hydrophobic (R2) to hydrophilic (R3 and R4) and tested as neat, or solvated with 10% or 20% ethanol, or 10% ethanol and 10% water. Three different photo-initiators were used: IS-1=0.25% CQ (camphorquinone)+1% EDMAB (ethyl 4-dimethylaminobenzoate); IS-2=1.25% TPO (diphenyl(2,4,6-trimethylbenzoyl)-phosphine oxide); IS-3=0.25% CQ+0.50% EDMAB+0.50% TPO. DC of resin blends was measured with a differential scanning calorimeter. Data were analyzed with a three-way ANOVA. RESULTS Neat resin type influenced DC, as R4 showed the highest values compared to R2 and R3 (p<0.05). Solvent had a significant effect on DC (p<0.05): dilution of resin blends with 10% or 20% ethanol or 10% ethanol+10% water increased the DC of all resins, except for R4. Initiators influenced the polymerization since neat resins and mixtures solvated with 10% or 20% ethanol showed their highest DC values when polymerized with IS-1 or IS-3 (p>0.05), while IS-2 or IS-3 increased the DC values of resins diluted with 10% ethanol and 10% water (p<0.05). CONCLUSIONS Water-compatible photo-initiators such as TPO should be included in the hydrophilic solvated adhesive formulation to ensure an appropriate DC of the adhesive layer.

Degree of conversion of resin blends in relation to ethanol content and hydrophilicity

OBJECTIVES To evaluate the degree of conversion of five experimental adhesive systems in relation to their hydrophilicity. The resin blends ranged from hydrophobic to hydrophilic and were tested as neat bonding agents, or solvated with increasing percentages of ethanol. The hypothesis tested was that extent of polymerization of resin blends is affected by resin hydrophilicity, solvent concentrations or time of polymerization. METHODS Five light-curing versions of neat experimental resin blends were submitted to investigation: (1) 70% E-BisADM, 28.75% TEGDMA; (2) 70% BisGMA, 28.7% TEGDMA; (3) 70% BisGMA, 28.7% HEMA; (4) 40% BisGMA, 30% TCDM, and 28.75% TEGDMA; (5) 40% BisGMA, 30% BisMP, and 28.75% HEMA. All blends included 1% EDMAB and 0.25% CQ. Ethanol in different weight percentages (A: 0%, B: 30%, C: 50%, D: 70% and E: 90%) was added to these resin blends simulating different formulation of adhesives. A differential scanning calorimeter was used to measure the degree of conversion of resin blends as a function of resin hydrophilicity, solvent concentration and time of curing. Data were analyzed with three-way ANOVA and Tukeys post hoc test. RESULTS Exotherms showed that degree of conversion was influenced by the hydrophilicity of the blends resin (p<.05), percentage of ethanol dilution (p<.05) and time of curing (p<.05). 30% ethanol dilution increased degree of conversion compared to neat compounds irrespective to resin type and curing time, showing the highest degree of conversion values of the study design. SIGNIFICANCE This study supports the hypothesis that high ethanol percentages (>50mass%) may compromise extent of polymerization kinetics of dental adhesives.

Flowability of composites is no guarantee for contraction stress reduction

OBJECTIVES The purpose of this study was to measure the contraction stress development of three flowable resin-composite materials (Grandio Flow, VOCO GmbH, Cuxhaven, Germany; Tetric Flow, Ivoclar Vivadent, Schaan, Liechtenstein; Filtek Supreme XT Flowable Restorative, 3M ESPE, ST. Paul, MN, USA) and an universal micro-hybrid composite resin (Filtek Z250, 3M ESPE, St. Paul, MN, USA) during photopolymerization with a halogen curing light, using a novel stress-measuring gauge. METHODS Curing shrinkage stress was measured using a stress-analyzer. Composites were polymerized with a halogen curing unit (VIP, Bisco Inc., Schaumburg, IL, USA) for 40s. The contraction force (N) generated during polymerization was continuously recorded for 180s after photo-initiation. Contraction stress (MPa) was calculated at 20s, 40s, 60s, 120s and 180s. Data were statistically analyzed. RESULTS Filtek Supreme XT Flowable Restorative exhibited the highest stress values compared to other materials (p<0.05), while the lowest values were recorded with Tetric Flow (p<0.05). Tetric Flow was also the only flowable composite showing stress values lower than the conventional composite Filtek Z250 (p<0.05). SIGNIFICANCE Flowable composites investigated with this experimental setup showed shrinkage stress comparable to conventional resin restorative materials, thus supporting the hypothesis that the use of flowable materials do not lead to marked stress reduction and the risk of debonding at the adhesive interface as a result of polymerization contraction is similar for both type of materials.

Influence of chlorhexidine on the degree of conversion and E-modulus of experimental adhesive blends

OBJECTIVES This study examined the effect of chlorhexidine (CHX) content on degree of conversion (DC) and E-modulus of experimental adhesive blends. The hypothesis tested was that increasing concentrations of CHX result in decreased DC and E-modulus in relation to adhesive hydrophilicity. METHODS Experimental adhesive blends with increasing hydrophilicity R2 (70% bisGMA, 28.75% TEGDMA); R3 (70% BisGMA, 28.75% HEMA); R4 (40% BisGMA, 30% TCDM, 28.75% TEGDMA); R5 (40% BisGMA, 30% BisMP, 28.75% HEMA) and different CHX concentrations (1 and 5%) were analyzed. 5% CHX could not be dissolved in R2. A differential scanning calorimeter was used to measure the DC of resin blends. Photopolymerized disks of the experimental comonomer mixtures (n=10/gp) were used to measure the E-modulus of each specimen using a biaxial flexure test. Data were analyzed with two-way ANOVA (resin type and CHX concentration) and Tukeys post hoc test. RESULTS The addition of 1% CHX did not significantly alter the DC of R2 and R3. Significant decrease in R3 DC values was observed when 5% CHX was added. CHX significantly increased the DC of R4 and R5. 1% CHX reduced the E-modulus of all resins (p<0.05) except for R2, in which the E-modulus was significantly increased (p<0.05). 5% CHX significantly reduced the E-modulus of resins R3 to R5 (p<0.05). SIGNIFICANCE In conclusion, increasing concentrations of CHX dissolved in resin blends had little adverse effect on DC but decreased the E-modulus 27-48% compared to controls. Solvation of CHX in ethanol prior to incorporation of CHX into R2 may permit higher CHX concentrations without lower polymer stiffness.

Influence of Luting Material Filler Content on Post Cementation

Luting of fiber posts to intra-radicular dentin represents the worst-case scenario in terms of control of polymerization shrinkage. This study tested the hypothesis that filler content of resin cements does not influence luting of fiber posts to intra-radicular dentin, by assaying polymerization stress, push-out bond strength, and nanoleakage expression. The polymerization stress of experimental cements containing 10%, 30%, 50%, or 70% in filler content was investigated. Post spaces were prepared in endodontically treated teeth, and fiber posts were cemented with the experimental cements. A push-out test was performed, and interfacial nanoleakage expression was analyzed. Results showed that luting cements with higher filler content were related to increased polymerization stress (p < 0.05), decreased push-out bond strength (p < 0.05), and increased interfacial nanoleakage expression (p < 0.05). Conversely, lower-stress luting materials increased bonding of fiber posts to intra-radicular dentin. Further in vivo studies are needed to investigate the long-term clinical performance of these materials.

Comparative experimental evaluation of guidewire use in urology.

OBJECTIVES To evaluate the characteristics and mechanical properties of five different guidewires principally used in urology to provide a guide to the best choice in every situation. This objective was achieved by performing mechanical tests on each guidewire and on the same guidewire in relationship to a real human ureter. Finally, the mechanical properties of a real human ureter were evaluated experimentally. METHODS Five different guidewires with a 0.035-in. external diameter were studied to determine their mechanical properties of interest: tip buckling, shaft permanent deformation, guide friction on the human ureter, and the force at which the tip perforated a real human ureter. RESULTS Nitinol guidewires with hydrophilic coating had the least dangerous tip in the tip buckling and tip piercing force tests and the lowest friction values on the friction guide test. The shaft of the polytetrafluoroethylene-coated guidewires was stiffer on the bending resistance and plastic deformation tests. CONCLUSIONS The ideal endourologic guidewire should be sufficiently flexible and lubricated to negotiate a tortuous ureter and pass possible obstructions. However, high strength against bending is also required when we need to pass a stent or catheter over a guidewire.

Combined aging effects of strain and thermocycling on unload deflection modes of nickel-titanium closed-coil springs: An in-vitro comparative study

INTRODUCTION There are no reports on the aging effects of thermocycling of nickel-titanium (NiTi) based coil springs, and few studies have investigated their superelasticity phases in full. In this study, we compared the mechanical properties of NiTi-based closed-coil springs after the combined aging effects of prolonged strain and thermocycling, as a reflection of the clinical situation. METHODS Ninety NiTi-based closed-coil springs were used, 30 each of the following types: (1) Nitinol (3M Unitek, Monrovia, Calif), (2) Ni-Ti (Ormco, Glendora, Calif), and (3) RMO (Rocky Mountain Orthodontics, Denver, Colo); all had similar dimensions (length, 12 mm). In each sample group, 2 equal subgroups of 15 coil springs were extended by either 50% (to 18 mm) or 150% (to 30 mm), immersed in artificial saliva, and kept at 37°C for 45 days. All springs underwent sessions of 1000 thermocycles (1 minute long) from 5°C to 55°C on days 22 and 45. Unload deflection curves from both the 50% and 150% extensions (according to their strain subgroups) were recorded by using a universal testing machine before the strain (baseline) and at both 22 and 45 days, immediately after thermocycling. RESULTS At baseline, the loads exerted by the NiTi-based coil springs varied from 99.8 to 245.1 gf for the RMO (50% strain) and Ni-Ti (150% strain) groups. Statistically significant, although small, differences were seen at each time point in both the 50% and 150% strain subgroups; generally, the highest and lowest values were recorded in the Ni-Ti and Nitinol groups (all, P <0.001). Only the Nitinol coil-spring group showed an acceptable superelasticity phase. The strain and thermocycling did not dramatically change the deactivation forces of any coil springs. CONCLUSIONS NiTi-based closed-coil springs might not have a superelasticity phase, and prolonged strain and thermocycling do not produce clinically relevant alterations in their deactivation forces.