Comparative evaluation of mechanical characteristics of nanofiller containing resin composites.

PURPOSE: To determine basic mechanical characteristics of six commercially available nanofiller containing resin composites compared to a microhybrid and a microfilled reference material. The tested hypothesis was that there are no differences in mechanical properties between the materials. METHODS: Durafill VS (DUR) and Filtek Z250 (Z250) were used as microfilled and microhybrid references. The nanofiller containing products were: Filtek Supreme XT (FIL), Grandio (GRA), Kalore (KAL), MI Flow (MIF), Tetric EvoCeram (TET), and Venus Diamond (VED). The following material characteristics were determined after 24 hours water storage (n = 6): Flexural strength and modulus (FM), yield stress (0.02%), tensile strength and modulus (TM), diametral tensile strength, Knoop hardness (KHN), and fracture toughness (KIC). RESULTS: The microfilled composite DUR consistently showed the lowest values for each property investigated. The group of nanofiller containing products could be subdivided into two groups: the nanohybrid products GRA and VED and the nanofilled FIL with higher values, on the one hand, and the flowable MIF, and the prepolymer containing composites KAL and TET, on the other. The mechanical performance of the microhybrid reference material Z250 was overall slightly better or in line with the nanohybrid and nanofilled materials. Stringent linear relationships were found between KHN and the moduli FM and TM, respectively (r > 0.95). Linear relations between the other materialvalues investigated were moderate to high.

In vitro dentin permeability after application of Gluma® desensitizer as aqueous solution or aqueous fumed silica dispersion.

OBJECTIVES: To assess and to compare the effects of Gluma® Desensitizer (GDL) with an experimental glutaraldehyde and HEMA containing fumed silica dispersion (GDG) on dentin permeability using a chemiluminous tracer penetration test. MATERIAL AND METHODS: Twenty disc-shaped dentin specimens were dissected from extracted human third molars. The dentin specimens were mounted in a split chamber device for determination of permeability under liquid pressure using a photochemical method. Ten specimens were randomly selected and allocated to the evaluation groups Gluma® Desensitizer as aqueous solution and glutaraldehyde/HEMA as fumed silica dispersion, respectively. Dentin disc permeability was determined at two pressure levels after removal of smear with EDTA, after albumin soaking, and after application of the desensitizing agents. Two desensitizer-treated and rinsed specimens of each group were examined by scanning electron microscopy (SEM) for surface remnants. RESULTS: Comparatively large standard deviations of the mean EDTA reference and albumin soaked samples permeability values reflected the differences of the dentin substrates. The mean chemiluminescence values of specimen treated with GDL and GDG, respectively, were significantly reduced after topical application of the desensitizing agents on albumin-soaked dentin. The effects of GDL and GDG on permeability were not significantly different. Treated specimens showed no surface remnants after rinsing. CONCLUSIONS: The experimental desensitizer gel formulation reduced dentin permeability as effectively as the original Gluma® Desensitizer solution.

Recommendation of lamivudine-to-entecavir switching treatment in chronic hepatitis B responders: Randomized controlled trial.

AIM: In the 2007-2008 guidelines of the study group (Ministry of Health, Labor and Welfare of Japan), lamivudine (LAM)-continuous treatment was recommended in patients treated with LAM for more than 3 years who maintained hepatitis B virus (HBV) DNA less than 2.6 log copies/mL, because in these patients LAM resistance might exist and switching treatment to entecavir (ETV) might cause ETV resistance. However, there was no evidence on whether switching treatment to ETV- or LAM-continuous treatment was better in those patients. In the present study, we performed a randomized controlled trial of LAM-to-ETV switching treatment. METHODS: Twenty-seven patients treated with LAM for more than 3 years whose HBV DNA levels were less than 2.6 log copies/mL were enrolled and randomly divided into two groups, LAM-continued group or switching to ETV group. Then, we examined incidence of virological breakthrough (VBT) and breakthrough hepatitis (BTH) in each group. RESULTS: There was no BTH in any of the patients. VBT was observed in six patients of the LAM group (6/15, 40%), and no patient of the ETV group (0/11, 0%) (P = 0.02). The differences of the proportion of cumulated VBT using a log-rank test with Kaplan-Meier analysis were significant between the LAM and ETV groups (P = 0.025). CONCLUSION: In patients treated with LAM for more than 3 years maintaining HBV DNA less than 2.6 log copies/mL, switching treatment to ETV is recommended at least during the 2 years' follow-up period.

In vitro dentin permeability after application of Gluma® desensitizer as aqueous solution or aqueous fumed silica dispersion

OBJECTIVES: To assess and to compare the effects of Gluma® Desensitizer (GDL) with an experimental glutaraldehyde and HEMA containing fumed silica dispersion (GDG) on dentin permeability using a chemiluminous tracer penetration test. MATERIAL AND METHODS: Twenty disc-shaped dentin specimens were dissected from extracted human third molars. The dentin specimens were mounted in a split chamber device for determination of permeability under liquid pressure using a photochemical method. Ten specimens were randomly selected and allocated to the evaluation groups Gluma® Desensitizer as aqueous solution and glutaraldehyde/HEMA as fumed silica dispersion, respectively. Dentin disc permeability was determined at two pressure levels after removal of smear with EDTA, after albumin soaking, and after application of the desensitizing agents. Two desensitizer-treated and rinsed specimens of each group were examined by scanning electron microscopy (SEM) for surface remnants. RESULTS: Comparatively large standard deviations of the mean EDTA reference and albumin soaked samples permeability values refected the differences of the dentin substrates. The mean chemiluminescence values of specimen treated with GDL and GDG, respectively, were signifcantly reduced after topical application of the desensitizing agents on albumin-soaked dentin. The effects of GDL and GDG on permeability were not signifcantly different. Treated specimens showed no surface remnants after rinsing. CONCLUSIONS: The experimental desensitizer gel formulation reduced dentin permeability as effectively as the original Gluma® Desensitizer solution.

Factors influencing marginal cavity adaptation of nanofiller containing resin composite restorations.

OBJECTIVES: The aim of this study was to investigate the effects of polymerization contraction, shrinkage stress and Young's modulus of nanofiller containing resin composites on early marginal adaptation of restorations in cavities. METHODS: Six nanofiller containing and two reference resin composites were studied. Marginal gap widths of restorations in cylindrical 4.2mm wide and 1.5mm deep dentin cavities, non-bonded or bonded with a self-etch adhesive, and in Teflon cavities of same dimensions were determined 15 min after irradiation (n=8). Polymerization shrinkage strains were measured using the bonded-disk (n=8) and a strain gage method (n=8). For determination of contraction stress the composites (n=10) were bonded to and cured in Araldit molds using a photoelastic method. Flexural moduli of the restoratives were studied according to ISO specification 4049 (n=5). Statistical analysis was performed with one- and two-way ANOVA, Kruskal-Wallis ANOVA test and post hoc tests (p<0.05). RESULTS: Only two nanofiller composites (Kalore, GC, Japan) and Venus Diamond (Heraeus Kulzer, Germany) showed consistently gap-free margins in bonded dentin cavities. The mean gap widths in non-bonded and in Teflon cavities were 6.1-12.8 and 14.1-25.5 µm, and linearly correlated (r(2)<0.85). Significant linear relationships were observed between strain, stress and marginal gap widths in non-bonded and Teflon cavities (p<0.01). Flexural moduli (15 min) were between 1.66 and 8.63 GPa. SIGNIFICANCE: Marginal cavity adaptation of restorations in bonded dentin cavities reflects complex interactions between adhesive bonding on the one hand, and polymerization contraction strain, stress and elastic modulus, on the other.

Surface texture and roughness of polished nanofill and nanohybrid resin composites.

Nanofiller-containing resin composites have gained appreciable market share in dentistry due to their claims of high mechanical strength and low polymerization contraction. In this study, the polishability of one nanofill (Filtek Supreme XT/FIL) and three nanohybrid materials (Grandio/GRA, Tetric EvoCeram/TET, Venus Diamond/VED) was investigated using surface profilometry and SEM. After the specimens were cured under a Mylar strip or pre-ground with 600-grit SiC paper, three polishing systems were applied and their polishing effects compared: diamond polishing points, a diamond paste, and urethane-backed aluminum oxide disks. Except for the profilometry results obtained by glass filler-containing GRA and VED with one polishing system that comprised the consecutive application of diamond particles and a diamond polishing paste, the final roughness (Ra) of all other specimens were lower than the clinically acceptable 0.2 microm threshold. The surface textures of the polished nanofill FIL and nanohybrid TET were uniformly smooth, whereas relief polishing effects and filler extrusion of varying extents were seen on the nanohybrid composites GRA and VED.

Sulcus depth reproduction with polyvinyl siloxane impression material: effects of hydrophilicity and impression temperature.

OBJECTIVE: To determine the sulcus penetration ability of hydrophilic and hydrophobic polyvinyl siloxane (PVS) impression materials by impression technique, temperature, and sulcus width. METHOD AND MATERIALS: Hydrophilic Flexitime (FLE; Heraeus Kulzer) and its hydrophobic counterpart (EXP) without surfactant were investigated, using light (L), monophase (M), and heavy (H) consistencies. A truncated steel cone surrounded by a 2-mm-deep and 50-, 100-, or 200-microm-wide sulcus, simulating the gingival tissue with agar, served as the test model. Impressions were made with single-mix (L or M) and double-mix (LM or LH) techniques at 23 degrees C and 37 degrees C, respectively. The reproduced sulcus heights were measured with a 3D laser scanner. Data were analyzed by ANOVA and Tukey HSD (P < .05). RESULTS: Irrespective of sulcus widths and temperature FLE-L penetrated deepest (> 1.9 mm); FLE-M, -LM, and-LH reproductions were shorter with narrow sulci. Reproductions of 50- and 100-microm sulci with EXP-L were shallower than with FLE-L. The shortest reproduction was, however, greater than 1.6 mm. CONCLUSIONS: In spite of some significant differences found in sulcus-reproducing ability with hydrophilic and hydrophobic impression materials applied at different impression-making temperatures and with different techniques, the practical relevance is limited.

Resistance of nanofill and nanohybrid resin composites to toothbrush abrasion with calcium carbonate slurry.

The aim of this study was to investigate the wear of four nanofilled resin composites using simulated toothbrushing for 50,000 cycles with calcium carbonate slurry. The depth of abrasion and roughness (Ra) were measured after each 10,000 brushing cycle. The surface texture of the worn samples was examined by SEM.The wear depths of the nanofill Filtek Supreme XT (FIL), the nanohybrides Grandio (GRA), Tetric EvoCeram (TET), and Venus Diamond (VED) increased linearly with numbers of brushing cycles or approximately 80, 12, 600, and 60 mum, respectively after 50,000 strokes. Surface roughness showed virtually no change between 10,000 and 50,000 brushing cycles; the ranking order was TET < FIL < GRA < VED. FIL showed rather uniform abrasion with nanoclusters protruding from the surface. TET was very smoothly abraded without signs of debonding of the prepolymerized particles, whereas GRA and VED showed pronounced wear of the matrix polymer surrounding larger glass filler particles.

Effects of opacity and oxygen inhibition of coating resin composites on bond strength to enamel.

The purpose of this in vitro investigation was to study the effects on bond strength to primed human enamel stemming from opacity and polymerization inhibition by oxygen due to two coating resins. The coating resins and primers used were White Coat and an experimental material, SIR. The bond strengths on fine-ground enamel were evaluated for three shades of each of these coating resins after 24-hour storage in water. In addition, their degrees of opacity and oxygen inhibition depths were measured. The mild self-etch primer solutions produced very shallow but distinct etching patterns for micromechanical retention of the coating resin. Significant linear relationships between bond strength on the one hand and opacity and oxygen inhibition depth on the other were found for the three shades of each coating resin. Generally, the bond strength mediated on enamel is sufficiently high when these resins are combined with their proprietary adhesives. Therefore, the decrease in bond strength with increasing opacity of the coating resin shades has to be taken into account during application and light-curing.

Effect of desensitizing agents on dentin permeability.

PURPOSE: To investigate the in vitro efficacy of two dentin desensitizing products at reducing liquid permeability through human dentin discs. The tested hypothesis was that the products, in spite of different chemical mechanisms were not different at reducing or eliminating flow through dentin discs. METHODS: Dentin slices (1 mm thick) were prepared from 16 extracted human third molars and their permeability was indirectly recorded in a split chamber model, using a chemiluminescence technique, after EDTA treatment (control), after soaking with albumin, and after desensitizer application. Two products were studied: MS Coat, a self-curing resin-containing oxalate product, and Gluma Desensitizer, a glutaraldehyde/HEMA-based agent without initiator. The dentin slices were mounted between an upper chamber, filled with an aqueous solution of 1% potassium ferricyanide and 0.3% hydrogen peroxide, and a lower chamber filled with 1% sodium hydroxide solution and 0.02% luminol. The upper solution was pressurized, and upon contact with the luminol solution a photochemical signal was generated and recorded as a measure of permeability throughout two consecutive pressurizing cycles at 2.5 and 13 kPa (26 and 133 cm H2O), respectively. RESULTS: The permeability of the control and albumin-soaked samples was similarly high. After application of the desensitizing agents, dentin permeability was reduced to virtually zero at both pressure levels (P < 0.001).

Discoloration of coating resins exposed to staining solutions in vitro.

The purpose of this in vitro investigation was to study the effects of coffee and tea immersion on surface discoloration of one commercial temporary resin coating material, White Coat (WHC; Kuraray Medical Inc., Tokyo, Japan), and an experimental one, SI-R20209 (SIR; Shofu Inc., Kyoto, Japan). Disk-shaped specimens were prepared, their colors were determined at baseline, and after immersion in water (control), tea and coffee solutions for 24, 48, and 72 hours. Very little discoloration was found with the water-stored specimens. Staining response was most pronounced after coffee immersion for White Coat and after tea immersion for the experimental material, exceeding the clinically acceptable discoloration threshold value of deltaE=3.3. However, most of the resin shades tested are likely to be sufficiently safe against heavy discoloration when used for short-term restoration only.

Rationale behind the design and comparative evaluation of an all-in-one self-etch model adhesive.

OBJECTIVE: To investigate and compare bonding and dentin sealing efficacy of a marketed all-in-one and an experimental model adhesive with minimum effective amounts of acidic monomer and water. MATERIALS AND METHODS: Composition of model adhesive (NAD) in mass%: UDMA (45), 4-META (20), H2O (7.5), and acetone (27.5). For characterization of a reasonable NAD application procedure shear bond strengths (SBS, n=8) were determined on human enamel and dentin. Clearfil S3 Bond (TSB; Kuraray) served as reference. SBSs were evaluated after 10 min, 1 and 7 days, and 1 month, marginal adaptation (n=8) was assessed in cylindrical butt-joint dentin cavities. Diffusive and convective water fluxes through 1mm thick adhesive-coated dentin disks (n=6) were qualitatively and quantitatively analyzed. RESULTS: SBSs proved that application of NAD in one coat with 20s agitated dwell time was > or =20 MPa, enamel SBSs (24h) were 25 MPa, p>0.05. Dentin SBSs for TSB and NAD were not different (p>0.05) at the four stages (means: 18.9, 23.5, 25.4, and 23.6 MPa). Five and seven of the eight bonded restorations with TSB and NAD were gap-free (p>0.05). Dentin disks treated with EDTA from both sides or one side only were highly permeable for liquid, whereas adhesive-coated dentin disks showed no permeability at 0 and 2.5 kPa water pressure. CONCLUSIONS: Within the limitations of this study the model adhesive tested represents a promising basic composition for all-in-one adhesives, eliminating common problems encountered with single step adhesives such as phase separation and permeability.

Sulcus reproduction with elastomeric impression materials: a new in vitro testing method.

OBJECTIVES: Aim of this study was to investigate the depth reproduction of differently wide sulci with elastomeric impression materials by single- and double-mix techniques using a tooth and sulcus model, simulating clinical conditions. METHODS: Impressions with one vinyl polysiloxane (VPS; FLE), two polyethers (PE; IMP and P2), and one hybrid VPS/PE elastomer (FUS) were taken from a truncated steel cone with a circumferential 2 mm deep sulcus, 50, 100 or 200 microm wide. The "root surface" was in steel and the "periodontal tissue" in reversible hydrocolloid. Single-mix impressions were taken with light-body (L) or monophase (M) pastes, double-mix impressions with L as syringe and M or heavy-body (H) as tray materials (n=8). Sulcus reproduction was determined by 3D laser topography of impressions at eight locations, 45 degrees apart. Statistical data analysis by ANOVA and multiple comparison tests (p<0.05). RESULTS: For 200 microm wide sulci, significant differences were found between impression materials only: FLE=IMP>FUS=P2. At 50 and 100 microm width, significant differences were found between materials (IMP>FUS=FLE>P2) and techniques (L+H=L+M>M>L). SIGNIFICANCE: The sulcus model is considered useful for screening evaluation of elastomeric impression materials ability to reproduce narrow sulci. All tested materials and techniques reproduced 200 microm wide sulci to almost nominal depth. Irrespective of the impression technique used, IMP showed the best penetration ability in 50 and 100 microm sulci. Double-mix techniques are more suitable to reproduce narrow sulci than single-mix techniques.

All-in-one self-etch model adhesives: HEMA-free and without phase separation.

OBJECTIVE: Aim of this study was to design HEMA-free all-in-one self-etch model adhesives without phase separation, and to investigate their efficiency on extracted human teeth. MATERIALS AND METHODS: Compositions of adhesives in mass% (1): UDMA (25), 4-META (20), H(2)O (0, 1, 2, 5, 10, 20, 35, and 45), balance of acetone or ethanol. (2): UDMA (35), 4-META or 4-MET (28), H(2)O (0, 2, 4, 5, 6, and 8), balance of acetone. Phase separation was evaluated on samples exposed to ambient atmosphere. Conventional shear bond strengths (SBS, n=8) were determined on human enamel and dentin. Marginal adaptation (MGW, n=8) was assessed in cylindrical butt-joint dentin cavities. RESULTS: Solutions (1) and (2) with 5 and 8% or less water content, respectively, showed no phase separation. SBSs on enamel were not different within the acetone- or ethanol-group and between the adhesive groups (1). Water content of adhesives (2) was a significant determinant of enamel SBSs, groups with 4-META or 4-MET were not different (p>0.05). Dentin SBSs with adhesives (1) were not different (p>0.05) within solvent groups, yet higher for acetone-dissolved adhesives (p<0.05). Dentin SBSs with adhesives (2) were different by water content and functional monomer (p<0.05). MGW for solutions (1) were smaller with acetone-dissolved than with ethanol-dissolved adhesives (p<0.001). Acetone solutions between 2 and 45% water content produced almost perfect marginal adaptation. Marginal adaptation of adhesives (2) was almost perfect at 5 through 8% water content. CONCLUSIONS: Simplified HEMA-free self-etch adhesives without phase separation were prepared without compromises on bonding efficiency to enamel and dentin.

Interactions of self-etch adhesives with resin composites.

OBJECTIVE: Aim of this in vitro study was to investigate the correlation of shear bond strength and marginal cavity adaptation, together with polymerization shrinkage and contraction stress, using the combination of four self-etch adhesives and three resin composites. MATERIALS AND METHODS: Interactions were studied between one two-step and three one-step adhesives, and the hybrid-type resin composites, Beautifil (BEU, Shofu) and Venus (VEN, Heraeus), and an experimental nano-hybrid resin composite NEUN (NEU, Heraeus). For all 12 combinations shear bond strengths (SBS) were determined on human dentin. Marginal adaptation (MGW) was assessed in cylindrical butt-joint dentin cavities. Further, polymerization contraction and contraction stress of the resin restoratives were measured. RESULTS: Significant determinants of SBSs on dentin were time of testing (10min or 24h) and adhesives (p<0.001). Marginal adaptation was best for NEU, followed by VEN and BEU. Only the resin composite used was a highly significant determinant of cavity adaptation. Polymerization shrinkage after 5min was 2.58, 2.74, and 1.53% for BEU, VEN, and NEU, respectively. Polymerization contraction stresses were largest for BEU, less for VEN, and smallest for NEU (p<0.05). CONCLUSIONS: No correlation was found between bond strength and marginal cavity adaptation. In contrast, reduced shrinkage and low polymerization contraction stress of resin composites were identified as important determinants of marginal cavity adaptation.

The role of oxygen inhibition of a self-etch adhesive on self-cure resin composite bonding.

PURPOSE: To evaluate the bond strengths on enamel and dentin with a self-etch adhesive (iBond), with or without oxygen-inhibited surface layer, or covered with intermediate self-curing resin, in combination with chemical-cured composite (Core Paste). METHODS: Bond strengths on human enamel and dentin (n = 8) were determined according to the following procedures: 1. Adhesive cured under ambient air. 2. Inhibited surface wiped with ethanol. 3. Adhesive cured under nitrogen. 4. Adhesive covered with glycerol during activation. 5. Adhesive coated with glycerol for 1 minute after activation. 6. As 5, but covered for 5 minutes. 7. Cured adhesive coated with intermediate self-curing resin. 8. As 7, but intermediate resin's amine component loaded with anion exchange resin in OH- form. Shear bond strengths (SBS) were measured after 24-hour storage in 37 degrees C water. RESULTS: SBSs on enamel (7.1 to 25.6 MPa) were, by ranking order (P< 0.05): 4 < 3, 5, 6 < 1, 2, 3, 6 <1, 2, 3, 7 < 1, 7, 8; SBSs on dentin (1.0 to 19.6 MPa): 1, 4, 5, 6 < 1, 2, 6 < 2, 3, 7 < 8. Oxygen inhibition had no adverse effect on enamel bond strengths. On dentin, all groups, apart from the anion exchange resin group (mean 19.6 MPa), showed bond strengths < 8 MPa. Dentin SBS of self-etch adhesive combined with self-cured resin was low, irrespective of the presence of an oxygen-inhibited layer. Deprotonization of the acidic adhesive monomer with an admixed anion exchange compound, added to an intermediate self-cured resin, was effective at overcoming the incompatibility.

Surface detail reproduction with new elastomeric dental impression materials.

OBJECTIVES: To compare the surface detail reproduction ability of 2 polyethers, 1 polyether-polyvinyl siloxane (PVS) hybrid, and 1 polyvinyl siloxane reference impression material when impressions of prepared dentin are made, and to determine the wettability of the nonset and set impression materials. METHOD AND MATERIALS: Impressions from air-dried or wet dentin surfaces were made with the light-bodied impression materials P2 Polyether (P2L), Impregum Garant L DuoSoft (IMP), the hybrid-type Fusion/Senn Light (SEN), and the PVS Flexitime Correct Flow (FLE). Roughness (Rz, Ra) was determined on 5 dentin specimens and 5 impressions (dry or wet) for each material. Data were analyzed using ANOVA and Duncan's test (a <.05). Wettability with water of nonset and set impression materials was recorded with an optical contact-angle measuring device. The set materials' wettability was determined on dry surfaces and after rinsing with water. RESULTS: Differential dentin surface reproduction with IMP, SEN, and FLE was between -2 and +2 Microm (Rz), and -0.2 and +0.2 Microm (Ra). Curing of P2L on dentin was inhibited. The contact angle of nonset IMP was less than 45 degrees, and initial angles for nonset SEN, FLE, and P2L were greater than 90 degrees. Early contact angles on rinsed FLE, P2L, and SEN were greater than 90 degrees. Angles on set IMP were consistently between initial 75 degrees and final 55 degrees. CONCLUSION: IMP, SEN, and FLE reproduce prepared dentin accurately, whereas P2L does not cure on dry or wet dentin. All materials have a reasonable potential of wetting moist surfaces.

Does application of phase-separated self-etching adhesives affect bond strength?

PURPOSE: To investigate whether application of three all-in-one self-etching adhesives in a phase-separated stage has an adverse effect on bonding to enamel and dentin. MATERIALS AND METHODS: The shear bond strengths (SBSs) on ground enamel and dentin of the adhesives G-Bond, Hybrid Bond, and iBond, combined with Venus composite, were determined. The adhesives were dispensed in a dish and applied either 1) immediately, 2) after 2 min, or 3) after 5 min dark storage under ambient conditions. The adhesives were shortly stirred with a microbrush and applied. Prior to light activation, the adhesives were air dried for 10 s with a strong air blast. Composite cylinders were produced in a cylindrical mold clamped on the treated surface. SBSs (n = 8) were determined in a universal testing machine at 1 mm/min crosshead speed after 24 h storage in 37 degrees C water. Data were statistically analyzed with Kruskal-Wallis ANOVA and the Mann-Whitney U-Test (p < 0.05). The qualitative compositions of the separated phases were determined by FTIR spectroscopy. RESULTS: In the separated stage, the adhesives showed acidic monomer-rich phases, containing all components of the original adhesive composition, and water-rich phases with minor amounts of mainly functional monomers dissolved. The SBSs of the individual adhesives applied on enamel or dentin at the different times after dispensing were not significantly different. CONCLUSION: Application of the adhesives tested either as homogeneous solution or in a phase-separated stage has no adverse effect on bonding strength to enamel or dentin when applied under the present study conditions.

Effect of oxygen inhibition of self-etching adhesives on enamel-dentin polymer bond.

PURPOSE: To determine effects of light curing of self-etching adhesives under ambient air or nitrogen on inhibition depths, enamel and dentin bond strengths, and marginal adaptation in dentin cavities. MATERIALS AND METHODS: The adhesives investigated were: AQ Bond (AQB, Sun Medical; Kyoto, Japan), iBond (IBO, Heraeus Kulzer; Hanau, Germany), One-Up Bond F II (OUB, Tokuyama; Tokyo, Japan), and Prompt L-Pop (PLP, 3M/ESPE; Seefeld, Germany). Inhibition layer thickness (ILT) was microscopically measured on 3 disk-shaped specimens each. Shear bond strengths (SBS) on enamel and dentin (n = 8) were determined after 10 min and 24 h water storage of bonded composite specimens (Venus, Heraeus Kulzer). The marginal adaptation of bonded Venus restorations in cylindrical dentin cavities was microscopically evaluated after 10 min of specimen storage (n = 8) in water. The data were statistically analyzed using parametric and nonparametric ANOVA and post-hoc tests at p < 0.05. RESULTS: Adhesive curing under air revealed significant ILT (microm) differences: IBO (4) < AQB (8) < PLP (12) < OUB (23). Upon curing in nitrogen atmosphere, no inhibition occurred with AQB, IBO, and PLP, and < 3 microm for OUB. SBSs on enamel after 10 min or 24 h did not differ according to curing atmospheres (p > 0.05). On dentin, SBSs were higher after curing under N2 (p < 0.05). Irrespective of the curing atmosphere, marginal adaptation was good for AQB and IBO and poor for PLP; OUB revealed significantly smaller gaps under N2 than under air curing. CONCLUSION: Oxygen inhibition of the four self-etching adhesives investigated had no or only moderate effects on bonding efficacy to enamel and dentin.

[Rheological study of hard resin for crown and bridge].

PURPOSE: For the purpose of evaluating the flow properties influencing the formativeness of commercial hard resin pastes used in the construction of crowns and bridges, we examined the behaviors of various resin pastes and their temperature dependence during manipulation. METHODS: Five types of hard resins currently in use for the construction of crowns and bridges in the clinical setting, namely, New Meta Color INFIS, Solidex, Ceramage, Gradia, and Estenia C&B, were examined. The components and flow properties of each resin paste were investigated in relation to the dentine and enamel colors. The viscosities of the resin pastes before curing were measured by a cone-plate viscometer. RESULTS: Each resin paste demonstrated a non-Newtonian flow, and the flow curve showed a hysteresis loop, in which the upward and downward curves were different. When the shear stress at the beginning of the holding time of the flow curve (20 degrees C, 25 degrees C, 30 degrees C) of each resin paste was measured, the shear stress at 20 degrees C was found to be significantly higher than that at 25 degrees C and 30 degrees C, and the shear stress at 25 degrees C was found to be significantly higher than that at 30 degrees C. The viscosity was found to be higher at lower temperatures than at higher temperatures. Comparison of the shear stresses at the beginning and at the end of the holding time revealed that the stress at the beginning of the holding time was significantly higher than that at the end of the holding time for all except the Estenia C&B resin paste. CONCLUSIONS: Each of the resin pastes used in the present study showed temperature dependence of its characteristics in the temperature range examined (20-30 degrees C) and thixotropic fluidity. However, the flow characteristics of these resin pastes differed significantly, suggesting that the flow characteristics may affect the manipulation of resin formativeness.