Determination of chemical species of fluoride during uptake mechanism of glass-ionomer cements with NMR spectroscopy

ObjectiveThe aim of the present study was to determine the chemical species formed inside glass-ionomer cements after fluoride uptake and to investigate the depth of penetration of fluoride ions within the cement matrix.MethodsAn experimental fluoride-free glass with composition 2SiO₂–AlO₃–CaO was produced. The glass powder was mixed with aqueous poly(acrylic acid) (PAA), and allowed to set. The resulting specimens were stored in 20 ml KF solution with 1000 ppm fluorine for 24 h and then placed into the same amount of water as for 24 h. A fluoride selective electrode was used to give the F concentration of the respective solutions. ¹⁹F MAS-NMR spectra were recorded on powdered cement specimens using a Bruker AVANCE-NEO 600 spectrometer. In addition, SEM observation and EDX chemical analysis were conducted on the cross-section of a carefully fractured specimen.ResultsFluoride was shown to be mainly present in the surface layers of the specimen after placement in the KF solution, and only a small fraction was re-released into water. ¹⁹F NMR spectroscopy showed that AlF complexes were formed within the cement.SignificanceThe fluoride taken up by a free-fluoride glass ionomer cement mostly occupies surface layers and is retained because it bonds to aluminum within the matrix. This finding explains why the majority of fluoride taken up by conventional glass ionomer cements is retained.     

Effect of chlorhexidine application on long-term shear bond strength of resin cements to dentin

PurposeThe purpose of this study was to investigate the effect of chlorhexidine [CH] on dentin bond strength of three resin cements after 1 year of water storage.MethodsA flat middle dentin surface was prepared on 120 extracted premolars. The teeth were randomly divided into 6 groups of 20 specimens each according to the resin cement used: Panavia F2.0, Variolink II, and RelyX Unicem, with or without CH application. After cementation of an indirect composite rod [Z250], one subgroup [n = 10] was tested after 24 h in water at 37 °C and the other subgroup [n = 10] was tested after 1 year storage in water plus thermocycling. A shear bond strength [SBS] test was performed. The data [in MPa] were analyzed with ANOVA and Tukey tests [P < 0.05].ResultsThree-way ANOVA [resin cement, CH and time] indicated that Variolink II had the highest strength [16.65 ± 3.60] and RelyX Unicem had the lowest strength [9.30 ± 4.07]. Chlorhexidine application increased SBS [13.31 ± 4.61] compared to samples without CH [12.16 ± 5.04] [P = 0.04]. Initial SBS [15.63 ± 4.37] was significantly higher than after 1 year of storage [9.85 ± 3.36] [P < 0.001]. Separate two-way ANOVA for 24-h and 1-year data showed that cement had a significant effect but CH and its interaction had no significant effect at 24 h, whereas at 1 year the two factors and their interaction differed significantly [P ≤ 0.001].ConclusionsChlorhexidine 2% can diminish the loss of bonding effectiveness over time associated to etch-and-rinse and self-etch cements, although it appears not have any effect on self-adhesive cement.     

Adhesive class I restorations in sound molar teeth incorporating combined resin-composite and glass ionomer materials: CAD-FE modeling and analysis

ObjectivesTo investigate the influence of different resin composite and glass ionomer cement material combinations in a “bi-layer” versus a “single-layer” adhesive technique for class I cavity restorations in molars using numerical finite element analysis (FEA).Materials and MethodsThree virtual restored lower molar models with class I cavities 4 mm deep were created from a sound molar CAD model. A combination of an adhesive and flowable composite with bulk fill composite (model A), of a glass ionomer cement with bulk fill composite (model B) and of an adhesive with bulk fill composite (model C), were considered. Starting from CAD models, 3D-finite element (FE) models were created and analyzed. Solid food was modeled on the occlusal surface and slide-type contact elements were used between tooth surface and food. Polymerization shrinkage was simulated for the composite materials. Physiological masticatory loads were applied to these systems combined with shrinkage. Static linear analyses were carried out. The maximum normal stress criterion was adopted as a measure of potential damage.ResultsAll models exhibited high stresses principally located along the tooth tissues–restoration interfaces. All models showed a similar stress trend along enamel–restoration interface, where stresses up to 22 MPa and 19 MPa was recorded in the enamel and restoration, respectively. A and C models showed a similar stress trend along the dentin-restoration interface with a lower stress level in model A, where stresses up to 11.5 MPa and 7.5 MPa were recorded in the dentin and restoration, respectively, whereas stresses of 17 MPa and 9 MPa were detected for model C. In contrast to A and C models, the model B showed a reduced stress level in dentin, in the lower restoration layer and no stress on the cavity floor.SignificanceFE analysis supported the positive effect of a “bi-layer” restorative technique in a 4 mm deep class I cavities in lower molars versus “single-layer” bulk fill composite technique.     

Microhardness of resin cements in the intraradicular environment: Effects of water storage and softening treament

ObjectivesTo analyze the microhardness of four dual-cure resin cements used for cementing fiber-reinforced posts under the following conditions: after 7 days of storage in water, after additional 24 h of immersion in 75% ethanol, and after 3 months of storage in water. Hardness measurements were taken at the cervical, middle and apical thirds along the cement line.MethodsRoot canals of 40 bovine incisors were prepared for post space. Fibrekor^® glass fiber-reinforced posts (Jeneric/Pentron) of 1 mm in diameter were cemented using Panavia F 2.0 (Kuraray), Variolink (Ivoclar-Vivadent), Rely X Unicem (3M ESPE) or Duolink (Bisco) (N = 10). After 7 days of water storage at 37 °C, half the sample (N = 5) was longitudinally sectioned and the initial microhardness measured along the cement line from cervical to apex. These same samples were further immersed in 75% ethanol for 24 h and reassessed. The remaining half (N = 5) was kept unsectioned in deionized water at 37 °C for 3 months, followed by sectioning and measuring. Data were analyzed by a series of two-way ANOVA and Tukey tests at α = 5%.ResultsStatistically significant differences were identified among the cements, thirds and conditions. Significant interactions were also observed between cements and thirds and between cements and conditions. Panavia F exhibited significantly higher initial microhardness than the other three cements, which showed no statistical difference among themselves. Variolink and Duolink showed significantly higher microhardness values in the cervical third, without significant difference among the thirds for the other cements. Immersion in ethanol significantly reduced the hardness values for all cements, regardless of the thirds. Storage in water for 3 months had no influence on the hardness of most of the cements, with the exception of Unicem that showed a significant increase in the hardness values after this period.SignificanceResults showed heterogeneity in the microhardness of the cements inside the canal. All cements presented some degree of softening after ethanol treatment, which suggests instability of the polymer. The quality of curing of resin cements in the root canal environment seems unpredictable and highly material dependent.     

Self-adhesive resin cement versus zinc phosphate luting material: A prospective clinical trial begun 2003

ObjectivesThe literature demonstrates that conventional luting of metal-based restorations using zinc phosphate cements is clinically successful over 20 years. This study compared the clinical outcomes of metal-based fixed partial dentures luted conventionally with zinc phosphate and self-adhesive resin cement.MethodsForty-nine patients (mean age 54 ± 13 years) received 49 metal-based fixed partial dentures randomly luted using zinc phosphate (Richter & Hoffmann, Berlin, Germany) or self-adhesive resin cement (RelyX Unicem Aplicap, 3M ESPE, Germany) at the University Medical Center Regensburg. The core build-up material was highly viscous glass ionomer; the finishing line was in dentin. The study included 42 posterior, 5 anterior crowns and two onlays. Forty-seven restorations were made of precious alloys, 2 of non-precious alloys. The restorations were clinically examined every year. The clinical performance was checked for plaque (0–5; PI, Quigley-Hein), bleeding (0–4; PBI; Mühlemann) and attachment scores. The examination included pulp vitality and percussion tests.StatisticsMeans of scores, standard deviation, cumulative survival and complication rates were calculated using life tables.ResultsThe mean observation time was 3.16 ± 0.6 years (min: 2.0; max: 4.5 years). During that time no restoration was lost, no recementation became necessary. One endodontic treatment was performed in the self-adhesive composite group after 2.9 years. At study end bleeding (1.44 RelyX Unicem vs. 1.25 zinc phosphate) and plaque (1.64 RelyX Unicem vs. 1.0 zinc phosphate) scores showed no statistically significant difference.SignificanceThe self-adhesive resin cement performed clinically as well and can be used as easily as zinc phosphate cement to retain metal-based restorations over a 38-month observation period.     

Improvement on properties of experimental resin cements containing an iodonium salt cured under challenging polymerization conditions

ObjectiveThe use of resin cements in clinical practice entails photopolymerization through prosthetic devices, which precludes light penetration. The objective of this study was to modify experimental resin cements (ERCs) with diphenyliodonium hexafluorophosphate (DPI) in an attempt to improve chemical and mechanical properties of materials cured with reduced irradiance and final radiant exposure.MethodsA co-monomer base containing a 1:1 mass ratio of 2.2-bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl]propane (bis-GMA) and triethyleneglycol dimethacrylate (TEGDMA) was prepared, with 1 mol% of camphorquinone and 2 mol% of ethyl 4-(dimethylamino)benzoate as initiator system. The resin was divided into 4 fractions according to the DPI concentrations (0, 0.5, 1 and 2 mol%). The challenging polymerization condition was simulated performing the light activation (12, 23 and 46 s) through a ceramic block (3 mm thick). The irradiance was assessed with a calibrated spectrometer (1320 mW/cm²), resulting in three levels of radiant exposure (0.58, 1.1 and 2.2 J/cm²). The polymerization kinetics was evaluated in real-time using a spectrometer (Near-IR). Water sorption and solubility was analyzed and the cohesive strength of resins obtained through the microtensile test. Polymerization stress was assessed by Bioman method.ResultsResins containing DPI had higher degree of conversion and rate of polymerization than the control (without DPI). The use of DPI reduced water sorption and solubility, and led to higher cohesive strength compared to resins without the iodonium salt. However, the stress of polymerization was higher for experimental resins with DPI.SignificanceEven under remarkably reduced irradiance, cements containing a ternary initiating system with an iodonium salt can present an optimal degree of conversion and chemical/mechanical properties.     

Mechanical properties of new self-adhesive resin-based cement

PurposeThe aim of this study was to compare the bonding strength, flexural strength, elastic modulus, water absorption and the expansion after water storage of new self-adhesive resin cements to commercially available dental cements.MethodsTwo types (hand-mix and auto-mix) of new self-adhesive resin cements (SAC-H and SAC-A, Kuraray Medical), one conventional resin cement (Panavia F2.0), three self-adhesive resin cements (Relyx Unicem, Maxcem and G-Cem), and two resin-modified glass-ionomer cements (Fuji Luting S and Vitremer) were used. Shear bond strengths, flexural strengths and elastic moduli (ISO 4049), water absorption (ISO 4049), and the expansion rate after water storage were investigated.ResultsBoth SAC-H and SAC-A provided adhesion to enamel and dentin, and had the same bond strength to gold alloy and zirconia as conventional resin cements. SAC-H and SAC-A had greater flexural strengths (86.4–93.5 MPa) than commercial self-adhesive resin cements or glass-ionomer cements. The elastic moduli of self-adhesive and glass-ionomer cements were 5.2–7.4 GPa and 2.3–3.4 GPa, respectively. The water absorption of SAC-H and SAC-A (26.3–27.7 μg/mm³) were significantly lower than commercial self-adhesive resin cements. SAC-H and SAC-A showed significantly lower expansion rates (0.17–0.26%) than commercial self-adhesive cements and glass-ionomer cements after 4 weeks water storage.ConclusionsIt is suggested that the new self-adhesive resin cements exhibited a favorable bonding capability and mechanical properties.     

Effect of pulpal pressure on the microtensile bond strength of luting resin cements to human dentin

ObjectivesThe objectives of this study were to examine the effect of pulpal pressure on the microtensile bond strength (mTBS) of luting resin cements to human dentin and the permeability of dentin surfaces pre-treated with an adhesive and a self-etching primer.MethodsCylindrical composite blocks were luted with resin cements (RelyX ARC, 3M ESPE: ARC; Panavia F, Kuraray Medical Inc.: PF; RelyX Unicem, 3M ESPE: UN) in the absence or presence of simulated pulpal pressure. The application of Adper Single Bond 2 (3M ESPE) and ED primer 2.0 (Kuraray) was performed under 0 cm H₂O. After each resin cement was applied, the pulpal pressure group was subjected to 20 cm H₂O of hydrostatic pressure for 10 min during the initial setting period. Testing for mTBS was performed on 0.9 mm × 0.9 mm sectioned beams after 24 h water-storage. Scanning electron microscopy was performed to investigate the fractured surfaces after mTBS testing and additional dentin surfaces that were treated by an etchant, ED primer 2.0 and UN. Fluid permeability was measured on dentin surfaces that were applied with Adper Single Bond 2 and ED primer 2.0.ResultsApplication of pulpal pressure reduced mTBS significantly in groups ARC and PF. Porous bonding interfaces due to water permeability through the cured adhesive were observed on fractured surfaces. Dentin surfaces that were applied with the adhesive and the primer were more permeable than smear layer-covered dentin. The mTBS of UN was significantly lower than ARC and PF regardless of the absence/presence of pulpal pressure.SignificanceFluid permeation during the initial setting period deteriorated the bonding quality of resin cements.     

Curing efficiency of four self-etching,self-adhesive resin cements

ObjectivesTo evaluate the degree of cure (%DC) of four self-etching, self-adhesive resin cements, and one conventional resin cement, in their self- and dual-curing mode.MethodsThe self-etching, self-adhesive resin cements studied were RelyX? Unicem (3M? ESPE? AG), Maxcem? (Kerr Corporation), Biscem? (Bisco, Inc.) and Multilink^® Sprint (Ivoclar Vivadent^® AG) and the classic resin cement was Multilink^® Automix (Ivoclar Vivadent^® AG). Twelve specimens of each material (1.8 mm × 4 mm × 4 mm) were prepared in room temperature (23 ± 1) °C following the manufacturers’ instructions. Six of them were treated as dual-cured, thus irradiated for 20 s with a halogen light curing unit and left undisturbed for 5 min. The other six were treated as self-cured and were not irradiated, but left in dark and dry conditions for 10 min. The assessment of the %DC was made using micro-ATR FTIR spectrometry.ResultsThe %DC in their self-curing mode was very low (10.82–24.93%), with Multilink Sprint exhibiting the highest values among the five. In the dual-curing mode the values obtained were also low (26.40–41.52%), with the exception of Multilink Automix (61.36%). Maxcem was found to have the lowest DC.SignificanceThe low %DC found raises questions as to whether these materials can be successfully used in clinical applications, where light attenuation takes place. Increased irradiation times could potentially lead to higher %DC, in applications where light is not completely blocked by the overlying restoration.     

Biocompatibility of self-adhesive resin cement with fibroblast cells

Statement of problemDental cements that release monomers that negatively impact adjacent oral soft tissues may adversely affect clinical outcomes. However, in vitro studies evaluating the cytotoxic and genotoxic potential of substances released from dental cements are lacking.PurposeThe purpose of this in vitro study was to define and compare the cytotoxicity and genotoxicity of the eluates of a self-adhesive resin cement (RelyX Unicem 2 Automix) autopolymerized and light polymerized with 2 other types of luting cements: a glass ionomer cement (Ketac Cem Easymix) and a resin-modified glass ionomer cement (Ketac Cem Plus).Material and methodsThe eluates were prepared, and 3T3 mouse fibroblast cells were exposed for 24 hours to serial eluate dilutions of the 3 types of cement. Cytotoxicity was determined by using a cell viability assessment through 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and crystal violet assays. Genotoxic effects were determined by using the cytokinesis-block micronucleus assay.ResultsCell viability was higher in the presence of the glass ionomer cement eluate than of the resin-modified glass ionomer cement and resin cement eluates. A pronounced decrease in viability was found when the cells were exposed to undiluted samples of resin-modified glass ionomer cement (around 50%) or resin cement (around 80% to 90%). No significant difference in cell viability was found between autopolymerized and light-polymerized resin cements. All cements induced a dose-dependent response of mononucleated cell formation. However, only the resin cements showed double strand breaks significant differences in the deoxyribonucleic acid (DNA) molecules against the basal DNA lesions that occurred spontaneously.ConclusionsThe glass ionomer cement was not found to be cytotoxic or genotoxic, whereas the eluates derived from the resin-modified glass ionomer cement and resin cement, independently of the polymerization method, were cytotoxic in fibroblast cells. Maximum cytotoxicity was observed in the presence of resin cement, which also showed genotoxicity, independently of being light polymerized.     

Reinforcement of experimental composite materials based on amorphous calcium phosphate with inert fillers

ObjectivesThe aim of this study was to examine the influence of the addition of glass fillers with different sizes and degrees of silanization percentages to remineralizing composite materials based on amorphous calcium phosphate (ACP).MethodsFour different materials were tested in this study. Three ACP based materials: 0-ACP (40 wt% ACP, 60 wt% resin), Ba-ACP (40 wt% ACP, 50 wt% resin, 10 wt% barium-glass) and Sr-ACP (40 wt% ACP, 50 wt% resin, 10 wt% strontium-glass) were compared to the control material, resin modified glass ionomer (Fuji II LC capsule, GC, Japan). The fillers and composites were characterized using scanning electron microscopy. Flexural strength and modulus were determined using a three-point bending test. Calcium and phosphate ion release from ACP based composites was measured using inductively coupled plasma atomic emission spectroscopy.ResultsThe addition of barium-glass fillers (35.4 (29.1–42.1) MPa) (median (25–75%)) had improved the flexural strength in comparison to the 0-ACP (24.8 (20.8–36.9) MPa) and glass ionomer control (33.1 (29.7–36.2) MPa). The admixture of strontium-glass (20.3 (19.5–22.2) MPa) did not have any effect on flexural strength, but significantly improved its flexural modulus (6.4 (4.8–6.9) GPa) in comparison to 0-ACP (3.9 (3.4–4.1) GPa) and Ba-ACP (4.6 (4.2–6.9) GPa). Ion release kinetics was not affected by the addition of inert fillers to the ACP composites.SignificanceIncorporation of barium-glass fillers to the composition of ACP composites contributed to the improvement of flexural strength and modulus, with no adverse influence on ion release profiles.     

Effect of water aging on microtensile bond strength of dual-cured resin cements to pre-treated sintered zirconium-oxide ceramics

ObjectivesTo evaluate the hydrolytic stability of different dual-cure resin cements when luted to zirconia ceramic.MethodsEighteen cylinder-shaped zirconia blocks (Cercon Zirconia, Dentsply) were conditioned with: Group 1, no treatment; Group 2, sandblasting (125 μm alumina–Al₂O₃-particles); Group 3, tribochemical silica coating (50 μm silica-modified Al₂O₃ particles). Ceramic blocks were duplicated in composite resin (Tetric Evo Ceram, Ivoclar-Vivadent). Composite disks were luted to pre-treated ceramic surfaces using: (1) Clearfil Esthetic Cement (CEC; Kuraray); (2) Rely X Unicem (RXU; 3M ESPE); (3) Calibra (CAL; Dentsply Caulk). After 24 h, bonded samples were cut into microtensile sticks (1 mm²). Half of the sticks were loaded in tension until failure (cross-head speed of 0.5 mm/min). The remaining half was tested after 6 months of water storage at 37 °C. Data was analyzed with three-way ANOVA and Tukey’s test (P <0.05). Fractographic analysis was performed by SEM.ResultsAfter 24 h, bond strength of CEC to zirconia was significantly higher than that of RXU and CAL, independently from the ceramic pre-treatment (P <0.001). Using CAL, all samples failed prematurely except when luting to sandblasted surfaces. After 6 months of water aging, bond strength of CEC significantly decreased. RXU did not significantly alter bond strengths. Adhesion of sandblasted specimens luted with CAL fell over time. Micromorphological alterations were evident after water storage.SignificanceResin–ceramic interfacial longevity depended on cement selection rather than on surface pre-treatments. CEC and RXU were both suitable for luting zirconia. Water aging played an important role in the durability of zirconia-to-composite chemical bonds.     

An evaluation of microleakage of various glass ionomer based restorative materials in deciduous and permanent teeth: An in vitro study

AimTo evaluate the microleakage of recently available glass ionomer based restorative materials (GC Fuji IX GP, GC Fuji VII, and Dyract) and compare their microleakage with the previously existing glass ionomer restorative materials (GC Fuji II LC) in primary and permanent teeth.MethodOne hundred and fifty (75 + 75) non-carious deciduous and permanent teeth were restored with glass ionomer based restorative materials after making class I cavities. Samples were subjected to thermocycling after storing in distilled water for 24 h. Two coats of nail polish were applied 1 mm short of restorative margins and samples sectioned buccolingually after storing in methylene blue dye for 24 h. Microleakage was assessed using stereomicroscope.ResultSignificant differences (P < 0.05) were found when inter group comparisons were done. Except when GC Fuji VII (Group III) was compared with GC Fuji II LC (Group II) and Dyract (Group IV), non-significant differences (P > 0.05) were observed. It was found that there was no statistically significant difference when the means of microleakage of primary teeth were compared with those of permanent teeth.ConclusionsGC Fuji IX GP showed maximum microleakage and GC Fuji VII showed least microleakage.     

Hertzian load-bearing capacity of a ceramic-reinforced glass ionomer cement stored wet and dry

ObjectiveTo investigate the development of the load-bearing capacity of a ceramic-reinforced glass ionomer cement (GIC), stored dry or wet, using Hertzian indentation.MethodsGIC discs 2 mm thick and 10 mm in diameter were made (Amalgomer CR, Advanced Healthcare, Tonbridge, Kent, UK), randomly divided into 8 groups and stored at 37 °C in air or artificial saliva (AS) for 1, 7, 30 and 90 days. Discs were tested by loading centrally using a 20 mm diameter hard steel ball while resting freely on a filled-nylon substrate (E: 10 GPa), at 23 °C in air. The failure load at the first bottom-initiated radial crack was detected acoustically.ResultsAll the failure loads of air-stored specimens were higher than those of AS-stored specimens. The failure load was relatively stable for air-stored specimens but showed a significant decreasing tendency for AS-stored specimens.SignificanceZirconia-reinforced GIC is sensitive to moisture. Artificial saliva storage has a detrimental effect on the failure load of ceramic-reinforced GIC that may indicate long-term deterioration in service.     

Influence of sandblasting granulometry and resin cement composition on microtensile bond strength to zirconia ceramic for dental prosthetic frameworks

ObjectivesTo evaluate the effect of the particle size of sandblasting and the composition of the resin cement on the microtensile bond strength (MTBS) to zirconia.MethodsForty zirconia blocks (Cercon, Dentsply) were polished and randomly treated as follows: Group 1 (NT): no treatment; Group 2 (APA-I): airborne particle abrasion (Cobra, Renfert) using 25-μm aluminium-oxide (Al₂O₃)-particles; Group 3 (APA-II): APA with 50-μm Al₂O₃-particles; and Group 4 (APA-III): APA using 110-μm Al₂O₃-particles. Ceramic blocks were duplicated in composite resin. Samples of each pretreatment group were randomly divided into two subgroups depending on the resin cement used for bonding the composite disks to the treated zirconia surfaces. Subgroup 1 (PAN), which was a 10-MDP-containing luting system, used Clearfil Ceramic Primer plus Panavia F 2.0 (Kuraray) and Subgroup 2 (BIF) used Bifix SE (VOCO) self-adhesive cement. After 24 h, bonded specimens were cut into 1 ± 0.1 mm² sticks. MTBS values were obtained using a universal testing machine (cross-head speed = 0.5 mm/min). Failure modes were recorded and the interfacial morphology of the debonded microbars was SEM-assessed. Two-way ANOVA, Student–Newman–Keuls tests, and the step-wise linear regression analysis were performed with the MTBS being the dependent variable (p < 0.05).ResultsDespite the sandblasting granulometry, PAN bonded to air-abraded surfaces attained the highest MTBS and frequently showed mixed fractures. BIF recorded no significant differences in MTBS depending on the conditioning method, and registered the highest rates of premature and adhesive failures.ConclusionsThe 10-MDP-containing luting system seems to be the most suitable to bond zirconium-oxide ceramic, mainly after sandblasting.     

Tensile bond strength of cast commercially pure titanium dowel and cores cemented with three luting agents

PurposeThe purpose of this study was to compare the tensile strength of commercially pure titanium dowels and cores cemented with zinc phosphate or resin cements.MethodsTwenty-one extracted human canines were endodontically treated. The root preparations were accomplished using Largo reamers (10 mm in depth and 1.7 mm in diameter). Acrylic resin patterns for the dowel and cores were made, and specimens were cast in commercially pure titanium (n = 7) and divided in three groups: TZ–CP Ti dowels luted with zinc phosphate luting agent, TP–CP Ti dowels luted with Panavia F and TR–CP Ti dowels luted with RelyX U100. Tensile strengths were measured in a universal testing machine at a crosshead speed of 0.5 mm/min. The results (N) were statistically analyzed by ANOVA and Tukey tests (α = 0.01).ResultsThe ANOVA indicated that there were significant differences among the groups tested. A Tukey multiple comparison procedure was performed and revealed statistically significant higher retention values for the dowel luted with RelyX U100 when compared with zinc phosphate or Panavia F.ConclusionCast commercially pure titanium dowels and cores fixed with RelyX U100 cement presented superior bond strength retention when compared to zinc phosphate and Panavia F.     

Effect of etching time and resin bond on the flexural strength of IPS e.max Press glass ceramic

ObjectiveTo evaluate the effect of hydrofluoric acid (HFA) etching time and resin cement bond on the flexural strength of IPS e.max^® Press glass ceramic.MethodsTwo hundred and ten bars, 25 mm × 3 mm × 2 mm, were made from IPS e.max^® Press ingots through lost-wax, hot-pressed ceramic fabrication technology and randomly divided into five groups with forty-two per group after polishing. The ceramic surfaces of different groups were etched by 9.5% hydrofluoric acid gel for 0, 20, 40, 60 and 120 s respectively. Two specimens of each group were selected randomly to examine the surface roughness and 3-dimensional topography with atomic force microscope (AFM), and microstructure was analyzed by the field emission scanning electron microscope (FE-SEM). Then each group were subdivided into two subgroups (n = 20). One subgroup of this material was selected to receive a thin (approximately 0.1 mm) layer of resin luting agent (Variolink N) whereas the other subgroup remained unaltered. Half of subgroup's specimens were thermocycled 10,000 times before a 3-point bending test in order to determine the flexural strength. Interface between resin cement and ceramic was examined with field emission scanning electronic microscope.ResultsRoughness values increased with increasing etching time. The mean flexural strength values of group 0 s, 20 s, 40 s, 60 s and 120 s were 384 ± 33, 347 ± 43, 330 ± 53, 327 ± 67 and 317 ± 41 MPa respectively. Increasing HF etching times reduced the mean flexural strength (p < 0.05). However, the mean flexural strength of each group, except group 0 s, increased significantly to 420 ± 31, 435 ± 50, 400 ± 39 and 412 ± 58 MPa after the application of dual-curing resin cement. In the present investigation, no significant differences after thermocycling on the flexural strengths were evident.SignificanceOvertime HF etching could have a wakening effect on IPS e.max^® Press glass ceramic, but resin cement bonding to appropriately etched surface would strengthen the dental ceramic.     

Mechanical properties of luting cements after water storage

This study determined the effect of water storage on flexural strength (FS) and compressive strength (CS) of 12 luting cements from different material classes. In addition, the influence of the curing method on the mechanical properties was investigated. The materials examined were two zinc phosphate cements (Harvard cement and Fleck's zinc cement), two glass ionomer cements (Fuji I and Ketac-Cem), three resin-modified glass ionomer cements (Fuji Plus, Fuji Cem and RelyX Luting), four resin cements (RelyX ARC, Panavia F, Variolink II and Compolute) and one self-adhesive universal resin cement (RelyX Unicem). The samples were prepared and tested according to ISO specifications. Specimens for FS and CS were loaded to fracture at a constant crosshead speed of 1 mm/minute. The mechanical properties were measured after the materials were stored in distilled water at a temperature of 37.0 +/- 1.0 degrees C for 24 hours and 150 days after mixing. In a one-way ANOVA, multiple mean value comparisons using Duncan's multiple comparison tests were performed. Resin cements had the highest flexural and compressive strengths, followed by self-adhesive universal resin cement. These materials were statistically stronger than resin-modified glass ionomer cements, glass ionomer cements and zinc phosphate cements.     

Development of calcium phosphate/sulfate biphasic cement for vital pulp therapy

ObjectivesBioactive calcium phosphate cement (CPC) has been used widely to repair bone defects because of its excellent biocompatibility and bioactivity. However, the poor handling properties, low initial mechanical strength, and long setting time of CPC limit its application in vital pulp therapy (VPT). The aim of this study was to synthesize biphasic calcium phosphate/sulfate cements and evaluate the feasibility of applying these cements in VPT.MethodsThe physical, chemical, and mechanical properties of CPC were improved by mixing the cement with various amounts of α-calcium sulfate hemihydrate (CSH). The hydration products and crystalline phases of the materials were characterized using scanning electron microscopy and X-ray diffraction analysis. In addition, the physical properties, such as the setting time, compressive strength, viscosity, and pH were determined. Water-soluble tetrazolium salt-1 and lactase dehydrogenase were used to evaluate cell viability and cytotoxicity.ResultsThe developed CPC (CPC/CSH cement), which contains 50 wt% CSH cement, exhibited no obvious temperature increase or pH change during setting when it was used as a paste. The initial setting time of the CPC/CSH biphasic cement was substantially shorter than that of CPC, and the initial mechanical strength was 23.7 ± 5.6 MPa. The CPC/CSH cement exhibited higher viscosity than CPC and, thus, featured acceptable handling properties. X-ray diffraction analysis revealed that the relative peak intensity for hydroxyapatite increased, and the intensity for calcium sulfate dehydrate decreased as the amount of CPC was increased. The cell viability and cytotoxicity test results indicated that the CPC/CSH cement did not harm dental pulp cells.SignificanceThe developed CPC/CSH biphasic cement exhibits substantial potential for application in VPT.     

Randomized clinical trial on effectiveness of silver diamine fluoride and glass ionomer in arresting dentine caries in preschool children

ObjectiveTo compare the effectiveness of annual topical application of silver diamine fluoride (SDF) solution, semi-annual topical application of SDF solution, and annual application of a flowable high fluoride-releasing glass ionomer in arresting active dentine caries in primary teeth.MethodsA total of 212 children, aged 3–4 years, were randomly allocated to one of three groups for treatment of carious dentine cavities in their primary teeth: Gp1-annual application of SDF, Gp2-semi-annual application of SDF, and Gp3-annual application of glass ionomer. Follow-up examinations were carried out every six months to assess whether the treated caries lesions had become arrested.ResultsAfter 24 months, 181 (85%) children remained in the study. The caries arrest rates were 79%, 91% and 82% for Gp1, Gp2 and Gp3, respectively (p = 0.007). In the logistic regression model using GEE to adjust for clustering effect, higher caries arrest rates were found in lesions treated in Gp2 (OR = 2.98, p = 0.007), those in anterior teeth (OR = 5.55, p < 0.001), and those in buccal/lingual smooth surfaces (OR = 15.6, p = 0.004).ConclusionAnnual application of either SDF solution or high fluoride-releasing glass ionomer can arrest active dentine caries. Increasing the frequency of application to every 6 months can increase the caries arrest rate of SDF application.Clinical significanceArrest of active dentine caries in primary teeth by topical application of SDF solution can be enhanced by increasing the frequency of application from annually to every 6 months, whereas annual paint-on of a flowable glass ionomer can also arrest active dentine caries and may provide a more aesthetic outcome.