Fatigue resistance of ultrathin CAD/CAM ceramic and nanoceramic composite occlusal veneers

ObjectiveThe fracture resistance of different ultrathin occlusal computer-aided design/computer-aided manufacturing (CAD/CAM) veneers was investigated under cyclic mechanical loading to restore combined enamel-dentin defects.MethodsEighty-four molars were reduced occlusally until extensive dentin exposure occurred with a remaining enamel ring. Twenty-four molars were ground flat for examination of highly standardized specimens, of which 8 were treated with uniformly flat 0.3 mm IPS Empress CAD and 0.3 and 0.5 mm IPS e.max CAD restorations. Sixty-four molars were anatomically prepared until dentin exposure and were restored using occlusal veneers with fissure/cusp thicknesses of 0.3/0.5 mm from 3 different dental CAD/CAM materials: IPS Empress CAD, IPS e.max CAD and Lava Ultimate CAD/CAM. Teeth were etched with 37% phosphoric acid, and occlusal veneers were bonded using an adhesive luting system (Syntac Primer, Adhesive, Heliobond and Variolink II). Specimens were placed under cyclic mechanical loading in a chewing simulator (1 million cycles at 50 N) and were examined for cracks after each cyclic loading sequence. The anatomical 0.3/0.5 mm IPS e.max CAD specimens experienced an additional 1 million cycles at 100 N. Kaplan–Meier survival curves and log-rank tests were used for data analysis.ResultsAll highly standardized and 0.3/0.5 mm IPS e.max CAD specimens tolerated cyclic loading. One anatomical Lava Ultimate CAD/CAM and 10 IPS Empress CAD specimens showed cracks.SignificanceUltrathin occlusal veneers of lithium disilicate ceramic and nanoceramic composite showed remarkably high fracture strength under cyclic mechanical loading. These veneers might be a tooth substance preserving option for restoring combined dentin–enamel defects.     

Polymerization contraction stress in resin–tooth bonds under hydrated and dehydrated conditions

ObjectiveThis study hypothesizes that, with enamel or dentin as a bonding substrate, intrinsic water affects the development of polymerization contraction stress in the bonds of self-etching adhesives during bonding.Materials and methodsThe influence of the water content in dentin and enamel (wetness with water as control and acetone-dried specimens) on the stress development in self-etching adhesives was determined with a tensilometer. Thin layers of self-etching primer and/or adhesive resins were created between a glass plate and a flat enamel or dentin surface.ResultsAfter an initial maximum shortly after light curing for 30 min, the contraction stress was decreased in the dentin (30–70%) and enamel (approximately 20%). In the acetone-dried specimens, the stress was continuously increased for 20–50%.SignificanceThe intrinsic water content of tooth tissue influences the initial polymerization of polymers. This effect is favorable for stress relief in resin restoration but causes unwanted nanoleakage channel formation in resin–tooth bonds.     

Effect of immediate dentin sealing on load-bearing capacity under accelerated fatigue of thin occlusal veneers made of CAD-CAM glass-ceramic and resin composite material

ObjectiveThe objective of this study was to assess the influence of immediate dentin sealing (IDS) on the fatigue behavior of laminate occlusal veneers fabricated with CAD/CAM lithium disilicate ceramic and resin composite.MethodsForty sound human molars were prepared and randomly divided into 4 groups (n = 10): RC–IDS+ (IDS and resin composite occlusal laminate veneer); RC–IDS- (resin composite occlusal laminate veneer without IDS); LD–IDS+ (IDS and lithium disilicate laminate veneer); LD–IDS- (lithium disilicate occlusal laminate veneer without IDS). The restorations were obtained using a digital workflow. After surface conditioning and bonding, thermocycling and accelerated fatigue tests (20 Hz, 5000 cycles with an initial load of 300 N, step-size of 100 N for 10,000 cycles, up to 1000 N, and then a step-size of 50 N until failure) were conducted. Fatigue data were recorded for both outcomes (crack or fracture) and statistically analyzed. Fractographic and adhesive interface analysis were conducted.ResultsThe indirect resin composite groups showed better fatigue behavior compared to lithium disilicate. IDS only had a positive effect for the survival of resin composite restorations for the ‘fracture’ outcome. Evident presence of micro-gaps at the adhesive interface in the LD–IDS- group could be noted.SignificanceImmediate dentin sealing improved fatigue resistance behavior of resin composite occlusal veneers. However, this effect was not observed in lithium disilicate veneers.     

The role of etching in bonding to enamel: A comparison of self-etching and etch-and-rinse adhesive systems

ObjectiveEtch and resin infiltration morphologies were compared for three self-etch adhesive (SEA) systems and eleven model etch-and-rinse (ERA) systems using various phosphoric acid (PA) concentrations with Adper Single Bond Plus (SB) adhesive. Matches for the morphologies were made between each SEA system and one of the PA/SB systems and bond strength measurements were made for all the systems. The hypothesis was that similar morphology would result in similar bond strength assuming micro-mechanical bonding is the mechanism of adhesion.MethodsThree specimens were prepared on polished (4000 grit) human enamel for each adhesive system to examine etch and resin infiltration morphology by SEM. For the latter, the adhesive systems were bonded using recommended methods and the enamel was dissolved in acid to reveal the resin. The etch patterns for the SEA systems were determined by rinsing off the material with water and acetone. Polished (4000 grit) human enamel was used with each adhesive system to determine 24-h resin composite to enamel shear bond strengths (SBS). A minimum of 10 specimens were used for each group. Data were analyzed by a one factor ANOVA and Fisher's PLSD post hoc test.ResultsThe SBS to polished enamel for two of the three SEA systems were statistically significantly greater (p < 0.05) than the PA/SB matched systems, indicating that chemical bonding might be partly responsible for the measured bond strength. All three SEA systems provided statistically lower (p < 0.05) SBS values than the PA/SB systems with PA concentrations between 2.5% and 40%.SignificanceAlthough chemical bonding may be present for some SEA systems it does not provide enough increase in bond strength to compete with the bond produced by ERA systems using phosphoric acid etching of enamel.     

Wear resistance of crowns made from different CAM/CAD materials

ObjectivesThe aim of this laboratory study was to evaluate the wear resistance of crowns made from current computer-aided design and computer-aided manufacture (CAD/CAM) materials. In addition, the abrasion of the steatite antagonist against these materials was compared.MethodsIdentically shaped crowns of lithium disilicate, zirconia-reinforced lithium disilicate and a polymer-infiltrated ceramic network (PICN) were fabricated with an occlusal thickness of 1.5 mm and a lateral wall thickness of 1.2 mm (n = 8). The crowns were cemented with a dual-polymerizing luting resin on composite resin dies. Using spherical steatite antagonists, all specimens were loaded with 49 N for 1,200,000 cycles in a mastication simulator with additional thermocycling. After 120,000, 240,000, 480,000, 960,000, and 1,200,000 cycles, precision impressions were made and investigated with a laser scanning microscope. The vertical and volume substance loss was measured. Additionally, the substance loss of the antagonists was evaluated after 1,200,000 loading cycles.ResultsNo significant difference (p > 0.05) was found in the median volume loss of the test materials after 1,200,000 cycles (lithium disilicate: 0.405 mm³, PICN: 0.362 mm³, zirconia-reinforced lithium disilicate: 0.340 mm³). The vertical substance loss of PICN (157 μm) was significantly lower (p ≤ 0.05) than that of lithium disilicate (201 μm) and zirconia reinforced lithium disilicate (191 μm). However, the substance loss of steatite against zirconia-reinforced lithium disilicate (0.191 mm³) was significantly lower (p ≤ 0.05) than against lithium disilicate (0.296 mm³) and PICN (0.531 mm³).SignificanceAll three CAD/CAM materials showed wear resistance that seems appropriate for clinical application. Also, the abrasion of the antagonist looks promising.     

Impact of hydrophilicity and length of spacer chains on the bonding of functional monomers

Objectives10-Methacryloyloxy-decyl-dihydrogen-phosphate (10-MDP) is currently considered as one of the most effective functional monomers for dental bonding, this in part thanks to its long and relatively hydrophobic spacer chain, adequately separating the polymerizable from the phosphate functionalities. This study compared functional monomers with different spacer chains’ length and hydrophilicity to 10-MDP on their dentin and enamel bonding performance.MethodsAtomic absorption spectroscopy (AAS) was used to characterize the chemical interaction. Micro-tensile bond strength (μTBS) and fractographic analyses were performed after 24 h and one year. Confocal micro-permeability and SEM nanoleakage assessments were also undertaken. The tested functional monomers were 2-MEP (2-carbon spacer), 10-MDP (10-carbon), 12-MDDP (12-carbon), MTEP (high hydrophilic polyether spacer chain) and CAP-P (intermediate hydrophilic ester spacer).ResultsAAS revealed clear differences (p < 0.05) in monomer-calcium salt formation in this order: 12-MDDP = 10-MDP > CAP-P > MTEP > 2-MEP. The highest initial dentin μTBS was obtained using 10-MDP or 12-MDDP. After 1-year aging, a significant drop (p < 0.05) in μTBS was observed for the adhesives with MTEP (enamel and dentin), 2-MEP (enamel) and CAP-P (enamel). MTEP presented the highest micro-permeability, while 2-MEP, CAP-P and MTEP showed increased nanoleakage after aging.SignificanceThese outcomes showed that more hydrophilic and shorter spacer chains may compromise the chemical interaction with calcium and the dentin/enamel bonding performance.     

Effectiveness of pretreatment with phosphoric acid,sodium hypochlorite and sulfinic acid sodium salt on root canal dentin resin bonding

PurposeThe purpose of this study was to evaluate the effect of pretreatment using phosphoric acid, sodium hypochlorite and sulfinic acid sodium salt on the bonding of one-step self-etching adhesives to root canal dentin.MethodsThirty-six single-rooted sound human premolars were randomly assigned into three groups before applying the one-step self-etching adhesive. These comprised a control group with no pretreatment, an NC group that received phosphoric acid and subsequent sodium hypochlorite gel pretreatments, and an NC + AC group that received an additional treatment with sulfinic acid sodium salt following the same pretreatment applied to the NC group. Microtensile bond strength measurements, bonding interface observations by scanning electron microscopy (SEM), elemental analyses by X-ray photoelectron spectroscopy (XPS) and degree of polymerization (DOP) analyses by Raman spectroscopy were subsequently performed.ResultsThe bond strength was significantly higher in the NC + AC group than in the other two groups (Control: P = 000.1 and NC: P = 0.004). SEM observations showed that resin tags were present in the dentinal tubules in the NC and NC + AC groups. Compared to the control group, the adhesive resin layer had a lower DOP in the NC group, while the DOP for the NC + AC group was higher than that of the NC specimens.ConclusionsBonding to root canal dentin was improved by applying sulfinic acid sodium salt in addition to treatment with phosphoric acid followed by sodium hypochlorite. The DOP of the adhesive resin was reduced by sodium hypochlorite and subsequently restored by applying sulfinic acid sodium salt.     

Long-term nanomechanical properties and gelatinolytic activity of titanium tetrafluoride-treated adhesive dentin interface

ObjectiveThis study investigated the effects of dentin pretreatment with 2.5% titanium tetrafluoride (TiF₄) on nanomechanical properties, and the in situ gelatinolytic activity of the dentin–resin interface, for up to 6 months.MethodsTwenty-four human teeth were prepared by exposing occlusal flat dentin surfaces, and were randomly assigned to experimental groups, according to application or non-application of a TiF₄ pretreatment, and to the adhesive systems (Clearfil SE Bond or Scotchbond Universal). Resin composite (Filtek Supreme Ultra) was built up incrementally on the teeth in all the groups. Then, the specimens were sectioned and randomly selected for evaluation at 24 h, 3 months and 6 months of storage time. The reduced modulus of elasticity (E_r) and the nanohardness of the underlying dentin, as well as the hybrid layer and the adhesive layer were measured using a nanoindenter. Gelatinolytic activity at the dentin–resin interfaces was assessed by in situ zymography using quenched fluorescein-conjugated gelatin at 24 h and 6 months. Statistical analyses were performed with ANOVA and Tukey’s tests.ResultsThere were no differences in E_r and nanohardness values between adhesives systems and pretreatment (p = 0.1250). In situ zymography showed significantly higher gelatinolytic activity after 6 months for all the experimental groups (p = 0.0004), but no differences between the adhesive systems (p = 0.7708) and the surface pretreatment (p = 0.4877). Significance: Dentin pretreatment with 2.5% TiF₄ followed by self-etching adhesive systems did not influence nanomechanical properties or gelatinolytic activity of the adhesive–dentin interface layers, over time.     

Dehydration and the dynamic dimensional changes within dentin and enamel

ObjectivesThe objectives of this study were to quantify the dimensional changes in dentin and enamel during dehydration, and to determine if there are differences between the responses of these tissues from young and old patients.MethodsMicroscopic digital image correlation (DIC) was used to evaluate deformation of dentin and enamel as a function of water loss resulting from free convection in air. Dimensional changes within both tissues were quantified for two patient age groups (i.e. young 18 ≤ age ≤ 30 and old 50 ≤ age) and in two orthogonal directions (i.e. parallel and perpendicular to the prevailing structural feature (dentin tubules or enamel prisms)). The deformation histories were used to estimate effective dehydration coefficients that can be used in quantifying the strains induced by dehydration.ResultsBoth dentin and enamel underwent contraction with water loss, regardless of the patient age. There was no significant difference between responses of the two age groups or the two orthogonal directions. Over 1 h of free convection, the average water loss in dentin was 6% and resulted in approximately 0.5% shrinkage. In the same time period the average water loss in the enamel was approximately 1% and resulted in 0.03% shrinkage. The estimated effective dehydration coefficients were ?810 μm/m/(% weight loss) and ?50 μm/m/(% weight loss) for dentin and enamel, respectively.SignificanceThe degree of deformation shrinkage resulting from dehydration is over a factor of magnitude larger in dentin than enamel.     

Bond strength of self-etch adhesives to pre-etched enamel

ObjectiveBond strengths of composite resin to enamel using four self-etch adhesive (SEA) systems were compared with the bond strength of an etch-and-rinse adhesive (ERA) system, for both polished enamel and enamel pre-etched with phosphoric acid. The objective was to determine if the pre-etching would increase the bond strengths of the SEA systems to match the ERA system.MethodsTen specimens were used for each adhesive to determine 24-h resin composite to enamel shear bond strengths (SBS) to polished (4000 grit) human enamel and this was repeated for the SEA systems for enamel that was pre-etched with phosphoric acid for 15 s. SEM analysis was made to assess the degree of etching and resin penetration into enamel for each of the adhesive systems. Data were analyzed by a two factor ANOVA with a Tukey HSD post hoc test.ResultsThe SBS to polished enamel for all four SEA systems were statistically significantly lower (p < 0.05) than the ERA control, but with pre-etched enamel there were no statistically significant differences (p > 0.05) between any of the adhesive systems. All four of the SEA systems demonstrated statistically significant increases in bond strength between bonding to polished and pre-etched enamel, ranging from 27% to 86%. The results of SEM analysis showed no differences in the resin penetration patterns of any of the adhesives for enamel that was etched with phosphoric acid.SignificancePre-etching enamel may enhance the bond strength of SEA systems to values comparable with those found with ERA adhesive systems, which may improve their overall performance in clinical use.     

Bonding strategies for MIH-affected enamel and dentin

Objectives

Aim of the present study was to evaluate resin composite adhesion to dental hard tissues affected by molar incisor hypomineralisation (MIH).

Influence of dentin pretreatment with 2.5% titanium tetrafluoride on inhibiting caries at the tooth-restoration interface in situ

ObjectiveInvestigate the effects of dentin pretreatment with 2.5% titanium tetrafluoride (TiF₄) aqueous solution followed by two-step self-etching (CLE/Clearfil SE Bond) and one-step self-etching adhesive systems (SBU/Single Bond Universal) on carious lesion inhibition at the tooth-restoration interface using an in situ model.DesignSixty-four cavities at the enamel-dentin junction of dental fragments were randomly distributed according to groups (n = 16): 1) TiF₄ + CLE; 2) TiF₄ + SBU; 3) CLE; 4) SBU. Cavities were restored using resin composite, and placed in intraoral palatal devices used by 16 volunteers for 21 days, to induce caries formation in situ. The fragments were then ground-flat to perform Knoop microhardness tests. Nine indentations were performed on each enamel and dentin substrate, subjacent to the restoration. Analysis of variance and Tukey’s test were applied.ResultsEnamel: groups receiving TiF₄ dentin pretreatment (regardless of adhesive system and tooth-restoration interface distance) presented higher hardness means at a depth of 25 μm from the outer tooth surface (p < 0.0001). Dentin: groups receiving CLE presented higher means when applying TiF₄ pretreatment, whereas groups restored with SBU presented higher means without pretreatment (p = 0.0003).ConclusionsDentin pretreatment with TiF₄ inhibited demineralization of the enamel interface in situ, regardless of the adhesive, and TiF₄ pretreatment followed by CLE application showed higher potential for inhibiting dentin demineralization at the interface.     

Effects of layering techniques on the micro-tensile bond strength to dentin in resin composite restorations

ObjectivesThe purpose of this work was to investigate the effects of layering techniques in resin composite restorations on the micro-tensile bond strength to the dentin of the occlusal cavity.MethodsHuman premolars were extracted and randomly divided into four groups. The occlusal enamel was then removed to expose a flat superficial dentin surface. Cavities 3.5 mm long and 3.5 mm wide were prepared to a depth 3 mm below the dentin surface. The adhesive Single Bond was applied according to the manufacturer's instructions. The teeth were then restored with Z100 resin composite as follows: Group 1 was restored in horizontal increments (three layers). Groups 2 and 3 were restored in different oblique increments (three layers). Group 4 was restored in oblique increments (four layers). After 24 h storage at 37 °C in water, all the teeth were sectioned to obtain bar-shaped specimens with a bonded surface area of approximately 0.9 mm × 0.9 mm. Dentin micro-tensile bond strength was measured at a crosshead speed of 0.5 mm/min. The results obtained were statistically analyzed using one-way ANOVA and SNK test at a significance level of P = 0.05. All fractures were then observed under a scanning electron microscope (SEM).ResultsThe results showed that there is a significant difference between the strength of the micro-tensile bonds to the dentin of occlusal cavities depending on which of the four layering restorative techniques was used (P < 0.01). SEM observation showed that failure patterns were most evidently interfacial cohesive failure.SignificanceLayering techniques in resin composite restorations affected the micro-tensile bond strength between the resin composite and the dentin. But the outcomes related to only Single Bond, as the same using other adhesives might have different outcomes.     

Monolithic crowns fracture analysis: The effect of material properties,cusp angle and crown thickness

ObjectivesThis study aimed to investigate the collective influence of material properties and design parameters on the fracture behavior of monolithic dental crowns.MethodsThree-dimensional (3D) models (N = 90) with different combinations of design parameters (thickness, cusp angle and occlusal notch geometry) and material type (lithium disilicate, feldspar ceramic, zirconia, hybrid resin ceramic and hybrid polymer-infiltrated ceramic) were developed for the failure analysis using extended finite element method (XFEM) to identify the stress distribution, crack initiation load, fracture surface area and fracture pattern. Analytical formulation, in vitro fracture tests and fractographic analysis of dedicated models were also performed to validate the findings of the XFEM simulation.ResultsFor all material types considered, crowns with a sharp occlusal notch design had a significantly lower fracture resistance against occlusal loading. In most of the models, greater crown thickness and cusp angle resulted in a higher crack initiation load. However, the effect of cusp angle was dominant when the angle was in the low range of 50° for which increasing thickness did not enhance the crack initiation load.SignificanceComparing the critical load of crack initiation for different models with the maximum biting force revealed that for the studied monolithic materials excluding zirconia, a design with a rounded occlusal notch, 70° cusp angle and medium thickness (1.5 mm occlusal) is an optimum combination of design parameters in terms of tooth conservation and fracture resistance. Zirconia crowns exhibited sufficient strength for a more conservative design with less thickness (1.05 mm occlusal) and sharper cusp angle (60°).     

Vertical and horizontal polymerization shrinkage in composite restorations

ObjectivePolymerization shrinkage developed in vertical and horizontal directions after light activation of light-curing composite restorative materials. The purpose of this study was to examine the effects of vertical and horizontal polymerization shrinkage on: (a) dimensional changes of resin composites in tooth cavities; (b) shear bond strengths to enamel and dentin; and (c) marginal gap width in a non-reacting Teflon mold.MethodsVertical and horizontal polymerization shrinkage in tooth cavities were measured immediately (3 min) after light activation. With the same time lapse, shear bond strengths to enamel and dentin and marginal gap widths in Teflon mold were also measured.ResultsThere was a significant correlation between vertical and horizontal polymerization shrinkage (r = 0.647, p = 0.043) in the tooth cavity. Composite materials which produced small vertical shrinkage also produced smaller horizontal shrinkage. Composite materials which produced small vertical shrinkage in the tooth cavity exhibited greater shear bond strengths to both enamel (r = −0.697, p = 0.025) and dentin (r = −0.752, p = 0.012). Composite materials which produced smaller horizontal shrinkage produced smaller marginal gap widths in the Teflon mold (r = 0.829, p = 0.003). No relationships were observed between horizontal shrinkage in the tooth cavity and shear bond strengths to both enamel and dentin (p > 0.05).SignificanceDuring the early stage of setting (<3 min) in tooth cavities, the vertical shrinkage of light-activated composite restorative materials was correlated with horizontal shrinkage.     

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.     

Nanoleakage,ultramorphological characteristics,and microtensile bond strengths of a new low-shrinkage composite to dentin after artificial aging

ObjectivesTo study the microtensile bond strengths and nanoleakage of low-shrinkage composite to dentin. The null hypotheses tested were (1) aging does not affect the bonding of low-shrinkage composite; (2) there is no difference in microtensile bond strengths and nanoleakage using different bonding strategies.Methods32 extracted molars were assigned to one of four groups: LS System Adhesive (LS, 3M ESPE); dentin etched for 15 s with phosphoric acid + LS System Adhesive (LSpa); Adper Single Bond Plus (SB, 3M ESPE); SB + LS Bond (SBLS). Occlusal dentin was exposed and restored with Filtek LS (3M ESPE). The samples were tested after 24 h or after 20,000 thermocycles and 6 months of aging. Teeth were sectioned with a cross-section of 0.8 ± 0.2 mm² and fractured at a crosshead speed of 1 mm/min. The data were submitted to ANOVA/Duncan's post hoc test, at p < 0.05. Five slabs from each group were selected and immersed in 50 wt% ammoniacal silver nitrate. Then, specimens were processed for SEM, the silver penetration was measured and data analyzed with Kruskal–Wallis at p < 0.05.ResultsNo statistically significant difference was found among the experimental groups for the factor dentin treatment (p = 0.165) and aging (p = 0.091). All experimental groups exhibit some degree of nanoleakage. There was no adhesion of Filtek LS applied directly over dentin surfaces treated with SB.SignificanceThe new low-shrinkage resin composite showed compatibility only with its dedicated adhesive. Pre-etching did not improve the bond strengths to low-shrinkage resin composite. Some degree of nanoleakage was evident in all groups.     

Morphological and chemical characterization of bonding hydrophobic adhesive to dentin using ethanol wet bonding technique

ObjectiveBisGMA, a widely used component in dentin adhesive has very good mechanical properties after curing, but is relatively hydrophobic and thus, does not adequately infiltrate the water wet demineralized dentin collagen. Developing techniques that would lead to optimum infiltration of the hydrophobic component into the demineralized dentin matrix is very important. The purpose of this study was to evaluate interfacial morphological and chemical characteristics of the resultant adhesive–dentin interface when the ethanol wet bonding technique is used with hydrophobic adhesives.Materials and methodsThe occlusal one-third of the crown was removed from six unerupted human third molars; a uniform smear layer was created with 600 grit SiC. The dentin surface was etched with 35% phosphoric acid for 15 s before applying BisGMA/HEMA model adhesive using either water wet or ethanol wet bonding technique. Five-micro-thick sections of adhesive/dentin interface specimens were cut and stained with Goldner's trichrome for light microscopy. Companion slabs were analyzed with SEM and micro-Raman spectroscopy.ResultsThe presence of ethanol in the demineralized dentin increased adhesive collagen encapsulation as indicated by trichrome staining. The SEM results confirmed that the ethanol wet bonding improved the quality of the interface. Micro-Raman spectral analysis of the dentin/adhesive interface indicated there was a gradual decrease in penetration of BisGMA component for specimens using water wet bonding, while relatively homogeneous distribution of the hydrophobic BisGMA component was noted in the interface with ethanol wet bonding.SignificanceWet bonding with ethanol instead of water permits better BisGMA infiltration improving the quality of interface. We speculate that the higher infiltration of hydrophobic BisGMA and better collagen encapsulation observed from the specimens using ethanol wet bonding would lead to more durable bonds because of improved resistance to hydrolytic attack.     

Effect of adhesive hydrophilicity and curing time on the permeability of resins bonded to water vs. ethanol-saturated acid-etched dentin

ObjectiveThis study examined the ability of five comonomer blends (R1–R5) of methacrylate-based experimental dental adhesives solvated with 10 mass% ethanol, at reducing the permeability of acid-etched dentin. The resins were light-cured for 20, 40 or 60 s. The acid-etched dentin was saturated with water or 100% ethanol.MethodHuman unerupted third molars were converted into crown segments by removing the occlusal enamel and roots. The resulting crown segments were attached to plastic plates connected to a fluid-filled system for quantifying fluid flow across smear layer-covered dentin, acid-etched dentin and resin-bonded dentin. The degree of conversion of the resins was measured using Fourier transform infrared spectroscopy.ResultApplication of the most hydrophobic comonomer blend (R1) to water-saturated dentin produced the smallest reductions in dentin permeability (31.9, 44.1 and 61.1% after light-curing for 20, 40 or 60 s, respectively). Application of the same blend to ethanol-saturated dentin reduced permeability of 74.1, 78.4 and 81.2%, respectively (p < 0.05). Although more hydrophilic resins produced larger reductions in permeability, the same trend of significantly greater reductions in ethanol-saturated dentin over that of water-saturated dentin remained. This result can be explained by the higher solubility of resins in ethanol vs. water.SignificanceThe largest reductions in permeability produced by resins were equivalent but not superior, to those produced by smear layers. Resin sealing of dentin remains a technique-sensitive step in bonding etch-and-rinse adhesives to dentin.     

Influence of the application of a pre-sintered surface augmentation on zirconia and lithium disilicate bonding using an adhesive composite resin cement

ObjectiveThe purpose of this laboratory study is to evaluate the application of a pre-sintered surface augmentation to zirconia (Zir) and lithium disilicate (LDS) ceramics on the delamination strength of adhesive resin cement. The applied surface augmentation was the ruling of lines to the pre-sintered surface of the ceramics.MethodsNinety milled Zir and sixty pressed LDS specimens (3 mm × 0.5 mm × 25 mm) were created and divided into five groups (n = 30). Group 1: Zir no surface treatment (control Zir-NT); Group 2: Zir airborne particle abraded (Zir-APA) with 30 μm CoJet; Group 3: Zir pre-sintered surface augmentation (Zir-SA); Group 4: LDS etched (control LDS-etched) and; Group 5: LDS with pre-sintered surface augmentation and etching (LDS-SA). A resin adhesive cement (3 mm × 1 mm × 8 mm) was then applied and cured to the ceramic specimens. The delamination strength values of the resin cement from the ceramic were recorded. The delamination strength data were analysed statistically using one-way ANOVA and Turkey post hoc analysis.ResultsThe mean delamination strength and standard deviation, when comparing only the Zir-SA to the resin cement were statistically different (p < 0.001); Zir-SA 63.42 ± 11.85, Zir-NT 26.82 ± 12.07, and Zir-APA 48.11 ± 17.85 MPa. Comparison between LDS groups were not significantly different (p = 0.193); LDS-etched 33.49 ± 16.07 and LDS-SA 28.83 ± 10.15 MPa. The delaminated Weibull modulus was highest for surface augmentation Zir specimens (m = 13.56) but decreasing to less than half for Zir-APA (m = 6.27) and Zir-NT (m = 5.68). The Weibull values for the LDS-SA and LDS-etched specimens was 5.63 and 3.38 respectively.SignificanceIncorporating the pre-sintered surface augmentation to zirconia improved the delamination strength and reliability of Zir to the resin cement but not for LDS.