Sillas Duarte

An in vitro evaluation of the long-term resin bond to a new densely sintered high-purity zirconium-oxide ceramic surface

STATEMENT OF PROBLEM Successful long-term bonding to zirconia ceramic remains a challenge, requiring special cements and surface roughening by airborne-particle abrasion, which might negatively affect the ceramic. PURPOSE The purpose of this study was to evaluate the shear bond strength (SBS) of composite resin cylinders to a modified zirconia surface using different luting techniques after thermal cycling. MATERIAL AND METHODS Composite resin (TPH3) cylinders with a diameter of 3 mm were bonded to zirconia ceramics (Procera Zirconia) with a modified surface (RZ) and a machined surface (MZ). Three different adhesive luting cements (Panavia F2.0, RelyX ARC, RelyX Unicem) in combination with and without airborne-particle abrasion (50-microm and 110-microm Al(2)O(3)) were used. RZ was bonded using all 3 cements with (50 mum) and without airborne-particle abrasion; with 110 microm, only Panavia F2.0 was used. MZ was bonded using only Panavia F2.0 with (50 microm, 110 microm) and without airborne-particle abrasion. SBS was tested in a universal testing machine (Instron) before and after 90 days of water storage and 20,000 thermal cycles (dwell time, 15 seconds). Statistical analysis was performed using a multifactorial ANOVA model with alpha=.05. RESULTS Mean SBS ranged from 10.1 to 20.0 MPa after 3 days and from 0.16 to 14.8 MPa after thermal cycling. Thermal cycling decreased SBS significantly. Airborne-particle abrasion significantly decreased SBS to the modified surface, regardless of cements used. SBS to the modified zirconia surface was significantly higher than to the machined surface. CONCLUSIONS SBS to the modified zirconia surface is higher than to airborne-particle-abraded, machined zirconia. Airborne-particle abrasion of the modified zirconia surface is not recommended.

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

OBJECTIVES To 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. METHODS 32 extracted molars were assigned to one of four groups: LS System Adhesive (LS, 3M ESPE); dentin etched for 15s 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 24h or after 20,000 thermocycles and 6 months of aging. Teeth were sectioned with a cross-section of 0.8+/-0.2mm(2) and fractured at a crosshead speed of 1mm/min. The data were submitted to ANOVA/Duncans post hoc test, at p<0.05. Five slabs from each group were selected and immersed in 50wt% ammoniacal silver nitrate. Then, specimens were processed for SEM, the silver penetration was measured and data analyzed with Kruskal-Wallis at p<0.05. RESULTS No 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. SIGNIFICANCE The 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.

Microtensile bond strengths and scanning electron microscopic evaluation of self-adhesive and self-etch resin cements to intact and etched enamel

STATEMENT OF PROBLEM The longevity of indirect adhesively cemented restorations is directly related to the bond quality of resin cements to dental tissues. Bonding to cervical enamel can generate significantly lower bond strengths than bonding to other enamel areas. The effect of enamel pretreatment on bond strengths of self-etch and self-adhesive resin cements to cervical enamel remains undetermined. PURPOSE The purpose of this study was to evaluate cervical enamel bond strengths of self-adhesive, self-etch resin cements according to acid pretreatment, using a total-etch resin cement as the control. MATERIAL AND METHODS The proximal surfaces of 20 extracted molars were sectioned to obtain 40 enamel rectangles with an area of 8.0 x 4.0 mm. The rectangular enamel specimens were assigned to 1 of 5 enamel experimental groups: intact enamel + RelyX Unicem (UN), etched enamel + UN (UNpa), intact enamel + Multilink (ML), etched enamel + ML (MLpa), and the total-etch-based RelyX ARC (RX; control group). Standard 8.0 x 4.0 x 6.0-mm composite resin blocks (Z250) were cemented to all specimens. The bonded enamel surfaces were sectioned into sticks with a cross-section of 0.8 +/-0.2 mm(2) and tested to failure in tension mode at a crosshead speed of 1 mm/min. The data were submitted to 1-way analysis of variance (ANOVA), followed by Tukeys HSD post hoc test (alpha=.05). Additionally, the enamel etching pattern was investigated for all experimental groups using field-emission electron microscopy. RESULTS Statistical analysis showed significant differences among different resin cements (P<.001) and phosphoric acid etching (P<.002). The highest mean (SD) bond strengths were obtained with UNpa (32.92 (4.23)) > RX (19.40 (9.47)). Acid etching of enamel before application of self-etch resin cement did not improve the mean bond strengths (SD) for self-etch resin cement [ML (5.38 (5.97)); MLpa (5.23 (1.1))]. Self-adhesive and self-etch resin cements yielded the lowest significant mean bond strengths (SD) when applied on intact enamel: UN (13.03 (2.82)) > ML (5.38 (5.97)). Scanning electron microscopy showed a consistent etching pattern for phosphoric acid-etched specimens. Self-etch and self-adhesive resin cements applied directly to intact enamel showed inconsistent areas of etching. CONCLUSIONS Etching cervical enamel surfaces resulted in significantly higher bond strengths for self-adhesive resin cement. For self-etch resin cement, etching did not improve bond strength.

Effect of low-elastic modulus liner and base as stress-absorbing layer in composite resin restorations

OBJECTIVES The aim of this study was to evaluate the effectiveness of liner and base materials to reduce the stress resulting from polymerization shrinkage. The null hypothesis tested was that the presence of low-viscosity liner and base materials under the composite resin restoration reduces the polymerization shrinkage stress. METHODS A quasi-three-dimensional photoelastic model of a second premolar with a class I preparation was restored using four experimental groups (n=7): RC, resin composite (Filtek Z250); FLRC, flowable liner (Filtek Flow)+resin composite restoration; VLRC, resin-modified glass-ionomer liner+resin composite restoration; and VBRC, resin-modified glass-ionomer base+resin composite restoration. The maximum shear stresses (tau(max)) were calculated along the adhesive interface in 13 predefined and standardized point locations. Data were submitted to one-way ANOVA, followed by a Tukeys post hoc test (p<0.05). RESULTS A significant difference was found among the experimental groups (p=0.001); therefore, the null hypothesis was rejected. The mean maximum shear stress was: 38.0kPa for RC, 52.1kPa for FLRC, 72.8kPa for VLRC, and 90.2kPa for VBRC. The polymerization shrinkage stress level from least to greatest was: RC<FLRC<VLRC<VBRC. The overall stress distribution in class I restoration indicated that stresses were primarily accumulated at the cavosurface and internal line angles. SIGNIFICANCE Using a flowable composite or resin-modified glass-ionomer as liner or base material under composite resin restoration increases the polymerization shrinkage stresses at the adhesive interface leading to a possible adhesive failure.

Influence of contamination and cleaning on bond strength to modified zirconia

OBJECTIVE To evaluate the influence of contamination and cleaning procedures on shear bond strength (SBS) to modified zirconia surfaces. METHODS One hundred zirconium-oxide ceramic disks fabricated with a rough modified surface (Nobel Bond), which allows more micromechanical interlocking for adhesive cementation, were divided into five groups. Groups were contaminated with organic (OC; human blood and saliva) and/or inorganic contaminants (IC; type IV dental stone). For cleaning, modified surfaces were etched with phosphoric acid for 1min (PA) or fired in a ceramic furnace up to 910 degrees C and cleaned in an ultrasonic bath in ethanol (FU). Following combinations of contamination and cleaning protocols were chosen: group 1: OC-PA; group 2: IC-FU; group 3: OC+IC-PA+FU; group 4: OC+IC-no cleaning; group 5: no contamination-no cleaning. Level of contamination and efficacy of cleaning were evaluated using X-ray photoelectron spectroscopy (XPS). Composite cylinders were bonded to the disks using dual curing adhesive resin cement (RelyX ARC). Fifty samples were subjected to 20,000 thermal cycles (TC). All samples were tested for SBS. Statistical analysis was performed using one-way ANOVA with alpha=0.05. RESULTS SBS ranged from 16.6 to 18.8MPa (non-TC) and 10.6-21.7MPa (TC). TC did not lower SBS, except for group 1. XPS showed that OC produced higher levels of carbon, nitrogen, and silica, whereas IC generated elevated levels of calcium, sulfur, carbon, and potassium. Cleaning with both procedures reduced contamination significantly. SIGNIFICANCE A combination of FU and PA is an efficient method for cleaning contaminated modified zirconia surfaces.

THE EFFECT of IMMEDIATE DENTIN SEALING on THE MARGINAL ADAPTATION and BOND STRENGTHS of TOTAL-ETCH and SELF-ETCH ADHESIVES

STATEMENT OF PROBLEM Sealing ability and bond strengths of total-etch and self-etch dentin adhesives used for immediate dentin sealing have not been assessed and established. PURPOSE The purpose of this study was to determine the effectiveness of immediate dentin sealing (IDS) using total-etch or self-etch dentin adhesives on microleakage and microtensile bond strength. MATERIAL AND METHODS Twenty recently extracted molars were selected, and standard MOD inlay preparations were made with the gingival margins located below the cemento-enamel junction. The teeth were assigned to 4 experimental groups (n=5) according to the indirect composite restoration cementation technique used: (1) immediate dentin sealing with Adper Single Bond (TEBI); (2) conventional adhesive cementation technique using Adper Single Bond (TEAI); (3) immediate dentin sealing using Adper Prompt L-Pop (SEBI); or (4) conventional adhesive cementation technique using Adper Prompt L-Pop (SEAI). The restored teeth were thermal cycled 1,000 times between 5 degrees and 55 degrees C and then immersed in 50% ammoniacal silver nitrate. Three specimens per restoration were evaluated for microleakage, according to predefined scores, and submitted to Friedmans test (alpha=.05). The specimens were then sectioned to obtain 0.8 +/-0.2-mm-thick sticks (with n ranging from 32 to 57 specimens) and submitted to microtensile bond strength (muTBS) testing. The obtained data were submitted to 2-way ANOVA test (alpha=.05). RESULTS None of the experimental groups demonstrated complete elimination of marginal microleakage. There were significant differences in microleakage of the tested adhesives (P>.001). IDS microleakage scores were similar to those obtained using the conventional cementation technique (CCT) for both adhesives. The highest mean bond strengths were obtained with TEBI (51.1 MPa), whereas SEAI showed the lowest mean bond strengths (1.7 MPa). IDS resulted in significantly higher bond strengths than CCT (P<.001). CONCLUSIONS Total-etch and self-etch adhesives have a significant effect on IDS. IDS resulted in high bond strengths for both adhesives; however, the microleakage was similar to that obtained with CCT. (J Prosthet Dent 2009;102:1-9).

Effect of Dental Finishing Instruments on the Surface Roughness of Composite Resins as Elucidated by Atomic Force Microscopy

Roughness increases significantly after finishing procedures. The aim of this study was to assess by the atomic force microscope (AFM) the effect of finishing instruments on the surface roughness of composite resins. A nanofiller composite resin (Filtek Supreme, 3M-F) and a microhybrid composite resin (Point 4, Kerr-P) were selected. The finishing procedures were done with a 30-blade carbide bur (C) and a 30-microm finishing diamond bur (D). Standardized specimens were produced and divided into six experimental groups (n=4) according to (1) composite resin, (2) absence of finishing (Mylar matrix-M), and (3) finishing instrument (FM, PM, FC, FD, PC, PD). The mean surface roughness was evaluated by AFM in the contact mode. FM and PM groups were assessed statistically by the Students T test, and FC, FD, PC, PD groups were submitted to variance analysis (ANOVA), both at 5% significance. The mean surface roughness values, in nanometers, were FM, 23.63 (b); FC, 283.88 (c); FD, 510.55 (d); PM, 12.52 (a); PC, 343.98 (c); PD, 531.64 (d). Microhybrid composite displayed less roughness than nanofiller composite in the absence of finishing procedures. The 30-blade carbide bur produced less roughness compared to the extra fine diamond bur.

Resin-bonded fixed partial dentures with a new modified zirconia surface: a clinical report.

This report describes the clinical application of a new modified zirconia surface. Resin-bonded fixed partial dentures were fabricated for nonprepared abutments, cemented, and evaluated for retention and esthetics. Initial evaluation of this new modified zirconia surface reveals acceptable mechanical and esthetic properties.

In vitro shear bond strength of dual-curing resin cements to two different high-strength ceramic materials with different surface texture

Objective. The purpose of this study was to evaluate the shear bond strength (SBS) of two dual-curing resin cements to two high-strength ceramics with different surface texture. Material and methods. Composite cylinders were bonded to aluminum oxide (A) and zirconium oxide (Z) ceramic disks with six different surfaces. Investigated surfaces were for both ceramics: dry-pressed Procera Crown (A1, Z1), machined Procera Bridge (A2, Z2), airborne particle abraded Procera bridge (A3, Z3). Additional surfaces were, for alumina, dry-pressed Procera Laminate (A4) and, for zirconia, two modified surfaces (Z4, Z5). Two adhesive resin cements were used (Clearfil Esthetic and RelyX ARC). SBS was tested in a universal testing machine before and after artificial aging by thermal cycling. Results. Mean SBS ranged from 6.1 to 38.4 MPa before and from 0.0 to 41.4 MPa after aging. Clearfil Esthetic in A3, A4, and Z3 performed better than RelyX ARC. Aging decreased SBS, except for Z1, Z4, and Z5. For alumina, A4 was higher in SBS than A2, but similar to A1 and A3. For zirconia, Z5 showed the highest SBS. Z4 was higher than Z2 and Z3, but similar to Z1. Conclusions. Shear bond strength to alumina and zirconia increases with surface roughness. The modified zirconia surface Z5 provides stable long-term shear bond strength and can be bonded to either of the two used cements.

Direct Resin-Based Composite Restorations — Clinical Challenges

With the increase in esthetic awareness and the widespread use of adhesive techniques, a resin composite has become the material of choice for anterior and posterior restorations. In spite of its advantages, polymerization shrinkage and the resulting stress are still a concern for clinicians. The shrinkage stress may cause cusp deflection, interfacial debonding or enamel cracks, leading to microleakage, post-operative sensitivity and secondary caries. The micro-mechanical nature of the interaction of dental adhesives with enamel and dentin is a result of the infiltration of resin monomers into the microporosities left by the acid etching and subsequent enveloping of the exposed enamel hydroxyapatite crystals and the dentin collagen fibers with the resulting polymer. The latest development in dental adhesives is based on simplification and reduced application time of the bonding procedure by using non-rinsing adhesives. These non-rinsing (or self-etch) adhesives do not require a separate acid-etch step as they condition and prime enamel and dentin simultaneously by infiltrating and partially dissolving hydroxyapatite to generate a resin-infiltrated zone with minerals and smear layer incorporated. In spite of their user-friendliness and low technique sensitivity, self-etch adhesives have resulted in low bonding effectiveness, behaving as semi-permeable membranes to allow movement of water across the dentin–resin interface and potentially leading to hydrolytic degradation. Recently, the role of metalloproteinases (MMPs), in inducing degradation of the dentin extracellular matrix components, has been highlighted in the literature along with the potential role of chlorhexidine in inhibiting the deleterious role of MMPs. The ultimate goal of a bonded restoration is to attain an intimate adaptation of the restorative material with the dental structure. This task is difficult to achieve as the bonding procedure is different for enamel and for dentin. The bonded interface undergoes degradation with time when a hermetic seal is not achieved. On the other hand, an improved sealing results in decreased post-operative sensitivity and higher resistance to the caries process. The stress resulting from the polymerization shrinkage of resin composites is also a factor that interferes with the bonding procedure as it may cause interfacial leakage and cusp deflection.