The Journal of Adhesive Dentistry, 06/2011

Purpose: To evaluate the effect on bond strength of 1, 2, or 3 coats of two one-step self-etching adhesives on dentin covered with two different smear layer thicknesses. Materials and Methods: Flat dentin surfaces from recently extracted third molars were wet ground with 60- or 600-grit SiC paper to produce smear layers of different thicknesses. Adper Easy Bond (3M ESPE) and Clearfil S3 Bond (Kuraray) were applied in 1, 2, or 3 consecutive coats after air drying each coat. ScotchBond Multi Purpose (3M) and Clearfil SE Bond (Kuraray) were used as controls. Composite resin crowns (Filtek Z250, 3M ESPE) were built up, stored for 24 h, and cut in x and y directions. Eight to twelve sticks (0.65 ± 0.05 mm2 of area) from the central area of each tooth were fractured in tension (0.5 mm/min). Sticks from each group were processed for interfacial micromorphological evaluation with SEM. Results: Three-way ANOVA revealed a significant interaction between factors (p 0.05). Tukey's post-hoc test showed that only when Adper Easy Bond was applied on dentin prepared with 600-grit SiC paper, microtensile bond strength was not significantly affected by the number of coatings. However, the effect of smear layer thickness was only statistically significant when the adhesives were applied in one coat, for both adhesives. When they were applied in two or three coats, smear layer thickness did not significantly affect bond strength (p > 0.05). Conclusions: The thickness of the smear layer affected the bond strength of both all-in-one adhesives. Additional coats can be beneficial to bond strength, especially with Clearfil S3 Bond. Keywords: smear layer, all-in-one adhesives, microtensile, bond strength, dentin

Purpose: To assess the influence of variations in the application technique of self-etching adhesive systems on the shear bond strength to dentin. Materials and Methods: The buccal surface of 255 extracted bovine teeth was ground to expose a flat dentin surface; the teeth were divided into four experimental groups. The self-etching adhesive systems One Up Bond F Plus, Clearfil SE Bond, Xeno III, and FuturaBond NR were used, and the etch-and-rinse adhesive Adper Single Bond 2 was used as the control group. One or two layers of the self-etching systems were actively or passively applied. Cylinders of composite resin were bonded to dentin, and after 24 h, specimens were shear tested in a universal testing machine at a crosshead speed of 1 mm/min. The data were submitted to two-way ANOVA, Dunnett's and Tukey's test (5%). Results: There were significant differences for the factors adhesive type, application method, and their interaction. All adhesive systems showed significant differences. The active application of two layers of self-etching bonding systems resulted in a significantly higher mean than the passive application method. Conclusion: The active application of self-etching adhesive systems tends to increase the dentin shear bond strength, and the influence of the application method depends on the tested adhesive. Keywords: self-etching adhesives, bond strength, dentin

Purpose: To evaluate the microtensile bond strength (µTBS) and acid-base resistant zone (ABRZ) of two dualcuring core systems to dentin using four curing modes. Materials and Methods: Sixty-four caries-free human molars were randomly divided into two groups according to two dual-curing resin core systems: (1) Clearfil DC Core Automix; (2) Estelite Core Quick. For each core system, four different curing modes were applied to the adhesive and core resin: (1) dual-cured and dual-cured (DD); (2) chemically cured and dual-cured (CD); (3) dual-cured and chemically cured (DC); (4) chemically cured and chemically cured (CC). The specimens were sectioned into sticks (n = 20 for each group) for the microtensile bond test. µTBS data were analyzed using two-way ANOVA and the Dunnett T3 test. Failure patterns were examined with scanning electron microscopy (SEM) to determine the proportion of each mode. Dentin sandwiches were produced and subjected to an acid-base challenge. After argon-ion etching, the ultrastructure of ABRZ was observed using SEM. Results: For Clearfil DC Core Automix, the µTBS values in MPa were as follows: DD: 29.1 ± 5.4, CD: 21.6 ± 5.6, DC: 17.9 ± 2.8, CC: 11.5 ± 3.2. For Estelite Core Quick, they were: DD: 48.9 ±5.7, CD: 20.5 ± 4.7, DC: 41.4 ± 8.3, CC: 19.1 ± 6.0. The bond strength was affected by both material and curing mode, and the interaction of the two factors was significant (p 0.001). Within both systems, there were significant differences among groups, and the DD group showed the highest µTBS (p 0.05). ABRZ morphology was not affected by curing mode, but it was highly adhesive-material dependent. Conclusion: The curing mode of dual-curing core systems affects bond strength to dentin, but has no significant effect on the formation of ABRZ. Keywords: curing modes, dual-curing core system, microtensile bond strength, acid-base resistant zone, dentin

Purpose: To evaluate the influence of bleaching on bond strength to enamel and subjacent dentin, and to determine whether a reduced application time (1 min) of the antioxidizing agent can obviate the compromised bond strength after bleaching. Materials and Methods: One hundred twelve bovine incisors were obtained, and the enamel and dentin surfaces were standardized to a thickness of 1 mm. The specimens were divided into two control groups (enamel and dentin without treatment) and 12 experimental groups (n = 10), based on the concentration of bleaching agents (carbamide peroxide 16% and hydrogen peroxide 35%), time interval between bleaching and restorative procedures (24 h; 24 h + sodium ascorbate (SA) 10%/1 min; 14 days), and substrate (enamel or dentin). All samples were submitted to the bleaching treatment on enamel. After the stipulated interval, a microshear test was performed. Results: The bleaching treatment compromised the bond strength to the enamel when the restoration was performed 24 h after the end of bleaching. The bond strength to dentin was not affected by bleaching. Conclusions: The SA 10% application for 1 min obviates the detrimental effect of bleaching on bond strength. The bleaching performed on enamel does not affect the bond strength to the subjacent dentin. Keywords: tooth bleaching, carbamide peroxide, hydrogen peroxide, bond strength, sodium ascorbate, adhesive system, enamel, dentin

Purpose: To evaluate the influence of provisional luting cements on the bonding performance of a resin-based self-adhesive luting cement to dentin vs that of currently used resin-based luting agents with different adhesion strategies. Materials and Methods: Forty-five prepared human molars were randomly and equally divided into three main groups according to the type of provisional luting cement applied: eugenol-containing provisional cement (Temp Bond, Kerr), eugenol-free provisional cement (Temp Bond NE, Kerr), and control where the provisionalization step was omitted. Each group was further subdivided into 3 groups based on the category of adhesive systems/ luting materials used: a two-step etch-and-rinse system (Single Bond/RelyX ARC; 3M ESPE) (RX), a two-step self-etching system (Clearfil Liner Bond 2V/ Panavia F; Kuraray) (PF), and a self-adhesive luting cement (Rely X Unicem; 3M ESPE) (RU). Finally, 9 groups of 5 teeth each were prepared for the microtensile test. Results: Two-way analysis of variance (ANOVA) and post-hoc Bonferroni tests revealed that definitive luting cement, provisional luting cement, and the interactions of these two factors had significant influences on dentin bond strength. The highest bond strength was obtained for PF (32.05 MPa), followed by RX (26.57 MPa) and RU (16.56 MPa) for the controls. Contamination with either eugenol-containing or eugenol-free provisional cement significantly decreased the bonding effectiveness of RX (19.08 and 19.69 MPa, respectively) and PF (14.21 and 16.67 MPa respectively) to dentin (p 0.05). RU showed comparable bond strength values before and after provisional cement (13.93 and 14.49 MPa, respectively) application (p > 0.05). Eugenol in provisional luting cement did not produce material-related alterations in the bonding performance of the resin luting cements tested (p > 0.05). Conclusion: Based on these results, the self-adhesive cement which was not influenced by the provisional cement application may be promising. However, long-term laboratory and clinical performance of this cement needs to be assessed before recommending it as an alternative to the technically more demanding approaches. Moreover, an effective surface cleansing procedure is critical to achieve a successful bond between the contaminated dentin and luting cement. Keywords: provisional cement, adhesive systems, microtensile bonding test

Purpose: To evaluate the surface pH, contact angle and microtensile bond strength (MTBS) of a resin-cement to feldspathic ceramic after various surface conditioning methods (SC). Materials and Methods: For pH measurements, 96 glass-ceramic disks were assigned into 12 groups (n = 8): SC1-pH: No ceramic surface conditioning (control); SC2-pH: hydrofluoric-acid (HF) 9% 1 min; SC3-pH: SC2-pH+wash/dry; SC4-pH: SC3-pH+silane; SC5-pH: HF 4% 1 min; SC6-pH: SC5-pH+wash/dry; SC7-pH: SC6 -pH +silane; SC8-pH: HF 5% 1 min; SC9-pH: SC8-pH+wash/dry; SC10-pH: SC9-pH+silane; SC11-pH: SC9-pH +neutralizer+wash/dry+sonic-cleaning; SC12-pH: SC11-pH+silane. For contact angle analysis, 40 disks were divided into 5 groups (n = 8): SC1-ca: no conditioning; SC2-ca: HF 9%+wash/dry; SC3-ca: HF 4%+wash/dry; SC4 -ca: HF 5%+wash/dry; SC5-ca: HF 5%+neutralizer+wash/dry+ultrasonic-cleaning. To evaluate the MTBS, 40 blocks were distributed into 4 groups SC (N = 10): SC1-bond: HF 9% 1 min+silane; SC2-bond: HF 4% 1 min+silane; SC3-bond: HF 5% 1 min+silane; SC4-bond: HF 5% 1 min+neutralizer+wash/dry+ultrasonic cleaning+silane. The resin cement was applied on the treated surfaces and bar specimens were produced that were submitted to 2 conditions: dry: immediate MTBS; TC: storage for 150 days and thermocycling 5000x. Fifty bar specimens were produced per group (n = 50). Contact angle and pH results were submitted to one-way ANOVA and Tukey's test (α = 0.05). Microtensile data were submitted to two-way ANOVA and Tukey's test (a = 0.05). Results: pH values were significantly higher for SC6-ph (11.5 ± 2.6) when compared to those of SC5-pH (2.7 ± 0.4), SC8-pH (2.7 ± 0.2) and SC2-pH (2.2 ± 0.2) (p 0.00, ANOVA). SC1-ca had the largest contact angle (48 ± 16 degrees) and SC3-ca the smallest (9.4 ± 7.7 degrees). The results of the MTBS test were as follows: independent of the storage condition, SC2-bond = SC1-bond > SC3-bond = SC4-bond. SC4-bond had the lowest MTBS value after TC (10.6 ± 2.6 MPa). Conclusion: The acid neutralization step appears to be dispensable, since the washing/drying promoted similar pH values. That condition promoted a high contact angle and unstable resin microtensile bond strength to glass ceramic. Keywords: glass ceramic, resin cement, pH, contact angle, bond durability

Purpose: To evaluate in vitro the influence of different cleaning methods after low-pressure air abrasion on the bond strength of a phosphate monomer-containing luting resin to zirconia ceramic. Materials and Methods: A total of 112 zirconia ceramic disks were divided into 7 groups (n = 16). In the test groups, disks were air abraded at low pressure (L) 0.05 MPa using 50-µm alumina particles. Prior to bonding, the disks were ultrasonically (U) cleaned either in isopropanol alcohol (AC), hydrofluoric acid (HF), demineralized water (DW), or tap water (TW), or they were used without ultrasonic cleaning. Disks air abraded at a high (H) pressure of 0.25 MPa and cleaned ultrasonically in isopropanol served as positive control; original (O) milled disks used without air abrasion served as the negative control group. Plexiglas tubes filled with composite resin were bonded with the adhesive luting resin Panavia 21 to the ceramic disks. Prior to testing tensile bond strength (TBS), each main group was further subdivided into 2 subgroups (n=8) which were stored in distilled water either at 37°C for 3 days or for 30 days with 7500 thermal cycles. Statistical analyses were conducted with two- and one-way analyses of variance (ANOVA) and Tukey's HSD test. Results: Initial tensile bond strength (TBS) ranged from 32.6 to 42.8 MPa. After 30 days storage in water with thermocycling, TBS ranged from 21.9 to 36.3 MPa. Storage in water and thermocycling significantly decreased the TBS of test groups which were not air abraded (p = 0.05) or which were air abraded but cleaned in tap water (p = 0.002), but not the TBS of the other groups (p > 0.05). Also, the TBS of air-abraded groups were significantly higher than the TBS of the original milled (p 0.01). Cleaning procedures did not significantly affect TBS either after 3 days or 30 days storage in water and thermocycling (p > 0.05). Conclusion: Air abrasion at 0.05 MPa and ultrasonic cleaning are important factors for improving bonding to zirconia ceramic. Keywords: zirconia ceramic-resin cement, bonding, cleaning methods

Purpose: Existing composite restorations on teeth are often remade prior to the cementation of fixed dental prostheses. The aim of this study was to evaluate the effect of static and cyclic loading on ceramic laminate veneers adhered to aged resin composite restorations. Materials and Methods: Eighty sound maxillary incisors were collected and randomly divided into four groups: group 1: control group, no restorations; group 2: two Class III restorations; group 3: two Class IV restorations; group 4: complete composite substrate. Standard composite restorations were made using a microhybrid resin composite (Anterior Shine). Restored teeth were subjected to thermocycling (6000 cycles). Window preparations were made on the labial surface of the teeth for ceramic laminate fabrication (Empress II). Teeth were conditioned using an etch-and-rinse system. Existing composite restorations representing the aged composites were silica coated (CoJet) and silanized (ESPE-Sil). Ceramic laminates were cemented using a bis-GMA-based cement (Variolink Veneer). The specimens were randomly divided into two groups and were subjected to either static (groups 1a, 2a, 3a, 4a) or cyclic loading (groups 1b, 2b, 3b, 4b). Failure type and location after loading were classified. Data were analyzed using one-way ANOVA and Tukey's test. Results: Significantly higher fracture strength was obtained in group 4 (330 ± 81 N) compared to the controls in group 1 (179 ± 120 N) (one-way ANOVA, p 0.05). Group 1b survived a lower mean number of cyclic loads (672,820 cycles) than teeth of groups 2b to 4b (846x103 to 873x103 cycles). Failure type evaluation after the fracture test showed predominantly adhesive failures between dentin and cement, but after cyclic loading, more cohesive fractures in the ceramic were seen. Conclusion: Ceramic laminate veneers bonded to conditioned aged composite restorations provided favorable results. Surface conditioning of existing restorations may eliminate the necessity of removing aged composite restorations. Keywords: biomimetics, cementation, ceramic veneer, cyclic loading, esthetic dentistry, glass ceramic, laminate, resin composite, silica coating, surface conditioning

Purpose: This study investigated the peel strength of two different soft liners to a polymethylmethacrylate (PMMA) denture base resin before and after thermocycling. Materials and Methods: The silicone-based soft liner materials tested were Molloplast B and Permaflex; the denture base material was a heat-cured acrylic resin, Meliodent. A total of 40 specimens was prepared using rectangular molds with dimensions of 100 x 10 x 2 mm for PMMA and 150 x 10 x 2 mm for soft liners, as described in ASTM-D903-93. For each of the liner materials, 10 specimens were packed against a cured PMMA denture base surface as recommended by the manufacturers. The other 10 specimens were packed against PMMA denture base dough and processed together. In each group, 5 of the specimens were tested directly, while the other 5 were thermocycled in a water bath (5°C to 55°C; 3000 cycles) before testing. Peel testing was performed using an Instron testing machine. Results: The results revealed that peel strength values of the Permaflex specimens prepared according to the manufacturer's recommendations were significantly higher than those of Molloplast B (p 0.05). However, when packing was done against uncured PMMA dough, the difference between the specimens of two liners was not significant. Thermocycling led to significant decreases in the peel strength of both Permaflex liner specimens packed against cured/uncured PMMA resin surfaces (p 0.05), whereas this process did not affect the strength of Molloplast B specimens. Conclusion: Results indicated that the material Molloplast B was superior to the material Permaflex in terms of peel strength when the specimens were simultaneously polymerized with PMMA and thermocycled. Keywords: peel strength, PMMA, silicone soft liners, thermocycling

Purpose: The aim of this retrospective clinical study was to evaluate the performance of direct composite restorations that were placed in patients with severe tooth wear requiring an increase of the occlusal vertical dimension. Methods and Materials: Eighteen patients with severe tooth wear, who had been treated in a private practice between April 1996 and July 2007, were selected. All subjects had been treated with direct composite resin restorations in increased vertical dimension using a three-step etch-and-rinse adhesive system and a hybrid composite resin. From the dental records, information about re-intervention and replacement of restorations was obtained. Patients were then clinically examined to evaluate the status of the restorations and interviewed about their satisfaction with the restorative treatment using a Visual Analogue Scale (VAS). Results: Eighteen patients (16 male, 2 female with an average age of 44.8 years) with severe tooth wear were included in the study. Time since treatment ranged from 6 months to 12 years and the mean observation time was 3.98 years. Of the 332 restored teeth, 23 restorations showed failures (6.9%). Eight restorations (2.4%) showed major fractures, 11 restorations (3.3%) showed minor fractures, and four restorations (1.2%) failed due to secondary caries. VAS data on a scale of 0 to 10 revealed high patient satisfaction with this type of restoration (mean 9.0). Conclusion: Treatments with direct hybrid composite restorations placed in an increased occlusal vertical dimension showed good clinical performance in patients with severe tooth wear. Keywords: tooth wear, composite, treatment, occlusal vertical dimension