The Journal of Adhesive Dentistry, 02/2011

Purpose: To evaluate whether the correlation between in vitro bond strength data and estimated clinical retention rates of cervical restorations after two years depends on pooled data obtained from multicenter studies or single-test data. Materials and Methods: Pooled mean data for six dentin adhesive systems (Adper Prompt L-Pop, Clearfil SE, OptiBond FL, Prime & Bond NT, Single Bond, and Scotchbond Multipurpose) and four laboratory methods (macroshear, microshear, macrotensile and microtensile bond strength test) (Scherrer et al, 2010) were correlated to estimated pooled two-year retention rates of Class V restorations using the same adhesive systems. For bond strength data from a single test institute, the literature search in SCOPUS revealed one study that tested all six adhesive systems (microtensile) and two that tested five of the six systems (microtensile, macroshear). The correlation was determined with a database designed to perform a meta-analysis on the clinical performance of cervical restorations (Heintze et al, 2010). The clinical data were pooled and adjusted in a linear mixed model, taking the study effect, dentin preparation, type of isolation and bevelling of enamel into account. A regression analysis was carried out to evaluate the correlation between clinical and laboratory findings. Results: The results of the regression analysis for the pooled data revealed that only the macrotensile (adjusted R2 = 0.86) and microtensile tests (adjusted R2 = 0.64), but not the shear and the microshear tests, correlated well with the clinical findings. As regards the data from a single-test institute, the correlation was not statistically significant. Conclusion: Macrotensile and microtensile bond strength tests showed an adequate correlation with the retention rate of cervical restorations after two years. Bond strength tests should be carried out by different operators and/or research institutes to determine the reliability and technique sensitivity of the material under investigation. Keywords: bond strength test, clinical relevance, Class V restorations, data pooling

Purpose: To evaluate the MMP-inhibitory effect of chlorhexidine when incorporated in the primer of a two-step selfetching adhesive (Clearfil SE Bond). Materials and Methods: Powdered dentin made from human teeth was treated with Clearfil SE Bond primers containing chlorhexidine of different concentrations for 20 s or for 2 min. The collagenolytic activity of the dentin powder was assayed using fluorescein-labelled collagen. Results: Untreated dentin powder contains a low but measurable level of intrinsic activity, which was significantly inhibited by 0.05% chlorhexidine. Treating dentin powder for 20 s with SE Bond primers containing chlorhexidine (0.5%, 1.0%, and 2.0%) reduced the collagenolytic activities by 15.6%, 44.9%, and 56.7% respectively. When treated for 2 min, only SE Bond primer containing 2.0% chlorhexidine could inhibit the collagenolytic activity by 41.1%. Conclusion: When incorporated in a two-step self-etching adhesive primer (Clearfil SE Bond primer), chlorhexidine can partially maintain its inhibitory effect on MMPs. Keywords: chlorhexidine, matrix metalloproteinases, self-etching adhesives, bond degradation, collagenolytic activity

Purpose: To evaluate the effect of chlorhexidine on the presence of collagen in aged resin-dentin bonds produced on sound and caries-affected dentin. Materials and Methods: Flat dentin surfaces were obtained from 16 sound molars, from which 8 were microbiologically processed for induction of caries. Single Bond 2 was applied to both sound and caries-affected substrates. In half of the teeth assigned for 6-month storage in water, the phosphoric acid demineralized dentin was impregnated with 2% chlorhexidine before the application of the adhesive. Specimens (2 x 2 x 5 mm) were produced and stored in water for 24 h, or 6 months in either water or mineral oil. The specimens were subjected to histological processing and sections were stained with Goldner's Trichrome. The thickness of the zone of exposed collagen was measured by optical microscopy and the data were subjected to two-way ANOVA and Tukey's test (α = 0.05). Results: There was no statistically significant difference (p > 0.05) between sound and caries-affected dentin regardless of the storage condition. For both substrates, significantly greater collagen exposure was observed after 6 months in water. Chlorhexidine-treated groups resulted in similar collagen exposure to that of the control and 6 months in water groups (p > 0.05), while no increase of the exposed collagen zone was observed after mineral oil storage. Conclusion: Aging in water resulted in degradation of the resin-dentin bond, as demonstrated by the increase of the zone of exposed collagen. However, the degradation of the exposed collagen was decelerated in the presence of chlorhexidine. Keywords: dental caries, dentin, adhesive systems, collagen, chlorhexidine, longevity

Purpose: To evaluate the effect of variations in 2-hydroxyethyl methacrylate (HEMA) concentrations in an experimental comonomer blend on degree of conversion, water sorption, solubility, and ultimate tensile strength of adhesive resin. Materials and Methods: The effect of HEMA content (0, 15, 30, and 50%wt - control, G15, G30, and G50 groups, respectively) was tested in an experimental comonomer blend of bis-GMA, bis-EMA, TEG-DMA, and HEMA. The degree of conversion, polymerization rate, ultimate tensile strength, water sorption, and solubility of the adhesive resin blends were determined. Results: At 40 s of light activation time, groups G30 and G50 showed a decrease of 30% and 61%, respectively, in degree of conversion compared to control. Water sorption and solubility differed for all groups, and was statistically higher in G50. For ultimate tensile strength, the control and G15 groups showed statistically higher values than the other groups (p 0.05). Conclusion: Higher HEMA content increases dental adhesive resin degradation. Keywords: adhesive systems, HEMA, real-time infrared, polymerization kinetics, water sorption, solubility

Purpose: To evaluate the microtensile bond strength (µTBS) of resin sealer on enamel substrates after cariogenic challenge. Materials and Methods: Enamel blocks were obtained from human third molars and randomly divided into 6 groups (n = 10) according to enamel substrates (S: sound, CL: caries-like lesion, or CLTF: caries-like lesion + topical fluoride application) and sealant material (F: FluroShield, or H: Helioseal Clear Chroma). Sealants were placed on enamel surfaces, stored in 100% humidity (24 h, 37°C), and longitudinally sectioned into hourglass shapes. According to the groups, pH cycling was applied and the µTBS test was performed. The fracture patterns were assessed by SEM. Results: Regarding substrates, the highest µTBS values in MPa were observed for CLTF enamel (26.0 ± 7.6), followed by S (22.0 ± 7.4) and CL (15.5 ± 4.9). A significant interaction was found between material and pH cycling (p = 0.0395). F (23.9 ± 7.6) showed higher µTBS values than H (18.3 ± 7.5) when submitted to pH cycling. The majority of samples presented mixed failure. Conclusions: Enamel substrate significantly affected µTBS, with the highest values for remineralized caries-like enamel lesions. Furthermore, µTBS values were dependent on both materials and pH cycling. Keywords: preventive therapy, microtensile bond strength, fissure sealing, enamel, caries-like lesion, cariogenic challenge model

Purpose: To compare the bond strengths of young and old dentin using a single-bottle etch-and-rinse adhesive system with two acid-etching times (15 s and 30 s), and to examine the correlation between dentin hardness and bond strength. Materials and Methods: Twenty-four molars from 18- to 22- or 55- to 60-year-old patients were prepared to expose the occlusal dentin, cut into two equal parts, and assigned to four groups (G), varying the etching time (15 s and 30 s) and dentin age (young [Y]or old [O]): G15Y, G30Y, G15O and G30O. After etching, AdperSingleBond (3M ESPE) adhesive was applied and the tooth was built up with a composite (Filtek Z250). The specimens were prepared for the microtensile bond strength test (µTBS) at a crosshead speed of 0.5 mm/min and the interfaces were observed under SEM. Also, the Knoop hardness (KHN) of young vs old dentin was measured. Results: The mean (± SD) µTBS (MPa) were: G15Y = 45.9 (± 10.7)a, G15O = 34.1 (± 9.4)b, G30Y = 48.6 (± 14.3)a and G30O = 47.7 (± 11.0)a. Two-way ANOVA showed no difference in µTBS between young and old dentin. Old dentin acid etched for 15 s (G15O) had a lower µTBS than when acid etched for 30 s (G30O). Dentin hardness was higher for old dentin (67.0 ± 4.8KHN) than young dentin (63.7 ± 2.9KHN) (p 0.004). No correlation between µTBS and dentin hardness was observed. Resin tags were larger and more numerous for young dentin. The hybrid layer formed in intertubular old dentin (G15O) was very thin. Conclusion: Bonding to old dentin with 30 s of etching time resulted in higher bond strength and more homogeneous hybrid layer formation than dentin acid etched for 15 s. Keywords: acid etching, dentin bonding agents, old dentin, bond strength, scanning electron microscopy, microtensile bond strength, microhardness, bonding systems, dentin

Purpose: To investigate the effect of pressure and distance during air drying on the microtensile bond strength (µTBS) of a single-step self-etching adhesive to bovine dentin. Materials and Methods: A total of 36 bovine molars was used in this study. Twenty-seven teeth were used for µTBS testing and 9 teeth for the evaluation of the resin/dentin interface. The teeth were divided into 9 groups according to the variation in solvent evaporation pressure and the distance from the dentin surface. The adhesive was applied according to the manufacturer's instructions. The pressure was adjusted using a pressure regulator and the distance was fixed by measuring the distance from the tip of the syringe to the flat dentin surface. Each tooth was restored with a composite crown 6 mm in height and was cut to produce composite/dentin rectangular sticks with a cross-sectional area approximately 1 mm2 and 12 mm in length. The sticks were tested in tension until failure at a crosshead speed of 0.5 mm/min. The fracture pattern was evaluated using a stereomicroscope under 40X magnification. For the resin/dentin interface, the samples were gold sputtered and examined using SEM operated at 20 kV. Results: Two-way ANOVA showed that both pressure and distance from the dentin surface significantly affect the µTBS of the single-step self-etching adhesive (p = 0.001). The interaction of the two independent variables (pressure and distance from dentin surface) showed a significant difference (p = 0.001). Conclusion: On the basis of the µTBS data generated in this study, the single-step self-etching adhesive used proved to be technique sensitive. Keywords: dentin bonding agent, microtensile bond strength, resin composite

Purpose: The objective of this study was to evaluate the effect of thermocycling (TC), self-adhesive resin cements and surface conditioning on the microtensile bond strength (µTBS) between feldspathic ceramic blocks and resin cements. Materials and Methods: Fifty-six feldspathic ceramic blocks (10 x 7 x 5 mm) (Vita Mark II) were divided into groups according to the factors "resin cement" (3 cements) and "surface conditioning" (no conditioning or conditioning [10% hydrofluoric acid etching for 5 min + silanization]) (n = 8): group 1: conditioning+Variolink II (control group); group 2: no conditioning+Biscem; group 3: no conditioning+RelyX U100; group 4: no conditioning+Maxcem Elite; group 5: conditioning+ Biscem; group 6: conditioning+RelyX U100; group 7: conditioning+Maxcem Elite. The ceramic-cement blocks were sectioned to produce non-trimmed bar specimens (adhered cross-sectional area: 1 ± 0.1 mm2), which were divided into two storage conditions: dry, µTBS immediately after cutting; TC (12,000x, 5°C/55°C). Statistical significance was deterimined using two-way ANOVA (7 strategies and 2 storage conditions) and the post-hoc Tukey test (p 0.05). Results: Resin cement and thermocycling affected the µTBS significantly (p = 0.001). In the dry condition, group 5 (18 ± 6.5 MPa) presented the lowest values of µTBS when compared to the other groups. TC decreased the mean µTBS values significantly (p 0.05) for all resin cements tested (9.7 ± 2.3 to 22.1 ± 6.3 MPa), except for the resin cement RelyX U100 (22.1 ± 6.3 MPa). In groups 3 and 4, it was not possible to measure µTBS, since these groups had 100% pre-test failures during sectioning. Moreover, the same occurred in group 2 after TC, where 100% failure was observed during thermocycling (spontaneous failures). Conclusion: Hydrofluoric acid etching and silanization of the feldspathic ceramic surface are essential for bonding self-adhesive resin cement to a feldspathic ceramic, regardless of the resin cement used. Non-etched ceramic is not recommended. Keywords: bond strength, feldspathic ceramic, resin cements, ceramic surface treatment, thermocycling

Purpose: To evaluate the effects of carboxylic and phosphate functional monomers on the bond strength and durability of an acrylic resin joined to a magnetizable stainless steel and its component metals. Materials and Methods: Disk specimens (10 and 8 mm in diameter and 2.5 mm thick) were prepared from SUS XM27 stainless steel, high-purity iron, and chromium metals. The specimens were ground with abrasive paper, and divided into an unprimed control group and 4 groups primed with: 1. Alloy Primer (thione and phosphate); 2. Estenia Opaque Primer (phosphate); 3. Mr. Bond (aliphatic carboxylic acid); or 4. Super-Bond C&B Liquid (aromatic carboxylic anhydride). The disks were bonded with tri-n-butylborane (TBB)-initiated resin, and the shear bond strengths were determined both before and after thermocycling (20,000 X, 5°C - 55°C). The debonded surfaces were analyzed using Xray diffraction (XRD). Results: The Alloy Primer and Estenia Opaque Primer materials containing 10-methacryloyloxydecyl dihydrogen phosphate (MDP) effectively bonded the steel (30.3 to 32.4 MPa) and iron (33.6 to 34.8 MPa), whereas the four acidic primers bonded chromium (24.6 to 32.3 MPa). X-ray diffractometry detected corroded iron at the debonded interface. Conclusion: Bearing in mind the limitations of the present study, the use of two primers with MDP is recommendable for bonding SUS XM27 steel with TBB-initiated resin. Iron was considered to be a corrosive factor at the adhesive interface, although the associated bonding characteristics were adequate. Keywords: butylborane, carboxylic acid, chromium, iron, phosphate, stainless steel

Purpose: To evaluate the effect that fissure depth and enamel conditioning protocols have on penetration abilities of resin-based and glass-ionomer fissure sealants. Materials and Methods: Fifty extracted human molars were randomized into 10 experimental groups. Conditioning was performed as follows: groups I and VI, no pretreatment; groups II and VII, 10% polyacrylic acid and 37% phosphoric acid, respectively; groups III and VIII, self-etching adhesive; groups IV and IX, Er:YAG laser; groups V and X, Er:YAG laser/10% polyacrylic acid and laser/37% phosphoric acid, respectively. In groups I to V, teeth were sealed with a glass-ionomer material, and in groups VI to X a resin-based sealant was used. The sealed teeth were sectioned and the penetration ability was evaluated using scanning electron microscopy (SEM). Results: Pretreatment with a suitable acid resulted in superior penetration of glass-ionomer and resin-based sealant when compared with other conditioning protocols (p 0.0001), except for the teeth treated with both Er:YAG laser and acid. Both conditioning protocol and fissure depth significantly affected the sealant penetration (p 0.0001), but fissure depth had a greater impact on fissure penetration than did conditioning protocol. Conclusion: Resin-based and glass-ionomer sealing materials show similar potential for pit-and-fissure penetration. Penetration of a fissure sealant is largely influenced by the fissure depth. Regarding the conditioning protocol, a pretreatment with a suitable acid is essential to obtain an adequate penetration of a sealing material. Keywords: fissure sealant, unground enamel, conventional adhesive system, self-etching adhesive system, fissure morphology, glass ionomer, resin composites

Purpose: The aim of the study was to assess the in vitro bond strength (BS) of glass fiber posts (GF) and carbon fiber posts (CF) in the cervical, middle, and apical thirds of root canals cemented with RelyX-Unicem (RX) and Cement-Post (CP). Materials and Methods: Forty maxillary canines were divided into 4 groups (n = 10) according to the cement and post used: group 1: GF and RX; group 2: CF and RX; group 3: GF and CP; group 4: CF and CP. The push-out test was applied in the cervical, middle and apical thirds of each specimen to assess bond strength of the cement/post complex to the root canal wall. The data obtained were submitted to ANOVA (Bonferroni test, p 0.05), and fracture analysis was done with SEM. Results: The GF posts presented the best results when cemented with RX and with CP (p 0.05). RX presented the highest BS values for both GF and CF (p 0.05). For all the groups, BS was higher in the cervical third, followed by the middle and apical thirds. Fracture analysis showed a predominance of cohesive fracture of posts for RX, and a predominance of adhesive fracture between dentin/cement, and mixed failure mode for CP. Conclusion: GF posts cemented with RX presented the highest BS values in all root thirds. Keywords: fiber post, luting agent, push-out bond testing, root thirds

Purpose: To obtain survival data on 32 fiber-reinforced fixed dental prostheses which were inserted in our department and to rate the quality of these restorations on the basis of esthetic, biological, and functional parameters. Materials and Methods: Thirty-two patients with fiber-reinforced fixed dental prostheses were included in the study. The fiber frameworks were made of a polymer-monomer-preimpregnated continuous unidirectional glass fiber material. The survival times, failure events, and clinical parameters were recorded. Restorations in function without previous failure were classified as "Overall Survival". The classification "Functional Survival" was assigned in the event of minor failure and subsequent repair. Loss of the restoration was regarded as "Failure". The quality rating was performed using modified USHPS/Ryge criteria. Results: The follow-up interval ranged from 2 to 64 months with a median follow-up time of 18.2 months. Twentyfour restorations were classified as "Overall Survival", seven were classified as "Functional Survival", and one was classified as "Failure". The overall survival at the median follow-up time was 74.4%. For the majority, the quality rating (USHPS/Ryge criteria) yielded clinically excellent results in all categories. No restoration was rated as insufficient or poor. Conclusion: Fiber-reinforced composite fixed dental prostheses provide sufficient stability and very good esthetic, biological, and functional performance in the case of specific clinical indications. Keywords: fiber-reinforced fixed dental prostheses, fiber-reinforced composites, continuous unidirectional glass fibers, clinical performance