The Journal of Adhesive Dentistry, 02/2018

Purpose: To systematically review the literature on laboratory studies to determine whether the bond strength of adhesives to primary teeth is similar to that to permanent teeth. Materials and Methods: This systematic review was conducted according to PRISMA and registered in PROSPERO (CRD42014015160). A comprehensive literature search was conducted considering in vitro studies published up to June 2015 in the PubMed/MEDLINE database, with no limit on year of publication. Two reviewers independently selected papers, extracted data and assessed the risk of bias. From 422 eligible studies, 42 were fully analyzed. Thirty-seven studies were ultimately included in the systematic review and meta-analysis. A global comparison was performed with a random-effects model at a significance level of p 0.05, expressed by the difference of means between the groups. The mean bond strengths and standard deviations were tabulated and statistical analyses were conducted in RevMan 5.1 (The Cochrane Collaboration). Results: There was a significant difference between groups, with permanent teeth presenting higher bond strength than primary teeth (p = 0.0005). When the enamel and dentin substrates were considered separately, dentin presented the same trend (p = 0.002), while for enamel there was no significant difference between the dentitions (p = 0.11). The majority of the studies had a high bias risk. Conclusion: Adhesives have higher bond strengths when applied to permanent than to primary teeth. This difference was also valid when the comparison was made between permanent and primary dentin. Keywords: permanent dentition, deciduous tooth, enamel, dentin, bond strength, systematic review

Purpose: To evaluate the microshear bond strength (µSBS) of composite cement bonded to two machined glass ceramics and its durability, comparing conventional surface conditioning (hydrofluoric acid + silane) to a one-step primer (Monobond Etch & Prime). Materials and Methods: Machined slices of lithium disilicate ceramic (LDC) (IPS e.max CAD) and feldspathic ceramic (FC) (VITA Mark II) glass ceramics were divided into two groups (n = 10) according to two factors: 1. surface treatment: HF+S (ca 5% hydrofluoric acid [IPS Ceramic Etching GEL] + silane coupling agent [SIL; Monobond Plus]) or MEP (single-component ceramic conditioner; Monobond Etch & Prime); 2. storage condition: baseline (without aging; tested 24 h after cementing) or aged (70 days of water storage + 12,000 thermal cycles). Composite cement (Multilink Automix, Ivoclar Vivadent) was applied to starch matrices on the treated ceramic surfaces and photoactivated. A µSBS test was performed (0.5 mm/min) and the failure pattern was determined. Contact angle and micromorphological analyses were also performed. Data were analyzed with Student's t-test (α = 5%). Results: For both ceramic materials, HF+S resulted in higher mean µSBS (MPa) at baseline (LDC: HF+S 21.2 ± 2.2 > MEP 10.4 ± 2.4; FC: HF+S 19.6 ± 4.3 > MEP 13.5 ± 5.4) and after aging (LDC: HF+S 14.64 ± 2.31 > MEP 9 ± 3.4; FC HF+S: 14.73 ± 3.33 > MEP 11.1 ± 3.3). HF+S resulted in a statistically significant decrease in mean µSBS after aging (p = 0.0001), while MEP yielded no significant reduction. The main failure type was adhesive between composite cement and ceramic. HF+S resuted in the lowest contact angle. Conclusions: Hydrofluoric acid + silane resulted in higher mean µSBS than Monobond Etch & Prime for both ceramics; however, Monobond Etch & Prime had stable bonding after aging. Keywords: bond strength, conditioning, contact angle, hydrofluoric acid etching, surface treatment, thermocycling, vitreous ceramics

Purpose: To evaluate the effect of cusp inclination and light-curing time on the microshear bond strength (μSBS) between zirconia and a dual-cure self-adhesive composite cement and zirconia. Materials and Methods: Forty U-shaped specimens with angled surfaces, simulating different cusp inclinations (0 degrees, 20 degrees, and 30 degrees), were fabricated from zirconia blocks (Zenostar, Wieland). The specimens were randomly divided into two groups (n = 20) according to different light-curing times of the adhesive composite cements (20 s and 40 s). Three polyethylene tubes filled with a dual-curing self-adhesive composite cement (Multilink Speed, Ivoclar Vivadent) were bonded to the surfaces of each specimen with light-curing times of 20 s and 40 s. The μSBS was tested using a universal testing machine with a crosshead speed of 0.5 mm/min. Failure analysis was performed. Two-way ANOVA (cusp inclination and light-curing time) followed by two independent samples t-test were used for statistical analyses (α = 0.05). Results: The composite cement showed various bond strengths to angled zirconia surfaces (7.07 ± 1.69 to 13.91 ± 3.11 MPa). The μSBS between composite cement and 0-degree zirconia surfaces was statistically higher than that of 20- and 30-degree zirconia surfaces. The composite cement light cured for 40 s showed nonsignificantly higher μSBS than did the composite cement cured for 20 s. Adhesive failure was the most common failure mode. Conclusions: Cusp inclination affected bond strength between the dual-curing self-adhesive composite cement and zirconia. Keywords: cusp inclination, light-curing time, microshear bond strength, composite cement, zirconia

Purpose: To determine the microtensile bond strength (µTBS) of two 2-step self-etch adhesives (SEAs) to bur-cut and uncut enamel. Materials and Methods: The buccal and lingual enamel surfaces of 15 teeth were ground flat ("bur-cut" enamel), while the enamel surface of another set of 15 teeth was solely prophylactically cleaned ("uncut" enamel). Resin composite was bonded to the surfaces using the GPDM-based SEA OptiBond XTR (Kerr), the 10-MDP-based SEA Clearfil SE Bond (Kuraray Noritake), or the 3-step etch-and-rinse adhesive (E&RA) OptiBond FL (Kerr) that served as the gold-standard control. After 1-week water storage at 37°C, specimens were serially cut into 1-mm2 stick-shaped microspecimens, of which half per tooth were further subjected to 20,000 thermocycles (TC) prior to µTBS testing. Data were statistically analyzed using ANOVA and the post-hoc Tukey test. The interfacial ultrastructure of the GPDM-based SEA OptiBond XTR with uncut and bur-cut enamel was additionally characterized with transmission electron microscopy (TEM). Results: After 1-week water storage and upon TC aging, both SEAs bonded significantly (p 0.05) less effectively to both bur-cut and uncut enamel than did the control OptiBond FL, except when OptiBond XTR was bonded to bur-cut enamel; then a similarly high µTBS was recorded (p > 0.05). TEM interfacial characterization revealed a tight interaction of Optibond XTR with both bur-cut and uncut enamel. Conclusion: The best bonding efficacy to enamel is still achieved by etching with phosphoric acid, following an E&R approach, while the higher etching efficacy of the GPDM-based SEA may result in equally effective bonding, provided that the enamel is bur-roughened first. Keywords: adhesion, etching, functional monomer, microtensile bond strength, TEM

Purpose: To evaluate the microtensile bond strength (µTBS) and nanoleakage (NL) of several universal adhesives to eroded dentin (ED), using etch-and-rinse (ER) or self-etch (SE) strategies, and to characterize the surface using two pH cycling models to erode dentin (citric acid and a soft drink). Materials and Methods: Molars were eroded either by soft-drink or citric acid cycling, or were left untreated as control (SD). For each surface, the following adhesives were applied: 1. All-Bond Universal; 2. Ambar Universal; 3. Clearfil Universal; 4. Futurabond U; 5. One Coat 7 Universal; 6. Peak Universal Bond; 7. Prime&Bond Elect; 8. Scotchbond Universal; 9. Tetric n-bond Universal, and 10. Xeno Select. After application of the composite, specimens were sectioned into composite-dentin sticks and tested under tension (0.5 mm/min). Selected sticks from each tooth were used to assess NL. The occlusal dentin surfaces after erosive cycling were examined using SEM. Data were analyzed by three-way ANOVA and Tukey's post-hoc test (a = 0.05). Results: In ED, there was no difference in μTBS and NL between ER and SE strategies (p > 0.61). Most μTBS and NL values obtained for ED were, respectively, lower and higher than those for SD (p 0.01), being worse for citric acid ED (p 0.001). Citric-acid-eroded dentin showed more enlarged tubules, with partial loss of peritubular dentin when compared to soft-drink eroded dentin. Conclusion: The different pH cycling models reduced μTBS and increased NL of the composite/eroded-dentin interface; however, in ED, the performance of the universal adhesives did not depend on the adhesive strategy used. Keywords: tooth erosion, universal adhesive, bond strength, nanoleakage, scanning electron microscopy

Purpose: To evaluate the biomechanics of endodontically treated incisors restored with a fiberglass post and a CAD/CAM lithium-disilicate ceramic crown with/without a ferrule after thermal and mechanical aging. Materials and Methods: Twenty bovine incisors were divided into two groups (n = 10): 1. Fe, with a ferrule of 2 mm, and 2. NFe, without a ferrule. After endodontic treatment, the teeth were restored using a fiberglass post (Exacto 3, Angelus) and composite core (Tetric Ceram, Ivoclar Vivadent). They then received a CAD/CAM lithium-disilicate ceramic crown (IPS e.max CAD) luted using a self-adhesive composite (RelyX Unicem 2, 3M Oral Care). All specimens were subjected to 20,000 thermocycles and 2,400,000 simulated chewing cycles. Ceramic crown and root dentin strains (µS) were measured using strain gauges (n = 10) during 100-N loading before and after the thermal and mechanical aging, and upon fracture loading. The specimens were subsequently loaded to fracture (N). The stress distribution was analyzed using 3D individualized finite-element models created by micro-CT of experimental samples (n = 3). Strain data were analyzed using two-way ANOVA and Tukey's HSD test. Fracture resistance was analyzed using Student's t-test and fracture mode was analyzed using the chi-squared test (α = 0.05). Results: After aging, NFe exhibited significantly higher root dentin deformation (buccal: 1248.0 ± 282.8; lingual: 516.2 ± 195.0; p 0.001) than Fe (buccal, 554.0 ± 233.8; lingual: 311.8 ± 159.0; p 0.001). The deformation measured on ceramic crowns was not influenced by ferrule presence or aging process. Significantly higher fracture resistance (N) was observed for the Fe (1099.6 ± 214.8) than the NFe group (675.3 ± 113.8) (p 0.001). The NFe group revealed a lower fracture resistance:root strain ratio than did the Fe group. The stress levels on root dentin and fiberglass were lower for the Fe group. Conclusion: The NFe group showed increased root dentin strain after the aging process. The Fe group revealed higher fracture resistance, lower stress concentration on root dentin and fewer catastrophic fractures. Keywords: fiberglass post, ferrule, CAD/CAM ceramic crown, strain-gauge test, fracture resistance, finite element analysis, thermal cycling, fatigue

Purpose: To assess the influence of titanium tetrafluoride (TiF4) solution on the adhesion of composite cement to commercially pure titanium (cp Ti). Materials and Methods: cp Ti plates with dimensions of 30 mm × 8 mm × 1.5 mm were machined and polished. The specimens were divided into seven groups according to the surface treatment as follows: group 1: control (machined); group 2: sandblasted with 110 µm Al2O3; group 3: hydrofluoric acid (HF); group 4: TiF4 (5%-5 min); group 5: TiF4 (5%-10 min); group 6: TiF4 (10%-5 min); and group 7: TiF4 (10%-10 min). One type of composite cement (Multilink Speed) was applied to each group for assessing the bond strength using strain energy release rate (G-value, J/m2) test. SEM analysis and surface roughness evaluation of cp Ti were carried out after treatment. The debonded specimens were examined with a stereomicroscope and SEM. Data were analyzed by the Kruskal-Wallis and Dunn's multiple comparison tests. Statistical significance was set at the 0.05 probability level. Results: All the tested groups showed significantly higher bond strengths compared with the control group (p 0.05). Surface treatment of cp Ti with TiF4 (10%-10 min) showed higher bond strength compared with sandblasting and HF groups (p 0.05). Surface topography of treated cp Ti showed alterations in surface roughness and morphology. Conclusion: Adhesion between composite cement and cp Ti could be improved by using TiF4 (10%-10 min) solution prior to composite cement application as an alternative technique to sandblasting and HF. Keywords: bond strength, cp Ti, composite cement, strain energy release rate, surface roughness, titanium tetrafluoride

Purpose: To evaluate the effects on the surface properties (morphology, roughness, microhardness, composition) and bond strength to composite of four types of base cements (Equia-Fil/EQF, Angelus white MTA/MTA, Biodentin/BDN and IRM/IRM) when treated with phosphoric acid etching (PAE) or two self-etch adhesives (Select One Prime & Bond and Clearfil S3 Bond). Materials and Methods: Disk-shaped specimens were prepared and stored until complete setting. The surfaces before and after treatments were examined by stereomicroscopy, optical profilometry, ATR-FTIR, and LV-SEM/EDX. Interfacial bond strength with composite was evaluated under shear loading (SBS) using a conventional bonding resin (Heliobond) on silane treated (SIL) specimens as a reference. Failure mode was evaluated using stereomicroscopy. Results: PAE induced compositional changes on MTA and BDN, forming a phosphate-rich surface layer, probably composed of Ca-P salts. Dissolution of the amorphous cement fractions was evident in all materials. SPB and CSB did not show remarkable changes apart from an increase in Si content on MTA. On all bases, PAE resulted in the highest values for most of the roughness parameters. SPB and CSB showed lower or equal average roughness (Sa) and percentage of additional surface area contributed by the texture (Sdr) compared to the control in MTA and EQL. In terms of SBS, the highest β (Weibull shape parameter) in MPa were MTA-SIL = 5.79, BDN-PAE = 3.67, and MTA-PAE = 3.46, whereas the highest α (Weibull scale parameter) were EQF-CSB = 9.08, BDN-PAE = 5.13, and BDN-SIL = 4.67. Adhesive failures with less than 20% of the bonding area were encountered in IRM-PAE and SIL, EQF-CBS and MTA-SIL. Conclusion: Each base material requires a different procedure for optimal bonding with composite. Phosphoric acid etching and application of the conventional bonding resin Heliobond is the preferred procedure for composite bonding to MTA, BDN, IRM, but for composite bonding to CSB for EQF, the mild self-etch adhesive is preferable. Keywords: base materials, composite, roughness, elemental and molecular analysis, shear bond strength

Purpose: To evaluate the effect of two endodontic sealers on the push-out bond strength between fiber posts and root canal wall after different storage times and verify the influence of the endodontic sealers on the degree of conversion of composite cements. Materials and Methods: A total of 180 bovine teeth were endodontically treated using two endodontic sealers, eugenol-based (Endofill, Dentsply Maillefer) or epoxy resin-based (AH Plus, Dentsply Maillefer). Subsequently, the specimens were stored in 100% relative humidity at 37°C for 24 h, 6 or 12 months. After the respective storage times, the root canals were prepared for fiber post cementation using two composite cements, RelyX U200 (3M) or Multilink Automix (Ivoclar Vivadent). The push-out test and the failure analysis were performed. Degree of conversion was analyzed using a Raman microscope, for which samples were prepared using composite cement only or composite cement plus endodontic sealer. Finally, the push-out data were subjected to statistical analysis and the degree of conversion in percent was calculated. Results: AH Plus sealer obtained the highest push-out bond strengths at 24 h and 6 months. There was no difference between the push-out bond strengths of AH Plus and Endofill sealer at 1 year (p 0.05). Moreover, the degree of conversion was affected by the Endofill sealer. Conclusion: The use of a eugenol-based sealer is not recommended because it affects the push-out bond strength of fiber posts. AH Plus sealer and a post-endodontic waiting time of 24 h is recommended. Keywords: degree of conversion, endodontic sealer, eugenol, fiber post, push-out bond strength test