RESEARCH AND EDUCATION Effect of surface treatment and aging on bond strength of composite resin onlays Maria Cura, DDS, PhD,a Inmaculada González-González, DDS,b Victoria Fuentes, DDS, PhD,c and Laura Ceballos, DDS, PhDd Advances in adhesive dentistry ABSTRACT have increased the use of inStatement of problem. Additional polymerization of indirect composite resins enhances their direct restorations.1-4 They are physical properties but lessens the potential for chemical bonding. indicated for extensive cavities Purpose. The purpose of this in vitro study was to evaluate the influence of different surface because the anatomic form, treatments and 6-month water storage on the microtensile bond strength (mTBS) of composite resin proximal contacts, and interonlays. proximal contour are more Material and methods. Composite resin onlays (Filtek Z250) randomly received 6 different surface easily and accurately obtained treatments: (1) airborne-particle abrasion with 27-mm alumina particles+Adper Scotchbond 1XT than with direct composite adhesive application, (2) airborne-particle abrasion with alumina particles+silane application resin restorations.5,6 Moreover, (ESPE SIL)+Adper Scotchbond 1XT, (3) airborne-particle abrasion with alumina indirect restorations are less particles+Scotchbond Universal adhesive, (4) tribochemical silica coating with 30-mm particles prone to fracture7 and ensure a (CoJet Sand)+Adper Scotchbond 1XT adhesive, (5) tribochemical silica coating+silane application+Adper Scotchbond 1XT, and (6) tribochemical silica coating+Scotchbond Universal better seal because the impact adhesive. Onlays were luted to fresh composite resin specimens with RelyX Ultimate resin of polymerization shrinkage cement. Bonded assemblies were stored in water for 24 hours or 6 months at 37 C and 8 on adhesion is insignificant. subjected to the mTBS test. Additional surface-treated composite resin onlays were analyzed with Several properties of india contact profilometer to determine average roughness, and micromorphologic changes were rect composite resins have analyzed with scanning electron microscopy. contributed to their selection Results. Airborne-particle abrasion with alumina followed by Adper Scotchbond 1XT or Scotchbond by practitioners over ceramic Universal adhesive application provided the highest bond strength values at 24 hours. Lower values materials. Composite resins were obtained after tribochemical silica coating. After 6 months of artificial aging, airborne-particle induce less wear of the abrasion with alumina or silica-coated alumina particles followed by Scotchbond Universal opposing tooth9 and are application yielded the greatest bond strength results. Airborne-particle abrasion with alumina easier to repair intraorally.10 produced the highest roughness values and a more irregular surface. Moreover, better marginal Conclusion. Adhesive selection seems to be relevant to the mTBS of luted composite resin onlays quality11 has been reported, after 6 months of water aging, as specimens treated with Scotchbond Universal, after alumina as well as greater fatigue reairborne-particle abrasion or tribochemical silica coating, yielded the highest values and better aging stability. (J Prosthet Dent 2016;116:389-396) sistance12 and fracture resistance,11,13 especially before their physical and mechanical properties,15 also lessens the luting procedure.14 However, the additional polytheir potential for chemical bonding because the merization of indirect composite resins, that enhances Products used in this study provided by 3M ESPE. This study is part of a thesis submitted in partial fulfilment of doctoral degree requirements of author I.G.-G. a Fellow Researcher, Department of Stomatology, Health Sciences Faculty, Rey Juan Carlos University, Madrid, Spain. b Doctoral student, Department of Stomatology, Health Sciences Faculty, Rey Juan Carlos University, Madrid, Spain. c Assistant Professor, Department of Stomatology, Health Sciences Faculty, Rey Juan Carlos University, Madrid, Spain. d Associate Professor, Department of Stomatology, Health Sciences Faculty, Rey Juan Carlos University, Madrid, Spain. THE JOURNAL OF PROSTHETIC DENTISTRY 389 390 Volume 116 Issue 3 MATERIAL AND METHODS Clinical Implications Treating the surfaces of indirect composite resin onlays with airborne-particle abrasion with alumina or silica-coated alumina particles followed by Scotchbond Universal application produces the greatest bond strength after 6 months of artificial aging. quantity of residual free carbon double bonds decreases.16 Several surface treatments have been proposed to increase composite resin roughness to provide mechanical interlocking of the adhesive15,17-27 and to increase the number of unreacted methacrylate groups in the larger surface area created.28 Specifically, airborneparticle abrasion with alumina has been shown to improve bond strength to repaired composite resin29-32 and to indirect composite resin restorations.20,33 Also, tribochemical silica coating has achieved promising results as it provides a silica deposit on the composite resin surface together with micromechanical retention.34 This silica-modified surface is reactive to silane coupling agents that also react with the methacrylate groups of the adhesive resins.30-32,35 Nevertheless, when both airborne-particle abrasion treatments have been compared, the results are controversial and the advantage of these chemical interactions has not been clearly demonstrated.29-31,36 Moreover, the benefit of silane agents application, alone or followed by a bonding agent, to indirect composite resins is not completely clear5,31,37 and would imply additional clinical steps. Recently, a new family of dental adhesives known as ‘‘universal’’ or ‘‘multimode’’ adhesive systems has been introduced. These adhesives can be applied either with the etch-and-rinse or the self-etch technique.38-41 In the case of Scotchbond Universal (3M ESPE), it contains silane in order to allow the luting of indirect restorations with fewer clinical steps.42,43 The purpose of this in vitro study was to evaluate the influence of different surface treatments, including alumina airborne-particle abrasion and tribochemical silica coating combined with an adhesive application, preceded or not by a silane coupling agent, or using a universal adhesive, on the microtensile bond strength (mTBS) of composite resin onlays after 24 hours and 6 months of artificial aging. The effect of such treatments on composite resin roughness and morphology was also determined. The null hypothesis was that the bond strength of indirect composite resins would not be influenced by the intaglio surface treatment or by 6 months of water storage. THE JOURNAL OF PROSTHETIC DENTISTRY The composition and application technique of the materials tested are listed in Table 1. All were used according to the manufacturers’ instructions. Two-mm thick increments of a microhybrid composite resin (Filtek Z250, A3 shade; 3M ESPE) were layered into a Teflon mold (8 mm diameter × 4 mm high) to obtain composite resin onlays (n=36). Each increment was then photopolymerized for 40 seconds (Elipar S10; 3M ESPE, output of 1200 mW/cm2). The specimens were removed from the mold and polymerized in a unit (Lumamat 100; Ivoclar Vivadent AG) with program 3 at 104 C and high light intensity for 25 minutes. The surfaces to be bonded were wet ground on a polishing machine (Beta; Buehler) using 600 grit SiC abrasive papers and then ultrasonically cleaned for 10 minutes in distilled water and air-dried. After 24 hours of dry storage, the composite resin onlays randomly received 1 of the 6 treatments listed in Table 2. Software (Excel; Microsoft Corp) was used to generate random numbers from 1 to 6, according to the experimental treatment, that were assigned to each composite resin onlay. Thirty-six additional fresh composite resin cylinders (Filtek Z250, Shade A1; 3M ESPE) (8 mm in diameter and 4 mm high) were luted to the pretreated substrates with resin cement (RelyX Ultimate, Shade A1; 3M ESPE). Each composite resin specimen was cemented maintaining a constant force of 9.8 N during the first 5 minutes to standardize the luting agent thickness.44 Photopolymerization was carried out with the same polymerization unit for 20 seconds buccally, 20 seconds lingually, and thereafter for 40 seconds from the occlusal surface. Specimens were randomly distributed using the Excel software program, according to the storage period, 24 hours or 6 months, and, in both cases, kept at 37 C and 100% relative humidity until mTBS testing. The bonded assemblies were sectioned perpendicularly to the adhesive interface in the x and y directions (IsoMet 5000; Buehler), and beams with a cross-sectional area of approximately 1 mm2 were obtained. The exact dimensions of the beams were determined with a digital caliper (Mitutoyo Corp). Specimens were glued (Loctite Super Glue-3 gel; Henkel) to the fixtures of a universal testing machine (Instron 3345; Instron Co) and stressed at a tensile load of 0.5 mm/min until failure. The bond strength values were calculated in megapascals (MPa). A single operator (I.G.-G.) determined the failure modes using a stereomicroscope (Olympus SZX7; Olympus Corp) at ×40 magnification to classify them as cohesive (in cement, in fresh composite resin, or in composite resin onlay); adhesive (between cement and fresh composite resin, composite resin onlay and cement, or both); or mixed (simultaneous adhesive and cohesive fractures). The percentage for each failure mode was then Cura et al September 2016 391 Table 1. Chemical composition and application technique of tested materials Material Chemical Composition Application Technique Adper Scotchbond 1XT Adhesive (3M ESPE) Bis-GMA, HEMA, dimethacrylate resins, ethanol, water, photoinitiator, 5 nm spherical silica particles, methacrylate copolymer of polyacrylic and polyitaconic acids Apply adhesive for 20 seconds with vigorous agitation Gently air-thin for 5 seconds Photopolymerize for 20 seconds Scotchbond Universal Adhesive (3M ESPE) MDP monomer, dimethacrylate resins, HEMA, Vitrebond copolymer (3M ESPE), filler, ethanol, water, initiators, silane Apply adhesive for 20 seconds with vigorous agitation Gently air-thin for 5 seconds Photopolymerize for 20 seconds. ESPE Sil (3M ESPE) 3-methacryloxypropyltrimethoxysilane, ethyl alcohol, methyl ethyl ketone Apply and allow volatile silane solution to dry for 5 minutes Filtek Z250 Shade: A3, A1 (3M ESPE) Organic matrix: Bis-GMA, UDMA, Bis-EMA, TEGDMA. Filler: 60% in volumen (range of 0.19-3.3 mm) zirconia and silica Photopolymerize for 40 seconds RelyX Ultimate (3M ESPE) Base paste: methacrylate monomers, radiopaque, silanated fillers, initiator components, stabilizers, rheologic additives Catalyst paste: methacrylate monomers, radiopaque alkaline (basic) fillers, initiator components, stabilizers, pigments, rheologic additives, fluorescence dye, dark polymerization activator Scotchbond Universal adhesive Automix cement Photopolymerize for 80 seconds Bis-GMA, bisphenol-glycidyl methacrylate; HEMA 2, hidroxyethyl methacrylate; MDP, methacryloyloxydecyl dihydrogen phosphate; UDMA, urethane dimethacrylate; Bis-EMA, ethoxylated bisphenol A glycol dimethacrylate; TEGDMA, triethylene glycol dimethacrylate. Table 2. Experimental treatments Surface Treatment Application Technique Al2O3+1XT Airborne-particle abrasion with an intraoral device (RONDOflex Plus 360; KaVo) filled with 27 mm alumina particles (RONDOflex; Kavo) for 10 seconds at a pressure of 0.25 MPa from a distance of 10 mm. Following surface conditioning, they were rinsed copiously with water and dried with air. Adper Scotchbond 1XT adhesive (3M ESPE) was applied and photopolymerized for 20 seconds with the same LED unit. Al2O3+Si+1XT Airborne-particle abrasion was performed as described for the preceding group and a silane agent (ESPE Sil; 3M ESPE) was applied and left undisturbed for 5 minutes. Adper Scotchbond 1XT adhesive was applied and photopolymerized. Al2O3+Universal Specimens were airborne-particle abraded as described earlier followed by Scotchbond Universal adhesive application according to manufacturer’s instructions. Subsequently, the solvent was gently evaporated and photopolymerized for 20 seconds. Silica+1XT Tribochemical silica coating with 30 mm particles (Cojet Sand; 3M ESPE) using the parameters described for the Al2O3+1XT group, followed by Adper Scotchbond 1XT adhesive application. Silica+Si+1XT Tribochemical silica coating, followed by the same silane agent and Adper Scotchbond 1XT adhesive application. Silica+Universal Tribochemical silica coating, followed by Scotchbond Universal adhesive application. calculated. After tensile testing, specimens with representative fracture patterns of each group were selected and also observed under a scanning electron microscope (XL30 ESEM; Philips) after gold sputter-coating (SCD 005 Sputter Coater; Bal-Tec). Additional composite resin specimens (n=6) were prepared to determine the surface roughness and topographic changes induced by the following surface treatments: polishing with 600 grit SiC papers; airborneparticle abrasion with 27 mm alumina particles (RONDOflex); and tribochemical silica coating with 30 mm particles (CoJet Sand). The surface roughness was determined by the parameter average roughness (Ra). Five successive measurements in different directions were made on each treated specimen with a contact profilometer (Mitutoyo Surftest SJ 301; Mitutoyo); the cutoff value for surface roughness was 0.8 mm, and the sampling length for each measurement was 2.4 mm. Another 3 specimens corresponding to the surface treatments described earlier were sputter-coated with gold and observed under the same scanning electron microscope. Also, 10 quantitative elemental analyses were carried out per specimen using energy-dispersive x-ray spectroscopy (EDS) (XL-30; EDAX) at ×5000 magnification. Cura et al A 2-way ANOVA was performed to analyze the effect of the composite resin surface treatment and the aging period on the mTBS of luted onlays. Multiple comparisons were evaluated using the Tukey-Kramer test. The Student t test was applied to compare the mTBS values before and after aging for each surface treatment. The Ra was analyzed by 1-way ANOVA and the Tukey test. All statistical tests were performed with software (IBM SPSS v19; IBM Corp) (a=.05). RESULTS The means and standard deviations of the mTBS values yielded for each experimental group are summarized in Table 3. The 2-way ANOVA revealed that bond strength values were significantly influenced by the intaglio surface treatment (P<.001), the aging period (P<.001), and the interaction between these factors (P<.001). Post hoc comparisons among the experimental groups showed that 24 hours after the luting procedure, airborne-particle abrasion with alumina particles followed by Adper Scotchbond 1XT or Scotchbond Universal adhesive application yielded the highest mTBS mean values. However, the lowest results were obtained THE JOURNAL OF PROSTHETIC DENTISTRY 392 Volume 116 Issue 3 Table 3. Mean mTBS values in MPa (standard deviation) to different treated indirect composite resins after 24 hours and 6 months of water storage Surface Treatment 24 hours mTBS Silica+Si+1XT 6 months n mTBS 98 (18)* A 36 52.8 (12.9)* C 40 Al2O3+Si+1XT 76.9 (19.9)* BC 52 54 (16.2)* C 43 Al2O3+Universal 97.5 (18.9) A 45 91 (19.15) A 40 Silica+1XT 74.3 (13.5)* BC 46 55.7 (20.5)* C 48 Silica+Si+1XT 83.3 (15.6)* B 44 68.3 (24.8)* B 47 Silica+Universal 71.2 (18.3) C 64 76.6 (15.8) b 46 Al2O3+1XT Silica+Universal n n, number of microbars tested. Different letters indicate statistically different mTBS values among groups (P<.05) for each evaluation period (24 hours or 6 months). *Statistical differences between mTBS results after 24 hours and 6 months of water storage. Silica+1XT Al2O3+Universal Al2O3+Si+1XT Al2O3+1XT 0% 50% 100% Cohesive cement Mixed Adhesive mixed Adhesive composite onlay cement Adhesive cement/A1 for specimens subjected to tribochemical silica coating and Scotchbond Universal application. After 6 months of water storage, the highest bond strength values corresponded to those of specimens airborne-particle abraded with alumina particles before Scotchbond Universal adhesive application, followed by composite resins treated with silica coating and the use of the same adhesive. The Student t test showed significant differences in the mTBS after 24 hours and 6 months of aging for all the experimental groups, except for specimens treated with Scotchbond Universal after airborne-particle abrasion, regardless of the powder selected. No failures occurred before testing for any of the experimental groups evaluated. The failure mode distribution observed for the different experimental groups is shown in Figure 1. After 24-hour storage, failures were primarily cohesive in resin cement, as can be seen in Figure 2A, followed by mixed failures. However, after 6 months of artificial aging, mixed failure was the predominant type for all the experimental groups (Fig. 2B), except for specimens treated with Scotchbond Universal adhesive, which for the most part, showed cohesive failures in the cement (Fig. 2C). One-way ANOVA showed that surface roughness was statistically different for the 3 treatments tested (P<.001). The ranking of the surface roughness values (Ra, mm) from the lowest to the highest was as follows: 600-grit SiC paper polishing (0.21 ±0.07) < tribochemical silica coating (0.65 ±0.09) < alumina airborne-particle abrasion (1.70 ±0.6). The effect of the 600 grit SiC paper polishing and airborne-particle abrasion either with 27 mm alumina powder or 30 mm silica-coated alumina particles on the composite resin topography is shown in Figure 3. As shown in Figure 3A, the polishing procedure produced scratches in the same direction. In contrast, airborneparticle abrasion with alumina or silica-coated alumina powder significantly altered the composite resin surface creating undercuts, grooves and edge-shaped THE JOURNAL OF PROSTHETIC DENTISTRY A Silica+Universal Silica+Si+1XT Silica+1XT Al2O3+Universal Al2O3+Si+1XT Al2O3+1XT 0% Cohesive cement Adhesive cement/A1 50% 100% Mixed Adhesive mixed Adhesive composite onlay cement B Figure 1. Failure mode distribution in percentage (%) for treated composite resin specimens after 24 hours (A) and 6 months (B) of water storage. microretentions (Fig. 3B, C). However, these modifications were slightly more irregular and noticeable after airborne-particle abrasion with alumina (Fig. 3B). EDS microanalysis showed an identical element distribution on composite resin surfaces airborne-particle abraded with alumina or CoJet Sand, with 30% of Zr and with 34% of Si. For composite resin surfaces polished with SiC paper, the composition was essentially the same, 31% Zr and 35% Si. DISCUSSION The present study examined the effect of 6 surface treatments of an indirect composite resin on its adhesive properties when luted to a direct one by means of a resin cement and on stability after 6 months of artificial aging. According to the results, the null hypothesis Cura et al September 2016 Figure 2. Representative micrographs of debonded composite resin surfaces (original magnification ×150). A, Large area of cement layer from specimen airborne-particle abraded with alumina particles before Adper Scotchbond 1XT application and fractured after 24 hours. B, Cement remnants layering on composite resin surface from specimen treated by tribochemical silica coating before Adper Scotchbond 1XT application and fractured after 6 months of aging. C, Large cement layer from experimental group in which composite resin onlay was silica coated before Scotchbond Universal adhesive application and fractured after 6 months of aging. was rejected as the composite resin surface conditioning and the aging period did affect bond strength results. Cura et al 393 Figure 3. Scanning electron micrographs of treated resin composite resin surfaces (original magnification ×1000). A, Polished with 600 grit SiC papers. B, Airborne-particle abraded with 27 mm alumina particles. C, Tribochemical silica coating with 30 mm particles (CoJet Sand). After 24 hours of water storage, airborne-particle abrasion with alumina particles followed by the application of Adper Scotchbond 1XT or Scotchbond Universal adhesives was the surface treatment that provided the highest mTBS mean values. Other authors have previously reported the effectiveness of this surface treatment as it creates micromechanical THE JOURNAL OF PROSTHETIC DENTISTRY 394 retentions and increases the wettability of the adhesive.14,21,31,33 Curiously, tribochemical silica-coated composite resins displayed lower mTBS mean values, although both powders were selected with a similar particle size (27 mm for alumina and 30 mm for silica-coated alumina), because a more relevant influence on bond strength has been attributed to different particle sizes than to their different chemical composition.29 Accordingly, microroughness results were significantly lower for tribochemical silica-coated composite resins than for airborne-particle abraded alumina, and, as shown in Figure 3, tribochemical silica coating produced a less uneven surface.29-31 Moreover, no differences in composite resin composition were detected between airborne-particle abrasion with alumina or silica-coated alumina powders29 by EDS analysis. Therefore, the microretentive pattern created by the surface treatment would have a main function on composite resin bond strength at 24 hours after luting. Previous studies have reported similar bond strength values for both airborne-particle abrasion techniques,29-31,36 without any advantage for tribochemical silica-coating followed or not by a silane coupling agent application.30,31 Moreover, in a clinical situation, with the presence of enamel and/or dentin, silica coating may adversely affect composite resin bond strength22 or marginal quality.45 However, in the present study, the presence of natural tooth tissues was avoided as onlay composite resins were luted to fresh composite resin in order to detect the effect of the different surface treatments without the interference of microstructural variations of natural dental tissues.1 Furthermore, in a clinical situation the adhesive substrate is mainly composite resin, in that it is usually used as a base or liner underneath inlay and onlay preparations to avoid unnecessary tissue sacrifice to accommodate the geometric restrictions of indirect restorations and functions as pulpal protection during the interim restoration phase.2,3,46 The adhesive interfaces established during indirect composite resin luting should remain stable over time,5,34 although in most studies the specimens are tested shortly after the luting procedure.5,18,20 In the present study, the effect of the surface treatments tested on bond strength was evaluated not only after 24 hours but also after 6 months of water storage. This storage time was chosen as it is the one commonly used to analyze the degradation of resin dentin bonds.39-41 Moreover, specimens were not sectioned before their storage to simulate a clinical situation in which the inner part of the restoration is protected by the external one and to follow the methodology previously used.23 According to the results obtained, a significant decrease in bond strength values was registered after the aging procedure24,25 for all experimental treatments, THE JOURNAL OF PROSTHETIC DENTISTRY Volume 116 Issue 3 except for specimens in which Scotchbond Universal adhesive was applied after alumina or silica-coated airborne-particle abrasion. Several studies have also reported a tendency for lower bond strength after an aging procedure,25 while other authors find adhesive interfaces stable for different evaluation periods.22,26 The better performance detected for composite resins treated with the universal adhesive is supported by previous studies that have found that the adhesive system used is a main influence on the composite resin bond strength after an aging procedure.17,22,26 In agreement with our results, Tantbirojn et al27 reported that the application of Scotchbond Universal adhesive to repair freshly polymerized or aged composite resin restored the cohesive strength of the original monolithic composite resin, unlike Adper Single Bond Plus. The hydrophilicity of the adhesives has been suggested as a reason for interface degradation due to water absorption over time.47,48 A possible explanation for the stability of specimens treated with Scotchbond Universal could be the incorporation of 10-MDP monomer in its formulation. This functional selfetching monomer is considered hydrophobic and relatively hydrolytically stable, keeping water at a distance.48 It is also present in Clearfil SE Bond adhesive (Kuraray), which exhibited higher repair bond strength of composite resin than other adhesives such as AdheSE One F (Ivoclar Vivadent AG) and Adper Scotchbond Multi-Purpose (3M ESPE) after 1 and 12 months of storage.26 The 10-MDP molecule also has the ability to react with zirconia49 to obtain aging resistant adhesion.50 According to EDS microanalyses of the composite resin used, Filtek Z250, around a 30% of Zr a 32% of Zr was detected, regardless of the surface treatment performed (alumina or silica-coated alumina airborne-particle abrasion), which could allow a chemical interaction between them. Moreover, RelyX Ultimate resin cement incorporates a dark polymerization activator for Scotchbond Universal adhesive in the catalyst paste that may have contributed to its better performance; this would be especially true after aging as this dual polymerization has been described as slower.51,52 Regarding the effect of silane application on composite resin luting, no clear benefit was detected in the present study as previously reported.29,31,37,44 Specifically, a significant decrease in bond strength was observed after 6 months of water storage when it was included as a separate step, possibly related to the high hydrophilicity of silane coupling agents.52 Finally, no failures occurred before testing for any of the experimental groups evaluated, revealing a high mTBS of the luted indirect composite resins.36 Regarding the type of failure, higher numbers of cohesive fractures were observed in groups with higher bond strength Cura et al September 2016 values, which is in agreement with observations of Eliasson et al.25 For specimens tested 24 hours after the luting procedure, cohesive failure in resin cement predominated for all groups. This indicated that the bond strength after surface treatments approaches the fracture strength of the resin cement evaluated. However, specimens after 6 months of water aging exhibited more mixed failures (predominantly between cement and composite resin onlay), which is compatible with a higher hydrolytic degradation in the adhesive interface, except in specimens treated with Scotchbond Universal, which mostly showed cohesive failures in cement. CONCLUSIONS Within the limitations of this in vitro study, airborneparticle abrasion with alumina followed by Adper Scotchbond 1XT or Scotchbond Universal adhesive application obtained higher adhesive strength values after 24 hours of water storage. However, the selection of the adhesive acquires relevance after 6 months of water aging as airborne-particle abrasion with alumina particles, silica-coated or not, followed by Scotchbond Universal adhesive provided the highest bond strength values and better aging stability. REFERENCES 1. 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THE JOURNAL OF PROSTHETIC DENTISTRY 396 Volume 116 Issue 3 43. Lührs AK, Pongprueksa P, De Munck J, Geurtsen W, Van Meerbeek B. Curing mode affects bond strength of adhesively luted composite CAD/CAM restorations to dentin. Dent Mater 2014;30:281-91. 44. Mazzitelli C, Monticelli F, Osorio R, Casucci A, Toledano M, Ferrari M. Effect of simulated pulpal pressure on self-adhesive cements bonding to dentin. Dent Mater 2008;24:1156-63. 45. Onisor I, Bouillaguet S, Krejci I. Influence of different surface treatments on marginal adaptation in enamel and dentin. J Adhes Dent 2007;9:297-303. 46. De Oyagüe RC, Monticelli F, Toledano M, Osorio E, Ferrari M, Osorio R. Influence of surface treatments and resin cement selection on bonding to densely-sintered zirconium-oxide ceramic. Dent Mater 2009;25:172-9. 47. Feitosa VP, Sauro S, Ogliari FA, Ogliari AO, Yoshihara K, Zanchi CH, et al. Impact of hydrophilicity and length of spacer chains on the bonding of functional monomers. 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J Mater Sci Mater Med 2004;15:1013-20. Corresponding author: Dr Laura Ceballos Health Sciences Faculty Rey Juan Carlos University Avda. Atenas s/n 28922, Alcorcón, Madrid SPAIN Email: laura.ceballos@urjc.es Acknowledgments The authors thank Roberto García-Quismondo Castro and Miguel A. Garrido for their help with SEM and microroughness analyses, respectively. Copyright © 2016 by the Editorial Council for The Journal of Prosthetic Dentistry. Noteworthy Abstracts of the Current Literature The concept of platform switching to preserve peri-implant bone level: Assessment of methodologic quality of systematic reviews Monje A, Pommer B Int J Oral Maxillofac Implants 2015;30:1084-92 Purpose. To assess the methodologic quality of systematic reviews on the effect of platform switching upon peri-implant marginal bone loss. Materials and Methods. An electronic literature search of several databases was conducted by two reviewers. Articles were considered for quality assessment if they met the following inclusion criterion: systematic reviews that aimed at investigating the effect of platform switching/mismatch on marginal bone levels around dental implants. Two independent examiners evaluated the review publications using two quality-ranking scales (assessment of multiple systematic reviews [AMSTAR] and Glenny checklist). Descriptive statistics were used to summarize the results, and Cohen’s kappa coefficients were calculated to appraise interrater agreement of each checklist. Results. Overall, five systematic reviews (including three of them with meta-analysis) were evaluated. The mean AMSTAR score ± standard deviation was 8.4 ± 2.6 (range, 4 to 11), and the mean Glenny score was 10.8 ± 2.9 (range, 6 to 14), showing high statistical correlation (rs = 0.98, P = .005). Cohen interexaminer test yielded values of k = 0.88 and k = 0.86 for the AMSTAR and Glenny checklist, respectively. The AMSTAR items rated positive in 78%, whereas 18% met the criteria for “no” and 4% were “not applicable.” Only one review article met all criteria. Items of the Glenny checklist rated positive in 73% and negative in 27%. All but one study with the lowest quality scores (finding no difference) demonstrated a clinical benefit of implant platform switching in preserving the peri-implant marginal bone loss. Conclusion. According to the quality-ranking scales appraised, substantial methodologic variability was found in systematic assessment of benefits with the platform switching concept to preserve peri-implant bone level. High-quality systematic reviews, however, generally favored platform switching over platform matching. Reprinted with permission of Quintessence Publishing. THE JOURNAL OF PROSTHETIC DENTISTRY Cura et al
