The Journal of Adhesive Dentistry, 06/2018

Purpose: To assess whether bovine teeth can be used as viable alternatives for human teeth in tensile and shear bond strength testing. Materials and Methods: Articles were selected from Web of Science, PubMed, Scopus, LILACS-Bireme, and BBO electronic databases using keywords obtained from Medical Subject Headings (MeSH). Of 1540 potentially eligible studies, 157 were selected for full text analysis. Five independent reviewers (Kappa = 0.89) selected the studies, abstracted information, and assessed quality based on standardized scales. After the analysis, 78 studies comparing bovine teeth to human teeth were found. Only 18 studies comparing bovine and human substrates in bond strength tests were included in the systematic review and 13 in the meta-analysis. Two authors independently selected the studies, extracted the data and assessed the risk of bias. Mean differences were obtained by comparing tensile and shear bond strengths between human and bovine teeth (permanent and deciduous) and considering enamel and dentin separately (subgroup analysis). Statistical analysis was performed using RevMan5.1, with a random-effect model, at a 5% significance level. Results: No significant difference was found between human and bovine teeth in tensile tests (p = 0.41) for dentin (p = 0.86), but there was a difference for enamel (p = 0.01). Regarding shear bond strength, no significant difference was found between human and bovine teeth (p = 0.16) either for enamel (p = 0.07) or dentin (p = 0.68). Regarding shear bond strength on deciduous teeth, no significant difference was found between human and bovine substrates (p = 0.54), either for enamel (p = 0.42) or dentin (p = 0.05). Most studies were at high (low or unclear) risk of bias. Conclusions: In shear bond strength testing, bovine teeth can be a suitable alternative for permanent and deciduous human teeth, for both enamel and dentin substrates. However, they may not be suitable for enamel tensile bond strength testing. The findings are based on low quality studies (considerable heterogeneity) and should be interpreted with caution. Keywords: dentin, enamel, human tooth, bovine tooth, bond strength

Purpose: To systematically review the literature to analyze the influence of endodontic irrigating solutions on the bond strength of adhesives to coronal enamel or dentin. Materials and Methods: The PubMed/MEDLINE, Web of Science and Scopus electronic databases were used to select laboratory studies related to the research question, without publication year or language limits. From 2461 potentially eligible studies, 2451 were selected for full-text analysis, and 97 were included in the systematic review. Two authors independently selected the studies, extracted the data, and assessed the risk of bias. Pooling bond strength data were calculated using RevMan5.1 with random effects model (α = 0.05), comparing control (no endodontic irrigating solution) and experimental groups (one or more endodontic solutions). Results: No significant difference was found between the control and experimental groups (p = 0.12) in the overall meta-analysis and in the meta-analysis excluding chlorhexidine (p = 0.06). High heterogeneity was found in the meta-analyses. Most included studies in the systematic review were scored as having a high risk of bias. Conclusion: The different endodontic irrigating solutions evaluated showed no negative influence on the bond strength of dental adhesives to coronal dental substrates. Keywords: dental bonding, bond strength, adhesive, irrigation

Purpose: Adhesively luted partial ceramic crowns have been documented to be clinically more durable than direct composite restorations when minimally invasively restoring large defects (replacing two cusps or more) in posterior teeth. The clinical longevity of such restorations is largely determined by the tooth-preparation design, material selection and adhesive luting procedure. The most frequently recorded failure in medium- to long-term clinical trials is fracture of the restoration. The clinical protocol of adhesively luted partial ceramic crowns can be optimized by taking the etiology of these restoration fractures into account. In this article, a simplified nonretentive bonded ceramic partial crown concept is presented that aims to achieve an adhesively luted ceramic restoration - composite cement - residual tooth structure biomechanical unit that maximally resists functional aging. Therefore, the three primary components of the bonded restoration-cement-tooth complex must function in synergy. Methods, Results and Discussion: The clinical protocol starts with a tooth preparation designed to optimally absorb chewing stress. A stable, internally rounded and gently sloping tooth-preparation design with all outer margins inclined towards the tooth center assures a favorable and homogenous stress distribution with low cyclic fatigue subjected to the adhesive interface. This preparation form additionally enables the dental technician to fabricate a well-seating and -fitting ceramic restoration of uniform thickness. As restoration material, monolithic lithium-disilicate glass ceramic is sufficiently strong for the partial crown indication and preferred in order to decrease the fracture risk. Clinically essential for a long-lasting restoration is the optimal bond that can be obtained by combined micromechanical interlocking and chemical bonding of composite cement to hydrofluoric acid-etched and silanized glass ceramic. Conclusion: The clinical effectiveness of this nonretentive bonded ceramic partial crown concept is confirmed by the overall high success rate as well as the very low fracture and debonding rate, as was recorded in long-term clinical trials. Keywords: overlay, onlay, tooth preparation, glass ceramic, indirect restoration

Purpose: To evaluate two different techniques for glass fiber-reinforced resin post (FRC) insertion by assessing the stress distribution under polymerization shrinkage or masticatory loading and measuring the pull-out bond strength to dentin. Materials and Methods: A model of an endodontically treated maxillary central incisor was used for three-dimensional simulation with two conditions: conventionally cemented (FRC) and relined (RFRC). The volumetric solids were exported to analysis software (ANSYS 17.2, ANSYS) in STEP (Standard for the Exchange of Product Data) format. All contacts were considered perfectly bonded between the geometries. Numerical models received a load of 100 N (45 degrees) on the lingual surface. The composite cement polymerization shrinkage was simulated by thermal analogy to obtain Von Mises, maximum principal stress, and shear stress. For in vitro evaluation, a pull-out bond strength test (n = 20/N = 40) was performed (50 Kgf, 1 mm/min) after mechanical cycling (in water at 37°C, 84 N, 2 bar, 45 degrees, 106 cycles, 4 Hz), and failure analysis was subsequently performed. The results were analyzed using one-way ANOVA and Tukey's test (α 0.05). Results: The FRC group showed more stress concentration in the cement layer. The RFRC group [(32 ± 13); (288 ± 129)] presented better performance than the FRC group [(6 ± 7); (152 ± 87)] for stress distribution and bond strength (p 0.05). Adhesive and mixed failures occurred in both groups. Conclusion: Relined fiberglass posts reduced the stress generated by polymerization shrinkage and showed greater bond strength to dentin. Keywords: endodontic fiber post, finite element analysis, shear strength, shrinkage stress

Purpose: The aim of this ex-vivo study was to evaluate the load capacity of direct or indirect endodontically restored maxillary central incisors with Class III defects, with or without glass-fiber posts. Materials and Methods: Seventy-two extracted human maxillary central incisors were endodontically treated and bi-proximal Class III cavities were prepared. Specimens were randomly allocated to six groups (n = 12): direct restoration with composite (C); direct restoration with composite and additional glass-fiber post (CP); ceramic veneer restoration (V), ceramic veneer restoration and additional glass-fiber post (VP), ceramic crown restoration (Cr), ceramic crown restoration and additional glass-fiber post (CrP). Specimens were exposed to thermomechanical loading (TML: 1.2 million cycles, 1 to 50 N; 6000 thermal cycles between 5°C and 55°C for 1 min each), and subsequently linearly loaded until failure (Fmax [N]) at an angle of 135 degrees 3 mm below the incisal edge on the palatal side. Statistical tests were performed using the Kruskall-Wallis and Mann-Whitney U-Test. Results: During dynamic loading by TML, one early failure occurred in group C, CP, and CrP. Subsequent linear loading resulted in mean fracture load values [N] of C = 483 ± 219, CP = 536 ± 281, V = 908 ± 293, VP = 775 ± 333, Cr = 549 ± 258, CrP = 593 ± 259. The Kruskal-Wallis test showed significant differences of load capacity between groups (p 0.05). Mann-Whitney U-test revealed significantly lower maximum fracture load values of group C compared to group V (p = 0.014), after Bonferroni-Holm correction. Non-restorable root fracture was the most frequent type of failure. Conclusion: Endodontically treated maxillary central incisors with Class III defects directly restored with composite are as loadable as indirect crown restorations. Compared to full-coverage restorations, less invasive veneers appear to be more beneficial. Additional placement of glass-fiber posts shows no positive effect. Keywords: all-ceramic crown, Class III restorations, direct composite restorations, endodontically treated teeth, indirect restoration, post and core, veneers

Purpose: To evaluate the roles of MDP and NaF in the bonding resin of a two-step self-etch adhesive (2-SEA) on enamel bonding performance. Materials and Methods: The experimental 2-SEAs were composed of an MDP-containing self-etching primer and four different bonding resins which were MDP- and NaF-free (00), MDP-containing and NaF-free (M0), MDP-free and NaF-containing (0F), and MDP- and NaF-containing (MF) adhesives. Microshear bond strength (µSBS) to enamel and ultimate tensile strength (UTS) of the adhesive resin were determined. The morphological characteristics of the adhesive-enamel interface after acid-base challenge were observed using SEM to evaluate the acid-base resistant zone (ABRZ). Results: No decrease in μSBS was observed even after thermocycling (TC) in 00, 0F and MF. However, the μSBS of M0 significantly decreased after TC. The UTS of M0 significantly decreased after 1- and 180-day storage in water. SEM observations indicated that ABRZ was present in all groups. However, formation of erosion beneath the ABRZ was observed in M0 and 00, whereas formation of a slope without erosion was observed at the bottom of the ABRZ in MF. Conclusion: In the experimental 2-SEAs, the addition of MDP alone to the adhesive resin did not contribute to an improvement in enamel bonding durability and interfacial morphology, whereas the addition of NaF in the adhesive resin demonstrated an enhancement of the bonding durability and improvement of acid resistance at the bonded interface. Keywords: two-step self-etch adhesive, acid-base resistant zone, enamel, MDP, microshear bond strength, NaF

Purpose: To evaluate the effect of the chemical formulation of liners on the shear bond strength (SBS) between lithium disilicate veneering ceramic and zirconia core. Materials and Methods: Four experimental groups (n = 12) were designed according to liner composition: negative control group (lithium and phosphorus removed from the conventional liner), Li group (lithium added to the negative control group), P group (phosphorus added to the negative control group), and Li+P group as the positive control (conventional liner). After applying the liner, lithium disilicate was pressed on zirconia. Specimens were stored in distilled water (37°C, 24 h) before testing the SBS. To test the SBS, shear force was applied perpendicular to the lithium disilicate-zirconia interface. The differences in the SBS between the veneer lithium disilicate and zirconia substructure were evaluated with one-way ANOVA (significance level of 0.05). Results: The presence or absence of lithium and phosphorus influenced the efficacy of the liner. The negative control and P groups showed mainly cohesive failures, and the Li group mainly showed mixed failures. Both adhesive and mixed failures were observed in the Li+P group. The groups including lithium showed significantly higher SBS than the negative control or Li+P group (p 0.05). The group including phosphorus, which showed higher crystallinity, showed significantly lower SBS than the negative control and Li+P groups (p 0.05). Conclusions: The differences in the composition of the liner can affect the wettability and reactivity, and as a result, the SBS was different. Keywords: zirconia, lithium disilicate, liner, shear bond strength, liner composition

Purpose: To evaluate the effect of a polymerization accelerator on the microtensile bond strength (µTBS) of etch-and-rinse and self-etch adhesives to eugenol-contaminated dentin. Materials and Methods: Sixty flat dentin surfaces were prepared from human molars. Half of the specimens were restored with zinc oxide eugenol temporary cement (IRM) (eugenol-contaminated group) and the other half remained without restoration (control group). After 24-h storage, the cement was mechanically removed. Then the specimens in each group were further divided into three subgroups based on the application procedure of a polymerization accelerator (p-toluenesulfinic acid sodium salt; Accel): no application, 10-s application, or 30-s application. After air drying, the dentin surfaces were bonded with either a three-step etch-and-rinse adhesive (OptiBond FL) or a two-step self-etch adhesive (Clearfil SE Bond) and restored with composite. After 24-h water storage, the bonded specimens were subjected to the µTBS test. Data were analyzed by three-way ANOVA and Dunnett's T3 test (p 0.05). Results: The eugenol-contaminated groups had significantly lower µTBS than the control groups with both types of adhesives (p 0.05), and the application of Accel significantly increased the compromised µTBS to eugenol-contaminated dentin. Optibond FL presented significantly higher µTBS to eugenol-contaminated dentin than did Clearfil SE Bond (p 0.05). Conclusion: The application of a polymerization accelerator on eugenol-contaminated dentin prior to adhesive resin application increased the μTBS of both the three-step etch-and-rinse and two-step self-etch adhesive. Keywords: eugenol, polymerization accelerator, adhesive resin, bond strength

Purpose: This study compared bond strength, durability, and mechanical properties of luting cements for bonding zirconia: a resin-modified glass ionomer cement (RMGIC), a conventional composite cement, and two self-adhesive composite cements. Materials and Methods: The air-abraded zirconia specimens were assigned to 12 groups (n = 30) to prepare bonded specimens. Classification was based on the pre-conditioning selection: none; primers containing 10-methacryloyloxydecyl dihydrogen phosphate (MDP); universal adhesives containing MDP. Further classification was done according to the type of luting cement: RMGIC; conventional composite cement; MDP-free self-adhesive composite cement; MDP-containing self-adhesive composite cement. The shear bond strength (SBS) was measured after 24 h of water storage or aging with 20,000 thermocycles plus an additional 60 days of water storage at 37°C. The elastic modulus and three-point bending strength were determined, and a related Weibull analysis of the four luting cements was performed. Results: The choice of luting cement and aging significantly affected the SBS. Aging decreased the SBS in most groups, except for those that used MDP-containing primers plus conventional composite cements. RMGIC had SBS (before and after aging) that were similar to the MDP-free self-adhesive composite cement. Use of MDP-containing products prior to conventional composite cements provided the highest initial SBS. However, pre-conditioning with MDP-containing products failed to increase the SBS of RMGIC. RMGIC showed lower elastic modulus and three-point bending strength than did the three composite cements. Conclusions: RMGIC is an alternative to composite cements for luting zirconia restorations. Conditioning with a primer containing MDP combined with conventional composite cement is more reliable. Keywords: yttria-stabilized tetragonal zirconia, phosphate ester monomer, resin-modified glass-ionomer cement, composite cement, surface treatment, bonding