The Journal of Adhesive Dentistry, 06/2009

The use of the ruby laser (693.4 nm) was first described in 1960, and it was applied for hard tissue ablation in 1964. Different wavelengths [Nd:YAG (1.065 µm), CO2 (9.6 µm), Ho:YAG (2.12 µm)] were consequently explored. Due to massive thermal side effects, these wavelengths caused increased temperature in dental pulp, as well as microcracks and carbonization. The use of this laser for dental hard tissue preparation was eventually abandoned. At the end of the 1980s, excimer lasers (ultraviolet) and the erbium laser (infrared) were developed, with the advantages of improved temperature control and smaller penetration depths. With the development of smaller devices and improved knowledge of how to limit damage to the surrounding tissues, new ablation techniques were established in the 1990s. There is still contradiction in the current literature, however, in that different wavelengths are advocated for hard tissue removal, and heterogeneity in laser parameters and power densities remain. In this review, the effects of the wavelengths presently used for cavity preparation are evaluated. We conclude that erbium lasers (Er:YAG and Er,Cr:YSGG) are most efficient and, with the right parameters, the thermal side effects are small. There is a substantial need for "gold standards", although this is difficult to establish in practice owing to different laser parameters (including pulse repetition rate, amount of cooling, energy delivered per pulse, and types of pulses) and target specificity (tissue interaction with sound or decayed enamel or dentin, and the extent of (de)mineralization) which influence tissue interaction. Keywords: laser, Er:YAG, Er, Cr:YSGG, Nd:YAG, Ho:YAG, CO2, cavity preparation, minimally invasive dentistry

Purpose: To elucidate how dentists access knowledge sources when choosing adhesive agents for bonded restoration and whether these resources influenced the selection of materials. Materials and Methods: A national survey was carried out involving dentists in South Korea. The questionnaire included the status of the operator, clinical techniques, and materials. A total of 12,193 e-mails were distributed, 2632 were opened by recipients, and 840 responses were collected. Results: For primary information resources in material selection, 55.8% (n = 469) of the responders mentioned continuing education. This selection criteria varied according to the working status of the clinician (p 0.0001). The choice of bonding system was influenced by of the length of the career (p 0.0001), and the preferred bonding systems differed according to the source of the information (p = 0.035). Conclusion: The popular bonding systems were not ranked according to the bonding strategy, but a preference was found for specific brands or manufacturers. To decrease the confusion of clinicians related to the selection of bonding materials, evidence-based guidelines need to be comprehensibly organized and efficiently approached in clinics. Keywords: adhesive dentistry, bonding, questionnaire, selection, information, evidence

Purpose: The etching of dental ceramics with a glassy matrix by means of hydrofluoric acid (HF) is highly effective and after the application of a silane coupling agent, a strong link between the adhesive and the ceramic is achieved. The purpose of this study was to investigate whether aqueous titanium tetrafluoride (TiF4) solution could be used as an alternative ceramic etchant or not. Materials and Methods: Seventy lithia-based all-ceramic specimens (IPS Empress 2, Ivoclar Vivadent) (diameter: 4 mm, height: 4 mm) were prepared and ultrasonically cleaned for 15 min in ethanol and deionized water, then divided into 1 control and 4 experimental groups (n = 14/group). The control group was acid etched with 4.9% HF for 20 s as described by the manufacturer. The experimental groups were treated with 2.5% TiF4 solution for 60 s, 2.5% TiF4 solution for 120 s and 5% TiF4 solution for 60 s, as well as 5% TiF4 solution for 120 s. Seven of the ceramic specimens in each group were luted to the other seven by a dual-curing cement (Variolink II, Ivoclar Vivadent,) with silane application (Monobond-S). After storage of luted specimens in deionized water at 37°C for 24 h, the specimens were embedded in plastic holders with cyanoacrylate, and the shear-bond strength (SBS) tests were performed with a Shimadzu universal testing machine at a crosshead speed of 0.5 mm/min. A one-way ANOVA and Bonferroni correction, followed by the Tukey test, were applied for statistical analysis. Scanning electron microscopic examination was performed to evaluate the pattern of debonding. Results: Significantly higher SBS values (p = 0.05) were obtained for the control group (28.71 ± 9.74). The SBS for 2.5%-60 s (25.25 ± 5.13) and 2.5%-120 s TiF4 (22.65 ± 5.68) were significantly higher than 5%-60 s (16.77 ± 3.92) and 5%-120 s TiF4 (18.54 ± 3.52) groups (p = 0.05). Differences between 60- and 120-s groups irrespective of TiF4 concentrations were insignificant (p > 0.05). Conclusion: Aqueous TiF4 solution exhibited similar shear bond strength values in comparison to commonly used HF and can be considered as an alternative ceramic etchant within the limitations of this preliminary report. Keywords: acid etching, titanium tetrafluoride, lithium disilicate, composite resin

Purpose: To investigate the effect of a phosphoric acid/sodium hypochlorite (NaOCl) mixture as a dentin conditioner on shear bond strength, the resin/dentin interface, as well as the surface area and tubular diameter of dentin. Materials and Methods: Thirty human molars were prepared for shear bond strength testing. The teeth were randomly divided into five groups according to the method of dentin conditioning. In group I, dentin was conditioned with 37% phosphoric acid, in group II dentin was conditioned with 37% phosphoric acid followed by application of 5.25% NaOCl, and in groups III, IV, and V, dentin was conditioned with a phosphoric acid/NaOCl mixture for 15, 30, and 60 s, respectively. A resin-based restorative composite disk was bonded to the occlusal surface of each tooth and shear bond strength was measured in a universal testing machine. The resin/dentin interface was evaluated using a scanning electron microscope (SEM). The surface area and tubular diameter for different conditioning methods were assessed using atomic force microscopy (AFM). The data were submitted to one-way ANOVA at a significance level of 0.05 followed by the Tukey-Kramer Multiple comparisons test. Results: Group III showed the highest shear bond strength value (36 MPa), which was significantly higher than groups I and II. SEM micrographs revealed hybrid layer formation for all groups except group II. AFM results showed that groups II and V have significantly higher surface areas and dentinal tubular diameters than other groups. Conclusion: The use of a phosphoric acid/NaOCl mixture as dentin conditioner improved the bond strength of an etch-and-rinse single-bottle adhesive to dentin. Keywords: sodium hypochlorite, dentin, adhesion, AFM

Purpose: To measure the demineralization capacity of 37% phosphoric acid and shear bond strength (SBS) of brackets attached on bovine enamel at different times after bleaching with 30% hydrogen peroxide. Materials and Methods: Four equally-sized pieces of each crown from 18 bovine incisors were randomly distributed among 7 groups (n = 10). After bleaching with 30% hydrogen peroxide for 1 h, specimens were stored in artificial saliva for 0 h, 24 h, or 1, 2, 3, or 4 weeks before bonding specimens to brackets. An unbleached group of specimens served as controls. Shear bond strength (SBS in MPa) was measured with a universal testing machine. Adhesive Remnant Index (ARI) scores were determined after failure of bracket bonds. To measure demineralized Ca2+, four 4 x 4 mm sections from each of 15 bovine incisors were randomly distributed among 4 groups (n = 15). Specimens were stored in artificial saliva for 0 h, 24 h or 7 days after bleaching and then immersed in 37% phosphoric acid solution. After 15 s, 30 s, and 60 s, 5-ml aliquots of solution were removed for spectrophotometry. Unbleached specimens served as controls. Results: Larger amounts of Ca2+ were extracted from the enamel by phosphoric acid up to 24 h after application of hydrogen peroxide, when there was also a significant decrease in bracket-enamel SBS. After 1 week, there were no changes in amounts of Ca2+ extracted, and SBS values returned towards unbleached values. Conclusion: Lower bracket-enamel SBS values at 24 h after bleaching are closely correlated with the larger amounts of Ca2+ extracted from the enamel. Keywords: 30% hydrogen peroxide, shear bond strength, brackets, decalcifying, phosphoric acid, spectrophotometry

Purpose: To systematically characterize the effect of time lapse, water storage, and selected contaminants on the bond strength of a nanofilled dental composite. Materials and Methods: Half-dumbbell-shaped samples were fabricated out of light-polymerizing composite resin. To function as substrates they were aged for 30 days in water. Prior to bonding, the substrates' surfaces were subjected to the following treatments: 1) Removing a 0.2- to 0.4-mm layer using a fluted carbide bur; 2) grit blasting with 50 µm alumina particles; 3) etching with phosphoric acid gel; 4) grit blasting followed by etching; 5) blasting with tribochemical particles followed by silane application; 6) sanding with 400-grit paper, air aging of the adherent half-sample before bonding; 7) surface contamination with saliva; 8) surface contamination with blood. In each group (n = 30), freshly polymerized (except in group 6) adherent half-samples were bonded to the substrate half-samples by a layer of unfilled adhesive resin. Fifteen full dumbbell-shaped specimens were subjected to tensile testing after 1 h and 15 after 7 days water storage. In a positive control group, freshly cured half-samples were bonded shortly after fabrication. The tensile strength was analyzed using Weibull statistics and presented in terms of the material's characteristic strength and shape parameter. Fractographs of the two weakest and strongest samples of each group were produced. The surfaces were searched to locate hackle, wake hackle and the origin of the fracture. Results: Surface roughness and time lapse increased the bond strength of the repaired specimens. All groups in which surface roughness was produced before bonding increased in repair strength. Post-bonding aging improved strength. Fractographs yielded interpretable data whenever larger surfaces of single phase bonding resin were present. Conclusion: 1) Roughening and etching an aged composite's surface prior to applying a coat of unfilled resin and the filled material increases repair bond strength by up to 100%. 2) The repair bond strength of a roughened aged composite is 25% to 30% inferior to the tensile strength of solid specimens. 3) After 7 days' storage in water, no detrimental effect could be seen from saliva or blood contamination if the surfaces were properly rinsed. Keywords: acrylic materials, repair, polymerization, bonding

Purpose: The purpose of this in vitro study was the evaluation of the bond strength and its durability to zirconia ceramic after using two phosphate monomer-containing primers. Materials and Methods: Plexiglas tubes filled with composite resin were bonded to zirconia ceramic disks (Cercon) which were air abraded (50 µm Al2O3 at 2.5 bar pressure) and ultrasonically cleaned in isopropanol for 3 min. Groups of 16 specimens each were bonded with Multilink Automix using either no primer (NO) or using a metal primer (AP: Alloy Primer, Kuraray) or a metal and zirconia primer (MZ: Metal/Zirconia Primer, Ivoclar Vivadent). Another group bonded with a phosphate monomer (MDP) containing resin (PF: Panavia F, Kuraray) served as control for an established bonding method to zirconia ceramic. Prior to tensile bond strength testing, subgroups of 8 bonded specimens were stored in distilled water (37°C) for either 3 or 150 days. Additionally, the 150-day specimens were thermocycled (TC) between 5° and 55° 37,500 times. Statistical analyses were conducted with the Wilcoxon rank sum test. Results: Without primer, the median initial bond strength of Multilink Automix to zirconia ceramic was relatively low (12.4 MPa). The primers improved the bond strength significantly (p = 0.05), increasing them to 38.5 MPa (Metal/Zirconia Primer) and 53.6 MPa (Alloy Primer). The Alloy Primer group did not differ significantly from the control group Panavia F with 51.8 MPa. After 150 days storage and TC, specimens without primer (NO) debonded spontaneously, while the other groups showed significantly reduced bond strengths ranging from 19.7 to 37.2 MPa. Conclusion: Using phosphate monomer-containing primers on air-abraded zirconia ceramic improves bonding to zirconia ceramic significantly. Keywords: artificial aging, zirconia ceramic, composite resin, tensile bond strength, ceramic primer, metal primer

Purpose: To assess the effects in vitro of sandblasting with 50-µm and 110-µm aluminum oxide grits and application of Goldbonder on bond strengths between porcelain and electroformed pure gold. Materials and Methods: Forty electroformed gold substrates and eight Ni-Cr alloy substrates were fabricated. All specimens were divided into 6 groups (8 specimens per group, the Ni-Cr alloy substrates were placed into group F), and exposed to various surface treatments: group A: No treatment; group B: sandblasted with 50-µm grit Al2O3; group C: sandblasted with 110-µm grit Al2O3; group D: sandblasted with 50-µm grit Al2O3 + Goldbonder; group E: sandblasted with 110-µm grit Al2O3 + Goldbonder; group F: sandblasted with 110-µm-grit Al2O3. Porcelain was built-up to form a cylindrical shape on the metal substrate surface and fired. All the metal-porcelain specimens were tested for shear bond strength. Results: The shear bond strength of group F was statistically higher than the other groups. Shear bond strengths of groups A to E were significantly affected by different surface treatments. Group A presented the lowest shear bond strength. In groups D and E, the mean bond strengths were statistically higher than groups A, B, and C. There were no differences between groups B and C, and groups D and E. Conclusion: Sandblasting with 50-µm or 100-µm grit aluminum oxide improved the bond strength between porcelain and electroformed pure gold. Goldbonder further improved the bond of the sandblasted gold substrate. Different grit sizes exerted the same effects on the gold-porcelain bond. Keywords: electroformed gold, porcelain, PFM, adhesion

Purpose: The effect of location and preparation design of abutment teeth and of preparation design on the survival and complication rate of metal-free, adhesively luted composite crowns (Artglass, Heraeus Kulzer) and their clinical performance was investigated in this controlled, randomized, prospective clinical study. Materials and Methods: After randomization, 114 single crowns (68 posterior, 46 anterior) were prepared either with a 0.5 mm chamfer finishing line or with a 0.5 mm shoulder combined with occlusal reduction of at least 1.5 mm. Buildups were made with a composite material, using the corresponding dentin adhesive. Crowns were manufactured on stone dies and intraorally adhesively luted with resin cement. Follow-up examinations were conducted after 1 month and 1, 2, 3, and 5 years. Documentation included failures and complications, occlusal contacts, plaque accumulation and patients' rating of esthetics and functionality. After 5 years, data for 83 single crowns had been obtained. Results: Within an observation period of 5 years, 18 complications occurred, including 13 major failures which resulted in replacement of the crowns, and 5 minor complications which could be repaired. All loosened crowns (n = 2) were successfully re-cemented. The Cox Regression did not reveal any effect of location or preparation design on complication rate. Calculation of the Kaplan-Meier survival curve on the basis of major failures indicated a probability of survival of 96% after 3 years and 88.5% after 5 years. Four Artglass crowns had no contact in static occlusion after 5 years and plaque accumulation was significantly higher than for control teeth. Esthetic and functional evaluation by patients revealed that acceptance was high. Conclusion: Metal-free composite crowns may be recommended for long-term temporary use. However, the complication rate and the increased plaque accumulation restrict the indication for permanent restorations. Keywords: clinical survival, complication rate, composite, single crown, adhesive cementation