The Journal of Adhesive Dentistry, 02/2002

The current trend in the development of dentin adhesives attempts to simplify bonding steps and make them more user-friendly. However, optimizing speed and efficiency should be accomplished without major tradeoffs in the quality or durability of resin bonds. Although dentin adhesives have improved tremendously over the past decade, postoperative sensitivity, incomplete marginal seal, premature bond degradation, biocompatibility, and compromised bonding to abnormal substrates are still considered potential problems associated with their use. Advances in different scientific disciplines will enrich the pool from which ideas may be drawn in designing future dentin adhesives. It is probably on the molecular level that we will see the greatest expansion of horizons. With the advances in biomimetics, future dentin adhesive monomers may contain domains derived from protein-based, underwater bioadhesives secreted by aquatic animals such as mussels and barnacles, making them less dependent on the surface energy of the bonding substrates as well as less susceptible to hydrolytic degradation. As adhesive joints produced by contemporary adhesives are brittle in nature, future adhesive design may incorporate biomimetic intermediate-strength domains that can undergo stepwise reversible unfolding in response to varying functional stress levels before ultimate catastrophic failure of the adhesive joint occurs. These domains may also re-establish folded configurations on stress relaxation, making the adhesive both strong and tough. Using the concept of controlled release, future adhesives may contain fluorescent biosensors that can detect pH changes around leaking restorations. They may even have the capacity to heal autonomously, in response to microcracks formed by functional stresses within the adhesive joint. The ability to self-diagnose and self-repair will increase the life expectancy of adhesive restorations. Future dentin adhesives may also assume a more instrumental role in therapeutics apart from caries prevention. These features may include the controlled release of noncollagenous proteins to promote remineralization of collagen matrices in sound and caries affected dentin, and growth factors to induce controlled formation of reparative dentin.

The effect of self-etching primer on the adhesion of tri-n-butylborane (TBB)-initiated resin cement to enamel has not been determined. This study evaluated the effectiveness of the self-etching primer by measuring the tensile bond strength between enamel and TBB-initiated methyl methacrylate (MMA) resin containing 4-methacryloxyethyl trimellitate anhydride (4-META). The self-etching primers were an aqueous mixture of 30 wt% methacryloxyethyl phosphate, 35 wt% 2-hydroxyethyl methacrylate, and ferric chloride. The concentration of ferric chloride was varied from 0 to 7 wt%. The bovine enamel surface was treated with self-etching primer for 30 s. After drying, a stainless steel rod was bonded to the enamel using TBB-initiated 4-META/MMA resin cement. The tensile bond strengths were measured after 1 day of immersion in 37°C water and after thermal cycles between 4°C and 60°C. The resin-enamel interface was observed under field-emission scanning electron microscopy (FE-SEM). The self-etching primer containing 5 wt% ferric chloride (Phosmer-5Fe) yielded the highest mean bond strength and significantly higher bond strengths than phosphoric acid etching after 1 day of immersion. After 5000 thermal cycles, the bond strength with Phosmer-5Fe was still significantly higher than that with phosphoric acid etching. FE-SEM images revealed tight bonding between the resin and enamel in the specimens of Phosmer-5Fe primer treatment. The self-etching primer treatment may be an alternative to phosphoric acid etching for the adhesion of TBB-initiated 4-META/MMA resin cement to enamel.

The purpose of this study was to assess the bond strength of two self-etching primers (SEP) to ground and unground enamel. Seventy-two bovine incisors were used in this study. The buccal enamel surface of 36 teeth was ground flat to resemble freshly cut enamel. The rest of the teeth were left intact. Two SEPs - Clearfil SE Bond, Kuraray (CSE) and Prompt L-Pop (3M ESPE) (LP) - and a conventional adhesive system, Scotchbond Multi-Purpose (3M ESPE) (SBMP) as a control, were used to bond a composite button to prepared and unprepared enamel. Microtensile test specimens were trimmed, resulting in a cylindrical cross-sectional area (0.21 mm2 to 0.47 mm2). These specimens were subjected to a tensile force at 1 mm/min until failure. Differences between adhesives and surface preparation were determined by two-way ANOVA. The samples were observed under SEM to evaluate the mode of failure. Bond strength values in MPa (SD) obtained from pooled data in descending order were: SBMP ground 44.54 (5.96), LP unground 42.97 (7.90), CSE unground 41.67 (11.28), LP ground 41.07 (12.07), CSE ground 38.56 (8.78), and SBMP unground 37.60 (9.55). No statistically significant differences were found (p = 0.5061) between surface preparation or adhesive systems. The mean in MPa (SD) of all the specimens that failed at the adhesive joint were: LP unground 47.13 (14.65), SBMP ground 45.28 (7.33), CSE unground 41.40 (11.07), SBMP unground 41.1 (10.04), CSE ground 39.96 (11.83), and LP ground 39.92 (15.45). No statistically significant differences were found (p = 0.5863). Failure occurred mainly at the adhesive interface. Surface preparation and adhesive treatment had no influence on resin composite microtensile bond strength to bovine enamel.

To determine the effects of using a ceramic primer, ceramic bonding agent, or a combination of primer/bonding agent on the long-term durability of the dual-cure resin cement/silicon oxide ceramic bond. Ceramic blocks (Vita Celay Blanks), A2M, were cut into 1-, 2-, and 3-mm-thick slices and polished using 600-grit SiC paper. Group 1 consisted of pairs of 1- and 3-mm-thick slices, and Group 2 of pairs of 2- and 3-mm-thick slices. Ceramic surfaces were treated with 40% phosphoric acid and silanated using one of three treatments: (1) Clearfil Liner Bond 2V Primer (2V Pr) and Porcelain Bond Activator (PBA), (2) Liner Bond 2V Primer/PBA and Liner Bond 2V Bond (2V Pr + Bd), and (3) Clearfil Photo Bond/PBA (P Bd). They were then bonded with a dual-cure resin cement (Panavia F) and light-cured for 20 s from each of six directions. After 24 h water storage at 37°C, 0.7-mm-thick slabs were serially sectioned. Immediately thereafter, after one and six weeks, and after one year of water storage, two slabs were randomly selected from each subgroup and sliced into beams for the microtensile bond strength (µTBS) test. Data were evaluated with three-way ANOVA and Fisher's PLSD test (p < 0.05) and failure modes determined using a laser-scanning confocal microscope. After 1 day, there were no significant differences between 2V Pr, 2V Pr + Bd, and P Bd (p > 0.05), whereas after one year, significant differences were found (p < 0.05). For Group 1, the µTBS of P Bd after one year of water storage was similar to that after one day. In both groups, µTBS of 2V Pr and 2V Pr + Bd significantly decreased over time (p < 0.05), which was accompanied by an increase in the percentage of complete adhesive failures. The chemical composition of the multicomponent ceramic primer/bonding agent significantly affects the long-term durability of the dual-cure resin cement/silicon oxide ceramic bond. The presence of water in a ceramic primer has a significant detrimental effect on resin-ceramic bond durability. In addition, the thickness of the ceramic restoration influences dual-cure resin cement/ceramic bond durability.

The objective of this in vitro study was to evaluate gingival microleakage in Class II total bond resin restorations in comparison to open sandwich technique restorations using different materials. Forty-eight human molar teeth were disinfected and stored in a 0.9% saline solution. In each tooth, two standardized Class II cavities (3 mm x 6 mm x 2 mm) were prepared with the gingival cavosurface margins located 1 mm below the cementoenamel junction. The teeth were divided into 4 equally sized groups (n = 12), and the proximal boxes were treated as follows: in Group 1, no base material was used and the cavity was restored using Syntac Sprint (SS) and Tetric Ceram (TC); in Groups 2, 3, and 4 the gingival portion of the cavity was restored with different base materials (Group 2, Dyract; Group 3, Vitremer; Group 4, Chelon-fil) prior to the placement of the composite resin. After a storage time of 7 days, the restorations were finished and polished. Then, specimens were submitted to thermocycling (500 cycles, 5°C to 55°C, 15 s dwell time) and immersed in a 0.5% methylene blue solution for 24 h. After washing, they were sectioned in a mesio-distal direction. Each restoration was evaluated under a stereomicroscope at 20X by 2 examiners and scored on a 0 to 3 scale according to the marginal leakage. Kappa statistics were used to evaluate the agreement between the examiners. Given the ordinal nature of the scoring system, data were submitted to a nonparametric repeated measures ANOVA. The results were confirmed with a parametric repeated measures ANOVA. Significant differences (p < 0.001) among the four groups with respect to dye penetration were detected, with the association Vitremer/Tetric showing the best results. The use of Vitremer in the open sandwich technique presents the lowest degree of microleakage among the treatments considered in this study.

The aim of this in vitro study was to evaluate the influence of occlusal finish line configuration on microleakage of indirect composite inlays. Forty-five recently extracted premolars were randomly assigned into three groups with different types of occlusal finish line preparations: bevel, chamfer, and butt joint. All restorations were made in Artglass (Heraeus Kulzer) and luted according to the manufacturer's recommendations. The teeth were sealed and then thermocycled 500 times between 5°C and 55°C. After that they were immersed in a 2% methylene blue (pH 7.2) solution for 24 hours. Each tooth was bisectioned in the buccal/lingual direction and then examined microscopically at each section to evaluate the microleakage score. The data were analyzed with chi-square and Fisher's Exact tests. There were no significant differences between the buccal margins of maxillary premolars with occlusal bevel or butt joint; the chamfer had the worst performance. In the buccal margin of mandibular premolars, the bevel and chamfer showed significantly smaller amounts of leakage than the butt joint. No significant differences were observed between the three types of occlusal cavosurface preparations in the lingual margin of maxillary and mandibular premolars. The finish line configuration, the position of the teeth in the arch, and the margin (buccal vs lingual) influenced microleakage. Whenever microleakage was observed in this study, it was always observed at the tooth-cement interface.

The objective of this work was to evaluate the in vivo long-term durability of bond strength and morphological appearance of interfaces between dentin and two adhesive systems. Class V cavities were prepared on the facial surfaces of 6 intact teeth of a monkey, and restored with Unifil Bond/Unifil F and Fuji Bond LC/Clearfil AP-X. One year later, 10 other teeth were restored with the same materials and the monkey was sacrificed after 24 hours. For in vitro examination, 6 more teeth were extracted from the monkey, restored in a similar manner with the two materials, and stored in 37°C water for 1 day. All specimens were subjected to the microtensile bond strength (µTBS) test. The debonded surfaces of specimens were morphologically observed with the FE-SEM. There were no statistically significant differences among the mean µTBS obtained for Unifil Bond/Unifil F under the three conditions (1 day and 1 year in vivo, and 1 day in vitro), and most specimens showed cohesive failure within resin composite (Unifil F). However, FE-SEM observations showed that resinous material within the hybrid layer made by Unifil Bond seemed to increase in porosity after 1 year. For Fuji Bond LC/Clearfil AP-X, µTBS at 1 day in vitro was significantly higher than that at 1 year in vivo, and bond strengths in vivo tended to decrease over time, although a statistically significant difference was not observed. From FE-SEM observations, most specimens showed cohesive failure within the adhesive (Fuji Bond LC). Bond strengths of the two adhesive systems tended to decrease for 1 year in vivo.