The Journal of Adhesive Dentistry, 01/2002

Despite large variations in the reported fracture strengths of dispersion strengthened, glass infiltrated, castable, pressable and machinable ceramics utilised for the construction of all-ceramic crowns, the annual clinical failure rate reported for these materials in the dental literature is remarkably consistent at ca 3%. These results emphasise that there may be little correlation between the average fracture strength and resultant clinical performance. Consequently, if ceramics are to be used for dental applications, then clearly more detailed information on the statistical variations in strength combined with the influence of cementation media are required. The effect of adhesive technology has been examined in laboratory and clinical studies. The laboratory studies focused on the effect of cement lute on crown performance, whilst surface degradation and strengthening effects with different systems were examined utilising conventional materials science techniques. Clinical studies focused on the failure rates of conventionally luted and adhesively luted crowns and inlays. There would appear to be evidence from clinical studies that crowns luted with a resin cement and with the placement procedure incorporating a dentine bonding stage have enhanced rates of survival. It is therefore concluded that the available research strongly suggests that the use of resin as a luting material for ceramic restorations is indicated, given the research from three differing sources - laboratory fracture studies comparing restorations luted with resin vs other materials, clinical studies, and laboratory studies examining the surface sealing/strengthening effect of resin on ceramic. Laboratory studies also confirm the enhanced resistance to fracture of crowns cemented with an adhesive procedure.

To assess the degree of nanoleakage of Class V preparations restored with three bonding agents using wet and dry bonding. Standardized Class V cavities were prepared in 66 human molars with cervical margins located in dentin. The composite was placed using one of three different dentin bonding agents with a moist or dry bonding technique (n = 11 per group). The teeth were stored in a 1% rhodamin-B solution for 24 h at 20°C, then rinsed with water, embedded in methacrylate, and sectioned parallel to the long axis of the tooth, separating the restorations into two parts. A confocal laser scanning microscope (CLSM) was used to visualize the layer 10 µm under the prepared surface of the section. The lengths of the dye-penetrated pathways were measured, representing the amount of nanoleakage. Differences in nanoleakage between the tested materials were proven to be statistically significant. The effect of drying had a significant influence on both the acetone-based and the ethanol-based material, but not on the water-based bonding resin. Dentin drying may have an influence on nanoleakage, depending upon the nature of the individual bonding agent.

The purpose of this study was to evaluate the in vitro dentin bond strengths of two dentin bonding systems in Class I cavities following fatigue load cycling (FLC) with thermal cycling (TC). Class I cavities were prepared in 12 human molars and restored with either Clearfil SE Bond (SE) and Clearfil AP-X resin composite (AP-X) or Single Bond (SB)/AP-X according to the manufacturers' instructions. After water storage for 1 week, untreated controls and test samples were subjected to 50,000 FLC with TC from 5°C to 55°C for 625 cycles and stored in water for 1 week. Microtensile bond strength (MTBS) tests were measured on the floor of the cavities at a crosshead speed of 1 mm/min. Data were statistically analyzed using one- and two-way ANOVA and Fisher's PLSD test at a 5% level of significance. The MPa results were: SE 30.5 ± 12.8 (control) and 23.2 ± 10.8 (50,000 FLC); SB 5.1 ± 9.2 (control) and 4.7 ± 5.7 (50,000 FLC). Bond strengths were not statistically significantly affected by FLC (p > 0.05); however, they were influenced by the bonding system (p 0.05). The MTBS of SE was significantly higher than that of SB (p 0.05) under FLC and TC test conditions. Over half of the SB specimens debonded during sample preparation, showing blister-like structures, suggesting that an over-wet phenomenon occurred on the cavity floor. SE produced excellent dentin bonds that were much stronger than those produced by SB, which was shown to be a technique-sensitive bonding system.

To determine the depth of cure resulting from three different curing devices in a photoactivated microhybrid composite through high-performance liquid chromatography (HPLC) analysis of leachable monomers. Three different curing units, a halogen lamp (Heliolux, Vivadent), a xenon lamp (Kreative Kuring, Allyn Welch), and a plasma-arc lamp (Apollo 95, DMDS) were investigated using a universal microhybrid composite (P 60, 3M) as the test material. To assess the effect of curing device variation, a flexural strength test was performed. In addition, samples of composite were prepared and cured "in contact" (0 mm between the sample surface and light-guide tip) and through a specific thickness of composite (1, 2, or 3 mm). The monomers (bis-GMA and UDMA) eluted from the samples were detected by HPLC. No significant differences were found in the mechanical properties of composite cured with different light sources. In contrast, the concentration of eluted monomers (bis-GMA, UDMA) at a depth of 2 mm and more was significantly higher for the specimens cured with the high-power curing devices than those cured with the traditional halogen lamp. Under these experimental conditions, high-power curing devices were shown to be inferior in the deep polymerization of resin composite when compared to a traditional halogen lamp.

To evaluate the effects of different curing strategies on the durability of the dual-cure resin cement/ceramic bond. Machinable ceramic blanks were cut into pairs of 3-mm-thick slices, which were then polished using wet 600-grit SiC paper. The slices were silanated using one of two ceramic priming systems: (1) Tokuso Ceramic Primer (TCP), and (2) K-etchant/Clearfil Liner Bond 2V Primer (LB2V)/Porcelain Bond Activator (PBA), and bonded with one of two dual-cure resin cements (Bistite II, Panavia F), to make four experimental groups. Each group was subjected to one of three curing strategies: (1) no light, (2) 20 s light exposure from one direction, and (3) 20 s light exposure from each of six directions. After 24 h water storage at 37°C, 0.7-mm-thick slabs were produced by serially sectioning perpendicular to the bonded interface. Immediately thereafter, and after one and six weeks of water storage, two slabs were randomly selected and sliced into beams for the microtensile bond strength (µTBS) test. Data were evaluated using Kruskal-Wallis and Wilcoxon rank tests (p 0.05), and failure modes determined using a laser-scanning confocal microscope. After priming with TCP, µTBS of Bistite II significantly increased over time when exposed to light, whereas the µTBS of the no-light group significantly decreased over time (p 0.05). After priming with TCP, µTBS of Panavia F increased over time, and after 6 weeks water storage, there were no significant differences in µTBS between the no-light and light-exposed groups (p > 0.05). Increases in µTBS were associated with increases in the number of cohesive failures in resin cement. After phosphoric acid treatment, priming with LB2V/PBA, and light exposure, µTBS of Bistite II remained stable, whereas that of Panavia F significantly reduced over time (p 0.05). The µTBS of no-light LB2V/PBA groups reduced significantly over time (p 0.05). The durability of the dual-cure resin cement/ceramic bond depends upon the multicomponent ceramic primer and the amount of light received by the resin cement.

This study compared the effect of water sorption on the extent of marginal gap reduction in two resin-modified glass-ionomer cements (RMGICs), two giomers, two compomers, and two resin composites over a twelve-week storage period. Artificial gaps were created in 160 borosilicate glass cylinders. One-half of the internal surface of each cylinder was blocked out with wax and the other half was sandblasted. The bonding surface was further treated with 4% hydrofluoric acid, rinsed, and then coated with silane. After removal of the wax, one coat of dentin adhesive was applied to the silane-treated surface of the cylinder, briefly air dried and light cured. Eight light-cured restorative materials were placed incrementally: Vitremer (V), Fuji II LC (FJ), Beautifil (B), Reactmer Paste (R), Compoglass F (C), F2000 (F), Filtek Z250 (Z), and Tetric-Ceram (T). For each material, ten specimens were stored in deionized water (W), and ten (control) in nonaqueous silicone fluid (O) at 37°C. The dimension of the same maximum gap created in each specimen was repeatedly measured at 0, 1, 2, 4, 6, 8, 10, and 12 weeks. R-W exhibited extensive hygroscopic expansion that resulted in cracking of 40% of glass cylinders after the 2nd week and 70% after the 4th week. One-way ANOVA of the other seven water groups showed significant differences (p 0.001) among gap widths measured at different time intervals in V-W, FJ-W, C-W, F-W. Both RMGICs had the most significant gap reduction during the first week (p 0.001). Both compomers exhibited delayed water-sorption characteristics, with more significant gap reduction observed in C-W. B-W was similar to the two resin composites Z-W and T-W and exhibited the least gap reduction. After the first week, there were no significant differences in the percentage reduction in marginal gaps for any of the groups (p > 0.05). Marginal gap reduction that results from water sorption is more extensive and rapid in RMGICs, followed by compomers, whereas composites are relatively stable. Reactmer Paste exhibits rapid and extensive expansion and should probably be avoided in tooth preparations that involve thin unsupported enamel.

The objective of this study was to evaluate the mechanical properties and bond strength of glass-ionomer cements (GICs) and resin-modified GICs (RM-GICs) that are indicated as restorative materials for the Atraumatic Restorative Treatment (ART) technique. Fifteen disk specimens for the diametral tensile strength (DTS) test and fifteen cylindrical specimens for the compressive strength (CS) test were made of each GIC: Ketac-Fil, Ketac-Molar (ESPE), Fuji IX and Fuji PLUS (GC). Forty human molars were sectioned and embedded in resin with either buccal or lingual surfaces exposed for the tensile bond strength (TBS) test. The surface was ground until a flattened area of enamel or dentin was obtained. After conditioning, inverted truncated cones of GICs were prepared on the flat tooth surfaces. The powder:liquid ratio of Fuji PLUS was adjusted for restorative purposes. Prior to testing, specimens were stored for 24 h (TBS test) and for 1 h, 24 h, and 7 days (CS and DTS tests) in deionized water at 37°C. They were then loaded at a crosshead speed of 1.0 mm/min for CS and 0.5 mm/min for DTS and TBS tests until failure occurred. The data were submitted to two-way ANOVA at 0.05 level of significance, followed by a Tukey-Kramer test for multiple comparisons. The mean CS values ranged from 90.27 to 170.73 MPa and DTS means from 6.21 to 22.32, with test periods from 1 h to 7 days. The means for TBS ranged from 4.90 to 11.36 MPa and from 2.52 to 5.55 MPa in enamel and dentin, respectively. No differences were found between materials with the CS test except at 1 hour. The resin-modified GIC (RM-GIC) had the highest DTS, with no changes between the test periods, and the highest TBS for both enamel and dentin. Among the GICs tested, RM-GIC showed higher values of DTS and TBS.