Names, manufacturers, compositions, and lot numbers of the products used in this study are shown in . Eighty human molars with no restorations or decay were used in this study. Saliva was collected from three smoker and three nonsmoker participants. These saliva samples were applied to the specimens the same day that they were collected, about 30 min after collection. The teeth, which had been extracted within 3 months of the initiation of this study, were stored in 0.25% sodium azide/saline solution at 4°C prior to specimen preparation. The teeth were sectioned mesiodistally with a slow-speed diamond saw (Isomet, Buehler, Lake Forest, IL, USA), and embedded in acrylic potting resin to make a total of 160 buccal or lingual specimens. The specimens were ground to expose the superficial dentin using 600-grit SiC paper (Buehler). The specimens were then randomly divided into four groups with different contamination conditions and a control group (n = 8) for each bonding system.
Products, manufacturers, and batch numbers of products
The treatment groups were contaminated with either smoker’s or non-smoker’s saliva, and the adhesives were applied according to manufacturers’ instructions. The bonding protocols used in the four treatment groups and the control group were as follows:
- Control group: adhesive was applied to dentin following the manufacturers’ instructions
- SA group: 10 μl of saliva was dispensed and rubbed on the dentin surface with an applicator for 10 s, followed by air drying for 5 s with a hard stream from a distance of 5 mm, followed by adhesive
- AS group: adhesive was applied, and then 10 μl of saliva was dispensed and rubbed on the dentin surface with an applicator for 10 s, followed by air drying for 5 s with a hard stream from a distance of 5 mm
- ASW group: adhesive was applied, and then 10 μl of saliva was dispensed and rubbed on the dentin surface with an applicator for 10 s. This was followed by a 5 s water rinse and a 5 s air dry with a hard stream from a distance of 5 mm
- ASWA group: adhesive was applied, and then 10 μl of saliva was dispensed and rubbed on the dentin surface with an applicator for 10 s, followed by a 5 s water rinse with a hard stream from a distance of 5 mm and a 5 s air dry. Then adhesive was reapplied
Bonding agents and resin composite [One-Up Bond F Plus (OUFP), Tokuyama Dental Corporation, Tsukuba, Japan; Adper Prompt L-Pop (APLP), 3M ESPE, St. Paul, MN, USA], and resin composite [TPH Spectrum (TPH), Denstply/Caulk, Milford, DE, USA] were bonded to the dentin surface by using a polytetrafluoroethylene jig in the shape of an inverted truncated cone with a diameter of 3 mm at the bonded surface and 5 mm at the top.20
The composite was dispensed in 2-mm increments and cured as recommended by the manufacturers (20 s per layer). Photopolymerization was accomplished with an Elipar Highlight (Kerr Demetron, Danbury, CT, USA) curing light. The light output was verified as greater than 450 mW cm−2
throughout the study with a curing radiometer (Kerr Demetron, Danbury, CT, USA).
The adhesion protocol followed for the APLP self-etching adhesive system was as follows:
- After preparation, lightly dry to remove excess water.
- Apply adhesive with a rubbing motion for 15 s.
- Gently but thoroughly air-dry to remove the aqueous solvent.
- Apply a second coat (no waiting time for the second layer).
- Gently but thoroughly air-dry to remove the aqueous solvent.
- Light cure for 10 s.
The adhesion protocol followed for the OUFP self-etching adhesive system was:
- Rinse the prepared cavity. If no cavity preparation has been made, clean the tooth surface with a rubber cup and a fluoride-free cleaning paste; rinse thoroughly with water.
- Remove water by blowing air to keep the cavity in a dry, or in a moist condition but without visible puddles or a shiny appearance.
- Using the provided dispenser, place one drop of bonding agent A and one drop of bonding agent B into the mixing well.
- Mix thoroughly and evenly until the mixed bonding agent turns completely and evenly pink.
- Apply the mixed bonding agent to the cavity, both the enamel and dentin, with the disposable applicator tip.
- After applying the mixed bonding agent, keep rubbing the mixed bonding agent on the surface for at least 10 s.
- OUFP does not require air blowing because it contains no volatile solvent such as ethanol or acetone.
- Light irradiate the mixed bonding agent for at least 10 s. keeping the curing light tip within about 2 mm from the cavity surface.
After the specimens were bonded, they were stored in water in an incubator at 37°C for 24 h. The specimens were then debonded under tension using a universal testing machine (Model 4465, Instron, Canton, MA, USA) at a crosshead speed of 0.5 mm/min. Bond strength means were calculated and compared using three-way analysis of variance (ANOVA; StatView, SAS Institute, Cary, NC, USA). Fisher’s protected least significant difference (PLSD) post hoc test (StatView, SAS Institute) was used to determine significant differences at the 0.05 level. Failure modes were observed under 10 × magnification and recorded.
For the SEM analysis, 20 additional extracted human molars with the same characteristics as those used for the bonding were ground with 600-grit SiC paper (Buehler) on the occlusal surface to expose the dentin.
These specimens were randomly divided into ten groups of two specimens per group and then treated and bonded as described above. The specimens were sectioned perpendicular to the adhesive interface with a slow-speed diamond saw (Isomet, Buehler) to produce two slices, each 2–3 mm thick. One slice was acid-etched with 5 N HCl for 30 s, followed by 5% NaOCl for 30 min, and then rinsed thoroughly with distillated water. The other slice was fractured perpendicularly to the interface. Each slice was then dehydrated with 33% ethanol for 30 min, 67% ethanol for 30 min, 85% ethanol for 30 min, and 100% ethanol for 1 h.
The specimens were left overnight to dry and then mounted on 12-mm aluminum stubs and sputter-coated with approximately 20 nm of gold-palladium alloy. The specimens were viewed at three levels of magnification (1000×, 2500×, and 5000×) and tilt angles in a Field Emission Philips XL30 SEM at high vacuum and 10 kV. Analyses of the dentin–adhesive interface characteristics were based on at least 20 images taken along the length of the interface.