Studies On A Novel Prime-and-rinse Approach And A Novel Chemical Aging Method For Evaluating Degradation Of Resin-dentin Bond

Part1:A novel prime-and-rinse approach for improving resin-enamel/dentin bondExperiment1:A novel prime-and-rinse approach for improving the enamel bond strengths of self-etch adhesivesObjectives:This study investigated the effects of a prime-and-rinse approach using10-MDP (10-methacryloxydecyl dihydrogen phosphate) alcohol-aqueous solution on the enamel micro-tensile bond strengths (MTBS) and the resin-enamel interfaces of (ultra)-mild one-step self-etch adhesives.Materials and Methods:Thirty-eight human third molars were used in this study. The buccal enamel surfaces were flattened with180-grit SiC paper and polished with320-grit SiC paper under running water. Thirty-two enamel surfaces were treated with15%10-MDP containing primer for15s and water-sprayed for30s, or not (serving as control). Subsequently, one of the four adhesive systems was applied to the polished enamel surface by following the application instructions of the respective manufacturer, and a resin-composite from the same manufacturer as the adhesive system was placed over the enamel surface in four1-mm thick increments (Clearfil S3Bond+Clearfil Majesty, Kuraray Co. Ltd., Tokyo, Japan; G Bond+Gradia Direct, GC, Tokyo, Japan; Adper Easy One+Z250,3M ESPE, St. Paul, MN, USA; i Bond+Charisma, Heraeus Kulzer GmbH, Hanau, Germany). Light-curing was performed using a light-curing unit (Radii Plus, SDI, Australia). After storage in distilled water for24h at37℃, twenty-four enamel-bonded specimens were sectioned longitudinally through the resin-enamel interfaces into multiple beams, each with a cross-sectional area of about1mm2. The beams were subjected to tensile loading with a micro-tensile tester until failure. The MTBS was calculated in megapascals (MPa). Factorial design ANOVA and one-way ANOVA were used to analyze all the MTBS data. After the MTBS tests, the modes of failure were determined by stereomicroscopy at50-fold magnification, and three representatively fractured specimens per subgroup were analyzed by an SEM (scanning electron microscope). The surfaces of six polished enamel specimens were either prirne-&-rinsed with10-MDP alcohol-aqueous solution or not as above-mentioned. The specimens were split through the middle of the specimens. The surfaces of half specimens and the fractured surfaces of another half were prepared for the SEM observation. Additional eight bonded specimens (one tooth each subgroup) were prepared as above-mentioned. Each specimen was sectioned into three0.5-mm thick slabs including the resin-enamel interface. All enamel slabs were prepared for TEM examination.Results:The pre-treatment with the10-MDP alcohol-aqueous solution resulted in significant increase of enamel MTBS for all adhesive systems (p<0.05). Regardless of the control group or the experimental groups, the adhesive Adper Easy One revealed the highest MTBS (p<0.05). There were no significant differences of the enamel MTBS among the other three adhesives (p>0.05). The predominant failure modes in all groups were mixed failure and adhesive failure. Overall, there were less adhesive failures in the experimental groups than in the control groups. The treatment with the10-MDP alcohol-aqueous solution removed most of the enamel smear layer and resulted in the exposure of HAp crystallites and lots of porosities among them. The SEM findings revealed that the adhesive failure actually occurred at the transition between adhesive layer and hybrid layer in the control groups, while it occurred at the bottom of the hybrid layer in the experimental groups. The TEM findings showed that a smear layer remained between adhesive and intact enamel in control groups, while, the smear layer was not detectable due to the pre-treatment of the10-MDP alcohol-aqueous solution in the experimental groups.Conclusion:A novel prime-and-rinse approach using10-MDP alcohol-aqueous solution could remove most of the enamel smear layer, slightly demineralize the enamel surfaces, increase the enamel surface roughness and surface areas, and greatly improve the enamel bond strengths prior to application of ultra-mild or mild self-etch adhesives.Experiment2:A novel prime-and-rinse approach for improving the dentin bond strengths of self-etch adhesivesObjectives:This study investigated the effects of a prime-and-rinse approach using10-MDP (10-methacryloxydecyl dihydrogen phosphate) alcohol-aqueous solution on the dentin micro-tensile bond strengths (MTBS) and the resin-dentin interfaces of (ultra)-mild one-step self-etch adhesives.Materials and Methods:Fifty-four human third molars were used in this study. The mid-coronal dentin was exposed using a slow-speed saw and polished with320-grit SiC paper under running water. Forty-eight dentin surfaces were treated with15%10-MDP containing primer for15s and water-sprayed for30s, or not (serving as control). Subsequently, one of the four adhesive systems was applied to the polished dentin surface by following the application instructions of the respective manufacturer, and a resin-composite from the same manufacturer as the adhesive system was placed over the dentin surface in four1-mm thick increments (Clearfil S3Bond+Clearfil Majesty, Kuraray Co. Ltd., Tokyo, Japan; G Bond+Gradia Direct, GC, Tokyo, Japan; Adper Easy One+Z250,3M ESPE, St. Paul, MN, USA; i Bond+Charisma, Heraeus Kulzer GmbH, Hanau, Germany). Light-curing was performed using a light-curing unit (Radii Plus, SDI, Australia). After storage in distilled water for24h at37℃, sixteen dentin-bonded specimens were sectioned longitudinally through the resin-dentin interfaces into multiple beams, each with a cross-sectional area of about1mm2. The beams were subjected to tensile loading with a micro-tensile tester until failure. Another sixteen dentin-bonded specimens were sectioned into resin-dentin beams as mentioned above and stored in water at37℃for14months before subjected to MTBS. The MTBS was calculated in megapascals (MPa). Factorial design ANOVA and one-way ANOVA were used to analyze all the MTBS data. After the MTBS tests, the modes of failure were determined by stereomicroscopy at50-fold magnification, and three representatively fractured specimens per subgroup were analyzed by the SEM. The surfaces of six polished dentin specimens were either prime-&-rinsed with10-MDP-containing primer or not as above-mentioned. The specimens were split through the middle of the specimens. The surfaces of half specimens and the fractured surfaces of another half were prepared for the SEM observation. Additional sixteen bonded specimens were prepared as above-mentioned. Each specimen was sectioned into three0.5-mm thick slabs including the resin-enamel interface. Half of the dentin slabs were subjected to TEM examination immediately after preparation while another half were stored in water at37℃for14months before TEM examination.Results:The pre-treatment with the10-MDP-containing primer resulted in significant increase of dentin MTBS for all adhesive systems (p<0.05). About2μm thick dentin smear layer was removed by the treatment with the10-MDP-containing primer, exposing thin fibril-like networks. Hydroxyapatite crystals remained abundantly within the hybrid layers of both control and experimental groups. After14months water storage, MTBS of all adhesive systems significantly decreased except for Adper Easy One. The predominant failure modes in all groups were mixed failure and adhesive failure. Overall, there were more adhesive failures after14months water storage.Conclusion B:Ten-MDP-containing primer could remove the dentin smear layer, slightly demineralize the dentin surfaces, and greatly improve the short-term (24h) and long-term (14m) dentin bond strengths prior to application of (ultra)-mild self-etch adhesives.Summary:The novel prime-and-rinse approach using10-MDP alcohol-aqueous solution could most of the enamel/dentin smear layer, greatly increase the short-term enamel/dentin MTBS, and greatly improve the long-term dentin MTBS prior to the application of the ultra-mild or mild self-etch adhesives. The prime-and-rinse approach might be the supplemental to the contemporary dental adhesive approaches Part2:A novel chemical aging method for evaluating degradation of resin-dentin bondObjectives:To investigate the use of10%NaOH solution as storage medium on dentin micro-tensile bond strengths (MTBS) and the micromorphology of resin-dentin interfaces.Materials and Methods:Mid-coronal dentin was exposed for45human third molars. One of five dentin adhesives investigated was applied to each dentin surface, followed by placement of a resin composite from the same manufacturer (Clearfil S3Bond+Clearfil Majesty, Clearfil SE Bond+Clearfil Majesty, Kuraray Co. Ltd.; Adper Easy One+Z250, Adper Single Bond2+Z250,3M ESPE; Gluma Comfort Bond+Charisma, Heraeus Kulzer). Bonded specimens were sectioned through resin-dentin interfaces into multiple beams with a cross-sectional area of about1mm2. The beams were kept in10wt%NaOH solution at37℃for0,2,4,6,8,10, or12h respectively prior to MTBS evaluation. The MTBS data were analyzed statistically. Failure modes were determined by stereomicroscopy. Representative fractured surfaces and resin-dentin interfaces were examined by scanning electron microscopy (SEM). Resin-dentin interfaces were also analyzed by transmission electron microscopy (TEM).Results:Dentin MTBS decreased significantly with increased storage time in NaOH. Micro-gaps appeared along the resin-dentin interfaces after NaOH treatment and became wider over time. An electron-dense hybrid layer was observed by TEM in the control group, while an electron-lucent band was detected at the resin-dentin interfaces of specimens treated with NaOH for8h.Conclusion:Aging of resin-dentin bonds in NaOH solution may be used as an expedited chemical aging method for evaluating degradation of dentin bond.