| BackgroundThe continuous development of dentin-bonding technology contributes to the rapid progress of resin aesthetic restorations. However, the limited durability caused by exposure of collagen fibrils and degradation of matrix metalloproteinase is still confusing the clinicians and patients. Biomimetic mineralization of collagen fibrils demonstrates the potential of collagen protection and offers a new probable solution. Nanoscale hydroxyapatite (nano-HAP) is widely used in repairing of bone tissue and enamel defects because of its excellent biological compatibility, while it has hardly achieved any significant progress in the remineralization of dentin collagen fibers. Nanoscale amorphous calcium phosphate(nano-ACP) could form intrafibrillar and extrafibrillar minerals with its unique mobility, and protect the denuded dentin collagen. Unluckily, long duration of mineralization compromises ACP’s further application and makes it only be a proof-of-concept strategy. Therefore, the application of nanoscale hydroxyapatite and shorten of the mineralization time of nanoscale amorphous calcium phosphate would be helpful to explore a possible approach to solve the defects of dentin-bonding. ObjectiveThe aim of this study is to evaluate the effect of pretreatments on demineralized dentin with nanoscale hydroxyapatite and nanoscale amorphous calcium phosphate, and detect the mineralization levels by different pretreatments.Methods1.20nm hydroxyapatite particles were prepared according to the ways Cai recommended, the specimens were tested with X-ray diffractometer to confirm the crystal structure. Nanoscale amorphous calcium phosphate were prepared with polyacrylic acid to mimic the sequestration.20extracted third molars of human were chosen and the enamel were removed by using a water-cooled low-speed diamond saw. The samples were polished, etched by gluma for15seconds and washed by deionized water for10seconds. Then the samples were randomly divided into four groups and treated as follows:(1)washed by deionized water and kept the dentin surface moist;(2)spreaded pure ethanol on the dentin surface three times and kept it moist;(3)spreaded0.22g/1HAP alcoholic solution for three times;(4)kept the samples in ACP solution containing STMP for a week, washed for10seconds. All the samples were bonded by single bond plus and formed with6mm resin crowns, stored in deionized water for24hours.2. All the samples were numbered by blind method. Each specimens was sectioned into1mm2beams and tensile bond strength was measured.3. The specimens were prepared with3mm2bonding interface, dried and imbedded by epoxide resin.70nm ultrathin sections were obtained and observed by transmission electron microscope.Result1.The XRD atlas of prepared nano-HAP compared to JCPDS standard value showed that the distribution of diffracted peak was in accordance with hydroxyapatite crystal, indicating the products were hydroxyapatite crystal.2. Microtensile bond strength test showed that the lowest bond strength was found for standard wet bonding (20.80±2.97MPa). while the highest bond strength was the specimens immersed into nano-ACP solution for a week(27.14±4.41MPa).All data was consistent with a normal distribution and the variance was homogeneous. The binding strengths of dentin pretreated with nano-HAP and nano-ACP for1week were significantly higher than that of wet bonding(P＜0.05). There was difference of bonding strength between nano-HAP and pure ethanol pretreatment (P<0.05), while that between nano-HAP and nano-ACP for1week was not significant (P>0.05)3. The observation of transmission electron microscope revealed that there were not any minerals in the mixed layer of wet bonding and ethanol specimens. Some accumulative HAP particles could be found in the mixed layer of nano-HAP pretreated samples, and a great amount of hydroxyapatite crystals were homogeneous distributed in mixed layer, intrafibrillar and extrafibrillar minerals were formed.ConclusionThe pretreatment of nano-HAP and nano-ACP solution could enhance the bonding strength of dentin bonding. However, HAP particles could not effectively infiltrate into collagen fibers and form minerals in the mixed layer, so further studies were need in order to maintain the HAP particles stable. Nano-ACP solution pretreatments for a week could significantly enhance the bonding strength and form homogeneous intrafibrillar and extrafibrillar minerals in the mixed layers. |
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