This study explores the interaction between bioactive glasses and dentin from extracted human teeth in simulated oral conditions. Bioactive glasses in the Na(2)O-CaO-P(2)O(5)-SiO(2) and MgO-CaO-P(2)O(5)-SiO(2) systems were prepared as polished disks. Teeth were prepared by grinding to expose dentin and etching with phosphoric acid. A layer of saliva was placed between the two, and the pair was secured with an elastic band and immersed in saliva at 37 degrees C for 5, 21 or 42 days. The bioactive glasses adhered to dentin, while controls showed no such interaction. A continuous interface between the bioactive glass and dentin was imaged using cryogenic-scanning electron microscopy (SEM). However, after alcohol dehydration and critical point drying, fracture occurred due to stresses from dentin shrinkage. SEM investigations showed a microstructurally different material at the fractured interface. Chemical analyses revealed that ions from the glass penetrated into the dentin and that the surface of the glass in contact with the dentin was modified. Microdiffractometry showed the presence of apatite at the interface. Bonding appears to be due to an affinity of collagen for the glass surface and chemical interaction between the dentin and glass, leading to apatite formation at the interface.
Bioactive glass disks from the MgO-CaO-P2O5-SiO2 system were placed in artificial saliva for time periods varying from 1 to 42 days. Surfaces were then analyzed using scanning electron microscopy (SEM) and x-ray diffraction to investigate surface morphologies and crystallinity. SEM examination exhibited dramatic surface changes as early as 2 d. X-ray results showed crystallinity in the form of apatite at 10 d, which became more developed though 42 d. The bioactive glass in water and non-bioactive glass in artificial saliva were used as controls; both exhibited no evidence of apatite formation on their surfaces through the 42 d time period. This study shows that bioactive glass reacts in artificial saliva to form apatite and that the apatite layer becomes better crystallized over an extended time period. These results give a better understanding of the surface changes and mineralization that occur over time and can be used to interpret results from in vitro and in vivo studies done on bioactive glass in the oral environment.
Bioactive glass powder in the MgO-CaO-P2O5-SiO2 system was mixed with water to create a bioactive glass paste. The paste was then placed in 8 cavities in molars of Sinclair mini-pigs, isolated using a light-cure composite filling, and left in vivo for 4 weeks. Additionally, 4 controls were run where the bioactive glass was placed in an inert polymer substrate and then incubated at 37°C for 4 weeks. Specimens were cut longitudinally in two halves and prepared for chemical and x-ray analyses. Qualitative results showed that the paste in the molars stayed intact while there was little or no paste left in the polymer substrate after cutting. This observation suggested that the paste in the natural tissue had structural integrity which could be caused by chemical changes and/or mineralization encouraged by contact with dentinal tubule fluid. X-ray analysis did not reveal any crystallinity in the paste at 4 weeks, but chemical alterations were confirmed by electron microprobe analysis. The chemical inhomogeneity of the individual elemental maps revealed the formation of Ca-P-rich/Si-poor areas. These distinct chemical variations were not seen in chemical analyses run on the bioactive glass paste in its initial state.
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