AFM Study On The Morphology Of Different Layers Of Carious Dentin

[Objective]Dental caries is one of the m ost co mmon diseases in de ntistry. While the traditional concept is removing all caries infected/affected dentin, which has a high risk of the pulp exposure, a new concept of keeping a part of caries infected dentin has been proposed. The question we need to answer of in this study is that whether residual caries infected/affected dentin would affect the bonding of dentin. As know to all, dentin caries is a progress ive infectious disease of the dental hard tissues. According to different layers, carious dentin m ay exhibit different morphologies. In dentin from the enamel to the deepest layer, the distinct areas of carious dentin are caries infected dentin and caries affected dentin. To our knowledge, there were few studies on the effects of different layers of carious dentin on dentin bonding in the past. The main aim of this study was to observe the effects of different layers of carious dentin on dentin bonding with applying the AFM and comparing their surface topography, and provide morphological basis for further study.[Methods]Third m olars, which were invaded by dentin caries, freshly extracted were collected. A specimen of midcoronal dentin up to the pulp cavity of uniform thickness was section ed perpend icular to the toot h’s long axis, o n whose surface contain caries-infected dentin, carie s-affected dentin and sound dentin. The surface of the specimen was wet polished with in increasingly fine grit s from600-to5000-grit SiC polishing paper and ultrasonically cleaned in deionized water for15m in. The specimen was stored in4℃deionized water before being used. In the air, before and after ac id etching, after NaCIO treatment, an AFM was used to observe the surface topography of the sound dentin, caries infected dentin and caries affected dentin in the specim en under the taping mode. At the sam e time, we get the height im age and amplitude image, and analysis the different morphology characteristics of three types of dentin.[Results]In the AFM photograph before acid etching, no rmal shape of dentin tubule orifices was found in sound dentin. Instead, dentin tubul e orifices with a distorted shape could be seen in caries infected dentin and car ies affected dentin. The surface topography of intertubular dentin were sim ilar among the three types of dentin. No collagen fibrils could be observed.After acid etching, observed with AFM, the size of the dentin tubule orifices of the three types of dentin all in creased obviously. Besides, the shape of the dentin tubule orifices of the three types of dentin was found in norm al structure. But the surface topography of intertubular dentin were still sim ilar, and th ere were still no collagen fibrils in intertubular dentin.After NaCIO treated, observed with AF M, a thin network of collagen fibrils was visible in the intertubular de ntin in sound dentin. Corresp ondingly, in caries affected dentin, only single collagen fibrils could be observed in the intertubular dentin, which were arranged irregularly. But in caries infected dentin, no collagen fibrils was found.[Conclusion]Compared with sound dentin, the shape of dentin tubule orifices in carious dentin(caries infected dentin and caries affected dentin) changed. After acid etching, the size of the dentin tubule orifices of the three types of dentin all increased as the result of demineralization, which may facilitate bonding material in. The effect o f caries on the surface top ography of dentin was m ainly re flected in the structure change of the intertubular dentin. Deeper th e dentin caries was, less the degradation the organic matrix and collagen fibrils in intertubular dentin happened. Then we arrived at our hypothesis that bonding strength increased when the depth of carious dentin increased and a large residual of caries infected dentin would affect the bonding strength of dentin, while the residual of caries affected dent in m ay affect less. The results prov ide morphological evidence, and help for further st udy on the ef fect of different layers of carious dentin on dentin bonding.