The influence of caries-affected dentin on bonding effect of  deciduous teeth

Aim The aim of this study was to investigate the influence of caries-affected dentin on bonding effect of deciduous teeth, in turn to provide guidance for caries removal strategy of deciduous tooth caries before bonding. Methods Extracted second deciduous molars with one adjacent surface carious were collected. The half tooth with caries adjacent surface were grouped into the caries-affected group (Group test), while the caries-free half were grouped into the control group (Group control). For the Group test, carious tissue was removed with slow speed ball drill under the indication of caries indicator. For the Group control, at the other side of the occlusal surface sound dentin was prepared to the similar deep level. Single bond Universal was applied according to the manufacture’s instructions. The defective part was filled with Shofu Beautifil II Namer, a commonly used resin composite in pediatric dentistry. Vertical sticks were obtained and subjected to tensile stress test. The morphology of the bonding surfaces were observed by scanning electron microscope and transmission electron microscopy. Results Electron microscope observation showed that there was no significant difference in morphology between caries-affected dentin and normal dentin. The minerals and smear layer were removed after acid etching, and the collagen network of dentin tubules and intertubular dentin was exposed. The surface of caries-affected dentin was relatively rough and partially decomposed. TEM images of the caries-affected deciduous tooth dentin showed that the hydroxyapatite was sparsely distributed in strips. In normal dentin, hydroxyapatite was thicker and denser. The acidic environment produced by the bacteria demineralized the dentin part, which corresponded to the surface morphology of the caries-affected dentin as seen by SEM. There was no significant difference in the micro-tensile strengths between Group test and Group control (P > 0.05). Conclusion In vitro, caries-affected deciduous tooth dentin could achieve similar bonding strength to normal tooth dentin when Single Bond Universal adhesive was applied. The results of this study may provide theoretical basis for partial caries removal strategy of deciduous tooth caries treatment.