Caries preventive effects of glass ionomer cement restorations with silver diamine fluoride pretreatment on the root surface of adjacent sound tooth: an in vitro study

OBJECTIVE: To investigate the caries preventive effects of conventional glass ionomer cement (CGIC) restorations with silver diamine fluoride (SDF) pretreatment on the root surface of adjacent sound human tooth in an in vitro model. MATERIAL AND METHODS: Human tooth blocks with cavities, treated with 38% SDF pretreatment and filled with CGIC restorations, served as the experimental group (Group‑1). Human tooth blocks with CGIC restorations without SDF pretreatment served as control (Group-2). A dentin specimen simulating the root surface of adjacent tooth was placed next to CGIC restoration. The set of CGIC restorations with dentin specimens underwent a cariogenic challenge using a consortium of Streptococcus mutans, Lacticaseibacillus casei, and Candida albicans. The growth kinetics, viability, and morphology of the biofilm on the dentin surface were evaluated using propidium monoazide-quantitative polymerase chain reaction (PMA-qPCR), confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM), respectively. The lesion depth, surface morphology, crystal characteristics, and collagen degradation of dentin specimens were determined using micro-computed tomography (Micro-CT), SEM, X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR), respectively. RESULTS: of all three microbes in Group-1 were lower than in Group-2 (p = 0.0001). CLSM showed that dead-to-live ratio in Group-1 and Group-2 was 0.85±0.14 and 0.57±0.09, respectively (p = 0.002). SEM revealed that Group-1 had sparsely distributed biofilm with damaged cells, in contrast to the dense and confluent biofilm observed in Group-2 on the dentin specimens. Micro-CT showed that mean lesion depth (µm) in Group-1 and Group-2 was 114±5 and 256±10, respectively (p = 0.0001). Compared to Group-1, SEM indicated that Group-2 had a marked loss of minerals with exposure of dentin collagen. XRD spectra showed that Group-1 had sharper hydroxyapatite reflections than Group-2. FTIR revealed that ratios of amide I to hydrogen phosphate of Group-1 and Group-2 were 0.11±0.03 and 0.19±0.04, respectively (p = 0.0029). CONCLUSION: This in vitro study demonstrates that SDF pretreatment enhances the caries preventive effects of CGIC on the root surface of adjacent sound tooth.