ObjectiveTo investigate the establishment, structural, and bonding interface characteristics of an artificial caries-affected dentin model with demineralization and discoloration as a basis of research on caries-affected dentin bonding repair.

MethodsOne hundred intact molars without caries were collected (acquired from Department of Oral and Maxillofacial Surgery, School & Hospital of Stomatology, Wuhan University from March to May 2023) and prepared as 5 mm thick dentin specimens. Then, they were screened and divided into 3 parts. One part of dentin specimens was subjected to bacterial biofilms to prepare artificial carious dentin (ACD). They were further ground by 600-grit SiC paper for 0, 12, 24, 36, and 48 s, respectively to obtain 5 groups with different layers of ACD: ACD-0, 12, 24, 36, and 48 s. Sound dentin was used as the control group. To determine the preparation parameter for artificial caries-affected dentin (ACAD), the first part of specimens was used for bacterial visualization observation ( n=3) and demineralization analysis experiments (micro-CT, Raman spectroscopy, and surface micro-hardness analyses, n=3). Another part of dentin specimens was allocated to 3 groups: control group (sound dentin), artificial caries-infected dentin group (ACD-0 s) and ACAD group (prepared according to the parameter determined by the experiments above). They were used for color tests ( n=10), Raman spectroscopy analysis ( n=6) and scanning electron microscope (SEM) observation ( n=1), thus comparing color, chemical composition and structure, and micro-morphology of 3 groups. The rest of dentin specimens were divided into 2 groups: sound dentin and ACAD ( n=6), which were bonded to composite resin with Single Bond Universal in a self-etch mode. Then, the bonding interface was measured using an electron probe micro-analyzer (EPMA).

ResultsThe depth of bacterial invasion for ACD-0 s was (142.4±25.8) μm. And obvious bacteria were observed in the dentin tubules for the ACD-12 s group. For micro-CT, the demineralization depth was (283.9±25.6) μm for ACD-0 s and (139.2±27.9) μm for ACD-36 s. The grey values in some regions of the dentin surface for ACD-48 s resembled those of sound dentin. For Raman spectroscopy, the peak ratio of phosphate to amide Ⅰ was significantly lower for ACD-24 s [4.2 (3.2,6.7)] than ACD-36 s [6.7 (6.0,7.7)] ( P<0.05). Additionally, there was no significant difference in surface micro-hardness between ACD-24 s [8.3 (7.0,10.2) HV] and ACD-36 s [10.2 (9.1,11.4) HV] ( P>0.05). The preparation parameter of ACAD was determined to be grinding for 36 s based on the experimental results above. The brightness (L ^* value) and the yellow-blue chromaticity (b ^* value) of ACAD (76.69±2.54, 33.15±1.89) were significantly lower than those of the control group (85.23±1.68, 35.87±1.55) ( P<0.05). The red-green chromaticity (a ^* value) of ACAD (5.38±1.20) was significantly higher than that of the control group (0.71±0.86) ( P<0.05). Moreover, the collagen structure parameter in Raman spectroscopy (the peak ratio of amide Ⅲ to CH ₂) of ACAD (1.089 7±0.038 5) was significantly higher than that of the control group (0.985 2±0.020 1) ( P<0.05). As shown in EPMA, the hybrid layer of ACAD [(4.72±1.03) μm] was significantly thicker than that of sound dentin [(3.02±0.66) μm] ( F=21.09, P<0.001) in a self-etch mode.

ConclusionsACAD is established through bacterial biofilm challenges followed by grinding for 36 s. It is partly demineralized and discolored with collagen structure changes, making it suitable for research on caries-affected dentin bonding.