Evaluation of the resin infiltration technique with the material icon® and the assessment of microhardness, penetration into artificial caries lesions and surface quality using AFM

The management of incipient caries lesions is still considered a delicate subject in modern dentistry. With many treatment options currently available, the search for the least invasive yet most effective technique has been the main goal in micro-invasive dentistry for many decades. One of the most promising treatment options involving the penetration of a low-viscosity resin into non-cavitated carious lesions located on smooth and proximal surfaces has recently been introduced. These 'infiltrant' materials occlude the micropore structures found in demineralised enamel and block the passages that bacteria and acid require to cause further dissolution of the enamel structure thus inhibiting lesion progression. Caries infiltration is considered a non-invasive treatment option for non-cavitated enamel lesions extending to the outer third of dentin which are not expected to show remineralisation or arrest by ways of other non-invasive treatments. Icon® is a commercially available resin infiltrant material developed solely for this purpose. The resin infiltration technique is a novel technique and further detailed studies are required to fully understand its current and full potential. Therefore, the aim of this study was to evaluate the microhardness (VHN) values of Icon® in comparison with sound and demineralised enamel in a large subject group as well as evaluate the penetration capability using Scanning Electron Microscopy (SEM) and surface quality (roughness) via Atomic Force Microscopy (AFM). Enamel specimens prepared from bovine incisors were randomly allocated into 3 groups: microhardness (n=60), SEM (n=10) and AFM (n=60), respectively. The microhardness group was divided into 3 subgroups: control (n=20), demineralisation (n=20) and Icon® (n=20) groups. AFM group was also divided into control (n=30) and Icon® (n=30) subgroups. For the microhardness group, in order to form a demineralisation window on each demineralisation and Icon® group sample, a 4x4 mm sticker was placed and the remaining sound enamel was covered in acid resistant clear nail varnish. Following a pilot study in which a suitable demineralisation time was distinguished, incipient caries lesions were formed. After the application of Icon®, the microhardness (VHN) values of each group was measured. For the SEM group, the same method previously described for the microhardness group was used but with 4x10 mm stickers on 10 bovine enamel samples. Following demineralisation, the infiltrant was applied according to the manufacturers instructions and sputtered with platin for the SEM evaluation. For the AFM group, the enamel samples (n=60) were prepared as previously described. The negative control group was polished with no applications applied to the surface. Following the application of Icon® , the samples were observed by AFM and the surface roughness was evaluated. As a result of this study, the mean VHN values of all groups were determined to be significantly different from one another (p=0,0001). VHN values in the demineralisation group were determined to be significantly lower than the negative control and Icon® groups (p=0,0001). No statistically significant difference was observed between mean VHN values for the negative contol and Icon® groups (p=0,073). In the SEM group, Icon® showed successful penetration abilities and an acceptable surface. It could be seen that the infiltrant occluded the micropores and filled in the prism cores that had previously showed dissolution. AFM images suggested that Icon® has a much rougher surface than the control group. When the AFM results were evaluated numerically, it could be seen that the Icon® group possessed statistically higher Sq (0,0001), Sa (0,0001), mean height (p=0,0001) and maximum deviation (p=0,01) values when compared with the control group. In conclusion, the present study shows that more studies are required in order to improve the surface roughness of this material. Properties such as decreased penetration time would be beneficial for child patients.