Inhibitive Effect Of Fluoride Releasing Restorative Materials On Enamel Artificial Caries

Secondary caries is one of the major causes of the failure of dental fillings and thegaps around a filling contribute to the formation of secondary caries. Many studies haveshown that different filling material presents different volume shrinkage during setting,resulting gaps in different size. Thus, to evaluate the inhibitive effect of dental fillingmaterials on secondary caries in vitro the gaps around a filling should be considered.Objectives:(1) To develop an artificial secondary caries mode with controlled size of gap aroundfilling materials.(2) To evaluate effect of some fluoride release filling materials on the development ofartificial secondary caries. Methods:(1) Development of artificial secondary caries mode for evaluation of filling materialsEnamel blocks of bovine incisors were restored with two filling materials (aconventional GIC and a fluoride-free control material) respectively with a gap of270μmin width between each filling material and enamel. Then all restorations were immersed ina partially saturated acidic buffer solution at37℃for3days. The surface enamelmicro-hardness of the enamel blocks were measured before and after demineralization andenamel demineralization was observed under polarization microscope for each restoration.(2) Effect of restorative materials on the development of enamel artificial cariesCavities composed of bovine enamel blocks were restored with five filling materialsrespectively, GIC, FujiⅡLC，Compoglass F，BeautifilⅡ and Charisma, and a gap of270μm in width was formed between each filling and enamel. Then all restorations weresubmitted to a demineralization by immersing in a partially saturated acidic buffer solutionat37℃for3days. The surface enamel microhardness of each enamel block was measuredbefore and after demineralization and the depth of demineralization was measured underpolarized-light microscope.(3) Evaluation of fluoride-releasing composite resins on enamel artificial cariesEnamel blocks of bovine incisors were restored with four fluoride-releasingcomposite resins (No.1, No.2, No.3, No.4) respectively with a gap of270μm in widthbetween the composite resin filling and enamel. Then all restorations were immersed in apartially saturated acidic buffer solution at37℃for3days. The surface enamelmicrohardness of the enamel blocks were measured before and after demineralization andthe depth of enamel demineralization was measured using polarized-light microscope foreach restoration.Results:(1) After demineralization the surface of all enamel block became chalky and their surfacehardness reduced significantly (P﹤0.05).(2) Polarizing microscope observation showed that there is a demineralized layer on each enamel surface.With the same material, depth of enamel demineralization of group thelarger gap is better than that of the smaller.(3) Enamel surface hardness of all restorations reduced significantly afterdemineralization (P﹤0.05), and the order of hardness reduction is as follows:Charisma＞BeautifilⅡ≈Compoglass F＞FujiⅡLC＞GIC (P﹤0.05). The order of thedepth of enamel demineralization along the surface and the interface near the gap forthe5materials is as follows: Charisma＞BeautifilⅡ≈Compoglass F＞FujiⅡLC＞GIC (P﹤0.05).(4) Enamel surface hardness of all restorations reduced significantly afterdemineralization (P﹤0.05), and the order of hardness reduction is as follows: No.4＞No.3＞No.1＞No.2(P﹤0.05). The order of surface enamel demineralization depth forthe four composite resins is as follows: No.4＞No.3＞No.1＞No.2(P﹤0.05). Theorder of enamel demineralization depth in the wall lesion for the four composite resinsis as follows: No.4＞No.3＞No.1＞No.2(P﹤0.05).Conclusions:(1) A secondary caries model was established successfully with characteristic of acontrollable gap between the filling materials and teeth structure, with eliminates theeffect of size of gap to secondary caries formation.(2) Cariostatic efficacy of glass ionomer cement is better than that of fluoride-freecomposite resin.(3) The four fluoride-release composite resins present different cariostatic efficacy, withthe resin containing aluminum fluoride calcium silicate glass powder showing the bestcariostatic efficacy, followed by the resin containing high content oftetrabutylammonium tetrafluoroborate is better than that of low content.The cariostaticefficacy of fluoride-release composite resin containing HEMA is better than that offluoride-release composite resin containing TEGDMA.