Fluoride Release And Caries-inhibitive Properties Of Restorative Materials

Secondary caries occurred at the margin of dental restoration is one of the major causes of the long-term failure, which has been attributed to the gap formatiom and resultant microleakage around the restoration. It has shown that the restoration materials with good ability of fluoride release can fluorinate dental hard tissue adjacent to the materialsand improve the tissue’s resistance to demineralization, which can delay or prevent secondary caries. Currently, sustained fluoride release capability and in vitro secondary caries prevention are the two common items used to evaluate fluoride release restorative materials. However, most reported studies about the marginal secondary caries around the restoration neglected the effect of the size of the gap between restoration material and the hard tooth tissue.Objectives: This study is intended(1) to evaluate the fluoride releasing capability of several commercially available dental restoration materials and three fluoride releasing composite resin developed by our group;(2) to evaluate their ability to inhibit or prevent secondary caries;(3) to discuss the relationship between the fluoride release capability and its ability to prevent secondary caries.Methods: 1.Test of the fluoride release capability of restorative materialsDisc specimens of nine restorative materials [Fuji IX, Fuji Ⅱ LC, Compoglass F, Beautif Ⅱ, Charisma, Tetric Ceram HB and three experimental fluoride-releasing composite resin(1#, 2#, 3#)] were prepared and then immersed in 5.0 ml 37 ℃ deionized water respectively. The fluoride release in each day for each specimen was tested using a fluoride-specific ion electrode.2.Influence of gap width to the formation of artificial secondary caries Restorations with marginal gap widths of 25, 50, 100, 190, 270 μm respectively were prepared on bovine enamel block with two restorative materials(glass ionomer cement Fuji IX and composite resin C harisma). Each specimen was immersed in 0.5 ml 37 ℃ deionized water for fluoridation of tooth enamel, followed by immersing in partially saturated acidic buffer solution to form artificial secondary caries around the restoratiom. The depth of enamel demineralization was observed and measured under polarization microscope and the surface microhardness of each enamel block was measured before and after demineralization.3.Evaluation of the ability of restorative materials to inhibit enamel artificial cariesRestorations with marginal gap width of 100μm were prepared using bovine enamel and nine restorative materials [Fuji IX,Fuji Ⅱ LC, Compoglass F, Beautif Ⅱ, C harisma, Tetric Ceram HB and three experimental fluoride-releasing composite resin(1#, 2#, 3#)], Each specimens were immersed in deionized water respectively for the fluoridation of tooth enamel at 37 ℃ water bath, followed by immersing in partially saturated acidic buffer solution to form artificial secondary caries around the restoratiom. The depth of enamel demineralization was observed and measured under polarization microscope and the surface microhardness of each enamel block was measured before and after demineralization.Results 1. In the first day of the immersion, all materials tested presented an initial high fluoride release which decreased sharply during the next 2~4 days., The fluoride release for each material decreased gradually during the following 4~7 days and decreased very slowly after 7 days. The fluoride release of all tested materials in descending order is: Fuji IX ≈ Fuji II LC > Compoglas F ≈ 1# experimental composite resin ≈ 3# experimental composite resin > Beautifil Ⅱ ≈ Charisma ≈ Tetric Ceram HB ≈ 2# experimental composite resin,(P<0.05).2. The depth of outer lesion was significantly greater than that of wall lesion for all materials tested. Charisma presented a significant deeper outer lesion than Fuji IX(P <0.01). The gap width has a significant impact on the depth of wall lesion in artificial secondary caries.With a gap width of 25 μm, no significant difference on wall lesion detected between fluoride release material(Fuji IX) and material without fluoride release(Charisma). When the gap width is 50~100μm, the two materials presented significant different in the wall lesion depth and the depth increased with incresing of the gap width. However, when the gap width was greater than 100μm, the depth of the wall lesion did not increase with the increasing of gap width.3. Hardness reduction rate and the depth of outer lesion of all the tseted materials in ascending order were: Fuji IX < FujiⅡ LC < 3# experimental composite resin ≈ Compoglass F ≈ 1# experimental composite resin < Beautif Ⅱ ≈ 2# experimental composite resin ≈ Tetric Ceram HB < Charisma(P <0.05). The depth of wall lesion in ascending order were: Fuji IX ≈ FujiⅡ LC < 3# experimental composite resin ≈ Compoglass F ≈ 1# experimental composite resin < 2 # experimental composite resin Beautif Ⅱ ≈ Tetric Ceram HB < Charisma(P <0.05).Conclusions: 1.Different type of the materials has different ability of fluoride release, with fluoride releasing glass ionomer cement being the strongest, followed by polyacid- modified composite resin.Common resin-based composite material is relatively poor in fluoride release. The composite resin can have excellent fluoride release properties by being added organic fluoride compounds such as fluoride-containing methacrylamide monomer or fat-soluble salt of organic fluoride compound. In contrast, the composite resins containing inorganic fluoride such as ytterbium fluoride and calcium aluminosilicate glass powder did not demonstrated powerfull fluoride release capacity.2. Secondary caries model with marginal gap can form clear outer lesion and wall lesion. The width of gap significantly affects the formation of caries on the cavity wall and the restorationwith a gap width of 50~100μm can fully demonstrated differences between fluoride release materials and without fluoride release materials.3. The secondary caries inhibitive capacity of restorative materials is closely related to fluoride release capability. The strongest capability of fluoride releasing by glass ionomer cement exhibited the strongest inhibition of secondary caries, followed by polyacid- modified composite resin. While common resin-based composite material is relatively poor both in fluoride release and caries prevention.The composite resin containing organic fluoride compounds such as fluoride-containing methacrylamide monomer or oil-soluble salt as fluoride source were able to inhibit secondary caries obvisouly around a restoration.