Influence of food-simulating solutions and surface finish on susceptibility to staining of aesthetic restorative materials
Introduction
Aesthetic restorative materials are marketed in various types with different physical characteristics and colours. For direct aesthetic restorations, four types of material are widely used: resin composites, polyacid-modified resin composites (‘compomers’), glass-ionomers and resin-modified glass-ionomers. Resin composites were introduced about 1970 and are now used principally for direct aesthetic restorations.1 Compomers, with improved handling properties and greater fluoride release than resin composites, were introduced in about 1995.1 Glass-ionomer cements (GICs) were introduced in about 1972,2 and in the early 1990s, resin-modified glass-ionomers (RM–GIC) were developed in order to overcome some of the disadvantages of conventional glass-ionomers.3 Considering aesthetics, resin composites offer advantages over other aesthetic materials. However, GICs are now popular because they release fluoride and adhere to both enamel and dentine.
Due to the wide use of tooth-coloured restorative materials, it is important to determine which ones are susceptible to colour change. To ensure excellent aesthetics it is necessary for tooth-coloured materials to maintain intrinsic colour stability and a resistance to surface staining. Previous studies4, 5, 6, 7 have shown that both resin composites (RBCs) and glass-ionomer cements (GICs) are susceptible to staining in various staining media. While some studies7, 8 have shown that the surface roughness of resin composites has a direct influence on susceptibility to staining, others9, 10 have reported no correlation between surface roughness and staining susceptibility. Chung11 reported that the smoothest surface of resin composites was obtained using a Mylar strip and that early finishing and polishing resulted in greater staining susceptibility. In the case of glass-ionomer cements, polished samples with rougher and more irregular surfaces have been shown to have higher staining susceptibility than those finished using a Mylar strip.12
In addition, exposure to the combined effects of food, stains and alcoholic beverages can result in surface damage.13, 14 Yap15 revealed that the roughness of resin composites was not significantly affected by storage in food-simulating solutions (FSS). Although, much work13, 14, 15, 16, 17, 18 has been done to determine the effects of FSS on surface characteristics, surface hardness and flexural strength of aesthetic restorative materials, susceptibility to staining of the materials after pre-immersion in FSS has not been widely investigated.
The objectives of this study were to determine the effect of food-simulating solutions on the susceptibility of tooth-coloured restorative materials to surface staining by five foodstuffs, and to assess the influence of surface finish on susceptibility to staining. The null hypothesis is that the surface finish, FSS and foodstuffs have no effect on staining susceptibility of tooth-coloured restorative materials.
Section snippets
Methods and materials
Six materials (Table 1) of shade A2 were selected. Five staining liquids (Table 2) and three food-simulating solutions (FSS) were used, the latter being distilled water, 10%, v/v ethanol/water and glyceryl tricoprylate coprate (Crodamol GTCC; Croda Singapore Pte Ltd, Singapore).
The experimental regimen is shown in Fig. 1. A total of 576 1 mm thick plastics rings, internal and external diameters of 12 and 16 mm, respectively, was prepared and surface polished with 1000-grit silicon carbide paper.
Results
The interaction between combinations of factors is shown in Fig. 2. There was no significant interaction between surface finish and FSS or between surface finish and stain (P>0.01). There was no significant interaction between FSS and stain or FSS and material. There was a strong interaction (box A) between surface finish and material (P<0.001), and (box B) between stain and material (P<0.001). Fig. 3 shows the main effects of all factors by ΔE3. For stains, ΔE3 was significantly higher for
Discussion
Colour determination in dentistry can be divided into two categories: visual and instrumental. Instrumental colorimetry can potentially eliminate subjective errors in colour assessment. Colorimetry is more exact than the naked eye in measuring slight differences in coloured objects on flat surfaces.19
In this study, the contribution of changes in L*, a*, and b* was different for each stain for each material. In general, for all materials, ΔL showed a significant decrease. For GICs, Δa generally
Conclusion
Within the limitations of this study, the following conclusions were drawn: surface finish and exposure to FSS were not found to be important factors in determining the susceptibility of most materials to surface staining, and the null hypothesis was therefore accepted in the first respect; all foodstuffs stained all materials and the null hypothesis was therefore rejected in the second respect; Fuji IX showed most resistance to staining and F2000 least; coffee, tea and red wine stained
Acknowledgements
The authors thank Halas Dental for providing the facility for using the spectrophotometer and A/Prof Ian Gordon for providing statistical advice and assistance.
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