Colour stability of composite resins: A clinical comparison Martin J. Tyas, BDS, PhD, GradDipHlthSc, AFCHSE, FADM*
Key words: Colour stability, composite resins. Abstract Ninety three Class Ill cavities were prepared in 66 patients, and restored with one of three resin-based restorative materials; a hybrid self-cure material, a microfine self-cure material, or a microfine lightcure material. Standardsets of clinical colour transparencies were used to evaluate colour match with the surrounding tooth and marginal discoloration over five years. After five years, all materials had become slightly darker, the microfine self-cure material significantly more so than the light-cure material. There was no significant development of marginal discoloration. (Received for publication November 1990. Accepted May 1991.)
Introduction Colour stability is a desirable property of resinbased restorative materials. Composite resins, however, contain a variety of organic compounds which may be responsible singly or collectively for internal (‘body’) discoloration.’ Such compounds include amines and benzoyl peroxide, which are necessary for the polymerization reaction, and hydroquinone monomethylether, which is an inhibitor.’ Several studies’.’ have suggested that selfcure composites discolour to a greater extent than light-cure materials. This has been attributed to the presence of aromatic amines in the former. The aim of this study was to evaluate clinically over five years the colour stability of three proprietary composite resins; two self-cure products (Silart and MiradaptS), and one light-cure product (Silwt).
*Senior Lecturer, School of Dental Science, The University of Melbourne. 88
Materials and method Ninety-three restorations were placed in 66 patients (34 Silw, 27 Silar, and 32 Miradapt) using conventional restorative procedures, utilizing quicksetting calcium hydroxide lining, 60 s enamel etching with etching liquid, 30 s washing and drying, and the placement of the restorative material following the manufacturer’s instructions. Restorations were polished after polymerization using the Soflext series of discs. After polishing, restorations were photographed at 1:l magnification on colour transparency film. Patients were recalled annually for 5 years, and at each recall a further 1: 1 photograph of the restoration was taken. The photographs were used as described previously3to assess the colour match and the degree of marginal discoloration. In this system, a score of 9 for colour match represents no difference between restoration and tooth, a score of 17 represents an extreme mismatch with the restoration darker than the tooth, and a score of 0 represents an extreme mismatch with the restoration lighter than the tooth. Marginal discoloration is scored on a scale of 0 to 8. One-way analysis of variance, followed by a Duncan multiple range test, was used to determine if any significant difference existed between colour or marginal staining between materials, firstly at base line, and secondly at five years. Paired t tests were used to assess significant changes in colour and marginal discoloration from base line to five years, for each material. The SPSS-X§ statistical package was used for calculation of summary data and significance tests.
t 3 M Dental Materials Division, St Paul, Minn. USA. tJohnson & Johnson, New Brunswick, NY, USA. BSPSS Inc., Chicago, Ill., USA. Australian Dental Journal 1992;37(2):88-90.
Table 1. Distribution of materials among teeth Teeth
Silux
Silar
Miradapt
Total
Upper incisors Upper canines Lower incisors Lower canines
24 6 0 4
22 1 0 4
25 6 1 0
71 13 1
Total
34
27
32
93
Table 2.
Silux
8
Mean colour match scores
8.1 (29)
8.8(17)
8.8(14)
8.9(14) 0.8
Number of restorations in parentheses. Vertical line joins significantly different values; p = 0.02.
Results The distribution of materials to teeth is shown in Table 1. Table 2 shows the colour match data, and Table 3 the marginal discoloration data. There was no significant difference in either property between materials at base line. After five years, all materials had become darker, but Silux not significantly so. The only significant difference between materials at five years was between Silux and Silar, with Silar significantly darker (p = 0.02). Marginal discoloration was effectively zero at base line, there was no significant difference between materials at five years, or between base line and five years for a given material.
Discussion In the two statistical significance tests in this paper, that is, inter-material comparison and intramaterial comparison, it was necessary to use different subsets of data for each comparison. For inter-material comparisons at base line (for colour match and marginal discoloration), all data for each material were used, since the scores for each material are independent of those for the other materials. A similar situation applies for the fiveyear inter-material comparisons. However, for intra-material comparison of base line and five-year results (for colour match and marginal discoloration), only those restorations scored at both base line and five years were included in the analysis (using a paired t test), since for each restoration the five-year value can depend on the base line value. In Tables 2 and 3, therefore, Australian Dental Journal 1992:37:2
Table 3. Mean marginal discoloration scores All restorations Base line
5 years
0.0 (33) 0.35 (17) Silux 0.09 (23) 0.58 (12) Silar Miradapt 0.08 (26) 0.62 (21)
Paired restorations Base line
5 years
p
0.0 (17) 0.35 (17) 0.16 0.0 (8) 0.62 (8) 0.35 0.0 (15) 0.53 (15) 0.12
Number of restorations in parentheses.
different means are given for each material at each time interval, depending on which raw data are used. This situation highlights the problem of patient attrition in clinical trials; patient attrition prevents data from all restorations being included in the analyses. The main findings of the present study were that both the self-cure materials darkened significantly over five years (p = 0.014 and p = 0.01 for Silar and Miradapt, respectively), the light-cure material did not, and that marginal staining was not a problem with any material. Several clinical studies have been carried out on the performance of the microfine self-cure material Silar.4-7The duration of these studies has ranged from 2-5 years7to 6 years: and one study compared Silar with Miradapt.6 Van Dijken6 compared Silar and Miradapt directly for several properties, including colour match and marginal discoloration, over 6 years. Miradapt showed good colour stability (5 per cent of restorations with unacceptable colour), while Silar showed poor colour stability (40 per cent unacceptable). Crumpler et d4reported that Silar and two other self-cure microfine materials displayed a poorer colour match after five years, compared with the conventional self-cure product Concise. t These are consistent with the results of the present study, in which Silar was less colour stable than the hybrid self-cure Miradapt. This finding is attributable to the volume of filler in the composite; because the resin matrix is responsible for the colour change, the amount of change will depend on the volume of matrix, which in turn depends on the volume of filler.8 Silar has approximately 3 1 per cent filler by volume, but the volume filler content of Miradapt is not known. However, Miradapt filler consists of barium glass and pyrogenic silica,6 and using the volume filler content of Concise of 57 per cent4 as a basis, Miradapt would be expected to have more than 60 per cent volume filler. The clinical findings above are generally supported by the laboratory results of Asmussen' and Tani et aL9 but are not consistent with those of 89
Davis and Mayhew' and Loeys et aL7 Davis and Mayhew' found that Silar was less colour stable than two self-cure small particle resins over three years although the difference was not significant, and Loeys et aL7 reported similarly but did not apply statistical tests. In comparing the self-cure material Silar with the light-cure material Silux with respect to colour at five years, Silar was significantly darker than Silux although at base line the colours were similar. The darkening of Silar was a 'body' discoloration, that is, arising from discoloration in the resin matrix from thermal or photochemical origin.1° Matrix colour change has often been attributed to oxidation of the amine accelerator or of unreacted methacrylate groups,'o but since commercial products (both self-cure and light-cure) contain a variety of amines and dimethacrylates, it is not possible to be unequivocal on which curing system is more colour stable.Io Further, light-cure materials can lighten on exposure to light as a result of bleaching of the camphoroquinone photoinitiator," which may offset the aminelmethacrylatedarkening. Marginal discoloration is due to microleakage at the margins of the restoration, and it is now well accepted that the acid-etch technique will enhance the quality of the compositelenamel margin and decrease or eliminate microleakage. In the present study, marginal discoloration was negligible after five years for any product, and no significant differences could be observed between products or between time intervals. These findings are partly consistent with those of van DijkenY6who reported no difference between the products used in his study (including Silar and Miradapt), but did find a significant amount of marginal discoloration developing in the 3-6 year interval. Crumpler et aL4 and Davis and Mayhew' both reported no difference in marginal discoloration between the various products used in their studies, both of which included a microfine and a small particlelhybrid composite. It appears therefore, that from the results of the present study, the microfine self-cure material Silar
90
was less colour stable than the microfine light-cure material Silux or the hybrid self-cure material Miradapt. Further, marginal staining was not a clinical problem for any product over five years.
References 1. Asmussen E. Factors affecting the colour stability of restorative resins. Acta Odontol Scand 1983;41:11-8. 2. Tyas MJ. The restoration of fractured incisors in children: a 1-year clinical study. Aust Dent J 1982;27:77-80. 3. Tyas MJ, Burns GA, Byrne PF, Cunningham PJ, Dobson BC, Widdop FT. Clinical evaluation of Scotchbond: One year results. Aust Dent J 1986;31:159-64. 4. Cnunpler DC, Heymann HO, Shugars DA, Bayne SC, Leinfelder KF. Five-year clinical investigationof one conventional composite and three microfilled resins in anterior teeth. Dent Mater 1988;4:2 17-22. 5. David RD, Mayhew RB. A clinical comparison of three anterior restorative resins at 3 years. J Am Dent Assoc 1986~112~659-63. 6. Van Dijken JWV. A clinical evaluation of anterior conventional, microfiller, and hybrid composite resin fillings. Ana Odontol Scand 1986;44:357-67. 7. Loeys K, Lambrechts P, Vanherle G, Davidson A. Material development and clinical performance of composite resins. J Prosthet Dent 1982;48:664-72. 8. Ruyter IE, Svendsen SA. Remaining methacrylate groups in composite restorative materials. Acta Odont Scand 1977;36:75-82. 9. Tani Y, Kawamura Y, Togaya T, Tsutsumi S, Ida K. In: Okabe T, Takahashi S, eds. Transactions International Congress on Dental Materials, Hawaii, 1989. Academy of Dental Materials and Japanese Society of Dental Materials 1989~289-90. 10. Cook WD, Beech DR, Tyas MJ. Structure and properties of methacrylate based dental restorative materials. Biomaterials 1985;6:362-8. 11. Cook WD, Chong MP. Colour stability and visual perception of dimethacrylate based composite resins. Biomaterials 1985;6:257-64.
Address for correspondenceheprints: Restorative Dentistry Section, School of Dental Science, The University of Melbourne, 7 1 1 Elizabeth Street, Melbourne, Victoria, 3000.
Australian Dental Journal 1992;37:2.