The purpose of this study was to evaluate the surface roughness and resistance to toothbrush

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1 Original paper Dental Materials Journal 22(3): , 2003 Tooth Brush Abrasion of Paint-on Resins for Shade Modification of Crown and Bridge Resins Koichi FUJII1,2, Seiji BAN1 and John F. McCabe2 1Department of Biomater ials Science, Field of Oral and Maxillofacial Rehabilitation, Course for Advanced Therapeutics, Kagoshima University Graduate School of Medical and Dental Sciences, Sakuragaoka, Kagoshima , Japan 2Dental Materials Science Unit, Department of Restorative Dentistry, The Dental School, University of Newcastle upon Tyne, Framlington Place, Newcastle upon Tyne, NE2 4BW, United Kingdom Received February 26, 2003/Accepted June 23, 2003 The purpose of this study was to evaluate the surface roughness and resistance to toothbrush abrasion of three experimental paint-on composite resins developed for the shade modification of crown and bridge resins. The paint-on resins had less filler volume fraction than restorative composites or the crown and bridge resins and consequently were of low viscosity. The maximum surface roughness (Rmax) and the maximum depth loss by abrasion for the paint-on resins following 40,000 cycles of brushing ranged from 2.45 to 4.07ƒÊm and 8.63 to 13.67ƒÊm, respectively. Rmax values were % lower than that for the crown and bridge resin subjected to the same test. Wear depth was % lower than for the crown and bridge resin. These results suggest that the paint-on resins are expected to have adequate resistance to toothbrush abrasion and may therefore be suitable for clinical use. Key words: Abrasion, Crown and bridge resin, Shade INTRODUCTION Crown and bridge resins are widely used as veneers on metal castings to provide restorations on anterior teeth1-5). The composite type crown and bridge resins have the advantage of relatively low cost and straightforward manipulation combined with acceptable aesthetics. However, the aesthetics are not comparable with those which can be achieved with ceramics, often because of a slight mismatch in the colour of the restoration and adjacent natural teeth6). Furthermore, the appearance of the resin veneer may deteriorate over time, due to water absorption caused by the relatively hydrophilic groups in the polyfunctional monomers which are used7), and due to the loss in surface gloss which results from abrasion or staining8,9). The resulting changes in appearance have a marked effect on levels of patient satisfaction. With these problems in mind, experimental paint-on resins designed for subtle shade modifications have been developed for use both at the chairside and in the dental laboratory.

2 FUJII et al. 245 The aim of this study was to assess the resistance of these paint-on resins to toothbrush abrasion when compared with one resin currently used in crown and bridge construction. MATERIALS AND METHODS Material Details of the materials used in the study are given in Table 1. All materials are based on a light activated UDMA matrix. The three paint-on resins (MP-A, MP-O and MP-T) contained an organic composite filler, were fluid and suitable for application by painting10,11) The commercially available crown and bridge resin (So-T) was designed for anterior usage and contained a hybrid glass filler. The specimens of So-T (8 ~24 ~1mm) were prepared using a polytetrafluoroethylene mould and glass cover plates to express excess material. Polymerization was achieved by exposure to a light curing unit (ƒ Light, LCR-1, Morita, Saitama, Japan). Specimens of the paint-on resins were prepared as follows: So-T specimens prepared as above were ground using abrasive paper (#600), sandblasted with alumina (50ƒÊm) and then treated with proprietary primer to produce a sample 0.8mm thick (reduced from 1mm). Paint-on resin was then applied to the primed surface and a uniform layer 0.2mm thick was achieved using a PTFE mould and glass plates as described previously. The paint-on material was cured by irradiation for 90s using a suitable light unit (UniXs, Kalzer, Germany). The top surface of each specimen (exposed to light activation) was used for abrasion testing in each case. Samples were stored in distilled water at 23 Ž for 24 h before testing. Toothbrush abrasion Abrasion testing was carried out using a toothbrush abrasion tester (K236, Table 1 Materials used in this study *Light intensities of ƒ Light and UniXS were 760 and 790mW, respectively (at the central part on the sample stage). **Kyoto, Japan, ***Osaka, Japan

3 246 ABRASION OF PAINT-ON RESIN FOR MODIFYING SHADE Tokyogiken, Kanagawa, Japan)12,13). The same brush (Perio. II M, Sunstar, Osaka, Japan) under a load of 350gf was used throughout13) and there was no perceptible change in the shape or nature of the nylon bristles over the whole period of testing. The abrasive was a slurry of a 1:1 ratio (g/g) of distilled water and toothpaste (White & White, Lion, Osaka, Japan) which contained a silica abrasive. The brushing machine operated at 90 brushing strokes per minute and each stroke involved a sliding distance of 60mm. A total of 40,000 brushing cycles was used for each test and maximum surface roughness (Rmax) and maximum depth abraded were determined at 20,000 and 40,000 cycles using a surface profile metre (Surfcom, 700A, Tokyo, Seimitsu, Japan). Weight loss was also used as an indicator of the amount of material lost by abrasion. Hardness, filter content, weight loss Vickers hardness (Hv) was measured under a load of 25gf for 25s using a microindentation hardness tester (MVK-E, Akashi, Hyogo, Japan). Nine measurements were made on surfaces of test specimens before abrasion testing was commenced. Filler content of each material was determined by the ashing of 0.3g of material as described in ISO ). The weight loss caused by abrasion was simply determined by the difference in weight of specimens before and after brushing. Specimens were observed after brushing using optical microscopy. Three specimens of each material were used in the determinations and statistical analysis was performed using one-way analysis of variance and Fishers Protected Least Significant Difference test. RESULTS AND DISCUSSION Fig. 1 shows examples of the surface profile traces for baseline and brushed samples (after 20,000 and 40,000 cycles) for each material. Table 2 gives values of Rmax for Fig. 1 Surface roughness curves after 20,000 and 40,000 cycles of three paint-on resins (MP- A, MP-O and MP-T) and crown and bridge resin (So-T).

4 FUJII et al. 247 Table 2 Maximum surface roughness (Rmax), maximum depth and weight loss as an indicator of the amount of material lost by abrasion, and Vickers hardness (Hv) before abrasion testing (): S.D. Fig. 2 Filler configuration of three paint-on resins (MP-A, MP-O and MP-T) and crown and bridge resin (So-T). each material after 20,000 and 40,000 cycles as well as maximum depth loss, abrasion weight loss and hardness. Filler content, determined ashing is included with material details given in Table 1. Rmax increased on increasing the number of brushing cycles from 20,000 to 40,000. Rmax of So-T was significantly greater than that of the paint-on products (p<0.05). The ranking of maximum depth loss was the same as that for Rmax and So-T gave a significantly grater maximum depth loss than any of the paint-on materials (p<0.05). The weight loss values, following abrasion, were also in the same ranking

5 248 ABRASION OF PAINT-ON RESIN FOR MODIFYING SHADE Fig. 3 Sliding surfaces of the specimens abraded after 40,000 cycles. order as Rmax and the weight loss for So-T was significantly greater than that for the paint-on materials (p<0.05). So-T was harder than the three paint-on resins (p<0.05). This was in line with the inorganic filler content values which were significantly greater for So-T than for the other products. The nature of the filler in the paint-on materials is not precisely known except that it is described as a ecomposite organic and/or inorganic filler f. Clearly the materials also contain significant quantities of inorganic material which remains after ashing (Table 1) and can be visualized in Fig. 2. These images were produced by dissolving the resin component of each paste in tetrahydrofuran and then viewing with a light microscope. Despite the greater filler content and hardness for So-T all the parameters used to evaluate roughness and abrasion for this product were inferior to those determined for the paint-on products. In fact, the pattern of the results suggested the possibility of an inverse relation between Rmax, depth loss and weight loss against hardness. For these materials harder products wore more rapidly and became rougher than softer products. It was certainly clear that the key wear parameters of Rmax, maximum depth wear and weight loss were very closely related and one can be predicted from the other. Materials which become rougher wear more rapidly. The reason for this behaviour may be apparent following observation of the surfaces of brushed specimens (Fig. 3). The surfaces of the paint-on materials had fine scratches associated with the effect of the abrasive in the toothpaste. The surface of So-T had larger

6 FUJII et al. 249 scratches which were probably caused by the abrasive effect of detached filler particles. This finding suggested that filler particles readily became detached from the surface of So-T and this may have been due to the relative softness of the matrix resin in addition to degradation of the silicone coupling agent which binds the filler to resin15). The current study was carried out with a single abrasive agent. A previous study reported that the wear rate and even the ranking order of wear for materials is sensitive to changes in the nature and particle size of the abrasive used in the paste16). Nevertheless, using any of the parameters for characterising wear of the paint-on resins investigated appears to have an abrasion resistance which is at least as good as that for a commercially available crown and bridge resin and may therefore be worthy of consideration for clinical use. ACKNOWLEDGEMENTS The authors acknowledge Heraeus Kulzer Japan Co., Ltd. for providing the materials used in this study, and colleagues in the Department of Biomaterials Science for technical assistance. REFERENCES 1) Tanoue, N., Matsumura, H. and Atsuta, M.: Curing depth of four composite veneering materials polymerized with different laboratory photo-curing units, J Oral Rehabil 25 (5): , ) Tanoue, N., Matsumura, H. and Atsuta, M.: Curing depth of a composite veneering material polymerized with seven different laboratory photo-curing units, J Oral Rehabil 25 (3): , ) Matsumura, H., Leinfelder, F.K. and Kawai, K.: Three-body wear of light-activated composite veneering materials, J Prosthet Dent 73 (3): , ) Fujii, K., Tsukada, G., Ueno, O., Imaizumi, A., Masuda, A. and Inoue, K.: Dynamic viscoelastic properties in torsion of four commercially available resins for crown and bridge, Dent Mater J 17 (3): , ) Kern, J., Strub, R., and Lu X.-Y.: Wear of composite resin veneering materials in a dual-axis chewing simulator, J Oral Rehabil 26 (5): , ) Smales, R.J. and Gerke, D.C.: Clinical evaluation of light-cured anterior resin composites over periods of up to 4 years, Am J Dent 5 (4): , ) Umemoto, K. and Kurata, S.: Basic study of a new denture base resin applying hydrophobic methacrylate monomer, Dent Mater J 16 (1): 21-30, ) Ryter, I.E., Nilner, K. and Moller, B.: Color stability of dental composite resin materials for crown and bridge veneers, Dent Mater 3 (4): , ) Um, C.M. and Ryter, I.E.: Staining of resin-based veneering materials with coffee and tea, Quintessence Int 22 (5): , ) Muraguchi, K., Minami, H., Kadokawa, A., Minesaki, Y., Onizuka, T. and Tanaka, T.: A study on paint type resin for esthetic for modification of prosthetic composite, J Jpn Prosthodont Soc Special Issue , 134, 2002 (in Japanese). 11) Arikawa, H., Kanie, T., Fujii, K., Homma, T., Takahashi, H. and Ban, S.: Optical properties of paint-on resins for shade modification of crown and bridge resins -Light transmittance characteristics-, Dent Mater J 22 (3): , (in press) 12) Tsuruta, S., Ozeki, Y., Kaji, T., Tanigawa, H., Hasegawa, T. and Hasegawa, J.: Abrasion of dental alloys by dentifrices containing hydroxyapatite, Aichi-Gakuin Univ 35 (2):

7 250 ABRASION OF PAINT-ON RESIN FOR MODIFYING SHADE , 1997 (in Japanese). 13) Fujii, K., Arikawa, H., Inoue, K., Onizuka, T. and Jimi, T.: Fundamental studies on abrasion resistance of dental resins Part 1. A method of measuring abrasion of dental resins, J Jpn Prosthodont Soc 27 (1): , 1983 (in Japanese). 14) International Organization for Standard, Specification ISO (E), Dentistry- Resinbased dental filling materials, Geneva, Switzerland. 15) Arikawa, H., Kuwahata, H., Seki, H., Kanie, T., Fujii, K. and Inoue, K.: Deterioration of mechanical pro Derties of composite resins, Dent Mater J 14 (1): 78-83, ) McCabe, J.F., Molyvda, S., Rolland, S.L., Rusby, S. and Carrick, T.E.: Two- and three-body wear of dental restorative materials, Int Dent J 52: , 2002.