Effectiveness of Surface Protection for Glass-Ionomer, Resin-Modified Glass-Ionomer and Polyacid-Modified Composite Resins

Dental Materials Journal 2009; 28(1): 96－101

Technical Report

Effectiveness of surface protection for glass-ionomer, resin-modified glass-ionomer and polyacid-modified composite resins

Serpil KARAOĞLANOĞLU1, Nilgün AKGÜL1, Hatice Nur ÖZDABAK1 and Hayati Murat AKGÜL2

1Department of Restorative Dentistry, School of Dentistry, Atatürk University, Erzurum 25240, Turkey 2Department of Oral Diagnosis and Oral Radiology, School of Dentistry, Atatürk University, Erzurum 25240, Turkey Corresponding author, Nilgün AKGÜL; E-mail: [email protected]

The purpose of this study was to evaluate the effectiveness of several surface protectors for a glass-ionomer, a resin- modified glass-ionomer, and a polyacid-modified resin cement by determining dye uptake spectrophotometrically. 378 samples, made up of Ionofil U, Vitremer, and Dyract, were prepared and divided into groups of seven each. Positive and negative control specimens remained unprotected while the experimental specimens were protected with Finishing Gloss, Protect-It, LC Varnish, Adper Single Bond, or a nail varnish. The experimental groups and positive controls were immersed in 0.05% methylene blue solution, while the negative controls were immersed in deionized water. Results were evaluated using variance analysis. Of the Ionofil U group, Adper Single Bond exhibited the least effective surface coating among the materials tested, while the best surface protection was obtained with LC Varnish in the Dyract group. However, no statistically significant differences were observed in the Vitremer group.

Key words: Surface protection, Glass-ionomer cement, Polyacid-modiﬁed composite resin

Received May 31, 2007: Accepted Dec 18, 2007

the resin phase and/or it can occur by light INTRODUCTION activation. Compared with conventional analogs, Conventional glass-ionomer cement, which is a resin-modified glass-ionomer cements have been popular restorative material commonly used in characterized as having a longer working time, a dentistry for a long time, is formed by an acid-base rapid set, improved appearance and translucency, reaction between aluminosilicate glass and a 40－ and higher early strength8,10). In particular, a 50％ aqueous solution of acrylic acid/itaconic acid remarkable feature of these materials is that they copolymer stabilized with a 5％ tartaric acid1-4). can be finished and polished on the same visit11). Ionomer cements are sensitive to hydration and To overcome the technique-sensitive mixing and dehydration during their initial setting and are handling properties of resin-modified glass-ionomer frequently protected by coating materials. Initial cements, new materials containing acid-decomposible setting occurs in a few minutes, but precipitation, glass and acidic polymerizable monomers substituting gelation, and hydration take at least 24 hours, and the polyalkenoic acid polymer were developed7,12). further etching continues slowly for a much longer These materials were termed as polyacid-modified period5). composite resins, commonly known as compomers. A In recent years, developments in the field of polyacid-modified resin (PMR) is a cross between a glass-ionomer cements have led to the introduction of glass-ionomer and composite in that it contains a hybrid versions6). These materials were enhanced to reactive fluoride glass and an acid as well as a overcome the problems of low initial mechanical monomer. One major and important difference strength and moisture sensitivity associated with between glass-ionomers and compomers lies herein: conventional cements, while preserving their clinical in the glass-ionomer the acid is present as a polymer, advantages such as self-adhesion to dental tissues while in the compomer the acid is present as a and fluoride release. These new materials were monomer and the polymer is formed by polymeriza- classified as resin-modified glass-ionomers6-8). tion of the monomers during curing. Another Resin-modified glass-ionomer cements have two significant difference is that PMR contains no water, setting mechanisms: the acid-base setting reaction and reaction between the glass and acidic monomer and polymerization reaction9). According to McLean takes place only as PMR takes up water from the et al.7), resin-modified glass-ionomers are materials environment13). that set concurrently via a dominant acid-base To reduce the susceptibility of conventional reaction and auxiliary photopolymerization. This glass-ionomer cement and its hybrid versions to latter reaction can occur due to the self-cure mode of hydration and dehydration problems, surface Dent Mater J 2009; 28(1): 96－101 97 protectors were suggested for these materials. In Specimen preparation for experimental groups light of this suggestion, materials referred to as These materials were prepared according to manu- covering agents or surface sealants have been facturers’ instructions and placed in teflon disks 4.00 developed specifically for rebonding of restorations. mm in diameter and 2.0 mm in height. These disks Today, several commercial products are available. were first slightly overfilled with each restorative They are resin materials with low viscosity and a material under evaluation. Strip bands were placed high flow rate, and that they present similar at both sides of each disk and then sandwiched compositions. Moreover, their application technique between two glass plates with a weight of 500 g. The is relatively simple14). specimens prepared for Vitremer and Dyract AP The application of surface protection seems to were light-cured for 40 seconds, while the Iounofil U preserve the water balance in the system15). Another specimens were left for 5 minutes for setting2,17). advantage of using such surface protectors is that After which, the plates and strip bands were they fill small surface voids and defects and may help removed, and one of the coating materials under to preserve the original color of the restorations by evalaution was applied with a brush on both exposed reducing the uptake of stains16). surfaces of the specimens twice, except for the The purpose of this study was to evaluate the positive and negative control groups. Excess material amount of dye absorbed by a conventional GIC, a was trimmed off, and the protected specimens were resin-modified GIC, and a polyacid-modified coated again. composite resin and to make an analysis of the effec- A total of 126 specimens were prepared with tiveness of various surface agents for these materials each material and randomly divided into seven by determining dye uptake spectrophotometrically. groups, each of which contained 18 restorations. The specimens to be coated with Adper Single Bond (3M Dental Products, St Paul, MN, USA) and Protect-It MATERIALS AND METHODS (Jeneric Pentron Inc., Wallingford, CT, USA) were Materials used etched with 37％ phosphoric acid for 15 and 20 A conventional glass-ionomer cement (Ionofil U, Voco, seconds respectively. Then, they were rinsed for 15 Cuxhaven, Germany), a resin-modified glass-ionomer seconds, gently air-dried, and light-cured for 20 cement (Vitremer, 3M Dental Products, St Paul, MN, seconds. The specimens with LC Varnish (Spofa USA), and a polyacid-modified resin composite Dental, A Kerr Company, Markova, Jicin, CZ) and (Dyract AP, DeTrey Dentsply, Konstanz, Germany) Finishing Gloss (3M Dental Products, St Paul, MN, were selected for this study (Table 1). USA) were not etched, but these coating materials were spread on the surface using a stream of air and

Table 1 Materials used in the present study Product Manufacturer Compositiona Ionoﬁl U Voco, Cuxhaven, Germany FAS, PAA, water

Vitremer 3M Dental Products, St Paul, MN, USA FAS, PMAA, HEMA

Dyract AP DeTrey, Dentsply, Konstanz, Germany UDMA, TCB, TEGDMA, Trimethacrylate resin Adper single bond 3M Dental Products, St Paul, MN, USA BisGMA, HEMA, copolymer of polyacrilic acid, photoinitiator, Protect it Jeneric/Pentron, Inc, Wallingford, CT, USA BisGMA, UDMA, TEGDMA, THFMA

Finishing gloss 3M Dental Products, St Paul, MN, USA BisGMA, TEGDMA

LC varnish Spofa Dental, A Kerr Company, Markova, Jicin, CZ BisGMA, UDMA

Nail varnish Colorama, CEIL-Com Exp Ltda, Sao Paulo, SP, Brazil Camphor, nitrocellulose, sulfonamide, toluene a Approximate composition as given by manufacturers. FAS: aluminium fluorosilicate glass, PPA: polyacrilic acid, PMAA: polymethacrylic acid, HEMA: hydroxyethylmethacry- late, UDMA: urethane dimethacrylate, TCB: carboxylic acid modified dimethacrylateS, TEGDMA: Triethyleneglycoldi- methacrylate, BisGMA: Bis-phenol A diglycidylmethacrylate. 98 Dent Mater J 2009; 28(1): 96－101 then irradiated for 20 seconds. The specimens coated dye per specimen, whereby lower values indicated with a nail varnish (Colorama, CEIL Com Exp Ind better effectiveness of the surface protector. Ltda, Sao Paulo, SP, Brazil) were merely left to dry for 2 minutes. Statistical analysis At the initial stage of statistical analysis, Dye penetration test homogeneity of variances was first tested for Following the application of the surface coatings, the normality. Due to the lack of variances, the specimens were immersed in 0.05％ methylene blue Kruskal－Wallis test was used for data analysis. solution at 37ºC, except for the negative control Further analyses were conducted with the Duncan specimens which were immersed in deionized water. test to highlight the significant differences between After 24 hours, the specimens were rinsed with the groups. deionized water and the surface coatings were removed with medium SofLex disks (3M Dental RESULTS Products, St. Paul, MN, USA) for 5 seconds. The method used to quantify the effectiveness of surface Table 2 shows the comparison in dye uptake among protection was adapted from Douglas and Zakariasen, the positive control specimens made from Vitremer, as described by Serra et al.18). The specimens were Ionofil U, and Dyract AP. Statistically significant removed from the teflon disks, and each one was differences were seen among the three materials with immersed separately in tubes containing 1 mL of Dyract AP having the lowest dye uptake, followed by 65％ nitric acid for 24 hours. After which, standard Ionofil U and Vitremer (p<0.0001). and experimental nitric acid solutions were diluted Table 3 shows the results of multiple with 2 mL of deionized water. The solutions were comparisons of surface protection for Ionofil U, filtered and centrifuged, and finally the absorbance of Vitremer, and Dyract AP. As seen in this table, the methylene blue in nitric acid was determined by a positive control groups for all the three restorative spectrophotometer (Samsung Syncmaster 750s) at materials allowed the greatest dye penetration, 600 nm. Dye uptake was expressed in micrograms of significantly different from the other surface

Table 2 Comparison of dye uptake with the positive control specimens from Vitremer, Ionoﬁl U, and Dyract AP Restorative Dye uptake (μg/specimen) Mean Median Materials n mean±SD Rank＊ Vitremer 18 18.18±2.59 17.67 40a

Inoﬁl U 18 14.30±5.49 15.35 33b

Dyract AP 18 2.32±0.10 2.37 9.5c ＊Different letters indicate values that are signiﬁcantly different at 0.0001％ probability level (Duncan test)

Table 3 Results of multiple comparisons of surface protection for Ionoﬁl U, Vitremer, and Dyract AP

Ionoﬁl U Vitremer Dyract AP Surface Protection Median Mean Median Mean Median Mean n (μg/specimen) Rank＊ (μg/specimen) Rank＊ (μg/specimen) Rank＊ Positive control 18 15.35 117.50a 17.80 117.50a 2.37 117.50a

Adper single bond 18 1.56 95.61b 1.02 70.53b 1.34 73.44b

Protect it 18 1.04 57.97bc 1.01 67.58b 1.33 70.17bcd

Finishing gloss 18 1.03 57.67bc 1.06 75.03b 1.27 60.03cde

Nail varnish 18 1.03 57.33bc 0.91 57.31b 1.27 64.31de

LC varnish 18 0.99 49.92bc 0.885 47.06b 1.19 49.56e

Negative control 18 0.00 9.50c 0.00 9.50c 0.00 9.50f ＊Different letters indicate values that are significantly different at 0.0001％ probability level (Duncan test) Dent Mater J 2009; 28(1): 96－101 99 treatments. addition of a photocurable capability did not signifi- For Ionofil U, ranking from the highest to the cantly reduce glass-ionomer cements’ susceptibility to lowest dye penetration values according to the hydration. On the contrary, it has been reported applied surface treatment was as follows: Positive that resin-modified GIC specimens absorbed control, Adper Single Bond, Protect-It, Finishing considerable amounts of moisture when stored in Gloss, nail varnish, LC Varnish, and negative control. either water or physiological saline solution21,25-27). As indicated earlier, the positive control group Water sorption appeared to be dependent on the presented a statistically higher dye uptake than the resin (HEMA) content23-25,30-32). Materials with higher others (x2=97.013, p<0.0001). In addition, the dye hydrophilic resin (HEMA) content are therofore amounts for the specimens coated with Adper Single expected to have a higher water sorption property. Bond were statistically higher than those of negative This was confirmed by Li and co-workers32) who found control specimens. that increased filler level in composite resins (i.e., For Vitremer, ranking from the highest to the lower resin content) resulted in lower water sorption. lowest dye penetration values was as follows: Positive The amount of hydrophilic resin (HEMA) in control, Finishing Gloss, Adper Single Bond, Protect- resin-modified GICs is approxmiately only 5％33). It, nail varnish, LC Varnish, and negative control. With this content, it behaves like a hydrogel. On the Statistically, no differences in surface protection other hand, the network resulting from the copoly- effectiveness were observed among the applied merization of acidic monomers and UDMA (urethane surface coating materials (p>0.05). However, the dye dimethacrylate) is less hydrophilic, such that the uptake of the coated specimens was statistically effect of water on Dyract AP was retarded29). These different from the negative and positive control differences in the structures of restorative materials specimens (x2=85.857, p<0.0001). indicated that the hydration feature of Dyract AP For Dyract AP, ranking from the highest to the was less than that of conventional and resin-modified lowest dye penetration values was as follows: Positive GICs ― and this observation also constituted one of control, Adper Single Bond, Protect-It, nail varnish, the findings of the present study. However, when Finishing Gloss, LC Varnish, and negative control. compared with the negative control group, it was The dye amounts for the positive and negative seen that Dyract AP also absorbed dye significantly. control specimens were statistically different from In a study by Cattani-Lorente et al.29), they the other groups (x2=83.870, p<0.0001). compared the physical qualities of a resin-modified glass-ionomer cement kept in water against those of a polyacid-modified composite resin material. They DISCUSSION found that the amount of water uptake in resin- The effect of water on the physical properties of modified glass-ionomer cement was higher and that restorative materials is the subject of many investi- it extended to a larger extent by behaving like a gations. While some studies have reported negative hydrogel. effects on physical properties as a result of water In the same vein, van Dijken12) observed that storage and subsequent sorption17,19-26), Mitra10) has non-protected Class III resin-modified GIC found no significant differences in properties restorations showed the highest color change, surface immediately after curing and extended storage in degradation, and roughness compared with polyacid- water. modified composite resin and composite resin In our study, the hydration properties of restorations. Besides, Beltrao et al.34) determined conventional glass-ionomer cement and its hybrid after a two-year clinical evaluation that while versions were also investigated. It was found that conventional Class III GIC restorations showed an resin-modified GIC, polyacid-modified composite improvement in esthetics, non-protected Class III resin, and conventional GIC specimens immersed in resin-modified GIC restorations showed color change methylene blue (positive control) presented a signifi- which could be caused by contamination during the cantly higher dye uptake. Further, it was determined residual acid-base reaction12). that there were statistically significant differences in In another study carried out to assess the water dye uptake among these materials. In particular, it uptake of dental materials, Meyer et al.30) made a was noted that the dye uptake amounts of Vitremer comparison among the conventional GIC, resin- and Ionofil U were much higher than that of Dyract modified GIC, and polyacid-modified composite AP. These differences in findings could be attributed resins. They determined that polyacid-modified to the properties and amounts of resin, especially of composite resin absorbed less water than hydrophilic resin7,28-30). conventional GIC and resin-modified GIC, and that Theoretically, it was thought that activation by resin-modified GIC absorbed the largest amount of light or chemical inhibitors of glass ionomers might water. Likewise, they also attributed this result to be effective against water sorption9). However, the the hydrophilic HEMA chains of the material. 100 Dent Mater J 2009; 28(1): 96－101

Similar results found by Small et al.35) after a protectors were applied on Vitremer, no statistically six-month storage in water further confirmed that significant differences in dye absorbing capacity were conventional and resin-modified GICs exhibited a observed. However, when compared with either greater water uptake than the polyacid-modified positive or negative control group, statistically composite resin, whereby water uptake was significant differences were found. In another study particularly rapid and higher for resin-modified GIC. by Cefaly et al.43), no significant differences in surface These results were consistent with those of the protection effectiveness were found for the Vitremer present study. group when nail varnish, flexible resin, protective It is noteworthy that both water uptake and glaze, and proprietary glaze were applied on three water loss of restorative materials can compromise different resin-modified glass-ionomer cements. On the physical properties of restorations17,19-24). If water the other hand, in a research conducted by Ribeiro et is lost due to desiccation, the reactions may stop and al.37), Heliobond light-activated bonding resin resulted surface crazing may occur19). If water is absorbed, in the least dye penetration whereas nail varnish the matrix will become chalky and erode rapidly19). resulted in the highest degree of dye penetration. In relation to this, surface protection is necessary Results of the current study suggested that and recommended for these materials12,17,36-38). The conventional GIC, resin-modified GIC, and polyacid- application of surface protection seems to preserve modified resin composite restorations could take up a the water balance in the system and provide considerable amount of dye, and that dye uptake sufficient early protection to prevent water gain or decreased with the use of a protective coating for all loss from materials15,17,36-40). For this reason, much of them. research has been carried out to evaluate the A comparison of protected and non-protected bonding and sealing capabilities of surface restorations is indeed important to verify the real coating agents19,30,36-43). Based on the results of influence of surface protection toward restoration these studies, the application of surface coating performance. Clinical studies are also necessary to over GIC and RMGIC restorations is strongly compare the advantages of different protective agents recommended19,36,37,40,41). over conventional GIC and its hybrid combinations. Hotta and Hirukawa41) applied a bonding agent At this juncture, it must be highlighted that tooth and a glazing agent on three restorative glass brushing and dietary habits can influence the ionomers and investigated the water resistance of retention of these agents. Therefore, results obtained these two materials. They observed that the water from clinical studies may differ from those obtained resistance of glazing agent was better than that of in our laboratory study. bonding agent, but the bonding agent had a small advantage of preventing water movement over glass- REFERENCES ionomer cement. In another study by Hotta et al.40), it was found that light-cured bonding agent and 1) Crisp S, Wilson AD. Reaction in glass-ionomer glazing agent were more effective than Ketac varnish cements: I. Decomposition of the powder. J Dent in decreasing water movement. However, they Res 1974; 53: 1408-1413. 2) Craig RG, Powers JM. Restorative dental materials, attributed this event to separating the varnish from th 42) 11 ed, Mosby Inc., St. Louis, 2002, pp.197-284. the surface. In the same vein, Lutz and Phillips 3) Upadhya NP, Kishore G. Glass ionomer cement ― determined that not all light-activated resin bonding the different generations. Trends Biomater Artif agents were successful in protecting the cement. Organs 2005; 18: 158-165. These differences in findings could be attributed to 4) Wilson AD. Developments in glass-ionomer cements. variations in the physical and chemical properties of Int J Prosthodont 1989; 2: 438-446. the resins. 5) Wilson AD, Paddon JM, Crisp S. The hydration of In our study, the effectiveness of different dental cements. J Dent Res 1979; 58: 1065-1071. surface protectors in preventing dye absorption was 6) Mathis RS, Ferracane JL. Properties of a glass- ionomer/resin-composite hybrid material. Dent evaluated. Results for surface protectors combined Mater 1989; 5: 355-358. with conventional GIC showed statistically significant 7) McLean JW, Nicholson JW, Wilson AD. Proposed differences in comparison with the positive control nomenclature for glass-ionomer dental cements and group. Further, Adper Single Bond absorbed signifi- related materials. Quintessence Int 1994; 25: 587- cantly more dye compared to the negative control 589. group. The results of our study agreed with those of 8) Uno S, Finger WJ, Fritz U. Long-term mechanical previous studies19,30,36-41). characteristics of resin-modified glass ionomer As for the results of the surface protectors restorative materials. Dent Mater 1996; 12: 64-69. 9) Wilson AD. Resin modified glass-ionomer cements. applied on Dyract AP, it was observed that LC Int J Prosthodont 1990; 3: 425-429. Varnish absorbed the least dye and Adper Single 10) Mitra SB. Adhesion to dentin and physical Bond absorbed the most. When the same surface Dent Mater J 2009; 28(1): 96－101 101

properties of a light-cured glass-ionomer liner/base. Quintessence Int 1995; 26: 351-358. J Dent Res 1991; 70: 72-74. 28) Iwami Y, Yamamoto H, Sato W, Kawai K, Torii M, 11) Yap AUJ, Tan S, Teh TY. The effect of polishing Ebisu S. Weight change of various light-cured systems on microleakage of tooth coloured restorative materials after water immersion. Oper restoratives: Part I. Conventional and resin-modified Dent 1998; 23: 132-137. glass-ionomer cements. J Oral Rehabil 2000; 27: 29) Cattani-Lorente MA, Dupuis V, Moya F, Payan J, 117-123. Meyer JM. Comparative study of the physical 12) Van Dijken JWV. 3-year clinical evaluation of properties of a polyacid-modified composite resin and compomer, a resin modified glass ionomer and a a resin-modified glass ionomer cements. Dent Mater resin composite in Class III restorations. Am J Dent 1999; 15: 21-32. 1996; 9: 195-198. 30) Meyer JM, Cattani-Lorente MA, Dupuis V. 13) De Trey/Dentsply, Konstanz, Germany. Technical Compomers: between glass-ionomer cements and information. composites. Biomaterials 1998; 19: 529-539. 14) Ramos RP, Chimello DT, Chinelatti MA, Dibb RG, 31) Yap AUJ. Resin-modified glass-ionomer cements: a Mondelli J. Effect of three surface sealants on comparison of water sorption characteristics. marginal sealing of Class V composite resin Biomaterials 1996; 17: 1897-1900. restorations. Oper Dent 2000; 25: 448-453. 32) Li Y, Swartz ML, Phillips RW, Moore BK, Roberts 15) Sidhu SK, Watson TF. In vitro surface treatment TA. Effect of filler content and size on properties of and water balance of resin-modified glass-ionomers. composites. J Dent Res 1985; 64: 1396-1401. J Dent Res 1995; 74: 475 (Abstract No. 599). 33) Mount GJ. Glass-ionomer cements: Past, present 16) Bouschlicher MR, Vargas MA. Effect of desiccation and future. Oper Dent 1994; 19: 82-90. on microleakage of glass-ionomer restorative 34) Beltrao HCP, Manfio AR, Navarro MFL, Souza materials. J Dent Res 1995; 74: 109 (Abstract No. MHS. Clinical evaluation of conventional versus 778). light-cured restorative glass ionomer cements. J 17) McLean JW. Clinical applications of glass-ionomer Dent Res 1996; 75: 65 (Abstract No. 383). cements. Oper Dent 1992; 5: 184-190. 35) Small ICB, Watson TF, Chadwick AV, Sidhu SK. 18) Serra MC, Navarro MFL, Freitas SFT, Carvalho Water sorption in resin-modified glass-ionomer RM, Cury JA, Retief DH. Glass-ionomer cement cements: An in vitro comparison with other surface protection. Am J Dent 1994; 7: 203-206. materials. Biomaterials 1998; 19: 545-550. 19) Chuang SF, Jin YT, Tsai PF, Wong TY. Effect of 36) Jevnikar P, Sersa I, Sepe A, Jarh O, Funduk N. various surface protections on the margin Effect of surface coating on water migration into microleakage of resin-modified glass ionomer resin-modified glass ionomer cements: a magnetic cements. J Prosthet Dent 2001; 86: 309-314. resonance micro-imaging study. Magn Reson 20) Nicholson JW, McLean JW. A preliminary report on Medicine 2000; 44: 686-691. the effect of storage in water on the properties of 37) Ribeiro AP, Serra MC, Paulillo LA, Rodrigues Junior commercial light-cured glass-ionomer cements. Br AL. Effectiveness of surface protection for resin- Dent J 1992; 173: 98-101. modified glass-ionomer materials. Quintessence Int 21) Hondrum SO. Storage stability of dental luting 1999; 30: 427-431. agents. J Prosthet Dent 1999; 81: 464-468. 38) Earl MSA, Mount GJ, Hume WR. The effect of 22) Feilzer AJ, Kakaboura AI, de Gee AJ, Davidson CL. varnishes and other surface treatments on water The influence of water sorption on the development movement across the surface of a glass ionomer of setting shrinkage stress in traditional and resin- cement: II. Austral Dent J 1989; 34: 326-329. modified glass ionomer cements. Dent Mater 1995; 39) Watson TF, Banerjee A. Effectiveness of glass- 11: 186-190. ionomer surface protection treatments: a scanning 23) Cattani-Lorente MA, Dupuis V, Payan J, Moya F, optical microscope study. Eur J Prosthodont Restor Meyer JM. Effect of water on the physical properties Dent 1993; 2: 85-90. of resin-modified glass ionomer cements. Dent 40) Hotta M, Hirukawa H, Yamamoto K. Effect of Mater 1995; 15: 71-78. coating materials on restorative glass-ionomer 24) Yap A, Lee CM. Water sorption and solubility of cement surface. Oper Dent 1992; 17: 57-61. resin-modified polyalkenoate cements. J Oral 41) Hotta M, Hirukawa H. Abrasion resistance of Rehabil 1997; 24: 310-314. restorative glass-ionomer cements with a light-cured 25) Anstice HM, Nicholson JW. Studies on the structure surface coating. Oper Dent 1994; 19: 42-46. of light-cured glass-ionomer cements. J Mater Sci 42) Lutz F, Phillips RW. A classification and evaluation Mater Med 1992; 3: 447-451. of composite resin systems. J Prosthet Dent 1983; 26) Kanchanavasita W, Pearson GJ, Anstice HM. 50: 480-488. Influence of humidity on dimensional stability of a 43) Cefaly DFG, Seabra BGM, Tapety CMC, Taga EM, range of ion-leachable cements. Biomaterials 1995; Valera F, Navarro MFL. Effectiveness of surface 16: 921-929. protection of resin modified glass-ionomer cements 27) Cho E, Kopel H, White SN. Moisture susceptibility evaluated spectrophotometrically. Oper Dent 2001; of resin-modified glass-ionomer materials. 26: 401-405.