Color stability of denture liners 150 550) in 55°C water bath resulted in an arrange- ment as Kooliner (1.52%) > DL (0.85%) > UH (0.45%) > Lucitone 550 (0.24%) > TR (0.14%). In the present study, DL showed poor color stability af- ter aging (∆E*=16.30). This result might be related to the amount of leaching residual monomer with color stability. Several studies have been done about the color measurements by using colorimeters21,22 and usu- ally these studies have been compared directly. The present results cannot be compared directly with previous studies because of the variations in the instruments used, sample sizes and condition- ing of the samples. Although the system of color change is not known exactly, it could be guessed by investigating how aging changes the physical and mechanical properties of denture liners.17,19 Test conditions used for in vitro studies do not subject the materials to the aqueous environment, microorganisms, abrasion, thermocycling, mate- rial thickness and cyclic loading. The properties of liner materials in the clinical situations still differ from laboratory testing.42 There also seems to be a need for extra researches to understand the effect of aging on color change mechanism. ocnLusIons Accelerated aging affected color stability of all the materials tested. The measurements showed that UP and MP are clinically reliable denture liner materials. From a clinical aspect, for long-term clinical serviceability, it seems reasonable to recommend the use of silicone based instead of acrylic based liner materials. rEFErEncEs 1. Fujii K, Arikawa H, Kanie T, Shinohara N, Inoue K. Effect of photo-irradiation on hardness of soft lining materials for denture base. J Oral Rehabil 2002;29:744-748. 2. Minami H, Suzuki S, Ohashi H, Kurashige H, Tanaka T. Ef- fect of surface treatment on the bonding of an autopoly- merizing soft denture liner to a denture base resin. Int J Prosthodont 2004;17:297-301. 3. Hayakawa I, Keh ES, Morizawa M, Muraoka G, Hirano S. A new polyisoprene-based light-curing denture soft lining material. J Dent 2003;31:269-274. 4. Garcia RM, Leon BT, Oliveira VB, Del Bel Cury AA. Effect of a denture cleanser on weight, surface roughness and ten- sile bond strength of two resilient denture liners. J Prosthet European Journal of Dentistry Dent 2003;89:489-494. 5. Garcia LT, Jones JD. Soft liners. Dent Clin North Am 2004;48:709-720. 6. Kawano F, Dootz ER, Koran III A, Craig RG. Sorption and sol- ubility of 12 soft denture liners. J Prosthet Dent 1994;72:393- 398. 7. Pinto JR, Mesquita MF, Henriques GE, de Arruda Nobilo MA. Effect of thermocycling on bond strength and elas- ticity of 4 long-term soft denture liners. J Prosthet Dent 2002;88:516-521. 8. Walters MGJ, Jagger RG, Polyzois GL. Wettability of sili- cone rubber maxillofacial prosthetic materials. J Prosthet Dent 1999;81:439-443. 9. Polyzois GL, Frangou MJ. Influence of curing method, sealer, and water storage on the hardness of a soft lining material over time. J Prosthodont 2001;10:42-45. 10. Haywood J, Basker RM, Watson CJ, Wood DJ. A compari- son of three hard chairside denture reline materials. Clini- cal evaluation. Eur J Prosthodont Restor Dent 2003;11:157- 163. 11. Parr GR, Rueggeberg FA. In vitro hardness, water sorption, and resin solubility of laboratory-processed and autopoly- merized long-term resilient denture liners over one year of water storage J Prosthet Dent 2002;88:139-144. 12. Anil N, Hekimoglu C, Sahin S. The effect of accelerated ag- ing on color stability of denture liners. J Oral Sci 1998;3:105- 108. 13. Al-Athel M, Jagger R, Jagger D. Effect of ageing on the bond strength of a permanent denture soft lining material. J Oral Rehabil 2002;29:992-996. 14. El-Hadary A, Drummond JL. Comparative study of water sorption, solubility, and tensile bond strength of two soft lining materials. J Prosthet Dent 2000;83:356-361. 15. Anil N, Hekimoglu C, Buyukbas N, Ercan MT. Microleakage study of various soft denture liners by autoradiography: Ef- fect of accelerated aging. J Prosthet Dent 2000; 84:394-399. 16. Leon BL, Del Bel Cury AA, Rodrigues Garcia RC. Water sorption, solubility, and tensile bond strength of resilient denture lining materials polymerized by different methods after thermal cycling. J Prosthet Dent 2005;93:282-287. 17. Anil N, Hekimoglu C, Sahin S. Color stability of heat-po- lymerized and auto-polymerized soft denture liners. J Pros- thet Dent 1999;81:481-484. 18. Jin C, Nikawa H, Makihira S, Hamada T, Furukawa M, Mu- rata H. Changes in surface roughness and colour stability of soft denture lining materials caused by denture cleans- ers. J Oral Rehabil 2003;30:125-130. 19. Kawano F, Koran A, Nuryanti A, Inoue S. Impact absorption of four processed soft denture liners as influenced by ac- celerated aging. Int J Prosthodont 1997;10:55-60.