Color Stability of Silicone or Acrylic Denture Liners: An in Vitro Investigation Gulfem Erguna, DDS, PhD Isil Cekic Nagasb, DDS AbstrAct Objectives: The aim of this study was to compare the color stability of three acrylic based hard liners (Ufi gel hard, Dura-Liner II, Tokuso Rebase) and two silicone based soft liners (Ufi gel perma- nent, Molloplast B) by using the colorimeter. Methods: Sixty disc-shaped samples, with uniform size of 10 mm diameter and 2 mm in thick- ness were fabricated for each material. Thirty samples were made as control group in distilled water and the remaining thirty samples were weathered in accelerated aging chamber. Color mea- surements were made before and after distilled water and aging. Data were statistically analyzed using nonparametric Kruskal-Wallis and Mann-Whitney U tests. Results: Data showed that there are significant differences among materials in both after dis- tilled water and aging treatments (P<.001). These results indicated that the most discolored liner material was Dura Liner II after aging (∆E*=16.30) and the least discolored material was Ufi gel permanent after distilled water (∆E*=0.41). Conclusions: Based on the results of this study, silicone based liner materials are considered to be more color stable than acrylic based liner materials. (Eur J Dent 2007;1:144-151) Key words: Silicone; Acrylic liners; Color stability. IntroducIno Denture lining materials are widely used for the base of a denture to reduce pain or to improve the fit between the denture and mucous membrane.1 They act as a cushion and provide an even distri- bution of functional load onto the stress-bearing mucosa.2 Application of a soft lining material to the dentures can also increase the patient’s mas- ticatory performance, biting force and improve the chewing rhythm.3 Denture lining materials can be classified a Associate Professor, Department of Prosthodontics, Faculty of Dentistry, Gazi University, Ankara, Türkiye b Research Assistant, Department of Prosthodontics, Faculty of Dentistry, Gazi University, Ankara, Türkiye Corresponding Author: Dr. Gulfem Ergun Address: Süslü sok. 14/9Tandoğan/Ankara 06580 Türkiye Tel.: +90 312 213 97 01 Fax: +90 312 223 92 26 E-mail : gulfem@gazi.edu.tr, ergungulfem@yahoo.com. as provisional or permanent, silicone rubber or acrylic resin, and can be either chemically or heat polymerized.4 A provisional liner is the one used intraorally for up to 30 days and a long-term liner is categorized as the one that maintains its soft- ness and elasticity for more than 30 days.5 Fur- thermore, in a study, a long term liner was clas- sified to be the one used for 1 year or longer.6 Silicone based lining materials are basically di- methylsiloxane polymers and do not contain plas- ticizer to produce softening effect.7 These lining materials are hydrophobic; this reduces water sorption, but simultaneously inhibits good affin- ity to the supporting tissues.8 Acrylic based lining materials are composed of the powder consisting of a higher methacrylate polymer (usually poly ethyl methacrylate) and a liquid of a higher meth- acrylate monomer (e.g. ethyl, n-butyl), in addition a plasticizer, commonly a phythalate.9,10 When im- 144 European Journal of Dentistry