title: The influence of cyclic stress on surface properties of soft liners.
abstract: Soft polymers used under tissue-supported prostheses have limited service life because of surface degradation.
  
  
  OBJECTIVE
  This paper evaluates the changes in surface properties and softness of soft relining materials after cyclic loading in water.
  
  
  METHODS
  3 polysiloxane (Silagum AM Comfort, Molloplast B, Mollosil Plus) and 2 acrylic-based (Vertex Soft, Astron LC Soft) proprietary soft relining materials and a vinyl polysiloxane (Imprint 2 Garant) as the reference impression material evaluated. A stainless steel block for detail reproduction was used on the basis of the apparatus recommended by the ISO 4823:1992 test method for preparing a standardized surface. A control group from each material was only subjected to water immersion. Non-destructive cyclic loading was carried out with a strain of 16.6 % and a frequency of 1.6 Hz 200,000 times in distilled water at 37 °C. The specimens were then duplicated and compared with the controls using roughness measurements, detail reproduction and Scanning Electron Microscope. Shore A hardness values before and after cycling were also measured.
  
  
  RESULTS
  After degradation in the form of mechanical cycling in water, loss of substance and loss of surface detail was observed. Surface properties and Shore A hardness values of acrylic-based soft liners changed significantly (p < 0.05).
  
  
  CONCLUSIONS
  The chemical composition of the soft relining materials seemed to affect their potential of preserving the surface texture and softness after mechanical cycling. Mechanical cycling influences the surface degradation process leading to changes of the surface texture. Polysiloxane-based materials preserved their softness, surface texture and surface smoothness better under cyclic loading compared to acrylic resin -based plasticized materials.
authors.affiliation: Clinic of Oral Diseases, Turku University Central Hospital, TYKS, Turku, Finland. mmutluay@utu.fi.|Department of Restorative Dentistry and Cariology, Institute of Dentistry, University of Turku, Lemminkaisenkatu 2, Turku, Finland. mmutluay@utu.fi.
authors.forename: M Murat
authors.initials: MM
authors.lastname: Mutluay
authors.affiliation: Clinic of Oral Diseases, Turku University Central Hospital, TYKS, Turku, Finland.|Department of Restorative Dentistry and Cariology, Institute of Dentistry, University of Turku, Lemminkaisenkatu 2, Turku, Finland.
authors.forename: Arzu
authors.initials: A
authors.lastname: Tezvergil-Mutluay
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry; D003764:Dental Materials / Q000737:chemistry*; D003799:Dental Stress Analysis; D003822:Denture Liners; D006244:Hardness; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D011145:Polyvinyls / Q000737:chemistry; D012833:Siloxanes / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties
chemical_list: D000180:Acrylic Resins; D003764:Dental Materials; D011145:Polyvinyls; D012833:Siloxanes; C034183:vinyl polysiloxane
keywords: Denture; Detail reproduction; Hardness; Polysiloxane; Roughness; Soft liner; Surface