title: Shore hardness and tensile bond strength of long-term soft denture lining materials.
abstract: BACKGROUND
  Reduced softness and separation from the denture base are the most significant problems of long-term soft lining materials.
  
  
  OBJECTIVE
  The purpose of this study was to evaluate the durometer Shore A hardness and tensile bond strength of long-term soft denture lining materials and to investigate the correlation between these 2 properties.
  
  
  METHODS
  A group of 7 soft lining materials, 6 silicone based (Dentusil, GC Reline Soft, GC Reline Ultrasoft, Mucopren Soft, Mucosoft, Sofreliner Tough) and 1 acrylic resin based (Durabase), were evaluated for durometer Shore A hardness and tensile bond strength to heat-polymerized denture base resin (Lucitone 199). A specially designed split mold and loading assembly with a swivel connector were used for the durometer Shore A hardness test and tensile bond strength test to improve accuracy and facilitate measurement. Three specimens of each product were stored in a 37°C water bath, and durometer Shore A hardness tests were carried out after 24 hours and 28 days. A tensile bond strength test was carried out for 10 specimens of each product, which were stored in a 37°C water bath for 24 hours before the test. Repeated-measures ANOVA, the Kruskal-Wallis and Duncan multiple range tests, and the Spearman correlation were used for statistical analyses.
  
  
  RESULTS
  The repeated-measures ANOVA found significant durometer Shore A hardness differences for the materials (P<.001) and the interaction effect (aging×materials) (P<.001). GC Reline Ultrasoft showed the lowest mean durometer Shore A hardness (21.30 ±0.29 for 24 hours, 34.73 ±0.47 for 28 days), and GC Reline Soft showed the highest mean durometer Shore A hardness (50.13 ±0.48 for 24 hours, 57.20 ±0.28 for 28 days). The Kruskal-Wallis test found a significant difference in the mean tensile bond strength values (P<.001). GC Reline Ultrasoft (0.82 ±0.32 MPa) and Mucopren Soft (0.96 ±0.46 MPa) had a significantly lower mean tensile bond strength (P<.05). GC Reline Soft had the highest mean tensile bond strength (2.99 ±0.43 MPa) (P<.05), and acrylic resin-based Durabase showed a significantly different tensile bond strength (1.32 ±0.16 MPa), except for Mucopren Soft, among the materials (P<.05). The tensile bond strength and Shore A hardness showed a statistically insignificant moderate positive correlation (r=0.571, P=.180 for Shore A hardness 24 hours versus tensile bond strength; r=0.607, P=.148 for Shore A hardness 28 days versus tensile bond strength).
  
  
  CONCLUSIONS
  Within the limitations of this study, significant differences were found in durometer Shore A hardness (with aging time) and tensile bond strength among the materials. Adhesive failure was moderately correlated with durometer Shore A hardness, especially after 28 days, but was not significant.
authors.affiliation: Graduate student, Department of Dental Materials and Research Center for Biomineralization Disorders, School of Dentistry, Chonnam National University, Gwangju, Korea.
authors.forename: Bong-Jun
authors.initials: BJ
authors.lastname: Kim
authors.affiliation: Professor, Department of Prosthodontics, School of Dentistry, Chonnam National University, Gwangju, Korea.
authors.forename: Hong-So
authors.initials: HS
authors.lastname: Yang
authors.affiliation: Graduate student, Department of Dental Materials and Research Center for Biomineralization Disorders, School of Dentistry, Chonnam National University, Gwangju, Korea.
authors.forename: Min-Geoung
authors.initials: MG
authors.lastname: Chun
authors.affiliation: Professor, Department of Dental Materials and Research Center for Biomineralization Disorders, School of Dentistry, Chonnam National University, Gwangju, Korea. Electronic address: yjpark@jnu.ac.kr.
authors.forename: Yeong-Joon
authors.initials: YJ
authors.lastname: Park
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry; D000268:Adhesiveness; D001840:Dental Bonding; D003764:Dental Materials / Q000737:chemistry*; D003819:Denture Bases; D003822:Denture Liners; D006244:Hardness; D006801:Humans; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D011145:Polyvinyls / Q000737:chemistry; D012828:Silicones / Q000737:chemistry; D012833:Siloxanes / Q000737:chemistry; D013314:Stress, Mechanical; D013696:Temperature; D013718:Tensile Strength; D013997:Time Factors; D014783:Viscosity; D014867:Water / Q000737:chemistry
chemical_list: D000180:Acrylic Resins; D003764:Dental Materials; D008689:Methacrylates; D011145:Polyvinyls; D012828:Silicones; D012833:Siloxanes; C034183:vinyl polysiloxane; D014867:Water; C040291:Lucitone