Effect of relining, water storage and cyclic loading on the flexural strength of a denture base acrylic resin.
OBJECTIVE
This study investigated the effect of relining, water storage and cyclic loading on the ultimate flexural strength (FS(U)) and on the flexural strength at the proportional limit (FS(Pl)) of a denture base acrylic resin (Lucitone 550-L).


METHODS
Rectangular bars of L were made (64 mm x 10 mm x 2 mm) and relined (1.3mm) with four relining resins (Kooliner-K, Ufi Gel Hard-UGH, Tokuso Rebase Fast-TR and New Truliner-NT). In addition, specimens relined with L and intact L specimens were made (64 mm x 10 mm x 3.3 mm). A three-point flexural test was applied on the specimens (n=10) after (1) polymerization; (2) water storage (30 days); (3) cyclic loading (10,000 cycles at 5 Hz) and (4) water storage (30 days)+cyclic loading. Data (MPa) were analyzed with three-way ANOVA and Tukey's HSD tests (alpha=0.05). To test for a possible correlation between FS(U) and FS(Pl), a linear regression coefficient "r" was calculated.


RESULTS
After water storage, L-UGH and L-TR demonstrated an increased FS(U) (41.49-50.64 MPa and 49.95-57.36 MPa, respectively) (P<0.05). Only L-TR demonstrated an increased FS(Pl) (20.58-24.21 MPa) after water storage (P<0.05). L-L had the highest FS(U) (between 78.57 and 85.09 MPa) and FS(Pl) (between 31.30 and 34.17 MPa) (P<0.05). The cyclic loading decreased the FS(U) and FS(Pl) of all materials (P<0.05). Regression analysis showed a strong linear correlation between the two variables (r=0.941).


CONCLUSIONS
Water storage improved the FS(U) of L-UGH and L-TR and the FS(Pl) of L-TR. L-L produced the highest FS(U) and FS(Pl). The FS(U) and FS(Pl) of all materials were detrimentally influenced by cyclic loading.
Department of Dental Materials and Prosthodontics, São Paulo State University, UNESP, Araraquara Dental School, São Paulo, Brazil.
José Maurício dos Santos Nunes
JM
Reis
Carlos Eduardo
CE
Vergani
Ana Cláudia
AC
Pavarina
Eunice Teresinha
ET
Giampaolo
Ana Lucia
AL
Machado
D000180:Acrylic Resins / Q000737:chemistry*; D003764:Dental Materials / Q000737:chemistry*; D003819:Denture Bases; D003822:Denture Liners; D003823:Denture Rebasing; D006801:Humans; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D018583:Pliability; D011108:Polymers / Q000737:chemistry; D012826:Silicone Elastomers / Q000737:chemistry; D013314:Stress, Mechanical; D013997:Time Factors; D014867:Water / Q000737:chemistry*
D000180:Acrylic Resins; D003764:Dental Materials; D008689:Methacrylates; D011108:Polymers; D012826:Silicone Elastomers; C503430:Tokuso Rebase Fast; C483158:Ufi gel; D014867:Water; C103363:kooliner; C071514:truliner; C040291:Lucitone