|Author:||Lam, Lai-yuen Stella|
|Title:||The effect of 35% hydrogen peroxide on the fracture toughness of hybrid composite resins|
|Other Title:||The effect of thirty-five per cent hydrogen peroxide on the fracture toughness of hybrid composite resins|
|Subject:||Gums and resins|
Hong Kong Polytechnic University -- Dissertations
Jockey Club Rehabilitation Engineering Centre
|Pages:||xi, 78,  leaves : ill. (some col.) ; 30 cm|
|Abstract:||Vital bleaching is getting popular to improve tooth esthetic. Few studies on the effects of bleaching agents on the mechanical properties of composite resins were available, and their results were conflicting. This study was to investigate the effect of 35% H2O2 on the fracture toughness of a popular hybrid composite resin in Hong Kong, the Total Performance Hybrid (TPH). Another hybrid composite Z100 was also evaluated so that our results could be compared to some existing literature data. During specimen making, each 2mm thick composite overlay was cured for 60 seconds by a QHL75TM Curing Light with intensity over 400mW/cm2. Bend specimens (26 mm x 4.8 mm x 2.5 mm) with a 2.5 mm crack were fabricated according to ASTM standard E399 and fractured in 3-point bending in a Hounsfield testing machine with a cross-head speed of 1 mm/mm. Tensile test specimens (60 mm x 10 mm x 2 nun) were fabricated according to ASTM standard D638M and subjected to uniaxial tension until fracture at the same cross-head speed. The tensile strength so obtained was used to calculate the minimum required crack length and specimen thickness for the bend specimens. The minimum specimen thickness required was in the range of 0.704 mm to 1.164 mm. As the specimen thickness in this study was around 2.5 mm, it was confirmed that the specimens in this study satisfied the plane strain condition required of the ASTM standard. The mean KIC of Z100 specimens for this study was 1.338+-0.4576 MPa.m1/2. The mean KIC for Z100 specimens obtained in a previous study was 1.53+-0.06 MPa.m1/2. Comparison by paired t-test indicated the difference between these two means was not significant at 帢=0.05. The mean KIC of TPH specimens not treated with 35% H2O2 was 1.253+-0.097 MPa.m1/2 The mean KIC of TPH specimens treated with 35% H2O2 for three hours was 1.454+-0.139 MPa.m1/2. The mean KIC of TPH specimens treated with 35% H2O2 for six hours was 1.319+-0.097 MIPa.m1/2. One-way ANOVA revealed that there was significant difference between the three samples' KIC values. Newman-Keuls multiple comparison test showed that the specimens treated with H2O2 for three hours had a significantly higher KIC than the specimens not treated with H2O2 and the specimens treated with H2O2 for six hours. The specimens treated with H2O2 for six hours also had a higher mean KIC than the specimens not treated with H2O2, but the difference was not significant. Hence, the aging of hybrid composite resin TPH in 35% H2O2 for up to six hours did not lower their Kics when compared with the control with no bleaching. Future studies are suggested for additional types of composite resins, carbamide peroxide and different exposure time for a more thorough investigation on the effects of bleaching agents on the fracture toughness of composite resins.|
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