Flexure Strength and Compressive Fracture Force of Aged Composite Resins

Bulk fracture of composite resins (CR) can be a factor in their  longevity. Aging of CR may relate to Flexure Strength and force require for bulk fracture.

Objective: To evaluate the Flexure Strength (FS) and Compresive Fracture Force (CF) of CR after NaOH aging treatment.

Method: : Shade A2 CR were shaped into 26x2x2mm rectangular FS samples and cured from the top and bottom with a >550Mw/cm2 light (40sec.). A control group(CG)(n=8) and test group(TG)(n=8) were made for each of the two CR: Gradia(GCG,GTG), and VoccoGrandio(VCG,VTG). Also, cylindrical 6mm-diameterx3mm CF samples (n=16) were made and cured (40sec.) in two layers from the top surface.  CG(n=8) and TG(n=8) tests were made for Gradia, Kalore and VoccoGrandio. CG and TG samples were placed in individual vials of deionized water or 0.1N NaOH at 60°C for 2 weeks. FS samples were tested to failure on an Instron at .05mm/min. and the FS was calculated. CF samples were Compression Fracture force tested by Vicker's diamond indentor 0.4mm inside the top edge until  fractured by an Instron at.05mm/min..

Result: Mean FS&[CF] were: GCG:112.5+/-34.8MPa[120+/-7.61lbs], GTG:128+/-19.4MPa[104.4+/-8.1lbs], VCG:137.4+/-5.3MPa[65.3+/-17.4lbs], VTG:127+/-36.5MPa[57.8+/-17.4.4lbs], KCG:[95.9+/-15.9lbs], KTG:[115.4+/-29.1lbs], ANOVA with  a Newman-Keuls test(N-Ktest) (p=0.05) or student-t tests were used to compare the CF of the CG and TG among CR while student compared the treatment effect of each composite and FS of the CR.

Conclusion:  For CF: GCG >KCG>VCG  and GTG=KTG>VTG in rank order of N-K test and GCG and GTG,Gradia only showed a slight aging effect in NaOH (SD) at p=.05.  The FS Student t-test showed no difference between composites or treatment of each CR. NaOH Aging was not  evident in the FS testing.