CrackPropagation Directions inUnfilled Resins

Posterior composite restorative materials undergo accelerated wearintheocclusal contact area, primarily through afatigue mechanism. Tofacilitate thetimely development ofnewandimproved materials, apredictive wearmodelisdesirable. Theobjective ofthis study wasto develop afinite element modelenabling investigators to predict crack propagation directions inresins usedasthe matrixmaterial incomposites, andtoverify these predictions byobserving cracks formed during thepin-on- discwearofa60:40BISGMA:TEGDMAresinandan EBPADMAresin. Laserconfocal scanning microscopy was usedtomeasure crack locations. Finite element studies were donebymeansofABAQUSsoftware, modeling acylinder sliding onamaterial withpre-existing surface-breaking cracks. Variables included modulus, cylinder/material friction coefficient, crack facefriction, andyield behavior. Experimental results weresurprising, sincemostcrack directions wereopposite previously published observations. Themajority ofsurface cracks, though initially orthogonal tothesurface, changed direction torun20to300fromthe horizontal inthedirection ofindenter movement. Finite element modeling established theimportance ofsubsurface shear stresses, since calculations provided evidence that cracks propagate inthedirection ofmaximumKII(O), inthe samedirection asthemotionoftheindenter, andatanangle ofapproximately 200.Thesefindings providethe foundation forapredictive modelofsliding wearinunfilled glassy resins.