Indentation Cracking of Composite Matrix Materials

Abstract

Composite restorative materials wear by a fatigue mechanism in the occlusal contact area. Here, tooth cusps and food debris cyclically indent the restoration. Modeling this phenomenon requires an understanding of material response to indentation. The question in this study was whether material response depends on indenter size and geometry, and also, whether polymers used in restorative materials should be considered elastic and brittle, or plastic and ductile for modeling purposes. Three resins used as matrices in proprietary restorative composites were the experimental materials. To ascertain the influence of glass transition temperature, liquid sorption, and small amounts of filler on indentation response, we prepared materials with various degrees of cure; some samples were soaked in a 50/50 water/ethanol solution, and 3 vol% silica was added in some cases. Indentation experiments revealed that no cracking occurred in any material after indentation by Vickers pyramid or spherical indenters with diameters equal to or smaller than 0.254 mm. Larger spherical indenters induced subsurface median and surface radial and/or ring cracks. Critical loads causing subsurface cracks were measured. Indentation with suitably large spherical indenters provoked an elastoplastic response in polymers, and degree of cure and Tg had less influence on critical load than soaking in solution. Crack morphology was correlated with yield strain. Commonly held assumptions regarding the brittle elastic behavior of composite matrix materials may be incorrect.

Silica film coating method for veneering resin composite

“…Although the glass-transition temperature of veneering resin composites varies with the type of monomer and the degree of conversion, for most materials it is more than 120˚C 20,21) . In the temperature environment of the present study, formation of silica from PHPS was possible at temperatures below that described above.…”

Resin composites in dentistry: the monomer systems

“…Among the latter is the glass transition temperature T^. T^ has been found to be well correlated to degree of conversion in polymers based on a number of different dimethacrylates (42,46). Depending of the conditions,, the values of Tg were found in the temperature range of 55°C-150°C (42,46).…”

Degradation, Fatigue, and Failure of Resin Dental Composite Materials

“…Inclined flaws or cracks are also observed in wear loading in many composite materials. Baran et al (1994, 1998) using an indenter to study wear, observed, that although the majority of surface cracks ran originally orthogonal to the surface, they changed direction to run 20 to 30° to the horizon in the direction of the indenter movement. In fact, it is believed that fracture characteristics of any composite material could be realistically investigated under combined fracture modes because the highly heterogeneous materials' microstructures give rise to curved crack paths.…”