applied fracture mechanics

Fracture of Dental Materials 117However, thanks to the rod and tubule orientations in the cervical and mid crown regions,the material characteristics of the enamel in these bendable regions are represented by theseries model, thereby allowing the tooth to flex somewhat and absorb mechanical energyrather than fracture.Figure 8. A tooth loaded in axial direction (blue arrow) responds in two ways. On the cusp tips, therods and the tubules are oriented parallel with the load and resulting in a material which modulus canbe predicted from a parallel model prediction. In the cervical region of the tooth, the modulus can bepredicted from a series model.Some basic science studies have been conducted to study the fracture behavior of enameland dentin through the years. In one such study [7] the investigators studied a mandibularmolar tooth restored with different Class II amalgam preparations. By use of finite elementanalysis, the stress distribution induced along the internal edges as a result of occlusal loadingwas calculated, and by use of Paris law the cyclic crack growth rate of sub-surface flawslocated along the dentinal internal edges was determined. Based on the assumptions used intheir calculations, they claimed that flaws located within the dentin along the buccal andlingual internal edges can reduce the fatigue life of restored teeth significantly. Sub-surfacecracks as short as 25 μm were capable of promoting tooth fracture well within 25 years fromthe time of restoration placement. Furthermore, cracks longer than 100 μm reduced thefatigue life of the tooth to less than 5 years. Consequently, sub-surface cracks introduced