The reduction in fatigue crack growth resistance of dentin with depth.

The fatigue crack growth resistance of dentin was characterized as a function of depth from the dentino-enamel junction. Compact tension (CT) specimens were prepared from the crowns of third molars in the deep, middle, and peripheral dentin. The microstructure was quantified in terms of the average tubule dimensions and density. Fatigue cracks were grown in-plane with the tubules and characterized in terms of the initiation and growth responses. Deep dentin exhibited the lowest resistance to the initiation of fatigue crack growth, as indicated by the stress intensity threshold (ΔK(th) ≈ 0.8 MPa•m(0.5)) and the highest incremental fatigue crack growth rate (over 1000 times that in peripheral dentin). Cracks in deep dentin underwent incremental extension under cyclic stresses that were 40% lower than those required in peripheral dentin. The average fatigue crack growth rates increased significantly with tubule density, indicating the importance of microstructure on the potential for tooth fracture. Molars with deep restorations are more likely to suffer from the cracked-tooth syndrome, because of the lower fatigue crack growth resistance of deep dentin.

Is malaria a predisposing factor for third molar pericoronitis in the tropics?

BACKGROUND: Malaria is an important disease in the tropics, and its role as a predisposing factor or co morbidity has been investigated in many diseases including HIV infection and tuberculosis. There are very few studies, which have investigated its role in oral and dental diseases. Our study aimed to demonstrate the possible role of malaria in predisposing to pericoronitis, an infection affecting impacted third molars predominantly. PATIENTS AND METHODS: Thirty-eight patients presenting with pericoronitis were tested for malaria parasites and results compared with that obtained from controls that were equally susceptible to pericoronitis but did not have the infection. RESULTS: 19.7% of the study group compared to 6.6% of control group had malaria parasite in their blood. This difference was statistically significant, P=0.018 (Fisher's exact). The odds ratio was 4.3 (95% CI=1.2-17.0). CONCLUSIONS: Malaria appears to be a predisposing factor to pericoronitis in this study. There is a need for further studies on the possible role of malaria in oral and dental diseases.