Ethnic background influences the crack growth resistance of dentin

Age related chemical and morphological changes in hard tissues often have undesired consequences on their physical and mechanical properties. While the importance of aging is becoming well recognized, there is an insufficient knowledge of whether ethnicity is also important to the aging process and consequent mechanical behavior of hard tissues.

Objectives: To quantify the influence of aging and ethnicity on the fatigue crack growth properties of human dentin.

Methods: Compact Tension (CT) specimens were sectioned from the coronal dentin of unrestored molars obtained from senior patients of the US (n=10, age=58±14) and Asia (n=10, age=63±10). All specimens were subjected to Mode I loads with stress ratio (R) and frequency of 0.1 and 5 Hz, respectively. Steady-state fatigue crack growth was quantified according to the Paris Law in terms of the crack growth exponent (m) and coefficient (C). In addition, Electron Dispersive X-ray Analysis (EDXA) and Scanning Electron Microscopy were performed to study differences in chemistry and structure.

Results: Overall, the fatigue crack growth rates ranged from 4E-7 to 1E-03 mm/cycle over a stress intensity range from 0.5 to 1.0 MPa•m^0.5. The average m for dentin from the Asian group (23.6±5.1) was not significantly different than that of the US group (22.1±5.1). However, the average crack growth coefficient (C) of the Asian group [7.3E-01 mm/cycle•(MPa•m^0.5)^-m] was significantly higher (p<0.001) than the US group [4.8E-03 (mm/cycle)•(MPa•m^0.5)^-m]. At a stress intensity range of 0.7 MPa•m^0.5 the rate of crack growth in the Asian group was over 100 times greater than that in the US group. There were no significant differences in morphology or chemistry between the Asian and US groups.

Conclusion: Preliminary results suggest that ethnic background is an important factor in evaluating the fatigue crack growth resistance of dentin.

(Supported by NSF BES 020521467 and NIDCR DE016904).