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Dentin grows more brittle with age

Scientists have quantified the fracture toughness of coronal dentin for cracks that extended perpendicular to the tubules, according to an article published in the October issue of Journal of the Mechanical Behavior of Biomedical Materials.

Researchers from University of Maryland, Baltimore, and Shanghai University performed an analysis using 14 third molars that had been extracted from patients between the ages of 18 and 83 years, which allowed them to compare and contrast the toughness of young, middle-aged and old dentin.

The research team, led by Dwayne D. Arola, PhD, of the Department of Mechanical Engineering, University of Maryland, Baltimore County, Baltimore, found that the average fracture toughness of the old dentin was approximately 30 percent lower than that of the young dentin. They noted that the reduction in fracture toughness seemed to depend on the number of lumens, which is important in determining the mineral-to-collagen ratio and the variation in the degree of age-related sclerosis, or embrittlement, throughout dentin.

Researchers also found that the reduction in fracture toughness depended, regardless of age, on the spatial orientation of the tubules. As they explained in the article, the degree of toughening with crack extension is lowest for those that extend perpendicular to the tubules. Although the toughness of dentin decreases with age, the degree of anisotropy—having a different value when measured in a different direction—in resistance to fracture does not.

"Many of the current practices in the field of restorative dentistry are based on knowledge of the tooth tissues," the authors concluded. "However, they have not necessarily been developed to accommodate changes in the mechanical properties that are associated with aging. Results of this investigation have provided further evidence that aging results in significant changes in the mechanical behavior of dentin and a reduction in the 'damage tolerance' of the tissue.

"With these findings in mind, the success of specific practices in the field of restorative dentistry may require special consideration in the treatment of seniors, or the development of age-sensitive methods of care."

The authors were supported by the National Institute of Dental and Craniofacial Research.