Dentin Grows More Brittle With Age

A number of studies indicate that dentin tends to become brittle and fracture more easily with age, potentially leading to the expensive repair and/or extraction of an otherwise healthy tooth. With more seniors now keeping their teeth for a lifetime, dentists have begun to ask why and how dentin fractures occur and whether anything can be done to prevent the problem. In a study by Nazari, et al, published in Journal of the Mechanical Behavior of Bio­medical Materials (October 2009), a group of National Institute of Dental and Cranifacial Research (NIDCR)-supported scientists provide some needed baseline data on the fracture toughness of aging human dentin. 

Most cracks and fractures in dentin within the crown region of a tooth (cor-onal dentin) run perpendicular to the tubules. Thus, in this study, the scientists for the first time quantified the fracture toughness of coronal dentin for cracks that extended perpendicular to the tubules. They performed their analysis using 14 wisdom teeth that had been extracted from pa­tients between the ages of 18 and 83. This allowed them to compare and contrast the toughness of young, middle-aged, and old dentin. The scientists found that the average fracture toughness of the old dentin was ap­prox­imately 30% lower than that of the young den­tin. They noted that the re­duction in fracture toughness seemed to depend on the number of lumens, or inner space of the tubules filled with mineral. This is important in determining the mineral-to-collagen ra­tio and thus the variation through­out dentin in the degree of age-related sclerosis, or embrittlement. The reduction also depended, regardless of age, on the spatial orientation of the tu­bules. As the authors ex­plained, the degree of toughening with crack extension is lowest for those that extend perpendicular to the tubules. Moreover, although the toughness of dentin de­creases with age, the degree of anisotropy in resistance to fracture does not. Ani­so­tropy is a physics term that means having a different val­ue when measured in different directions. 

“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.”