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Study Confirms Dentin Grows More Brittle With Age

September 15, 2009

Young dentin

Just about everyone knows that our bones grow more brittle and susceptible to fracture with age.  But bones aren’t the only hard tissue in the body that might be a problem in our latter years.  A number of studies indicate that dentin, the load-bearing core of our teeth located below the enamel, tends to become brittle and fracture more easily with age, potentially leading to the expensive repair or extraction of an otherwise healthy tooth.  The problem has been poorly appreciated for centuries – and with good reason.  Until a generation ago, most seniors already had lost most or all of their natural teeth by their retirement years.  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 the October issue of the Journal of the Mechanical Behavior of Biomedical Materials, a group of NIDCR-supported scientists provide some needed baseline data on the fracture toughness of aging human dentin.  But first a little dentin physiology.  Like bone, dentin consists of an organic collagen matrix supported by the mineral hydroxyapatite.  However, dentin contains a unique network of microscopic channels, called tubules, which radiate outward away from the dental pulp.  Keep this in mind because most cracks and fractures in dentin within the crown region of a tooth (coronal 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. 

Old dentinAfter a series of tests, the scientists 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, 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 term in physics 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.” 

  • Nazari A, Bajaj D, Zhang D, Romberg E, and Arola D, “Aging and the reduction in fracture toughness of human dentin,” Journal of the Mechanical Behavior of Biomedical Materials: 2009; 2:550-559. 


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This page last updated: February 26, 2014