The role of organic proteins on the crack growth resistance of human enamel

Abstract

With only 1% protein by weight, tooth enamel is the most highly mineralized tissue in mammals. The focus of this study was to evaluate contributions of the proteins on the fracture resistance of this unique structural material. Sections of enamel were obtained from the cusps of human molars and the crack growth resistance was quantified using a conventional fracture mechanics approach with complementary finite element analysis. In selected specimens the proteins were extracted using a potassium hydroxide treatment. Removal of the proteins resulted in approximately 40% decrease in the fracture toughness with respect to the fully proteinized control. The loss of organic content was most detrimental to the extrinsic toughening mechanisms, causing over 80% reduction in their contribution to the total energy to fracture. This degradation occurred by embrittlement of the unbroken bridging ligaments and consequent reduction in the crack closure stress. Although the organic content of tooth enamel is very small, it is essential to crack growth toughening by facilitating the formation of unbroken ligaments and in fortifying their potency. Replicating functions of the organic content will be critical to the successful development of bio-inspired materials that are designed for fracture resistance.

On the importance of aging to the crack growth resistance of human enamel

“…8b. That behavior is consistent with the observations reported in previous studies for crack extension transverse to the enamel rods as a result of indentations [23] or occurring by incremental crack growth [32]. …”

“…A detailed description of the hybrid method applied to evaluations on the resistance to fracture of enamel has been presented [32]. Briefly, a 2D half model of the enamel inset CT specimen was developed using commercial software (ABAQUS Standard, Version 6.9, Dassault Systems).…”

Structural Analysis of Enamel in Teeth from Head-and-Neck Cancer Patients Who Underwent Radiotherapy

“…Lastly, it is relevant to mention that the interprismatic components of enamel act as natural and complex polymers with viscoelastic properties that allow a homogeneous distribution of masticatory loads [He and Swain, 2008;Yahyazadehfar and Arola, 2015]. Thus, we can only suggest that possible radiation-related damage to the organic component of cervical enamel, in association with other factors, such as a high level of psychosocial stress experienced by these patients (and consequent tooth grinding and clenching), a lower thickness of cervical region enamel, high stress concentration by masticatory forces in this particular enamel area, and a dehydrated oral environment, could establish a synergic effect leading to a higher risk of cervical enamel fractures and delamination [Dejak and Romanowicz, 2003;Gonen et al, 2012].…”

Initial and long-term bond strengths of one-step self-etch adhesives with silane coupling agent to enamel-dentin-composite in combined situation

“…After 12-month water storage, enamel bond strengths of all the experimental groups significantly decreased with cohesive failure in enamel. These results would indicate reduction of mechanical properties of enamel subsurface which might be due to alteration of mineral content and/ or deterioration of enamel organic matrix [32][33][34] . For the dentin substrate, adding silane coupling agent significantly reduced the 24-h dentin bond strengths of the SO and BM systems, in which all the groups showed mixed failures.…”