Fracture Toughness of Human Enamel

Hassan, R.; Caputo, Angelo A.; Bunshah, R.F.

doi:10.1177/00220345810600040901

Cited by 123 publications

(95 citation statements)

References 7 publications

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“…The mean K IC value of young enamel measured in this study was 1.1870.27 MPa Á m 1/2 , which was in accordance with that reported in previous studies (Hassan et al, 1981;Xu et al, 1998;White et al, 2001). In both old and young enamel, the mean K IC value increased from the outer to the middle layer and then exhibited a slight decrease from the middle to the inner layer, and the changes from the outer to the middle layer were more pronounced (po0.05).…”

Section: Discussionsupporting

confidence: 92%

“…Therefore, the fracture toughness of human enamel has been primarily evaluated using indentation methods. The reported micro-indentation fracture toughness of human enamel has been found to be 0.4-1.5 MPa m 1/2 (Hassan et al, 1981;White et al, 2001;Park et al, 2008a;Hayashi-Sakai et al, 2012). The variability of these results is partly attributed to the type of tooth (e.g., canine, premolar, and molar), the tested location, and the enamel microstructure.…”

Section: Introductionmentioning

confidence: 99%

“…As a result, the fracture toughness of enamel also exhibits variations. Hassan et al (1981) reported that the fracture toughness of enamel has a tendency to increase from the incisal to the cervical sections. The micro-indentation tests performed on cross-sections of enamel by Xu et al (1998) showed that the fracture toughness of enamel is not single-valued but varies based on the enamel rod orientations.…”

Section: Introductionmentioning

confidence: 99%

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Spatial distribution of the human enamel fracture toughness with aging

Zheng

Song

et al. 2013

Journal of the Mechanical Behavior of Biomedical Materials

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Enamel AgingMineral content a b s t r a c t A better understanding of the fracture toughness (KIC) of human enamel and the changes induced by aging is important for the clinical treatment of teeth cracks and fractures. We conducted microindentation tests and chemical content measurements on molar teeth from "young" (18≤age≤25) and "old" (55≤age) patients. The KIC and the mineral contents (calcium and phosphorus) in the outer, the middle, and the inner enamel layers within the cuspal and the intercuspal regions of the crown were measured through the Vickers toughness test and Energy Dispersive X-Ray Spectroscopy (EDS), respectively. The elastic modulus used for the KIC calculation was measured through atomic force microscope (AFM)-based nanoindentation tests. In the outer enamel layer, two direction-specific values of the KIC were calculated separately (direction I, crack running parallel to the occlusal surface; direction II, perpendicular to direction I). The mean KIC of the outer enamel layer was lower than that of the internal layers (po0.05). No other region-related differences in the mechanical properties were found in both groups. In the outer enamel layer, old enamel has a lower KIC, II and higher mineral contents than young enamel (po0.05). The enamel surface becomes more prone to cracks with aging partly due to the reduction in the interprismatic organic matrix observed with the maturation of enamel.

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Section: Discussionsupporting

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Spatial distribution of the human enamel fracture toughness with aging

Zheng

Song

et al. 2013

Journal of the Mechanical Behavior of Biomedical Materials

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“…This value is broadly consistent with the value of 0.95 MPa⅐m 1/2 reported for pooled data from four assorted human teeth (37), the range of 0.52 to 1.30 MPa⅐m 1/2 reported for axial sections of four human third molars (31), and a range of 0.9 to 1.3 MPa reported for human incisors (22). However, direct comparison should only be made with the erupted mature incisal enamel of 6-week mice.…”

Section: Discussionsupporting

confidence: 89%

Ectopic Expression of Dentin Sialoprotein during Amelogenesis Hardens Bulk Enamel

White

Paine

Ngan

et al. 2007

Journal of Biological Chemistry

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Dentin sialophosphpoprotein (Dspp) is transiently expressed in the early stage of secretory ameloblasts. The secretion of ameloblast-derived Dspp is short-lived, correlates to the establishment of the dentinoenamel junction (DEJ), and is consistent with Dspp having a role in producing the specialized firstformed harder enamel adjacent to the DEJ. Crack diffusion by branching and dissipation within this specialized first-formed enamel close to the DEJ prevents catastrophic interfacial damage and tooth failure. Once Dspp is secreted, it is subjected to proteolytic cleavage that results in two distinct proteins referred to as dentin sialoprotein (Dsp) and dentin phosphoprotein (Dpp). The purpose of this study was to investigate the biological and mechanical contribution of Dsp and Dpp to enamel formation. Transgenic mice were engineered to overexpress either Dsp or Dpp in their enamel organs. The mechanical properties (hardness and toughness) of the mature enamel of transgenic mice were compared with genetically matched and age-matched nontransgenic animals. Dsp and Dpp contributions to enamel formation greatly differed. The inclusion of Dsp in bulk enamel significantly and uniformly increased enamel hardness (20%), whereas the inclusion of Dpp weakened the bulk enamel. Thus, Dsp appears to make a unique contribution to the physical properties of the DEJ. Dsp transgenic animals have been engineered with superior enamel mechanical properties.Until recently, it was believed that ectoderm-derived ameloblasts and ectomesenchyme-derived odontoblasts only expressed matrix proteins that were exclusive to themselves. But it is now known that there is also a transient expression of dentin sialophosphpoprotein (Dspp) 2 in early ameloblasts, adjacent to the dentinoenamel junction (DEJ) (1-6). We propose that Dspp has a role in producing the specialized first-formed harder enamel adjacent to the DEJ. Such a localized spatio-temporal pattern of Dspp protein expression may contribute to remarkable crack-resistant properties of the DEJ.Specialized highly mineralized first-formed enamel, and specialized tubule-rich mantle dentin have long been known to be present close to the DEJ interface (7-9). Although there is an abrupt transition between dentin and enamel tissues at the DEJ interface (10 -13), it is now known that the DEJ area functions as a broad mechanical zone (14 -17). Crack diffusion by branching and dissipation within the specialized first-formed enamel close to the DEJ prevents catastrophic interfacial damage and tooth failure (18,19).We tested the prediction that overexpression of Dspp proteins throughout enamel formation would produce altered enamel material properties. In this study, we have examined the mechanical properties of enamel of transgenic mice that overexpress either Dsp or Dpp in ameloblasts within their enamel organs. EXPERIMENTAL PROCEDURESOur strategy was to ascertain the functions of selected known proteins acting during enamel biomineralization by overexpressing them in quantity and time so that a l...

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“…For example, measurements with Vickers indents (Indentation Crack Lengths Method, [26]) gave a small fracture toughness of the order of 1 MPa m 1/2 [27,28,29]. This led to the prevailing opinion that enamel is a brittle material.…”

Section: Dental Enamel Of Bovine Teethmentioning

confidence: 99%