Determination of fracture toughness of human permanent and primary enamel using an indentation microfracture method

Abstract

The purpose of the present study was to examine the fracture toughness and Vickers microhardness number of permanent and primary human enamel using the indentation microfracture method. Crack resistance and a parameter indirectly related to fracture toughness were measured in 48 enamel specimens from 16 permanent teeth and 12 enamel specimens obtained from six primary teeth. The Vickers microhardness number of the middle portion was greater than the upper portion in primary enamel. The fracture toughness was highest in the middle portion of permanent enamel, because fracture toughness greatly depends upon microstructure. These findings suggest that primary teeth are not miniature permanent teeth but have specific and characteristic mechanical properties.

Spatial distribution of the human enamel fracture toughness with aging

“…In contrast, acute decussation in the middle and the inner enamel layers retards crack growth through the deflection, twist, and fracture of the prisms (Bajaj and Arola, 2009). Furthermore, it is easier for cracks to propagate parallel to the long axis of the prisms than to cut through the enamel rods (White et al, 2001;Hassan et al, 1981;He and Swain, 2007;Hayashi-Sakai et al, 2012). As shown in this study, the K IC,II value of the outer layer of both young and old enamel is lower than the corresponding K IC,I (po0.05), which suggests that the elongation of cracks along the straight prisms of the outer enamel is easier.…”

“…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.…”

On the Mechanics of Fatigue and Fracture in Teeth

“…Over the last three decades the fracture behavior of enamel has been primarily evaluated using the indentation approach. According to the results of these studies, the average indentation fracture resistance (or apparent toughness) ranges between roughly 0.5 and 1 MPaÁm 0.5 [67,71,[97][98][99]. Due to limitations of the indentation fracture approach, Bajaj and Arola [88,89] evaluated the crack growth resistance of human enamel using a conventional fracture mechanics approach employing the enamel inset CT specimen (Fig.…”

Indentation damage and crack repair in human enamel

“…When evaluated by the indentation technique, the apparent fracture toughness ranges from roughly 0.4 to 1.5 MPa m 1/2 [e.g. Hassan et al 1981; Xu et al, 1998; White et al, 2001; Park et al, 2008b; Padmanabhan et al, 2010; Hayashi-Sakai et al, 2012]. The resistance to crack growth has also been evaluated using a conventional fracture mechanics approach [e.g.…”