Fig. 1. Overall appearances and micrographs of the bioinspired ceramic-polymer composites with nacre-like (a) lamellar and (b) brick-and-mortar architectures which resemble, respectively, the human tooth dentin and enamel in their hardness and Young's modulus. Light gray: ceramic phase; dark gray: polymer phase. (c) Representative microstructures of human tooth enamel on the polished occlusal cross-section. The inset shows the overall appearance of a premolar tooth. The micrograph in (c) is adapted with permission from Ref. [35].

Fig. 2. (a) Schematic illustration of the reciprocating ball-on-flat sliding configuration for the wear tests of bioinspired composites against human tooth enamel. The appearance of the tooth cusp tip used for wear tests is also shown (right panel). (b) Schematic illustration of the longitudinal (L) and transverse (T) directions for the sliding motion of human enamel against bioinspired composites with respect to their nacre-like lamellar and brick-and-mortar architectures.

Fig. 3. Variations in the coefficient of friction (COF) with time for the bioinspired ceramic-polymer composites with nacre-like (a) lamellar and (b) brick-and-mortar architectures wearing against human enamel along different directions. (c) Corresponding data for 3Y-TZP is shown as a comparison. (d) Comparison of the average COFs between groups by excluding the initial increasing stage. The differences are statistically insignificant between longitudinal and transverse directions when considering each individual architectural type. “☆” indicates statistically significant differences between lamellar and brick-and-mortar architectures when considering the same direction. “#” indicates statistically significant differences between bioinspired composites and 3Y-TZP.

Fig. 4 (a) Representative tomographic morphologies of the tip region for a tooth cusp sample before and after wearing with bioinspired ceramic-polymer composites (by taking the case for lamellar architecture along the transverse direction as an example). Comparison of (b) the diameter of circular wear pattern, (c) wear volume, and (d) wear rate of human tooth enamel after wearing against different materials and along different directions. Statistically significant differences between different architectural types of bioinspired composites when considering the same direction are indicated by “☆”. Statistically significant differences between bioinspired composites and 3Y-TZP are indicated by “#”.

Fig. 5. Representative wear morphologies of human tooth enamel after wearing against bioinspired composites with nacre-like (a, b) lamellar and (c, d) brick-and-mortar architectures along (a, c) longitudinal and (b, d) transverse directions at a relatively coarse scale of tens of micrometers. (e) Higher-magnification micrographs of the wear morphologies of human tooth enamel at a finer scale.

Fig. 6. Representative wear morphologies of bioinspired ceramic-polymer composites with nacre-like (a, b) lamellar and (c, d) brick-and-mortar architectures after wearing against human enamel along (a, c) longitudinal and (b, d) transverse directions.

Fig. 7. Schematic illustrations of the micro-wear mechanisms of bioinspired ceramic-polymer composites with nacre-like (a, b) lamellar and (c, d) brick-and-mortar architectures wearing against human tooth enamel along (a, c) longitudinal and (b, d) transverse directions. Dark brown: ceramic phase; light brown: polymer phase. (e) Wear mechanisms of the antagonist human tooth enamel at different length scales. HAP: hydroxyapatite.