Mechanical Properties of Enamel Nanocomposite

Table 1

A literature survey on nanomechanical and mechanical properties of human teeth.

Human teeth details	Measurement method and load	𝐻 (GPa)	𝐸 (GPa)	𝐾IC (MPa · m^0.5); (ND: not determined)	Remarks	𝐾IC modelling; (Y/N)	Year/reference number
First molar	Compressive strength		Cusp enamel: 84.1; Side enamel: 77.9	ND	𝜎𝑐^a Cusp enamel: 0.384 GPa; 𝜎𝑐^a Side enamel: 0.372 GPa	N	1961 [22]
Premolar	3-point; bending; Strain rate: 0.13 mm/min			ND	Enamel: 𝑊𝑓1^a = 13 J⋅m^−2; 𝑊𝑓2^a = 200 J · m^−2; Dentin: 𝑊𝑓1^a = 550 J · m^−2; 𝑊𝑓2^a = 270 J · m^−2	N	1976 [23]
Two incisors, one molar and one canine	MI^a; 𝑃^a=300 and 500 gf			Enamel: 0.7–1.27	Direction of fracture is believed to be dependent on the orientation of the indenter head relative to the local enamel structures	N	1981 [24]
Third molars	MMI^a; MI^a; 𝑃^a = 2, 3, 5, 10, 20 and 50 N	Enamel: 3.37; Dentin: 0.57	Enamel: 80; Dentin: 20	Enamel; Parallel—1.3; Perpendicular—0.52		N	1998 [25]
Incisor	NI^a; 𝑃^a = 300–2500 𝜇N	Enamel: 4.8; Dentin: 0.8	Enamel: 98; Dentin: 25	ND		N	2000 [26]
Incisor	MI^a; 𝑃=500 gf	Enamel: 3		Enamel; Parallel—0.9; Perpendicular—1.3	Amelogenin nanospheres permit crystallite growth in preferred orientations, but ameloblastin inhibit crystallite growth	N	2001 [27]
First molar	NI^a; 𝑃^a = 20 mN	HE^a: 0.53; SE^a: 3.2	HE^a: 14.49; SE^a: 77.25	ND	Mechanical properties of HE^a are significantly lower than those of the SE^a	N	2004 [16]
Third molars	NI^a; 𝑃max(𝑝)^a: 1000 𝜇N; 𝑃max(𝑠)^a: 300 𝜇N	Loading: 𝑃𝑟^a—4.3𝑆^a—1.1; Unloading: 𝑃𝑟^a—3.9; 𝑆^a—1.4	Loading: 𝑃𝑟^a—83.4; 𝑆^a—39.5; Unloading: 𝑃𝑟^a—77.1; 𝑆^a—41.2	ND		N	2005 [8]
Premolar	NI^a; P^a = 1–450 mN		Enamel TS^a: 100–60; CS^a: 80–40	ND	The top surface is stiffer than the cross-section	N	2006 [17]
Molar	CSR^a: 0.05, 0.005, and 0.0005 s^−1			ND	𝐺𝑝 = 0.05–0.23; GPa	Used TSC model to determine 𝐸	2006 [18]
Molar enamel	NI^a; CSR^a: 0.05 s^−1	For; ℎ𝑓^a = 100–2000 nm,; 𝐻 = 5.7–3.6	For; ℎ𝑓^a = 100–2000 nm,; 𝐸 = 104–70	ND	The decrease in 𝐻, 𝐸 values with depth is speculated to be associated with microstructure evolution that is induced by the indenter tip	Used rule of Mixtures to determine 𝐸	2007 [10]
Premolar	BI^a and SI^a; 𝑃^a=250 mN	SE^a: 4.49; DE^a: 5.01; RE^a: 4.15; Dry: 4.78; BE^a: 5.94		ND	HAP nanocrystallites are parallel, diverge from the rod axis by 15–45°, and are at angle of 60° to the central, tail, and edge of the rod, respectively	N	2007 [28]
Molar (hypomineralized) and a sound premolar	NI^a; 𝑃^a= 1–500 mN (SE^a); 𝑃^a = 1–200 mN (HE^a)		75–45 as 𝑐𝑟^a increased from 0.8–6.1 𝜇m; 𝐸sound= 60–80	ND	Elastic modulus is highly dependent on the contact size during loading	Used FEM^a of Spears and the rule of mixtures to determine 𝐸	2007 [12]
Third molars	NI^a; LR^a: 1 mN/s; 𝑃max: 5 mN	𝐻young = 4; 𝐻old = 4	𝐸young = 84.4; 𝐸old = 91.1	ND		N	2008 [29]
Third molars	MI^a: 𝑃^a=0.1, 0.25, 0.5, 1, 2, 3, and 5 N.; NI^a: 𝑃^a = 5 mN	Young; 𝐼𝑒^a = 3.1; 𝑀𝑒^a = 3.5; 𝑂𝑒^a = 4.1; Old; 𝐼𝑒^a = 3; 𝑀𝑒^a = 3.4; 𝑂𝑒^a = 4	Young; 𝐼𝑒^a = 75; 𝑀𝑒^a = 82; 𝑂𝑒^a = 87; Old; 𝐼𝑒^a = 79; 𝑀𝑒^a = 90; 𝑂𝑒^a = 100	Young; 𝐼𝑒^a = 0.95; 𝑀𝑒^a = 0.88; 𝑂𝑒^a = 0.88; Old; 𝐼𝑒^a = 0.88; 𝑀𝑒^a = 0.73; 𝑂𝑒^a = 0.67	Brittleness (𝜇m^−1); Young; 𝐼𝑒^a = 305; 𝑀𝑒^a = 375; 𝑂𝑒^a = 393; Old; 𝐼𝑒^a = 313; 𝑀𝑒^a = 582; 𝑂𝑒^a = 897	N	2008 [30]
Third molars	Cyclic loading; 𝑃max = 3–5 N and 1-2 N for HAP			0.9 (3 times that of HAP)	Crack growth occurred primarily along the prism boundaries	N	2008 [31]
Defective premolars, sound premolars	NI^a; 𝑃^a≤500 mN		𝐸perp: 10.9; 𝐺^a: 2.6	ND	HAP nanocrystals make 33° angle with the loading direction	Used a SMPCS^a model to determine 𝐸	2008 [13]
Third molar	MI^a; 𝑃^a = 160 gf	Enamel: 3.5		ND		N	2008 [32]
Third molar	NI^a with spheroconical tip; 𝑃^a = 5 and 11 mN		Enamel: 123	ND	𝐼^ast: 1.6 GPa and 𝐼sr^a: 0.6% at a 𝑐𝑟^a of 250 nm and a total penetration depth of 7 nm	N	2009 [33]
Third molars	Cyclic loading; 𝑃max = 3–6 N		𝑂𝑒 = 90; 𝐼𝑒 = 70	𝐾𝑐(forward) = 2.11; 𝐾𝑐(backward) = 1.17	𝑆^art in the forward direction: 4 J/m^2; 𝑆^art in the forward direction: 10 J/m^2	N	2009 [34]
Molar	MI^a at 0.98, 1.96, 2.94, 4.9, and 9.8 N	3.33, 3.51, 3.22, 3.31 and 3.22		0.85, 0.87, 0.88, 0.94, and 0.98		N	2010 [35]
Incisors	NI^a: 𝑃^a = 500 𝜇N	Enamel rod: head—5.01; tail—4.52; axial sec—4.58	Enamel rod: head—102.56; tail—97.3; axial sec—97.72	ND	𝜇𝑒: head—0.087; tail—0.094; axial sec—0.108	N	2011 [36]
Molars	NI^a; 𝑃^a = 2 mN	E: 7; D: 1	E: 95; D: 19	ND	Cracks in the DEJ travelled along structures with dentin characteristics	N	2011 [4]

aCSR: constant strain rate, MMI: modified microindentation, and 𝜎_𝑐: ultimate compressive strength.
𝑊_𝑓1: work of fracture for parallel specimen; 𝑊_𝑓2: work of fracture for perpendicular specimen.
MI: microindentation, NI: nanoindentation, and BI: the Berkovich indentation.
SI: spherical indentation, HE: hypomineralized enamel, SE: sound enamel, DE: dehydrated enamel, RE: rehydrated enamel, BE: burnt enamel, TS: top section, CS: cross-section, and LR: loading rate.
𝑃: applied load; 𝑃_max(𝑝): maximum load applied for enamel prisms.
𝑃_max(𝑠): maximum load applied for enamel sheath, 𝑃_𝑟: enamel prism, and 𝑆: enamel sheath.
ℎ_𝑓: final depth of penetration, 𝑐_𝑟: contact radius, 𝐼_𝑒: inner enamel, 𝑀_𝑒: middle enamel, 𝑂_𝑒: outer enamel, FEM: finite element modeling of Spears, 𝐼_st: indentation stress, and 𝐼_sr: indentation strain,
𝜇_𝑒: coefficient of friction of enamel rod; 𝐺: shear modulus of enamel nanocomposite.
𝑆_rt: strain energy release rate; SMPCS: staggered mineral-protein composite structure model.
𝐺_𝑝: shear modulus of enamel protein matrix.