Average bond strength in enamel adhesion:
Bond strength of enamel is higher than bond strength to dentin.
Enamel is 20-50 MPa.
Dentin is 15-25 MPa depending on agent used. 
Reference-Sturdevant 6th ed  Pg: 116
5-10 MPa
20-50 MPa
50-70 MPa
70-100 MPa