The silicon-oxygen bonds in ${\mathrm{SiO}}_2$ are best described as:

$\mathrm{Si}-\mathrm{O}$ bonds are polar as well as covalent.

Each silicon atom in silica, ${\mathrm{SiO}}_2$, is linked to four oxygen atoms by covalent bonds. With Si at the center and 4 $\mathrm{O}$ atoms at each of the four corners, the ${\mathrm{SiO}}_2$ unit shapes a standard tetrahedron.