An orthodontic adhesive includes a curable resin monomer component; a quaternary curing initiator system; and filler. Another orthodontic adhesive having a W/C ratio (working time to curing time ratio) of at least 10, 12, 14 or 20, includes a curable resin monomer component; a curing initiator system; and filler. The adhesives are suitable as light-curing and may include a colorant. Suitable colorants include reversible, thermochromic dyes. The adhesive may also include a resin toughening component.