The 'teeth' of a comb are the spikes that glide through your
hair when you use it. These teeth are fixed into the back of the
comb which is rigid and keeps the comb straight. The 'tooth edge'
of the comb is therefore the edge of the comb where all the teeth
are separate and rough when you feel it - opposite to the back of
the comb which is smooth. If you run your thumb nail down the tooth
edge of a come all the teeth will make a 'plinking' sound.