The thickness of the nail plate is determined By the length of the nail matrix. Longer matrix = thicker nail plate; shorter matrix = thinner nail plate.
Damage to the matrix can effectively shorten the matrix and cause the plate grow thinner.
If the damage is only in a small area of the matrix, this can cause a shallow groove in the plate. The more extensive the damage, the deeper the groove. Deep enough and this could lead to a split running the length of the nail plate.
Source Doug Schoon
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