Complex sentence: One study compared patients with ingrown toenails to healthy controls and found no difference in the shape of toenails between patients and the control group, they suggested that treatment should not be based on the correction of a non-existent nail deformity.
Split into simpler sentences: One study compared patients with ingrown toenails to healthy controls and found no difference in the shape of toenails between those of patients and of the control group. The study suggested that treatment should not be based on the correction of a non-existent nail deformity.