Six mongrel dogs were used. The melanin pigmentation in canine gingiva were classified into slight, moderate and severe according to the extent of pigmentation and divided into local and diffuse types according to the range. Following general and local anesthesia, 90% phenol was applied to the pigmented gingiva of the subjects with small cotton balls until the surface was etched to be whitish and was neutralized with small cotton balls soaked by 95% alcohol. The contralateral pigmented gingiva to the one treated with phenol, was treated by surgical deepithelialization. At 1, 3 and 8 weeks, the treated gingiva was examined clinically and evaluated histologically following H-E stain, and HMB 45 stain for melanocyte after biopsy.

In the phenol treated sites, epithelium and connective tissue healed normally and there was no pigmentation at 1 week. At 3 weeks of healing, melanin repigmentation was observed in the severe local type and moderate to severe diffuse type.

In the surgically deepithelialized sites, healing was delayed, compared to phenol treated sites and the infiltration of the inflammatory cells and congestion in connective tissue was shown at 1 week. At 3 weeks, healing was completed and there was a partial melanin repigmentation.

At 8 weeks of healing, the extent and the range of repigmentation were increased in both group according to the extent or range priot to depigmentation procedure.

These results suggpriorest that the removal of melanin pigmentation with 90% phenol application result in normal healing process of gingiva. However, in the severe local type and moderate to severe diffuse type, sites treated with phenol showed repigmentation at 3 week, which was earlier than surgical deepithelialized sites. Therefore it is required to select appropriate method according to initial condition of pigmentation.