PURPOSE: This study was designed to study the discolored gingiva adjacent to porcelain fused to metal (PFM) crowns in terms of ultrastructure, SOD and GSH activities in 40 cases.

• 摘要目的：观察40例金属烤瓷冠修复患者变色牙龈的超微结构，测定其中超氧化物歧化酶(SOD)和还原型谷胱甘肽(GSH)的活性，探讨牙龈变色的机制。