The purpose of presenting paper is to demonstrate the influencing factors of the marginal fitness of fixed bridge.

Two cases of fixed bridge were surgically removed without destroying any components. One of fixed bridge was a posterior bridge as in 7-5 4|, and abutments were made with full cast crowns. Another one of fixed bride was an anterior bride as in 1|-2, and abutments were made with porcelain fused to metal crowns. Those fixed bridge were sectioned mesio-distally and bucco-lingually, and were measured the width of the cement line under the microscope.

The following observation were made,

1, The average width of cement line at the crown margins of 4|, 5|, 7| were 265μm, 260μm, 340μm, and 1|, |2 were 300μm, 405μm.

2, Overhanging margins and excessive or short margins were observed.

3, Inadequate margins fitness were due to lack of accurate therapeutic technique.