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What is A 25 year old male patient complains of food lodgement in his lower right back tooth. On intra-oral examination occlusal caries is seen with 46. During cavity preparation, access to the distal gingival margin was achieved by a GMT. The second number in the instrument formula for this instrument would be? and explain in detail?
The gingival margin trimmer is designed to produce a proper bevel on gingival enamel margins of proximoocclusal preparations. When the second number in the formula is 90 to 100, the pair is used on the distal gingival margin. When this number is 85 to 75, the pair is used to bevel the mesial margin. The 100 and 75 pairs are for inlay/onlay preparations with steep gingival bevels. The 90 and 85 pairs are for amalgam preparations with gingival enamel bevels that decline gingivally only slightly. Among other uses for these instruments is the rounding or beveling of the axiopulpal line angle of two-surface preparations.
Ref: Sturdevant's art and science of operative dentistry. 4th edition page 315