Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:Lamellar split bone grafting The lamellar split osteotomy is a surgical technique that was developed in the late 1980s and was reported in the literature in 1990.[5,6] This technique allows changing in the position of the outer bone cortex by splitting it in situ as you would a segment of cranial bone on the back table.
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