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:Microstructural elements such as ‘tufts’—hypocalcified, protein-filled fissures that emanate into the enamel from the enamel–dentin junction [1, 27, 28]—are likely to have a strong influence on where radial and margin cracks initiate, by providing favored starting points for fractures [12, 21].
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