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:…did not influence the recovery period from hypoesthesia, and recovery period of hypoesthesia of lower lip following SSRO was strongly associated with the sagittal split area and the distance between the plate (the most medial point of screw) and the mental foramen (Hashiba et al., 2007, 2008).
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