Chewing efficiency Chewing efficiency was assessed with a previously developed and validated colour-mixing ability test, or bolus-kneading test, using chewing gum 18. The specimens used for this study were developed and produced for the 8020 Promotion Foundation (Japan) specifically for assessing masticatory performance in a research setting (Lotte™,Tokyo) and to be similar to the originally described method 19. The gum was composed of two individually packed beads (pink and azure colour) with similar hardness Shore Scale OO, Ø 2.4 mm, 1.11 N, pink beads: mean depth of indentation 0.2±0.01mm, mean Durometer 93.7; azure beads mean depth of indentation 0.1±0.02mm, mean Durometer 95.1). The two beads were manually stuck together and had a dimension of 18.8x14.2x3.9 mm; they were placed on the participant's tongue. The task was to chew the specimen for twenty cycles whilst being monitored by the operator (ED). The gum bolus was then retrieved from the oral cavity, placed into a plastic bag, pressed to a 1 mm thick wafer and both sides were scanned at 300dpi (Epson Perfection V750 Pro, Seiko Epson Corp., Japan).