Methods: 67 volunteers, aged between 25 and 75 years (29 males, 38 females), presenting a good oral health, no malocclusion or dysfunction, were selected. The muscular activity of right and left masseter and temporalis muscles was recorded by electromyography (EMG) using surface electrodes. The mandibular displacements were simultaneously recorded using an electromagnetic system with miniature coils, stuck on the central incisors. Each volunteer was instructed to chew and swallow 3 replicates of 4 visco-elastic model foods of increasing hardness (4x3=12 samples). The number of masticatory cycles, mean muscular work and total muscular work for the 4 muscles, and the vertical amplitude of the mandible displacements were chosen to describe masticatory adaptation to increase hardness.
Results: (1) Masticatory frequency did not change with food hardness, (2) Adaptability to increased hardness did not change with age, (3) Ageing induced an increase in the number of masticatory cycles (0.303 cycles per year) and of the total muscular work required for the complete masticatory sequence, (4) Masticatory frequency and mean muscular work required during an individual cycle were kept constant throughout ageing.
Conclusion: The energy used to chew the model foods increases with age. This is probably associated with a set of modifications such as the decrease of oral tissues motility, the slowing down of nervous conduction, the modification of salivary production and other oral or general alterations due to normal ageing. An efficient mastication is, however, compatible with ageing as long as a good oral health is maintained.
This work was supported by a grant n°4M411D (INSERM), and a scholarship (IFRO).