Contributory role of the tongue and mandible in modulating the in-mouth air cavity at rest.

OBJECTIVES: The tongue-to-palate distance influences the volume of the in-mouth air cavity (IMAC), thus conditioning the entry of aromatic compounds to the olfactory mucosa site. This study was set out to record the IMAC volume by measuring tongue-to-palate distance at rest. MATERIALS AND METHODS: Twelve young adults in good general health were tested--lips contacting, with at-rest posture of the tongue and jaw during a silent reading task. Observations in this study were limited to pre- and post-swallowing sequences. The tongue-to-palate distance was measured using three electromagnetic sensors placed on the tongue upper surface. IMAC volume was evaluated from a geometrical model, taking into account the tongue-to-palate distance, the IMAC transversal distance measured from dental casts and historic data giving the anterior-posterior distance of the oral cavity. RESULTS: (1) In the at-rest posture, the tongue-to-palate distance was significantly greater at the posterior sensor level. (2) A vertical shift in tongue posture at rest frequently appeared following deglutition. The upward shifts were of larger amplitude and more frequent than the downward shifts. (3) Evaluation of the IMAC volume gave an approximate value of 12 ml at rest. (4) The chin sensor at rest was 2.8 ± 0.8 mm below its position when in occlusion. CONCLUSION: The tongue and mandible contribute to shaping the IMAC volume. CLINICAL RELEVANCE: These and other results suggest that deglutition changes tongue-to-palate distance and influences aroma release during mastication/deglutition acts through modulation of the IMAC volume.

Retro-nasal aroma release is correlated with variations in the in-mouth air cavity volume after empty deglutition.

We hypothesized that interindividual differences in motor activities during chewing and/or swallowing were determining factors for the transfer of volatile aroma from the in-mouth air cavity (IMAC) toward the olfactory mucosa. In our first experiment, we looked for changes in IMAC volume after saliva deglutition in 12 healthy subjects. The mean IMAC volume was measured after empty deglutition using an acoustic pharyngometer device. Based on the time course of the IMAC volume after swallowing, we discerned two groups of subjects. The first group displayed a small, constant IMAC volume (2.26 mL ±0.62) that corresponded to a high tongue position. The second group displayed a progressive increase in IMAC (from 6.82 mL ±2.37 to 22.82 mL ±3.04) that corresponded to a progressive lowering of the tongue to its resting position. In our second experiment, we investigated the relationship between IMAC volume changes after deglutition and the level of aroma release at the nostril. For this purpose, the release of menthone was measured at the nostril level in 25 subjects who consumed similar amounts of a mint tablet. The subjects were separated into two groups corresponding to two levels of menthone release: high (H) and low (L). The mean volume of IMAC was measured during and after empty deglutition. Group H displayed a small, constant amplitude of IMAC volume change after deglutition, while Group L displayed a progressive increase in IMAC. It is likely that Group H continuously released the aroma through the veloglossal isthmus as the mint was consumed, while Group L trapped the aroma in the oral cavity and then released it into the nasal cavity upon swallowing. These results show that the in vivo aroma release profile in humans depends closely on the different motor patterns at work during empty deglutition.

Time-course changes of muscle protein synthesis associated with obesity-induced lipotoxicity.

The object of the study was to investigate the sequential changes of protein synthesis in skeletal muscle during establishment of obesity, considering muscle typology. Adult Wistar rats were fed a standard diet for 16 weeks (C; n = 14), or a high-fat, high-sucrose diet for 16 (HF16; n = 14) or 24 weeks (HF24; n = 15). Body composition was measured using a dual-energy X-ray absorptiometry scanner. The fractional synthesis rates (FSRs) of muscle protein fractions were calculated in tibialis anterior (TA) and soleus muscles by incorporation of l-13C-valine in muscle protein. Muscle lipid and mitochondria contents were determined using histochemical analysis. Obesity occurred in an initial phase, from 1 to 16 weeks, with an increase in weight (P < 0.05), fat mass (P < 0.001), muscle mass (P < 0.001) and FSR in TA (actin: 5.3 ± 0.2 vs. 8.8 ± 0.5% day−1, C vs. HF16, P < 0.001) compared with standard diet. The second phase, from 16 to 24 weeks, was associated with a weight stabilization, a decrease in muscle mass (P < 0.05) and a decrease in FSR in TA (mitochondrial: 5.6 ± 0.2 vs. 4.2 ± 0.4% day−1, HF16 vs. HF24, P < 0.01) compared with HF16 group. Muscle lipid content was increased in TA in the second phase of obesity development (P < 0.001). Muscle mass, lipid infiltration and muscle protein synthesis were differently affected, depending on the stage of obesity development and muscle typology. Chronic lipid infiltration in glycolytic muscle is concomitant with a reduction of muscle protein synthesis, suggesting that muscle lipid infiltration in response to a high-fat diet is deleterious for the incorporation of amino acid in skeletal muscle proteins.

Is the goal of mastication reached in young dentates, aged dentates and aged denture wearers?

The objective of the present study was to assess the impact of age and dentition status on masticatory function. A three-arm case-control study was performed. Group 1 (n 14) was composed of young fully dentate subjects (age 35.6 +/- 10.6 years), group 2 (n 14) of aged fully dentate subjects (age 68.8 +/- 7.0 years) and group 3 (n 14) of aged full denture wearers (age 68.1 +/- 7.2 years). Mastication adaptation was assessed in the course of chewing groundnuts and carrots to swallowing threshold. Particle size distribution of the chewed food, electromyographic (EMG) activity of the masseter and temporalis muscles during chewing, and resting and stimulated whole saliva rates were measured. Aged dentate subjects used significantly more chewing strokes to reach swallowing threshold than younger dentate subjects (P < 0.05), with increased particle size reduction, longer chewing sequence duration (P < 0.05) and greater total EMG activity (P < 0.05) for both groundnuts and carrots. In addition, aged denture wearers made significantly more chewing strokes than aged dentate subjects (P < 0.001) to reach swallowing threshold for groundnuts. Particle size reduction at time of swallowing was significantly poorer for denture wearers than for their aged dentate counterparts, despite an increase in chewing strokes, sequence duration and EMG activity per sequence. Masticatory function was thus adapted to ageing, but was impaired in denture wearers, who failed to adapt fully to their deficient masticatory apparatus.