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Chewing Indicators between Adults with Down Syndrome and Controls

¹ EA 3847, Faculty of Dentistry, University of Auvergne, 11 bvd Charles de Gaulle, 63000 Clermont-Ferrand, France;
² Faculty of Dentistry, McGill University, Montreal, Canada; and
³ Centre Hospitalier Universitaire, service d’Odontologie, Clermont-Ferrand, France;

^* corresponding author, martine.hennequin{at}u-clermont1.fr

	ABSTRACT

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Down syndrome induces a neuromotor deficiency that affects the orofacial musculature, and thus could be implicated in the feeding difficulties affecting people with this disease. This study aimed to investigate the differences in chewing indicators between a group of 11 adults with Down syndrome and a group of 12 healthy subjects without Down syndrome. Chewing ability was evaluated by means of video recordings taken during a standardized meal that included 10 natural foods. The variables collected were masticatory time, number of masticatory cycles, chewing frequency, number of open masticatory cycles, and number of food refusals. There were several differences in both directions for masticatory time and number of masticatory cycles between the two groups. In addition, with the exception of purée, the group with Down syndrome had significantly lower mean chewing frequency than the reference group, and was unable to eat all the foods presented.

KEY WORDS: Down syndrome • mastication • video evaluation.

	INTRODUCTION

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Down syndrome is an autosomal anomaly whose incidence varies from 1.03 to 1.66 per 1000 births (Hahn and Shaw, 1993; Stoll et al., 1998). Its prevalence continues to increase, despite ante-natal screening during appropriate health and social care (Janicki et al., 1999). The overexpression of the 21 chromosome induces poor neuromotor control, muscle weakness, and dysmorphology. As a consequence, people with Down syndrome have a high prevalence of developmental, anatomical, and functional abnormalities associated with the orofacial complex (Fischer-Brandies 1988; Hennequin et al., 2000a). Feeding is particularly affected and has been investigated in infants and children (Gisel et al., 1984a,b; Unonu and Johnson, 1992; Spender et al., 1996), but not in adults. It is probable that if early acquisition of the basic functions of mastication and swallowing is altered, then dysfunction will persist into adulthood.

If we are to develop therapies to improve the masticatory function of those with Down syndrome, a systematic evaluation of the process needs to be undertaken. The evaluation of mastication in populations with intellectual disability is difficult, due to their limited ability to cooperate. Self-evaluation questionnaires have been shown to be valid tools for the clinical evaluation of mastication (Feine et al., 1994). However, their use in people with cognitive disabilities is largely limited to instruments that can be completed by a third party (Allison and Hennequin, 2000). Furthermore, subjective evaluation is complicated by the observation that neither pain nor discomfort is declared by persons with Down syndrome (Hennequin et al., 2000b), and, moreover, the parental perception of pain is less discriminatory for the children with Down syndrome than for their siblings (Hennequin et al., 2003). As an alternative, video evaluation of chewing in people with Down syndrome has been found to be valid. It has been demonstrated that masticatory time, number of masticatory cycles, number of open masticatory cycles, and number of food refusals are valid indicators of chewing ability in healthy, fully dentate, young subjects (Hennequin et al., 2005) and in people with Down syndrome (Allison et al., 2004). The chewing time, the number of chewing cycles, and the chewing frequency are good direct descriptors of mastication. More particularly, the number of masticatory cycles performed with an open mouth characterizes various degrees of tongue protrusion (Hennequin et al., 2005). These indicators could be used to describe the chewing process in people with Down syndrome before and after surgical, prosthetic, or orthodontic procedures. However, prior to the evaluation of therapeutic procedures, it is necessary that the masticatory process, during daily meals, be described for people with Down syndrome.

This study aimed to evaluate differences in indicators of chewing between a group of adults with Down syndrome and a reference group without Down syndrome, using video recordings taken during a standardized meal. The test hypothesis was that chewing indicators differ in persons with Down syndrome compared with the reference group.

	MATERIALS & METHODS

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Subjects
A convenience sample of 11 adults with Down syndrome (ages 17–43 yrs; five females, six males; mean age, 31.6 yrs ± SD 8.5) and 12 unmatched healthy subjects (ages 20–32 yrs; five females, seven males; mean age, 22.9 yrs ± SD 6.6) was recruited in a special dental care service during a one-year period. Nineteen persons with Down syndrome were approached to participate in the study, and eight were not included for the following reasons: full-denture wearer (one), partial denture wearer (one), fewer than 20 natural teeth (two), or the presence of caries or periodontitis (four). The subjects were differentiated according to their capacity for social integration: One subject was working in a normal environment, five were working in a protected environment, and five were attending day care centers without working. The orofacial abnormalities induced by trisomy 21 were present to various degrees between individuals. None of the subjects reported difficulty eating, and all reported eating a normal diet. The reference group was not matched specifically by age, gender, dental status, or any other variable. Matching by age and gender specifically was not necessary, given that all subjects were healthy young adults, and gender does not affect chewing and age except at the extremes. To match by dental status would be impossible, since people with Down syndrome inherently have many dental anomalies absent in people without the syndrome (Hennequin et al., 1999). The study was conducted in accordance with the guidelines of the ethical committee of the Université d’Auvergne. Written consent was obtained from subjects or, in the case of those with Down syndrome, their parents. For the latter group, individual patient information was tailored to the subject’s degree of cognitive disability, and all subjects with Down syndrome gave verbal consent.

Variables
Variables were collected by face-view, video-recorded observation of subjects eating standardized quantities of 10 foods. The video recordings were taken at lunch time, following a subject’s appointment at the Dental Hospital. The meal included 10 natural foods that were proposed 4 consecutive times each. The foods and their order were: (1) 10 peanut halves, (2) a whole raw carrot, (3) a 3 x 1.5 cm sausage, (4) a 2 x 2 cm piece of beefsteak, (5) a 4 x 2 cm piece of French baguette, (6) half a round hard cheese (5 cm diameter), (7) a whole apple, (8) a whole banana, (9) a spoonful of apple purée, and (10) a 3 x 2 x 0.5 cm piece of chocolate. All subjects declared that they liked the proposed foods. One subject in the reference group refused the chocolate for medical reasons.

Video sequences were observed in a random order by an individual who did not know the subjects. This was done to ensure the absence of systematic bias in the observation of the videos due to viewing order. The variables collected included masticatory time (the number of seconds between the moment food was placed in the mouth and the end of the last chewing cycle), number of masticatory cycles (number of "closing" masticatory actions during the masticatory time), and number of open masticatory cycles (number of masticatory actions undertaken with an open mouth during the masticatory time). Compared with the "masticatory cycles" variable, "open masticatory cycles" was characterized when a gap appeared between the lips during the chewing cycle. Additionally, the number of times foods were rejected was recorded. Chewing frequency was also generated through the ratio "masticatory cycles/masticatory time".

Statistical Analyses
Differences in continuous variable mean scores ("masticatory time", "masticatory cycles", "open masticatory cycles", and "chewing frequency") for Down syndrome and reference groups were evaluated by a two-tailed t test, controlling for food type. Differences in food refusals were analyzed through the generation of odds ratios, controlling for food type.

	RESULTS

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The group with Down syndrome had a longer mean masticatory time than the reference group for peanuts, sausage, bread, and chocolate, with a tendency for a longer masticatory time with carrots (Table 1). However, the mean masticatory time values were shorter for the Down syndrome group than for the reference group for beef and purée. The group with Down syndrome had a higher mean number of masticatory cycles than the reference group for peanuts and bread, but a lower mean number of masticatory cycles than the reference group for beef and cheese (Table 1). The differences in mean "open masticatory cycles" by group for each food were very consistent, with the group with Down syndrome always having a higher mean "open masticatory cycles" score (Table 1). The group with Down syndrome demonstrated a significantly lower mean chewing frequency for all foods, with the exception of the purée, when compared with the reference group (Fig.). Furthermore, values of the "chewing frequency" variable by group status were fairly consistent across all foods.

View larger version (24K): [in this window] [in a new window]   Figure. Variations in mean chewing frequency by food type and genetic status (in subjects either with or without Down syndrome). The n values, means, and standard deviations are presented in Table 1. The group with Down syndrome demonstrated a significantly poorer mean chewing frequency for all foods except purée when compared with the reference group. Probability of the mean chewing frequency for the group with Down syndrome and the reference group being in the same distribution as tested by t test: ***p 0.001, **p 0.01, *p 0.05, ns = difference non-significant.

	DISCUSSION

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The study limitations primarily concerned the nature and the size of the two samples. The small sample size limited the power of the study to demonstrate differences. However, many of the hypothesized differences were demonstrated, thereby suggesting that this small sample was sufficiently powerful. Nevertheless, the generalizibility of the findings to other members of the Down syndrome and non-Down syndrome populations is limited, due to the biases inherent in the sample recruitment strategy. Another limitation concerned the fact that the different test foods were not calibrated in form and size. Nevertheless, the objective of the study was to evaluate masticatory function for socially relevant foods, rather than test foods.

There was a relatively constant relationship between the masticatory time and the number of masticatory cycles within both groups, but this relationship was different between the two groups. The chewing frequency variations were previously studied according to the rheological properties of the food. Large variations in chewing frequency were found when the subjects were eating foods of different rheological properties (Steiner et al., 1974; Kohyama et al., 2003). However, the chewing frequency remained constant when the subjects chewed foods of different hardnesses, but with the same rheological property (e.g., plastic, brittle, or elastic) (Peyron et al., 2002). The current study is the first to investigate the same phenomenon in people with problematic feeding. If this is demonstrated in other groups with limited masticatory function (e.g., those with oral cancer or neurological disorders), it means that the chewing frequency can be used to compare chewing ability between groups and possibly within groups undergoing treatment.

This study emphasized the functional incapacities and consequent adaptive behavior that people with Down syndrome may develop. Table 1 shows that, for some visco-elastic foods, like beef and cheese, mastication in the Down syndrome group was shorter and/or consisted of fewer cycles, while for brittle foods (peanut, bread, and chocolate), those subjects needed more time and/or more cycles. More persons in the Down syndrome group refused the hardest foods (carrot, apple). It may be assumed that persons with Down syndrome adapt their ingestive strategy according to food texture. The food granulometry, which forms the bolus, and the cohesion and the plasticity of the whole bolus are key factors in triggering a "safe swallow" (Prinz and Lucas, 1997; Peyron et al., 2004). This study showed that persons with Down syndrome developed at least three strategies during eating. Some foods, deemed too difficult to chew, were swallowed before the food bolus could reach the optimal granulometry to be digested in the stomach, and as soon as it had reached the optimal plasticity to be swallowed safely. Other foods were chewed until swallowed for a longer time and/or with more cycles. Food refusals could be a third strategy for the foods that could not be bitten or chewed. Even if these foods could be bitten, the mastication process could be too poor for the bolus to be mixed with saliva. Thus, the bolus could not reach the optimal plasticity for a "safe swallow". As a consequence, the food was refused. Such difficulties affect a great proportion of people with Down syndrome. In children with Down syndrome and over 8 yrs of age, 38.4% of subjects were unable to eat all types of foods, while 41.9% and 24.2% had difficulty eating a whole apple or chewing meat, respectively (Hennequin et al., 2000a).

Mastication deficiency has different consequences on the digestive process and in nutrition (Hutton et al., 2002; Sheiham et al., 2002). The problems of constipation, digestion, and intestinal and esophageal obstruction may be related to the tendency of these subjects to swallow food morsels whole (Abalan et al., 1990; Mercier and Poitras, 1992; N’Gom and Woda, 2002). Gastrointestinal defects have been found to be 20 times more common in the population with Down syndrome than in control subjects (Torfs and Christianson, 1998). In a group of 204 children with Down syndrome, 40% over 8 yrs of age suffer from constipation (Hennequin et al., 2000a). Moreover, persons with Down syndrome have a high frequency of obesity and bulimia (Calvert et al., 1976; Unonu and Johnson, 1992). Ability to chew could be implicated in such feeding problems. Thus, improving coordination and strength during mastication could help to optimize the nutritional status of people with Down syndrome. Several studies based on similar physiotherapeutic concepts have already been carried out (Carlstedt et al., 2003). From this study, it appeared that chewing frequency could be used in further studies as an evaluative criterion for a subject’s ability to adapt chewing strategy to food texture.

The role of poor mastication in the nutritional problems encountered in people with Down syndrome has never been discussed or investigated. Yet, nutritional deficiencies may appear if food choices are limited due to masticatory dysfunction. A person with Down syndrome who has difficulty eating raw fruits or vegetables may leave him/herself open to deficiencies in certain vitamins or minerals. He/she will tend to eat softer foods, often high in carbohydrates and cholesterol. Such a situation often leads to the development of obesity for two reasons: (1) The caloric intake from soft foods is high, and (2) the satiety action of mastication is inadequate for soft food. Also, it has been suggested that digestive malabsorption in Down syndrome might aggravate immunological deficiency and cause chronic malnutrition, increasing the problems of early aging (Abalan et al., 1990; Gonzalez et al., 2001).

In conclusion, this study demonstrates a systematic decrease in chewing frequency, across a variety of foods, in people with Down syndrome compared with a group without Down syndrome. It also demonstrates that "masticatory time", "number of masticatory cycles", "number of open masticatory cycles", and the number of times foods were rejected differed between the two groups. This study opens the way for more extensive clinical investigation of the masticatory function of people with Down syndrome and others with similar functional problems. Moreover, these results are useful to educate parents and professionals who are working with people with Down syndrome about masticatory difficulties. Indeed, in most of cases, the deficiencies in chewing or swallowing and their social consequences are attributed to mental deficiency rather than to a somatic incapacity.

	ACKNOWLEDGMENTS

 
We acknowledge the support of the "Groupe d’Etudes pour l’Insertion Sociale des personnes porteuses d’une trisomie 21 (GEIST 21) du Puy de Dôme" in their collaboration in this study. We also acknowledge the financial support of the Coopération France-Québec, Programme Sciences et Technologie en Santé-Recherche Médicale. Co-author Feine, an Associate Editor of the JDR, was not involved in the review/decision process for this manuscript.

Received November 17, 2004; Last revision June 15, 2005; Accepted July 25, 2005

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