Speech and DS

The speech of most children with typical development is fully intelligible at age 4 years, even though their phonological systems are not yet complete.3 However, speech and language are a major problem for many children with DS. Even those who are relatively capable in other areas of life may have great difficulty in communicating with people who do not know them well. This can bring about a restriction of opportunities for full integration and participation in society.4

There is considerable individual variation in the delay of language acquisition in children with DS,56 but only about 5% of these children have extremely limited speech and must rely on a small number of single words and signs.7 Their early vocabulary development is delayed by an average 8–9 months in comparison with typically developing children.5

Language acquisition of children with DS is probably affected by both development delay and specific disorders in certain language areas.8 The phonological system of those children is influenced by several factors that can create difficulties in perceiving and producing speech.3 These factors include: neurological development of the language,9 language learning environment,38 hearing loss,3 subtypes of DS,2 motor coordination and timing deficit,7 and orofacial characteristics.3710

Orofacial Characteristics

Children with DS frequently have differences in the oral-facial structures and in the functional movements that affect speech production.7 Persons with DS have skeletal and muscular systems that differ from those individuals without DS. The skeletal system is characterized by absent or deficient bone growth and a smaller oral cavity. The muscular system is characterized by absent and extra muscles in the facial region, a large muscular tongue, and hypotonicity. Any of these factors is likely to influence motor movements associated with speech and to negatively impact the articulatory and phonatory abilities of children with DS.3 The reduced muscle tone in the lips and cheeks contributes to an imbalance of forces on the teeth, with the force of the tongue having a greater influence. In turn, this contributes to the open bite often seen in children with DS. On the other hand, the primary skeletal abnormality affecting the orofacial structures in DS is an underdevelopment or hypoplasia of the midface region. In many persons this hypoplasia also causes a prognathic Class III occlusal relationship which, in turn, contributes to an open bite.10

Anterior Open Bite

Anterior open bite probably affects less than 5% of children.11 Teeth play an important role in speech production, but the relationship between tooth position and speech remains controversial. The ability of patients to adapt their speech to compensate for abnormal tooth position is recognized, but the mechanisms for this adaptation remain incompletely understood. While certain irregularities show a relationship with speech disorders, this does not appear to correlate with the severity of the malocclusion. Therefore, tooth position may play a role in articulatory speech disorders which, although not the most severe, represent 50% to 60% of all speech disorders.12

Anterior open bite is, however, the most frequent type of malocclusion involved in phonological disorders. Nicolá and Jonathan12 stated that 63% of the cases with open bite have an alteration in speech. They also mentioned that Bernstein13 concluded that the defects in speech are not related to any malocclusion except anterior open bite. The precise influence of each factor is difficult to determine and may vary from one child to another.36 In some cases, their speech remains unintelligible throughout childhood and adolescence.3 Studies reported in the literature have tried to determine if the malocclusion, specifically the open bite, could be associated with a higher difficulty in the articulation of the speech in children with DS.

This study aimed to estimate the prevalence of anterior open bite and to determine whether there is an association between this type of malocclusion and the presence of speech disorders in a group of Mexican children with DS (DG) and a control group of Mexican pediatric patients without disabilities (CG).

Ethical Implications

The design and conduct of this study complied with the regulations for the protection of human subjects stipulated by the organizations where data collection took place.

Environment

Using a case-control study design, we recruited 57 children, aged 3 to 15 years, with DS studying at The John Langdon Down Foundation in 2003. The Foundation is a not-for-profit organization located in Mexico City that offers programs delivering psychopedagogical support and advice to persons with DS and their families. To participate in this study, volunteers provided verbal consent to an oral examination, including parental questionnaire, dental impressions, and a speech test. Their guardians/parents provided written consent.

The 57 students had no orthodontic appliances, nor were they wearing oral prostheses. They had no history of previous orthodontic therapy, and they were free of conditions such as autism, cerebral palsy, intellectual disability more than mild, sinusitis, asthma, cleft lip and palate, or hearing loss more than 15 dB. By an ethical implication all the children had a history of previous speech therapy. They had the eight incisors. This group (DG) was further divided into two subgroups: Subgroup 1 included children with DS without anterior open bite and Subgroup 2 included children with DS with anterior open bite.

Study children were matched (1:1) by age to participants in the CG who did not have disabilities. The 57 children from the CG were outpatients seeking dental care at the admissions clinic of the Dental School, Universidad Nacional. The CG participants were free of systemic diseases and chronic medication use, had no orthodontic appliances or oral prostheses, and had no history of previous orthodontic therapy or speech therapy. They had eight incisors erupted. Children in the CG agreed to participate in the study as part of the preliminary evaluation undertaken by all first-time patients attending the admission clinic. The CG was also divided into two subgroups: Subgroup 3 included children without disabilities and without anterior open bite. Subgroup 4 included children without disabilities, but with anterior open bite.

In both groups, all the children were from the same geographic area and belonged to the same socioeconomic status. They were all monolingual speakers of Spanish. Their guardians/parents were native Spanish speakers, and the mothers of the children had the same level of education (bachelor's degree). The information was obtained from each child's medical history. A parental questionnaire also collected information regarding medical history.

Variables Collected

We diagnosed anterior open bite using the dental study casts. Anterior open bite was defined as the absence of contact and existence of a vertical space between the maxillary and mandibular incisors in centric relation. Because people with DS frequently have a Class III malocclusion, the children included in this sample were considered with open bite regardless of the presence or absence of anterior crossbite. The examiner (a pediatric dentist) performed standardization training by evaluating 25 casts of patients not included in the study population reexamined 7 days after the first assessment. The kappa value (intraexaminer reliability) was 1.00.

A speech test was done to determine the phonetic errors. The phonological analysis used in this study was the same employed routinely by The John Langdon Down Foundation. A speech therapist and a pediatric dentist showed 58 pictures of common objects to each child which he or she was required to name. The two examiners recorded the phonological errors. A total of 5 vowel sounds: /a/, /e/, /i/, /o/, and /u/; 18 single consonant sounds: /b/, /ch/, /d/, /f/, /g/, /j/, /k/, /l/, /m/, /n/, /ñ/, /p/, /r/, /rr/, /s/, /t/, /x/, and /y/; 8 homosyllabic consonant sounds: /bl/, /fl/, /gl/, /kl/, /pl/, /br/, /dr/, and /tr/; 17 heterosyllabic consonant sounds: /kt/, /ld/, /ls/, /lt/, /mb/, /mp/, /nf/, /nj/, /nt/, /ny/, /rb/, /rs/, /rm/, /rt/, /sb/, /sk/, and /st/; and 9 diphthong sounds: /ai/, /au/, /ei/, /ia/, /ie/, /io/, /iu/, /ua/, and /ue/ were studied.

The single consonants were analyzed taking into account three word positions: initial, medial, and final. Error types analyzed were omissions, substitutions, distortions, and additions of phonemes. A word was considered correct if it was named or repeated without any omission, substitution, distortion, or addition of a sound. The standardization of the two examiners was carried out by evaluating 25 patients not included in the study population, on two occasions. To apply the speech test, the kappa value for the intraexaminer reliability obtained by the pediatric dentist was 0.93, and by the speech therapist was 0.95. The kappa value for the interexaminer reliability was 0.93.

Statistical Analysis

We used SPSS (version 12.0) for data analysis. To estimate whether there was a significant difference between the prevalence of anterior open bite in both groups, as well as in the percentages by error type of the children of each subgroup, χ² test was applied. Because error means by types and phonemes were also calculated, one-way analyses of variance (ANOVA) followed by the Tukey post hoc test were used to determine whether there were statistically significant differences among subgroups.

Prevalence of Anterior Open Bite

In the DG 18 (31.6%) children showed anterior open bite, whereas in the CG 13 (22.8%) children presented this malocclusion. There was a significant difference between them (χ² = 24.6; P < .001).

Speech Disorders Associated With Anterior Open Bite

The percentages of the children from the four subgroups that presented some error type can be seen in Table 1. When comparing the percentages to determine whether any significant differences existed between the subgroups of the children with DS and the children without disabilities, we observed a significant difference only in the presence of additions in the children of the Subgroups 1 and 2 (χ² = 4.59; P < .05).

Table 1.  Frequencies and Percent of Children From the Four Subgroups With Speech Disorders by Error Type^a

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The means by error types that occurred in the children of the four subgroups are shown in Table 2. These mean values were compared, through the one-way ANOVA test and the Tukey post hoc test, and marked with an asterisk when there was any statistically significant difference between two subgroups. There was a significant difference among the subgroups of different groups in all the cases except in the substitution of the heterosyllabic consonants (F = 2.72; P =.068) and of diphthongs (F = 1.23; P = .302). When comparing means of error type by omissions and substitutions, we found that the two subgroups belonging to the CG (Subgroups 3 and 4) manifested the lower means.

Table 2.  Mean, Standard Deviation, and Statistically Significant Difference of Error Type Among the Four Studied Subgroups^a

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On the other hand, we observed no significant differences between the subgroups when analyzing the error type by distortion (F = 2.42; P = .070). Finally, when we compared the means by additions made in each of the four subgroups, significant differences were present only by additions of initial single consonants between the subgroups of children without anterior open bite (Subgroups 1 and 3) (F = 3.72; P = .014), as well as by additions of final single consonants among the children with DS without anterior open bite (Subgroup 1), and the children of the two subgroups belonging to the CG (Subgroups 3 and 4) (F = 5.57; P < .001). In all the cases the lower means were presented in the subgroups of the CG (Subgroups 3 and 4).