Orofacial function in children with speech sound disorders

Abstract

Speech sound disorder (SSD) is one of the most common neurodevelopmental disorders in children and can have different aetiologies and outcome. Speech difficulties often co-exist with other disorders, such as motor difficulties and orofacial dysfunction. These co-existent difficulties may have the same biological background. It is important to assess and describe orofacial function in children with SSD, as it may be relevant in differential diagnostics of speech disorders. Orofacial dysfunction can lead to eating difficulties, saliva leakage, reduced oral clearance, reduced mimic, deviations in speech production, voice and resonance and malocclusion. The overall aim of this project was to investigate and describe orofacial function, speech characteristics, occlusion, and other co-existing symptoms in children with SSD persisting after the age of six years.

This PhD project consisted of four prospective cross-sectional studies. The participants included 61 children with SSD aged 6.0-16.7 years (mean age 8.5), 14 girls and 47 boys, and 44 children with typical speech development (TSD) aged 6.0-12.2 years (mean age, 8.8), 19 girls and 25 boys. In Study I, orofacial function was assessed with NOT-S together with phonetic transcription of consonant and vowel production and perceptual ratings of nasality in the participants with SSD. Parents also completed the Intelligibility in Context Scale (ICS) and a questionnaire including anamnestic questions. In Study II, a kinematic assessment of lip and jaw movement was made with a 3D motion analysis and the results were compared for children with SSD and children with TSD. In Study III, the prevalence, type, and severity of malocclusions in children with SSD and TSD were assessed using the IOTN-DHC index. In Study IV, orofacial function in the SSD group and TSD group, respectively, was further assessed by using a bite force meter, the two-coloured chewing gum test, a bite block for jaw stability and oral stereognosis. The results of the two groups were compared and related to malocclusions in the SSD group.

The results showed that all participants had impaired consonant production to a varying degree. Many participants also had impaired vowel production. Half of the participants were found to have deviant nasality. Children with SSD had worse performance on all orofacial function assessments than children with TSD, especially regarding assessments involving jaw stability and sensory function. In addition, children with SSD had a higher prevalence of malocclusions and displayed more functional than structural malocclusions compared the TSD group. The malocclusions were also rated as more severe. In children with SSD, those with poorer orofacial function were at greater risk of malocclusion. General motor difficulties and other neurodevelopmental disorders were reported in children with SSD.

The findings from this thesis suggest that children with persistent SSD are at risk of orofacial dysfunction, malocclusions, general motor difficulties and other neurodevelopmental disorders, and should therefore be screened for co-occurring disorders. Children with SSD and poor orofacial function are at greater risk of malocclusion. Clinicians working with children with SSD need to have knowledge and awareness of this co-occurrence and a multi-professional approach is necessary to ensure appropriate care. An assessment of orofacial function is important when describing the characteristics of children with SSD, as it adds valuable information in differential diagnostics and in future genetic testing.