Clinical Analysis in Speech and Language Therapy: Occlusal Class and Speech Production

Occlusal class refers to the manner that the upper (maxilla) and lower (mandible) dental arches relate. This relation was first described by Angle [1], who proposed a malocclusion classification based on the relative position of the maxillary first molar. Malocclusion refers to the misalignment of teeth and/or incorrect relation between the teeth of the two dental arches. Class I malocclusion, presents a normal molar relationship, but the other teeth have problems like spacing, crowding, over or under eruption. In Class II malocclusion, or distocclusion, the upper molars are placed not in the mesiobuccal groove but anteriorly to it. The anterior dental relation can vary, originating two subclasses: division 1, when the maxillary incisors are positioned forward to the lower incisors resulting in marked overjet; division 2, when there is linguoversion (retroversion) of the maxillary central incisors. Class III malocclusion, or mesiocclusion, refers to an advancement of the lower dental arch [1]. Occlusal class has been shown [2] to be directly related to articulatory perturbation of speech sounds such as fricatives. Understanding the influence of occlusal class in stomatognathic functions requires a thorough assessment of the craniofacial configuration. The size, form and relative position of the craniofacial bones may be in the origin of malocclusions and functional disorders. X-Ray Microbeam Speech Production Database (XRMB-SPD) is a speech production database, created at Wisconsin University, USA, that uses X-Ray Microbeam technology to collect a vast amount of coordinate data describing articulatory movements, and also includes acoustic and electroglotographic data collected simultaneously [3]. XRMB-SPD articulatory data are presented in a two dimensional xy mid-saggital plane that includes: palate line, posterior pharynx wall line, lips, tongue and mandible. The coordinates of each mobile structure refer to an 8 pellet system distributed through the oral cavity: lower lip, upper lip, mandibular incisor, mandibular first molar and tongue (4 pellets) [3]. The speech samples result from different tasks, including word and sentence reading, isolated productions, and non-verbal oral movements. The speaker sample includes 57 male and female speakers of American English, with an average age of 21. The database includes individual parameters characterizing each subject (e.g., dental information), which allowed us to study the relations between speech production and occlusal class [3]. The present study was concerned with the variations of different malocclusion class subjects, namely: (a) the description of articulatory structures involved in speech production; (b) the comparison of acoustic features and articulatory processes in vowel and consonant productions; (c) the characterization of the functional adaptations found.