title: The effect of wearing custom-made mouthguards on the aeroacoustic properties of Japanese sibilant /s/.
abstract: OBJECTIVE
  There have been many reports on the discomfort of speech when wearing oral appliances. Fricatives articulated in an oral cavity can be difficult to pronounce when oral appliances are worn, because the oral cavity is partially changed by their installation. Sibilant /s/, one fricative, is especially difficult to pronounce when wearing oral appliances. This study investigates the effect of the difference in the setting positions of the palatal margin of custom-made mouthguards on the aeroacoustic characteristics of sibilant /s/.
  
  
  METHODS
  Eighteen subjects (11 women and seven men) participated. The palatal margin of mouthguards was set at the gingival line for nine subjects and 4 mm from the line for another nine subjects. Acoustical analyses examined the difference of the palatal margins of the mouthguards on the autocorrelation coefficient, the zero crossing count, and the spectral peaks of sibilant /s/.
  
  
  RESULTS
  The results showed that the zero crossing count of the waveforms and the spectral peaks of sibilant /s/ were significantly broadened and shifted toward the low-frequency range with the mouthguard whose palatal margin extended 4 mm from the gingival line than the mouthguard whose palatal margin was set at the gingival line.
  
  
  CONCLUSIONS
  We believe that a more appropriate palatal mouthguard design for custom-made mouthguards can be made by considering the aeroacoustical effects. Our study supported the mouthguard whose palatal margin was set at the gingival line by considering the influence on pronouncing sibilant /s/. We believe that a more appropriate palatal mouthguard design for custom-made mouthguards can be made based on the balance of aeroacoustical effects and mechanical requirements.
authors.affiliation: Department of Mechanical Science and Bioengineering, Graduate School of Engineering Science, Osaka University, Toyonaka-shi, Osaka, Japan. nozaki@me.es.osaka-u.ac.jp
authors.forename: Kazunori
authors.initials: K
authors.lastname: Nozaki
authors.forename: Yoshinobu
authors.initials: Y
authors.lastname: Maeda
authors.forename: Hiroo
authors.initials: H
authors.lastname: Tamagawa
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D004867:Equipment Design; D005260:Female; D006801:Humans; D007564:Japan; D008297:Male; D009064:Mouth Protectors; D010159:Palate / Q000033:anatomy & histology; D010700:Phonetics; D012737:Sex Factors; D013061:Speech Acoustics