title: Influence of continuous use of a vacuum-forming machine for mouthguard thickness after thermoforming.
abstract: OBJECTIVE
  Mouthguards can reduce the risk of sports-related injuries such as tooth fracture or avulsion, but the sheet material and thickness have a large effect on their efficacy and safety. The aim of this study was to investigate the effect of the continuous use of a vacuum-forming machine on mouthguard thickness.
  
  
  METHODS
  Ethylene vinyl acetate sheets and olefin copolymer sheets were used for thermoforming with a vacuum-forming machine. The working model was trimmed to a height of 23 mm at the maxillary central incisor and 20 mm at maxillary first molar. During molding, the model was placed at the center of the vacuum unit. Three molding conditions were investigated (i) molding was carried out after the sag at the center of the softened sheet was 15 mm below the clamp (control); (ii) sheet heating started 5 minutes after the control, and molding in the same way as the control (AF5); and (iii) sheet heating started 10 minutes after the control, and molding in the same way as the control (AF10). Under each condition, vacuum forming was conducted for 30 seconds. Sheet thickness after fabrication was determined for the incisal edge, labial surface, cusp, and buccal surface using a special caliper accurate to 0.1 mm. The differences of the molding conditions on the thickness in each sheet material were analyzed by one-way analysis of variance and Bonferroni's multiple comparison tests.
  
  
  RESULTS
  For both sheet materials, significant differences between the control and AF5 were observed at all measurement points (P<.01), but not between the control and AF10. Compared with the control, AF5 was thinner and AF10 was a similar thickness.
  
  
  CONCLUSIONS
  The continuous use of a vacuum-forming machine led to a reduction in the thickness of the mouthguard. Intervals of 10 minutes are necessary to achieve consistent molding.
authors.affiliation: Department of Physiology, The Nippon Dental University School of Life Dentistry at Niigata, Japan.
authors.forename: Mutsumi
authors.identifier: http://orcid.org/0000-0003-3276-7321
authors.initials: M
authors.lastname: Takahashi
authors.affiliation: RITEC Limited Company, Osaka, Japan.
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Araie
authors.affiliation: Department of Physiology, The Nippon Dental University School of Life Dentistry at Niigata, Japan.
authors.forename: Yoshihide
authors.initials: Y
authors.lastname: Satoh
authors.affiliation: Department of Physiology, The Nippon Dental University School of Life Dentistry at Niigata, Japan.
authors.forename: Shin-Ichi
authors.initials: SI
authors.lastname: Iwasaki
mesh_terms: D000475:Alkenes / Q000737:chemistry; D004867:Equipment Design; D006801:Humans; D008422:Materials Testing; D009064:Mouth Protectors; D019876:Sports Equipment; D014618:Vacuum; D014753:Vinyl Compounds / Q000737:chemistry
chemical_list: D000475:Alkenes; D014753:Vinyl Compounds; C011566:vinyl acetate
keywords: continuous use; mouthguard; shape change; thermoforming; thickness; vacuum formation