title: Difference in water accumulation patterns between solid and closed hollow obturators under a thermal cycle.
abstract: Water accumulation in the hollow space of a maxillary obturator is a continuing problem, and it is unclear whether the porosity of acrylic resin is involved in the mechanism. The purposes of the study were to evaluate the effect of a hollow space in the resin obturator on water sorption under a thermal cycle and to determine factors associated with water accumulation in the obturator. Twenty solid spheres (30-mm diameter) and 40 hemispheres (30-mm diameter, 1.5 mm thickness) were fabricated from heat-polymerized acrylic resin. Closed hollow specimens consisted of 2 hemispheres joined with autopolymerizing resin. Ten solid and 10 closed hollow specimens were immersed in distilled water, whereas the other specimens were stored at 100% relative humidity. Each specimen was thermocycled (5°C-37°C) with a dwell time of 12 hours and weighed every 12 hours for 180 days. Of the 20 closed hollow specimens, 16 showed no water accumulation (8 in distilled water, 8 at 100% humidity). The weight of these specimens became saturated by day 90, with increases from the initial weight of 1.41% at 5°C and 1.36% at 37°C. By day 180, the weights of the solid specimens had increased by 0.96% at 5°C and 0.94% at 37°C. Weight fluctuation associated with temperature was observed for both types of specimens and for all storage conditions. It is concluded that water accumulation inside a closed hollow obturator is not directly related to the water absorption properties of the acrylic resin but is related to thermal damage of the obturator.
authors.affiliation: Department of Geriatric Dentistry, Tohoku University Hospital, Sendai, Japan. tsuboi@m.tohoku.ac.jp
authors.forename: Akito
authors.initials: A
authors.lastname: Tsuboi
authors.forename: Takeshi
authors.initials: T
authors.lastname: Sakurai
authors.forename: Makoto
authors.initials: M
authors.lastname: Watanabe
mesh_terms: D000042:Absorption; D000704:Analysis of Variance; D003764:Dental Materials / Q000737:chemistry; D006358:Hot Temperature; D006813:Humidity; D008422:Materials Testing; D010158:Palatal Obturators; D019904:Polymethyl Methacrylate / Q000737:chemistry*; D016062:Porosity; D011474:Prosthesis Design; D013499:Surface Properties; D014867:Water / Q000737:chemistry*
chemical_list: D003764:Dental Materials; D014867:Water; D019904:Polymethyl Methacrylate