Effects of aging procedures on the molecular, biochemical, morphological, and mechanical properties of vacuum-formed retainers.
The influence of intraoral exposure procedures on the physical characteristics of thermoplastic vacuum-formed retainers (VFRs) is still unclear. The effects of thermoforming and intraoral use on the molecular, chemical, morphological, and mechanical properties of thermoplastic VFRs were investigated. VFRs with a 0.8-mm-thick thermoplastic PETG sheet acquired from 48 patients were investigated with two aging procedures, including vacuum forming and intraoral exposure, for 2-week and 6-month. Eight evaluating sites for thermoplastic VFRs were assessed with seven analytical techniques. LM, SEM, and AFM microscopic findings showed that the surface characteristics increased with increasing in vivo exposure time (a four-fold increase) and varied depending on the sites evaluated (an occlusal surface). Raman and EDX spectroscopic findings showed that aging procedures led to a significant change in the molecular composition of VFRs, leading to a decrease in the composition rate of carbon (C) and the presence of silicon (Si), phosphorus (P), and calcium (Ca). Compressive strength and tensile tests showed that aging procedures led to a significant increase (P<0.01) in ultimate tensile strength, elastic modulus, the stored energy at a 6-mm deflection (u6 mm), and the compressed load at a 3-mm deflection (σ3 mm). Thermoforming led to a smoother surface and no crystallization of PETG sheets. Intraoral exposure accelerated changes in surface morphology, tensile strength, and elastic modulus of VFRs. This change was site-specific and enhanced with an increase in intraoral exposure time. Therefore, thermoforming and in vivo oral exposure procedures led to the molecular, morphological, and mechanical properties of thermoplastic VFRs.
Department of Orthodontics, School of Dentistry, Kyung Hee University, Seoul 130-702, Republic of Korea.
Hyo-Won
HW
Ahn
Department of Orthodontics, School of Dentistry, Kyung Hee University, Seoul 130-702, Republic of Korea.
Hye-Ryun
HR
Ha
Center for Dental Materials, Kyung Hee University, Seoul 130-701, Republic of Korea; Department of Dental Materials, School of Dentistry, Kyung Hee University, Seoul 130-702, Republic of Korea.
Ho-Nam
HN
Lim
Department of Biomedical Engineering, College of Medicine, Kyung Hee University, Seoul 130-701, Republic of Korea; Department of Medical Engineering, Kyung Hee University, Seoul 130-701, Republic of Korea. Electronic address: medchoi@khu.ac.kr.
Samjin
S
Choi
D008422:Materials Testing; D055595:Mechanical Phenomena; D018704:Orthodontic Retainers; D011108:Polymers / Q000737:chemistry*; D013696:Temperature; D013997:Time Factors; D014618:Vacuum
D011108:Polymers
Intraoral exposure; PETG sheets; Physical properties; Thermoforming; Thermoplastic vacuum-formed retainers