Differential scanning calorimetry (DSC) and temperature-modulated DSC study of three mouthguard materials.
OBJECTIVE
Employ differential scanning calorimetry (DSC) and temperature-modulated DSC (TMDSC) to investigate thermal transformations in three mouthguard materials and provide insight into their previously investigated energy absorption.


METHODS
Samples (13-21mg) were obtained from (a) conventional ethylene vinyl acetate (EVA), (b) Pro-form, another EVA polymer, and (c) PolyShok, an EVA polymer containing polyurethane. Conventional DSC (n=5) was first performed from -80 to 150 degrees C at a heating rate of 10 degrees C/min to determine the temperature range for structural transformations. Subsequently, TMDSC (n=5) was performed from -20 to 150 degrees C at a heating rate of 1 degrees C/min. Onset and peak temperatures were compared using ANOVA and the Tukey-Kramer HSD test. Other samples were coated with a gold-palladium film and examined with an SEM.


RESULTS
DSC and TMDSC curves were similar for both conventional EVA and Pro-form, showing two endothermic peaks suggestive of melting processes, with crystallization after the higher-temperature peak. Evidence for crystallization and the second endothermic peak were much less prominent for PolyShok, which had no peaks associated with the polyurethane constituent. The onset of the lower-temperature endothermic transformation is near body temperature. No glass transitions were observed in the materials. SEM examination revealed different surface morphology and possible cushioning effect for PolyShok, compared to Pro-form and EVA.


CONCLUSIONS
The difference in thermal behavior for PolyShok is tentatively attributed to disruption of EVA crystal formation, which may contribute to its superior impact resistance. The lower-temperature endothermic peak suggests that impact testing of these materials should be performed at 37 degrees C.
Meng
Frank H
FH
Section of Orthodontics, College of Dentistry, The Ohio State University, Columbus, OH 43218, USA.
Schricker
Scott R
SR
Brantley
William A
WA
Mendel
Deborah A
DA
Rashid
Robert G
RG
Fields
Henry W
HW
Vig
Katherine W L
KW
Alapati
Satish B
SB
D000704:Analysis of Variance; D002152:Calorimetry, Differential Scanning; D003460:Crystallization; D003799:Dental Stress Analysis; D006358:Hot Temperature; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D009064:Mouth Protectors; D044367:Phase Transition; D011145:Polyvinyls; D018709:Statistics, Nonparametric; D044366:Transition Temperature
D011145:Polyvinyls; C016438:ethylenevinylacetate copolymer