Properties of athletic mouth protectors and materials.
The properties of a variety of mouth protectors and sheet materials used to fabricate custom mouth protectors were determined in order to recommend limits for a specification. Hardness, water sorption, water solubility, impact absorption, and tear strength were measured, and limits for these properties were suggested.
Characterization of mouthguard materials: physical and mechanical properties of commercialized products.
OBJECTIVES
Contemporary mouthguard materials need to perform consistently over a wide range of possible temperatures (-20 to 40 degrees C). Therefore the specific aim of this study was to characterize commercialized mouthguard materials' properties and investigate the effect of temperature on these properties.


METHODS
Five commercially representative thermoplastic mouthguard materials (Essix Resin, Erkoflex, Proform-regular, Proform-laminate, and Polyshok) were tested. The durometer hardness, water absorption, tear strength, and impact attenuation of the mouthguard materials were measured according to ASTM D2240-05, D570-98 (2005), D624-00, and ASTM D6110-06f (modified) guidelines. Tests were conducted on five separate specimens at both room 23+/-2 degrees C and intra-oral 37+/-2 degrees C temperatures. Independent t-tests (alpha=0.05) were used to test for differences between room and intra-oral temperatures.


RESULTS
Material hardness decreased (p<0.05) from room to intra-oral temperatures for all mouthguard materials. Water absorption increased (p<0.05) from room to intra-oral temperatures for all mouthguard materials. Tear strength decreased (p<0.05) from room to intra-oral temperatures for all mouthguard materials. Impact attenuation between room and intra-oral temperatures was different (p<0.05) for the Erkoflex, Proform-laminate, and Polyshok material respectfully. However, there was no difference between temperatures for the Essix Resin (p=.058) or Proform-regular (p=.275) materials.


SIGNIFICANCE
Temperature measureably affects the physical and mechanical properties of mouthguard materials. It is particularly noteworthy that none of the commercialized products met current ANSI and SAI standards for impact attenuation.
Measurement of Stresses in Fixed-Bridge Restorations Using a Brittle Coating Technique
Three principal methods used to study stresses in materials are photoelastic stress analysis, brittle lacquer-coating techniques, and electronic strain gauges. A number of studies have been conducted using models and the photoelastic method' to examine stress patterns in oneand two-surface inlays, complete dentures, teeth and supporting bone, and rests used in partial dentures. Strain gauges4 9-13 have been used in the evaluations of stresses of mastication, but brittle lacquer coatings have not been used to any extent in the measurement of stresses in dental restorations.4 Brittle lacquers have been used in the study of stresses in the human mandible and other bones under static and dynamic loading.14' The brittle lacquer coatings are particularly useful in detecting and measuring strains at the surface of the structure as well as indicating the direction and sequence of the tensile strains. Although the method is not as accurate as strain gauges, it is an excellent means of obtaining an over-all picture of the pattern of the stress distribution." The information obtained using brittle lacquers may be used, therefore, as a basis for more detailed studies with strain gauges. It was the purpose of this investigation to study the general stress patterns in typical fixedbridge restorations using various static loading conditions and a brittle lacquer-coating technique.