The essential work of fracture of thermoplastic orthodontic retainer materials.
OBJECTIVE
To investigate whether oral cleansing agents affect the essential work of fracture (EWF) and plastic work of fracture (PWF) for two types of orthodontic thermoplastic retainer materials.


METHODS
Polyethylene-terephthalate-glycol (PETG; Tru-Tain Splint) and polypropylene/ethylene-propylene rubber (PP-EPR) blend (Essix-C+) sheets were compared. For each material, six sets of 25 sheets were thermoformed into double-edge-notched-tension specimens; subsets of five specimens were formed with internotch distances (L) equal to 6, 8, 10, 12, or 14 mm, respectively. Sets were stored (160 hours, 25 degrees C) in air (DRY), distilled water (DW), Original Listerine (LIS), mint Crest ProHealth (CPH), 3% hydrogen peroxide (HP), or Polident solution (POL). Specimens were fractured in tension at 2.54 mm/min. Areas under load-elongation curves were measured to determine total work of fracture (W(f)). Linear regressions (W(f) vs L [n = 25]) yielded intercepts (EWF) and slopes (PWF). Ninety-five percent confidence intervals were used to evaluate differences in EWF and PWF estimates.


RESULTS
PP-EPR blends showed higher EWFs after storage in HP vs storage in DW. PP-EPR blend showed higher EWFs after storage in CPH vs PETG. After HP storage, PP-EPR exhibited lower PWFs than with any other storage conditions. PP-EPR exhibited higher PWFs than PETG after storage in DRY, DW, and LIS.


CONCLUSIONS
Compared with DW, none of the cleansers decreased the energy to initiate fracture. With one exception, no cleanser decreased the energy to continue plastic fracture extension. In PP-EPR blend, increased resistance to fracture initiation was observed with CPH and HP, yet, surprisingly, HP decreased resistance to plastic fracture growth.
Pascual
Albert L
AL
Department of Orthodontics, University of Kentucky, Lexington, 40536-0297, USA.
Beeman
Cynthia S
CS
Hicks
E Preston
EP
Bush
Heather M
HM
Mitchell
Richard J
RJ
D000891:Anti-Infective Agents, Local / Q000737:chemistry; D001881:Borates / Q000737:chemistry; D002594:Cetylpyridinium / Q000737:chemistry; D003764:Dental Materials / Q000737:chemistry*; D003799:Dental Stress Analysis / Q000295:instrumentation; D003820:Denture Cleansers / Q000737:chemistry; D004338:Drug Combinations; D006801:Humans; D006861:Hydrogen Peroxide / Q000737:chemistry; D008422:Materials Testing; D009067:Mouthwashes / Q000737:chemistry*; D018704:Orthodontic Retainers; D016877:Oxidants / Q000737:chemistry; D010969:Plastics / Q000737:chemistry*; D011092:Polyethylene Glycols / Q000737:chemistry; D011093:Polyethylene Terephthalates / Q000737:chemistry; D011095:Polyethylenes / Q000737:chemistry; D011126:Polypropylenes / Q000737:chemistry; D012408:Rubber / Q000737:chemistry; D012459:Salicylates / Q000737:chemistry; D013314:Stress, Mechanical; D013431:Sulfates / Q000737:chemistry; D013499:Surface Properties; D013729:Terpenes / Q000737:chemistry
D000891:Anti-Infective Agents, Local; D001881:Borates; C505193:Crest Pro-Health mouthrinse; D003764:Dental Materials; D003820:Denture Cleansers; D004338:Drug Combinations; D009067:Mouthwashes; D016877:Oxidants; D010969:Plastics; D011093:Polyethylene Terephthalates; D011095:Polyethylenes; D011126:Polypropylenes; D012459:Salicylates; D013431:Sulfates; D013729:Terpenes; C475920:polyethylene terephthalate glycol; D011092:Polyethylene Glycols; C057473:Listerine; C102654:Polident; D012408:Rubber; D006861:Hydrogen Peroxide; D002594:Cetylpyridinium