Effect of bleaching on subsurface micro-hardness of composite and a polyacid modified composite.
OBJECTIVE
To investigate the influence of different bleaching techniques on subsurface physical properties of composite and polyacid modified composite tested via determination of micro-hardness.


METHODS
Specimens of Tetric Flow, Tetric EvoCeram and Compoglass were light cured (2.5mm thickness) and stored in artificial saliva for 2 weeks (n=12/group). The samples were only removed for application of the following bleaching agents in a humid atmosphere: Either Vivastyle (1h/d), Whitestrips (30min/d), sodium-perborate-water mixture (once for 72h), Simply White (1h/d), or Opalescence XtraBoost (1st and 5th day for 15min) were applied on the surfaces of the samples. Untreated specimens served as negative controls, samples treated with ethyl alcohol for 1h acted as positive controls. After the bleaching period, samples were cross-sectioned and the micro-hardness (Knoop) of different subsurface levels (0.1mm-2.0mm) was determined.


RESULTS
All bleaching techniques significantly reduced the Knoop-hardness of the restoratives compared to untreated controls. Thereby, bleaching significantly affected not only superficial but also the deep layers of the specimens: in superficial layers (0.1mm, 0.2mm) lowest micro-hardness values amounted to 69.5% and 76.3% of the respective untreated controls (Compoglass/Vivastyle). In deeper subsurface levels, the lowest hardness was observed with Opalescence/Tetric EvoCeram (0.3mm: 78.3%; 0.4mm: 80%; 0.5mm: 80.5%; 1.0mm: 84.2%; 2.0mm: 84.4%).


CONCLUSIONS
Bleaching with the tested bleaching agents softens the adhesive restorative materials examined. Due to the fact that subsurface layers are also affected, polishing of the surface may not suffice for re-establishing the physical properties of the surface of the fillings.
Department of Operative Dentistry and Periodontology, University of Freiburg, Hugstetter St. 55, D-79106 Freiburg, Germany. christian.hannig@uniklinik-freiburg.de
Christian
C
Hannig
Sebastian
S
Duong
Klaus
K
Becker
Edgar
E
Brunner
Elke
E
Kahler
Thomas
T
Attin
D001881:Borates / Q000737:chemistry; D000077463:Carbamide Peroxide; D020770:Compomers / Q000737:chemistry*; D003188:Composite Resins / Q000737:chemistry*; D003764:Dental Materials / Q000737:chemistry*; D003775:Dental Polishing; D004338:Drug Combinations; D000431:Ethanol / Q000737:chemistry; D005899:Glass Ionomer Cements / Q000737:chemistry; D005942:Gluconates / Q000737:chemistry; D006244:Hardness; D006801:Humans; D006861:Hydrogen Peroxide / Q000737:chemistry; D008422:Materials Testing; D016877:Oxidants / Q000737:chemistry*; D010545:Peroxides / Q000737:chemistry; D012464:Saliva, Artificial / Q000737:chemistry; D012824:Silicic Acid; D012997:Solvents / Q000737:chemistry; D013499:Surface Properties; D014073:Tooth Bleaching / Q000379:methods*; D014100:Toothpastes; D014508:Urea / Q000031:analogs & derivatives / Q000737:chemistry
D001881:Borates; C105428:Compoglass; D020770:Compomers; D003188:Composite Resins; C488279:Crest whitestrips; D003764:Dental Materials; D004338:Drug Combinations; D005899:Glass Ionomer Cements; D005942:Gluconates; D016877:Oxidants; D010545:Peroxides; D012464:Saliva, Artificial; D012997:Solvents; C501891:Tetric EvoCeram; D014100:Toothpastes; C500417:Vivastyle; C546060:hydrated silica gel-based toothpaste; C452226:tetric flow composite resin; D012824:Silicic Acid; D000077463:Carbamide Peroxide; D000431:Ethanol; D014508:Urea; D006861:Hydrogen Peroxide; C027707:sodium perborate