Effect of bleaching on subsurface micro-hardness of composite and a polyacid modified composite

Hannig, Christian; Duong, Sebastian; Becker, Klaus; Brunner, Edgar; Kahler, Elke; Attin, Thomas

doi:10.1016/j.dental.2006.01.008

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Volume 23, Issue 2 , Pages 198-203, February 2007

Effect of bleaching on subsurface micro-hardness of composite and a polyacid modified composite

Christian Hannig
- Department of Operative Dentistry and Periodontology, University of Freiburg, Hugstetter St. 55, D-79106 Freiburg, Germany
- Department of Operative Dentistry, Preventive Dentistry and Periodontology, University of Göttingen, Robert-Koch-Str. 40, 37075 Göttingen, Germany
- Correspondence to: Department of Operative Dentistry and Periodontology, University of Freiburg, Hugstetter St. 55, D-79106 Freiburg, Germany. Tel.: +49 761 270 4957; fax: +49 761 270 4762.
Sebastian Duong
- Department of Operative Dentistry, Preventive Dentistry and Periodontology, University of Göttingen, Robert-Koch-Str. 40, 37075 Göttingen, Germany
Klaus Becker
- Department of Operative Dentistry, Preventive Dentistry and Periodontology, University of Göttingen, Robert-Koch-Str. 40, 37075 Göttingen, Germany
- Clinic for Preventive Dentistry, Periodontology and Cariology, University of Zürich, Plattenstr. 11, 8032 Zürich, Switzerland
Edgar Brunner
- Department of Medical Statistics, University of Göttingen, Humboldtallee 32, 37075 Freiburg, Germany
Elke Kahler
- Department of Medical Statistics, University of Göttingen, Humboldtallee 32, 37075 Freiburg, Germany
Thomas Attin
- Department of Operative Dentistry, Preventive Dentistry and Periodontology, University of Göttingen, Robert-Koch-Str. 40, 37075 Göttingen, Germany
- Clinic for Preventive Dentistry, Periodontology and Cariology, University of Zürich, Plattenstr. 11, 8032 Zürich, Switzerland

Received 5 September 2005; accepted 10 January 2006.

Abstract

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%).

Significance

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.

Keywords: Composite, Bleaching, Micro-hardness, Restoration, Polyacid modified resin composite