title: In Vitro Comparative Study of Two Different Bleaching Agents on Micro-hardness Dental Enamel.
abstract: OBJECTIVE
  To evaluate the effect of home-use bleaching agent containing 16% Carbamide Peroxide (CP) and in-office bleaching agent containing 38% Hydrogen Peroxide (HP) on enamel micro-hardness.
  
  
  METHODS
  An in vitroexperimental study.
  
  
  METHODS
  Department of Operative Dentistry and Science of Dental Materials at Dr. Ishrat-ul-Ebad Khan Institute of Oral Health Sciences, Dow University of Health Sciences and Material Engineering Department of NED University of Engineering and Technology, Karachi, from July to December 2014.
  
  
  METHODS
  Atotal of 90 enamel slabs from 45 sound human 3rd molar were randomly divided into 3 groups. Each group contained 30 specimens (n=30). Group 1 was kept in artificial saliva at 37°C in incubator during the whole experiment. However, Groups 2 and 3 were treated with power whitening gel and tooth whitening pen respectively. After bleaching session, specimens were thoroughly rinsed with deionized water again for 10 seconds and then stored in artificial saliva at 37°C in incubator. Artificial saliva was changed after every 2 days. The Vickers hardness tester (Wolpert 402 MVD, Germany) was adjusted to a load of 0.1 kg (100 gm) and dwell time of 5 seconds. Three Vickers were performed on each specimen using a hardness tester according to the ISO 6507-3:1998 specification. Micro-hardness measurements were performed before and after bleaching at day 1, 7 and 14.
  
  
  RESULTS
  In the control group, the baseline micro-hardness was 181.1 &plusmn;9.3 which was reduced after the storage on day 1, 7 and 14 (p = 0.104). In Group 2, baseline micro-hardness was 180.4 &plusmn;10.1 which was reduced to 179.79 &plusmn;10.0 units after day 1. Whereas, on day 7 and 14, the values of micro-hardness were 179.8 &plusmn;10 and 179.7 &plusmn;10.29, respectively (p=0.091). Furthermore, the baseline micro-hardness in Group 3 was 174.0 &plusmn;22.9 units which was reduced to 173 &plusmn;23 on day 1, 170 &plusmn;30 on day 7 and 173 &plusmn;23 on day 14 (p = 0.256). The statistically insignificant difference was found among micro-hardness values of different bleaching agents (p = 0.118).
  
  
  CONCLUSIONS
  Bleaching with 38% Hydrogen Peroxide (HP) and 16% Carbamide Peroxide (CP) resulted in insignificant effect on surface micro-hardness of enamel.
authors.affiliation: Department of Science of Dental Materials, Ziauddin College of Dentistry, Ziauddin University, Karachi.
authors.forename: Nazish
authors.initials: N
authors.lastname: Fatima
authors.affiliation: Department of Operative Dentistry, Dow University Health Sciences, Karachi.
authors.forename: Syed Yawar
authors.initials: SY
authors.lastname: Ali Abidi
authors.affiliation: Department of Materials Engineering, NED University of Engineering and Technology, Karachi.
authors.forename: Ashraf Ali
authors.initials: AA
authors.lastname: Meo
mesh_terms: D057886:Bleaching Agents; D000077463:Carbamide Peroxide; D003743:Dental Enamel / Q000187:drug effects*; D003764:Dental Materials; D003804:Dentin / Q000187:drug effects*; D006244:Hardness / Q000187:drug effects; D006801:Humans; D006861:Hydrogen Peroxide / Q000627:therapeutic use*; D010545:Peroxides; D012464:Saliva, Artificial; D014073:Tooth Bleaching / Q000009:adverse effects* / Q000379:methods*; D017001:Tooth Demineralization / Q000503:physiopathology; D014089:Tooth Remineralization / Q000379:methods*; D014508:Urea / Q000031:analogs & derivatives
chemical_list: D057886:Bleaching Agents; D003764:Dental Materials; D010545:Peroxides; D012464:Saliva, Artificial; D000077463:Carbamide Peroxide; D014508:Urea; D006861:Hydrogen Peroxide